WO2023184304A1 - 新型正极极片、二次电池、电池模块、电池包及用电装置 - Google Patents

新型正极极片、二次电池、电池模块、电池包及用电装置 Download PDF

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WO2023184304A1
WO2023184304A1 PCT/CN2022/084292 CN2022084292W WO2023184304A1 WO 2023184304 A1 WO2023184304 A1 WO 2023184304A1 CN 2022084292 W CN2022084292 W CN 2022084292W WO 2023184304 A1 WO2023184304 A1 WO 2023184304A1
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positive electrode
active material
layer
range
cathode active
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PCT/CN2022/084292
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English (en)
French (fr)
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季成
李白清
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宁德时代新能源科技股份有限公司
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Priority to PCT/CN2022/084292 priority Critical patent/WO2023184304A1/zh
Priority to EP22912793.1A priority patent/EP4280307A4/en
Priority to CN202280017103.1A priority patent/CN116897446B/zh
Priority to US18/351,998 priority patent/US20230361284A1/en
Publication of WO2023184304A1 publication Critical patent/WO2023184304A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the technical field of secondary batteries, and in particular to a new type of positive electrode plate, secondary battery, battery module, battery pack and electrical device.
  • secondary batteries are widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, Military equipment, aerospace and other fields. Due to the great development of secondary batteries, higher requirements have been put forward for their energy density, cycle performance and safety performance.
  • the existing lithium iron manganese phosphate makes the secondary battery have poor dynamic performance and low cell rate performance, which cannot meet the needs of power batteries.
  • the existing secondary batteries made of lithium iron phosphate as the cathode active material have excellent cycle stability and safety, but the existence of one-dimensional lithium ion channels inside them and the existence of two phases of LiFePO 4 and FePO 4 during the charge and discharge process
  • the internal phase change resistance of the material increases during the charge and discharge process, resulting in poor dynamic performance of the secondary battery, low cell rate performance, short low-temperature cycle life, and low low-temperature capacity retention rate.
  • This application was made in view of the above issues, and its purpose is to provide a new type of positive electrode plate, secondary battery, battery module, battery pack and power device to solve the problems of secondary batteries made of existing positive electrode active materials. Problems include low energy density, poor kinetic performance, low rate performance, short low-temperature cycle life, and low low-temperature cycle capacity retention rate.
  • the first aspect of the present application provides a positive electrode sheet, including a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector; the positive electrode film layer has a single-layer structure or a multi-layer structure; When the positive electrode film layer has a single-layer structure, at least one positive electrode film layer simultaneously contains a first positive electrode active material and a second positive electrode active material having a core-shell structure; and/or, when the positive electrode film layer has a multi-layer structure, at least At least one layer of a positive electrode film layer contains both a first positive electrode active material and a second positive electrode active material having a core-shell structure; the first positive electrode active material includes an inner core, a first coating layer covering the inner core, and a second positive electrode active material covering the inner core.
  • the cladding layer includes crystalline pyrophosphate Li a MP 2 O 7 and/or M b (P 2 O 7 ) c
  • the second cladding layer includes crystalline phosphate XPO 4
  • the third cladding layer includes carbon; wherein , A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge; R Including one or more elements selected from B, Si, N and S; Any value within the range
  • M in crystalline pyrophosphate Li a MP 2 O 7 and M b (P 2 O 7 ) c each independently includes selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, One or more elements among
  • crystalline means that the degree of crystallinity is above 50%, that is, between 50% and 100%. Crystallinity less than 50% is called glassy state.
  • the crystalline pyrophosphates and crystalline phosphates of the present application have a crystallinity of 50% to 100%. Pyrophosphate and phosphate with a certain degree of crystallinity are not only conducive to giving full play to the pyrophosphate coating layer's ability to hinder manganese dissolution and the phosphate coating layer's excellent ability to conduct lithium ions and reduce interface side reactions, but also make the pyrophosphate The phosphate coating layer and the phosphate coating layer can achieve better lattice matching, thereby achieving a tight bond between the coating layer and the coating layer.
  • this application provides a new type of lithium manganese phosphate core by doping element A at the manganese position and doping element R at the phosphorus position, and sequentially performs three-layer coating on the surface of the core.
  • the first cathode active material has a core-shell structure.
  • the first cathode active material can significantly reduce manganese dissolution and reduce the lattice change rate. When used in secondary batteries, it can significantly improve the high-temperature cycle performance and cycle stability of secondary batteries. properties, high temperature storage performance, rate performance, safety performance and improve the capacity of secondary batteries.
  • the first positive electrode active material and the second positive electrode active material are mixed and used.
  • the advantages of the two materials complement each other, which improves the energy density of the secondary battery.
  • the secondary battery has excellent kinetic performance, rate performance, Low temperature cycle life and low temperature cycle capacity retention.
  • a second aspect of the present application provides a positive electrode sheet, including a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector; at least one positive electrode film layer has a multi-layer structure, and any positive electrode film layer has a multi-layer structure.
  • the positive electrode film layer includes a first positive electrode active material and a second positive electrode active material having a core-shell structure in different layers; the first positive electrode active material includes a core, a first coating layer covering the core, and a first coating layer coating the core.
  • the layer contains crystalline pyrophosphate Li a MP 2 O 7 and/or M b (P 2 O 7 ) c
  • the second cladding layer contains crystalline phosphate XPO 4
  • the third cladding layer contains carbon
  • R includes selected One or more elements from B, Si, N and S; any value
  • M in crystalline pyrophosphate Li a MP 2 O 7 and M b (P 2 O 7 ) c each independently includes selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, One or more elements among Zr
  • the first positive electrode active material can significantly reduce manganese dissolution and lattice change rate, and can significantly improve the high-temperature cycle performance, cycle stability, high-temperature storage performance, rate performance, and safety of secondary batteries when used in secondary batteries. performance and improve the capacity of secondary batteries.
  • This application combines the first positive electrode active material and the second positive electrode active material.
  • the advantages of the two materials complement each other, which improves the energy density of the secondary battery.
  • the secondary battery has excellent rate performance, dynamic performance, and low temperature. Cycle life and low temperature cycle capacity retention.
  • a third aspect of the present application provides a positive electrode sheet, including a positive current collector and positive electrode film layer A and positive electrode film layer B respectively disposed on two surfaces of the positive electrode current collector; positive electrode film layer A and positive electrode film layer B respectively Independently a single-layer structure or a multi-layer structure; at least one layer of the cathode film layer A contains a first cathode active material with a core-shell structure, and at least one layer of the cathode film layer B contains a second cathode active material.
  • the first positive active material includes an inner core, a first cladding layer covering the inner core, a second cladding layer covering the first cladding layer, and a third cladding layer covering the second cladding layer; wherein, the inner core Containing Li 1+x Mn 1-y A y P 1-z R z O 4 , the first cladding layer contains crystalline pyrophosphate Li a MP 2 O 7 and/or M b (P 2 O 7 ) c , The second cladding layer includes crystalline phosphate XPO 4 and the third cladding layer includes carbon; wherein A includes selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni , one or more elements from Co, Ga, Sn, Sb, Nb and Ge; R includes one or more elements selected from B, Si, N and S; x is selected from the range of -0.100-0.100 Any value of _ _ _ _ M each independently includes one or more elements selected from
  • the first cathode active material of the present application can significantly reduce the dissolution of manganese and reduce the lattice change rate.
  • it can significantly improve the high-temperature cycle performance, cycle stability, high-temperature storage performance, and rate performance of secondary batteries. , safety performance and improve the capacity of secondary batteries.
  • This application combines the first positive electrode active material and the second positive electrode active material.
  • the advantages of the two materials complement each other, which improves the energy density of the secondary battery.
  • the secondary battery has excellent rate performance, dynamic performance, and low temperature. Cycle life and low temperature cycle capacity retention.
  • the above limitation on the numerical range of y is not only a limitation on the stoichiometric number of each element as A, but also on the stoichiometric number of each element as A.
  • Limitation of the sum of stoichiometric numbers For example, when A is two or more elements A1, A2...An, the stoichiometric numbers y1, y2...yn of A1, A2...An each need to fall within the numerical range of y defined in this application, and y1 , y2...yn and the sum must also fall within this numerical range.
  • R is two or more elements
  • the limitations on the numerical ranges of the stoichiometric numbers of R, M, and X in this application also have the above meaning.
  • the above-mentioned limitation on the numerical range of e is not only a limitation on the stoichiometric number of each element as D, but also on each As a definition of the sum of the stoichiometric numbers of the elements of D.
  • the stoichiometric numbers e1, e2...en of D1, D2...Dn must fall within the numerical range for e defined in this application, and e1 The sum of , e2...en also needs to fall within this numerical range.
  • the carbon mass accounts for 0.1%-4% of the mass of the carbon-coated LiFePO 4 ; and/or the carbon mass accounts for the carbon mass. 0.1%-4% of the mass of coated LiFe d De PO 4 .
  • Using the second positive electrode active material with the above-mentioned carbon mass content can further ensure that the secondary battery has excellent rate performance, kinetic performance and low-temperature cycle performance, and has a high energy density.
  • the mass ratio of the first cathode active material to the second cathode active material is 1:7-7:1, optionally 1:4-4:1, and further can be Select 1:3-3:1, such as 1:7, 1:5, 1:3, 1:2, 3:5, 1:1, 5:3, 2:1, 3:1, 5:1 , 7:1.
  • A is selected from one or more elements selected from Fe, Ti, V, Ni, Co and Mg.
  • doping elements within the above range, it is beneficial to enhance the doping effect. On the one hand, it further reduces the lattice change rate, thereby inhibiting the dissolution of manganese and reducing the consumption of electrolyte and active lithium. On the other hand, it is also beneficial to The surface oxygen activity is further reduced and the interface side reaction between the first positive electrode active material and the electrolyte is reduced, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.
  • R is an element selected from the group consisting of B, Si, N and S.
  • the ratio of y to 1-y is selected from 1:10 to 1:1, optionally from 1:4 to 1:1. As a result, the energy density, cycle performance and rate performance of the secondary battery are further improved.
  • the ratio of z to 1-z is selected from 1:9 to 1:999, optionally from 1:499 to 1:249.
  • the interplanar spacing range of the crystalline pyrophosphate in the first coating layer is 0.293-0.470 nm, and the crystallographic direction (111)
  • the included angle range is 18.00°-32.00°;
  • the interplanar spacing range of the crystalline phosphate in the second coating layer is 0.244-0.425nm, and the included angle range of the crystal direction (111) is 20.00°-37.00°.
  • the first coating layer and the second coating layer in the cathode active material of the present application both use crystalline materials, and their interplanar spacing and included angle range are within the above range. As a result, the impurity phase in the coating layer can be effectively avoided, thereby increasing the gram capacity of the material and improving the cycle performance and rate performance of the secondary battery.
  • the carbon in the third coating layer is a mixture of SP2 form carbon and SP3 form carbon, optionally, SP2 form carbon and SP3 form carbon.
  • the molar ratio is any value in the range of 0.1-10, and can be any value in the range of 2.0-3.0.
  • This application improves the overall performance of the secondary battery by limiting the molar ratio of SP2 form carbon to SP3 form carbon within the above range.
  • the coating amount of the first coating layer is greater than 0 and less than or equal to 6% by weight, optionally greater than 0 and less than or equal to 5.5% by weight, more optionally is greater than 0 and less than or equal to 2% by weight, based on the weight of the core; and/or
  • the coating amount of the second coating layer is greater than 0 and less than or equal to 6% by weight, optionally greater than 0 and less than or equal to 5.5% by weight, and more optionally 2-4% by weight, based on the weight of the core; and /or
  • the coating amount of the third coating layer is greater than 0 and less than or equal to 6 wt%, optionally greater than 0 and less than or equal to 5.5 wt%, more optionally greater than 0 and less than or equal to 2 wt%, based on the core Weight scale.
  • the coating amount of the three coating layers is preferably within the above range, so that the core can be fully coated without sacrificing the first cathode activity.
  • the dynamic performance and safety performance of the secondary battery can be further improved.
  • the thickness of the first coating layer is 1-10 nm.
  • the thickness of the first coating layer ranges from 1 to 10 nm, it can avoid the possible adverse effects on the dynamic properties of the material when it is too thick, and can avoid the inability to effectively block transition metal ions when it is too thin. Migration issues.
  • the thickness of the second coating layer is 2-15 nm.
  • the thickness of the second coating layer is in the range of 2-15nm, the surface structure of the second coating layer is stable and side reactions with the electrolyte are small. Therefore, interface side reactions can be effectively reduced, thereby improving the high-temperature performance of the secondary battery. .
  • the thickness of the third coating layer is 2-25 nm.
  • the electrical conductivity performance of the material can be improved and the compaction density performance of the battery pole piece prepared using the first cathode active material can be improved.
  • the manganese element content in the first cathode active material, based on the weight of the first cathode active material, is in the range of 10% by weight to 35% by weight, optionally in the range of 15% by weight. %-30% by weight, more optionally within the range of 17%-20% by weight.
  • the content of manganese element is within the above range, which can effectively avoid problems such as deterioration in structural stability and density reduction that may be caused by excessive manganese element content.
  • This can improve the performance of the secondary battery such as cycle, storage and compaction density; and can avoid problems such as low voltage platform that may be caused if the manganese content is too small, thus improving the energy density of the secondary battery.
  • the content of phosphorus element in the first cathode active material, based on the weight of the first cathode active material, is in the range of 12% by weight to 25% by weight, optionally in the range of 15% by weight. Within the range of weight %-20 weight %.
  • the content of phosphorus element is within the above range, which can effectively avoid the following situation: if the content of phosphorus element is too large, the covalency of P-O may be too strong and the Affects the conductivity of small polarons, thereby affecting the conductivity of the material; if the content of phosphorus is too small, it may cause the pyrophosphate in the core, the first cladding layer and/or the phosphate in the second cladding layer to crystallize The stability of the lattice structure decreases, thus affecting the overall stability of the material.
  • the weight ratio of the manganese element to the phosphorus element ranges from 0.90 to 1.25, optionally from 0.95 to 0.95. 1.20.
  • the weight ratio of manganese element to phosphorus element is within the above range, which can effectively avoid the following situation: if the weight ratio is too large, it may lead to increased dissolution of transition metals. Affects the stability of the material and the cycle and storage performance of the secondary battery; if the weight ratio is too small, the discharge voltage platform of the material may decrease, thereby reducing the energy density of the secondary battery.
  • the lattice change rate of the first cathode active material before and after complete deintercalation of lithium is 4% or less, optionally 3.8% or less, and more preferably 2.0-3.8%. .
  • the first cathode active material with a core-shell structure of the present application can achieve a lattice change rate of less than 4% before and after deintercalation of lithium. Therefore, using the first cathode active material can improve the gram capacity and rate performance of the secondary battery.
  • the Li/Mn anti-site defect concentration of the first cathode active material is 4% or less, optionally 2.2% or less, and more preferably 1.5-2.2%.
  • the compacted density of the first cathode active material at 3T is 2.2g/cm 3 or more, optionally 2.2g/cm 3 or more and 2.8g/cm 3 the following. Therefore, as the compaction density increases, the weight of the first positive electrode active material per unit volume increases, which is more conducive to increasing the volumetric energy density of the secondary battery.
  • the surface oxygen valence state of the first cathode active material is -1.90 or less, optionally -1.90 to -1.98. Therefore, by limiting the surface oxygen valence state of the first positive electrode active material within the above range, the interface side reaction between the first positive electrode material and the electrolyte can be reduced, thereby improving the battery cell cycle, high-temperature storage gas production and other performances.
  • the sum of the mass of the first cathode active material and the second cathode active material accounts for 88%-98.7% of the mass of the cathode plate. This further ensures that the secondary battery has excellent rate performance, kinetic performance and low-temperature cycle performance, as well as high energy density.
  • a fourth aspect of the present application provides a secondary battery, including the positive electrode plate of any one of the first to third aspects of the present application.
  • a fifth aspect of the present application provides a battery module including the secondary battery of the fourth aspect of the present application.
  • a sixth aspect of the present application provides a battery pack, including the battery module of the fifth aspect of the present application.
  • a seventh aspect of the present application provides an electrical device, including at least one selected from the group consisting of the secondary battery of the fourth aspect of the present application, the battery module of the fifth aspect of the present application, and the battery pack of the sixth aspect of the present application. kind.
  • FIG. 1 is a schematic diagram of a first positive electrode active material of a three-layer coating structure according to an embodiment of the present application.
  • FIG. 2 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG. 3 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 2 .
  • Figure 4 is a schematic diagram of a battery module according to an embodiment of the present application.
  • Figure 5 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 6 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 5 .
  • FIG. 7 is a schematic diagram of a power consumption device using a secondary battery as a power source according to an embodiment of the present application.
  • FIG 8 is a schematic diagram of the battery structure made of the positive electrode plate P1 of the present application.
  • Figure 9 is a schematic diagram of the battery structure made of the positive electrode plate P2 of the present application.
  • FIG 10 is a schematic diagram of the battery structure made of the positive electrode plate P3 of the present application.
  • FIG 11 is a schematic diagram of the battery structure made of the positive electrode plate P8 of the present application.
  • Figure 12 is a schematic diagram of the battery structure made of the positive electrode plate P10 of the present application.
  • Figure 13 is a schematic diagram of the battery structure made of the positive electrode plate P11 of the present application.
  • Figure 14 is a schematic diagram of the battery structure made of the positive electrode plate P12 of the present application.
  • Figure 15 is a schematic diagram of the battery structure made of the positive electrode plate P17 of the present application.
  • Figure 16 is a schematic diagram of the battery structure made of the positive electrode plate P18 of the present application.
  • FIG 17 is a schematic diagram of the battery structure made of the positive electrode plate P23 of the present application.
  • Figure 18 is a schematic diagram of the battery structure made of the positive electrode plate P24 of the present application.
  • Figure 19 is a schematic diagram of the battery structure made of the positive electrode plate P26 of the present application.
  • Figure 20 is a schematic diagram of the battery structure made of the positive electrode plate P27 of the present application.
  • Ranges disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5.
  • the numerical range “a-b” represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers.
  • the numerical range “0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations.
  • a certain parameter is an integer ⁇ 2
  • a method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • step (c) means that step (c) can be added to the method in any order.
  • the method may include steps (a), (b) and (c), and may also include step (a). , (c) and (b), and may also include steps (c), (a) and (b), etc.
  • condition "A or B” is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).
  • coating layer refers to the material layer coating the core.
  • the material layer can completely or partially cover the core.
  • coating layer is only for convenience of description. It is not intended to limit the invention.
  • the term “thickness of the coating layer” refers to the thickness of the material layer coating the core in the radial direction of the core.
  • Secondary batteries also known as rechargeable batteries or storage batteries, refer to batteries that can be recharged to activate active materials and continue to be used after the battery is discharged.
  • a secondary battery normally includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte.
  • active ions such as lithium ions
  • the isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows active ions to pass through.
  • the electrolyte is between the positive electrode piece and the negative electrode piece and mainly plays the role of conducting active ions.
  • An embodiment of the first aspect of the present application provides a positive electrode sheet, including a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector; the positive electrode film layer has a single-layer structure or a multi-layer structure; when the positive electrode film When the cathode film layer is a single-layer structure, at least one cathode film layer contains both a first cathode active material and a second cathode active material with a core-shell structure; and/or, when the cathode film layer is a multi-layer structure, at least one cathode film layer At least one of the layers contains both a first cathode active material and a second cathode active material having a core-shell structure; the first cathode active material includes a core, a first coating layer covering the core, and a first coating layer.
  • the positive electrode film layer is a single-layer structure or a multi-layer structure
  • the two positive electrode film layers are independently a single-layer structure or a multi-layer structure.
  • the positive electrode film layer has a single-layer structure refers to when one or two positive electrode film layers have a single-layer structure
  • the positive electrode film layer has a multi-layer structure refers to when one or two positive electrode film layers have a multi-layer structure.
  • the first cathode active material of the present application can improve the gram capacity, cycle performance and safety performance of the secondary battery. Although the mechanism is not yet clear, it is speculated that the first cathode active material of the present application has a core-shell structure.
  • the manganese position and the phosphorus position of the lithium manganese phosphate core with element A and element R respectively, not only can manganese be effectively reduced Dissolution, thereby reducing the manganese ions migrating to the negative electrode, reducing the electrolyte consumed due to the decomposition of the SEI film, improving the cycle performance and safety performance of the secondary battery, and can also promote the adjustment of the Mn-O bond, reduce the lithium ion migration barrier, and promote Lithium ion migration improves the rate performance of secondary batteries; by coating the core with a first coating layer including crystalline pyrophosphate, the migration resistance of manganese can be further increased, its dissolution can be reduced, and the surface miscellaneous lithium content can be reduced.
  • the element A doped at the manganese position of lithium manganese phosphate also helps to reduce the lattice change rate of lithium manganese phosphate during the deintercalation process of lithium and improves the structural stability of the first cathode material. , greatly reducing the dissolution of manganese and reducing the oxygen activity on the particle surface; the element R doped at the phosphorus site also helps to change the ease of change of the Mn-O bond length, thereby improving electronic conductivity and lowering the lithium ion migration barrier. Promote lithium ion migration and improve the rate performance of secondary batteries.
  • This application improves the energy density of the secondary battery by mixing the first positive electrode active material and the second positive electrode active material.
  • the advantages of the two materials complement each other; the internal lattice structure of the first positive electrode active material and the second positive electrode active material
  • the skeleton is stable.
  • the doping elements in the first cathode active material can effectively reduce the migration energy barrier of lithium ions, which is conducive to the rapid deintercalation of lithium ions.
  • the unique second package of the first cathode active material The coating significantly improves the electronic conductivity, and the first cathode active material is evenly dispersed around the second cathode active material, thereby improving the overall electronic conductivity of the mixed material, thus improving the cell rate performance and kinetic performance of the secondary battery.
  • the lattice change of the first positive active material is low, which reduces material polarization under low temperature conditions and effectively improves the low-temperature cycle life and low-temperature cycle capacity retention rate of the secondary battery.
  • a positive electrode film layer C and a positive electrode film layer D are respectively provided on both surfaces of the positive electrode current collector.
  • the positive electrode film layer C has a multi-layer structure
  • the positive electrode film layer D has a single-layer structure.
  • at least one of the cathode film layers C contains both the first cathode active material and the second cathode active material; optionally, the cathode film layer D contains one or both of the first cathode active material and the second cathode active material. kind; optionally, the remaining layers in the positive electrode film layer C include the first positive electrode active material or the second positive electrode active material.
  • a positive electrode film layer C and a positive electrode film layer D are respectively provided on both surfaces of the positive electrode current collector.
  • the positive electrode film layer C has a multi-layer structure
  • the positive electrode film layer D has a single-layer structure.
  • the cathode film layer D contains both the first cathode active material and the second cathode active material; optionally, any layer in the cathode film layer C contains the first cathode active material or the second cathode active material.
  • one positive electrode film layer is respectively provided on both surfaces of the positive electrode current collector, each positive electrode film layer has a multi-layer structure, and at least one layer of each positive electrode film layer is simultaneously A first cathode active material and a second cathode active material are included; optionally, the remaining layers in the cathode film layer include the first cathode active material or the second cathode active material.
  • An embodiment of the second aspect of the present application provides a positive electrode sheet, including a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector; at least one positive electrode film layer has a multi-layer structure, any one having multiple
  • the cathode film layer of the layer structure contains a first cathode active material and a second cathode active material having a core-shell structure in different layers; the first cathode active material includes a core, a first coating layer covering the core, and a coating layer.
