WO2023206131A1 - 磷酸铁锂正极极片及其相关的二次电池、电池模块、电池包和用电装置 - Google Patents

磷酸铁锂正极极片及其相关的二次电池、电池模块、电池包和用电装置 Download PDF

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WO2023206131A1
WO2023206131A1 PCT/CN2022/089518 CN2022089518W WO2023206131A1 WO 2023206131 A1 WO2023206131 A1 WO 2023206131A1 CN 2022089518 W CN2022089518 W CN 2022089518W WO 2023206131 A1 WO2023206131 A1 WO 2023206131A1
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iron phosphate
lithium iron
optionally
positive electrode
battery
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PCT/CN2022/089518
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English (en)
French (fr)
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杜香龙
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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 KR1020247007293A priority Critical patent/KR20240039040A/ko
Priority to EP22938729.5A priority patent/EP4318672A1/en
Priority to CN202280035187.1A priority patent/CN117413385A/zh
Priority to PCT/CN2022/089518 priority patent/WO2023206131A1/zh
Priority to US18/382,876 priority patent/US20240047647A1/en
Publication of WO2023206131A1 publication Critical patent/WO2023206131A1/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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • H01M4/364—Composites as mixtures
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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
    • H01M4/5805—Phosphides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/20—Mountings; Secondary casings or frames; Racks, modules or packs; Suspension devices; Shock absorbers; Transport or carrying devices; Holders
    • H01M50/204—Racks, modules or packs for multiple batteries or multiple cells
    • H01M50/207—Racks, modules or packs for multiple batteries or multiple cells characterised by their shape
    • H01M50/209—Racks, modules or packs for multiple batteries or multiple cells characterised by their shape adapted for prismatic or rectangular cells
    • 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 lithium batteries, and in particular to a lithium iron phosphate cathode plate and related secondary batteries, battery modules, battery packs and electrical devices.
  • lithium-ion 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.
  • energy storage power systems such as hydraulic, thermal, wind and solar power stations
  • power tools electric bicycles, electric motorcycles, electric vehicles, Military equipment, aerospace and other fields.
  • lithium iron phosphate batteries have attracted attention due to their large capacity and good safety performance.
  • secondary batteries are more and more widely used, people have higher and higher requirements for the kinetic performance and cycle performance of lithium iron phosphate batteries. How to develop a lithium iron phosphate battery with good kinetic performance and cycle performance? Lithium iron phosphate batteries are still an urgent issue for technicians to solve.
  • This application was made in view of the above-mentioned issues, and its purpose is to provide a lithium iron phosphate positive electrode plate and its related secondary batteries, battery modules, battery packs and electrical devices, and to provide a secondary battery using the positive electrode plate.
  • the battery has good kinetic properties and cycle performance.
  • a first aspect of the application provides a lithium iron phosphate cathode plate, including a cathode current collector and a cathode active material located on the cathode current collector, wherein the cathode active material includes
  • the first lithium iron phosphate particles have a volume average particle size D50 of 60-300nm, optionally 60-200nm, and a specific surface area greater than 15m 2 /g, optionally 15-25m 2 /g; and
  • the volume average particle diameter D50 is greater than 800nm, and can be selected from 1000-1500nm.
  • the specific surface area is less than 10m 2 /g, and the second lithium iron phosphate particle can be selected from 5-10m 2 /g.
  • the positive electrode sheet described in the first aspect of the application includes two types of lithium iron phosphate particles with different particle sizes and specific surface areas, which can give full play to their respective advantages and improve the dynamic performance and performance of secondary batteries using the positive electrode sheet. Cycle performance.
  • the content of the first lithium iron phosphate particles is 1-97%, optionally 18-68%, and more optionally 36-68%, based on the lithium iron phosphate cathode
  • the content of the second lithium iron phosphate particles is 3-99%, optionally 32-82%, and more optionally 32-64%, based on the total weight of the positive electrode film layer in the lithium iron phosphate positive electrode sheet. .
  • the secondary battery made from the positive electrode sheet described in the first aspect of the present application has good kinetic performance and cycle performance.
  • the weight ratio of the first lithium iron phosphate particles to the second lithium iron phosphate particles is 1:0.1- 9, optional 1:0.4-4, more optional 1:0.4-1.5.
  • the kinetic performance and cycle performance of the corresponding battery can be further improved.
  • the carbon content in the first lithium iron phosphate particles is 1.2-2.7%, optionally 1.4-2.2%, more optionally 1.4-2.0%, based on the first Total weight of lithium iron phosphate particles;
  • the carbon content in the second lithium iron phosphate particles is 0.7-1.3%, optionally 1-1.2%, more optionally 1.1-1.2%, based on the total weight of the second lithium iron phosphate particles.
  • the compacted density of the positive electrode film layer in the lithium iron phosphate positive electrode sheet is 2-2.45g/cm 3 , optionally 2.1-2.3g/cm 3 , more optionally 2.15-2.25g/cm 3 .
  • the first lithium iron phosphate particles and the second lithium iron phosphate particles are distributed in layers.
  • the second lithium iron phosphate particle layer is located on the surface of the cathode current collector, and the first lithium iron phosphate particle layer is located between the second lithium iron phosphate particle layer and the cathode current collector. relatively superficially.
  • the first lithium iron phosphate particle layer is located above the second lithium iron phosphate particle layer. , the kinetic performance and cycle performance of the corresponding secondary battery can be further improved.
  • the thickness of the first lithium iron phosphate particle layer is 65-250 ⁇ m, optionally 80-140 ⁇ m, and more optionally 100-140 ⁇ m;
  • the thickness of the second lithium iron phosphate particle layer is 60-250 ⁇ m, optionally 60-120 ⁇ m, and more optionally 60-100 ⁇ m.
  • each lithium iron phosphate particle layer When the thickness of each lithium iron phosphate particle layer is within the above range, on the one hand, it helps to improve the cycle performance of the secondary battery, and on the other hand, it can also prevent the thickness of each layer from being too large and damaging the dynamic performance of the secondary battery.
  • the thickness ratio of the first lithium iron phosphate particle layer and the second lithium iron phosphate particle layer is 1:0.1-9, optionally 1:0.4-1.5, or more The optional value is 1:0.4-1.
  • the thickness ratio of the first lithium iron phosphate particle layer and the second lithium iron phosphate particle layer is within the above range, it is helpful to further improve the kinetic performance and cycle performance of the corresponding secondary battery.
  • the area density of the first lithium iron phosphate particle layer is 0.1-0.3g/1540.25mm 2 , optionally 0.15-0.25g/1540.25mm 2 , more optionally 0.15-0.25g/1540.25mm 2 . 0.2g/1540.25mm 2 ;
  • the surface density of the second lithium iron phosphate particle layer is 0.1-0.3g/1540.25mm 2 , optionally 0.15-0.25g/1540.25mm 2 , more optionally 0.15-0.2g/1540.25mm 2 .
  • a second aspect of the application provides a secondary battery, including the lithium iron phosphate positive electrode sheet of the first aspect of the application.
  • the secondary battery can be produced by a method commonly used in the art.
  • a third aspect of the present application provides a battery module including the secondary battery of the second aspect of the present application.
  • the battery module can be prepared by methods commonly used in the art.
  • a fourth aspect of the application provides a battery pack, including the battery module of the third aspect of the application.
  • the battery pack can be prepared by methods commonly used in the art.
  • a fifth aspect of the present application provides an electrical device, including at least one selected from the secondary battery of the second aspect of the present application, the battery module of the third aspect of the present application, or the battery pack of the fourth aspect of the present application. kind.
  • the electrical device can be prepared by methods commonly used in the art.
  • the lithium iron phosphate positive electrode sheet of the present application includes first lithium iron phosphate particles with a volume average particle diameter D50 of 60-300 nm and a specific surface area greater than 15 m 2 /g, and first lithium iron phosphate particles with a volume average particle diameter D50 greater than 800 nm and a specific surface area less than 10 m 2 2 /g of the second lithium iron phosphate particles.
