WO2024239157A1 - 正极极片、电池及用电装置 - Google Patents

正极极片、电池及用电装置 Download PDF

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Publication number
WO2024239157A1
WO2024239157A1 PCT/CN2023/095341 CN2023095341W WO2024239157A1 WO 2024239157 A1 WO2024239157 A1 WO 2024239157A1 CN 2023095341 W CN2023095341 W CN 2023095341W WO 2024239157 A1 WO2024239157 A1 WO 2024239157A1
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WIPO (PCT)
Prior art keywords
active material
positive electrode
electrode active
material layer
mixed
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PCT/CN2023/095341
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English (en)
French (fr)
Inventor
秦鹏程
张乐
刘强
孙宇
李白清
金海族
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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Priority to CN202380068950.5A priority Critical patent/CN119998956A/zh
Priority to PCT/CN2023/095341 priority patent/WO2024239157A1/zh
Publication of WO2024239157A1 publication Critical patent/WO2024239157A1/zh
Anticipated expiration legal-status Critical
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    • 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 field of batteries, and in particular to a positive electrode sheet, a battery and an electrical device.
  • the positive electrode active material layer made by mixing two positive electrode active materials has certain optimization improvements in energy density or safety performance compared with the positive electrode active material layer made of a single active material.
  • the inventor of the present application found that when positive electrode active materials with large shrinkage differences are mixed in similar amounts, the dynamic performance of the entire battery is poor.
  • the present application provides a positive electrode sheet, a battery and an electrical device, which can improve the dynamic performance of the battery.
  • the present application provides a positive electrode plate, comprising a current collector and an active material layer arranged on at least one side surface of the current collector, the active material layer comprising at least one mixed active material layer; in the mixed active material layer, the positive electrode active material comprises a first positive electrode active material and a second positive electrode active material, the shrinkage rate T2 of the second positive electrode active material is greater than the shrinkage rate T1 of the first positive electrode active material, and T2-T1 ⁇ 0.3%, and the proportion of the first positive electrode active material or the second positive electrode active material is 55% to 95% of the total mass of the positive electrode active material in the mixed active material layer.
  • the mixed active material layer mainly contains two different types of positive electrode active materials mixed and matched: one type is a positive electrode active material with a small shrinkage rate (shrinkage rate is T1), and the other type is a positive electrode active material with a large shrinkage rate (shrinkage rate is T2).
  • shrinkage rate is T1
  • T2 positive electrode active material with a large shrinkage rate
  • shrinkage rate is T2
  • the first positive electrode active material or the second positive electrode active material accounts for 65% to 80% of the total mass of the positive electrode active material.
  • the mass of the positive electrode active material with a large shrinkage rate or the positive electrode active material with a small shrinkage rate accounts for a large proportion, which reduces the problem of poor kinetic performance caused by mixing materials with large shrinkage rates and similar contents in the same layer.
  • the value range of T1 is 0.3%-5.5%, and the value range of T2 is 1%-7%.
  • the value range of T1 is 0.5%-4%, and the value range of T2 is 3%-6.5%.
  • the average particle size R2 of the second positive electrode active material is greater than the average particle size R1 of the first positive electrode active material, and R2/R1 ⁇ 2, optionally, 100 ⁇ R2/R1 ⁇ 5, optionally, 100 ⁇ R2/R1 ⁇ 10.
  • Mixing the second positive electrode active material with a large shrinkage rate and a large average particle size with the first positive electrode active material with a small shrinkage rate and a small average particle size to form a mixed active material layer is beneficial to improving the energy density of the battery.
  • the solution of this embodiment can further improve the kinetic performance of the battery.
  • the active material layer includes at least two sub-layers, wherein at least one of the sub-layers is the mixed active material layer.
  • the two adjacent sublayers are respectively a first mixed active material layer and a second mixed active material layer
  • the shrinkage rate of the first positive electrode active material in the first mixed active material layer is T1
  • the shrinkage rate of the second positive electrode active material is T2, T2-T1 ⁇ 0.3%
  • the positive electrode active material in the second mixed active material layer includes a third positive electrode active material and a fourth positive electrode active material
  • the shrinkage rate of the third positive electrode active material is T1'
  • the shrinkage rate of the fourth positive electrode active material is T2', T2'-T1' ⁇ 0.3%.
  • the active material layers are layered, and at least two adjacent layers are mixed active material layers, which is also an embodiment that can be included in the present application, and can improve the problem of poor dynamic performance.
  • the difference between T2 and T1' is not greater than 1%, and/or the difference between T2' and T1 is not greater than 1%. If the difference in shrinkage of the positive electrode active material in the two mixed active material layers is too large, the interface contact is poor, affecting the kinetic performance.
  • the first mixed active material layer is closer to the current collector than the second mixed active material layer, and the value of T2-T1 is less than the value of T2'-T1'.
  • one of the two adjacent sub-layers is a mixed active material layer, and the other is a single active material layer, and the positive electrode active material of the single active material layer includes a first positive electrode active material or a second positive electrode active material. Since the shrinkage rate of the first positive electrode active material and the second positive electrode active material is quite different, the first positive electrode active material or the second positive electrode active material is separately arranged, which can improve the kinetic performance of the entire active material layer.
  • the single active material layer is closer to the current collector than the mixed active material layer.
  • the single active material layer is in contact with the current collector, reducing the problem of poor contact between the active material layer and the current collector due to the large difference in shrinkage rate between the first positive electrode active material and the second positive electrode active material.
  • the positive electrode active material of the single active material layer includes a first positive electrode active material. This embodiment is an alternative solution that can improve the problem of poor kinetic performance.
  • the mixed active material layer contains a linear conductive agent; optionally, in the mixed active material layer, the mass proportion of the linear conductive agent with a length of ⁇ 1 ⁇ m is 0.2% to 1%; optionally, the linear conductive agent includes at least one of carbon nanotubes, carbon fibers and linear graphene.
  • a certain proportion of linear conductive materials is added to the mixed active material layer and dispersed around different positive electrode active materials to reduce the deterioration of the conductive network caused by the mutual separation of the two types of positive electrode active materials due to the difference in shrinkage during the charge and discharge process, play a connecting and conducting role, and keep the conductive network stable when the contact interface of different types of positive electrode active materials changes.
  • the active material layer includes at least two sublayers, and in the two adjacent sublayers, the porosity of the sublayer away from the current collector is ⁇ 30%, and the porosity of the sublayer adjacent to the current collector is ⁇ 50%;
  • the porosity of the sublayer away from the current collector is ⁇ 50%, and the porosity of the sublayer adjacent to the current collector is ⁇ 60%.
  • the sublayer away from the current collector has sufficient contact with the electrolyte, and the sublayer adjacent to the current collector has less contact with the electrolyte.
  • the present application provides a battery, comprising a battery cell consisting of a negative electrode plate and the positive electrode plate provided in the first aspect.
  • the present application provides an electrical device, comprising a battery provided according to the second aspect.
  • FIG1 is a schematic structural diagram of a vehicle according to some embodiments of the present application.
  • FIG2 is a schematic diagram of an exploded structure of a battery according to some embodiments of the present application.
  • FIG3 is a schematic diagram of the structure of a battery cell provided in some embodiments of the present application.
  • the term "and/or" is only a description of the association relationship of associated objects, indicating that three relationships may exist.
  • a and/or B can represent: A exists alone, A and B exist at the same time, and B exists alone.
  • the character "/" in this article generally indicates that the associated objects before and after are in an "or" relationship.
  • connection and “fixed” should be understood in a broad sense.
  • connection can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements.
  • connection and “fixed” should be understood in a broad sense.
  • it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements.
  • Power batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as military equipment and aerospace and other fields. With the continuous expansion of the application field of power batteries, the market demand is also constantly expanding.
  • the power battery can be a lithium-ion battery.
  • lithium ions are released from the positive electrode active material, transmitted through the electrolyte, and embedded in the negative electrode active material through the isolation membrane.
  • the positive electrode active material layer made based on the mixture of different positive electrode active materials has improved energy density or safety performance compared with the positive electrode active material layer of a single active material.
  • the inventors found that after the positive electrode active materials with large shrinkage differences were mixed in similar amounts, the kinetic performance of the entire battery was still poor.
  • the positive electrode sheet layered based on lithium manganese iron phosphate and ternary materials has certain optimization and improvement in kinetic performance compared with the positive electrode sheet with a single active material, but the single-layer active material in this layered positive electrode sheet is single, and the full advantages of layered coating cannot be brought into play.
  • this method of distinguishing the upper and lower layers based on the type of material has a single perspective, which limits the scope of application of the layered technology.
  • a positive electrode plate is designed.
  • clear positive electrode plate design principles and design basis are provided to improve the battery's kinetic performance and increase the battery's cycle life.
  • the battery cells disclosed in the embodiments of the present application can be used in, but are not limited to, electrical devices such as vehicles, ships, or aircraft.
  • the embodiment of the present application provides an electric device using a battery as a power source
  • the electric device may be, but is not limited to, a mobile phone, a tablet, a laptop, an electric toy, an electric tool, a battery car, an electric car, a ship, a spacecraft, etc.
  • the electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc.
  • the spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, etc.
  • FIG. 1 is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of the present application.
  • a battery 100 is disposed inside the vehicle 1000, and the battery 100 can be disposed at the bottom, head, or tail of the vehicle 1000.
  • the battery 100 can be used to power the vehicle 1000, for example, the battery 100 can be used as an operating power source for the vehicle 1000.
  • the vehicle 1000 may further include a controller 200 and a motor 300 , wherein the controller 200 is used to control the battery 100 to supply power to the motor 300 , for example, to meet the power requirements of starting, navigating, and driving the vehicle 1000 .
  • the battery 100 can not only serve as an operating power source for the vehicle 1000, but also serve as a driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.
  • Fig. 2 is a schematic diagram of the exploded structure of a battery 100 provided in some embodiments of the present application.
  • the battery 100 includes a box body 10 and a battery cell 20 , wherein the battery cell 20 is accommodated in the box body 10 .
  • the box body 10 is used to provide a storage space 11 for the battery cell 20.
  • the box body 10 may include a first portion 12 and a second portion 13, and the first portion 12 and the second portion 13 cover each other to define the storage space 11 for accommodating the battery cell 20.
  • the connection between the first portion 12 and the second portion 13 can be sealed by a sealing member (not shown in the figure), and the sealing member can be a sealing ring, a sealant, etc.
  • the first part 12 and the second part 13 can be in various shapes, such as a cuboid, a cylinder, etc.
  • the first part 12 can be a hollow structure with one side open to form a receiving cavity for accommodating the battery cell 20, and the second part 13 can also be a hollow structure with one side open to form a receiving cavity for accommodating the battery cell 20, and the open side of the second part 13 covers the open side of the first part 12, thereby forming a box body 10 with a receiving space 11.
  • the first part 12 can also be a hollow structure with one side open
  • the second part 13 can be a plate-like structure, and the second part 13 covers the open side of the first part 12, thereby forming a box body 10 with a receiving space 11.
  • the battery 100 there can be one or more battery cells 20. If there are more than one battery cell 20, the multiple battery cells 20 can be connected in series, in parallel, or in mixed connection. Mixed connection means that the multiple battery cells 20 are both connected in series and in parallel. Multiple battery cells 20 can be directly connected in series, in parallel, or in mixed connection, and then the whole formed by the multiple battery cells 20 is accommodated in the box 10; of course, multiple battery cells 20 can also be connected in series, in parallel, or in mixed connection to form a battery module, and then multiple battery modules are connected in series, in parallel, or in mixed connection to form a whole, and accommodated in the box 10.
  • the battery cell 20 can be cylindrical, flat, rectangular, or in other shapes. Figure 2 exemplarily shows the case where the battery cell 20 is square.
  • the battery 100 may further include a busbar component (not shown), and the multiple battery cells 20 may be electrically connected via the busbar component to achieve series connection, parallel connection, or mixed connection of the multiple battery cells 20 .
  • FIG3 is a schematic diagram of the structure of a battery cell 20 provided in some embodiments of the present application
  • FIG4 is an exploded view of a battery cell 20 provided in some embodiments of the present application.
  • the battery cell 20 may include a housing 21, an end cap assembly 22, and an electrode assembly 23.