  • A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge;
  • R includes one or more elements selected from B, Si, N and S; x is selected from any value in the range of -0.100 to 0.100; y is selected from any value in the range of 0.001 to 0.500; z is selected from 0.001 to Any value within the range of 0.100; M in crystalline pyrophosphate Li
  • the first cathode active material of the present application can improve the gram capacity and kinetic performance of secondary batteries, can effectively reduce manganese dissolution, reduce the lattice change rate and reduce the oxygen activity on the particle surface, reduce the migration of manganese ions to the negative electrode, and reduce SEI
  • the electrolyte consumed due to membrane decomposition improves the cycle performance and safety performance of the secondary battery;
  • the first positive active material can promote lithium ion migration and improve the rate performance of the secondary battery;
  • the first positive active material can reduce interface side reactions and reduce Generate gas and improve the storage performance, cycle performance and safety performance of secondary batteries.
  • This application improves the energy density of the secondary battery by mixing the first positive electrode active material and the second positive electrode active material.
  • the advantages of the two materials complement each other; the internal lattice structure of the first positive electrode active material and the second positive electrode active material
  • the skeleton is stable.
  • the doping elements in the first cathode active material can effectively reduce the migration energy barrier of lithium ions, which is conducive to the rapid deintercalation of lithium ions.
  • the unique second package of the first cathode active material The coating significantly improves the electronic conductivity, and the first cathode active material is evenly dispersed around the second cathode active material, thereby improving the overall electronic conductivity of the mixed material, thus improving the cell rate performance and kinetic performance of the secondary battery.
  • the lattice change of the first positive active material is low, which reduces material polarization under low temperature conditions and effectively improves the low-temperature cycle life and low-temperature cycle capacity retention rate of the secondary battery.
  • one positive electrode film layer is respectively provided on two surfaces of the positive electrode current collector, each positive electrode film layer has a multi-layer structure, and two adjacent layers in each positive electrode film layer A first positive electrode active material and a second positive electrode active material are respectively included.
  • a positive electrode film layer E and a positive electrode film layer F are respectively provided on both surfaces of the positive electrode current collector.
  • the positive electrode film layer E has a multi-layer structure
  • the positive electrode film layer F has a single-layer structure.
  • the two adjacent layers in the cathode film layer E respectively contain the first cathode active material and the second cathode active material; optionally, the remaining layers in the cathode film layer E and the cathode film layer F each independently contain the first cathode active material. material or second positive active material.
  • An embodiment of the third aspect of the present application provides a positive electrode sheet, including a positive electrode current collector and positive electrode film layer A and positive electrode film layer B respectively disposed on two surfaces of the positive electrode current collector; positive electrode film layer A and positive electrode film
  • the layers B are each independently a single-layer structure or a multi-layer structure; at least one layer of the cathode film layer A contains a first cathode active material with a core-shell structure, and at least one layer of the cathode film layer B contains a second cathode active material.
  • the first positive active material includes an inner core, a first cladding layer covering the inner core, a second cladding layer covering the first cladding layer, and a third cladding layer covering the second cladding layer;
  • the core contains a substance with the chemical formula Li 1+x Mn 1-y A y P 1-z R z O 4
  • the first coating layer contains crystalline pyrophosphate Li a MP 2 O 7 and/or M b ( P 2 O 7 ) c
  • the second coating layer includes crystalline phosphate XPO 4
  • the third coating layer includes carbon
  • A includes selected from Zn, Al, Na, K, Mg, Mo, W, Ti, One or more elements from V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge
  • R includes one or more elements selected from B, Si, N and S
  • x is selected From any value in the range of -0.100-0.100
  • y is selected from any value in the range 0.001-0.500
  • the first cathode active material of the present application can improve the gram capacity and kinetic performance of secondary batteries, can effectively reduce manganese dissolution, reduce the lattice change rate and reduce the oxygen activity on the particle surface, reduce the migration of manganese ions to the negative electrode, and reduce SEI
  • the electrolyte consumed due to membrane decomposition improves the cycle performance and safety performance of the secondary battery;
  • the first positive active material can promote lithium ion migration and improve the rate performance of the secondary battery;
  • the first positive active material can reduce interface side reactions and reduce Generate gas and improve the storage performance, cycle performance and safety performance of secondary batteries.
  • This application improves the energy density of the secondary battery by mixing the first positive electrode active material and the second positive electrode active material.
  • the advantages of the two materials complement each other; the internal lattice structure of the first positive electrode active material and the second positive electrode active material
  • the skeleton is stable.
  • the doping elements in the first cathode active material can effectively reduce the migration energy barrier of lithium ions, which is conducive to the rapid deintercalation of lithium ions.
  • the unique second package of the first cathode active material The coating significantly improves the electronic conductivity, and the first cathode active material is evenly dispersed around the second cathode active material, thereby improving the overall electronic conductivity of the mixed material, thus improving the cell rate performance and kinetic performance of the secondary battery.
  • the lattice change of the first positive active material is low, which reduces material polarization under low temperature conditions and effectively improves the low-temperature cycle life and low-temperature cycle capacity retention rate of the secondary battery.
  • the above-mentioned limitation on the numerical range of y is not only a limitation on the stoichiometric number of each element as A , is also a limitation on the sum of the stoichiometric numbers of each element as A.
  • the stoichiometric numbers y1, y2...yn of A1, A2...An each need to fall within the numerical range of y defined in this application, and y1 , y2...yn and the sum must also fall within this numerical range.
  • R is two or more elements
  • the limitations on the numerical ranges of the stoichiometric numbers of R, M, and X in this application also have the above meaning.
  • the above-mentioned limitation on the numerical range of e is not only a limitation on the stoichiometric number of each element as D, but also on each As a definition of the sum of the stoichiometric numbers of the elements of D.
  • the stoichiometric numbers e1, e2...en of D1, D2...Dn must fall within the numerical range for e defined in this application, and e1 The sum of , e2...en also needs to fall within this numerical range.
  • A is selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn
  • Q, L, E, K are each independently selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co , one of Ga, Sn, Sb, Nb and Ge, optionally, at least one of Q, L, E and K is Fe.
  • one of n1, n2, n3, and n4 is zero, and the rest are not zero; more optionally, two of n1, n2, n3, and n4 are zero, and the rest are not zero; also optionally, Three of n1, n2, n3, and n4 are zero, and the rest are not zero.
  • doping One, two or three of the above-mentioned A elements in addition, it is advantageous to dope one or two R elements at the phosphorus site, which is beneficial to uniform distribution of doping elements.
  • the values of x, y and z are such that the entire core remains electrically neutral.
  • the size of x is affected by the valence sizes of A and R and the sizes of y and z to ensure that the entire system is electrically neutral. If the value of x is too small, the lithium content of the entire core system will be reduced, affecting the gram capacity of the material.
  • the y value will limit the total amount of all doping elements. If y is too small, that is, the doping amount is too small, the doping elements will have no effect. If y exceeds 0.5, the Mn content in the system will be less, affecting the material's properties. voltage platform.
  • the R element is doped at the P position. Since the PO tetrahedron is relatively stable, and an excessive z value will affect the stability of the material, the z value is limited to 0.001-0.100.
  • the entire core system remains electrically neutral, which can ensure that there are as few defects and impurities in the first positive electrode active material as possible. If there is an excess of transition metal (such as manganese) in the first cathode active material, since the structure of the material system itself is relatively stable, the excess transition metal is likely to precipitate in the form of elemental elements, or form a heterogeneous phase inside the crystal lattice, which remains Electrical neutrality can minimize such impurities. In addition, ensuring the electrical neutrality of the system can also generate lithium vacancies in the material in some cases, thereby making the material's dynamic properties better.
  • transition metal such as manganese
  • the values of a, b and c satisfy the condition that the crystalline pyrophosphate Li a MP 2 O 7 or M b (P 2 O 7 ) c maintains electrical neutrality.
  • crystalline means that the degree of crystallinity is above 50%, that is, between 50% and 100%. Crystallinity less than 50% is called glassy state.
  • the crystalline pyrophosphates and crystalline phosphates of the present application have a crystallinity of 50% to 100%. Pyrophosphate and phosphate with a certain degree of crystallinity are not only conducive to giving full play to the pyrophosphate coating layer's ability to hinder manganese dissolution and the phosphate coating layer's excellent ability to conduct lithium ions and reduce interface side reactions, but also make the pyrophosphate The phosphate coating layer and the phosphate coating layer can achieve better lattice matching, thereby achieving a tighter combination of the coating layers.
  • the crystallinity of the first coating layer material crystalline pyrophosphate and the second coating layer material crystalline phosphate of the first cathode active material can be determined by conventional techniques in the art. It can be tested by means such as density method, infrared spectroscopy, differential scanning calorimetry and nuclear magnetic resonance absorption method, and it can also be tested by, for example, X-ray diffraction method.
  • a specific X-ray diffraction method for testing the crystallinity of the first coating layer crystalline pyrophosphate and the second coating layer crystalline phosphate of the first cathode active material may include the following steps:
  • the crystallinity of the pyrophosphate and phosphate in the coating layer can be adjusted, for example, by adjusting the process conditions of the sintering process, such as sintering temperature, sintering time, and the like.
  • pyrophosphate serves as the first coating layer to effectively isolate the doped metal ions from the electrolyte.
  • the structure of crystalline pyrophosphate is stable. Therefore, crystalline pyrophosphate coating can effectively inhibit the dissolution of transition metals and improve cycle performance.
  • the bonding between the first cladding layer and the core is similar to a heterojunction, and the strength of the bonding is limited by the degree of lattice matching.
  • the degree of bonding between the first cladding layer and the core is measured mainly by calculating the mismatch between the lattice constants of the core and the cladding. In this application, after the A and R elements are doped in the core, compared with undoped elements, the matching between the core and the first cladding layer is improved, and the core and the pyrophosphate cladding layer can be closer ground together.
  • crystalline phosphate is selected as the second coating layer, firstly, because it has a high lattice match (mismatch) with the crystalline pyrophosphate of the first coating layer. The degree is only 3%); secondly, the stability of phosphate itself is better than that of pyrophosphate, and coating pyrophosphate with it is helpful to improve the stability of the material.
  • the structure of crystalline phosphate is very stable and has excellent ability to conduct lithium ions. Therefore, coating with crystalline phosphate can effectively reduce interfacial side reactions on the surface of the first cathode active material, thereby improving secondary batteries. High temperature cycle and storage performance.
  • the lattice matching between the second cladding layer and the first cladding layer is similar to the above-mentioned combination between the first cladding layer and the core.
  • the lattice mismatch is less than 5%, the lattice matching is relatively small. Well, the two are easily combined closely.
  • the main reason why carbon is used as the third layer of coating is that the carbon layer has better electronic conductivity. Since electrochemical reactions occur when used in secondary batteries and require the participation of electrons, in order to increase electron transmission between particles and at different locations on the particles, materials with excellent conductive properties can be used. Carbon coating. Carbon coating can effectively improve the conductive performance and desolvation ability of the first cathode active material.
  • Figure 1 is a schematic diagram of an ideal first cathode active material with a three-layer coating structure.
  • the innermost circle schematically represents the core, which is the first cladding layer, the second cladding layer, and the third cladding layer from the inside to the outside.
  • This figure represents the ideal state where each layer is completely covered. In practice, each layer of coating can be fully covered or partially covered.
  • the carbon mass accounts for 0.1%-4% of the mass of the carbon-coated LiFePO 4 ; and/or the carbon mass accounts for 0.1%-4% of the mass of the carbon-coated LiFePO4.
  • d D e PO 4 mass 0.1%-4%.
  • the mass ratio of the first cathode active material to the second cathode active material is 1:7-7:1, optionally 1:4-4:1, further Optional 1:3-3:1, such as 1:7, 1:5, 1:3, 1:2, 3:5, 1:1, 5:3, 2:1, 3:1, 5: 1. 7:1.
  • the secondary battery has high energy density, excellent kinetic properties, excellent rate performance, long low-temperature cycle life and high low-temperature cycle capacity retention rate, and reduce interface side reactions.
  • A in the first cathode active material, is selected from one or more elements selected from Fe, Ti, V, Ni, Co and Mg.
  • doping elements within the above range, it is beneficial to enhance the doping effect. On the one hand, it further reduces the lattice change rate, thereby inhibiting the dissolution of manganese and reducing the consumption of electrolyte and active lithium. On the other hand, it is also beneficial to The surface oxygen activity is further reduced and the interface side reaction between the first positive electrode active material and the electrolyte is reduced, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.
  • R is an element selected from the group consisting of B, Si, N and S.
  • the ratio of y to 1-y is selected from 1:10 to 1:1, optionally from 1:4 to 1:1.
  • y represents the sum of the stoichiometric numbers of the Mn-site doping element A.
  • the ratio of z to 1-z is selected from 1:9 to 1:999, optionally from 1:499 to 1:249.
  • z represents the sum of stoichiometric numbers of the P-site doping elements R.
  • the crystalline pyrophosphate in the first coating layer has a interplanar spacing ranging from 0.293 to 0.470 nm, and the crystallographic orientation is (111)
  • the included angle range is 18.00°-32.00°; the interplanar spacing range of the crystalline phosphate in the second coating layer is 0.244-0.425nm, and the included angle range of the crystal direction (111) is 20.00°-37.00°.
  • the first coating layer and the second coating layer in the first cathode active material of the present application both use crystalline materials.
  • Crystalline pyrophosphate and crystalline phosphate within the above-mentioned crystal plane spacing and included angle range can more effectively suppress the lattice change rate and Mn dissolution of lithium manganese phosphate during the lithium deintercalation process, thereby improving the performance of secondary batteries.
  • the crystalline pyrophosphate and crystalline phosphate in the coating layer can be characterized by conventional technical means in the art, or by means of a transmission electron microscope (TEM), for example. Under TEM, the core and cladding layers can be distinguished by testing the interplanar spacing.
  • TEM transmission electron microscope
  • the specific testing method for the interplanar spacing and angle of crystalline pyrophosphate and crystalline phosphate in the coating layer may include the following steps:
  • the difference between the interplanar spacing range of crystalline pyrophosphate and the existence of crystalline phosphate can be directly judged by the value of the interplanar spacing.
  • the carbon in the third coating layer is a mixture of SP2 form carbon and SP3 form carbon, optionally, SP2 form carbon and SP3 form
  • the molar ratio of carbon is any value in the range of 0.1-10, and optionally any value in the range of 2.0-3.0.
  • the molar ratio of SP2 form carbon to SP3 form carbon may be about 0.1, about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8 , about 0.9, about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, or about 10, or within any range of any of the above values.
  • the overall electrical performance of the secondary battery is improved.
  • the following situation can be avoided: If the carbon in the cladding layer is all amorphous SP3 form, the conductivity is poor; if they are all graphitized SP2 form, although the conductivity is good, there are few lithium ion paths, which is not conducive to the deintercalation of lithium.
  • limiting the molar ratio of SP2 form carbon to SP3 form carbon within the above range can not only achieve good conductivity but also ensure the passage of lithium ions, which is beneficial to the realization of secondary battery functions and its cycle performance.
  • the mixing ratio of the SP2 form and the SP3 form of the third cladding carbon can be controlled by sintering conditions such as sintering temperature and sintering time.
  • sintering conditions such as sintering temperature and sintering time.
  • sucrose is used as the carbon source to prepare the third coating layer
  • the sucrose is cracked at high temperature and deposited on the second coating layer.
  • both SP3 and SP2 forms will be produced. of carbon coating.
  • the ratio of SP2 form carbon and SP3 form carbon can be controlled by selecting high temperature cracking conditions and sintering conditions.
  • the structure and characteristics of the carbon in the third coating layer can be measured by Raman spectroscopy.
  • the specific test method is as follows: by peak splitting the energy spectrum of the Raman test, Id/Ig is obtained (where Id is the peak of SP3 form carbon Intensity, Ig is the peak intensity of SP2 form carbon), thereby confirming the molar ratio of the two.
  • the coating amount of the first coating layer is greater than 0 and less than or equal to 6% by weight, optionally greater than 0 and less than or equal to 5.5% by weight, and more preferably Selected to be greater than 0 and less than or equal to 2% by weight, based on the weight of the core; and/or
  • the coating amount of the second coating layer is greater than 0 and less than or equal to 6% by weight, optionally greater than 0 and less than or equal to 5.5% by weight, and more optionally 2-4% by weight, based on the weight of the core; and /or
  • the coating amount of the third coating layer is greater than 0 and less than or equal to 6 wt%, optionally greater than 0 and less than or equal to 5.5 wt%, more optionally greater than 0 and less than or equal to 2 wt%, based on the core Weight scale.
  • the coating amount of each layer is not zero.
  • the coating amount of the three coating layers is preferably within the above range, so that the core can be fully coated without sacrificing the grams of the cathode active material.
  • the dynamic performance and safety performance of secondary batteries can be further improved.
  • the coating amount is within the above range, the following situations can be avoided: Too little coating means that the thickness of the coating layer is thin, which may not effectively hinder the migration of transition metals; Excessive amount means that the coating layer is too thick, which will affect the migration of Li+ and thus affect the rate performance of the material.
  • the coating amount within the above range, the following situations can be avoided: too much coating may affect the overall platform voltage of the material; too little coating may not achieve sufficient Covering effect.
  • the carbon coating mainly plays the role of enhancing electron transmission between particles.
  • the structure also contains a large amount of amorphous carbon, the density of carbon is low. Therefore, if the coating amount is too high, If it is large, it will affect the compaction density of the pole piece.
  • the thickness of the first coating layer is 1-10 nm.
  • the thickness of the first cladding layer may be about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, or about 10 nm. , or within any range of any of the above values.
  • the thickness of the first coating layer ranges from 1 to 10 nm, it can avoid the possible adverse effects on the dynamic properties of the material when it is too thick, and can avoid the inability to effectively block transition metal ions when it is too thin. Migration issues.
  • the thickness of the second coating layer is 2-15 nm.
  • the thickness of the second cladding layer may be about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm , about 11nm, about 12nm, about 13nm, about 14nm, about 15nm, or within any range of any of the above values.
  • the thickness of the second coating layer is in the range of 2-15nm, the surface structure of the second coating layer is stable and the side reaction with the electrolyte is small. Therefore, the interface side reaction can be effectively reduced, thereby improving the secondary High temperature performance of the battery.
  • the thickness of the third coating layer is 2-25 nm.
  • the thickness of the third cladding layer may be about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10nm, about 11nm, about 12nm, about 13nm, about 14nm, about 15nm, about 16nm, about 17nm, about 18nm, about 19nm, about 20nm, about 21nm, about 22nm, about 23nm, about 24nm or about 25nm, or among the above Any value within any range.
  • the electrical conductivity of the material can be improved and the compaction density performance of the battery pole piece prepared using the first cathode active material can be improved.
  • the thickness test of the coating layer is mainly carried out through FIB.
  • the specific method may include the following steps: randomly select a single particle from the first cathode active material powder to be tested, and cut a slice with a thickness of about 100 nm from the middle position or near the middle position of the selected particle. , then perform TEM testing on the sheet, measure the thickness of the coating layer, measure 3-5 positions, and take the average value.
  • the manganese element content is in the range of 10% to 35% by weight, optionally 15% by weight, based on the weight of the first cathode active material. In the range of weight % - 30 weight %, more optionally in the range of 17 weight % - 20 weight %.
  • the content of manganese may correspond to the content of the core.
  • the content of manganese element is within the above range, which can effectively avoid problems such as deterioration in structural stability and density reduction that may be caused by excessive manganese element content.
  • This can improve the performance of the secondary battery such as cycle, storage and compaction density; and can avoid problems such as low voltage platform that may be caused if the manganese content is too small, thus improving the energy density of the secondary battery.
  • the content of phosphorus element is in the range of 12% to 25% by weight based on the weight of the first cathode active material, optionally in Within the range of 15% to 20% by weight.
  • the content of phosphorus element is within the above range, which can effectively avoid the following situation: if the content of phosphorus element is too large, the covalency of P-O may be too strong and the Affects the conductivity of small polarons, thereby affecting the conductivity of the material; if the content of phosphorus is too small, it may cause the pyrophosphate in the core, the first cladding layer and/or the phosphate in the second cladding layer to crystallize The stability of the lattice structure decreases, thus affecting the overall stability of the material.
  • the weight ratio of the manganese element to the phosphorus element ranges from 0.90 to 1.25, optionally 0.95 -1.20.
  • the weight ratio of manganese element to phosphorus element is within the above range, which can effectively avoid the following situation: the weight ratio is too large, which means too much manganese element and increased manganese dissolution. , affecting the stability and gram capacity of the first positive electrode active material, and thus affecting the cycle performance and storage performance of the secondary battery; if the weight ratio is too small, it means that too much phosphorus element will easily form impurity phases, which will cause the material to deteriorate. The discharge voltage platform drops, thereby reducing the energy density of the secondary battery.
  • the measurement of manganese and phosphorus elements can be carried out using conventional technical means in this field.
  • the following method is used to determine the content of manganese and phosphorus: dissolve the material in dilute hydrochloric acid (concentration 10-30%), use ICP to test the content of each element in the solution, and then measure and convert the content of manganese. Get its weight ratio.
  • the lattice change rate of the first cathode active material before and after complete deintercalation of lithium is 4% or less, optionally 3.8% or less, and more preferably 2.0-3.8 %.
  • the lithium deintercalation process of lithium manganese phosphate is a two-phase reaction.
  • the interfacial stress of the two phases is determined by the lattice change rate before and after lithium deintercalation.
  • the first cathode active material with a core-shell structure of the present application can achieve a lattice change rate of less than 4% before and after deintercalation of lithium. Therefore, the use of the first cathode active material can improve the rate performance of the secondary battery.
  • the lattice change rate can be measured by methods known in the art, such as X-ray diffraction (XRD).
  • the Li/Mn anti-site defect concentration of the first cathode active material is 4% or less, optionally 2.2% or less, and more preferably 1.5-2.2%.
  • the Li/Mn anti-site defect in this application refers to the interchange of positions of Li + and Mn 2+ in the LiMnPO 4 crystal lattice.
  • the Li/Mn antisite defect concentration refers to the percentage of Li + exchanged with Mn 2+ to the total amount of Li + .
  • the Li/Mn antisite defect concentration can be tested in accordance with JIS K 0131-1996, for example.
  • the first cathode active material with a core-shell structure of the present application can achieve the above-mentioned lower Li/Mn anti-site defect concentration.
  • the inventor of the present application speculates that because Li + and Mn 2+ will exchange positions in the LiMnPO 4 lattice, and the Li + transmission channel is a one-dimensional channel, Mn 2+ is in Li + It will be difficult to migrate in the channel, thus hindering the transport of Li + . Therefore, the first cathode active material with a core-shell structure of the present application has a low concentration of Li/Mn anti-site defects within the above range. Therefore, it is possible to avoid Mn 2+ from hindering the transport of Li + and at the same time improve the first cathode. Gram capacity development and rate performance of active materials.
  • the first cathode active material has a compacted density at 3T of 2.2 g/cm or more, optionally 2.2 g/cm or more and 2.8 g/cm 3 or less.
  • the higher the compaction density the greater the weight of the active material per unit volume. Therefore, increasing the compaction density is beneficial to increasing the volumetric energy density of the battery core.
  • the compacted density can be measured according to GB/T24533-2009.
  • the surface oxygen valence state of the first cathode active material is -1.90 or less, optionally -1.90 to -1.98.
  • the stable valence state of oxygen is originally -2.
  • its surface valence state is below -1.7.
  • EELS electron energy loss spectroscopy
  • the sum of the masses of the first cathode active material and the second cathode active material accounts for 88% to 98.7% of the mass of the cathode plate. This further ensures that the secondary battery has excellent rate performance, kinetic performance and low-temperature cycle performance, as well as high energy density.
  • the primary particles of the first cathode active material have an average particle diameter in the range of 50-500 nm, and the volume median particle diameter Dv50 is in the range of 200-300 nm. Since particles will agglomerate, the actual measured secondary particle size after agglomeration may be 500-40000nm. The size of the first positive active material particles will affect the processing of the material and the compacted density performance of the pole piece.
  • the average particle size of the primary particles is too small, which may cause particle agglomeration, difficulty in dispersion, and requires more bonding agent, resulting in poor brittleness of the electrode piece; the average particle size of the primary particles of the first positive electrode active material is too large, which may cause larger gaps between particles and reduce the compacted density.