  • this helps to give full play to the respective advantages of the first lithium iron phosphate particles and the second lithium iron phosphate particles, thereby improving the performance of the secondary battery including the positive electrode sheet. Dynamic performance and cycle performance.
  • this application distinguishes lithium iron phosphate particles by specific surface area, which can avoid the problem that the first lithium iron phosphate particles are easy to agglomerate when distinguishing lithium iron phosphate particles only by particle size.
  • the particle size parameter fails.
  • the battery modules, battery packs and electrical devices of the present application include the secondary battery provided by the present application, and thus have at least the same advantages as the secondary battery.
  • Figure 1 is a scanning electron microscope image of the first lithium iron phosphate particle of the present application. It can be seen from Figure 1 that the single particle size of the first lithium iron phosphate particle is small, and a large number of single particles are agglomerated together.
  • Figure 2 is a scanning electron microscope image of the second lithium iron phosphate particle of the present application. It can be seen from Figure 2 that the particle size of the second lithium iron phosphate particles is relatively large and is not easy to agglomerate together.
  • FIG 3 shows the DC internal resistance (DCR) of the secondary battery corresponding to Embodiment 1 of the present application at different temperatures.
  • the DCR of the secondary battery corresponding to Example 1 is 18.26 m ⁇ at -25°C
  • the DCR at -10°C is 10.45m ⁇
  • the DCR at 25°C is 1.72m ⁇ .
  • Figure 4 shows the DC internal resistance (DCR) of the secondary battery corresponding to Comparative Example 1 of the present application at different temperatures.
  • the DCR of the secondary battery corresponding to Comparative Example 1 is 24.81m ⁇ at -25°C, 13.91m ⁇ at -10°C, and 3.14m ⁇ at 25°C.
  • Figure 5 shows the DC internal resistance (DCR) of the secondary battery corresponding to Comparative Example 2 of the present application at different temperatures.
  • FIG. 6 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG. 7 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 6 .
  • Figure 8 is a schematic diagram of a battery module according to an embodiment of the present application.
  • Figure 9 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 10 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 9 .
  • FIG. 11 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.
  • 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
  • the 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) may be added to the method in any order.
  • the method may include steps (a), (b) and (c). , may also include steps (a), (c) and (b), 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).
  • distinguishing lithium iron phosphate particles by particle size and specific surface area at the same time can avoid the failure of the particle size parameter due to the easy agglomeration of the first lithium iron phosphate particles when distinguishing lithium iron phosphate particles only by particle size. Condition.
  • the inventor further studied and found that by changing the carbon content of the first lithium iron phosphate particles and the second lithium iron phosphate particles, regulating the dosage ratio of each lithium iron phosphate particle, and further coating different lithium iron phosphate particles in layers and regulating each The layer thickness can further improve the kinetic performance and cycle performance of the corresponding secondary battery.
  • a first aspect of the present application provides a lithium iron phosphate cathode plate, including a cathode current collector and a cathode active material located on the cathode current collector, wherein the cathode active material includes:
  • the first lithium iron phosphate particles have a volume average particle size D50 of 60-300nm, optionally 60-200nm, and a specific surface area greater than 15m 2 /g, optionally 15-25m 2 /g; and
  • the volume average particle diameter D50 is greater than 800nm, and can be selected from 1000-1500nm.
  • the specific surface area is less than 10m 2 /g, and the second lithium iron phosphate particle can be selected from 5-10m 2 /g.
  • the positive electrode sheet described in this application includes first lithium iron phosphate particles and second lithium iron phosphate particles, which can give full play to the small DC internal resistance and good dynamic performance of the first lithium iron phosphate particles and the large compaction of the second lithium iron phosphate particles. , the advantage of not easily causing gel, effectively improving the kinetic performance and cycle performance of the corresponding secondary battery.
  • this application distinguishes lithium iron phosphate particles by specific surface area, which can avoid the failure of the particle size parameter due to the easy agglomeration of the first lithium iron phosphate particles when distinguishing lithium iron phosphate particles only by particle size.
  • the positive electrode sheet of the present application includes a positive electrode current collector and a positive electrode active material, wherein the positive electrode current collector has two surfaces opposite in its own thickness direction, and the positive electrode active material is disposed on any of the two opposite surfaces of the positive electrode current collector. Either or both.
  • the volume average particle size D50 and specific surface area can be measured by methods commonly used in this field.
  • the D50 particle size can be measured according to GB/T 19077-2016/ISO 13320:2009, and the D50 particle size can be measured according to GB/T 19587-2004 " Gas adsorption BET method determines the specific surface area of solid materials ⁇ Measure the specific surface area.
  • the content of the first lithium iron phosphate particles is 1-97%, optionally 18-68%, and more optionally 36-68%, based on the lithium iron phosphate cathode The total weight of the positive electrode film layer in the pole piece;
  • the content of the second lithium iron phosphate particles is 3-99%, optionally 32-82%, and more optionally 32-64%, based on the total weight of the positive electrode film layer in the lithium iron phosphate positive electrode sheet. .
  • the amount of the first lithium iron phosphate particles can be 19.4%, 38.8%, 48.5%, 58.2%, 64.7% or 67.9%; the amount of the second lithium iron phosphate particles can be 29.1%, 32.3%, 38.8 %, 48.5%, 58.2% or 77.6%.
  • the amount of the first lithium iron phosphate particles is too much, more first lithium iron phosphate particles may agglomerate, which is not conducive to mass production and improvement of energy density.
  • the content of the second lithium iron phosphate particles is too much, the dynamic performance of the battery may be deteriorated and the battery life may be shortened.
  • the contents of both lithium iron phosphate particles are within the above range, the corresponding secondary battery has lower DC internal resistance and longer life.
  • the weight ratio of the first lithium iron phosphate particles to the second lithium iron phosphate particles is 1:0.1- 9, optional 1:0.4-4, more optional 1:0.4-1.5.
  • the weight ratio of the first lithium iron phosphate particles to the second lithium iron phosphate particles may be 1:4, 2:3, 1:1, 3:2, 2:1 or 7:3.
  • the kinetic performance and cycle performance of the corresponding battery can be further improved.
  • the carbon content in the first lithium iron phosphate particles is 1.2-2.7%, optionally 1.4-2.2%, more optionally 1.4-2.0%, based on the first Total weight of lithium iron phosphate particles;
  • the carbon content in the second lithium iron phosphate particles is 0.7-1.3%, optionally 1-1.2%, more optionally 1.1-1.2%, based on the total weight of the second lithium iron phosphate particles.
  • the carbon content in the lithium iron phosphate particles can be measured by methods commonly used in this field. For example, it can be tested by infrared absorption method. Specifically, the sample to be tested is burned in an oxygen flow to generate CO 2 . Since under a certain pressure, the energy of CO 2 absorbing infrared rays is proportional to its concentration, the carbon content can be calculated based on the measured energy change of CO 2 gas before and after it flows through the infrared absorber.
  • the tap density of the first lithium iron phosphate particles is 1-1.4g cm -3 , optionally 1.1-1.3g cm -3 , and more optionally 1.15-1.25 g cm -3 .
  • the tap density of the second lithium iron phosphate particle powder is 1.2-1.6g cm -3 , optionally 1.3-1.5g cm -3 , more optionally 1.35-1.45 g cm -3 .
  • the tap density of lithium iron phosphate particles can be measured by methods commonly used by those skilled in the art, for example, it can be measured according to GB/T 5162-2006/ISO3953:1993.
  • the compacted density of the first lithium iron phosphate particle powder is 2-2.2g/cm 3 .
  • the second lithium iron phosphate particle powder has a compacted density of 2-2.45g/cm 3 .
  • compacted density can be measured by methods commonly used by those skilled in the art.
  • the compacted density of the positive electrode film layer in the lithium iron phosphate positive electrode sheet is 2-2.45g/cm 3 , optionally 2.1-2.3g/cm 3 , more optionally 2.15-2.25g/cm 3 .
  • the compacted density of the positive electrode film layer can be measured by methods commonly used in this field. As an example, you can first take the positive electrode sheet per unit area and weigh its mass m1, then weigh the mass m2 of the positive electrode foil per unit area, then subtract m2 from m1 to get the mass of the positive electrode film layer, and then divide by The thickness of the positive electrode film (thickness of the electrode minus the thickness of the foil) can be used to obtain the compacted density of the positive electrode film.