  • the housing 21 has an opening 211
  • the electrode assembly 23 is accommodated in the housing 21, and the end cap assembly 22 is used to cover the opening 211.
  • the shape of the housing 21 can be determined according to the specific shape of the electrode assembly 23.
  • the housing 21 can be a rectangular parallelepiped structure.
  • FIG3 and FIG4 exemplarily show the case where the housing 21 and the electrode assembly 23 are square.
  • the shell 21 may also be made of a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc., and the embodiment of the present application does not impose any special restrictions on this.
  • the end cap assembly 22 includes an end cap 221 and an electrode terminal 222.
  • the end cap assembly 22 is used to seal the opening 211 of the housing 21 to form a closed installation space (not shown), and the installation space is used to accommodate the electrode assembly 23.
  • the installation space is also used to accommodate an electrolyte, such as an electrolyte.
  • the end cap assembly 22 is a component for outputting the electrical energy of the electrode assembly 23.
  • the electrode terminal 222 in the end cap assembly 22 is used to be electrically connected to the electrode assembly 23, that is, the electrode terminal 222 is electrically connected to the tab of the electrode assembly 23.
  • the electrode terminal 222 is connected to the tab through the current collecting member 24 to achieve electrical connection between the electrode terminal 222 and the tab.
  • the opening 211 of the shell 21 can be one or two. If the opening 211 of the shell 21 is one, the end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22, and the two electrode terminals 222 are respectively used to electrically connect to the positive pole ear and the negative pole ear of the electrode assembly 23. If the opening 211 of the shell 21 is two, for example, the two openings 211 are provided on opposite sides of the shell 21, and the end cap assembly 22 can also be two, and the two end cap assemblies 22 are respectively covered at the two openings 211 of the shell 21.
  • the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal, which is used to electrically connect to the positive pole ear of the electrode assembly 23; the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal, which is used to electrically connect to the negative electrode sheet of the electrode assembly 23.
  • the battery cell 20 may further include an insulating protective member 25 fixed to the periphery of the electrode assembly 23, and the insulating protective member 25 is used to insulate and isolate the electrode assembly 23 from the housing 21.
  • the insulating protective member 25 is a tape bonded to the periphery of the electrode assembly 23.
  • the positive electrode plate includes a current collector and an active material layer arranged on at least one side surface of the current collector, the active material layer includes at least one mixed active material layer; in the mixed active material layer, the positive electrode active material includes a first positive electrode active material and a second positive electrode active material, the shrinkage rate T2 of the second positive electrode active material is greater than the shrinkage rate T1 of the first positive electrode active material, and T2-T1 ⁇ 0.3%, the first positive electrode active material or the second positive electrode active material accounts for 55% to 95% of the total mass of the positive electrode active material in the mixed active material layer, and accordingly, the second positive electrode active material or the first positive electrode active material accounts for 5% to 45% of the total mass of the positive electrode active material.
  • the shrinkage rate (expansion rate) in this application refers to the degree of volume expansion change of the positive electrode active material during the charge and discharge process.
  • the test method for the shrinkage rate of the positive electrode active material is: a certain positive electrode active material is used as the only positive electrode active material to form a fresh electrode sheet, wherein the active material layer is formed by mixing the positive electrode active material, the binder PVDF, and the conductive agent according to the mass ratio of 97wt%:1.5wt%:1.5wt%.
  • the cross-sectional images of the active material layer in the fully charged state and the fully discharged state of the battery are taken by scanning electron microscopy (the active material layer is cut in the direction perpendicular to the surface of the current collector, and the cross-section is taken by scanning electron microscopy), and the particle size of the positive electrode material in the fully charged state is calculated as L1 and the particle size in the fully discharged state is L2.
  • the shrinkage rate of the positive electrode material is L1-L2/L2.
  • the calculation method of the particle size L1 or L2 is: take 20 particles in the picture, measure the particle size of the 20 particles, and take the average value, which is the particle size value.
  • the shrinkage rate of the positive electrode active material is a property of the material itself. By specifically selecting the composition of the positive electrode active material, a positive electrode active material with a specific shrinkage rate can be obtained.
  • other layers such as an adhesive layer, may be provided between the current collector and the active material layer.
  • the first positive electrode active material or the second positive electrode active material accounts for 65% to 80% of the total mass of the positive electrode active material
  • the second positive electrode active material or the first positive electrode active material accounts for 20% to 35% of the total mass of the positive electrode active material.
  • the proportion of the second positive electrode active material can be 65%, 70%, 75% or 80% of the total mass of the positive electrode active material, or any value within the above two numerical ranges
  • the proportion of the first positive electrode active material can be 20%, 25%, 30% or 35% of the total mass of the positive electrode active material, or any value within the above two numerical ranges.
  • the proportion of the first positive electrode active material can be 65%, 70%, 75% or 80% of the total mass of the positive electrode active material, or any value within the above two numerical ranges; the proportion of the second positive electrode active material can be 20%, 25%, 30% or 35% of the total mass of the positive electrode active material, or any value within the above two numerical ranges.
  • the value range of T1 is 0.3%-5.5%, and the value range of T2 is 1%-7%.
  • the value range of T1 is 0.5%-4%
  • the value range of T2 is 3%-6.5%
  • T2-T1 ⁇ 1% is optionally,
  • T1 can be 0.3%, 0.5%, 1%, 2%, 3%, 4%, 4.5% or 5.5%, or any value between the above two values;
  • T2 can be 1%, 2%, 3%, 4%, 5%, 6%, 2.5%, 6.5% or 7%, or any value between the above two values.
  • the first positive electrode active material may be one positive electrode active material, or may include two or even more positive electrode active materials with different shrinkage rates, the shrinkage rate of each positive electrode active material meets the shrinkage rate difference requirement with the second positive electrode active material, and the shrinkage rate difference between the positive electrode active materials in the first positive electrode active material is 0 to 0.5%.
  • the shrinkage rate difference between the first positive electrode active materials may be 0, 0.1%, 0.2%, 0.3%, 0.4% or 0.5%.
  • the second positive electrode active material can be a positive electrode active material, or it can include two or even more positive electrode active materials with different shrinkage rates, the shrinkage rate of each positive electrode active material meets the shrinkage rate difference requirement with the second positive electrode active material, and the shrinkage rate difference between the positive electrode active materials in the second positive electrode active material is 0 to 1%.
  • the shrinkage rate difference between the second positive electrode active materials can be 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or 1%.
  • the first positive electrode active material includes a positive electrode active material with a shrinkage rate of T1a and a positive electrode active material with a shrinkage rate of T1b
  • the second positive electrode active material includes a positive electrode active material with a shrinkage rate of T2a and a positive electrode active material with a shrinkage rate of T2b, T2b ⁇ T2a>T1b ⁇ T1a, and T2a-T1b ⁇ 0.3%.
  • the difference between T1b-T1a is 0-0.5%
  • the difference between T2b-T2a is 0-1%.
  • the sum of the mass of the first positive electrode active material and the second positive electrode active material is 90% to 100% of the total mass of the positive electrode active material; optionally, the sum of the mass of the first positive electrode active material and the second positive electrode active material is 95% to 100% of the total mass of the positive electrode active material; optionally, in the mixed active material, the sum of the mass of the first positive electrode active material and the second positive electrode active material is 98% to 100% of the total mass of the positive electrode active material.
  • the proportion of the first positive electrode active material (T1) with a small shrinkage rate or the second positive electrode active material (T2) with a large shrinkage rate is more than 55%, and the total proportion of these two types of positive electrode active materials is more than 90%, which can allow a small amount of positive electrode active material with a shrinkage rate between T1 and T2 to exist.
  • the average particle size R2 of the second positive electrode active material is greater than the average particle size R1 of the first positive electrode active material, and R2/R1 ⁇ 2, which can be optionally 100 ⁇ R2/R1 ⁇ 5, or optionally 100 ⁇ R2/R1 ⁇ 10, R1 can be any value between 0.1 ⁇ m and 0.4 ⁇ m, and R2 can be any value between 1 ⁇ m and 20 ⁇ m.
  • the active material layer includes at least two sub-layers, wherein at least one sub-layer is a mixed active material layer.
  • the two adjacent sub-layers are respectively a first mixed active material layer and a second mixed active material layer
  • the shrinkage rate of the first positive electrode active material in the first mixed active material layer is T1
  • the shrinkage rate of the second positive electrode active material is T2
  • the positive electrode active material in the second mixed active material layer includes a third positive electrode active material and a fourth positive electrode active material
  • the shrinkage rate of the third positive electrode active material is T1'
  • the shrinkage rate of the fourth positive electrode active material is T2', T2'-T1' ⁇ 0.3%.
  • the two sublayers have different positive electrode active materials, for example, the second positive electrode active material with a larger shrinkage rate in the two adjacent sublayers is a different substance, and the first positive electrode active material with a smaller shrinkage rate in the two adjacent sublayers is a different substance; or, the proportion of the positive electrode active materials in the two sublayers is different, for example, the proportion of the second positive electrode active material with a larger shrinkage rate in the two adjacent sublayers is different.
  • the first mixed active material layer on one side of the dividing line contains a first positive electrode active material (T1) with a small shrinkage rate during charge and discharge and a second positive electrode active material (T2) with a large shrinkage rate, T2-T1 ⁇ 0.3%, and the mass of the first positive electrode active material (T1) with a small shrinkage rate or the second positive electrode active material (T2) with a large shrinkage rate accounts for a large proportion, accounting for 55% to 95% of the total mass of the positive electrode active materials in the first mixed active material layer;
  • the second mixed active material layer on the other side of the dividing line also contains a third positive electrode active material (T1') with a small shrinkage rate during charge and discharge and a fourth positive electrode active material (T2') with a large shrinkage rate, T2'-T1' ⁇ 0.3%, and the mass of the third positive electrode active material (T1') with a small shrinkage rate or the fourth positive electrode active material (T2') with a large shrinkage rate accounts for a large proportion,
  • the second positive electrode active material with a large shrinkage rate in the two mixed active material layers can be the same substance or different substances, and the first positive electrode active material with a small shrinkage rate in the two mixed active material layers can be the same substance or different substances.
  • the difference between T2 and T1' is not greater than 1%, and/or the difference between T2' and T1 is not greater than 1%.
  • the shrinkage difference of the positive electrode active material of the two mixed active material layers is small.
  • the first mixed active material layer is closer to the current collector than the second mixed active material layer, and the value of T2-T1 is less than the value of T2'-T1'.
  • the difference between T2 and T1 of the mixed active material layer on the same side gradually increases from the direction adjacent to the current collector to the direction away from the current collector.
  • the mass of the first positive electrode active material or the second positive electrode active material in a single active material layer, is 95% to 100% of the total mass of the positive electrode active material; optionally, the mass of the first positive electrode active material or the second positive electrode active material is 98% to 100% of the total mass of the positive electrode active material.
  • the sum of the masses of the first positive electrode active material or the second positive electrode active material in a single active material layer may be 95%, 96%, 97%, 98%, 99% or 100% of the total mass of the positive electrode active material, or may be any value within the above two numerical ranges.
  • the single active material layer is closer to the current collector than the mixed active material layer.
  • the positive electrode active material of the single active material layer includes a first positive electrode active material.
  • active material layers are disposed on both sides of the current collector; optionally, the active material layers on both sides of the current collector are symmetrical about the current collector. All sublayers are symmetrically disposed about the current collector, and the materials and thicknesses of the two symmetrical sublayers are exactly the same.
  • the positive electrode active material is selected from lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), quaternary material (NCMA), lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), modified doped lithium manganese iron phosphate, lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium-rich cathode material (Li-rich cathode) and lithium nickel manganese oxide, as well as at least one of the doped or coated materials of the above materials.
  • NCM lithium nickel cobalt manganese oxide
  • NCA lithium nickel cobalt aluminum oxide
  • NCMA quaternary material
  • LFP lithium iron phosphate
  • LMFP lithium manganese iron phosphate
  • LCO lithium cobalt oxide
  • LMO lithium manganese oxide
  • Li-rich cathode lithium nickel manganese oxide
  • the first positive electrode active material includes at least one of a spinel structure positive electrode material or an olivine structure positive electrode material.