  • the lattice change rate and Mn dissolution of lithium manganese phosphate during the lithium deintercalation process can be effectively suppressed, thereby improving the high-temperature cycle stability and high-temperature storage performance of the secondary battery.
  • the median particle size Dv50 refers to the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%.
  • the median particle diameter Dv50 of the material can be determined using laser diffraction particle size analysis. For example, refer to the standard GB/T 19077-2016 and use a laser particle size analyzer (such as Malvern Master Size 3000) for measurement.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • the metal foil aluminum foil can be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer.
  • the composite current collector can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the positive electrode film layer may further include other positive electrode active materials for batteries known in the art.
  • the cathode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds.
  • the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination.
  • lithium transition metal oxides may include, but are not limited to, lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide , at least one of lithium nickel manganese oxide and its modified compounds.
  • lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium manganese phosphate (such as LiMnPO 4 ), composites of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and composite materials of lithium manganese iron phosphate and carbon. A sort of.
  • the positive electrode film layer optionally further includes a binder.
  • the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene tripolymer. At least one of a meta-copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer and a fluorine-containing acrylate resin.
  • the positive electrode film layer optionally further includes a conductive agent.
  • the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the preparation method of the first cathode active material includes the following steps:
  • the core chemical formula is Li 1+x Mn 1-y A y P 1-z R z O 4 , where x is any value in the range of -0.100-0.100, and y is in the range of 0.001-0.500 Any value of One or more elements from Sb, Nb and Ge, optionally one or more elements from Fe, Ti, V, Ni, Co and Mg, R is selected from B, Si, N and S One or more elements, optionally, R is an element selected from B, Si, N and S;
  • Coating step Provide Li a MP 2 O 7 and/or M b (P 2 O 7 ) c and XPO 4 suspension respectively, add the core material to the above suspension and mix, and obtain the first positive electrode after sintering Active material, where 0 ⁇ a ⁇ 2, 1 ⁇ b ⁇ 4, 1 ⁇ c ⁇ 6, the values of a, b and c satisfy the following conditions: making crystalline pyrophosphate Li a MP 2 O 7 or M b (P 2 O 7 ) c maintains electrical neutrality; M is each independently selected from one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al; One or more elements from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al;
  • the first positive active material has a core-shell structure, which includes an inner core, a first cladding layer covering the core, a second cladding layer covering the first cladding layer, and a third cladding layer covering the second cladding layer.
  • Three coating layers The first coating layer includes crystalline pyrophosphate Li a MP 2 O 7 and/or M b (P 2 O 7 ) c .
  • the second coating layer includes crystalline phosphate XPO 4 .
  • the cladding is carbon.
  • the step of providing the core material includes the following steps:
  • Step (1) Mix and stir the manganese source, the dopant of element A and the acid in a container to obtain manganese salt particles doped with element A;
  • Step (2) Mix the manganese salt particles doped with element A with a lithium source, a phosphorus source and a dopant of element R in a solvent to obtain a slurry, which is then sintered under the protection of an inert gas atmosphere to obtain a doped element.
  • the core of A and element R where the core doped with element A and element R is Li 1+x Mn 1-y A y P 1-z R z O 4 , where x is in the range of -0.100-0.100 Any value, y is any value in the range of 0.001-0.500, z is any value in the range of 0.001-0.100,
  • A is selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr , one or more elements among Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more elements among Fe, Ti, V, Ni, Co and Mg
  • R is One or more elements selected from B, Si, N and S, optionally, R is one element selected from B, Si, N and S.
  • the preparation method of the present application has no particular limitation on the source of materials.
  • the source of a certain element may include one of the elements, sulfates, halides, nitrates, organic acid salts, oxides or hydroxides of the element. or more, the precursor is the source that can achieve the purpose of the preparation method of the present application.
  • the dopant of element A is selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr , Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, each element, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, hydrogen One or more of the oxides.
  • the dopant of element R is an inorganic acid of one or more elements selected from B, Si, N and S. , one or more of sub-acid, organic acid, sulfate, chloride, nitrate, organic acid salt, oxide and hydroxide.
  • the manganese source in the step of providing the core material, may be a manganese-containing substance known in the art that can be used to prepare lithium manganese phosphate.
  • the manganese source may be one or more selected from the group consisting of elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.
  • the acid in the step of providing the core material, may be selected from organic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, silicic acid, silicic acid, and organic acids such as oxalic acid. of one or more. In some embodiments, the acid is a dilute organic acid with a concentration of 60% by weight or less.
  • the lithium source in the step of providing the core material, may be a lithium-containing substance known in the art that can be used to prepare lithium manganese phosphate.
  • the lithium source is one or more selected from lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate.
  • the phosphorus source in the step of providing the core material, may be a phosphorus-containing material known in the art that can be used to prepare lithium manganese phosphate.
  • the phosphorus source is one or more selected from diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate and phosphoric acid.
  • the step of providing the core material after the manganese source, the dopant of element A and the acid react in the solvent to obtain the manganese salt suspension doped with element A , the suspension is filtered, dried, and sanded to obtain element A-doped manganese salt particles with a particle size of 50-200 nm.
  • the slurry in step (2) is dried to obtain powder, and then the powder is sintered to obtain doped element A and element R kernel.
  • step (1) is mixed at a temperature of 20-120°C, optionally 40-120°C; and/or
  • step (1) Stirring in step (1) is carried out at 400-700rpm for 1-9h, optionally 3-7h.
  • reaction temperature in step (1) can be carried out at about 30°C, about 50°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C or about 120°C. ; Stirring in step (1) is carried out for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours or about 9 hours; optionally, in step (1)
  • the reaction temperature and stirring time can be within any range of any of the above values.
  • step (2) is mixed at a temperature of 20-120°C, optionally 40-120°C, for 1-12 h.
  • the reaction temperature in step (2) can be carried out at about 30°C, about 50°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C or about 120°C.
  • Mixing in step (2) is carried out for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, about 10 hours, about 11 hours or about 12 hours hours; optionally, the reaction temperature and mixing time in step (2) can be within any range of any of the above values.
  • the prepared core and the cathode active material produced therefrom have fewer lattice defects, which is beneficial to inhibiting manganese dissolution and reducing the interaction between the cathode active material and the electrolyte. Interfacial side reactions, thereby improving the cycle performance and safety performance of secondary batteries.
  • the pH of the solution in the step of providing the core material, in the process of preparing dilute manganese acid particles doped with A element and R element, the pH of the solution is controlled to be 3.5-6, optionally Preferably, the pH of the solution is controlled to be 4-6, more optionally, the pH of the solution is controlled to be 4-5. It should be noted that in this application, the pH of the resulting mixture can be adjusted by methods commonly used in the art, for example, by adding acid or alkali.
  • the molar ratio of the manganese salt particles to the lithium source and the phosphorus source is 1:0.5-2.1:0.5-2.1, optionally, doped with The molar ratio of the manganese salt particles mixed with element A to the lithium source and phosphorus source is about 1:1:1.
  • the sintering conditions in the process of preparing the A element and R element doped lithium manganese phosphate are: in an inert gas or a mixture of an inert gas and hydrogen.
  • sintering at 600-950°C for 4-10 hours in an atmosphere; optionally, sintering can be performed at about 650°C, about 700°C, about 750°C, about 800°C, about 850°C or about 900°C for about 2 hours, About 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours or about 10 hours; optionally, the sintering temperature and sintering time can be in any range of any of the above values.
  • the sintering temperature and sintering time can be in any range of any of the above values.
  • the protective atmosphere is a mixed gas of 70-90 volume % nitrogen and 10-30 volume % hydrogen.
  • the coating step includes:
  • the first coating step dissolve the source of element M, the phosphorus source and the acid, and optionally the lithium source in a solvent to obtain a first coating layer suspension; combine the core obtained in the core step with the first coating The first coating layer suspension obtained in the step is thoroughly mixed, dried, and then sintered to obtain a material covered by the first coating layer;
  • the second coating step dissolve the source of element
  • the second coating layer suspension obtained in the second coating step is thoroughly mixed, dried, and then sintered to obtain a material covered with two coating layers;
  • the third coating step Dissolve the carbon source in the solvent and fully dissolve it to obtain a third coating layer solution; then add the two-layer coating layer-coated material obtained in the second coating step to the third coating layer solution , mix evenly, dry, and then sinter to obtain a material covered with three coating layers, that is, the positive active material.
  • the source of element M is selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al.
  • the respective elements carbonates, sulfates, chlorides, nitrates, organic acid salts, oxides, and hydroxides of one or more elements.
  • the source of element X is selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al
  • the respective elements carbonates, sulfates, chlorides, nitrates, organic acid salts, oxides, and hydroxides of one or more elements.
  • the carbon source is one or more selected from starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.
  • the pH of the solution in which the source of element M, the phosphorus source and the acid and optionally the lithium source are dissolved is controlled to be 3.5-6.5, and then stirred And react for 1-5h, then heat the solution to 50-120°C and maintain this temperature for 2-10h, and/or, sintering is performed at 650-800°C for 2-6 hours.
  • the reaction proceeds fully during the first coating step.
  • the reaction is carried out for about 1.5 hours, about 2 hours, about 3 hours, about 4 hours, about 4.5 hours or about 5 hours.
  • the reaction time may be within any range of any of the above values.
  • the pH of the solution is controlled to be 4-6.
  • the solution is heated to about 55°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C, or about 120°C, and Maintain at this temperature for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours or about 10 hours; optionally, in the first coating step , the heating temperature and holding time can be within any range of any of the above values.
  • the sintering in the first coating step, can be at about 650°C, about 700°C, about 750°C, or about 800°C for about 2 hours, about 3 hours, about 4 hours, about 5 hours, or about 6 hours; optionally, the sintering temperature and sintering time can be within any range of any of the above values.
  • the first coating step by controlling the sintering temperature and time within the above range, the following situation can be avoided: when the sintering temperature in the first coating step is too low and the sintering time is too short, the first coating The crystallinity of the layer is low and there are more amorphous substances, which will lead to a decrease in the effect of inhibiting metal dissolution, thus affecting the cycle performance and high-temperature storage performance of the secondary battery; and when the sintering temperature is too high, the first coating layer will The appearance of impurity phases will also affect its effect of inhibiting metal dissolution, thereby affecting the cycle and high-temperature storage performance of secondary batteries; when the sintering time is too long, the thickness of the first coating layer will increase, affecting the migration of Li + , thus affecting the gram capacity and rate performance of the material.
  • the second coating step after the source of element -150°C and maintain this temperature for 2-10h, and/or, sintering is performed at 500-700°C for 6-10 hours.
  • the reaction proceeds fully.
  • the reaction is carried out for about 1.5 hours, about 2 hours, about 3 hours, about 4 hours, about 4.5 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, About 9 hours or about 10 hours.
  • the reaction time of the reaction can be within any range of any of the above values.
  • the solution is heated to about 65°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C, about 120°C, about 130°C, about 140°C. °C or about 150°C, and keep at this temperature for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours or about 10 hours; optional
  • the heating temperature and the holding time may be within any range of any of the above values.
  • step of providing the core material and the first and second coating steps, before sintering that is, in the preparation of the core material in which the chemical reaction occurs (steps (1)-(2)) and in the first
  • step of providing the core material and the first and second coating steps, before sintering that is, in the preparation of the core material in which the chemical reaction occurs (steps (1)-(2)) and in the first
  • step of providing the core material and the first and second coating steps, before sintering that is, in the preparation of the core material in which the chemical reaction occurs (steps (1)-(2)) and in the first
  • the reaction temperature and reaction time by selecting the appropriate reaction temperature and reaction time as above, the following situations can be avoided: when the reaction temperature is too low, the reaction cannot occur or the reaction rate is slow; When the temperature is too high, the product decomposes or forms impurity phases; when the reaction time is too long, the product particle size is larger, which may increase the time and difficulty of subsequent processes; when the reaction time is too short, the reaction is incomplete and less product is obtained.
  • the sintering can be performed at about 550°C, about 600°C, or about 700°C for about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours; optionally
  • the sintering temperature and sintering time can be within any range of any of the above values.
  • the second coating step by controlling the sintering temperature and time within the above range, the following situation can be avoided: when the sintering temperature in the second coating step is too low and the sintering time is too short, it will cause the second coating The crystallinity of the layer is low and the amorphous state is more, which reduces the surface reactivity of the material, thereby affecting the cycle and high-temperature storage performance of the secondary battery.
  • the sintering temperature is too high, impurities will appear in the second coating layer. Phase will also affect its effect of reducing the surface reactivity of the material, thereby affecting the cycle and high-temperature storage performance of the secondary battery.
  • the sintering time is too long, the thickness of the second coating layer will increase, affecting the voltage platform of the material. , thereby reducing the energy density of the material.
  • the sintering in the third coating step is performed at 700-800°C for 6-10 hours.
  • the sintering can be performed at about 700°C, about 750°C, or about 800°C for about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours; optionally
  • the sintering temperature and sintering time can be within any range of any of the above values.
  • the third coating step by controlling the sintering temperature and time within the above range, the following situation can be avoided: when the sintering temperature in the third coating step is too low, it will lead to a degree of graphitization of the third coating layer Decrease, affecting its conductivity, thereby affecting the gram capacity of the material; when the sintering temperature is too high, the degree of graphitization of the third coating layer will be too high, affecting the transmission of Li + , thus affecting the gram capacity of the material, etc.; When the sintering time is too short, the coating layer will be too thin, affecting its conductivity, thereby affecting the gram capacity of the material; when the sintering time is too long, the coating layer will be too thick, affecting the compaction density of the material.
  • drying is performed at 100°C to 200°C, optionally 110°C to 190°C, more optionally 120°C to 180°C, or even
  • the optional drying temperature is 120°C to 170°C
  • the most optional is 120°C to 160°C
  • the drying time is 3-9h
  • the optional 4-8h is the most optional is 5-7h
  • the secondary battery prepared by the first cathode active material preparation method of the present application has reduced dissolution of Mn and Mn-site doping elements after cycling, and has high-temperature stability, high-temperature cycle performance and Rate performance is improved.
  • the sources of raw materials are wide, the cost is low, and the process is simple, which is conducive to industrialization.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.
  • the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material.
  • the composite current collector can be formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative active material may be a negative active material known in the art for batteries.
  • the negative active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, and the like.
  • the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon carbon composites, silicon nitrogen composites and silicon alloys.
  • the tin-based material may be selected from at least one of elemental tin, tin oxide compounds and tin alloys.
  • the present application is not limited to these materials, and other traditional materials that can be used as battery negative electrode active materials can also be used. Only one type of these negative electrode active materials may be used alone, or two or more types may be used in combination.
  • the negative electrode film layer optionally further includes a binder.
  • the binder may be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), At least one of polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • the negative electrode film layer optionally further includes a conductive agent.
  • the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the negative electrode film layer optionally includes other auxiliaries, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like.
  • thickeners such as sodium carboxymethylcellulose (CMC-Na)
  • the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative active materials, conductive agents, binders and any other components in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode piece can be obtained.
  • a solvent such as deionized water
  • the electrolyte plays a role in conducting ions between the positive and negative electrodes.
  • the type of electrolyte in this application can be selected according to needs.
  • the electrolyte can be liquid, gel, or completely solid.
  • the electrolyte is liquid and includes an electrolyte salt and a solvent.
  • the electrolyte salt may be selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluoroborate, lithium dioxaloborate, lithium difluorodioxalate phosphate and lithium tetrafluoroxalate phosphate.
  • the solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
  • the electrolyte optionally also includes additives.
  • additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.
  • the secondary battery further includes a separator film.
  • a separator film There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.
  • the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.
  • the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.
  • the secondary battery may include an outer packaging.
  • the outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.
  • FIG. 2 shows a square-structured secondary battery 5 as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.
  • FIG. 4 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • the above-mentioned battery modules can also be assembled into a battery pack.
  • the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application.
  • the secondary battery, battery module, or battery pack can be used as a power source for the power-consuming device, or as an energy storage unit of the power-consuming device.
  • Electric devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric Trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.
  • secondary batteries, battery modules or battery packs can be selected according to its usage requirements.
  • Fig. 7 is an electrical device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.
  • a battery pack or battery module can be used.
  • preparation examples of the present application will be described.
  • the preparation examples described below are illustrative and are only used to explain the present application and are not to be construed as limitations of the present application. If specific techniques or conditions are not specified in the preparation examples, the techniques or conditions described in literature in the field or the product instructions should be followed. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.
  • Step S1 Preparation of Fe, Co, V and S co-doped manganese oxalate
  • Step S2 Preparation of core Li 0.997 Mn 0.60 Fe 0.393 V 0.004 Co 0.003 P 0.997 S 0.003 O 4
  • Step S3 Preparation of the first coating layer suspension
  • Li 2 FeP 2 O 7 solution Dissolve 7.4g lithium carbonate, 11.6g ferrous carbonate, 23.0g ammonium dihydrogen phosphate and 12.6g oxalic acid dihydrate in 500mL deionized water, control the pH to 5, then stir and keep at room temperature The reaction was carried out for 2 hours to obtain a solution, and then the temperature of the solution was raised to 80°C and maintained at this temperature for 4 hours to obtain a first coating layer suspension.
  • Step S4 Coating of the first coating layer
  • step S2 Add 1571.9g of the doped lithium manganese phosphate core material obtained in step S2 to the first coating layer suspension (coating material content is 15.7g) obtained in step S3, stir and mix thoroughly for 6 hours, and mix evenly Finally, it was transferred to an oven at 120°C for drying for 6 hours, and then sintered at 650°C for 6 hours to obtain the pyrophosphate-coated material.
  • Step S5 Preparation of the second coating layer suspension
  • Step S6 Coating of the second coating layer
  • step S4 Add 1586.8g of the pyrophosphate-coated material obtained in step S4 to the second coating layer suspension obtained in step S5 (coating material content is 47.1g), stir and mix thoroughly for 6 hours, and mix evenly Finally, it was transferred to an oven at 120°C for drying for 6 hours, and then sintered at 700°C for 8 hours to obtain a two-layer coated material.
  • Step S7 Preparation of the third coating layer aqueous solution
  • sucrose aqueous solution Dissolve 37.3g of sucrose in 500g of deionized water, then stir and fully dissolve to obtain a sucrose aqueous solution.
  • Step S8 Coating of the third coating layer
  • step S6 Add 1633.9g of the two-layer coating material obtained in step S6 to the sucrose solution obtained in step S7, stir and mix together for 6 hours. After mixing evenly, transfer to a 150°C oven to dry for 6 hours, and then sinter at 700°C for 10 hours. A three-layer coated material is obtained.
  • the positive electrode active materials of Preparation Examples 2 to 42 and Comparative Examples 1 to 17 were prepared in a manner similar to Preparation Example 1. The differences in the preparation of the positive electrode active materials are shown in Tables 1-6.
  • Comparative Examples 1-2, 4-10 and 12 are not coated with the first layer, so there are no steps S3-S4; Comparative Example 1-11 is not coated with the second layer, so there are no steps S5-S6.
  • the slurry of the positive electrode active material in Preparation Example 1 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • the slurry of the positive electrode active material in Preparation Example 43 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • Film P2 The slurry of the positive electrode active material in Preparation Example 43 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • Film P2 The slurry of the positive electrode active material in Preparation Example 43 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode. Film P2.
  • the slurry of the cathode active material in Preparation Example 1 was evenly coated on one side of the aluminum foil in a coating amount of 0.019 g/cm 2
  • the slurry of the cathode active material in Preparation Example 43 was evenly coated in a coating amount of 0.2 g/cm 2 Coat it on the other side of the aluminum foil, vacuum dry it at a high temperature of 100-120°C for 14 hours, and compact it with a roller press to obtain the positive electrode piece P3.
  • the slurry of the positive electrode active material in Preparation Example 44 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019 g/cm 2 , and the rest was the same as Example 3 to obtain the positive electrode sheet P4.
  • the slurry of the cathode active material in Preparation Example 1 was evenly coated on one side of the aluminum foil in a coating amount of 0.019g/cm 2
  • the slurry of the cathode active material in Preparation Example 44 was evenly coated in a coating amount of 0.019g/cm 2 Coating on the other side of the aluminum foil, the rest is the same as in Example 3 to obtain the positive electrode sheet P5.
  • the slurry of the cathode active material in Preparation Example 43 was evenly coated on one side of the aluminum foil in a coating amount of 0.019g/cm 2
  • the slurry of the cathode active material in Preparation Example 44 was evenly coated in a coating amount of 0.019g/cm 2 Coating on the other side of the aluminum foil, the rest is the same as in Example 3 to obtain the positive electrode piece P6.
  • the slurry of the cathode active material in Preparation Example 1 and the slurry of the cathode active material in Preparation Example 43 were sequentially coated on both sides of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 , and then, at 100 to 120 °C high temperature vacuum drying for 14 hours, and compacted by a roller press to obtain the positive electrode piece P7.
  • the slurry of the cathode active material in Preparation Example 43 and the slurry of the cathode active material in Preparation Example 1 were sequentially coated on both sides of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 , and the others were the same as in Example 7. , obtain the positive electrode piece P8.
  • the slurry of the cathode active material in Preparation Example 1 and the slurry of the cathode active material in Preparation Example 44 were sequentially coated on both sides of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 , and the others were the same as in Example 7. , to obtain the positive electrode piece P9.
  • the slurry of the cathode active material in Preparation Example 44 and the slurry of the cathode active material in Preparation Example 1 were sequentially coated on both sides of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 , and the others were the same as in Example 7. , obtain the positive electrode piece P10.
  • the slurry of the cathode active material in Preparation Example 43 and the slurry of the cathode active material in Preparation Example 44 were sequentially coated on both sides of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 .
  • Others were the same as in Example 7. , to obtain the positive electrode piece P11.
  • the slurry of the cathode active material in Preparation Example 44 and the slurry of the cathode active material in Preparation Example 43 were sequentially coated on both sides of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 .
  • Others were the same as in Example 7. , to obtain the positive electrode piece P12.
  • the slurry of the cathode active material in Preparation Example 1 and the slurry of the cathode active material in Preparation Example 43 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 1 was applied.
  • the coating amount of the slurry was 0.020g/cm 2 . Then, it was vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain the cathode plate P13.
  • the slurry of the cathode active material in Preparation Example 1 and the slurry of the cathode active material in Preparation Example 43 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 43 was applied.
  • the coating amount of the slurry was 0.020g/cm 2 .
  • the rest was the same as in Example 13 to obtain the cathode plate P14.
  • the slurry of the cathode active material in Preparation Example 1 and the slurry of the cathode active material in Preparation Example 43 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 44 was applied.
  • the coating amount of the slurry was 0.020g/cm 2 .
  • the rest was the same as in Example 13 to obtain the cathode plate P15.
  • the slurry of the cathode active material in Preparation Example 43 and the slurry of the cathode active material in Preparation Example 1 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 1 was applied.
  • the coating amount of the slurry was 0.020g/cm 2 .
  • the rest was the same as in Example 13 to obtain the cathode plate P16.
  • the slurry of the cathode active material in Preparation Example 43 and the slurry of the cathode active material in Preparation Example 1 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 43 was applied.
  • the coating amount of the slurry was 0.020g/cm 2 .
  • the rest was the same as in Example 13 to obtain the cathode plate P17.
  • the slurry of the cathode active material in Preparation Example 43 and the slurry of the cathode active material in Preparation Example 1 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 44 was applied.
  • the coating amount of the slurry was 0.020g/cm 2 .
  • the rest was the same as in Example 13 to obtain the cathode plate P18.
  • the slurry of the cathode active material in Preparation Example 1 and the slurry of the cathode active material in Preparation Example 44 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 1 was applied, and the coating amount of the slurry was 0.020g/cm 2 . Otherwise, it was the same as Example 13 to obtain the cathode plate P19.