  • the first lithium iron phosphate particles and the second lithium iron phosphate particles are distributed in layers.
  • the second lithium iron phosphate particle layer is located on the surface of the cathode current collector, and the first lithium iron phosphate particle layer is located between the second lithium iron phosphate particle layer and the cathode current collector. relatively superficially.
  • the spatial structure design at the pole piece level also has a significant impact on the performance of lithium secondary batteries, especially for pole piece designs containing two or more active materials.
  • the performance of the battery can be further improved through the spatial structure design of the pole pieces.
  • two kinds of lithium iron phosphate particles are coated in layers, especially the second lithium iron phosphate particle is coated on the surface of the positive electrode current collector, and the first lithium iron phosphate particle is coated on the second
  • the respective advantages of the two lithium iron phosphate particles can be more effectively utilized to improve the kinetic performance and cycle performance of the secondary battery.
  • the thickness of the first lithium iron phosphate particle layer is 65-250 ⁇ m, optionally 80-140 ⁇ m, and more optionally 100-140 ⁇ m;
  • the thickness of the second lithium iron phosphate particle layer is 60-250 ⁇ m, optionally 60-120 ⁇ m, and more optionally 60-100 ⁇ m.
  • the thickness of the first lithium iron phosphate particle layer may be, for example, 80 nm, 100 nm, 120 nm or 140 nm
  • the thickness of the second lithium iron phosphate particle layer may be, for example, 60 nm, 80 nm, 100 nm or 120 nm.
  • the thickness of the first lithium iron phosphate particle layer and the second lithium iron phosphate particle layer can be measured by methods commonly used in the art.
  • the thickness of the positive electrode film layer can be measured first, and then determined based on the dosage ratio of the first lithium iron phosphate particles and the second lithium iron phosphate particles.
  • the thickness of the lithium iron phosphate particle layer is too large, the dynamic performance of the battery may be deteriorated; on the contrary, if the thickness of the lithium iron phosphate particle layer is too small, the advantages of the double-layer coating may not be fully utilized and the battery performance cannot be further improved.
  • the thickness ratio of the first lithium iron phosphate particle layer to the second lithium iron phosphate particle layer is 1:0.1-9, optionally 1:0.4-1.5, or more.
  • the optional value is 1:0.4-1.
  • the thickness ratio of the first lithium iron phosphate particle layer to the second lithium iron phosphate particle layer is 2:3, 1:1, 3:2 or 7:3.
  • the thickness ratio of the first lithium iron phosphate particle layer and the second lithium iron phosphate particle layer is within the above range, it is helpful to further improve the kinetic performance and cycle performance of the corresponding secondary battery.
  • the area density of the first lithium iron phosphate particle layer is 0.1-0.3g/1540.25mm 2 , optionally 0.15-0.25g/1540.25mm 2 , more optionally 0.15-0.25g/1540.25mm 2 . 0.2g/1540.25mm 2 ;
  • the surface density of the second lithium iron phosphate particle layer is 0.1-0.3g/1540.25mm 2 , optionally 0.15-0.25g/1540.25mm 2 , more optionally 0.15-0.2g/1540.25mm 2 .
  • Coating methods commonly used in this field can be adopted, such as blade coating, roller coating, slit extrusion coating, etc.
  • 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.
  • Composite current collectors 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 lithium iron phosphate positive electrode sheet further includes a binder.
  • the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of fluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PTFE polytetrafluoroethylene
  • VDF polytetrafluoroethylene
  • PTFE polytetrafluoroethylene
  • vinylidene fluoride-tetrafluoroethylene-propylene terpolymer vinylidene fluoride-hexafluoropropylene-
  • the binder accounts for 0.1-3.5%, optionally 0.5-2.5%, of the total weight of the positive electrode film layer.
  • the lithium iron phosphate positive electrode sheet 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 conductive agent accounts for 0.05-2.0%, optionally 0.1-1.5%, of the total weight of the positive electrode film layer.
  • the lithium iron phosphate positive electrode sheet also includes other additives, such as surfactants, wetting agents, rheology modifiers, etc.
  • the additive may be selected from the group consisting of higher fatty acid salts, higher alkyl sulfonates, alkylaryl sulfonates, alkali metals such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, etc. Salts such as lithium salt, perfluoroalkylsulfonimide salt, one or more of methyl octanoate, n-butyl pivalate or lauryl acetate.
  • the other additives account for 0.05-2.0%, optionally 0.1-1.5%, of the total weight of the positive electrode film layer.
  • the positive electrode sheet can be prepared in the following manner: using the above-mentioned components for preparing the positive electrode sheet, such as first lithium iron phosphate particles and second lithium iron phosphate particles, a conductive agent, a binder and any Other components such as surfactants are dispersed in solvents (such as N-methylpyrrolidone) to form positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, it can be Get the positive electrode piece.
  • solvents such as N-methylpyrrolidone
  • the cathode slurry of the first lithium iron phosphate particles and the cathode slurry of the second lithium iron phosphate particles may be prepared separately, and the cathode slurry of the second lithium iron phosphate particles may be coated on On the side close to the current collector, the positive electrode slurry of the first lithium iron phosphate particles is coated on the surface of the second lithium iron phosphate particle layer on the side away from the current collector.
  • the mixture is stirred until the viscosity is 7000-15000 mPa.s, and then shipped immediately.
  • a second aspect of the application provides a secondary battery, which includes the lithium iron phosphate positive electrode sheet described in the first aspect of the application.
  • the secondary battery can be prepared by methods commonly used in the art. For example, the positive electrode sheet, the negative electrode sheet and the separator can be rolled into an electrode assembly according to a certain process, and then the electrolyte is injected into the resulting electrode assembly, and the secondary battery described in this application can be prepared through sealing and other processes.
  • a secondary battery typically includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator.
  • active ions are inserted and detached back and forth between the positive and negative electrodes.
  • the electrolyte plays a role in conducting ions between the positive and negative electrodes.
  • 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 ions to pass through.
  • 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, where 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 can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polysodium acrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), poly At least one of methacrylic 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 also includes other auxiliaries, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.
  • auxiliaries such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.
  • 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 an electrolyte solution.
  • the electrolyte solution includes electrolyte salts and solvents.
  • 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 further 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 selected.
  • 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.
  • a third aspect of the present application provides a battery module, including the secondary battery described in the second aspect of the present application.
  • a fourth aspect of the application provides a battery pack, including the battery module described in the third aspect of the application.
  • a fifth aspect of the present application provides an electrical device, including at least one of the secondary battery of the second aspect of the present application, the battery module of the third aspect, or the battery pack of the fourth aspect of the present application.
  • the secondary battery, battery module, or battery pack may be used as a power source for the electrical device, or may be used as an energy storage unit for the electrical device.
  • the electric device 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, and electric golf carts). , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.
  • a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.
  • 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. 6 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. 8 shows the 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.
  • FIG 11 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.
  • the device may be a mobile phone, a tablet, a laptop, etc.
  • the device is usually required to be thin and light, and a secondary battery can be used as a power source.
  • the first lithium iron phosphate particles (D50 is 300nm, BET is 15.8m 2 /g, and the carbon content is 1.4%), and the second lithium iron phosphate particles (D50 is 1000nm, BET is 10m 2 /g, and the carbon content is 1.2%).
  • PVDF polyvinylidene fluoride
  • conductive agent acetylene black were added to the stirring tank at a weight ratio of 48.5%:48.5%:2.2:0.8 for mixing. Stir for 15 minutes at a revolution speed of 25 rpm and a rotation speed of 800 rpm.
  • the solvent N-methylpyrrolidone (NMP) was then added to the above dry mixture at a solid content of 60%.
  • the mixture was stirred at a revolution speed of 25 rpm and a rotation speed of 300 rpm for 15 minutes. Then adjust the revolution speed to 25 rpm, the rotation speed to 1200 rpm, and stir for 220 min to make the mixture evenly dispersed. Then continue stirring at a revolution speed of 25 rpm and a rotation speed of 500 rpm, adjust the viscosity of the mixture to 10000 mPa.s, and then ship it immediately to obtain a mixed slurry.