  • the first positive electrode active material includes at least one of a spinel structure positive electrode material and an olivine structure positive electrode material, and it is easy to obtain a positive electrode active material layer with a small shrinkage rate.
  • the first positive electrode active material includes Li 1+x Mn 1-y A y P 1-z R z O 4 , wherein x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, and z is any value in the range of 0.001 to 0.100.
  • A includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from the group consisting of B, S, Si and N.
  • the compound Li1 + xMn1-yAyP1 - zRzO4 can be purchased as a commercial product, or can be prepared according to the following preparation method.
  • the preparation method of the compound Li1 + xMn1-yAyP1 - zRzO4 can include the following steps:
  • step (3) transferring the slurry obtained in step (2) to a spray drying device for spray drying and granulation to obtain granules;
  • step (3) Sintering the particles obtained in step (3) to obtain a positive electrode active material.
  • the manganese source may be a manganese-containing substance known in the art that can be used to prepare lithium manganese phosphate.
  • the manganese source may be selected from elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, manganese carbonate, or a combination thereof.
  • the acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, organic acid such as oxalic acid, etc., for example, oxalic acid.
  • the source of element R is selected from at least one of sulfate, borate, nitrate and silicate of element R.
  • the source of element A is selected from at least one of simple substance, oxide, phosphate, oxalate, carbonate and sulfate of A.
  • the first positive electrode active material includes Li a A e Mn 1-f B f P 1-g C g O 4-n D n ;
  • A includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo and W;
  • B includes one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge;
  • C includes one or more elements of B, S, Si and N;
  • D includes one or more elements of S, F, Cl and Br;
  • a is selected from the range of 0.9 to 1.1
  • e is selected from the range of 0.001 to 0.1
  • f is selected from the range of 0.001 to 0.5
  • g is selected from the range of 0.001 to 0.1
  • n is selected from the range of 0.001 to 0.1
  • the first positive active material is electrically neutral.
  • LiaAxMn1 -yByP1 - zCzO4 - nDn compound is actually a specific LiMPO4 material, and its preparation method can refer to Li1 +xMn1 - yAyP1 - zRzO4 , which is not limited here.
  • the second positive electrode active material includes a layered structure positive electrode material, which makes it easy to obtain a positive electrode active material layer with a large shrinkage rate.
  • the chemical formula of the above-mentioned doped modified ternary material includes LiNi m Co i Mn k A 1-mik O 2 , wherein 0.5 ⁇ m ⁇ 0.98, 0.02 ⁇ i ⁇ 0.18, and 0 ⁇ k ⁇ 0.35.
  • the mixed active material layer contains a linear conductive agent (with an aspect ratio greater than 1); optionally, in the mixed active material layer, the mass proportion of the linear conductive agent with a length of ⁇ 1 ⁇ m is 0.2% to 1%; optionally, the linear conductive agent includes at least one of carbon nanotubes, carbon fibers and linear graphene.
  • the mixed active material layer contains a certain proportion of linear conductive substances to maintain the stability of the conductive network.
  • the active material layer includes at least two sublayers, and among the two adjacent sublayers, the porosity of the sublayer away from the current collector is ⁇ 30%, and the porosity of the sublayer adjacent to the current collector is ⁇ 50%; optionally, the porosity of the sublayer away from the current collector is ⁇ 50%, and the porosity of the sublayer adjacent to the current collector is ⁇ 60%.
  • Porosity refers to the volume ratio of pores existing in the active material layer before charge and discharge.
  • the porosity can be determined by the gas replacement method. Specifically, according to the embodiments of the present application, it can be determined by referring to GB/T 24586-2009 through the following steps: the pole piece is immersed in dimethyl carbonate (DMC), cleaned and dried. If it is a fresh pole piece, it does not need to be cleaned. The sample is placed in a sample cup, the number of samples is recorded to calculate the apparent volume, the sample is placed in a true density tester, and the true volume is determined by the gas replacement method.
  • the pole piece porosity is the percentage of the pore volume in the pole piece to the total volume of the pole piece.
  • the porosity of the sub-layer away from the current collector can be 30%, 40%, 50%, 60% or 70%, and the porosity of the sub-layer adjacent to the current collector can be 50%, 55%, 60%, 65%, 70% or 75%.
  • the mass ratio of the positive electrode active material in the sub-layer is 89.0% to 98.0%.
  • 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 binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PTFE polytetrafluoroethylene
  • vinylidene fluoride-tetrafluoroethylene-propylene terpolymer vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer
  • tetrafluoroethylene-hexafluoropropylene copolymer tetrafluoroethylene-he
  • the coating weight of each sub-layer with a coating area of 1540.25 mm2 is at least 50 mg, and is generally 50-200 mg.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • aluminum foil may be used as the metal foil.
  • the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base.
  • the composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.
  • a solvent such as N-methylpyrrolidone
  • the present application further provides a battery, comprising a negative electrode sheet, a separator and a battery cell composed of the positive electrode sheet provided above.
  • the battery includes any form of a single cell, a battery module, or a battery pack.
  • the negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector has two surfaces opposite to each other in its 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.
  • a metal foil a copper foil may 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 substrate.
  • the composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative electrode active material may adopt the negative electrode active material for the battery known in the art.
  • the negative electrode 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, etc.
  • 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 negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.
  • the negative electrode film layer may further include a binder.
  • the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • a conductive agent which 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 may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).
  • a thickener eg, sodium carboxymethyl cellulose (CMC-Na)
  • the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.
  • a solvent such as deionized water
  • the present application has no particular limitation on the type of isolation membrane, and any known porous 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 membrane can be a single-layer film or a multi-layer composite film, without particular limitation.
  • the materials of each layer can be the same or different, without particular limitation.
  • the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.
  • the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the 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 package, such as a bag-type soft package.
  • the material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.
  • the battery cell also includes an electrolyte, which conducts ions between the positive electrode and the negative electrode.
  • the electrolyte can be in liquid or gel form.
  • the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.
  • the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.
  • the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
  • the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.
  • additives such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.
  • the present application provides an electrical device, including the battery cell provided above or the battery provided above.
  • the first material is LiMn1 -y1-y2Fey1Tiy2P1 - zSizO4 , where y1+y2 is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, and the material composition of different shrinkage rates is slightly different;
  • the second material is Li1.00NimCoiMnkO2 , where 0.5 ⁇ m ⁇ 0.98 , 0.02 ⁇ i ⁇ 0.18, 0 ⁇ k ⁇ 0.35 ,
  • the preparation method of the compound LiMn 0.22 Fe 0.78 PO 4 comprises:
  • Step S1 Preparation of Fe-doped manganese oxalate
  • Step S2 Preparation of LiMn 0.22 Fe 0.78 PO 4
  • step S1 Take 1791.4 g of ferromanganese oxalate (calculated as C 2 O 4 Mn 0.22 Fe 0.78 ⁇ 2H 2 O) prepared in step S1, 369.4 g of lithium carbonate and 1150.1 g of ammonium dihydrogen phosphate, add them into 20 L of deionized water, stir them thoroughly, and uniformly mix and react at 80° C. for 10 h to obtain slurry. Transfer the slurry into a spray drying device for spray drying and granulation, and dry it at a temperature of 250° C. to obtain a powder. In a protective atmosphere (90% nitrogen and 10% hydrogen), sinter the powder in a roller kiln at 700° C. for 4 h.
  • a protective atmosphere 90% nitrogen and 10% hydrogen
  • the preparation method of carbon-coated LiMn 0.22 Fe 0.78 PO 4 comprises:
  • step S1 Take 1791.4 g of ferromanganese oxalate (calculated as C 2 O 4 Mn 0.22 Fe 0.78 ⁇ 2H 2 O) prepared in step S1, 369.4 g of lithium carbonate, 1150.1 g of ammonium dihydrogen phosphate, and 0.005 mol of sucrose, add them into 20 L of deionized water, stir them thoroughly, and uniformly mix and react at 80° C. for 10 h to obtain a slurry. Transfer the slurry into a spray drying device for spray drying and granulation, and dry it at a temperature of 250° C. to obtain a powder. In a protective atmosphere (90% nitrogen and 10% hydrogen), sinter the powder in a roller kiln at 700° C. for 4 h.
  • a protective atmosphere 90% nitrogen and 10% hydrogen
  • the preparation method of the compound Li 1.001 Mn 0.999 Fe 0.001 P 0.999 Si 0.001 O 4 comprises:
  • Step S1 Preparation of Fe-doped manganese oxalate
  • Step S2 Preparation of Li 1.001 Mn 0.999 Fe 0.001 P 0.999 Si 0.001 O 4
  • step S1 Take 1789.6g of ferromanganese oxalate (calculated as C 2 O 4 Mn 0.999 Fe 0.001 ⁇ 2H 2 O) prepared in step S1, 369.8g of lithium carbonate, 1148.9g of ammonium dihydrogen phosphate and 0.8g of silicic acid, add them into 20L of deionized water, stir them thoroughly, and evenly mix and react at 80°C for 10h to obtain slurry. Transfer the slurry into a spray drying device for spray drying and granulation, and dry it at a temperature of 250°C to obtain a powder. Sinter the powder in a roller kiln at 700°C for 4h in a protective atmosphere (90% nitrogen and 10% hydrogen).
  • lithium manganese iron phosphate material doped with other elements are the same as the preparation steps of the aforementioned compound B, the only difference is that silicic acid is replaced as the source of the corresponding element (such as titanium tetrachloride), and the raw material ratio is adjusted to satisfy the molar ratio in the chemical formula of the corresponding compound.
  • the layered structure positive electrode material is commercially available.
  • a positive electrode active material, a binder PVDF, and a conductive agent carbon black are mixed in a mass ratio of 97wt%:1.5wt%:1.5wt% and dispersed in N-methylpyrrolidone.
  • the positive electrode active material is divided into a first material and a second material.
  • the average particle size of the first material is 0.2 ⁇ m, and the average particle size of the second material is 1 ⁇ m.
  • the first material is Li 1.00 Mn 0.36 Fe 0.64 PO 4 , and its shrinkage rate T1 is 2.5%.
  • the second material is Li 1.00 Ni 0.59 Co 0.14 Mn 0.27 O 2 , and its shrinkage rate T2 is 3%.
  • the mass ratio of the first material to the second material is 35%:65%, and a positive electrode active material slurry A1 is prepared.
  • the positive electrode active material slurry A1 was coated on both sides of the aluminum foil with a coating weight of 200 mg/1540.25 mm 2 to obtain a positive electrode sheet.
  • the lithium-ion secondary battery is composed of the main materials of positive electrode sheet, negative electrode sheet, diaphragm and electrolyte, and mechanical parts such as aluminum shell and top cover.
  • the compression of the positive electrode sheet is 2.35 and the thickness is 213 ⁇ m;
  • the negative electrode material includes the negative electrode active material, adhesive, conductive agent and their contents respectively: 96.5% graphite + 1.3% SBR + 1.1CMC% + 0.4% SP, the compression is 1.65, and the thickness is 142 ⁇ m;
  • the solvent, electrolyte additive, lithium salt and their contents of the electrolyte are respectively: ethylene carbonate, dimethyl carbonate and 1,2-propylene carbonate are mixed in a volume ratio of 1:1:1, and then LiPF 6 is uniformly dissolved in the above solution to obtain an electrolyte.
  • the concentration of LiPF 6 is 1mol/L.
  • the positive electrode plate, the negative electrode plate and the separator are formed into a bare cell, the bare cell is insulated and coated and then loaded into an aluminum shell, and the top cover is welded to obtain a dry cell; the dry cell is baked and injected with electrolyte, and then formed and aged to obtain a hard shell battery.
  • a positive electrode active material, a binder PVDF, and a conductive agent carbon black are mixed in a mass ratio of 97wt%:1.5wt%:1.5wt% and dispersed in N-methylpyrrolidone.
  • the positive electrode active material is divided into a first material and a second material.
  • the average particle size of the first material is 0.2 ⁇ m, and the average particle size of the second material is 1 ⁇ m.
  • the first material is Li 1.00 Mn 0.36 Fe 0.64 PO 4 , and its shrinkage rate T1 is 2.5%.
  • the second material is Li 1.00 Ni 0.59 Co 0.14 Mn 0.27 O 2 , and its shrinkage rate T2 is 3%.