  • the slurry of the cathode active material in Preparation Example 1 and the slurry of the cathode active material in Preparation Example 44 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 43 was applied.
  • the coating amount of the slurry was 0.020g/cm 2 .
  • the rest was the same as in Example 13 to obtain the cathode plate P20.
  • the slurry of the cathode active material in Preparation Example 1 and the slurry of the cathode active material in Preparation Example 44 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 44 was applied.
  • the coating amount of the slurry was 0.020g/cm 2 .
  • the rest was the same as in Example 13 to obtain the cathode plate P21.
  • the slurry of the cathode active material in Preparation Example 44 and the slurry of the cathode active material in Preparation Example 1 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 1 was applied, and the coating amount of the slurry was 0.020g/cm 2 . Otherwise, it was the same as Example 13 to obtain the cathode plate P22.
  • the slurry of the cathode active material in Preparation Example 44 and the slurry of the cathode active material in Preparation Example 1 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 43 was applied.
  • the coating amount of the slurry was 0.020g/cm 2 .
  • the rest was the same as in Example 13 to obtain the cathode plate P23.
  • the slurry of the cathode active material in Preparation Example 44 and the slurry of the cathode active material in Preparation Example 1 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 44 was applied.
  • the coating amount of the slurry was 0.020g/cm 2 .
  • the rest was the same as in Example 13 to obtain the cathode plate P24.
  • the slurry of the cathode active material in Preparation Example 43 and the slurry of the cathode active material in Preparation Example 44 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 1 was applied.
  • the coating amount of the slurry was 0.020g/cm 2 .
  • the rest was the same as in Example 13 to obtain the cathode plate P25.
  • the slurry of the cathode active material in Preparation Example 43 and the slurry of the cathode active material in Preparation Example 44 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 43 was applied.
  • the coating amount of the slurry was 0.020g/cm 2 .
  • the rest was the same as in Example 13 to obtain the cathode plate P26.
  • the slurry of the cathode active material in Preparation Example 43 and the slurry of the cathode active material in Preparation Example 44 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 44 was applied.
  • the coating amount of the slurry was 0.020g/cm 2 .
  • the rest was the same as in Example 13 to obtain the cathode plate P27.
  • the slurry of the cathode active material in Preparation Example 44 and the slurry of the cathode active material in Preparation Example 43 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 1 was applied.
  • the coating amount of the slurry was 0.020g/cm 2 .
  • the rest was the same as in Example 13 to obtain the cathode plate P28.
  • the slurry of the cathode active material in Preparation Example 44 and the slurry of the cathode active material in Preparation Example 43 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 43 was applied.
  • the coating amount of the slurry was 0.020g/cm 2 .
  • the rest was the same as in Example 13 to obtain the cathode plate P29.
  • the slurry of the cathode active material in Preparation Example 44 and the slurry of the cathode active material in Preparation Example 43 were sequentially coated on the A side of the aluminum foil.
  • the coating amount of each layer of slurry was 0.010g/cm 2 and evenly distributed on the B side of the aluminum foil.
  • the slurry of the cathode active material in Preparation Example 44 was applied.
  • the coating amount of the slurry was 0.020g/cm 2 .
  • the rest was the same as in Example 13 to obtain the cathode plate P30.
  • the slurry of the cathode active material in Preparation Example 45 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a cathode. Film P31.
  • the slurry of the positive active material in Preparation Example 46 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • the slurry of the positive electrode active material in Preparation Example 47 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • Film P33 The slurry of the positive electrode active material in Preparation Example 47 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode. Film P33.
  • the slurry of the positive active material in Preparation Example 48 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • Film P34 The slurry of the positive active material in Preparation Example 48 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode. Film P34.
  • the slurry of the positive electrode active material in Preparation Example 49 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • Film P35 The slurry of the positive electrode active material in Preparation Example 49 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode. Film P35.
  • the slurry of the positive electrode active material in Preparation Example 50 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • Film P36 The slurry of the positive electrode active material in Preparation Example 50 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • Film P36 The slurry of the positive electrode active material in Preparation Example 50 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • Film P36 The slurry of the positive electrode active material in
  • the slurry of the positive electrode active material in Preparation Example 51 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode. Film P37.
  • the slurry of the positive electrode active material in Preparation Example 52 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • the slurry of the positive electrode active material in Preparation Example 53 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode. Film P39.
  • the slurry of the positive electrode active material in Preparation Example 54 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • Film P40 The slurry of the positive electrode active material in Preparation Example 54 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode. Film P40.
  • the slurry of the positive electrode active material in Preparation Example 55 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • the slurry of the positive electrode active material in Preparation Example 56 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • Film P42 The slurry of the positive electrode active material in Preparation Example 56 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode. Film P42.
  • the slurry of the positive electrode active material in Preparation Example 57 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode. Film P43.
  • the slurry of the positive active material in Preparation Example 58 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • Film P44 The slurry of the positive active material in Preparation Example 58 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode. Film P44.
  • the slurry of the cathode active material in Preparation Example 59 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a cathode. Film P45.
  • the slurry of the positive electrode active material in Preparation Example 60 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • the slurry of the positive electrode active material in Preparation Example 61 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • the slurry of the positive electrode active material in Preparation Example 62 was evenly coated on both sides of the current collector aluminum foil at a coating amount of 0.019g/ cm2 , vacuum dried at a high temperature of 100 to 120°C for 14 hours, and compacted with a roller press to obtain a positive electrode.
  • the first layer refers to the layer in contact with the surface of the aluminum foil
  • the second layer refers to the layer provided on the first layer
  • the first positive active material is the positive active material prepared in Preparation Example 1
  • the second positive active material is the positive active material of Preparation Example 43, Preparation Example 45, and Preparation Examples 47-54.
  • the mass ratio of the negative active material artificial graphite, conductive agent superconducting carbon black (Super-P), binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethylcellulose (CMC-Na) is 95%: Dissolve 1.5%: 1.8%: 1.7% in deionized water, stir thoroughly and mix evenly to obtain a negative electrode slurry with a viscosity of 3000 mPa.s and a solid content of 52%; coat the negative electrode slurry on a 6 ⁇ m negative electrode current collector copper foil , then baked at 100°C for 4 hours to dry, and rolled to obtain a negative electrode piece with a compacted density of 1.75g/cm3.
  • the positive active material sample is prepared into a buckle, and the above buckle is charged at a small rate of 0.05C until the current is reduced to 0.01C. Then take out the positive electrode piece from the battery and soak it in dimethyl carbonate (DMC) for 8 hours. Then it is dried, scraped into powder, and particles with a particle size less than 500nm are screened out. Take a sample and calculate its unit cell volume v1 in the same way as the above-mentioned test of fresh samples, and use (v0-v1)/v0 ⁇ 100% as the lattice change rate (unit cell volume change rate) before and after complete deintercalation of lithium.
  • DMC dimethyl carbonate
  • the fresh full batteries prepared in each of the above preparation examples and comparative examples were allowed to stand for 5 minutes, and then discharged to 2.5V at 1/3C. Let it stand for 5 minutes, charge at 1/3C to 4.3V, and then charge at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. Let it stand for 5 minutes, and record the charging capacity at this time as C0. Discharge to 2.5V according to 1/3C, let it sit for 5 minutes, then charge to 4.3V according to 3C, let it stand for 5 minutes, record the charging capacity at this time as C1.
  • the 3C charging constant current ratio is C1/C0 ⁇ 100%.
  • the full battery made of the positive electrode active material of each of the above preparation examples and comparative examples was discharged to a cut-off voltage of 2.0V using a 0.1C rate after being cycled at 45°C until the capacity decayed to 80%. Then disassemble the battery, take out the negative electrode piece, randomly pick 30 discs of unit area (1540.25mm 2 ) on the negative electrode piece, and use Agilent ICP-OES730 to test the inductively coupled plasma emission spectrum (ICP). Calculate the amounts of Fe (if the Mn site of the cathode active material is doped with Fe) and Mn based on the ICP results, and then calculate the dissolution amount of Mn (and Fe doped at the Mn site) after cycles. The test standard is based on EPA-6010D-2014.
  • the cathode active material sample prepared above Take 5 g of the cathode active material sample prepared above and prepare a buckle according to the above preparation method of buckle. Charge with a small rate of 0.05C until the current is reduced to 0.01C. Then take out the positive electrode piece from the battery and soak it in DMC for 8 hours. Then it is dried, scraped into powder, and particles with a particle size less than 500nm are screened out. The obtained particles were measured with electron energy loss spectroscopy (EELS, the instrument model used was Talos F200S), and the energy loss near-edge structure (ELNES) was obtained, which reflects the density of states and energy level distribution of the element. According to the density of states and energy level distribution, the number of occupied electrons is calculated by integrating the valence band density of states data, thereby deducing the valence state of the charged surface oxygen.
  • EELS electron energy loss spectroscopy
  • ELNES energy loss near-edge structure
  • Dissolve 5g of the positive active material prepared above in 100ml aqua regia (concentrated hydrochloric acid: concentrated nitric acid 1:3) (concentrated hydrochloric acid concentration ⁇ 37%, concentrated nitric acid concentration ⁇ 65%), and use ICP to test the content of each element of the solution. content, and then measure and convert the content of manganese element or phosphorus element (amount of manganese element or phosphorus element/amount of cathode active material * 100%) to obtain its weight ratio.
  • the button batteries prepared in the above preparation examples and comparative examples were charged to 4.3V at 0.1C, then charged at a constant voltage at 4.3V until the current was less than or equal to 0.05mA, left to stand for 5 minutes, and then charged at 0.1 C is discharged to 2.0V.
  • the discharge capacity at this time is the initial gram capacity, recorded as D0.
  • the full cells prepared in each of the above preparation examples and comparative examples were stored at 60° C. at 100% state of charge (SOC). Measure the open circuit voltage (OCV) and AC internal resistance (IMP) of the battery cells before, after and during storage to monitor SOC, and measure the volume of the battery cells. The full battery was taken out after every 48 hours of storage, and the open circuit voltage (OCV) and internal resistance (IMP) were tested after leaving it for 1 hour. After cooling to room temperature, the cell volume was measured using the drainage method.
  • SOC state of charge
  • the drainage method is to first separately measure the gravity F 1 of the battery cell using a balance that automatically converts units based on the dial data, then completely places the battery core in deionized water (density is known to be 1g/cm 3 ), and measures the battery core at this time.