  • the above mixed slurry is coated on an aluminum foil with a thickness of 13 ⁇ m according to an area density of 0.3g/ 1540.25mm2 , and is coated on both sides. After that, the solvent is removed by drying and cooling, so that the compacted density of the positive electrode film layer is 2.2g/cm 3 . After cutting, the positive electrode sheet of Example 1 was obtained.
  • SBR binder styrene-butadiene rubber
  • CMC-Na thickener sodium carboxymethylcellulose
  • a commercially available PP-PE copolymer microporous film with a thickness of 16 ⁇ m and an average pore diameter of 80 nm was used.
  • the positive electrode piece, isolation film, and negative electrode piece in order so that the isolation film is in the middle of the positive and negative electrode pieces for isolation, and wind it to obtain a cylindrical bare body with a height of 146mm and a diameter of 44.8mm on the upper and lower surfaces.
  • Batteries. The distance between the positive electrode piece and the negative electrode piece is 16 ⁇ m, and the distance between the isolation film and the positive electrode piece and the negative electrode piece is about 0 ⁇ m.
  • the bare battery core is placed in the outer package, 100g of the above electrolyte is injected and packaged to obtain a secondary battery.
  • Example 1 Except for the particle size, specific surface area, carbon content, and dosage of the first lithium iron phosphate particles and the second lithium iron phosphate particles used, other conditions are the same as in Example 1. The specific conditions are detailed in Table 1. .
  • Embodiment 12 The other conditions of Embodiment 12 are the same as those of Embodiment 1, except that the weight of the first lithium iron phosphate particles: polyvinylidene fluoride (PVDF) and the conductive agent acetylene black is 97:2.2:0.8. The ratio is added to the mixing tank. After the slurry is prepared, it is coated on an aluminum foil with a thickness of 13 ⁇ m according to an area density of 0.3g/ 1540.25mm2 to form the first active material layer; then the second lithium iron phosphate particles are coated according to the second layer.
  • PVDF polyvinylidene fluoride
  • acetylene black 97:2.2:0.8.
  • the ratio is added to the mixing tank. After the slurry is prepared, it is coated on an aluminum foil with a thickness of 13 ⁇ m according to an area density of 0.3g/ 1540.25mm2 to form the first active material layer; then the second lithium iron phosphate particles are coated according to the second layer.
  • Lithium iron diphosphate particles polyvinylidene fluoride (PVDF) and conductive agent acetylene black are added into the mixing tank at a weight ratio of 97:2.2:0.8. After the slurry is prepared, the slurry is coated with an area density of 0.3g/ 1540.25mm2 Distributed on the upper surface of the first active material layer.
  • PVDF polyvinylidene fluoride
  • conductive agent acetylene black are added into the mixing tank at a weight ratio of 97:2.2:0.8. After the slurry is prepared, the slurry is coated with an area density of 0.3g/ 1540.25mm2 Distributed on the upper surface of the first active material layer.
  • the usage amounts of the first lithium iron phosphate particles and the second lithium iron phosphate particles are the same as in Example 1, that is, the total amount of the upper and lower layers is the same as in Example 1.
  • the thickness of the first lithium iron phosphate particle layer on the obtained positive electrode sheet was 100 ⁇ m, and the thickness of the second lithium iron phosphate particle layer was 100 ⁇ m.
  • Example 13 12 Except that the second lithium iron phosphate particles are coated on the surface of the aluminum foil as the first active material layer, and the first lithium iron phosphate particle layer is coated on the top of the second lithium iron phosphate particle layer, other conditions and examples of Example 13 12 same.
  • Example 14-16 Except for changing the amount of lithium iron phosphate particles used so that the corresponding thicknesses of the first lithium iron phosphate particle layer/the second lithium iron phosphate particle layer are 80 ⁇ m/120 ⁇ m, 120 ⁇ m/80 ⁇ m, and 140 ⁇ m/60 ⁇ m respectively, other aspects of Examples 14-16 The conditions are the same as those in Example 13, and the specific conditions are shown in Table 1.
  • Comparative Example 4 Other conditions of Comparative Example 4 were the same as Example 13 except that the thicknesses of the first lithium iron phosphate particle layer/the second lithium iron phosphate particle layer were 16 ⁇ m/184 ⁇ m respectively.
  • Reference standard GB/T 19077-2016/ISO 13320:2009 particle size distribution laser diffraction method Use a laser particle size analyzer (Malvern 3000, MasterSizer 3000) to test, and use a helium-neon red light source as the main light source. Take a clean small beaker, add 1g of the sample to be tested, add 20ml of deionized water (sample concentration ensures opacity of 8-12%), add a drop of surfactant to reduce the surface tension of the water to facilitate the infiltration of the particles, and set the frequency to 53KHz /120W ultrasonic for 5 minutes to ensure that the sample is completely dispersed. Turn on the laser particle size analyzer, clean the optical system, and automatically test the background. Stir the ultrasonicated solution to be tested to make it disperse evenly, put it into the sample pool as required, and start measuring the particle size. The measurement results can be read from the instrument.
  • a laser particle size analyzer Malvern 3000, MasterSizer 3
  • test method refers to the standard GB/T19587-2004 "Determination of specific surface area of solid materials by gas adsorption BET method".
  • the secondary batteries prepared in the Examples and Comparative Examples were charged with a constant current of 1C (i.e., the current value that completely discharges the theoretical capacity within 1 hour) to 3.65V, and then charged with a constant voltage of 3.65V until the current was 0.05 C, let it sit for 5 minutes, then discharge it to 2.5V at a constant current of 1C, and let it stand for 30 minutes.
  • This is a charge and discharge cycle process. Record the battery capacity C0 at this time.
  • the battery is charged and discharged n times, and the battery capacity after n cycles is recorded as C1.
  • the cycle capacity retention rate of the battery at 25°C C1/C0 ⁇ 100%. Record the number of cycles n corresponding to the measured battery cycle capacity retention rate of 80%.
  • the secondary batteries prepared in Examples 1-16 of the present application have smaller DCR and better cycle performance than the batteries of Comparative Examples 1-4.
  • the dosage and spatial distribution of the first lithium iron phosphate particles and the second lithium iron phosphate particles can be further improved.