  • the mass ratio of the first material to the second material is 35%:65%, and a positive electrode active material slurry A1 is prepared.
  • the concentration of LiPF 6 is 1mol/L.
  • the positive electrode plate, the negative electrode plate and the separator are formed into a bare cell, the bare cell is insulated and coated and then loaded into an aluminum shell, and the top cover is welded to obtain a dry cell; the dry cell is baked and injected with electrolyte, and then formed and aged to obtain a hard shell battery.
  • the first material forming the positive electrode active material slurry A2 in step (1) is Li 1.00 Mn 0.36 Fe 0.64 PO 4 , whose shrinkage rate T1' is 2.5%
  • the second material is Li 1.00 Ni 0.59 Co 0.14 Mn 0.27 O 2 , whose shrinkage rate T2' is 3% (the first material and the second material are the same as those in the positive electrode active material slurry A1), but the mass ratio of the first material to the second material is 20%:80%.
  • the first material used to form the positive electrode active material slurry A1 in step (1) is Li 1.00 Mn 0.36 Fe 0.64 PO 4 , whose shrinkage rate T1 is 2.5%
  • the second material is Li 1.00 Ni 0.59 Co 0.14 Mn 0.27 O 2 , whose shrinkage rate T2 is 3%
  • the first material used to form the positive electrode active material slurry A2 is Li 1.00 Mn 0.36 Fe 0.64 PO 4 , whose shrinkage rate T1' is 2.5%
  • the second material is Li 1.00 Ni 0.82 Co 0.12 Mn 0.06 O 2 , whose shrinkage rate T2' is 5%
  • the rest is the same as Example 2.
  • the first material used to form the positive electrode active material slurry A1 in step (1) is Li 1.00 Mn 0.77 Fe 0.20 Ti 0.03 PO 4 , whose shrinkage rate T1 is 4.5%
  • the second material is Li 1.00 Ni 0.89 Co 0.07 Mn 0.04 O 2 , whose shrinkage rate T2 is 6.5%
  • the first material used to form the positive electrode active material slurry A2 is Li 1.00 Mn 0.22 Fe 0.78 PO 4 , whose shrinkage rate T1' is 0.3%
  • the second material is Li 1.00 Ni 0.89 Co 0.07 Mn 0.04 O 2 , whose shrinkage rate T2' is 6.5%
  • the rest is the same as Example 2.
  • step (1) the mass ratio of the first material and the second material in forming the positive electrode active material slurry A2 is 65%:35%, the rest is the same as Example 2.
  • the positive electrode active material slurry A1 is coated on the surface of the positive electrode that has been coated with the positive electrode active material slurry A2, that is, A1 in this embodiment is A2 in Example 1, and A2 in this embodiment is A2 in Example 1, to obtain a positive electrode sheet, and the rest is the same as Example 2.
  • the positive electrode active material, the binder PVDF, and the conductive agent carbon black are mixed in a mass ratio of 97wt%:1.5wt%:1.5wt% and dispersed in N- methylpyrrolidone .
  • the positive electrode active material is divided into a first material and a second material.
  • the first material is Li1.00Mn0.36Fe0.64PO4 , and its shrinkage rate T1* is 2.5%.
  • the second material is Li1.00Ni0.82Co0.12Mn0.06O2 , and its shrinkage rate T2* is 5%.
  • the mass ratio of the first material to the second material is 35%:65 % , and a positive electrode active material slurry A3 is prepared.
  • the first material forming the positive electrode active material slurry A1 is Li 1.00 Mn 0.36 Fe 0.64 PO 4 , whose shrinkage rate T1 is 2.5%
  • the second material is divided into a second material a and a second material b
  • the second material a is Li 1.00 Ni 0.59 Co 0.14 Mn 0.27 O 2 , whose shrinkage rate T2a is 3%
  • the second material b is Li 1.00 Ni 0.82 Co 0.12 Mn 0.06 O 2 , whose shrinkage rate T2b is 5%
  • the mass ratio of the first material to the second material is 35%: (30%+35%);
  • the positive electrode active material slurry A2 is formed using the same materials as the above-mentioned positive electrode active material slurry A2, but the mass ratio of the first material to the second material is 40%: (40%+20%).
  • the positive electrode active material used to form the positive electrode active material slurry A2 in step (1) is the second material used to form the positive electrode active material slurry A1, the rest is the same as that of Example 2.
  • the process is the same as that of Example 1 except that the average particle size of the first material forming the positive electrode active material slurry A1 in step (1) is 0.5 ⁇ m and the average particle size of the second material is 1 ⁇ m.
  • the process is the same as that of Example 1 except that the average particle size of the first material forming the positive electrode active material slurry A1 in step (1) is 0.2 ⁇ m and the average particle size of the second material is 2 ⁇ m.
  • step (1) the mass ratio of the first material and the second material to form the positive electrode active material slurry A1 is 50%:50%, and the mass ratio of the first material and the second material to form the positive electrode active material slurry A2 is 50%:50%, the rest is the same as Example 2.
  • step (1) the mass ratio of the first material and the second material in forming the positive electrode active material slurry A1 is 50%:50%, the rest is the same as in Example 1.
  • the average particle size of all the first materials used in Examples 1 to 15 and Comparative Examples 1 to 2 is 0.2 ⁇ m, and the average particle size of all the second materials is 1 ⁇ m.
  • the hard shell batteries obtained in Examples 1 to 13 and Comparative Examples 1 to 2 are subjected to cycle tests:
  • the active material layer of the positive electrode plates of Examples 1 to 15 contains at least one layer of positive electrode active material with a large shrinkage rate and a small shrinkage rate, wherein the mixed positive electrode material layer is formed in a large mass proportion of the large shrinkage rate material or the small shrinkage rate material, which can effectively improve the kinetic performance of the battery.
  • the capacity retention rate of the battery is increased and the impedance growth of the battery is reduced, that is, the kinetic performance of the battery is improved.
  • the positive electrode sheet active material layer of Example 1 is a mixed positive electrode material layer formed by a positive electrode active material with a large shrinkage rate and a small shrinkage rate in a high-low mass ratio, which can significantly improve the dynamic performance of the battery.
  • the active material layer of Example 14 is a mixed positive electrode material layer formed by a positive electrode active material with a small shrinkage rate and a large shrinkage rate in a high-low mass ratio, which can also improve the dynamic performance of the battery.
  • the positive electrode sheet of embodiment 8 has a layer that meets the shrinkage difference requirement of the positive electrode active material with a large shrinkage rate and a small shrinkage rate, and the positive electrode active material with a large shrinkage rate accounts for a large proportion, which can improve the dynamic performance of the battery.
  • the two layers of the positive electrode sheet of embodiment 2 meet the shrinkage difference requirement of the positive electrode active material with a large shrinkage rate and a small shrinkage rate.
  • the shrinkage difference requirement, and the large shrinkage positive electrode active material accounts for a large proportion, which can significantly improve the battery's kinetic performance.
  • the active material layer of the positive electrode sheet of Example 15 is arranged in layers, and each layer is a mixed positive electrode material layer formed by a high-low mass ratio of positive electrode active materials with small shrinkage and large shrinkage, which can also improve the battery's kinetic performance.
  • the positive electrode sheets of Examples 2 to 5 are provided with two layers of mixed positive electrode material layers, and the mass proportion of the positive electrode active material with a large shrinkage rate in the positive electrode active material of the mixed positive electrode material layer is 55% to 95%, and can be optionally 65% to 80%. After the battery is cycled multiple times, the capacity retention rate of the battery can be improved and the impedance growth of the battery can be reduced.
  • the difference in shrinkage rates of the positive electrode active materials with large shrinkage rates and small shrinkage rates in the mixed active material layer adjacent to the current collector side of the positive electrode plate of Example 2 is smaller than the difference in shrinkage rates on the side away from the current collector, which can improve the capacity retention rate of the battery and reduce the impedance growth of the battery.
  • the positive electrode plate of Example 10 adopts a multi-layer mixed positive electrode material layer, and each layer of the mixed positive electrode material layer of the positive electrode plate of Example 11 adopts a variety of positive electrode active materials, and the positive electrode active materials with a large shrinkage rate account for a large proportion, both of which can improve the capacity retention rate of the battery and reduce the impedance growth of the battery.
  • the positive electrode plates of Examples 12 to 13 are provided with adjacent mixed active material layers and single active material layers with only one type of positive electrode active material.
  • the positive electrode active material of the single active material layer is one type of positive electrode active material in the mixed active material layer, which can improve the capacity retention rate of the battery and reduce the impedance growth of the battery after the battery is cycled multiple times, that is, improve the kinetic performance of the battery.
  • Example 1 All the first materials used in Example 1, Examples 16-17, and Comparative Example 2 are the same, with a shrinkage rate of 2.5%, and all the second materials are the same, with a shrinkage rate of 3%.
  • the difference is that the average particle size R1 of the first material and the average particle size R2 of the second material are not completely the same, or the mass ratio of the first material and the second material is different.
  • the hard shell battery obtained in Examples 16-17 was cycle tested using the same method as above, and the performance of the battery obtained is shown in Table 2:
  • the positive electrode active material in the mixed active layer is made of a second material with a large shrinkage rate and a first material with a small shrinkage rate, and the average particle size (R2) of the second material and the average particle size (R1) of the first material are mixed according to R2/R1 ⁇ 2, R2/R1 ⁇ 5, and R2/R1 ⁇ 10.