  • the thickness test of the coating layer mainly uses FIB to cut a slice with a thickness of about 100nm from the middle of a single particle of the cathode active material prepared above, and then perform a TEM test on the slice to obtain the original TEM test picture and save the original picture format (xx.dm3) .
  • the thickness of the selected particles was measured at three locations and averaged.
  • This test is performed by Raman spectroscopy. By peak splitting the energy spectrum of the Raman test, Id/Ig is obtained, where Id is the peak intensity of SP3 form carbon, and Ig is the peak intensity of SP2 form carbon, thereby confirming the molar ratio of the two.
  • ACSTEM Spherical aberration electron microscopy
  • the secondary battery is discharged at 1C for 48 minutes, then discharged at the specified maximum discharge current for 10 seconds, then left to stand for 30 minutes, and then charged at the specified maximum charging current for 10 seconds;
  • the secondary battery using the positive electrode plate P3-P30 Compared with the secondary battery using the positive electrode plate P2, the secondary battery using the positive electrode plate P3-P30 has higher energy density, higher low-temperature discharge capacity retention rate, higher specific power, and longer low-temperature cycle life. Secondary batteries with positive electrode plates P3-P12, P14-15, P17-18, P20-P22, P24, and P26-P30 have a longer normal temperature cycle life;
  • the secondary battery using the positive electrode plate P32 has higher energy density, higher low-temperature discharge capacity retention rate, higher specific power, and longer low-temperature cycle life;
  • the positive electrode pieces P41-P48 include the first positive electrode active material and the second positive electrode active material, and the positive electrode pieces P33-P40 only include the same amount of the corresponding second positive electrode active material, which is different from the positive electrode including only the second positive electrode active material.
  • the secondary battery produced by the cathode sheet including the first cathode active material and the second cathode active material has higher energy density, higher low-temperature discharge capacity retention rate, higher specific power, and longer low-temperature cycle life. ;
  • the secondary battery produced by the positive electrode sheet of the present application has higher energy density, better dynamic performance, higher cell rate performance, longer low-temperature cycle life, higher low-temperature cycle capacity retention rate, and is safer at the same time. high.

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Abstract

本申请提供了一种新型正极极片、二次电池、电池模块、电池包和用电装置；其中，正极极片包括正极集流体和设置在其至少一表面上单层或多层结构的正极膜层；正极膜层为单层结构时，至少一个正极膜层包含第一及第二正极活性材料；和/或，正极膜层为多层结构时，至少一正极膜层的至少一层包含第一及第二正极活性材料；第一正极活性材料包括内核Li 1+xMn 1-yA yP 1-zR zO 4、包括晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c的第一包覆层、包括晶态磷酸盐XPO 4的第二包覆层和第三包覆层；第三包覆层为碳。本申请正极极片所制二次电池的能量密度高，电芯倍率性能高，动力学性能和低温性能好，循环性能好，安全性高。

Description

新型正极极片、二次电池、电池模块、电池包及用电装置 技术领域
本申请涉及二次电池技术领域，尤其涉及一种新型正极极片、二次电池、电池模块、电池包和用电装置。
背景技术
近年来，随着二次电池的应用范围越来越广，二次电池广泛应用于水力、火力、风力和太阳能电站等储能电源系统，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。由于二次电池取得了极大的发展，因此对其能量密度、循环性能和安全性能等也提出了更高的要求。现有的磷酸锰铁锂使得二次电池的动力学性能较差、电芯倍率性能较低，不能满足动力电池需求。现有的磷酸铁锂作为正极活性材料所制的二次电池具有优异的循环稳定性和安全性，但其内部一维锂离子通道的存在以及充放电过程中LiFePO 4和FePO 4两相的存在使充放电过程中材料内部相变阻力变大，导致二次电池的动力学性能差、电芯倍率性能低、低温循环寿命短、低温容量保持率低。
发明内容
本申请是鉴于上述课题而进行的，其目的在于，提供一种新型正极极片、二次电池、电池模块、电池包和用电装置，以解决采用现有正极活性材料所制二次电池的能量密度低、动力学性能差、倍率性能低、低温循环寿命短、低温循环容量保持率低的问题。
为了达到上述目的，本申请第一方面提供了一种正极极片，包括正极集流体和设置在正极集流体的至少一个表面上的正极膜层；正极膜层为单层结构或多层结构；当正极膜层为单层结构时，至少一个正极膜层同时包含具有核-壳结构的第一正极活性材料和第二正极活性材料；和/或，当正极膜层为多层结构时，至少一个正极膜层的至少一层中同时包含具有核-壳结构的第一正极活性材料和第二正极活性 材料；第一正极活性材料包括内核、包覆内核的第一包覆层、包覆第一包覆层的第二包覆层和包覆第二包覆层的第三包覆层；其中，内核包含Li 1+xMn 1-yA yP 1-zR zO 4，第一包覆层包含晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，第二包覆层包含晶态磷酸盐XPO 4，第三包覆层包含碳；其中，A包括选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素；R包括选自B、Si、N和S中的一种或多种元素；x选自-0.100至0.100范围内的任意数值；y选自0.001至0.500范围内的任意数值；z选自0.001至0.100范围内的任意数值；晶态焦磷酸盐Li aMP 2O 7和M b(P 2O 7) c中的M各自独立地包括选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；a选自0至2范围内的任意数值；b选自1至4范围内的任意数值；c选自1至6范围内的任意数值；X包括选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；第二正极活性材料选自LiFePO 4、碳包覆LiFePO 4、LiFe dD ePO 4和碳包覆LiFe dD ePO 4中的一种或多种，其中，D独立地包括选自Ti、Zn、Co、Mn、La、V、Mg、Al、Nb、W、Zr、Nb、Sm、Cr、Cu和B中的一种或多种元素，d独立地选自0.99至0.999的范围，并且d+e＝1。
本文中，晶态意指结晶度在50％以上，即50％-100％。结晶度小于50％的称为玻璃态。本申请的晶态焦磷酸盐和晶态磷酸盐的结晶度为50％至100％。具备一定结晶度的焦磷酸盐和磷酸盐不但有利于充分发挥焦磷酸盐包覆层阻碍锰溶出和磷酸盐包覆层优异的导锂离子的能力、减少界面副反应的功能，而且能够使得焦磷酸盐包覆层和磷酸盐包覆层能够更好的进行晶格匹配，从而能够实现包覆层和包覆层之间紧密的结合。
由此，本申请通过在磷酸锰锂的锰位掺杂元素A并在磷位掺杂元素R得到掺杂的磷酸锰锂内核并在内核表面依次进行三层包覆，提供了一种新型的具有核-壳结构的第一正极活性材料，第一正极活性材料能够实现显著降低的锰溶出以及降低晶格变化率，应用于二次 电池中能显著改善二次电池的高温循环性能、循环稳定性、高温储存性能、倍率性能、安全性能并且提高二次电池的容量。
本申请通过将第一正极活性材料和第二正极活性材料混合使用，两种材料的优势互补，提升了二次电池的能量密度，同时使二次电池兼具优良的动力学性能、倍率性能、低温循环寿命和低温循环容量保持率。
本申请第二方面提供了一种正极极片，包括正极集流体和设置在正极集流体的至少一个表面上的正极膜层；至少一个正极膜层为多层结构，任一具有多层结构的正极膜层在不同层中分别包含具有核-壳结构的第一正极活性材料和第二正极活性材料；第一正极活性材料包括内核、包覆内核的第一包覆层、包覆第一包覆层的第二包覆层和包覆第二包覆层的第三包覆层；其中，内核包含Li 1+xMn 1-yA yP 1-zR zO 4，第一包覆层包含晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，第二包覆层包含晶态磷酸盐XPO 4，第三包覆层包含碳；其中，A包括选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素；R包括选自B、Si、N和S中的一种或多种元素；x选自-0.100至0.100范围内的任意数值；y选自0.001至0.500范围内的任意数值；z选自0.001至0.100范围内的任意数值；晶态焦磷酸盐Li aMP 2O 7和M b(P 2O 7) c中的M各自独立地包括选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；a选自0至2范围内的任意数值；b选自1至4范围内的任意数值；c选自1至6范围内的任意数值；X包括选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；第二正极活性材料选自LiFePO 4、碳包覆LiFePO 4、LiFe dD ePO 4和碳包覆LiFe dD ePO 4中的一种或多种，其中，D独立地包括选自Ti、Zn、Co、Mn、La、V、Mg、Al、Nb、W、Zr、Nb、Sm、Cr、Cu和B中的一种或多种元素，d独立地选自0.99至0.999范围内的任意数值，并且d+e＝1；可选地，任一具有多层结构的正极膜层在相邻层中分别包含第一正极活性材料和第二正极活性材料。
由此，第一正极活性材料能够实现显著降低锰溶出以及降低晶格变化率，应用于二次电池中能显著改善二次电池的高温循环性能、循环稳定性、高温储存性能、倍率性能、安全性能并且提高二次电池的容量。
本申请将第一正极活性材料和第二正极活性材料组合使用，两种材料的优势互补，提升了二次电池的能量密度，同时使二次电池兼具优良的倍率性能、动力学性能、低温循环寿命和低温循环容量保持率。
本申请第三方面提供了一种正极极片，包括正极集流体和分别设置在正极集流体的两个表面上的正极膜层A和正极膜层B；正极膜层A和正极膜层B各自独立地为单层结构或多层结构；正极膜层A的至少一层中包含具有核-壳结构的第一正极活性材料，同时，正极膜层B的至少一层中包含第二正极活性材料；第一正极活性材料包括内核、包覆内核的第一包覆层、包覆第一包覆层的第二包覆层和包覆第二包覆层的第三包覆层；其中，内核包含Li 1+xMn 1-yA yP 1-zR zO 4，第一包覆层包含晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，第二包覆层包含晶态磷酸盐XPO 4，第三包覆层包含碳；其中，A包括选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素；R包括选自B、Si、N和S中的一种或多种元素；x选自-0.100-0.100范围内的任意数值；y选自0.001-0.500范围内的任意数值；z选自0.001-0.100范围内的任意数值；晶态焦磷酸盐Li aMP 2O 7和M b(P 2O 7) c中的M各自独立地包括选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；a选自0-2范围内的任意数值；b选自1-4范围内的任意数值；c选自1-6范围内的任意数值；X包括选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；第二正极活性材料选自LiFePO 4、碳包覆LiFePO 4、LiFe dD ePO 4和碳包覆LiFe dD ePO 4中的一种或多种，其中，D独立地包括选自Ti、Zn、Co、Mn、La、V、Mg、Al、Nb、W、Zr、Nb、Sm、Cr、Cu和B中的一种或多种元素，d独立地选自0.99至0.999范围内的任意数值，并且d+e＝1。
由此，本申请第一正极活性材料能够实现显著降低锰溶出以及降低晶格变化率，应用于二次电池中能显著改善二次电池的高温循环性能、循环稳定性、高温储存性能、倍率性能、安全性能并且提高二次电池的容量。
本申请将第一正极活性材料和第二正极活性材料组合使用，两种材料的优势互补，提升了二次电池的能量密度，同时使二次电池兼具优良的倍率性能、动力学性能、低温循环寿命和低温循环容量保持率。
除非另有说明，否则上述化学式中，当A为两种以上元素时，上述对于y数值范围的限定不仅是对每种作为A的元素的化学计量数的限定，也是对各个作为A的元素的化学计量数之和的限定。例如当A为两种以上元素A1、A2……An时，A1、A2……An各自的化学计量数y1、y2……yn各自均需落入本申请对y限定的数值范围内，且y1、y2……yn之和也需落入该数值范围内。类似地，对于R为两种以上元素的情况，本申请中对R、M、X化学计量数的数值范围的限定也具有上述含义。
除非另有说明，否则化学式LiFe dD ePO 4中，当D为两种以上元素时，上述对于e数值范围的限定不仅是对每种作为D的元素的化学计量数的限定，也是对各个作为D的元素的化学计量数之和的限定。例如当D为两种以上元素D1、D2……Dn时，D1、D2……Dn各自的化学计量数e1、e2……en各自均需落入本申请对e限定的数值范围内，且e1、e2……en之和也需落入该数值范围内。
在第一方面至第三方面的任意实施方式中，第二正极活性材料中，碳质量占所述碳包覆LiFePO 4的质量的0.1％-4％；和/或，碳质量占所述碳包覆LiFe dD ePO 4的质量的0.1％-4％。采用上述碳质量含量的第二正极活性材料，能进一步保证二次电池具有优良的倍率性能、动力学性能和低温循环性能，且具有较高的能量密度。
在第一方面至第三方面的任意实施方式中，第一正极活性材料与第二正极活性材料的质量比为1:7-7:1，可选为1:4-4:1，进一步可选为1:3-3:1，例如1:7、1:5、1:3、1:2、3:5、1:1、5:3、2:1、3:1、5:1、7:1。以保证二次电池兼具较高的能量密度、优良的动力学性能、优 良的倍率性能、较长的低温循环寿命和较高的低温循环容量保持率，减少界面副反应。
在第一方面至第三方面的任意实施方式中，第一正极活性材料中，A选自Fe、Ti、V、Ni、Co和Mg中的一种或多种元素。通过在上述范围内对掺杂元素进行选择，有利于增强掺杂效果，一方面进一步减小晶格变化率，从而抑制锰的溶出，减少电解液和活性锂的消耗，另一方面也有利于进一步降低表面氧活性，减少第一正极活性材料与电解液的界面副反应，从而改善二次电池的循环性能和高温储存性能。
在第一方面至第三方面的任意实施方式中，第一正极活性材料中，R选自B、Si、N和S中的一种元素。通过在上述范围内对掺杂元素进行选择，能进一步地改善二次电池的倍率性能、提高电导率，从而提升二次电池的克容量、循环性能和高温性能。
在第一方面至第三方面的任意实施方式中，第一正极活性材料中，y与1-y的比值选自1:10至1:1，可选为1:4至1:1。由此，进一步提升二次电池的能量密度、循环性能和倍率性能。
在第一方面至第三方面的任意实施方式中，第一正极活性材料中，z与1-z的比值选自1:9至1:999，可选为1:499至1:249。由此，进一步提升二次电池的能量密度、循环性能和倍率性能。
在第一方面至第三方面的任意实施方式中，第一正极活性材料中，第一包覆层中的晶态焦磷酸盐的晶面间距范围为0.293-0.470nm，晶向(111)的夹角范围为18.00°-32.00°；第二包覆层中的晶态磷酸盐的晶面间距范围为0.244-0.425nm，晶向(111)的夹角范围为20.00°-37.00°。
本申请的正极活性材料中的第一包覆层和第二包覆层均使用晶态物质，它们的晶面间距和夹角范围在上述范围内。由此，能够有效避免包覆层中的杂质相，从而提升材料的克容量，提升二次电池的循环性能和倍率性能。
在第一方面至第三方面的任意实施方式中，第一正极活性材料中，第三包覆层的碳为SP2形态碳与SP3形态碳的混合物，可选地，SP2形态碳与SP3形态碳的摩尔比为在0.1-10范围内的任意数值，可选为在2.0-3.0范围内的任意数值。
本申请通过将SP2形态碳与SP3形态碳的摩尔比限制在上述范围内，提升了二次电池的综合性能。
在第一方面至第三方面的任意实施方式中，第一包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为大于0且小于或等于2重量％，基于内核的重量计；和/或
第二包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为2-4重量％，基于内核的重量计；和/或
第三包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为大于0且小于或等于2重量％，基于内核的重量计。
本申请的具有核-壳结构的第一正极活性材料中，三层包覆层的包覆量优选在上述范围内，由此能够对内核进行充分包覆，并同时在不牺牲第一正极活性材料克容量的前提下，进一步改善二次电池的动力学性能和安全性能。
在第一方面至第三方面的任意实施方式中，第一正极活性材料中，第一包覆层的厚度为1-10nm。本申请中，当第一包覆层的厚度范围为1-10nm时，能够避免过厚时可能产生的对材料的动力学性能的不利影响，且能够避免过薄时不能有效阻碍过渡金属离子的迁移的问题。
在第一方面至第三方面的任意实施方式中，第一正极活性材料中，第二包覆层的厚度为2-15nm。当第二包覆层的厚度在2-15nm范围内时，第二包覆层的表面结构稳定，与电解液的副反应小，因此能够有效减轻界面副反应，从而提升二次电池的高温性能。
在第一方面至第三方面的任意实施方式中，第一正极活性材料中，第三包覆层的厚度为2-25nm。当第三包覆层的厚度范围为2-25nm时，能够提升材料的电导性能并且改善使用第一正极活性材料制备的电池极片的压实密度性能。
在第一方面至第三方面的任意实施方式中，第一正极活性材料中，基于第一正极活性材料的重量计，锰元素含量在10重量％-35重量％ 范围内，可选在15重量％-30重量％范围内，更可选在17重量％-20重量％范围内。
本申请的具有核-壳结构的第一正极活性材料中，锰元素的含量在上述范围内，能够有效避免若锰元素含量过大可能会引起的材料结构稳定性变差、密度下降等问题，从而提升二次电池的循环、存储和压实密度等性能；且能够避免若锰元含量过小可能会导致的电压平台低等问题，从而提升二次电池的能量密度。
在第一方面至第三方面的任意实施方式中，第一正极活性材料中，基于第一正极活性材料的重量计，磷元素的含量在12重量％-25重量％范围内，可选在15重量％-20重量％范围内。
本申请的具有核-壳结构的第一正极活性材料中，磷元素的含量在上述范围内，能够有效避免以下情况：若磷元素的含量过大，可能会导致P-O的共价性过强而影响小极化子导电，从而影响材料的电导率；若磷元素的含量过小，可能会使内核、第一包覆层中的焦磷酸盐和/或第二包覆层中的磷酸盐晶格结构的稳定性下降，从而影响材料整体的稳定性。
在第一方面至第三方面的任意实施方式中，第一正极活性材料中，基于第一正极活性材料的重量计，锰元素和磷元素的重量比范围为0.90-1.25，可选为0.95-1.20。
本申请的具有核-壳结构的第一正极活性材料中，锰元素与磷元素的重量比在上述范围内，能够有效避免以下情况：若该重量比过大，可能会导致过渡金属溶出增加，影响材料的稳定性和二次电池的循环及存储性能；若该重量比过小，可能会使材料的放电电压平台下降，从而使二次电池的能量密度降低。
在第一方面至第三方面的任意实施方式中，第一正极活性材料在完全脱嵌锂前后的晶格变化率为4％以下，可选为3.8％以下，更可选为2.0-3.8％。
本申请的具有核-壳结构的第一正极活性材料能够实现4％以下的脱嵌锂前后的晶格变化率。因此使用第一正极活性材料能够改善二次电池的克容量和倍率性能。
在第一方面至第三方面的任意实施方式中，第一正极活性材料的Li/Mn反位缺陷浓度为4％以下，可选为2.2％以下，更可选为1.5-2.2％。通过Li/Mn反位缺陷浓度在上述范围内，能够避免Mn 2+阻碍Li +的传输，同时提升第一正极活性材料的克容量和二次电池的倍率性能。
在第一方面至第三方面的任意实施方式中，第一正极活性材料在3T下的压实密度为2.2g/cm 3以上，可选地为2.2g/cm 3以上且2.8g/cm 3以下。由此，提高压实密度，则单位体积的第一正极活性材料的重量增大，越有利于提高二次电池的体积能量密度。
在第一方面至第三方面的任意实施方式中，第一正极活性材料的表面氧价态为-1.90以下，可选地为-1.90至-1.98。由此，通过如上将第一正极活性材料的表面氧价态限定在上述范围内，能够减轻第一正极材料与电解液的界面副反应，从而改善电芯的循环，高温存储产气等性能。
在第一方面至第三方面的任意实施方式中，第一正极活性材料和第二正极活性材料的质量之和占正极极片的质量的88％-98.7％。进一步保证二次电池具有优良的倍率性能、动力学性能和低温循环性能，且具有较高的能量密度。
本申请的第四方面提供一种二次电池，包括本申请第一方面至第三方面中任一的正极极片。
本申请的第五方面提供一种电池模块，包括本申请的第四方面的二次电池。
本申请的第六方面提供一种电池包，包括本申请的第五方面的电池模块。
本申请的第七方面提供一种用电装置，包括选自本申请的第四方面的二次电池、本申请的第五方面的电池模块和本申请的第六方面的电池包中的至少一种。
附图说明
图1是本申请一实施方式的三层包覆结构的第一正极活性材料的示意图。
图2是本申请一实施方式的二次电池的示意图。
图3是图2所示的本申请一实施方式的二次电池的分解图。
图4是本申请一实施方式的电池模块的示意图。
图5是本申请一实施方式的电池包的示意图。
图6是图5所示的本申请一实施方式的电池包的分解图。
图7是本申请一实施方式的二次电池用作电源的用电装置的示意图。
图8是本申请正极极片P1所制电池结构的示意图。
图9是本申请正极极片P2所制电池结构的示意图。
图10是本申请正极极片P3所制电池结构的示意图。
图11是本申请正极极片P8所制电池结构的示意图。
图12是本申请正极极片P10所制电池结构的示意图。
图13是本申请正极极片P11所制电池结构的示意图。
图14是本申请正极极片P12所制电池结构的示意图。
图15是本申请正极极片P17所制电池结构的示意图。
图16是本申请正极极片P18所制电池结构的示意图。
图17是本申请正极极片P23所制电池结构的示意图。
图18是本申请正极极片P24所制电池结构的示意图。
图19是本申请正极极片P26所制电池结构的示意图。
图20是本申请正极极片P27所制电池结构的示意图。
附图标记说明：
1电池包；2上箱体；3下箱体；4电池模块；5二次电池；51壳体；52电极组件；53顶盖组件。
具体实施方式
以下，适当地参照附图详细说明具体公开了本申请的正极极片、二次电池、电池模块、电池包和用电装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说 明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，方法包括步骤(a)和(b)，表示方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，提到方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到方法，例如，方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地， 以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
如果没有特别的说明，在本申请中，术语“包覆层”是指包覆在内核上的物质层，物质层可以完全或部分地包覆内核，使用“包覆层”只是为了便于描述，并不意图限制本发明。
如果没有特别的说明，在本申请中，术语“包覆层的厚度”是指包覆在内核上的物质层在内核径向上的厚度。
[二次电池]
二次电池又称为充电电池或蓄电池，是指在电池放电后可通过充电的方式使活性材料激活而继续使用的电池。
通常情况下，二次电池包括正极极片、负极极片、隔离膜及电解液。在电池充放电过程中，活性离子(例如锂离子)在正极极片和负极极片之间往返嵌入和脱出。隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使活性离子通过。电解液在正极极片和负极极片之间，主要起到传导活性离子的作用。
[正极极片]
本申请第一方面的实施方式提供一种正极极片，包括正极集流体和设置在正极集流体的至少一个表面上的正极膜层；正极膜层为单层结构或多层结构；当正极膜层为单层结构时，至少一个正极膜层同时包含具有核-壳结构的第一正极活性材料和第二正极活性材料；和/或，当正极膜层为多层结构时，至少一个正极膜层的至少一层中同时包含具有核-壳结构的第一正极活性材料和第二正极活性材料；第一正极活性材料包括内核、包覆内核的第一包覆层、包覆第一包覆层的第二包覆层和包覆第二包覆层的第三包覆层；其中，内核包含化学式Li 1+xMn 1-yA yP 1-zR zO 4的物质，第一包覆层包含晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，第二包覆层包含晶态磷酸盐XPO 4，第三包覆层包含碳；其中，A包括选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、 Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素；R包括选自B、Si、N和S中的一种或多种元素；x选自-0.100至0.100范围内的任意数值；y选自0.001至0.500范围内的任意数值；z选自0.001至0.100范围内的任意数值；晶态焦磷酸盐Li aMP 2O 7和M b(P 2O 7) c中的M各自独立地包括选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；a选自0至2范围内的任意数值；b选自1至4范围内的任意数值；c选自1至6范围内的任意数值；X包括选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；第二正极活性材料为选自LiFePO 4、碳包覆LiFePO 4、LiFe dD ePO 4和碳包覆LiFe dD ePO 4中的一种或多种，其中，D独立地包括选自Ti、Zn、Co、Mn、La、V、Mg、Al、Nb、W、Zr、Nb、Sm、Cr、Cu和B中的一种或多种元素，d独立地选自0.99至0.999范围内的任意数值，并且d+e＝1。
需要说明的是：当正极极片包括两个正极膜层时，“正极膜层为单层结构或多层结构”指两个正极膜层各自独立地为单层结构或多层结构，“当正极膜层为单层结构时”指一个或两个正极膜层为单层结构时，“当正极膜层为多层结构时”指一个或两个正极膜层为多层结构时。
本申请第一正极活性材料能够提高二次电池的克容量、循环性能和安全性能。虽然机理尚不清楚，但推测是本申请的第一正极活性材料为核-壳结构，其中通过对磷酸锰锂内核的锰位和磷位分别掺杂元素A和元素R，不仅可有效减少锰溶出，进而减少迁移到负极的锰离子，减少因SEI膜分解而消耗的电解液，提高二次电池的循环性能和安全性能，还能够促进Mn-O键调整，降低锂离子迁移势垒，促进锂离子迁移，提高二次电池的倍率性能；通过对内核包覆包括晶态焦磷酸盐的第一包覆层，能够进一步增大锰的迁移阻力，减少其溶出，并减少表面杂锂含量、减少内核与电解液的接触，从而减少界面副反应、减少产气，提高二次电池的高温存储性能、循环性能和安全性能；通过进一步包覆具有优异导锂离子的能力的晶态磷酸盐包覆层，可以使第一正极活性材料的表面的界面副反应有效降低，进而改善二次电池的高温循环及存储性能；通过再进一步包覆碳层作为第三包覆层，能 够进一步提升二次电池的安全性能和动力学性能。此外，在内核中，在磷酸锰锂的锰位掺杂的元素A还有助于减小该材料在脱嵌锂过程中磷酸锰锂的晶格变化率，提高第一正极材料的结构稳定性，大大减少锰的溶出并降低颗粒表面的氧活性；在磷位掺杂的元素R还有助于改变Mn-O键长变化的难易程度，从而改善电子电导并降低锂离子迁移势垒，促进锂离子迁移，提高二次电池的倍率性能。