Abstract

提供了一种磷酸铁锂正极极片，包括正极集流体和位于正极集流体上的正极活性材料，其中正极活性材料包括：体积平均粒径D50为60-300nm、可选为60-200nm，比表面积大于15m 2/g、可选为15-25m 2/g的第一磷酸铁锂颗粒；和体积平均粒径D50大于800nm、可选为1000-1500nm，比表面积小于10m 2/g、可选为5-10m 2/g的第二磷酸铁锂颗粒。应用磷酸铁锂正极极片制得的二次电池具备良好的动力学性能和循环性能。

Description

磷酸铁锂正极极片及其相关的二次电池、电池模块、电池包和用电装置 技术领域
本申请涉及锂电池技术领域，尤其涉及一种磷酸铁锂正极极片及其相关的二次电池、电池模块、电池包和用电装置。
背景技术
近年来，随着锂离子电池的应用范围越来越广泛，锂离子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。在众多电池类型中，磷酸铁锂电池由于容量大和良好的安全性能而受到人们的关注。然而，随着二次电池的应用越来越广泛，人们对磷酸铁锂电池的动力学性能和循环性能的要求也越来越高，如何开发出一款具备良好的动力学性能和循环性能的磷酸铁锂电池仍然是技术人员亟需解决的课题。
发明内容
本申请是鉴于上述课题而进行的，其目的在于，提供一种磷酸铁锂正极极片及其相关的二次电池、电池模块、电池包和用电装置，应用所述正极极片的二次电池具备良好的动力学性能和循环性能。
本申请的第一方面提供了一种磷酸铁锂正极极片，包括正极集流体和位于所述正极集流体上的正极活性材料，其中所述正极活性材料包括
体积平均粒径D50为60-300nm、可选为60-200nm，比表面积大于15m 2/g、可选为15-25m 2/g的第一磷酸铁锂颗粒；和
体积平均粒径D50大于800nm、可选为1000-1500nm，比表面积小于10m 2/g、可选为5-10m 2/g的第二磷酸铁锂颗粒。
本申请第一方面所述的正极极片包括两种不同粒径、比表面积的磷酸铁锂颗粒，可充分发挥其各自的优势，改善应用所述正极极片的二次电池的动力学性能和循环性能。
在任意实施方式中，可选地，所述第一磷酸铁锂颗粒的含量为1-97％、可选为18-68％、更可选为36-68％，基于所述磷酸铁锂正极极片中正极膜层的总重量计；
所述第二磷酸铁锂颗粒的含量为3-99％、可选为32-82％、更可选为32-64％，基于所述磷酸铁锂正极极片中正极膜层的总重量计。
当两种磷酸铁锂颗粒的用量均在上述范围内时，由本申请第一方面所述正极极片制得的二次电池具备良好的动力学性能和循环性能。
在任意实施方式中，可选地，在所述磷酸铁锂正极极片的活性物质层中，所述第一磷酸铁锂颗粒与所述第二磷酸铁锂颗粒的重量比为1∶0.1-9，可选为1∶0.4-4，更可选为1∶0.4-1.5。
通过调整第一磷酸铁锂颗粒和第二磷酸铁锂颗粒的用量比，可进一步改善相应电池的动力学性能和循环性能。
在任意实施方式中，可选地，所述第一磷酸铁锂颗粒中的碳含量为1.2-2.7％，可选为1.4-2.2％，更可选为1.4-2.0％，基于所述第一磷酸铁锂颗粒的总重量计；
所述第二磷酸铁锂颗粒中的碳含量为0.7-1.3％，可选为1-1.2％更可选为1.1-1.2％，基于所述第二磷酸铁锂颗粒的总重量计。
当两种磷酸铁锂颗粒的碳含量均在上述范围内时，可进一步改善相应二次电池的性能。
在任意实施方式中，可选地，所述磷酸铁锂正极极片中正极膜层的压实密度为2-2.45g/cm 3、可选为2.1-2.3g/cm 3、更可选为2.15-2.25g/cm 3。
在任意实施方式中，可选地，在所述磷酸铁锂正极极片中的活性物质层中，所述第一磷酸铁锂颗粒和所述第二磷酸铁锂颗粒分层分布。
在任意实施方式中，可选地，所述第二磷酸铁锂颗粒层位于正极集流体的表面上，所述第一磷酸铁锂颗粒层位于所述第二磷酸铁锂颗 粒层与正极集流体相对的表面上。
通过调控第一磷酸铁锂颗粒层和第二磷酸铁锂层的分布，尤其是当第二磷酸铁锂颗粒层位于集流体表面，第一磷酸铁锂颗粒层位于第二磷酸铁锂颗粒层上部时，可进一步改善对应二次电池的动力学性能和循环性能。
在任意实施方式中，可选地，所述第一磷酸铁锂颗粒层的厚度为65-250μm、可选为80-140μm、更可选为100-140μm；
所述第二磷酸铁锂颗粒层的厚度为60-250μm、可选为60-120μm、更可选为60-100μm。
当各磷酸铁锂颗粒层的厚度在上述范围内时，一方面有助于提升二次电池的循环性能，另一方面也可避免各层厚度过大而有损二次电池的动力学性能。
在任意实施方式中，可选地，所述第一磷酸铁锂颗粒层与所述第二磷酸铁锂颗粒层的厚度之比为1∶0.1-9、可选为1∶0.4-1.5、更可选为1∶0.4-1。
当第一磷酸铁锂颗粒层和第二磷酸铁锂颗粒层的厚度之比在上述范围内时，有助于进一步改善对应二次电池的动力学性能和循环性能。
在任意实施方式中，可选地，所述第一磷酸铁锂颗粒层的面密度为0.1-0.3g/1540.25mm 2，可选为0.15-0.25g/1540.25mm 2，更可选为0.15-0.2g/1540.25mm 2；
所述第二磷酸铁锂颗粒层的面密度为0.1-0.3g/1540.25mm 2，可选为0.15-0.25g/1540.25mm 2，更可选为0.15-0.2g/1540.25mm 2。
本申请的第二方面提供一种二次电池，包括本申请第一方面的磷酸铁锂正极极片。二次电池可通过本领域通常使用的方法进行制备。
本申请的第三方面提供一种电池模块，包括本申请的第二方面的二次电池。电池模块可通过本领域通常使用的方法进行制备。
本申请的第四方面提供一种电池包，包括本申请的第三方面的电池模块。电池包可通过本领域通常使用的方法进行制备。
本申请的第五方面提供一种用电装置，包括选自本申请的第二方面的二次电池、本申请的第三方面的电池模块或本申请的第四方面的电池包中的至少一种。用电装置可通过本领域通常使用的方法进行制备。
[有益效果]
在本申请的磷酸铁锂正极极片中，包括体积平均粒径D50为60-300nm、比表面积大于15m 2/g的第一磷酸铁锂颗粒和体积平均粒径D50大于800nm、比表面积小于10m 2/g的第二磷酸铁锂颗粒，一方面，这有助于充分发挥第一磷酸铁锂颗粒和第二磷酸铁锂颗粒各自的优势，从而改善包括所述正极极片的二次电池的动力学性能和循环性能，另一方面，本申请通过比表面积对磷酸铁锂颗粒进行区分，可避免仅通过粒径对磷酸铁锂颗粒进行区分时，由于第一磷酸铁锂颗粒容易团聚而导致粒径这一参数失灵的情况。
本申请的电池模块、电池包和用电装置包括本申请提供的二次电池，因而至少具有与所述二次电池相同的优势。
附图说明
图1是本申请第一磷酸铁锂颗粒的扫描电镜图。从图1中可以看出，第一磷酸铁锂颗粒的单颗粒粒径较小，并且大量的单颗粒团聚在了一起。
图2是本申请第二磷酸铁锂颗粒的扫描电镜图。从图2中可以看出，第二磷酸铁锂颗粒的粒径比较大，不容易团聚在一起。
图3是本申请实施例1对应的二次电池在不同温度下的直流内阻(DCR)。从图3中可以看出，实施例1对应的二次电池在-25℃下的DCR为18.26mΩ，在-10℃下的DCR为10.45mΩ，在25℃下的DCR为1.72mΩ。
图4是本申请对比例1对应的二次电池在不同温度下的直流内阻(DCR)。从图4中可以看出，对比例1对应的二次电池在-25℃下的DCR为24.81mΩ，在-10℃下的DCR为13.91mΩ，在25℃下的DCR为3.14mΩ。
图5是本申请对比例2对应的二次电池在不同温度下的直流内阻(DCR)。
图6是本申请一实施方式的二次电池的示意图。
图7是图6所示的本申请一实施方式的二次电池的分解图。
图8是本申请一实施方式的电池模块的示意图。
图9是本申请一实施方式的电池包的示意图。
图10是图9所示的本申请一实施方式的电池包的分解图。
图11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。
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磷酸铁锂正极极片及其制造方法、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，所述方法包括步骤(a)和(b)，表示所述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，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(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，所述“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，本申请所提到的“以上”、“以下”包含本数。