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Abstract

本申请实施例提供一种正极极片、电池及用电装置，涉及电池领域。正极极片包括集流体和设置于集流体的至少一侧表面的活性材料层，活性材料层包括至少两层子层，混合活性材料层中，正极活性材料包括第一正极活性材料和第二正极活性材料，第二正极活性材料的收缩率T2大于第一正极活性材料的收缩率T1，且T2-T1≥0.3％，且第一正极活性材料或第二正极活性材料的占比为混合活性材料层中的正极活性材料总质量的55％～95％。该正极极片能够改善电池的动力学性能。

Description

正极极片、电池及用电装置 技术领域
本申请涉及电池领域，具体涉及一种正极极片、电池及用电装置。
背景技术
节能减排是汽车产业可持续发展的关键，电动车辆由于其节能环保的优势成为汽车产业可持续发展的重要组成部分。对于电动车辆而言，电池技术又是关乎其发展的一项重要因素。
基于两种正极活性材料混合制作的正极活性材料层，相对于单一活性材料的正极活性材料层，能量密度或者安全性能等有一定的优化改善。
发明内容
本申请的发明人发现，收缩率差异较大的正极活性材料按照相近用量混合后，整个电池的动力学性能较差。本申请提供一种正极极片、电池及用电装置，能够改善电池的动力学性能。
第一方面，本申请提供了一种正极极片，包括集流体和设置于所述集流体的至少一侧表面的活性材料层，所述活性材料层包括至少一层混合活性材料层；所述混合活性材料层中，正极活性材料包括第一正极活性材料和第二正极活性材料，所述第二正极活性材料的收缩率T2大于所述第一正极活性材料的收缩率T1，且T2-T1≥0.3％，第一正极活性材料或第二正极活性材料的占比为所述混合活性材料层中的正极活性材料总质量的55％～95％。
本申请实施例的技术方案中，其中的混合活性材料层主要含有两类不同的正极活性材料混用搭配：一类是小收缩率的正极活性材料(收缩率为T1)，另一类是大收缩率的正极活性材料(收缩率为T2)。混合活性材料层的两类正极活性材料之间存在一定程度的收缩率差异，且大收缩率的正极活性材料或小收缩率的正极活性材料的质量占比较大，如此降低了收缩率差异较大且含量相近的材料混合在同一层中，导致的动力学性能较差的问题。
在一些实施例中，混合活性材料层中，第一正极活性材料或第二正极活性材料的占比为正极活性材料总质量的65％～80％。大收缩率的正极活性材料或小收缩率的正极活性材料的质量占比较大，降低了收缩率差异较大且含量相近的材料混合在同一层中导致的动力学性能较差的问题。
在一些实施例中，T1的取值范围为0.3％-5.5％，T2的取值范围为1％-7％。通过对正极活性材料选择、配合，实现对两类正极活性材料的收缩率进行差异化调整。
在一些实施例中，T1的取值范围为0.5％-4％，T2的取值范围为3％-6.5％。
在一些实施例中，第二正极活性材料的平均粒径R2大于第一正极活性材料的平均粒径R1，且R2/R1≥2，可选地，100≥R2/R1≥5，可选地，100≥R2/R1≥10。将大收缩率、大平均粒径的第二正极活性材料和小收缩率、小平均粒径的第一正极活性材料混合，形成混合活性材料层有利于提升电池的能量密度，同时，相比于将粒径差异较大的活性材料按照相近用量同时放在同一层中进行混合，本实施例的方案能够进一步提高电池的动力学性能。
在一些实施例中，所述活性材料层包括至少两层子层，其中至少一层所述子层为所述混合活性材料层。
在一些实施例中，相邻设置的两层所述子层分别为第一混合活性材料层和第二混合活性材料层，所述第一混合活性材料层中的所述第一正极活性材料的收缩率为T1，所述第二正极活性材料的收缩率为T2，T2-T1≥0.3％，所述第二混合活性材料层中的正极活性材料包括第三正极活性材料和第四正极活性材料，所述第三正极活性材料的收缩率为T1’，所述第四正极活性材料的收缩率为T2’，T2’-T1’≥0.3％。活性材料层进行了分层，而且其中至少相邻的两层均为混合活性材料层，也是本申请可包含的实施方式，能够改善动力学性能较差的问题。
在一些实施例中，T2和T1’的差值不大于1％，和/或，T2’和T1的差值不大于1％。若两层混合活性材料层的正极活性材料的收缩率差值太大，界面接触不好，影响动力学性能。
在一些实施例中，第一混合活性材料层相比所述第二混合活性材料层更靠近所述集流体，所述T2-T1的值小于所述T2’-T1’的值。
在一些实施例中，相邻设置的两层子层中的一层为混合活性材料层，另一层为单活性材料层，单活性材料层的正极活性材料包括第一正极活性材料或第二正极活性材料。由于第一正极活性材料和第二正极活性材料的收缩率差异较大，将第一正极活性材料或第二正极活性材料单独设置，能够提高整个活性物质层的动力学性能。
在一些实施例中，单活性材料层比混合活性材料层更靠近集流体。单活性材料层与集流体接触，减小因第一正极活性材料和第二正极活性材料的收缩率差异较大导致活性材料层和集流体接触不好的问题。
在一些实施例中，单活性材料层的正极活性材料包括第一正极活性材料。本实施例为一种可替代方案，能够改善动力学性能较差的问题。
在一些实施例中，混合活性材料层中含有线性导电剂；可选地，混合活性材料层中，长度≥1μm的线性导电剂的质量占比为0.2％～1％；可选地，线性导电剂包括碳纳米管、碳纤维和线状石墨烯中的至少一种。在混合活性材料层中加入一定比例的线性导电物质，分散在不同正极活性材料周围，降低充放电过程中两类正极活性材料因收缩率差异带来的相互分离而造成的导电网络恶化，起到连接导通作用，在不同类的正极活性材料的接触界面变化时，保持导电网络稳定。
在一些实施例中，活性材料层包括至少两层子层，相邻的两层子层中，远离集流体一侧的子层的孔隙率≥30％，邻近集流体一侧的子层的孔隙率≥50％；
可选地，远离集流体一侧的子层的孔隙率≥50％，邻近集流体一侧的子层的孔隙率≥60％。活性材料层中，远离集流体一侧的子层接触电解液充足，邻近集流体一侧的子层接触电解液量少，通过不同子层的孔隙率设置不同，能够使电解液在不同子层内均充分浸润。
第二方面，本申请提供了一种电池，包括负极极片和第一方面提供的正极极片组成的电芯。
第三方面，本申请提供了一种用电装置，包括根据第二方面提供的电池。
上述说明仅是本申请技术方案的概述，为了能够更清楚了解本申请的技术手段，而可依照说明书的内容予以实施，并且为了让本申请的上述和其它目的、特征和优点能够更明显易懂，以下特举本申请的具体实施方式。
附图说明
通过阅读对下文优选实施方式的详细描述，各种其他的优点和益处对于本领域普通技术人员将变得清楚明了。附图仅用于示出优选实施方式的目的，而并不认为是对本申请的限制。而且在全部附图中，用相同的附图标号表示相同的部件。在附图中：
图1为本申请一些实施例的车辆的结构示意图；
图2位本申请一些实施例的电池的分解结构示意图；
图3为本申请一些实施例提供的电池单体的结构示意图；
图4为本申请一些实施例的电池单体的分解结构示意图。
图标：1000-车辆；100-电池；10-箱体；11-容纳空间；12-第一部分；13-第二部分；20-电池单体；21-外壳；211-开口；22-端盖组件；221-端盖；222-电极端子；23-电极组件；24-集流构件；25-绝缘保护件；200-控制器；300-马达。
具体实施方式
下面将结合附图对本申请技术方案的实施例进行详细的描述。以下实施例仅用于更加清楚地说明本申请的技术方案，因此只作为示例，而不能以此来限制本申请的保护范围。
除非另有定义，本文所使用的所有的技术和科学术语与属于本申请的技术领域的技术人员通常理解的含义相同；本文中所使用的术语只是为了描述具体的实施例的目的，不是旨在于限制本申请；本申请的说明书和权利要求书及上述附图说明中的术语“包括”和“具有”以及它们的任何变形，意图在于覆盖不排他的包含。
在本申请实施例的描述中，技术术语“第一”“第二”等仅用于区别不同对象，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量、特定顺序或主次关系。在本申请实施例的描述中，“多个”的含义是两个以上，除非另有明确具体的限定。
在本文中提及“实施例”意味着，结合实施例描述的特定特征、结构或特性可以包含在本申请的至少一个实施例中。在说明书中的各个位置出现该短语并不一定均是指相同的实施例，也不是与其它实施例互斥的独立的或备选的实施例。本领域技术人员显式地和隐式地理解的是，本文所描述的实施例可以与其它实施例相结合。
在本申请实施例的描述中，术语“和/或”仅仅是一种描述关联对象的关联关系，表示可以存在三种关系，例如A和/或B，可以表示：单独存在A，同时存在A和B，单独存在B这三种情况。另外，本文中字符“/”，一般表示前后关联对象是一种“或”的关系。
在本申请实施例的描述中，技术术语“厚度”、“上”、“下”、“前”、“后”“顶”、“底”、“内”、“外”等指示的方位或位置关系为基于附图所示的方位或位置关系，仅是为了便于描述本申请实施例和简化描述，而不是指示或暗示所指的装置或元件必须具有特定的方位、以特定的方位构造和操作，因此不能理解为对本申请实施例的限制。
在本申请实施例的描述中，除非另有明确的规定和限定，技术术语“连接”、“固定”等术语应做广义理解，例如，可以是固定连接，也可以是可拆卸连接，或成一体；也可以是机械连接，也可以是电连接；可以是直接相连，也可以通过中间媒介间接相连，可以是两个元件内部的连通或两个元件的相互作用关系。对于本领域的普通技术人员而言，可以根据具体情况理解上述术语在本申请实施例中的具体含义。
目前，从市场形势的发展来看，动力电池的应用越加广泛。动力电池不仅被应用于水力、火力、风力和太阳能电站等储能电源系统，而且还被广泛应用于电动自行车、电动摩托车、电动汽车等电动交通工具，以及军事装备和航空航天等多个领域。随着动力电池应用领域的不断扩大，其市场的需求量也在不断地扩增。
动力电池可以是锂离子电池，在锂离子电池充电过程中，锂离子从正极活性物质脱出，通过电解液进行传输，经过隔离膜，嵌入负极活性物质。目前，基于不同正极活性材料混合制作的正极活性材料层，相对于单一活性材料的正极活性材料层，能量密度或安全性能等方面有提升，但是，发明人发现收缩率差异较大的正极活性材料按照相近用量混合后，整个电池的动力学性能依旧较差。另外，基于磷酸锰铁锂和三元材料进行分层的正极极片，相对于单一活性物质的正极极片，动力学性能也有一定的优化改善，但这种分层的正极极片中单层的活性物质单一，无法发挥分层涂布的全部优势。并且，这种以材料种类为标准区分上下层，视角单一，限制了分层技术的应用范围。
基于以上考虑，为了解决混合制作的活性材料层的性能提升受到限制的问题，设计了一种正极极片，通过对锂离子电池正极极片进行精细的结构化设计，提供明确的正极极片设计原则和设计依据，改善电池的动力学性能，提升电池的循环寿命。
本申请实施例公开的电池单体可以但不限用于车辆、船舶或飞行器等用电装置中。
本申请实施例提供一种使用电池作为电源的用电装置，用电装置可以为但不限于手机、平板、笔记本电脑、电动玩具、电动工具、电瓶车、电动汽车、轮船、航天器等等。其中，电动玩具可以包括固定式或移动式的电动玩具，例如，游戏机、电动汽车玩具、电动轮船玩具和电动飞机玩具等等，航天器可以包括飞机、火箭、航天飞机和宇宙飞船等等。
以下实施例为了方便说明，以本申请一实施例的一种用电装置为车辆1000为例进行说明。
请参照图1，图1为本申请一些实施例提供的车辆1000的结构示意图。车辆1000的内部设置有电池100，电池100可以设置在车辆1000的底部或头部或尾部。电池100可以用于车辆1000的供电，例如，电池100可以作为车辆1000的操作电源。
车辆1000还可以包括控制器200和马达300，控制器200用来控制电池100为马达300供电，例如，用于车辆1000的启动、导航和行驶时的工作用电需求。
在本申请一些实施例中，电池100不仅仅可以作为车辆1000的操作电源，还可以作为车辆1000的驱动电源，代替或部分地代替燃油或天然气为车辆1000提供驱动动力。
图2为本申请一些实施例提供的电池100的分解结构示意图。请参阅图2，电池100包括箱体10和电池单体20，电池单体20收容于箱体10内。
箱体10用于为电池单体20提供容纳空间11。在一些实施例中，箱体10可以包括第一部分12和第二部分13，第一部分12与第二部分13相互盖合，以限定出用于容纳电池单体20的容纳空间11。当然，第一部分12与第二部分13的连接处可通过密封件(图未示出)来实现密封，密封件可以是密封圈、密封胶等。