本申请通过将第一正极活性材料和第二正极活性材料混合使用，两种材料的优势互补，提升了二次电池的能量密度；第一正极活性材料和第二正极活性材料的内部晶格结构骨架稳定，在充放电过程中，第一正极活性材料中的掺杂元素能有效降低锂离子的迁移能垒，有利于锂离子的快速脱嵌，另外，第一正极活性材料特有的第二包覆层使得电子电导性显著提升，第一正极活性材料均匀分散在第二正极活性材料周围，从而提升了混合材料整体的电子导电性，因此提高了二次电池的电芯倍率性能和动力学性能。且第一正极活性材料的晶格变化较低，降低了低温条件下材料极化，有效改善二次电池的低温循环寿命和低温循环容量保持率。
在第一个方面的一些实施方式中，在正极集流体的两个表面上分别设置有正极膜层C和正极膜层D，正极膜层C为多层结构，正极膜层D为单层结构，正极膜层C中的至少一层同时包含第一正极活性材料和第二正极活性材料；可选地，正极膜层D包含第一正极活性材料和第二正极活性材料中的一种或两种；可选地，正极膜层C中的其余层包含第一正极活性材料或第二正极活性材料。
在第一个方面的一些实施方式中，在正极集流体的两个表面上分别设置有正极膜层C和正极膜层D，正极膜层C为多层结构，正极膜层D为单层结构，正极膜层D同时包含第一正极活性材料和第二正极活性材料；可选地，正极膜层C中的任一层包含第一正极活性材料或第二正极活性材料。
在第一个方面的一些实施方式中，在正极集流体的两个表面上分别设置有一个正极膜层，每个正极膜层都为多层结构，每个正极膜层中的至少一层同时包含第一正极活性材料和第二正极活性材料；可选 地，正极膜层中的其余层包含第一正极活性材料或第二正极活性材料。
本申请第二个方面的实施方式提供一种正极极片，包括正极集流体和设置在正极集流体的至少一个表面上的正极膜层；至少一个正极膜层为多层结构，任一具有多层结构的正极膜层在不同层中分别包含具有核-壳结构的第一正极活性材料和第二正极活性材料；第一正极活性材料包括内核、包覆内核的第一包覆层、包覆第一包覆层的第二包覆层和包覆第二包覆层的第三包覆层；其中，内核包含Li 1+xMn 1-yA yP 1-zR zO 4，第一包覆层包含晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，第二包覆层包含晶态磷酸盐XPO 4，第三包覆层包含碳；其中，A包括选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素；R包括选自B、Si、N和S中的一种或多种元素；x选自-0.100至0.100范围内的任意数值；y选自0.001至0.500范围内的任意数值；z选自0.001至0.100范围内的任意数值；晶态焦磷酸盐Li aMP 2O 7和M b(P 2O 7) c中的M各自独立地包括选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；a选自0至2范围内的任意数值；b选自1至4范围内的任意数值；c选自1至6范围内的任意数值；X包括选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；第二正极活性材料选自LiFePO 4、碳包覆LiFePO 4、LiFe dD ePO 4和碳包覆LiFe dD ePO 4中的一种或多种，其中，D独立地包括选自Ti、Zn、Co、Mn、La、V、Mg、Al、Nb、W、Zr、Nb、Sm、Cr、Cu和B中的一种或多种元素，d独立地选自0.99至0.999范围内的任意数值，并且d+e＝1；可选地，任一具有多层结构的正极膜层在相邻层中分别包含第一正极活性材料和第二正极活性材料。
本申请第一正极活性材料能够提高二次电池的克容量和动力学性能，可有效减少锰溶出、降低晶格变化率并降低颗粒表面的氧活性，减少迁移到负极的锰离子，减少因SEI膜分解而消耗的电解液，提高二次电池的循环性能和安全性能；第一正极活性材料能促进锂离子迁 移，提高二次电池的倍率性能；第一正极活性材料能减少界面副反应、减少产气，提高二次电池的存储性能、循环性能和安全性能。
本申请通过将第一正极活性材料和第二正极活性材料混合使用，两种材料的优势互补，提升了二次电池的能量密度；第一正极活性材料和第二正极活性材料的内部晶格结构骨架稳定，在充放电过程中，第一正极活性材料中的掺杂元素能有效降低锂离子的迁移能垒，有利于锂离子的快速脱嵌，另外，第一正极活性材料特有的第二包覆层使得电子电导性显著提升，第一正极活性材料均匀分散在第二正极活性材料周围，从而提升了混合材料整体的电子导电性，因此提高了二次电池的电芯倍率性能和动力学性能。且第一正极活性材料的晶格变化较低，降低了低温条件下材料极化，有效改善二次电池的低温循环寿命和低温循环容量保持率。
在第二个方面的一些实施方式中，在正极集流体的两个表面上分别设置有一个正极膜层，每个正极膜层都为多层结构，每个正极膜层中的相邻两层分别包含第一正极活性材料和第二正极活性材料。
在第二个方面的一些实施方式中，在正极集流体的两个表面上分别设置有正极膜层E和正极膜层F，正极膜层E为多层结构，正极膜层F为单层结构，正极膜层E中的相邻两层分别包含第一正极活性材料和第二正极活性材料；可选地，正极膜层E中的其余层和正极膜层F各自独立地包含第一正极活性材料或第二正极活性材料。
本申请第三个方面的实施方式提供一种正极极片，包括正极集流体和分别设置在正极集流体的两个表面上的正极膜层A和正极膜层B；正极膜层A和正极膜层B各自独立地为单层结构或多层结构；正极膜层A的至少一层中包含具有核-壳结构的第一正极活性材料，同时，正极膜层B的至少一层中包含第二正极活性材料；第一正极活性材料包括内核、包覆内核的第一包覆层、包覆第一包覆层的第二包覆层和包覆第二包覆层的第三包覆层；其中，内核包含化学式为Li 1+xMn 1-yA yP 1-zR zO 4的物质，第一包覆层包含晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，第二包覆层包含晶态磷酸盐XPO 4，第三包覆层包含碳；其中，A包括选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、 Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素；R包括选自B、Si、N和S中的一种或多种元素；x选自-0.100-0.100范围内的任意数值；y选自0.001-0.500范围内的任意数值；z选自0.001-0.100范围内的任意数值；晶态焦磷酸盐Li aMP 2O 7和M b(P 2O 7) c中的M各自独立地包括选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；a选自0-2范围内的任意数值；b选自1-4范围内的任意数值；c选自1-6范围内的任意数值；X包括选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；第二正极活性材料选自LiFePO 4、碳包覆LiFePO 4、LiFe dD ePO 4和碳包覆LiFe dD ePO 4中的一种或多种，其中，D独立地包括选自Ti、Zn、Co、Mn、La、V、Mg、Al、Nb、W、Zr、Nb、Sm、Cr、Cu和B中的一种或多种元素，d独立地选自0.99至0.999范围内的任意数值，并且d+e＝1。
本申请第一正极活性材料能够提高二次电池的克容量和动力学性能，可有效减少锰溶出、降低晶格变化率并降低颗粒表面的氧活性，减少迁移到负极的锰离子，减少因SEI膜分解而消耗的电解液，提高二次电池的循环性能和安全性能；第一正极活性材料能促进锂离子迁移，提高二次电池的倍率性能；第一正极活性材料能减少界面副反应、减少产气，提高二次电池的存储性能、循环性能和安全性能。
本申请通过将第一正极活性材料和第二正极活性材料混合使用，两种材料的优势互补，提升了二次电池的能量密度；第一正极活性材料和第二正极活性材料的内部晶格结构骨架稳定，在充放电过程中，第一正极活性材料中的掺杂元素能有效降低锂离子的迁移能垒，有利于锂离子的快速脱嵌，另外，第一正极活性材料特有的第二包覆层使得电子电导性显著提升，第一正极活性材料均匀分散在第二正极活性材料周围，从而提升了混合材料整体的电子导电性，因此提高了二次电池的电芯倍率性能和动力学性能。且第一正极活性材料的晶格变化较低，降低了低温条件下材料极化，有效改善二次电池的低温循环寿命和低温循环容量保持率。
除非另有说明，否则在第一个至第三个方面的化学式中，当A 为两种以上元素时，上述对于y数值范围的限定不仅是对每种作为A的元素的化学计量数的限定，也是对各个作为A的元素的化学计量数之和的限定。例如当A为两种以上元素A1、A2……An时，A1、A2……An各自的化学计量数y1、y2……yn各自均需落入本申请对y限定的数值范围内，且y1、y2……yn之和也需落入该数值范围内。类似地，对于R为两种以上元素的情况，本申请中对R、M、X化学计量数的数值范围的限定也具有上述含义。
除非另有说明，否则化学式LiFe dD ePO 4中，当D为两种以上元素时，上述对于e数值范围的限定不仅是对每种作为D的元素的化学计量数的限定，也是对各个作为D的元素的化学计量数之和的限定。例如当D为两种以上元素D1、D2……Dn时，D1、D2……Dn各自的化学计量数e1、e2……en各自均需落入本申请对e限定的数值范围内，且e1、e2……en之和也需落入该数值范围内。
在第一个至第三个方面的一些实施方式中，当A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种、两种、三种或四种元素时，A y为Q n1L n2E n3K n4，其中n1+n2+n3+n4＝y，且n1、n2、n3、n4均为正数且不同时为零，Q、L、E、K各自独立地为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge的一种，可选地，Q、L、E、K中至少一个为Fe。可选地，n1、n2、n3、n4之一为零，其余不为零；更可选地，n1、n2、n3、n4中的两个为零，其余不为零；还可选地，n1、n2、n3、n4中的三个为零，其余不为零。内核Li 1+xMn 1-yA yP 1-zR zO 4中，在锰位掺杂一种、两种、三种或四种上述A元素是有利的，可选地，掺杂一种、两种或三种上述A元素；此外，在磷位掺杂一种或两种R元素是有利的，这样有利于使掺杂元素均匀分布。
在第一个至第三个方面中，x、y和z的值满足以下条件：使整个内核保持电中性。
内核Li 1+xMn 1-yA yP 1-zR zO 4中，x的大小受A和R的价态大小以及y和z的大小的影响，以保证整个体系呈现电中性。如果x的值过小， 会导致整个内核体系的含锂量降低，影响材料的克容量发挥。y值会限制所有掺杂元素的总量，如果y过小，即掺杂量过少，掺杂元素起不到作用，如果y超过0.5，会导致体系中的Mn含量较少，影响材料的电压平台。R元素掺杂在P的位置，由于P-O四面体较稳定，而z值过大会影响材料的稳定性，因此将z值限定为0.001-0.100。
另外，在第一个至第三个方面中，整个内核体系保持电中性，能够保证第一正极活性材料中的缺陷和杂相尽量少。如果第一正极活性材料中存在过量的过渡金属(例如锰)，由于该材料体系本身结构较稳定，那么多余的过渡金属很可能会以单质的形式析出，或在晶格内部形成杂相，保持电中性可使这样的杂相尽量少。另外，保证体系电中性还可以在部分情况下使材料中产生锂空位，从而使材料的动力学性能更优异。
在第一个至第三个方面中，a、b和c的值满足以下条件：使晶态焦磷酸盐Li aMP 2O 7或M b(P 2O 7) c保持电中性。
在第一个至第三个方面中，晶态意指结晶度在50％以上，即50％-100％。结晶度小于50％的称为玻璃态。本申请的晶态焦磷酸盐和晶态磷酸盐的结晶度为50％至100％。具备一定结晶度的焦磷酸盐和磷酸盐不但有利于充分发挥焦磷酸盐包覆层阻碍锰溶出和磷酸盐包覆层优异的导锂离子的能力、减少界面副反应的功能，而且能够使得焦磷酸盐包覆层和磷酸盐包覆层能够更好的进行晶格匹配，从而能够实现包覆层更紧密的结合。
在第一个至第三个方面中，第一正极活性材料的第一包覆层物质晶态焦磷酸盐和第二包覆层物质晶态磷酸盐的结晶度可以通过本领域中常规的技术手段来测试，例如通过密度法、红外光谱法、差示扫描量热法和核磁共振吸收方法测量，也可以通过例如，X射线衍射法来测试。
具体的X射线衍射法测试第一正极活性材料的第一包覆层晶态焦磷酸盐和第二包覆层晶态磷酸盐的结晶度的方法可以包括以下步骤：
取一定量的第一正极活性材料粉末，通过X射线测得总散射强 度，它是整个空间物质的散射强度之和，只与初级射线的强度、第一正极活性材料粉末化学结构、参加衍射的总电子数即质量多少有关，而与样品的序态无关；然后从衍射图上将结晶散射和非结晶散射分开，结晶度即是结晶部分散射对散射总强度之比。
需要说明的是，在第一个至第三个方面中，包覆层中的焦磷酸盐和磷酸盐的结晶度例如可通过调整烧结过程的工艺条件例如烧结温度、烧结时间等进行调节。
在第一个至第三个方面中，由于金属离子在焦磷酸盐中难以迁移，因此焦磷酸盐作为第一包覆层可以将掺杂金属离子与电解液进行有效隔离。晶态焦磷酸盐的结构稳定，因此，晶态焦磷酸盐包覆能够有效抑制过渡金属的溶出，改善循环性能。
在第一个至第三个方面中，第一包覆层与核之间的结合类似于异质结，其结合的牢固程度受晶格匹配程度的限制。晶格失配在5％以下时，晶格匹配较好，两者容易结合紧密。紧密的结合能够保证在后续的循环过程中，包覆层不会脱落，有利于保证材料的长期稳定性。第一包覆层与核之间的结合程度的衡量主要通过计算核与包覆各晶格常数的失配度来进行。本申请中，在内核中掺杂了A和R元素后，与不掺杂元素相比，内核与第一包覆层的匹配度得到改善，内核与焦磷酸盐包覆层之间能够更紧密地结合在一起。
在第一个至第三个方面中，选择晶态磷酸盐作为第二包覆层，首先，是因为它与第一层包覆物晶态焦磷酸盐的晶格匹配度较高(失配度仅为3％)；其次，磷酸盐本身的稳定性好于焦磷酸盐，用其包覆焦磷酸盐有利于提高材料的稳定性。晶态磷酸盐的结构很稳定，其具有优异导锂离子的能力，因此，使用晶态磷酸盐进行包覆能够使第一正极活性材料的表面的界面副反应得到有效降低，从而改善二次电池的高温循环及存储性能。第二包覆层和第一包覆层之间的晶格匹配方式等，与上述第一包覆层和核之间的结合情况相似，晶格失配在5％以下时，晶格匹配较好，两者容易结合紧密。
在第一个至第三个方面中，碳作为第三层包覆的主要原因是碳层的电子导电性较好。由于在二次电池中应用时发生的是电化学反应， 需要有电子的参与，因此，为了增加颗粒与颗粒之间的电子传输，以及颗粒上不同位置的电子传输，可以使用具有优异导电性能的碳来进行包覆。碳包覆可有效改善第一正极活性材料的导电性能和去溶剂化能力。
图1为理想中的三层包覆结构的第一正极活性材料的示意图。如图所示，最里面的圆示意表示内核，由内向外依次为第一包覆层、第二包覆层、第三包覆层。该图表示的是每层均完全包覆的理想状态，实践中，每一层包覆层可以是完全包覆，也可以是部分包覆。
在第一个至第三个方面的一些实施方式中，第二正极活性材料中，碳质量占碳包覆LiFePO 4的质量的0.1％-4％；和/或，碳质量占碳包覆LiFe dD ePO 4的质量的0.1％-4％。采用上述碳质量含量的第二正极活性材料，能进一步保证二次电池具有优良的倍率性能、动力学性能和低温循环性能，且具有较高的能量密度。
在第一个至第三个方面的一些实施方式中，第一正极活性材料与第二正极活性材料的质量比为1:7-7:1，可选为1:4-4:1，进一步可选为1:3-3:1，例如1:7、1:5、1:3、1:2、3:5、1:1、5:3、2:1、3:1、5:1、7:1。以保证二次电池兼具较高的能量密度、优良的动力学性能、优良的倍率性能、较长的低温循环寿命和较高的低温循环容量保持率，减少界面副反应。
在第一个至第三个方面的一些实施方式中，第一正极活性材料中，A选自Fe、Ti、V、Ni、Co和Mg中的一种或多种元素。通过在上述范围内对掺杂元素进行选择，有利于增强掺杂效果，一方面进一步减小晶格变化率，从而抑制锰的溶出，减少电解液和活性锂的消耗，另一方面也有利于进一步降低表面氧活性，减少第一正极活性材料与电解液的界面副反应，从而改善二次电池的循环性能和高温储存性能。
在第一个至第三个方面的一些实施方式中，第一正极活性材料中，R选自B、Si、N和S中的一种元素。通过在上述范围内对掺杂元素进行选择，能进一步地改善二次电池的倍率性能、提高电导率，从而提升二次电池的克容量、循环性能和高温性能。
在第一个至第三个方面的一些实施方式中，第一正极活性材料中，y与1-y的比值选自1:10至1:1，可选为1:4至1:1。此处y表示Mn位掺杂元素A的化学计量数之和。在满足上述条件时，进一步提升了二次电池的能量密度、循环性能和倍率性能。
在第一个至第三个方面的一些实施方式中，第一正极活性材料中，z与1-z的比值选自1:9至1:999，可选为1:499至1:249。此处z表示P位掺杂元素R的化学计量数之和。在满足上述条件时，进一步提升了二次电池的能量密度、循环性能和倍率性能。
在第一个至第三个方面的一些实施方式中，第一正极活性材料中，第一包覆层中的晶态焦磷酸盐的晶面间距范围为0.293-0.470nm，晶向(111)的夹角范围为18.00°-32.00°；第二包覆层中的晶态磷酸盐的晶面间距范围为0.244-0.425nm，晶向(111)的夹角范围为20.00°-37.00°。
本申请第一正极活性材料中的第一包覆层和第二包覆层均使用晶态物质。在上述晶面间距和夹角范围内的晶态焦磷酸盐和晶态磷酸盐，能够更有效地抑制脱嵌锂过程中磷酸锰锂的晶格变化率和Mn溶出，从而提升二次电池的高温循环性能、循环稳定性和高温储存性能。对于包覆层中的晶态焦磷酸盐和晶态磷酸盐，可通过本领域中常规的技术手段进行表征，也可以例如借助透射电镜(TEM)进行表征。在TEM下，通过测试晶面间距可以区分内核和包覆层。
包覆层中的晶态焦磷酸盐和晶态磷酸盐的晶面间距和夹角的具体测试方法可以包括以下步骤：
取一定量的经包覆的第一正极活性材料样品粉末于试管中，并在试管中注入溶剂如酒精，然后进行充分搅拌分散，然后用干净的一次性塑料吸管取适量上述溶液滴加在300目铜网上，此时，部分粉末将在铜网上残留，将铜网连带样品转移至TEM样品腔中进行测试，得到TEM测试原始图片，保存原始图片。
将上述TEM测试所得原始图片在衍射仪软件中打开，并进行傅里叶变换得到衍射花样，量取衍射花样中衍射光斑到中心位置的距离，即可得到晶面间距，夹角根据布拉格方程进行计算得到。
晶态焦磷酸盐的晶面间距范围和晶态磷酸盐的存在差异，可通过晶面间距的数值直接进行判断。
在第一个至第三个方面的一些实施方式中，第一正极活性材料中，第三包覆层的碳为SP2形态碳与SP3形态碳的混合物，可选地，SP2形态碳与SP3形态碳的摩尔比为在0.1-10范围内的任意数值，可选为在2.0-3.0范围内的任意数值。
在第一个至第三个方面的一些实施方式中，SP2形态碳与SP3形态碳的摩尔比可为约0.1、约0.2、约0.3、约0.4、约0.5、约0.6、约0.7、约0.8、约0.9、约1、约2、约3、约4、约5、约6、约7、约8、约9或约10，或在上述任意值的任意范围内。
本申请中，“约”某个数值表示一个范围，表示该数值±10％的范围。
通过选择碳包覆层中碳的形态，从而提升二次电池的综合电性能。具体来说，通过使用SP2形态碳和SP3形态碳的混合形态并将SP2形态碳和SP3形态碳的比例限制在一定范围内，能够避免以下情况：如果包覆层中的碳都是无定形SP3形态，则导电性差；如果都是石墨化的SP2形态，则虽然导电性良好，但是锂离子通路少，不利于锂的脱嵌。另外，将SP2形态碳与SP3形态碳的摩尔比限制在上述范围内，既能实现良好的导电性，又能保证锂离子的通路，因此有利于二次电池功能的实现及其循环性能。
第三包覆层碳的SP2形态和SP3形态的混合比可以通过烧结条件例如烧结温度和烧结时间来控制。例如，在使用蔗糖作为碳源制备第三包覆层的情况下，使蔗糖在高温下进行裂解后，在第二包覆层上沉积同时在高温作用下，会产生既有SP3形态也有SP2形态的碳包覆层。SP2形态碳和SP3形态碳的比例可以通过选择高温裂解条件和烧结条件来调控。
第三包覆层碳的结构和特征可通过拉曼(Raman)光谱进行测定，具体测试方法如下：通过对Raman测试的能谱进行分峰，得到Id/Ig(其中Id为SP3形态碳的峰强度，Ig为SP2形态碳的峰强度)，从而确认两者的摩尔比。
在第一个至第三个方面的一些实施方式中，第一包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为大于0且小于或等于2重量％，基于内核的重量计；和/或
第二包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为2-4重量％，基于内核的重量计；和/或
第三包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为大于0且小于或等于2重量％，基于内核的重量计。
本申请中，每一层的包覆量均不为零。
本申请的具有核-壳结构的第一正极活性材料中，三层包覆层的包覆量优选在上述范围内，由此能够对内核进行充分包覆，并同时在不牺牲正极活性材料克容量的前提下，进一步改善二次电池的动力学性能和安全性能。
对于第一包覆层而言，通过包覆量在上述范围内，则能够避免以下情况：包覆量过少则意味着包覆层厚度较薄，可能无法有效阻碍过渡金属的迁移；包覆量过大则意味着包覆层过厚，会影响Li+的迁移，进而影响材料的倍率性能。
对于第二包覆层而言，通过包覆量在上述范围内，则能够避免以下情况：包覆量过多，可能会影响材料整体的平台电压；包覆量过少，可能无法实现足够的包覆效果。
对于第三包覆层而言，碳包覆主要起到增强颗粒间的电子传输的作用，然而由于结构中还含有大量的无定形碳，因此碳的密度较低，因此，如果包覆量过大，会影响极片的压实密度。
在第一个至第三个方面的一些实施方式中，第一正极活性材料中，第一包覆层的厚度为1-10nm。
在第一个至第三个方面的一些实施方式中，第一包覆层的厚度可为约2nm、约3nm、约4nm、约5nm、约6nm、约7nm、约8nm、约9nm或约10nm，或在上述任意数值的任意范围内。
本申请中，当第一包覆层的厚度范围为1-10nm时，能够避免过厚时可能产生的对材料的动力学性能的不利影响，且能够避免过薄时不能有效阻碍过渡金属离子的迁移的问题。
在第一个至第三个方面的一些实施方式中，第一正极活性材料中，第二包覆层的厚度为2-15nm。
在第一个至第三个方面的一些实施方式中，第二包覆层的厚度可为约2nm、约3nm、约4nm、约5nm、约6nm、约7nm、约8nm、约9nm、约10nm、约11nm、约12nm、约13nm、约14nm、约15nm，或在上述任意数值的任意范围内。
本申请中，当第二包覆层的厚度在2-15nm范围内时，第二包覆层的表面结构稳定，与电解液的副反应小，因此能够有效减轻界面副反应，从而提升二次电池的高温性能。
在第一个至第三个方面的一些实施方式中，第一正极活性材料中，第三包覆层的厚度为2-25nm。
在第一个至第三个方面的一些实施方式中，第三层包覆层的厚度可为约2nm、约3nm、约4nm、约5nm、约6nm、约7nm、约8nm、约9nm、约10nm、约11nm、约12nm、约13nm、约14nm、约15nm、约16nm、约17nm、约18nm、约19nm、约20nm、约21nm、约22nm、约23nm、约24nm或约25nm，或在上述任意数值的任意范围内。
本申请中，当第三包覆层的厚度范围为2-25nm时，能够提升材料的电导性能并且改善使用第一正极活性材料制备的电池极片的压实密度性能。
包覆层的厚度大小测试主要通过FIB进行，具体方法可以包括以下步骤：从待测第一正极活性材料粉末中随机选取单个颗粒，从所选颗粒中间位置或中间位置附近切取100nm左右厚度的薄片，然后对薄片进行TEM测试，量取包覆层的厚度，测量3-5个位置，取平均值。
在第一个至第三个方面的一些实施方式中，第一正极活性材料中，基于第一正极活性材料的重量计，锰元素含量在10重量％-35重量％ 范围内，可选在15重量％-30重量％范围内，更可选在17重量％-20重量％范围内。
在本申请中，在仅第一正极活性材料的内核中含有锰的情况下，锰的含量可与内核的含量相对应。
本申请的具有核-壳结构的第一正极活性材料中，锰元素的含量在上述范围内，能够有效避免若锰元素含量过大可能会引起的材料结构稳定性变差、密度下降等问题，从而提升二次电池的循环、存储和压实密度等性能；且能够避免若锰元含量过小可能会导致的电压平台低等问题，从而提升二次电池的能量密度。
在第一个至第三个方面的一些实施方式中，第一正极活性材料中，基于第一正极活性材料的重量计，磷元素的含量在12重量％-25重量％范围内，可选在15重量％-20重量％范围内。
本申请的具有核-壳结构的第一正极活性材料中，磷元素的含量在上述范围内，能够有效避免以下情况：若磷元素的含量过大，可能会导致P-O的共价性过强而影响小极化子导电，从而影响材料的电导率；若磷元素的含量过小，可能会使内核、第一包覆层中的焦磷酸盐和/或第二包覆层中的磷酸盐晶格结构的稳定性下降，从而影响材料整体的稳定性。
在第一个至第三个方面的一些实施方式中，第一正极活性材料中，基于第一正极活性材料的重量计，锰元素和磷元素的重量比范围为0.90-1.25，可选为0.95-1.20。
本申请具有核-壳结构的第一正极活性材料中，锰元素与磷元素的重量比在上述范围内，能够有效避免以下情况：该重量比过大，意味着锰元素过多，锰溶出增加，影响第一正极活性材料的稳定性和克容量发挥，进而影响二次电池的循环性能及存储性能；该重量比过小，意味着磷元素过多，则容易形成杂相，会使材料的放电电压平台下降，从而使二次电池的能量密度降低。
锰元素和磷元素的测量可采用本领域中常规的技术手段进行。特别地，采用以下方法测定锰元素和磷元素的含量：将材料在稀盐酸中 (浓度10-30％)溶解，利用ICP测试溶液各元素的含量，然后对锰元素的含量进行测量和换算，得到其重量占比。
在第一个至第三个方面的一些实施方式中，第一正极活性材料在完全脱嵌锂前后的晶格变化率为4％以下，可选为3.8％以下，更可选为2.0-3.8％。
磷酸锰锂(LiMnPO 4)的脱嵌锂过程是两相反应。两相的界面应力由脱嵌锂前后的晶格变化率大小决定，晶格变化率越小，界面应力越小，Li +传输越容易。因此，减小内核的晶格变化率将有利于增强Li +的传输能力，从而改善二次电池的倍率性能。本申请具有核-壳结构的第一正极活性材料能够实现4％以下的脱嵌锂前后的晶格变化率，因此使用第一正极活性材料能够改善二次电池的倍率性能。晶格变化率可通过本领域中已知的方法，例如X射线衍射图谱(XRD)测得。
在第一个至第三个方面的一些实施方式中，第一正极活性材料的Li/Mn反位缺陷浓度为4％以下，可选为2.2％以下，更可选为1.5-2.2％。
本申请Li/Mn反位缺陷，指的是LiMnPO 4晶格中，Li +与Mn 2+的位置发生互换。相应地，Li/Mn反位缺陷浓度指的是与Mn 2+发生互换的Li +占Li +总量的百分比。本申请中，Li/Mn反位缺陷浓度例如，可以依据JIS K 0131-1996进行测试。
本申请具有核-壳结构的第一正极活性材料能够实现上述较低的Li/Mn反位缺陷浓度。虽然机理尚不十分清楚，但本申请发明人推测，由于LiMnPO 4晶格中，Li +与Mn 2+会发生位置互换，而Li +传输通道为一维通道，因此Mn 2+在Li +通道中将难以迁移，进而阻碍Li +的传输。由此，本申请具有核-壳结构的第一正极活性材料由于Li/Mn反位缺陷浓度较低，在上述范围内，因此，能够避免Mn 2+阻碍Li +的传输，同时提升第一正极活性材料的克容量发挥和倍率性能。
在第一个至第三个方面的一些实施方式中，第一正极活性材料在3T下的压实密度为2.2g/cm 3以上，可选地为2.2g/cm 3以上且2.8g/cm 3以下。压实密度越高，单位体积活性材料的重量越大，因此提高压实密度有利于提高电芯的体积能量密度。压实密度可依据GB/T24533-2009测量。
在第一个至第三个方面的一些实施方式中，第一正极活性材料的表面氧价态为-1.90以下，可选地为-1.90至-1.98。
氧的稳定价态本为-2价，价态越接近-2价，其得电子能力越强，即氧化性越强，通常情况下，其表面价态在-1.7以下。本申请通过如上将第一正极活性材料的表面氧价态限定在上述范围内，能够减轻第一正极材料与电解液的界面副反应，从而改善电芯的循环，高温存储产气等性能。
表面氧价态可通过本领域中已知的方法测量，例如通过电子能量损失谱(EELS)测量。
在第一个至第三个方面的一些实施方式中，第一正极活性材料和第二正极活性材料的质量之和占正极极片的质量的88％-98.7％。进一步保证二次电池具有优良的倍率性能、动力学性能和低温循环性能，且具有较高的能量密度。
在第一个至第三个方面的一些实施方式中，第一正极活性材料的一次颗粒的平均粒径范围为50-500nm，体积中值粒径Dv50在200-300nm范围内。由于颗粒会发生团聚，因此实际测得团聚后的二次颗粒大小可能为500-40000nm。第一正极活性材料颗粒的大小会影响材料的加工和极片的压实密度性能。通过选择一次颗粒的平均粒径在上述范围内，从而能够避免以下情况：第一正极活性材料的一次颗粒的平均粒径太小，可能会引起颗粒团聚，分散困难，并且需要较多的粘结剂，导致极片脆性较差；第一正极活性材料的一次颗粒的平均粒径太大，可能会使颗粒间的空隙较大，压实密度降低。
通过上述方案，能够有效抑制脱嵌锂过程中磷酸锰锂的晶格变化率和Mn溶出，从而提升二次电池的高温循环稳定性和高温储存性能。
本申请中，中值粒径Dv50是指材料累计体积分布百分数达到50％时所对应的粒径。在本申请中，材料的中值粒径Dv50可采用激光衍射粒度分析法测定。例如参照标准GB/T 19077-2016，使用激光粒度分析仪(例如Malvern Master Size 3000)进行测定。
通过工艺控制(例如，对各种源的材料进行充分混合、研磨)，能够保证各元素在晶格中均匀分布，不出现聚集的情况。A元素和R 元素掺杂后的磷酸锰锂的XRD图中的主要特征峰位置与未掺杂的LiMnPO 4的一致，说明掺杂过程没有引入杂质相，因此，内核性能的改善主要是来自元素掺杂，而不是杂相导致的。本申请发明人在制备第一正极活性材料后，通过聚焦离子束(简称FIB)切取已制备好的第一正极活性材料颗粒的中间区域，通过透射电子显微镜(简称TEM)以及X射线能谱分析(简称EDS)进行测试发现，各元素分布均匀，未出现聚集。
在第一个至第三个方面的一些实施方式中，正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将金属材料(铝、铝合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在第一个至第三个方面的一些实施方式中，正极膜层还可包含本领域公知的用于电池的其它正极活性材料。作为示例，正极活性材料可包括以下材料中的至少一种：橄榄石结构的含锂磷酸盐、锂过渡金属氧化物及其各自的改性化合物。但本申请并不限定于这些材料，还可以使用其他可被用作电池正极活性材料的传统材料。这些正极活性材料可以仅单独使用一种，也可以将两种以上组合使用。其中，锂过渡金属氧化物的示例可包括但不限于锂镍氧化物(如LiNiO 2)、锂锰氧化物(如LiMnO 2、LiMn 2O 4)、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物及其改性化合物等中的至少一种。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸锰锂(如LiMnPO 4)、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料中的至少一种。