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)。
发明人在实际工作中意外发现，通过将不同粒径的磷酸铁锂颗粒结合使用，可有效改善对应二次电池的动力学性能和循环性能。此外，同时通过粒径和比表面积对磷酸铁锂颗粒进行区分，可避免仅通过粒 径对磷酸铁锂颗粒进行区分时，由于第一磷酸铁锂颗粒容易团聚而导致粒径这一参数失灵的情况。
发明人进一步研究发现，通过改变第一磷酸铁锂颗粒和第二磷酸铁锂颗粒的碳含量、调控各磷酸铁锂颗粒的用量比，并进一步将不同磷酸铁锂颗粒分层涂布且调控各层厚度，可进一步改善对应二次电池的动力学性能和循环性能。
[正极极片]
本申请的第一方面提供一种磷酸铁锂正极极片，包括正极集流体和位于所述正极集流体上的正极活性材料，其中所述正极活性材料包括：
体积平均粒径D50为60-300nm、可选为60-200nm，比表面积大于15m 2/g、可选为15-25m 2/g的第一磷酸铁锂颗粒；和
体积平均粒径D50大于800nm、可选为1000-1500nm，比表面积小于10m 2/g、可选为5-10m 2/g的第二磷酸铁锂颗粒。
本申请所述正极极片包括第一磷酸铁锂颗粒和第二磷酸铁锂颗粒，可充分发挥第一磷酸铁锂颗粒直流内阻小、动力学性能良好以及第二磷酸铁锂颗粒压密大、不易出现凝胶的优势，有效改善对应二次电池的动力学性能和循环性能。此外，本申请通过比表面积对磷酸铁锂颗粒进行区分，可避免仅通过粒径对磷酸铁锂颗粒进行区分时，由于第一磷酸铁锂颗粒容易团聚而导致粒径这一参数失灵的情况。
作为示例，本申请的正极极片包括正极集流体和正极活性材料，其中正极集流体具有在其自身厚度方向相对的两个表面，正极活性物质设置在正极集流体相对的两个表面的其中任意一者或两者上。
在本申请中，体积平均粒径D50和比表面积可以通过本领域通常使用的方法进行测量，例如可根据GB/T 19077-2016/ISO 13320：2009测量D50粒径，根据GB/T19587-2004《气体吸附BET法测定固态物质比表面积》测量比表面积。
在一些实施方式中，可选地，所述第一磷酸铁锂颗粒的含量为 1-97％、可选为18-68％、更可选为36-68％，基于所述磷酸铁锂正极极片中正极膜层的总重量计；
所述第二磷酸铁锂颗粒的含量为3-99％、可选为32-82％、更可选为32-64％，基于所述磷酸铁锂正极极片中正极膜层的总重量计。
作为示例，第一磷酸铁锂颗粒的用量可为19.4％、38.8％、48.5％、58.2％、64.7％或67.9％；所述第二磷酸铁锂颗粒的用量可为29.1％、32.3％、38.8％、48.5％、58.2％或77.6％。
当第一磷酸铁锂颗粒的用量过多时，可能会存在较多的第一磷酸铁锂颗粒发生团聚，从而不利于量产和提高能量密度。类似地，当第二磷酸铁锂颗粒的含量过多时，可能恶化电池的动力学性能，缩短电池寿命。当两种磷酸铁锂颗粒的含量均在上述范围内时，对应二次电池具备较低的直流内阻和较长的寿命。
在一些实施方式中，可选地，在所述磷酸铁锂正极极片的活性物质层中，所述第一磷酸铁锂颗粒与所述第二磷酸铁锂颗粒的重量比为1∶0.1-9，可选为1∶0.4-4，更可选为1∶0.4-1.5。例如，所述第一磷酸铁锂颗粒与所述第二磷酸铁锂颗粒的重量比可以为1∶4、2∶3、1∶1、3∶2、2∶1或7∶3。
通过调整第一磷酸铁锂颗粒和第二磷酸铁锂颗粒的用量比，可进一步改善相应电池的动力学性能和循环性能。
在一些实施方式中，可选地，所述第一磷酸铁锂颗粒中的碳含量为1.2-2.7％，可选为1.4-2.2％，更可选为1.4-2.0％，基于所述第一磷酸铁锂颗粒的总重量计；
所述第二磷酸铁锂颗粒中的碳含量为0.7-1.3％，可选为1-1.2％更可选为1.1-1.2％，基于所述第二磷酸铁锂颗粒的总重量计。
当两种磷酸铁锂颗粒的碳含量均在上述范围内时，可进一步改善相应二次电池的性能。
在本申请中，可通过本领域通常使用的方法来测量磷酸铁锂颗粒中的碳含量，例如可通过红外吸收法进行测试，具体为将待测试样在氧气流中燃烧，生成CO 2。由于在一定压力下，CO 2吸收红外线的能 量与其浓度成正比，因此根据测出的CO 2气体流经红外吸收器前后的能量变化，可计算出含碳量。
在一些实施方式中，可选地，所述第一磷酸铁锂颗粒粉末的振实密度为1-1.4g cm -3、可选为1.1-1.3g cm -3、更可选为1.15-1.25g cm -3。
在一些实施方式中，可选地，所述第二磷酸铁锂颗粒粉末的振实密度为1.2-1.6g cm -3，可选为1.3-1.5g cm -3，更可选为1.35-1.45g cm -3。
需要说明的是，磷酸铁锂颗粒粉末的振实密度可通过本领域技术人员通常使用的方法来测量，例如，可根据GB/T 5162-2006/ISO3953：1993进行测量。
在一些实施方式中，可选地，所述第一磷酸铁锂颗粒粉末的压实密度为2-2.2g/cm 3。
在一些实施方式中，可选地，所述第二磷酸铁锂颗粒粉末的压实密度为2-2.45g/cm 3。
类似地，可通过本领域技术人员通常使用的方法来测量压实密度。作为示例，可通过以下方法来测量压实密度：取一定量的粉末放于压实专用模具中，然后将模具放在压实密度仪器上，设置不同压力，在设备上可以读出不同压力下粉末的厚度(卸压后的厚度)，通过ρ＝m/v，计算出压实密度。
在一些实施方式中，可选地，所述磷酸铁锂正极极片中正极膜层的压实密度为2-2.45g/cm 3、可选为2.1-2.3g/cm 3、更可选为2.15-2.25g/cm 3。正极膜层的压实密度可通过本领域中通常使用的方法进行测定。作为示例，可首先取单位面积的正极极片，称量其质量m1，然后再称量单位面积的正极箔材的质量m2，然后用m1减去m2得正极膜层的质量，然后除以所述正极膜层的厚度(极片厚度减去箔材厚度)即可得正极膜层的压实密度。
在一些实施方式中，可选地，在所述磷酸铁锂正极极片中的活性物质层中，所述第一磷酸铁锂颗粒和所述第二磷酸铁锂颗粒分层分布。
在一些实施方式中，可选地，所述第二磷酸铁锂颗粒层位于正极集流体的表面上，所述第一磷酸铁锂颗粒层位于所述第二磷酸铁锂颗 粒层与正极集流体相对的表面上。
本领域技术人员理解，极片层面的空间结构设计也对锂二次电池的性能有显著影响，尤其是对于含有两种及以上活性材料的极片设计。通过极片空间结构设计可以进一步提升电池的性能。具体到本申请，当将两种磷酸铁锂颗粒分层涂布，尤其是将第二磷酸铁锂颗粒涂布在正极集流体的表面上，并将第一磷酸铁锂颗粒涂布在第二磷酸铁锂颗粒层的表面上，从而形成双层分布结构时，可更有效地发挥两种磷酸铁锂颗粒的各自优势，改善二次电池的动力学性能和循环性能。
在一些实施方式中，可选地，所述第一磷酸铁锂颗粒层的厚度为65-250μm、可选为80-140μm、更可选为100-140μm；
所述第二磷酸铁锂颗粒层的厚度为60-250μm、可选为60-120μm、更可选为60-100μm。
作为示例，所述第一磷酸铁锂颗粒层的厚度例如可以为80nm、100nm、120nm或140nm，所述第二磷酸铁锂颗粒层的厚度例如可以为60nm、80nm、100nm或120nm。第一磷酸铁锂颗粒层和第二磷酸铁锂颗粒层的厚度可通过本领域通常使用的方法进行测定。例如，可首先测得正极膜层厚度，然后通过第一磷酸铁锂颗粒和第二磷酸铁锂颗粒的用量比例关系确定。
磷酸铁锂颗粒层的厚度过大，可能会恶化电池的动力学性能；相反，磷酸铁锂颗粒层的厚度过小，可能会导致无法充分发挥双层涂布的优势，不能进一步改善电池性能。
在一些实施方式中，可选地，所述第一磷酸铁锂颗粒层与所述第二磷酸铁锂颗粒层的厚度之比为1∶0.1-9、可选为1∶0.4-1.5、更可选为1∶0.4-1。例如，所述第一磷酸铁锂颗粒层与所述第二磷酸铁锂颗粒层的厚度之比为2∶3、1∶1、3∶2或7∶3。
当第一磷酸铁锂颗粒层和第二磷酸铁锂颗粒层的厚度之比在上述范围内时，有助于进一步改善对应二次电池的动力学性能和循环性能。
在一些实施方式中，可选地，所述第一磷酸铁锂颗粒层的面密度 为0.1-0.3g/1540.25mm 2，可选为0.15-0.25g/1540.25mm 2，更可选为0.15-0.2g/1540.25mm 2；
所述第二磷酸铁锂颗粒层的面密度为0.1-0.3g/1540.25mm 2，可选为0.15-0.25g/1540.25mm 2，更可选为0.15-0.2g/1540.25mm 2。
需要说明的是，本申请对涂布方法并无特别限制，可采用本领域通常使用的涂布方法，例如可通过刮刀涂布、辊涂、狭缝挤压涂布等。