第一部分12和第二部分13可以是多种形状，比如，长方体、圆柱体等。第一部分12可以是一侧开口以形成有容纳电池单体20的容纳腔的空心结构，第二部分13也可以是一侧开口以形成有容纳电池单体20的容纳腔的空心结构，第二部分13的开口侧盖合于第一部分12的开口侧，则形成具有容纳空间11的箱体10。当然，如图2所示，也可以是第一部分12为一侧开口的空心结构，第二部分13为板状结构，第二部分13盖合于第一部分12的开口侧，则形成具有容纳空间11的箱体10。
在电池100中，电池单体20可以是一个、也可以是多个。若电池单体20为多个，多个电池单体20之间可串联或并联或混联，混联是指多个电池单体20中既有串联又有并联。多个电池单体20之间可直接串联或并联或混联在一起，再将多个电池单体20构成的整体容纳于箱体10内；当然，也可以是多个电池单体20先串联或并联或混联组成电池模块，多个电池模块再串联或并联或混联形成一个整体，并容纳于箱体10内。电池单体20可呈圆柱体、扁平体、长方体或其它形状等。图2示例性的示出了电池单体20呈方形的情况。
在一些实施例中，电池100还可以包括汇流部件(图未示出)，多个电池单体20之间可通过汇流部件实现电连接，以实现多个电池单体20的串联或并联或混联。
图3为本申请一些实施例提供的电池单体20的结构示意图，图4为本申请一些实施例提供的电池单体20的爆炸图。请参阅图3和图4，电池单体20可以包括外壳21、端盖组件22和电极组件23。外壳21具有开口211，电极组件23容纳于外壳21内，端盖组件22用于封盖于开口211。
外壳21的形状可根据电极组件23的具体形状来确定。比如，若电极组件23为长方体结构，外壳21则可选用长方体结构。图3和图4示例性的示出了外壳21和电极组件23为方形的情况。
外壳21的材质也可以是多种，比如，铜、铁、铝、不锈钢、铝合金等，本申请实施例对此不作特殊限制。
端盖组件22包括端盖221和电极端子222。端盖组件22用于封盖外壳21的开口211，以形成一密闭的安装空间(图未示出)，安装空间用于容纳电极组件23。安装空间还用于容纳电解质，例如电解液。端盖组件22作为输出电极组件23的电能的部件，端盖组件22中的电极端子222用于与电极组件23电连接，即电极端子222与电极组件23的极耳电连接，比如，电极端子222与极耳通过集流构件24连接，以实现电极端子222与极耳的电连接。
需要说明的，外壳21的开口211可以是一个，也可以是两个。若外壳21的开口211为一个，端盖组件22也可以为一个，端盖组件22中则可设置两个电极端子222，两个电极端子222分别用于与电极组件23正极极耳和负极极耳电连接。若外壳21的开口211为两个，比如，两个开口211设置在外壳21相对的两侧，端盖组件22也可以为两个，两个端盖组件22分别盖合于外壳21的两个开口211处。在这种情况下，可以是一个端盖组件22中的电极端子222为正极电极端子，用于与电极组件23的正极极耳电连接；另一个端盖组件22中的电极端子222为负极电极端子，用于与电极组件23的负极片电连接。
在一些实施例中，如图4所示，电池单体20还可以包括固定于电极组件23外周的绝缘保护件25，绝缘保护件25用于绝缘隔离电极组件23与外壳21。示例性的，绝缘保护件25为粘接于电极组件23的外周的胶带。在一些实施例中，电极组件23的数量为多个，绝缘保护件25围设于多个电极组件23的外周，并将多个电极组件23形成一个整体结构，以保持电极组件23结构稳定。
根据本申请的一些实施例，正极极片包括集流体和设置于集流体的至少一侧表面的活性材料层，活性材料层包括至少一层混合活性材料层；混合活性材料层中，正极活性材料包括第一正极活性材料和第二正极活性材料，第二正极活性材料的收缩率T2大于第一正极活性材料的收缩率T1，且T2-T1≥0.3％，第一正极活性材料或第二正极活性材料的占比为混合活性材料层中的正极活性材料总质量的55％～95％，相应地，第二正极活性材料或第一正极活性材料占比为正极活性材料总质量的5％～45％。
本申请中的收缩率(膨胀率)是指正极活性材料在充放电过程中的体积膨胀变化程度，正极活性材料收缩率测试方法为：将某种正极活性材料作为唯一正极活性材料形成新鲜极片，其中的活性材料层是将正极活性材料、粘结剂PVDF、导电剂按照97wt％:1.5wt％:1.5wt％的质量比混合形成。通过扫描电镜拍摄电池满充状态和满放状态下的活性材料层截面图片(沿垂直于集流体表面的方向，切割活性材料层，对断面做扫面电镜拍摄)，计算正极材料在满充状态下的粒径为L1和满放状态下的粒径L2，正极材料的收缩率为L1-L2/L2。粒径L1或L2的计算方法为：取图片中的20个颗粒，测量20个颗粒的粒径，取平均值，即为粒径值。
正极活性材料的收缩率是材料本身的属性，通过对正极活性材料的组成进行特定选择，能够获得具有特定收缩率的正极活性材料。
本申请中的一些实施例中，集流体和活性材料层之间还可以设置其他层，比如粘接层。
根据本申请的一些实施例，混合活性材料层中，第一正极活性材料或第二正极活性材料的占比为正极活性材料总质量的65％～80％，第二正极活性材料或第一正极活性材料的占比为正极活性材料总质量的20％～35％。作为示例性地，第二正极活性材料的占比可以为正极活性材料总质量的65％、70％、75％或80％，也可以为上述两个数值范围内的任意值；第一正极活性材料的占比可以为正极活性材料总质量的20％、25％、30％或35％，也可以为上述两个数值范围内的任意值。或者，第一正极活性材料的占比可以为正极活性材料总质量的65％、70％、75％或80％，也可以为上述两个数值范围内的任意值；第二正极活性材料的占比可以为正极活性材料总质量的20％、25％、30％或35％，也可以为上述两个数值范围内的任意值。
根据本申请的一些实施例，T1的取值范围为0.3％-5.5％，T2的取值范围为1％-7％。
根据本申请的一些实施例，T1的取值范围为0.5％-4％，T2的取值范围为3％-6.5％，可选地，T2-T1≥1％。
示例性地，T1可以为0.3％、0.5％、1％、2％、3％、4％、4.5％或5.5％，或上述两个数值之间的任意值；T2可以为1％、2％、3％、4％、5％、6％、2.5％、6.5％或7％，或上述两个数值之间的任意值。
第一正极活性材料可以是一种正极活性材料，也可以包含两种甚至更多种不同收缩率的正极活性材料，每种正极活性材料的收缩率均满足与第二正极活性材料的收缩率差值要求，第一正极活性材料中的正极活性材料之间的收缩率差值为0～0.5％，示例性地，第一正极活性材料之间的收缩率差异可以为0、0.1％、0.2％、0.3％、0.4％或0.5％。
同样地，第二正极活性材料可以是一种正极活性材料，也可以包含两种甚至更多种不同收缩率的正极活性材料，每种正极活性材料的收缩率满足与第二正极活性材料的收缩率差值要求，第二正极活性材料中的正极活性材料之间的收缩率差值为0～1％，示例性地，第二正极活性材料之间的收缩率差异可以为0、0.1％、0.2％、0.3％、0.4％、0.5％、0.6％、0.7％、0.8％或1％。
作为一种实施方式，第一正极活性材料包含收缩率为T1a的正极活性材料和收缩率为T1b的正极活性材料，第二正极活性材料包含收缩率为T2a的正极活性材料和收缩率为T2b的正极活性材料，T2b≥T2a>T1b≥T1a，且T2a-T1b≥0.3％。T1b-T1a的差值为0～0.5％，T2b-T2a的差值为0～1％。可选地，第一正极活性材料为一种正极活性材料，T1a＝T1b，该第一正极活性材料的收缩率可认为是唯一值，第二正极活性材料为一种正极活性材料，T2a＝T2b，该第二正极活性材料的收缩率可认为是唯一值。
根据本申请的一些实施例，混合活性材料层中，第一正极活性材料和第二正极活性材料的质量之和为正极活性材料总质量的90％～100％；可选地，第一正极活性材料和第二正极活性材料的质量之和为正极活性材料总质量的95％～100％；可选地，混合活性材料中，第一正极活性材料和第二正极活性材料的质量之和为正极活性材料总质量的98％～100％。示例性地，第一正极活性材料和第二正极活性材料的质量之和可以为正极活性材料总质量的90％、92％、95％、96％、97％、98％、99％或100％，也可以为上述两个数值范围内的任意值。
混合活性材料层中，小收缩率的第一正极活性材料(T1)或大收缩率的第二正极活性材料(T2)的占比在55％以上，这两类正极活性材料的总占比达到90％以上，可以允许少量收缩率在T1～T2之间的正极活性材料存在。
根据本申请的一些实施例，第二正极活性材料的平均粒径R2大于第一正极活性材料的平均粒径R1，且R2/R1≥2，可选为100≥R2/R1≥5，可选为100≥R2/R1≥10，R1可以为0.1μm～0.4μm之间的任意值，R2可以为1μm～20μm之间的任意值。
根据本申请的一些实施例，活性材料层包括至少两层子层，其中至少一层子层为混合活性材料层。
通过对锂离子电池正极极片进行结构化设计，得到分层优化的正极极片，不同收缩率的正极活性材料按照一定质量比例搭配，有利于极片动力学及寿命的提升。
在本申请的一些实施例中，相邻设置的两层子层分别为第一混合活性材料层和第二混合活性材料层，第一混合活性材料层中的第一正极活性材料的收缩率为T1，第二正极活性材料的收缩率为T2，T2-T1≥0.3％，第二混合活性材料层中的正极活性材料包括第三正极活性材料和第四正极活性材料，第三正极活性材料的收缩率为T1’，第四正极活性材料的收缩率为T2’，T2’-T1’≥0.3％。
本申请中的活性材料层为分层结构，指活性材料层包括具有明显分界线的两层子层或多层子层，分界线是指相邻两层子层的组成不同，在接触位置所形成的划分线，相邻的两层相接触的位置可能存在交叉，即形成过渡层。示例性地，两层子层具有不同的正极活性材料，比如相邻的两层子层中收缩率较大的第二正极活性材料是不同的物质，相邻的两层子层中收缩率较小的第一正极活性材料是不同的物质；或者，两层子层中正极活性材料的比例存在不同，比如相邻的两层子层中收缩率较大的第二正极活性材料的占比不同。
分界线一侧的第一混合活性材料层包含在充放电过程中小收缩率的第一正极活性材料(T1)和大收缩率的第二正极活性材料(T2)，T2-T1≥0.3％，且小收缩率的第一正极活性材料(T1)或大收缩率的第二正极活性材料(T2)质量占比较大，占比为第一混合活性材料层中的正极活性材料总质量的55％～95％；分界线另一侧的第二混合活性材料层也包含在充放电过程中小收缩率的第三正极活性材料(T1’)和大收缩率的第四正极活性材料(T2’)，T2’-T1’≥0.3％，且小收缩率的第三正极活性材料(T1’)或大收缩率的第四正极活性材料(T2’)质量占比较大，占比为第二混合活性材料层中的正极活性材料总质量的55％～95％。
对于两层混合活性材料层中的大收缩率的第二正极活性材料，可以是相同的物质，也可以是不同的物质，对于两层混合活性材料层中的小收缩率的第一正极活性物质，可以是相同的物质，也可以是不同的物质。
可根据性能设计需求调整，充分发挥分层设计的优势。
在本申请的一些实施例中，T2和T1’的差值不大于1％，和/或，T2’和T1的差值不大于1％。作为一种可替代方案，两层混合活性材料层的正极活性材料的收缩率差异较小。
在本申请的一些实施例中，第一混合活性材料层相比第二混合活性材料层更靠近集流体，T2-T1的值小于T2’-T1’的值。可选地，同一侧的混合活性材料层的T2与T1的差值从邻近至远离集流体的方向逐渐增大。通过不同位置的混合活性材料层的T2与T1的差值设置成不同，充分发挥分层设计的优势。
在本申请的一些实施例中，相邻设置的两层子层分别为混合活性材料层和单活性材料层，单活性材料层的正极活性材料包括第一正极活性材料或第二正极活性材料，且第一正极活性材料或第二正极活性材料的质量为正极活性材料总质量的90％～100％。
分界线一侧的混合活性材料层包含在充放电过程中小收缩率的第一正极活性材料(T1)和大收缩率的第二正极活性材料(T2)，且小收缩率的第一正极活性材料(T1)或大收缩率的第二正极活性材料(T2)质量占比较大；分界线另一侧的单活性材料层的正极活性材料包含第一正极活性材料或第二正极活性材料(T1或T2)，可根据性能设计需求调整，充分发挥分层设计的优势。
在本申请的一些实施例中，单活性材料层中，第一正极活性材料或第二正极活性材料的质量为正极活性材料总质量的95％～100％；可选地，第一正极活性材料或第二正极活性材料的质量为正极活性材料总质量的98％～100％。示例性地，单活性材料层中的第一正极活性材料或第二正极活性材料的质量之和可以为正极活性材料总质量的95％、96％、97％、98％、99％或100％，也可以为上述两个数值范围内的任意值。
在本申请的一些实施例中，单活性材料层比混合活性材料层更靠近集流体。
在本申请的一些实施例中，单活性材料层的正极活性材料包括第一正极活性材料。
在本申请的一些实施例中，集流体的两侧分别设置有活性材料层；可选地，集流体两侧的活性材料层关于集流体对称。所有的子层关于集流体对称设置，相对称的两层的子层的材质、厚度完全相同。