在第一个至第三个方面的一些实施方式中，正极膜层还可选地包括粘结剂。作为示例，粘结剂可以包括聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物及含氟丙烯酸酯树脂中的至少一种。
在第一个至第三个方面的一些实施方式中，正极膜层还可选地包括导电剂。作为示例，导电剂可以包括超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在第一个至第三个方面中，第一正极活性材料的制备方法，包括以下步骤：
提供内核材料的步骤：内核化学式为Li 1+xMn 1-yA yP 1-zR zO 4，其中x为在-0.100-0.100范围内的任意数值，y为在0.001-0.500范围内的任意数值，z为在0.001-0.100范围内的任意数值，A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，可选为Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，R为选自B、Si、N和S中的一种或多种元素，可选地，R为选自B、Si、N和S中的一种元素；
包覆步骤：分别提供Li aMP 2O 7和/或M b(P 2O 7) c以及XPO 4悬浊液，将内核材料加入到上述悬浊液中并混合，经烧结获得第一正极活性材料，其中0≤a≤2，1≤b≤4，1≤c≤6，a、b和c的值满足以下条件：使晶态焦磷酸盐Li aMP 2O 7或M b(P 2O 7) c保持电中性；M各自独立地为选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb或Al中的一种或多种元素；X为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb或Al中的一种或多种元素；
其中，第一正极活性材料具有核-壳结构，其包括内核、包覆内核的第一包覆层、包覆第一包覆层的第二包覆层以及包覆第二包覆层的第三包覆层，第一包覆层包括晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，第二包覆层包括晶态磷酸盐XPO 4，第三包覆层为碳。
在第一个至第三个方面的一些实施方式中，提供内核材料的步骤包括以下步骤：
步骤(1)：将锰源、元素A的掺杂剂和酸在容器中混合并搅拌，得到掺杂有元素A的锰盐颗粒；
步骤(2)：将掺杂有元素A的锰盐颗粒与锂源、磷源和元素R的掺杂剂在溶剂中混合并得到浆料，在惰性气体气氛保护下烧结后得到掺杂有元素A和元素R的内核，其中，掺杂有元素A和元素R的 内核为Li 1+xMn 1-yA yP 1-zR zO 4，其中x为在-0.100-0.100范围内的任意数值，y为在0.001-0.500范围内的任意数值，z为在0.001-0.100范围内的任意数值，A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，可选为Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，R为选自B、Si、N和S中的一种或多种元素，可选地，R为选自B、Si、N和S中的一种元素。
本申请的制备方法对材料的来源并没有特别的限制，某种元素的来源可包括该元素的单质、硫酸盐、卤化物、硝酸盐、有机酸盐、氧化物或氢氧化物中的一种或多种，前体是该来源可实现本申请制备方法的目的。
在第一个至第三个方面的一些实施方式中，提供内核材料的步骤中，元素A的掺杂剂为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素各自的单质、碳酸盐、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种。
在第一个至第三个方面的一些实施方式中，提供内核材料的步骤中，元素R的掺杂剂为选自B、Si、N和S中的一种或多种元素各自的无机酸、亚酸、有机酸、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种。
在第一个至第三个方面的一些实施方式中，提供内核材料的步骤中，锰源可为本领域已知的可用于制备磷酸锰锂的含锰物质。作为示例，锰源可为选自单质锰、二氧化锰、磷酸锰、草酸锰、碳酸锰中的一种或多种。
在第一个至第三个方面的一些实施方式中，提供内核材料的步骤中，酸可为选自盐酸、硫酸、硝酸、磷酸、硅酸、亚硅酸等有机酸和有机酸如草酸中的一种或多种。在一些实施方式中，酸为浓度为60重量％以下的稀的有机酸。
在第一个至第三个方面的一些实施方式中，提供内核材料的步骤中，锂源可为本领域已知的可用于制备磷酸锰锂的含锂物质。作为示 例，锂源为选自碳酸锂、氢氧化锂、磷酸锂、磷酸二氢锂中的一种或多种。
在第一个至第三个方面的一些实施方式中，提供内核材料的步骤中，磷源可为本领域已知的可用于制备磷酸锰锂的含磷物质。作为示例，磷源为选自磷酸氢二铵、磷酸二氢铵、磷酸铵和磷酸中的一种或多种。
在第一个至第三个方面的一些实施方式中，提供内核材料的步骤中，在锰源、元素A的掺杂剂与酸在溶剂中反应得到掺杂有元素A的锰盐悬浮液后，将悬浮液过滤，烘干，并进行砂磨以得到粒径为50-200nm的经元素A掺杂的锰盐颗粒。
在第一个至第三个方面的一些实施方式中，提供内核材料的步骤中，将步骤(2)中的浆料进行干燥得到粉料，然后将粉料烧结得到掺杂有元素A和元素R的内核。
在第一个至第三个方面的一些实施方式中，步骤(1)在20-120℃、可选为40-120℃的温度下进行混合；和/或
步骤(1)中搅拌在400-700rpm下进行1-9h，可选地为3-7h。
可选地，步骤(1)中的反应温度可在约30℃、约50℃、约60℃、约70℃、约80℃、约90℃、约100℃、约110℃或约120℃进行；步骤(1)中搅拌进行约2小时、约3小时、约4小时、约5小时、约6小时、约7小时、约8小时或约9小时；可选地，步骤(1)中的反应温度、搅拌时间可在上述任意数值的任意范围内。
在第一个至第三个方面的一些实施方式中，步骤(2)在20-120℃、可选为40-120℃的温度下进行混合1-12h。可选地，步骤(2)中的反应温度可在约30℃、约50℃、约60℃、约70℃、约80℃、约90℃、约100℃、约110℃或约120℃进行；步骤(2)中混合进行约2小时、约3小时、约4小时、约5小时、约6小时、约7小时、约8小时、约9小时、约10小时、约11小时或约12小时；可选地，步骤(2)中的反应温度、混合时间可在上述任意数值的任意范围内。
当内核颗粒制备过程中的温度和时间处于上述范围内时，制备获得的内核以及由其制得的正极活性材料的晶格缺陷较少，有利于抑制 锰溶出，减少正极活性材料与电解液的界面副反应，从而改善二次电池的循环性能和安全性能。
在第一个至第三个方面的一些实施方式中，提供内核材料的步骤中，在制备A元素和R元素掺杂的稀酸锰颗粒的过程中，控制溶液pH为3.5-6，可选地，控制溶液pH为4-6，更可选地，控制溶液pH为4-5。需要说明的是，在本申请中可通过本领域通常使用的方法调节所得混合物的pH，例如可通过添加酸或碱。
在第一个至第三个方面的一些实施方式中，在步骤(2)中，锰盐颗粒与锂源、磷源的摩尔比为1：0.5-2.1：0.5-2.1，可选地，掺杂有元素A的锰盐颗粒与锂源、磷源的摩尔比为约1：1：1。
在第一个至第三个方面的一些实施方式中，提供内核材料的步骤中，制备A元素和R元素掺杂的磷酸锰锂过程中的烧结条件为：在惰性气体或惰性气体与氢气混合气氛下在600-950℃下烧结4-10小时；可选地，烧结可在约650℃、约700℃、约750℃、约800℃、约850℃或约900℃下烧结约2小时、约3小时、约4小时、约5小时、约6小时、约7小时、约8小时、约9小时或约10小时；可选地，烧结的温度、烧结时间可在上述任意数值的任意范围内。在制备A元素和R元素掺杂的磷酸锰锂过程中，烧结温度过低以及烧结时间过短时，会导致材料内核的结晶度较低，会影响整体的性能发挥，而烧结温度过高时，材料内核中容易出现杂相，从而影响整体的性能发挥；烧结时间过长时，材料内核颗粒长的较大，从而影响克容量发挥，压实密度和倍率性能等。
在第一个至第三个方面的一些实施方式中，提供内核材料的步骤中，保护气氛为70-90体积％氮气和10-30体积％氢气的混合气体。
在第一个至第三个方面的一些实施方式中，包覆步骤包括：
第一包覆步骤：将元素M的源、磷源和酸以及任选地锂源，溶于溶剂中，得到第一包覆层悬浊液；将内核步骤中获得的内核与第一包覆步骤获得的第一包覆层悬浊液充分混合，干燥，然后烧结，得到第一包覆层包覆的材料；
第二包覆步骤：将元素X的源、磷源和酸溶于溶剂中，得到第二包覆层悬浊液；将第一包覆步骤中获得的第一包覆层包覆的材料与第二包覆步骤获得的第二包覆层悬浊液充分混合，干燥，然后烧结，得到两层包覆层包覆的材料；
第三包覆步骤：将碳源溶于溶剂中，充分溶解得到第三包覆层溶液；然后将第二包覆步骤中获得的两层包覆层包覆的材料加入第三包覆层溶液中，混合均匀，干燥，然后烧结得到三层包覆层包覆的材料，即正极活性材料。
在第一个至第三个方面的一些实施方式中，包覆步骤中，元素M的源为选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb或Al中的一种或多种元素各自的单质、碳酸盐、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种。
在第一个至第三个方面的一些实施方式中，包覆步骤中，元素X的源为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb或Al中的一种或多种元素各自的单质、碳酸盐、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种。
元素A、R、M、X各自的源的加入量取决于目标掺杂量，锂源、锰源和磷源的用量之比符合化学计量比。
作为示例，碳源为选自淀粉、蔗糖、葡萄糖、聚乙烯醇、聚乙二醇、柠檬酸中的一种或多种。
在第一个至第三个方面的一些实施方式中，第一包覆步骤中，控制溶解有元素M的源、磷源和酸以及任选地锂源的溶液pH为3.5-6.5，然后搅拌并反应1-5h，然后将溶液升温至50-120℃，并保持该温度2-10h，和/或，烧结在650-800℃下进行2-6小时。
在第一个至第三个方面的一些实施方式中，在第一包覆步骤中，反应充分进行。可选地，在第一包覆步骤中，反应进行约1.5小时、约2小时、约3小时、约4小时、约4.5小时或约5小时。可选地，第一包覆步骤中，反应的反应时间可在上述任意数值的任意范围内。
在第一个至第三个方面的一些实施方式中，在第一包覆步骤中，控制溶液pH为4-6。可选地，在第一包覆步骤中，将溶液升温至约 55℃、约60℃、约70℃、约80℃、约90℃、约100℃、约110℃或约120℃，并在该温度下保持约2小时、约3小时、约4小时、约5小时、约6小时、约7小时、约8小时、约9小时或约10小时；可选地，第一包覆步骤中，升温的温度和保持时间可在上述任意数值的任意范围内。
在第一个至第三个方面的一些实施方式中，在第一包覆步骤中，烧结可在约650℃、约700℃、约750℃、或约800℃下烧结约2小时、约3小时、约4小时、约5小时或约6小时；可选地，烧结的温度、烧结时间可在上述任意数值的任意范围内。
在第一包覆步骤中，通过将烧结温度和时间控制在以上范围内，可以避免以下情况：当第一包覆步骤中的烧结温度过低以及烧结时间过短时，会导致第一包覆层的结晶度低，非晶态物质较多，这样会导致抑制金属溶出的效果下降，从而影响二次电池的循环性能和高温存储性能；而烧结温度过高时，会导致第一包覆层出现杂相，也会影响到其抑制金属溶出的效果，从而影响二次电池的循环和高温存储性能等；烧结时间过长时，会使第一包覆层的厚度增加，影响Li +的迁移，从而影响材料的克容量发挥和倍率性能等。
在第一个至第三个方面的一些实施方式中，第二包覆步骤中，将元素X的源、磷源和酸溶于溶剂后，搅拌并反应1-10h，然后将溶液升温至60-150℃，并保持该温度2-10h，和/或，烧结在500-700℃下进行6-10小时。
可选地，在第二包覆步骤中，反应充分进行。可选地，在第二包覆步骤中，反应进行约1.5小时、约2小时、约3小时、约4小时、约4.5小时、约5小时、约6小时、约7小时、约8小时、约9小时或约10小时。可选地，第二包覆步骤中，反应的反应时间可在上述任意数值的任意范围内。
可选地，在第二包覆步骤中，将溶液升温至约65℃、约70℃、约80℃、约90℃、约100℃、约110℃、约120℃、约130℃、约140℃或约150℃，并在该温度下保持约2小时、约3小时、约4小时、约5小时、约6小时、约7小时、约8小时、约9小时或约10小时； 可选地，第二包覆步骤中，升温的温度和保持时间可在上述任意数值的任意范围内。
在提供内核材料的步骤和第一包覆步骤和第二包覆步骤中，在烧结之前，即，在发生化学反应的内核材料的制备中(步骤(1)-(2))以及在第一包覆层悬浮液和第二包覆层悬浮液的制备中，通过如上选择适当的反应温度和反应时间，从而能够避免以下情况：反应温度过低时，则反应无法发生或反应速率较慢；温度过高时，产物分解或形成杂相；反应时间过长时，产物粒径较大，可能会增加后续工艺的时间和难度；反应时间过短时，则反应不完全，获得的产物较少。
可选地，在第二包覆步骤中，烧结可在约550℃、约600℃或约700℃下烧结约6小时、约7小时、约8小时、约9小时或约10小时；可选地，烧结的温度、烧结时间可在上述任意数值的任意范围内。
在第二包覆步骤中，通过将烧结温度和时间控制在以上范围内，可以避免以下情况：当第二包覆步骤中的烧结温度过低以及烧结时间过短时，会导致第二包覆层的结晶度低，非晶态较多，降低材料表面反应活性的性能下降，从而影响二次电池的循环和高温存储性能等；而烧结温度过高时，会导致第二包覆层出现杂相，也会影响到其降低材料表面反应活性的效果，从而影响二次电池的循环和高温存储性能等；烧结时间过长时，会使第二包覆层的厚度增加，影响材料的电压平台，从而使材料的能量密度下降等。
在第一个至第三个方面的一些实施方式中，第三包覆步骤中的烧结在700-800℃下进行6-10小时。可选地，在第三包覆步骤中，烧结可在约700℃、约750℃或约800℃下烧结约6小时、约7小时、约8小时、约9小时或约10小时；可选地，烧结的温度、烧结时间可在上述任意数值的任意范围内。
在第三包覆步骤中，通过将烧结温度和时间控制在以上范围内，可以避免以下情况：当第三包覆步骤中的烧结温度过低时，会导致第三包覆层的石墨化程度下降，影响其导电性，从而影响材料的克容量发挥；烧结温度过高时，会造成第三包覆层的石墨化程度过高，影响Li +的传输，从而影响材料的克容量发挥等；烧结时间过短时，会导 致包覆层过薄，影响其导电性，从而影响材料的克容量发挥；烧结时间过长时，会导致包覆层过厚，影响材料的压实密度等。
在上述第一包覆步骤、第二包覆步骤、第三包覆步骤中，干燥均在100℃至200℃、可选为110℃至190℃、更可选为120℃至180℃、甚至更可选为120℃至170℃、最可选为120℃至160℃的干燥温度下进行，干燥时间为3-9h、可选为4-8h，更可选为5-7h，最可选为约6h。
通过本申请第一正极活性材料的制备方法所制备的第一正极活性材料，其制备的二次电池在循环后Mn与Mn位掺杂元素的溶出量降低，且高温稳定性、高温循环性能和倍率性能得到改善。另外，原料来源广泛、成本低廉，工艺简单，有利于实现工业化。
[负极极片]
负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极膜层，负极膜层包括负极活性材料。
作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极膜层设置在负极集流体相对的两个表面中的任意一者或两者上。
在一些实施方式中，负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，负极活性材料可采用本领域公知的用于电池的负极活性材料。作为示例，负极活性材料可包括以下材料中的至少一种：人造石墨、天然石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂等。硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的至少一种。锡基材料可选自单质锡、锡氧化合物以及锡合金中的至少一种。但本申请并不限定于这些材料，还可以使 用其他可被用作电池负极活性材料的传统材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
在一些实施方式中，负极膜层还可选地包括粘结剂。作为示例，粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的至少一种。
在一些实施方式中，负极膜层还可选地包括导电剂。作为示例，导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，负极膜层还可选地包括其他助剂，例如增稠剂(如羧甲基纤维素钠(CMC-Na))等。
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组分，例如负极活性材料、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成负极浆料；将负极浆料涂覆在负极集流体上，经烘干、冷压等工序后，即可得到负极极片。
[电解质]
电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以是液态的、凝胶态的或全固态的。
在一些实施方式中，电解质为液态的，且包括电解质盐和溶剂。
在一些实施方式中，电解质盐可选自六氟磷酸锂、四氟硼酸锂、高氯酸锂、六氟砷酸锂、双氟磺酰亚胺锂、双三氟甲磺酰亚胺锂、三氟甲磺酸锂、二氟磷酸锂、二氟草酸硼酸锂、二草酸硼酸锂、二氟二草酸磷酸锂及四氟草酸磷酸锂中的至少一种。
在一些实施方式中，溶剂可选自碳酸亚乙酯、碳酸亚丙酯、碳酸甲乙酯、碳酸二乙酯、碳酸二甲酯、碳酸二丙酯、碳酸甲丙酯、碳酸乙丙酯、碳酸亚丁酯、氟代碳酸亚乙酯、甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯、1,4-丁内酯、环丁砜、二甲砜、甲乙砜及二乙砜中的至少一种。
在一些实施方式中，电解液还可选地包括添加剂。作为示例，添加剂可以包括负极成膜添加剂、正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温或低温性能的添加剂等。
[隔离膜]
在一些实施方式中，二次电池中还包括隔离膜。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。
在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施方式中，二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，图2是作为一个示例的方形结构的二次电池5。
在一些实施方式中，参照图3，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于开口，以封闭容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于容纳腔内。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个 或多个，本领域技术人员可根据具体实际需求进行选择。
在一些实施方式中，二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块的应用和容量进行选择。
图4是作为一个示例的电池模块4。参照图4，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以为一个或多个，具体数量本领域技术人员可根据电池包的应用和容量进行选择。
图5和图6是作为一个示例的电池包1。参照图5和图6，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
另外，本申请还提供一种用电装置，用电装置包括本申请提供的二次电池、电池模块、或电池包中的至少一种。二次电池、电池模块、或电池包可以用作用电装置的电源，也可以用作用电装置的能量存储单元。用电装置可以包括移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等，但不限于此。
作为用电装置，可以根据其使用需求来选择二次电池、电池模块或电池包。
图7是作为一个示例的用电装置。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
[制备例]
以下，说明本申请的制备例。下面描述的制备例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。制备例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
本申请制备例涉及的原材料来源如下：
Figure PCTCN2022084292-appb-000001
正极活性材料及其浆料的制备
制备例1
步骤S1:制备Fe、Co、V和S共掺杂的草酸锰
将689.6g碳酸锰、455.27g碳酸亚铁、4.65g硫酸钴、4.87g二氯化钒加入混料机中充分混合6h。然后将得到的混合物转入反应釜中，并加入5L去离子水和1260.6g二水合草酸，加热至80℃，以500rpm的转速充分搅拌6h，混合均匀，直至反应终止无气泡产生，得到Fe、Co、和V共掺杂的草酸锰悬浮液。然后将悬浮液过滤，在120℃下烘干，再进行砂磨，得到粒径为100nm的草酸锰颗粒。
步骤S2：制备内核Li 0.997Mn 0.60Fe 0.393V 0.004Co 0.003P 0.997S 0.003O 4
取(1)中制备的草酸锰1793.1g以及368.3g碳酸锂、1146.6g磷酸二氢铵和4.9g稀硫酸，将它们加入到20L去离子水中，充分搅拌，在80℃下均匀混合反应10h，得到浆料。将浆料转入喷雾干燥设备中进行喷雾干燥造粒，在250℃的温度下进行干燥，得到粉料。在保护气氛(90％氮气和10％氢气)中，在700℃下将粉料在辊道窑中进行烧结4h，得到内核材料。采用电感耦合等离子体发射光谱(ICP)对内核材料进行元素含量检测，得到内核化学式为上述所示。
步骤S3：第一包覆层悬浊液的制备
制备Li 2FeP 2O 7溶液：将7.4g碳酸锂，11.6g碳酸亚铁，23.0g磷酸二氢铵和12.6g二水合草酸溶于500mL去离子水中，控制pH为5，然后搅拌并在室温下反应2h得到溶液，之后将该溶液升温到80℃并保持此温度4h，得到第一包覆层悬浊液。
步骤S4：第一包覆层的包覆
将步骤S2中获得的掺杂后的1571.9g磷酸锰锂内核材料加入到步骤S3中获得的第一包覆层悬浊液(包覆物质含量为15.7g)中，充分搅拌混合6h，混合均匀后，转入120℃烘箱中干燥6h，然后在650℃下烧结6h得到焦磷酸盐包覆后的材料。
步骤S5：第二包覆层悬浊液的制备
将3.7g碳酸锂、11.6g碳酸亚铁、11.5g磷酸二氢铵和12.6g二水合草酸溶于1500mL去离子水中，然后搅拌并反应6h得到溶液，之后将该溶液升温到120℃并保持此温度6h，得到第二包覆层悬浊液。
步骤S6：第二包覆层的包覆
将步骤S4中获得的1586.8g的焦磷酸盐包覆后的材料加入到步骤S5中得到的第二包覆层悬浊液(包覆物质含量为47.1g)中，充分搅拌混合6h，混合均匀后，转入120℃烘箱中干燥6h，然后700℃烧结8h得到两层包覆后的材料。
步骤S7：第三包覆层水溶液的制备
将37.3g蔗糖溶于500g去离子水中，然后搅拌并充分溶解，得到蔗糖水溶液。
步骤S8：第三包覆层的包覆
将步骤S6中获得的两层包覆的材料1633.9g加入到步骤S7中得到的蔗糖溶液中，一同搅拌混合6h，混合均匀后，转入150℃烘箱中干燥6h，然后在700℃下烧结10h得到三层包覆后的材料。
制备例2至42及对比例1至17
以类似于制备例1的方法制作制备例2至42和对比例1至17的正极活性材料，正极活性材料的制备中的不同之处参见表1-6。
其中，对比例1-2、4-10和12未包覆第一层，因此没有步骤S3-S4；对比例1-11未包覆第二层，因此没有步骤S5-S6。
Figure PCTCN2022084292-appb-000002
Figure PCTCN2022084292-appb-000003
Figure PCTCN2022084292-appb-000004
Figure PCTCN2022084292-appb-000005
Figure PCTCN2022084292-appb-000006
Figure PCTCN2022084292-appb-000007
Figure PCTCN2022084292-appb-000008
Figure PCTCN2022084292-appb-000009
Figure PCTCN2022084292-appb-000010
Figure PCTCN2022084292-appb-000011
Figure PCTCN2022084292-appb-000012
Figure PCTCN2022084292-appb-000013
Figure PCTCN2022084292-appb-000014
Figure PCTCN2022084292-appb-000015
Figure PCTCN2022084292-appb-000016
Figure PCTCN2022084292-appb-000017
Figure PCTCN2022084292-appb-000018
Figure PCTCN2022084292-appb-000019
正极极片的制备
实施例1
将制备例1正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P1。
实施例2
将制备例43正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P2。
实施例3
将制备例1正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂布在铝箔的一面上，将制备例43正极活性材料的浆料以0.2g/cm 2的涂布量均匀涂布在铝箔的另一面上，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P3。
实施例4
将制备例44正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，其他与实施例3相同，得到正极极片P4。
实施例5
将制备例1正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂布在铝箔的一面上，将制备例44正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂布在铝箔的另一面上，其他与实施例3相同，得到正极极片P5。
实施例6
将制备例43正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂布在铝箔的一面上，将制备例44正极活性材料的浆料以0.019g/cm 2 的涂布量均匀涂布在铝箔的另一面上，其他与实施例3相同，得到正极极片P6。
实施例7
在铝箔的两面均依次涂布制备例1正极活性材料的浆料和制备例43正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，然后，在100～120℃高温真空干燥14h，辊压机压实，得到正极极片P7。
实施例8
在铝箔的两面均依次涂布制备例43正极活性材料的浆料和制备例1正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，其他与实施例7相同，得到正极极片P8。
实施例9
在铝箔的两面均依次涂布制备例1正极活性材料的浆料和制备例44正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，其他与实施例7相同，得到正极极片P9。
实施例10
在铝箔的两面均依次涂布制备例44正极活性材料的浆料和制备例1正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，其他与实施例7相同，得到正极极片P10。
实施例11
在铝箔的两面均依次涂布制备例43正极活性材料的浆料和制备例44正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，其他与实施例7相同，得到正极极片P11。
实施例12
在铝箔的两面均依次涂布制备例44正极活性材料的浆料和制备例43正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，其他与实施例7相同，得到正极极片P12。
实施例13
在铝箔的A面依次涂布制备例1正极活性材料的浆料和制备例43正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例1正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，然后，在100～120℃高温真空干燥14h，辊压机压实，得到正极极片P13。
实施例14
在铝箔的A面依次涂布制备例1正极活性材料的浆料和制备例43正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例43正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P14。
实施例15
在铝箔的A面依次涂布制备例1正极活性材料的浆料和制备例43正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例44正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P15。
实施例16
在铝箔的A面依次涂布制备例43正极活性材料的浆料和制备例1正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例1正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P16。
实施例17
在铝箔的A面依次涂布制备例43正极活性材料的浆料和制备例1正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例43正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P17。
实施例18
在铝箔的A面依次涂布制备例43正极活性材料的浆料和制备例1正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例44正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P18。
实施例19
在铝箔的A面依次涂布制备例1正极活性材料的浆料和制备例44正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例1正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P19。
实施例20
在铝箔的A面依次涂布制备例1正极活性材料的浆料和制备例44正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例43正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P20。