在一些实施方式中，所述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。
在一些实施方式中，可选地，所述磷酸铁锂正极极片还包括粘结剂。作为示例，所述粘结剂可以包括聚偏二氟乙烯(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。
在一些实施方式中，可选地，所述粘结剂占正极膜层总重量的0.1-3.5％，可选为0.5-2.5％。
在一些实施方式中，可选地，所述磷酸铁锂正极极片还包括导电剂。作为示例，所述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。
在一些实施方式中，可选地，所述导电剂占正极膜层总重量的0.05-2.0％，可选为0.1-1.5％。
在一些实施方式中，可选地，所述磷酸铁锂正极极片还包括其他添加剂，例如表面活性剂、润湿剂、流变改性剂等。作为示例，所述添加剂例如可选自高级脂肪酸盐、高级烷基磺酸盐、烷基芳基磺酸盐，月桂酸、肉豆蔻酸、棕榈酸、硬脂酸、油酸等的碱金属盐如锂盐，全 氟烷基磺酰亚胺盐，辛酸甲酯、新戊酸正丁酯或乙酸月桂酯等中的一种或多种。
在一些实施方式中，可选地，所述其他添加剂占正极膜层总重量的0.05-2.0％，可选为0.1-1.5％。
在一些实施方式中，可以通过以下方式制备正极极片：将上述用于制备正极极片的组分，例如第一磷酸铁锂颗粒和第二磷酸铁锂颗粒、导电剂、粘结剂和任意其他的组分如表面活性剂分散于溶剂(例如N-甲基吡咯烷酮)中，形成正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，即可得到正极极片。
在一些实施方式中，可选地，可分别制备第一磷酸铁锂颗粒的正极浆料和第二磷酸铁锂颗粒的正极浆料，并将第二磷酸铁锂颗粒的正极浆料涂布在靠近集流体一侧，将第一磷酸铁锂颗粒的正极浆料涂布在第二磷酸铁锂颗粒层表面远离集流体一侧。
在一些实施方式中，可选地，在制备正极浆料时，将混合物搅拌至粘度为7000-15000mPa.s，然后立即出货。
[二次电池]
本申请的第二方面提供一种二次电池，其包括本申请第一方面所述的磷酸铁锂正极极片。二次电池可采用本领域通常使用的方法进行制备。例如，可将正极极片、负极极片和隔离膜按照一定的工艺卷绕成电极组件，然后向所得电极组件中注入电解液，经密封等工序即可制备本申请所述二次电池。
通常情况下，二次电池包括正极极片、负极极片、电解质和隔离膜。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。电解质在正极极片和负极极片之间起到传导离子的作用。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，同时可以使离子通过。
关于二次电池的其他部件如负极极片、电解质和隔离膜的说明如下文中所述。
[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，所述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，所述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。所述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。所述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。所述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。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，所述电解质采用电解液。所述电解液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，所述电解液还可选地包括添加剂。例如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。
本申请的第三方面提供一种电池模块，包括本申请第二方面所述的二次电池。
本申请的第四方面提供一种电池包，包括本申请第三方面所述的电池模块。
本申请的第五方面提供一种用电装置，包括本申请第二方面的二次电池、第三方面的电池模块或第四方面的电池包中的至少一种。所述二次电池、电池模块、或电池包可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述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。
作为所述用电装置，可以根据其使用需求来选择二次电池、电池模块或电池包。
另外，以下适当参照附图对本申请的二次电池、电池模块、电池包和用电装置进行说明。
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6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7，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能够盖设于所述开口，以封闭所述容纳腔。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封装于所述容纳腔内。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8是作为一个示例的电池模块4。参照图8，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9和图10是作为一个示例的电池包1。参照图9和图10，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。
图11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。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。 该装置通常要求轻薄化，可以采用二次电池作为电源。
实施例
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施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。
本申请实施例中涉及的正极活性材料如下表所示：
Figure PCTCN2022089518-appb-000001
实施例1
正极极片的制备
将第一磷酸铁锂颗粒(D50为300nm、BET为15.8m 2/g、碳含量为1.4％)、第二磷酸铁锂颗粒(D50为1000nm、BET为10m 2/g、碳含量为1.2％)、聚偏二氟乙烯(PVDF)、导电剂乙炔黑按照48.5％∶48.5％∶2.2∶0.8的重量比加入到搅拌罐中进行混合。以25rpm的公转速度、800rpm的自转速度搅拌15分钟。然后向上述干混物中按照60％的固含量加入溶剂N-甲基吡咯烷酮(NMP)。之后以25rpm的公转速度、300rpm的自转速度搅拌15分钟。随后调节公转速度为25rpm、自转速度为1200rpm，搅拌220min，使混合物均匀分散。然后以25rpm的公转速度、500rpm的自转速度继续搅拌，调节混合物的粘度为10000mPa.s，然后立即出货，得到混合浆料。将上述混合浆料按照0.3g/1540.25mm 2的面密度涂布在厚度为13μm的铝箔上，涂覆两面。之后经过烘干除去溶剂，并进行冷却，使得正极膜层的压实密度为2.2g/cm 3。经过分切后，得到实施例1的正极极片。
负极极片的制备
将负极活性物质人造石墨、导电剂乙炔黑、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC-Na)按照重量比为96∶1∶2∶1溶于溶剂去离子水中，搅拌混合均匀后制备成负极浆料。将负极浆料按9.7mg/cm 2的涂敷密度均匀涂覆在负极集流体铜箔上，经过烘干、冷压、分切得到负极极片。
电解液
在氩气气氛手套箱中(H 2O＜0.1ppm，O 2＜0.1ppm)，将有机溶剂碳酸亚乙酯(EC)/碳酸甲乙酯(EMC)按照体积比3/7混合均匀，加入12.5重量％(基于碳酸亚乙酯/碳酸甲乙酯溶剂的重量计)LiPF 6溶解于上述有机溶剂中，搅拌均匀，得到电解液。
隔离膜