在一些实施例中，正极活性材料选自于镍钴锰酸锂(NCM)、镍钴铝酸锂(NCA)、四元材料(NCMA)、磷酸铁锂(LFP)、磷酸锰铁锂(LMFP)、改性掺杂的磷酸锰铁锂、锂钴氧化物(LCO)、锂锰氧化物(LMO)、富锂正极材料(Li-rich cathode)和镍锰酸锂以及以上材料的掺杂或包覆材料中的至少一种。
在本申请的一些实施例中，第一正极活性材料包括尖晶石结构正极材料或者橄榄石结构正极材料中的至少一种。
第一正极活性材料包括尖晶石结构正极材料或者橄榄石结构正极材料中的至少一种，易于获得较小收缩率的正极活性材料层。
在本申请一些实施方式中，第一正极活性材料包括Li1+xMn1-yAyP1-zRzO4，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包括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B、S、Si和N中的一种或多种元素。
化合物Li1+xMn1-yAyP1-zRzO4可以购买市售产品，也可以按照以下制备方法制得，化合物Li1+xMn1-yAyP1-zRzO4的制备方法可以包括以下步骤：
(1)将锰源、锰位掺杂的元素A源和酸在溶剂中溶解并搅拌，生成掺杂元素A的锰盐的悬浊液，将悬浊液过滤并烘干滤饼，得到掺杂了元素A的锰盐；
(2)将锂源、磷源和元素R源、溶剂和由步骤(1)获得的掺杂了元素A的锰盐加入反应容器中研磨并混合，得到浆料；
(3)将由步骤(2)获得的浆料转移到喷雾干燥设备中进行喷雾干燥造粒，得到颗粒；
(4)将由步骤(3)获得的颗粒进行烧结，得到正极活性材料。
在任意实施方式中，锰源可为本领域已知的可用于制备磷酸锰锂的含锰物质，例如锰源可选自单质锰、二氧化锰、磷酸锰、草酸锰、碳酸锰中的一种或它们的组合。
酸选自盐酸、硫酸、硝酸、磷酸、有机酸如草酸等中的一种或多种，例如可为草酸。元素R源选自元素R的硫酸盐、硼酸盐、硝酸盐和硅酸盐中的至少一种。元素A源选自A的单质、氧化物、磷酸盐、草酸盐、碳酸盐和硫酸盐中的至少一种。
进一步地，在本申请一些实施方式中，第一正极活性材料包括LiaAeMn1-fBfP1-gCgO4-nDn；
其中，A包括Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素；
B包括Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素；
C包括B、S、Si和N中的一种或多种元素；
D包括S、F、Cl和Br中的一种或多种元素；
a选自0.9至1.1的范围，e选自0.001至0.1的范围，f选自0.001至0.5的范围，g选自0.001至0.1的范围，n选自0.001至0.1的范围，并且第一正极活性材料为电中性的。
需要说明的是，LiaAxMn1-yByP1-zCzO4-nDn化合物实际为一种具体的LiMPO4材料，其制备方法可参考Li1+xMn1-yAyP1-zRzO4，在此不做限定。
第二正极活性材料包括层状结构正极材料，易于获得较大收缩率的正极活性材料层。
进一步地，在本申请一些实施方式中，第二正极活性材料包括三元材料镍钴锰酸锂、三元材料镍钴铝酸锂或者掺杂改性三元材料中的至少一种。
进一步地，在本申请一些实施方式中，上述的掺杂改性三元材料的化学式包括LiNimCoiMnkA1-m-i-kO2，其中0.5≤m≤0.98，0.02≤i≤0.18，0≤k≤0.35。
在一些实施例中，混合活性材料层中含有线性导电剂(长径比大于1)；可选地，混合活性材料层中，长度≥1μm的线性导电剂的质量占比为0.2％～1％；可选地，线性导电剂包括碳纳米管、碳纤维和线状石墨烯中的至少一种。混合活性材料层含有一定比例的线性导电物质维护导电网络的稳定。
在一些实施例中，活性材料层包括至少两层子层，相邻的两层子层中，远离集流体一侧的子层的孔隙率≥30％，邻近集流体一侧的子层的孔隙率≥50％；可选地，远离集流体一侧的子层的孔隙率≥50％，邻近集流体一侧的子层的孔隙率≥60％。
孔隙率是指活性材料层未经过充放电时，内部本身存在的孔隙体积占比，根据本申请的实施例，孔隙率可以通过气体置换法进行确定，具体的，根据本申请的实施例，可以参考GB/T 24586-2009，通过下列步骤确定：将极片浸渍于碳酸二甲酯(DMC)中清洗并晾干，若为新鲜极片则无需清洗。将样品装入样品杯，记录样品数计算表观体积，将样品置于真密度测试仪，利用气体置换法测定真体积。极片孔隙率即为极片中的孔体积占极片总体积的百分比，计算公式：孔隙率＝(V-V0)/V×100％，其中V0为真体积，V为表观体积；表观体积V＝S*H*A，S为极片表面积，H为极片厚度，A为极片样品数。
可选地，相邻的两层子层中，远离集流体一侧的子层的孔隙率可以为30％、40％、50％、60％或70％，邻近集流体一侧的子层的孔隙率可以为50％、55％、60％、65％、70％或75％。
在一些实施例中，子层中正极活性材料的质量比例为89.0％～98.0％。
在一些实施方式中，正极极片的子层均通过包括上述符合设计原则的正极活性材料、导电剂和粘结剂的正极浆料制备得到，子层中正极活性物质占子层总质量的89.0％～98.0％，导电剂占正极极片总质量的0.4％～5.0％，粘结剂占正极极片总质量的0.6％-7.0％。
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。
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。
为满足实际生产需求，每层子层涂布面积1540.25mm2的涂布重量最小为50mg，一般为50-200mg。
在一些实施方式中，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，例如正极活性材料、导电剂、粘结剂和任意其他的组分分散于溶剂(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。
根据本申请的一些实施例，本申请还提供了一种电池，包括负极极片、隔离膜和上述提供的正极极片组成的电芯。电池包括单体电池、电池模组、电池包中的任意一种形式。
[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。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。
[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。
[电解质]
电池单体还包括电解质，电解质在正极极片和负极极片之间起到传导离子的作用。电解质可以是液态的或凝胶态的。
在一些实施方式中，电解质采用电解液。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，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。
根据本申请的一些实施例，本申请提供了一种用电装置，包括根据上述提供的电池单体或上述提供的电池。
接下来参照下面的示例更详细地描述一个或多个实施例。当然，这些示例并不限制一个或多个实施例的范围。
实验中所采用的正极活性材料中，第一材料均为LiMn1-y1-y2Fey1Tiy2P1-zSizO4，其中，y1+y2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，且不同收缩率的材料组成略微不同；第二材料均为Li1.00NimCoiMnkO2，其中0.5≤m≤0.98，0.02≤i≤0.18，0≤k≤0.35，
m+i+k＝1，且不同收缩率的材料组成略微不同。
下面列举了一些正极活性材料的制备方法及来源以更好地对本申请进行说明。
【第一材料】
A、化合物LiMn0.22Fe0.78PO4的制备方法包括：
步骤S1：制备Fe掺杂的草酸锰
将252.9g碳酸锰和903.7g碳酸亚铁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，得到草酸锰铁颗粒。
步骤S2：制备LiMn0.22Fe0.78PO4
取步骤S1中制备的草酸锰铁(以C2O4Mn0.22Fe0.78·2H2O计)1791.4g以及369.4g碳酸锂和1150.1g磷酸二氢铵，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。
碳包覆LiMn0.22Fe0.78PO4的制备方法包括：
取步骤S1中制备的草酸锰铁(以C2O4Mn0.22Fe0.78·2H2O计)1791.4g以及369.4g碳酸锂和1150.1g磷酸二氢铵，以及0.005mol蔗糖，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。
其他未掺杂的磷酸锰铁锂材料的制备步骤与前述化合物A制备步骤相同，区别仅在于改变碳酸锰和碳酸亚铁的含量，使其满足对应化合物的化学式中的锰和铁的摩尔比即可。
也可以直接通过市售购买。
B、化合物Li1.001Mn0.999Fe0.001P0.999Si0.001O4的制备方法包括：
步骤S1：制备Fe掺杂的草酸锰
将1148.2g碳酸锰和1.2g碳酸亚铁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，得到草酸锰铁颗粒。
步骤S2：制备Li1.001Mn0.999Fe0.001P0.999Si0.001O4
取步骤S1中制备的草酸锰铁(以C2O4Mn0.999Fe0.001·2H2O计)1789.6g以及369.8g碳酸锂、1148.9g磷酸二氢铵和0.8g亚硅酸，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。
掺杂其他元素(如Ti)的磷酸锰铁锂材料的制备步骤与前述化合物B制备步骤相同，区别仅在于替换亚硅酸为对应元素的来源(如四氯化钛)，并调整原料配比使其满足对应化合物的化学式中的摩尔比即可。
也可以直接通过市售购买获得。
【第二材料】
层状结构正极材料通过市售购买获得。
实施例1
(1)制备正极极片
将正极活性材料、粘结剂PVDF、导电剂炭黑按照97wt％:1.5wt％:1.5wt％的质量比混合，并分散于N-甲基吡咯烷酮中，正极活性材料分为第一材料和第二材料，第一材料的平均粒径为0.2μm，第二材料的平均粒径为1μm，第一材料为Li1.00Mn0.36Fe0.64PO4，其收缩率T1为2.5％，第二材料为Li1.00Ni0.59Co0.14Mn0.27O2，其收缩率T2为3％，第一材料和第二材料的质量比例为35％：65％，制成正极活性物质浆料A1。
将正极活性物质浆料A1涂覆在铝箔两侧表面，涂覆重量为200mg/1540.25mm2，得到正极极片。
(2)制备锂离子二次电池
锂离子二次电池用正极极片、负极极片、隔膜和电解液这几种主材和铝壳和顶盖等机械件构成，正极极片的压度为2.35，厚度为213μm；负极材料的负极活性材料、粘接剂、导电剂及其含量分别为：96.5％石墨+1.3％SBR+1.1CMC％+0.4％SP，压密为1.65，厚度为142μm；电解液的溶剂、电解液添加剂、锂盐及其含量分别为：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LiPF6均匀溶解在上述溶液中，得到电解液。该电解液中，LiPF6的浓度为1mol/L。具体是将正极极片、负极极片和隔膜形成裸电芯，裸电芯进行绝缘包覆后装入铝壳，焊接顶盖得到干电芯；将干电芯进行烘烤后注入电解液，进行化成和老化，得到硬壳电池。
实施例2
(1)制备正极极片
将正极活性材料、粘结剂PVDF、导电剂炭黑按照97wt％:1.5wt％:1.5wt％的质量比混合，并分散于N-甲基吡咯烷酮中，正极活性材料分为第一材料和第二材料，第一材料的平均粒径为0.2μm，第二材料的平均粒径为1μm，第一材料为Li1.00Mn0.36Fe0.64PO4，其收缩率T1为2.5％，第二材料为Li1.00Ni0.59Co0.14Mn0.27O2，其收缩率T2为3％，第一材料和第二材料的质量比例为35％：65％，制成正极活性物质浆料A1。
将正极活性材料、粘结剂PVDF、导电剂炭黑按照97wt％:1.5wt％:1.5wt％的质量比混合，并分散于N-甲基吡咯烷酮中，正极活性材料分为第一材料和第二材料，第一材料的平均粒径为0.2μm，第二材料的平均粒径为1μm，第一材料为Li1.001Mn0.999Fe0.001P0.999Si0.001O4，其收缩率T1’为3.2％，第二材料为Li1.00Ni0.82Co0.12Mn0.06O2，其收缩率T2’为5％，第一材料和第二材料的质量比例为35％：65％，制成正极活性物质浆料A2。