实施例21
在铝箔的A面依次涂布制备例1正极活性材料的浆料和制备例44正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例44正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P21。
实施例22
在铝箔的A面依次涂布制备例44正极活性材料的浆料和制备例1正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例1正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P22。
实施例23
在铝箔的A面依次涂布制备例44正极活性材料的浆料和制备例1正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例43正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P23。
实施例24
在铝箔的A面依次涂布制备例44正极活性材料的浆料和制备例1正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例44正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P24。
实施例25
在铝箔的A面依次涂布制备例43正极活性材料的浆料和制备例44正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例1正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P25。
实施例26
在铝箔的A面依次涂布制备例43正极活性材料的浆料和制备例44正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例43正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P26。
实施例27
在铝箔的A面依次涂布制备例43正极活性材料的浆料和制备例44正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例44正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P27。
实施例28
在铝箔的A面依次涂布制备例44正极活性材料的浆料和制备例43正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例1正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P28。
实施例29
在铝箔的A面依次涂布制备例44正极活性材料的浆料和制备例43正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例43正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P29。
实施例30
在铝箔的A面依次涂布制备例44正极活性材料的浆料和制备例43正极活性材料的浆料，每层浆料的涂布量均为0.010g/cm 2，在铝箔的B面均匀涂布制备例44正极活性材料的浆料，浆料的涂布量为0.020g/cm 2，其他与实施例13相同，得到正极极片P30。
实施例31
将制备例45正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P31。
实施例32
将制备例46正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂 在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P32。
实施例33
将制备例47正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P33。
实施例34
将制备例48正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P34。
实施例35
将制备例49正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P35。
实施例36
将制备例50正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P36。
实施例37
将制备例51正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P37。
实施例38
将制备例52正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机 压实，得到正极极片P38。
实施例39
将制备例53正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P39。
实施例40
将制备例54正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P40。
实施例41
将制备例55正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P41。
实施例42
将制备例56正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P42。
实施例43
将制备例57正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P43。
实施例44
将制备例58正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机 压实，得到正极极片P44。
实施例45
将制备例59正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P45。
实施例46
将制备例60正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P46。
实施例47
将制备例61正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P47。
实施例48
将制备例62正极活性材料的浆料以0.019g/cm 2的涂布量均匀涂在集流体铝箔的两面，在100～120℃的高温下真空干燥14h，辊压机压实，得到正极极片P48。
以上各正极极片的参数见表10。
表10正极极片参数
Figure PCTCN2022084292-appb-000020
Figure PCTCN2022084292-appb-000021
Figure PCTCN2022084292-appb-000022
Figure PCTCN2022084292-appb-000023
Figure PCTCN2022084292-appb-000024
“*”：第1层指与铝箔表面接触的一层，第2层指设置在第1层上的一层。
“#”：第一正极活性材料为制备例1制得的正极活性材料，第二正极活性材料为制备例43、制备例45、制备例47-54的正极活性材料。
负极极片的制备
将负极活性材料人造石墨、导电剂超导炭黑(Super-P)、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC-Na)按照质量比为95％：1.5％：1.8％：1.7％溶于去离子水中，充分搅拌混合均匀后，得到粘度3000mPa.s、固含52％的负极浆料；将负极浆料涂覆在6μm的负极集流体铜箔上，之后在100℃烘烤4小时以烘干，辊压，得到压实密度为1.75g/cm3的负极极片。
隔离膜
采用聚丙烯膜。
电解液的制备
将碳酸乙烯酯、碳酸二甲酯和1，2-丙二醇碳酸酯按体积比1:1:1混合，然后将LiPF 6均匀溶解在上述溶液中，得到电解液。该电解液中，LiPF 6的浓度为1mol/L。
全电池的制备
采用上述的正极极片，按照负极极片、隔膜、正极极片的顺序，采用卷绕法形成裸电芯，分别冲切出铝极耳和铜极耳，得到裸电芯；通过转接片将两个裸电芯铜与铜极耳，铝与铝极耳一起焊接到电池顶盖上，对裸电芯进行包裹绝缘后，将裸电芯装入铝壳中，将顶盖与铝壳焊接形成干电芯，对干电芯进行烘烤除水后注入电解液，对电池进行化成和老化，相应地得到全电池。其中，正极极片P1、P2、P3、P8、P10、P11、P12、P17、P18、P23、P24、P26、P27所制的电池结构如图8-20所示。
扣式电池的制备
将上述的正极极片与负极、电解液一起在扣电箱中组装成扣式电池(下文也称“扣电”)。
I.正极活性材料的性能测试
1.晶格变化率测试方法:
在25℃恒温环境下，将正极活性材料样品置于XRD(型号为Bruker D8 Discover)中，采用1°/min对样品进行测试，并对测试数据进行整理分析，参照标准PDF卡片，计算出此时的晶格常数a0、b0、c0和v0(a0，b0和c0表示晶胞各个方面上的长度大小，v0表示晶胞体积，可通过XRD精修结果直接获取)。
采用上述的扣电制备方法，将正极活性材料样品制备成扣电，并对上述扣电以0.05C小倍率进行充电，直至电流减小至0.01C。然后将扣电中的正极极片取出，并置于碳酸二甲酯(DMC)中浸泡8小时。然后烘干，刮粉，并筛选出其中粒径小于500nm的颗粒。取样并按照与上述测试新鲜样品同样的方式计算出其晶胞体积v1，将(v0-v1)/v0×100％作为其完全脱嵌锂前后的晶格变化率(晶胞体积变化率)。
2.Li/Mn反位缺陷浓度的测定:
将“晶格变化率测量方法”中测试的XRD结果与标准晶体的PDF(Powder Diffraction File)卡片对比，得出Li/Mn反位缺陷浓度。具 体而言，将“晶格变化率测量方法”中测试的XRD结果导入通用结构分析系统(GSAS)软件中，自动获得精修结果，其中包含了不同原子的占位情况，通过读取精修结果获得Li/Mn反位缺陷浓度。
3.压实密度的测定:
取5g的上述制得的正极活性材料粉末放于压实专用模具(美国CARVER模具，型号13mm)中，然后将模具放在压实密度仪器上。施加3T的压力，在设备上读出压力下粉末的厚度(卸压后的厚度)，通过ρ＝m/v，计算出压实密度，其中使用的面积值为标准的小图片面积1540.25mm 2。
4. 3C充电恒流比的测定:
在25℃恒温环境下，将上述各个制备例和对比例制备的新鲜全电池静置5min，按照1/3C放电至2.5V。静置5min，按照1/3C充电至4.3V，然后在4.3V下恒压充电至电流小于等于0.05mA。静置5min，记录此时的充电容量为C0。按照1/3C放电至2.5V，静置5min，再按照3C充电至4.3V，静置5min，记录此时的充电容量为C1。3C充电恒流比即为C1/C0×100％。
3C充电恒流比越高，说明二次电池的倍率性能越好。
5.过渡金属Mn(以及Mn位掺杂的Fe)溶出测试:
将45℃下循环至容量衰减至80％后的上述各个制备例和对比例的正极活性材料所制的全电池采用0.1C倍率进行放电至截止电压2.0V。然后将电池拆开，取出负极极片，在负极极片上随机取30个单位面积(1540.25mm 2)的圆片，用Agilent ICP-OES730测试电感耦合等离子体发射光谱(ICP)。根据ICP结果计算其中Fe(如果正极活性材料的Mn位掺杂有Fe的话)和Mn的量，从而计算循环后Mn(以及Mn位掺杂的Fe)的溶出量。测试标准依据EPA-6010D-2014。
6.表面氧价态的测定:
取5g上述制得的正极活性材料样品按照上述扣电的制备方法制备成扣电。对扣电采用0.05C小倍率进行充电，直至电流减小至0.01C。然后将扣电中的正极极片取出，并置于DMC中浸泡8小时。然后烘干，刮粉，并筛选出其中粒径小于500nm的颗粒。将所得颗粒用电 子能量损失谱(EELS，所用仪器型号为Talos F200S)进行测量，获取能量损失近边结构(ELNES)，其反映元素的态密度和能级分布情况。根据态密度和能级分布，通过对价带态密度数据进行积分，算出占据的电子数，从而推算出充电后的表面氧的价态。
7.正极活性材料中锰元素和磷元素的测量:
将5g上述制得的正极活性材料在100ml逆王水(浓盐酸：浓硝酸＝1：3)中(浓盐酸浓度～37％，浓硝酸浓度～65％)溶解，利用ICP测试溶液各元素的含量，然后对锰元素或磷元素的含量进行测量和换算(锰元素或磷元素的量/正极活性材料的量*100％)，得到其重量占比。
8.扣式电池初始克容量测量方法:
在2.5-4.3V下，将上述各制备例和对比例制备的扣式电池按照0.1C充电至4.3V，然后在4.3V下恒压充电至电流小于等于0.05mA，静置5min，然后按照0.1C放电至2.0V，此时的放电容量为初始克容量，记为D0。
9.全电池60℃存储30天电芯膨胀测试:
在60℃下，存储100％充电状态(SOC)的上述各个制备例和对比例制备的全电池。在存储前后及过程中测量电芯的开路电压(OCV)和交流内阻(IMP)以监控SOC，并测量电芯的体积。其中在每存储48h后取出全电池，静置1h后测试开路电压(OCV)、内阻(IMP)，并在冷却至室温后用排水法测量电芯体积。排水法即先用表盘数据自动进行单位转换的天平单独测量电芯的重力F 1，然后将电芯完全置于去离子水(密度已知为1g/cm 3)中，测量此时的电芯的重力F 2，电芯受到的浮力F 浮即为F 1-F 2，然后根据阿基米德原理F 浮＝ρ×g×V 排，计算得到电芯体积V＝(F 1-F 2)/(ρ×g)。
由OCV、IMP测试结果来看，本实验过程中直至存储结束，全部实施例的电池始终保持99％以上的SOC。
存储30天后，测量电芯体积，并计算相对于存储前的电芯体积，存储后的电芯体积增加的百分比。
10.全电池45℃下循环性能测试:
在45℃的恒温环境下，在2.5-4.3V下，按照1C充电至4.3V，然后在4.3V下恒压充电至电流≤0.05mA，静置5min，然后按照1C放电至2.5V，容量记为D n(n＝0,1,2,……)。重复前述过程，直至容量衰减(fading)到80％，记录此时的重复次数，即为45℃下80％容量保持率对应的循环圈数。
11.晶面间距和夹角测试:
取1g上述制得的各正极活性材料粉末于50mL的试管中，并在试管中注入10mL质量分数为75％的酒精，然后进行充分搅拌分散30分钟，然后用干净的一次性塑料吸管取适量上述溶液滴加在300目铜网上，此时，部分粉末将在铜网上残留，将铜网连带样品转移至TEM(Talos F200s G2)样品腔中进行测试，得到TEM测试原始图片，保存原始图片格式(xx.dm3)。
将上述TEM测试所得原始图片在DigitalMicrograph软件中打开，并进行傅里叶变换(点击操作后由软件自动完成)得到衍射花样，量取衍射花样中衍射光斑到中心位置的距离，即可得到晶面间距，夹角根据布拉格方程进行计算得到。
通过得到的晶面间距和相应夹角数据，与其标准值比对，即可对不同包覆层的物质及晶态进行识别。
12.包覆层厚度测试:
包覆层的厚度大小测试主要通过FIB从上述制得的正极活性材料单个颗粒中间切取100nm左右厚度的薄片，然后对薄片进行TEM测试，得到TEM测试原始图片，保存原始图片格式(xx.dm3)。
将上述TEM测试所得原始图片在DigitalMicrograph软件中打开，通过晶格间距和夹角信息，识别出包覆层，量取包覆层的厚度。
对所选颗粒测量三个位置处的厚度，取平均值。
13.第三层包覆层碳中SP2形态和SP3形态摩尔比的测定:
本测试通过拉曼(Raman)光谱进行。通过对Raman测试的能谱进行分峰，得到Id/Ig，其中Id为SP3形态碳的峰强度，Ig为SP2形态碳的峰强度，从而确认两者的摩尔比。
14.内核化学式及不同包覆层组成的测定:
采用球差电镜仪(ACSTEM)对正极活性材料内部微观结构和表面结构进行高空间分辨率表征，结合三维重构技术得到正极活性材料的内核化学式及不同包覆层的组成。
制备例和对比例的正极活性材料的性能测试结果参见下面的表格。
Figure PCTCN2022084292-appb-000025
Figure PCTCN2022084292-appb-000026
Figure PCTCN2022084292-appb-000027
Figure PCTCN2022084292-appb-000028
Figure PCTCN2022084292-appb-000029
Figure PCTCN2022084292-appb-000030
Figure PCTCN2022084292-appb-000031
Figure PCTCN2022084292-appb-000032
Figure PCTCN2022084292-appb-000033
Figure PCTCN2022084292-appb-000034
Figure PCTCN2022084292-appb-000035
Figure PCTCN2022084292-appb-000036
Figure PCTCN2022084292-appb-000037
Figure PCTCN2022084292-appb-000038
Figure PCTCN2022084292-appb-000039
IV.电池测试
采用正极极片P2-P48制备的二次电池进行如下测试：
(1)按照国标GB 38031-2020“电动汽车用动力蓄电池安全要求”中的方法测定二次电池的能量密度；
(2)按照国标GBT31486-2015“电动汽车用动力蓄电池电性能要求及试验方法”测定二次电池的-20℃低温放电容量保持率(充放电循环两次)，以获取电池的动力学数据；
(3)按照国标GBT31484-2015“电动汽车用动力蓄电池循环寿命要求及试验方法”中的标准循环测试方法测试二次电池80％SOH的常温循环寿命；
(4)参考国标GBT31484-2015“电动汽车用动力蓄电池循环寿命要求及试验方法”中的标准循环测试方法，将测试过程温度调整为-10℃，充放电电流调整为0.33C，其余条件不变，测试二次电池80％SOH的低温循环寿命；
(5)参考国标GBT31486-2015“电动汽车用动力蓄电池电性能要求及试验方法”测定二次电池20％SOC的比功率数据，详细步骤如下：
a)以国标GBT31486-2015中6.3.4方法充电；
b)室温下，二次电池以1C电流放电48min后按照规定的最大放电电流放电10s，然后再静置30min，再以规定的最大充电电流充电10s；
c)采用10s充放电的放电能量除以10s充放电时间的方法，以此计算电芯的比功率(W/kg)。
上述结果见表17。
表17电池测试的结果
Figure PCTCN2022084292-appb-000040
Figure PCTCN2022084292-appb-000041
Figure PCTCN2022084292-appb-000042
根据上述结果可知：
与采用正极极片P2的二次电池相比，采用正极极片P3-P30的二次电池的能量密度更高、低温放电容量保持率更高、比功率更高、低温循环寿命更长，采用正极极片P3-P12、P14-15、P17-18、P20-P22、P24、P26-P30的二次电池的常温循环寿命更长；
与采用正极极片P31的二次电池相比，采用正极极片P32的二次电池的能量密度更高、低温放电容量保持率更高、比功率更高、低温循环寿命更长；
正极极片P41-P48包含第一正极活性材料和第二正极活性材料，正极极片P33-P40仅包含等量的与之对应的第二正极活性材料，与仅包含第二正极活性材料的正极极片相比，包含第一正极活性材料和第二正极活性材料的正极极片所制二次电池的能量密度更高、低温放电容量保持率更高、比功率更高、低温循环寿命更长；
以上说明，本申请正极极片所制二次电池的能量密度更高，动力学性能更好，电芯倍率性能更高，低温循环寿命更长，低温循环容量保持率更高，同时安全性更高。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本申请的范围内。

Claims (20)

  1. 一种正极极片，包括正极集流体和设置在所述正极集流体的至少一个表面上的正极膜层；所述正极膜层为单层结构或多层结构；当所述正极膜层为单层结构时，至少一个所述正极膜层同时包含具有核-壳结构的第一正极活性材料和第二正极活性材料；和/或，当所述正极膜层为多层结构时，至少一个所述正极膜层的至少一层中同时包含具有核-壳结构的第一正极活性材料和第二正极活性材料；
    所述第一正极活性材料包括内核、包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层和包覆所述第二包覆层的第三包覆层；所述内核包含Li 1+xMn 1-yA yP 1-zR zO 4，所述第一包覆层包含晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，所述第二包覆层包含晶态磷酸盐XPO 4，所述第三包覆层包含碳；
    其中，
    所述A包括选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素；
    所述R包括选自B、Si、N和S中的一种或多种元素；
    所述x选自-0.100至0.100范围内的任意数值；
    所述y选自0.001至0.500范围内的任意数值；
    所述z选自0.001至0.100范围内的任意数值；
    所述晶态焦磷酸盐Li aMP 2O 7和M b(P 2O 7) c中的M各自独立地包括选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素，
    所述a选自0至2范围内的任意数值；
    所述b选自1至4范围内的任意数值；
    所述c选自1至6范围内的任意数值；
    所述X包括选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；
    所述第二正极活性材料为选自LiFePO 4、碳包覆LiFePO 4、LiFe dD ePO 4和碳包覆LiFe dD ePO 4中的一种或多种，其中，所述D独 立地包括选自Ti、Zn、Co、Mn、La、V、Mg、Al、Nb、W、Zr、Nb、Sm、Cr、Cu和B中的一种或多种元素，所述d独立地选自0.99至0.999范围内的任意数值，并且d+e＝1。
  2. 一种正极极片，包括正极集流体和设置在所述正极集流体的至少一个表面上的正极膜层；至少一个所述正极膜层为多层结构，任一具有多层结构的正极膜层在不同层中分别包含具有核-壳结构的第一正极活性材料和第二正极活性材料；
    所述第一正极活性材料包括内核、包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层和包覆所述第二包覆层的第三包覆层；其中，所述内核包含Li 1+xMn 1-yA yP 1-zR zO 4，所述第一包覆层包含晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，所述第二包覆层包含晶态磷酸盐XPO 4，所述第三包覆层包含碳；
    其中，
    所述A包括选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素；
    所述R包括选自B、Si、N和S中的一种或多种元素；
    所述x选自-0.100至0.100范围内的任意数值；
    所述y选自0.001至0.500范围内的任意数值；
    所述z选自0.001至0.100范围内的任意数值；
    所述晶态焦磷酸盐Li aMP 2O 7和M b(P 2O 7) c中的M各自独立地包括选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；
    所述a选自0至2范围内的任意数值；
    所述b选自1至4范围内的任意数值；
    所述c选自1至6范围内的任意数值；
    所述X包括选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；
    所述第二正极活性材料为选自LiFePO 4、碳包覆LiFePO 4、LiFe dD ePO 4和碳包覆LiFe dD ePO 4中的一种或多种，其中，所述D独 立地包括选自Ti、Zn、Co、Mn、La、V、Mg、Al、Nb、W、Zr、Nb、Sm、Cr、Cu和B中的一种或多种元素，所述d独立地选自0.99至0.999范围内的任意数值，并且d+e＝1；
    可选地，任一具有多层结构的所述正极膜层在相邻层中分别包含所述第一正极活性材料和所述第二正极活性材料。
  3. 一种正极极片，包括正极集流体和分别设置在所述正极集流体的两个表面上的正极膜层A和正极膜层B；所述正极膜层A和所述正极膜层B各自独立地为单层结构或多层结构；所述正极膜层A的至少一层中包含具有核-壳结构的第一正极活性材料，同时，所述正极膜层B的至少一层中包含第二正极活性材料；
    所述第一正极活性材料包括内核、包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层和包覆所述第二包覆层的第三包覆层；其中，所述内核包含Li 1+xMn 1-yA yP 1-zR zO 4，所述第一包覆层包含晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，所述第二包覆层包含晶态磷酸盐XPO 4，所述第三包覆层包含碳；
    其中，
    所述A包括选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素；
    所述R包括选自B、Si、N和S中的一种或多种元素；
    所述x选自-0.100-0.100范围内的任意数值；
    所述y选自0.001-0.500范围内的任意数值；
    所述z选自0.001-0.100范围内的任意数值；
    所述晶态焦磷酸盐Li aMP 2O 7和M b(P 2O 7) c中的M各自独立地包括选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素，
    所述a选自0-2范围内的任意数值；
    所述b选自1-4范围内的任意数值；
    所述c选自1-6范围内的任意数值；
    所述X包括选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、 Nb和Al中的一种或多种元素；
    所述第二正极活性材料为选自LiFePO 4、碳包覆LiFePO 4、LiFe dD ePO 4和碳包覆LiFe dD ePO 4中的一种或多种，其中，所述D独立地包括选自Ti、Zn、Co、Mn、La、V、Mg、Al、Nb、W、Zr、Nb、Sm、Cr、Cu和B中的一种或多种元素，所述d独立地选自0.99至0.999的范围，并且d+e＝1。
  4. 根据权利要求1至3中任一项所述的正极极片，其中，所述第二正极活性材料中，
    碳质量占所述碳包覆LiFePO 4的质量的0.1％-4％；和/或，
    碳质量占所述碳包覆LiFe dD ePO 4的质量的0.1％-4％。
  5. 根据权利要求1至4中任一项所述的正极极片，其中，所述第一正极活性材料与所述第二正极活性材料的质量比为1:7-7:1，可选为1:4-4:1。
  6. 根据权利要求1至5中任一项所述的正极极片，其中，所述第一正极活性材料中，
    所述A选自Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，和/或，
    所述R选自B、Si、N和S中的一种元素，和/或，
    所述y与1-y的比值选自1:10至1:1，可选为1:4至1:1，和/或，
    所述z与1-z的比值选自1:9至1:999，可选为1:499至1:249。
  7. 根据权利要求1至6中任一项所述的正极极片，其中，所述第一正极活性材料中，所述第一包覆层中的晶态焦磷酸盐的晶面间距范围为0.293-0.470nm，晶向(111)的夹角范围为18.00°-32.00°；所述第二包覆层中的晶态磷酸盐的晶面间距范围为0.244-0.425nm，晶向(111)的夹角范围为20.00°-37.00°。
  8. 根据权利要求1至7中任一项所述的正极极片，其中，所述第一正极活性材料中，所述第三包覆层的碳为SP2形态碳与SP3形态碳的混合物，可选地，所述SP2形态碳与SP3形态碳的摩尔比为在0.1-10范围内的任意数值，可选为在2.0-3.0范围内的任意数值。
  9. 根据权利要求1至8中任一项所述的正极极片，其中，所述第一正极活性材料中，
    所述第一包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为大于0且小于或等于2重量％，基于所述内核的重量计；和/或
    所述第二包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为2-4重量％，基于所述内核的重量计；和/或
    所述第三包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为大于0且小于或等于2重量％，基于所述内核的重量计。
  10. 根据权利要求1至9中任一项所述的正极极片，其中，所述第一正极活性材料中，
    所述第一包覆层的厚度为1-10nm；和/或
    所述第二包覆层的厚度为2-15nm；和/或
    所述第三包覆层的厚度为2-25nm。
  11. 根据权利要求1至10中任一项所述的正极极片，其中，所述第一正极活性材料中，基于第一正极活性材料的重量计，
    锰元素含量在10重量％-35重量％范围内，可选在15重量％-30重量％范围内，更可选在17重量％-20重量％范围内；和/或，
    磷元素的含量在12重量％-25重量％范围内，可选在15重量％-20重量％范围内；和/或，
    锰元素和磷元素的重量比范围为0.90-1.25，可选为0.95-1.20。
  12. 根据权利要求1至11中任一项所述的正极极片，其中，所述第一正极活性材料在完全脱嵌锂前后的晶格变化率为4％以下，可选为3.8％以下，更可选为2.0-3.8％。
  13. 根据权利要求1至12中任一项所述的正极极片，其中，所述第一正极活性材料的Li/Mn反位缺陷浓度为4％以下，可选为2.2％以下，更可选为1.5-2.2％。
  14. 根据权利要求1至13中任一项所述的正极极片，其中，所述第一正极活性材料在3T下的压实密度为2.2g/cm 3以上，可选地为2.2g/cm 3以上且2.8g/cm 3以下。
  15. 根据权利要求1至14中任一项所述的正极极片，其中，所述第一正极活性材料的表面氧价态为-1.90以下，可选地为-1.90至-1.98。
  16. 根据权利要求1至15中任一项所述的正极极片，其中，所述第一正极活性材料和所述第二正极活性材料的质量之和占所述正极极片的质量的88％-98.7％。
  17. 一种二次电池，包括权利要求1至16中任一项所述的正极极片。
  18. 一种电池模块，包括权利要求17所述的二次电池。
  19. 一种电池包，包括权利要求18所述的电池模块。
  20. 一种用电装置，包括选自权利要求17所述的二次电池、权利要求18所述的电池模块和权利要求19所述的电池包中的至少一种。
PCT/CN2022/084292 2022-03-31 2022-03-31 新型正极极片、二次电池、电池模块、电池包及用电装置 WO2023184304A1 (zh)

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