使用市售的厚度为16μm、平均孔径为80nm的PP-PE共聚物微孔薄膜(来自卓高电子科技公司，型号20)。
二次电池
将正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正负极片中间起到隔离的作用，并卷绕得到尺寸为高度为146mm、上下表面直径为44.8mm的圆柱裸电芯。所述正极极片与负极极片之间的间距为16μm，所述隔离膜与正极极片和负极极片之间的间距约为0μm。将裸电芯置于外包装中，注入100g上述电解液并封装，得到二次电池。
实施例2-11
除使用的第一磷酸铁锂颗粒和第二磷酸铁锂颗粒的粒径、比表面积、碳含量，以及磷酸铁锂颗粒的用量不同以外，其他条件与实施例1相同，具体条件详见表1。
实施例12
实施例12与实施例1的其他条件相同，区别在于将第一磷酸铁锂颗粒按照第一磷酸铁锂颗粒：聚偏二氟乙烯(PVDF)、导电剂乙炔黑为97∶2.2∶0.8的重量比加入到搅拌罐中，制得浆料后按照0.3g/1540.25mm 2的面密度涂布在厚度为13μm的铝箔上，为第一层活性物质层；然后将第二磷酸铁锂颗粒按照第二磷酸铁锂颗粒：聚偏二氟乙烯(PVDF)、导电剂乙炔黑为97∶2.2∶0.8的重量比加入到搅拌罐中，制得浆料后按照0.3g/1540.25mm 2的面密度涂布在第一层活性物质层的上表面。
第一磷酸铁锂颗粒和第二磷酸铁锂颗粒的用量与实施例1相同，即上下层总量与实施例1相同。所得正极极片上第一磷酸铁锂颗粒层的厚度为100μm，第二磷酸铁锂颗粒层的厚度为100μm。
实施例13
除将第二磷酸铁锂颗粒涂布在铝箔表面作为第一活性物质层，将第一磷酸铁锂颗粒层涂布在第二磷酸铁锂颗粒层上部以外，实施例13的其他条件与实施例12相同。
实施例14-16
除改变磷酸铁锂颗粒的用量，使得第一磷酸铁锂颗粒层/第二磷酸铁锂颗粒层对应的厚度分别为80μm/120μm、120μm/80μm和140μm/60μm以外，实施例14-16的其他条件与实施例13相同，具体条件详见表1。
对比例1-3
除使用的第一磷酸铁锂颗粒和第二磷酸铁锂颗粒的粒径、比表面积、碳含量，以及磷酸铁锂的用量不同以外，对比例1-3的其他条件与实施例1相同，具体条件详见表1。
对比例4
除第一磷酸铁锂颗粒层/第二磷酸铁锂颗粒层的厚度分别为16μm/184μm以外，对比例4的其他条件与实施例13相同。
相关参数测试方法
1.扫描电镜测试
将适量待测磷酸铁锂颗粒制样，使用ZEISS sigma 300扫描电子显微镜参照标准JY/T010-1996，对样品形貌进行观测。
2.体积平均粒径D50测试
参考标准GB/T 19077-2016/ISO 13320：2009粒度分布激光衍射法。使用激光粒度仪(马尔文3000，MasterSizer 3000)测试，主光源使用氦氖红光光源。取一洁净小烧杯加入待测样品1g，加入20ml 去离子水(样品浓度保证遮光度为8-12％)，加入一滴表面活性剂来降低水的表面张力以有助于颗粒的浸润，以53KHz/120W超声5min，确保样品完全分散。打开激光粒度仪，清洗光路系统后，自动测试背景。搅拌已超声的待测溶液，使其分散均匀，按要求放入样品池中，开始测量粒径。从仪器中即可读得测量结果。
3.BET测试
测试方法参考标准GB/T19587-2004《气体吸附BET法测定固态物质比表面积》。
4.DCR测试
取电池，进行充放电测试。先将电池在25℃条件下进行满充，满充后搁置30min。搁置后以1C放电倍率放电30min，调节至50％SOC，搁置10min。调节温箱温度为-10℃，搁置120min，测得放电初始电压。然后以3C放电速率放电10s，并记录放电过程中的最低电压，然后搁置10min，用3C放电初始电压与3C放电过程中最低电压差值除以电流值(放电倍率为3C，电流为78A)即得DCR。
5.循环性能测试
在25℃下，将实施例和对比例制备得到的二次电池以1C(即1h内完全放掉理论容量的电流值)恒流充电至3.65V，之后以3.65V恒压充电至电流为0.05C，静置5min，然后以1C恒流放电至2.5V，静置30min，此为一个充放电循环过程，记录此时的电池容量C0。按照此方法对电池进行n次循环充放电，记录n次循环后的电池容量记为C1。则电池在25℃下的循环容量保持率＝C1/C0×100％。记录测得电池的循环容量保持率为80％时所对应的循环圈数n。
Figure PCTCN2022089518-appb-000002
Figure PCTCN2022089518-appb-000003
根据上述结果可知，本申请的实施例1-16制得的二次电池均比对比例1-4的电池具备更小的DCR和更好的循环性能。此外，通过调整第一磷酸铁锂颗粒和第二磷酸铁锂颗粒的用量和空间分布，可以进一步改善二次电池的动力学性能和循环性能。
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 (14)

  1. 一种磷酸铁锂正极极片，包括正极集流体和位于所述正极集流体上的正极活性材料，其中所述正极活性材料包括：
    体积平均粒径D50为60-300nm、可选为60-200nm，比表面积大于15m 2/g、可选为15-25m 2/g的第一磷酸铁锂颗粒；和
    体积平均粒径D50大于800nm、可选为1000-1500nm，比表面积小于10m 2/g、可选为5-10m 2/g的第二磷酸铁锂颗粒。
  2. 根据权利要求1所述的磷酸铁锂正极极片，其中
    所述第一磷酸铁锂颗粒的含量为1-97％、可选为18-68％、更可选为36-68％，基于所述磷酸铁锂正极极片中正极膜层的总重量计；
    所述第二磷酸铁锂颗粒的含量为3-99％、可选为32-82％、更可选为32-64％，基于所述磷酸铁锂正极极片中正极膜层的总重量计。
  3. 根据权利要求1或2所述的磷酸铁锂正极极片，其中
    在所述磷酸铁锂正极极片的活性物质层中，所述第一磷酸铁锂颗粒与所述第二磷酸铁锂颗粒的重量比为1∶0.1-9，可选为1∶0.4-4，更可选为1∶0.4-1.5。
  4. 根据权利要求1至3中任一项所述的磷酸铁锂正极极片，其中
    所述第一磷酸铁锂颗粒中的碳含量为1.2-2.7％，可选为1.4-2.2％，更可选为1.4-2.0％，基于所述第一磷酸铁锂颗粒的总重量计；
    所述第二磷酸铁锂颗粒中的碳含量为0.7-1.3％，可选为1-1.2％更可选为1.1-1.2％，基于所述第二磷酸铁锂颗粒的总重量计。
  5. 根据权利要求1至4中任一项所述的磷酸铁锂正极极片，其中所述磷酸铁锂正极极片中的正极膜层的压实密度为2-2.45g/cm 3、可选为2.1-2.3g/cm 3、更可选为2.15-2.25g/cm 3。
  6. 根据权利要求1至5中任一项所述的磷酸铁锂正极极片，其中在所述磷酸铁锂正极极片中的活性物质层中，所述第一磷酸铁锂颗粒和所述第二磷酸铁锂颗粒分层分布。
  7. 根据权利要求6所述的磷酸铁锂正极极片，其中所述第二磷酸铁锂颗粒层位于正极集流体的表面上，所述第一磷酸铁锂颗粒层位于所述第二磷酸铁锂颗粒层与正极集流体相对的表面上。
  8. 根据权利要求6或7所述的磷酸铁锂正极极片，其中所述第一磷酸铁锂颗粒层的厚度为65-250μm、可选为80-140μm、更可选为100-140μm；
    所述第二磷酸铁锂颗粒层的厚度为60-250μm、可选为60-120μm、更可选为60-100μm。
  9. 根据权利要求6至8中任一项所述的磷酸铁锂正极极片，其中所述第一磷酸铁锂颗粒层与所述第二磷酸铁锂颗粒层的厚度之比为1∶0.1-9、可选为1∶0.4-1.5、更可选为1∶0.4-1。
  10. 根据权利要求6至9中任一项所述的磷酸铁锂正极极片，其中所述第一磷酸铁锂颗粒层的面密度为0.1-0.3g/1540.25mm 2，可选为0.15-0.25g/1540.25mm 2，更可选为0.15-0.2g/1540.25mm 2；
    所述第二磷酸铁锂颗粒层的面密度为0.1-0.3g/1540.25mm 2，可选为0.15-0.25g/1540.25mm 2，更可选为0.15-0.2g/1540.25mm 2。
  11. 一种二次电池，包括根据权利要求1至10中任一项所述的磷酸铁锂正极极片。
  12. 一种电池模块，包括权利要求11所述的二次电池。
  13. 一种电池包，包括权利要求12所述的电池模块。
  14. 一种用电装置，包括选自权利要求11所述的二次电池、权利要求12所述的电池模块或权利要求13所述的电池包中的至少一种。
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