将正极活性物质浆料A1涂覆在铝箔两侧表面，涂覆重量为100mg/1540.25mm2，将正极活性物质浆料A2涂覆在上述已经涂有正极活性物质浆料A1的正极表面，涂覆重量为100mg/1540.25mm2，得到正极极片。
(2)制备锂离子二次电池
锂离子二次电池用正极极片、负极极片、隔膜和电解液这几种主材和铝壳和顶盖等机械件构成，正极极片的压度为2.35，厚度为213μm；负极材料的负极活性材料、粘接剂、导电剂及其含量分别为：96.5％石墨+1.3％SBR+1.1CMC％+0.4％SP，压密为1.65，厚度为142μm；电解液的溶剂、电解液添加剂、锂盐及其含量分别为：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LiPF6均匀溶解在上述溶液中，得到电解液。该电解液中，LiPF6的浓度为1mol/L。具体是将正极极片、负极极片和隔膜形成裸电芯，裸电芯进行绝缘包覆后装入铝壳，焊接顶盖得到干电芯；将干电芯进行烘烤后注入电解液，进行化成和老化，得到硬壳电池。
实施例3
除了步骤(1)中形成正极活性物质浆料A1的第一材料和第二材料的质量比例为5％：95％，形成正极活性物质浆料A2的第一材料和第二材料的质量比例为5％：95％，其他与实施例2相同。
实施例4
除了步骤(1)中形成正极活性物质浆料A1的第一材料和第二材料的质量比例为35％：65％，形成正极活性物质浆料A2的第一材料和第二材料的质量比例为5％：95％，其他与实施例2相同。
实施例5
除了步骤(1)中形成正极活性物质浆料A2的第一材料为Li1.00Mn0.36Fe0.64PO4，其收缩率T1’为2.5％，第二材料为Li1.00Ni0.59Co0.14Mn0.27O2，其收缩率T2’为3％(第一材料和第二材料的选用与正极活性物质浆料A1中的材料相同)，但第一材料和第二材料的质量比例为20％：80％，其他与实施例2相同。
实施例6
除了步骤(1)中形成正极活性物质浆料A1的第一材料为Li1.00Mn0.36Fe0.64PO4，其收缩率T1为2.5％，第二材料为Li1.00Ni0.59Co0.14Mn0.27O2，其收缩率T2为3％，形成正极活性物质浆料A2的第一材料为Li1.00Mn0.36Fe0.64PO4，其收缩率T1’为2.5％，第二材料为Li1.00Ni0.82Co0.12Mn0.06O2，其收缩率T2’为5％，其他与实施例2相同。
实施例7
除了步骤(1)中形成正极活性物质浆料A1的第一材料为Li1.00Mn0.77Fe0.20Ti0.03PO4，其收缩率T1为4.5％，第二材料为Li1.00Ni0.89Co0.07Mn0.04O2，其收缩率T2为6.5％，形成正极活性物质浆料A2的第一材料为Li1.00Mn0.22Fe0.78PO4，其收缩率T1’为0.3％，第二材料为Li1.00Ni0.89Co0.07Mn0.04O2，其收缩率T2’为6.5％，其他与实施例2相同。
实施例8
除了步骤(1)中，形成正极活性物质浆料A2的第一材料和第二处材料的质量比例为65％：35％，其他与实施例2相同。
实施例9
除了步骤(1)中将正极活性物质浆料A2涂覆在铝箔两侧表面，同时，将正极活性物质浆料A1涂覆在上述已经涂有正极活性物质浆料A2的正极表面，即本实施例中的A1为实施例1中的A2，本实施例中的A2为实施例1中的A2，得到正极极片，其他与实施例2相同。
实施例10
除了步骤(1)中，将正极活性材料、粘结剂PVDF、导电剂炭黑按照97wt％:1.5wt％:1.5wt％的质量比混合，并分散于N-甲基吡咯烷酮中，正极活性材料分为第一材料和第二材料，第一材料为Li1.00Mn0.36Fe0.64PO4，其收缩率T1*为2.5％，第二材料为Li1.00Ni0.82Co0.12Mn0.06O2，其收缩率T2*为5％，第一材料和第二材料的质量比例为35％：65％，制成正极活性物质浆料A3。
将正极活性物质浆料A1涂覆在铝箔两侧表面，涂覆重量为70mg/1540.25mm2，将正极活性物质浆料A2涂覆在上述已经涂有正极活性物质浆料A1的正极表面，涂覆重量为 70mg/1540.25mm2，将正极活性物质浆料A3涂覆在上述已经涂有正极活性物质浆料A2的正极表面，涂覆重量为60mg/1540.25mm2，得到正极极片。
其他与实施例2相同。
实施例11
除了步骤(1)中，形成正极活性物质浆料A1的第一材料为Li1.00Mn0.36Fe0.64PO4，其收缩率T1为2.5％，第二材料分为第二材料a和第二材料b，第二材料a为Li1.00Ni0.59Co0.14Mn0.27O2，其收缩率T2a为3％，第二材料b为Li1.00Ni0.82Co0.12Mn0.06O2，其收缩率T2b为5％，第一材料和第二材料的质量比例为35％：(30％+35％)；
形成正极活性物质浆料A2采用与上述正极活性物质浆料A2相同的材料，但第一材料和第二材料的质量比例为40％：(40％+20％)。
其他与实施例2相同。
实施例12
除了步骤(1)中形成正极活性物质浆料A2的正极活性材料为形成正极活性物质浆料A1所采用的第一材料，其他与实施例2相同。
实施例13
除了步骤(1)中形成正极活性物质浆料A2的正极活性材料为形成正极活性物质浆料A1所采用的第二材料，其他与实施例2相同。
实施例14
除了步骤(1)中形成正极活性物质浆料A1的第一材料和第二材料的质量比例为65％：35％，其他与实施例1相同。
实施例15
除了步骤(1)中形成正极活性物质浆料A1的第一材料和第二材料的质量比例为65％：35％，形成正极活性物质浆料A2的第一材料和第二材料的质量比例为65％：35％，其他与实施例2相同。
实施例16
除了步骤(1)中形成正极活性物质浆料A1的第一材料的平均粒径为0.5μm，第二材料的平均粒径为1μm，其他与实施例1相同。
实施例17
除了步骤(1)中形成正极活性物质浆料A1的第一材料的平均粒径为0.2μm，第二材料的平均粒径为2μm，其他与实施例1相同。
对比例1
除了步骤(1)中，形成正极活性物质浆料A1的第一材料和第二处材料的质量比例为50％：50％，形成正极活性物质浆料A2的第一材料和第二处材料的质量比例为50％：50％，其他与实施例2相同。
对比例2
除了步骤(1)中，形成正极活性物质浆料A1的第一材料和第二处材料的质量比例为50％：50％，其他与实施例1相同。
为了证明膨胀率对电池性能的影响，实施例1～15和对比例1～2中所采用的所有第一材料的平均粒径均为0.2μm，所有第二材料的平均粒径均为1μm，将实施例1～13和对比例1～2所得的硬壳电池进行循环测试：
在25℃的恒温环境下，将全电池按照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1C放电至2.5V，记录此时的放电容量为D0，阻抗为X0。重复前述充放电循环500圈，记录最后一次的放电容量为D1，阻抗为X1，计算容量保持率为D1/D0×100％，阻抗增长率为(D1-D0)/D0×100％。
检测得到的电池的性能如表1所示：
表1电池的性能

结合表1的结果可知：
与对比例1～2相比，实施例1～15的正极极片的活性材料层至少含有一层大收缩率、小收缩率的正极活性材料按照大收缩率材料或小收缩率材料大质量占比形成的混合正极材料层，能够有效改善电池的动力学性能，在电池多次循环使用后，提高电池的容量保持率和降低电池的阻抗增长，即改善电池的动力学性能。
与对比例2相比，实施例1的正极极片活性材料层为一层大收缩率、小收缩率的正极活性材料按照高低质量比例形成的混合正极材料层，能够显著改善电池的动力学性能。实施例14的活性材料层为一层小收缩率、大收缩率的正极活性材料按照高低质量比例形成的混合正极材料层，也能够改善电池的动力学性能。
与对比例1的正极极片中活性材料层为分层的结构相比，实施例8的正极极片有一层满足大收缩率、小收缩率的正极活性材料的收缩率差值要求，且大收缩率的正极活性材料大占比，能够改善电池的动力学性能，实施例2的正极极片两层均满足大收缩率、小收缩率的正极活性材料的收 缩率差值要求，且大收缩率的正极活性材料大占比，能够明显改善电池的动力学性能。实施例15的正极极片的活性材料层分层设置，且每层均为小收缩率、大收缩率的正极活性材料按照高低质量比例形成的混合正极材料层，也能够改善电池动力学性能。
与对比例1相比，实施例2～5的正极极片中设置有两层混合正极材料层，混合正极材料层的正极活性材料中大收缩率的正极活性材料的质量占比为55％～95％，可选为65％～80％时，能够在电池多次循环使用后，提高电池的容量保持率和降低电池的阻抗增长。
与实施例9相比，实施例2的正极极片中邻近集流体一侧的混合活性材料层中大收缩率、小收缩率的正极活性材料的收缩率差值比远离集流体一侧的收缩率差值更小，能够提高电池的容量保持率和降低电池的阻抗增长。
与对比例1相比，实施例10的正极极片采用多层混合正极材料层，实施例11的正极极片的每层混合正极材料层采用多种正极活性材料，且大收缩率的正极活性材料大占比，均能够提高电池的容量保持率和降低电池的阻抗增长。
与对比例1相比，实施例12～13的正极极片设置相邻的混合活性材料层和仅有一类正极活性材料的单活性材料层，单活性材料层的正极活性材料为混合活性材料层中的一类正极活性材料，能够在电池多次循环使用后，提高电池的容量保持率和降低电池的阻抗增长，即改善电池的动力学性能。
实施例1和实施例16～17、对比例2中所采用的所有第一材料相同，收缩率为2.5％，所有第二材料相同，收缩率为3％，区别在于第一材料的平均粒径R1和第二材料的平均粒径R2不完全相同，或者第一材料和第二材料的质量比例不同。采用上述相同的方法对实施例16～17所得的硬壳电池进行循环测试，检测得到的电池的性能如表2所示：
表2电池的性能
结合表2的结果可知：
混合活性层中的正极活性材料采用大收缩率的第二材料、小收缩率的第一材料选用，且第二材料的平均粒径(R2)和第一材料的平均粒径(R1)按照R2/R1≥2混合，可选R2/R1≥5，可选R2/R1≥10，能够在电池多次循环使用后，提高电池的容量保持率和降低电池的阻抗增长，即改善电池的动力学性能。
以上所描述的实施例是本申请一部分实施例，而不是全部的实施例。本申请的实施例的详细描述并非旨在限制要求保护的本申请的范围，而是仅仅表示本申请的选定实施例。基于本申请中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。

Claims (16)

  1. 一种正极极片，其特征在于，包括集流体和设置于所述集流体的至少一侧表面的活性材料层，所述活性材料层包括至少一层混合活性材料层；所述混合活性材料层中，正极活性材料包括第一正极活性材料和第二正极活性材料，所述第二正极活性材料的收缩率T2大于所述第一正极活性材料的收缩率T1，且T2-T1≥0.3％，所述第一正极活性材料或所述第二正极活性材料的占比为所述混合活性材料层中的正极活性材料总质量的55％～95％。
  2. 根据权利要求1所述的正极极片，其特征在于，所述混合活性材料层中，所述第一正极活性材料或所述第二正极活性材料的占比为所述正极活性材料总质量的65％～80％。
  3. 根据权利要求1或2所述的正极极片，其特征在于，所述T1的取值范围为0.3％-5.5％，所述T2的取值范围为1％-7％。
  4. 根据权利要求1～3任一项所述的正极极片，其特征在于，所述T1的取值范围为0.5％-4％，所述T2的取值范围为3％-6.5％。
  5. 根据权利要求1～4任一项所述的正极极片，其特征在于，所述第二正极活性材料的平均粒径R2大于所述第一正极活性材料的平均粒径R1，且R2/R1≥2，可选地，100≥R2/R1≥5，可选地，100≥R2/R1≥10。
  6. 根据权利要求1～5任一项所述的正极极片，其特征在于，所述活性材料层包括至少两层子层，其中至少一层所述子层为所述混合活性材料层。
  7. 根据权利要求6所述的正极极片，其特征在于，相邻设置的两层所述子层分别为第一混合活性材料层和第二混合活性材料层，所述第一混合活性材料层中的所述第一正极活性材料的收缩率为T1，所述第二正极活性材料的收缩率为T2，T2-T1≥0.3％，所述第二混合活性材料层中的正极活性材料包括第三正极活性材料和第四正极活性材料，所述第三正极活性材料的收缩率为T1’，所述第四正极活性材料的收缩率为T2’，T2’-T1’≥0.3％。
  8. 根据权利要求7所述的正极极片，其特征在于，T2和T1’的差值不大于1％，和/或，T2’和T1的差值不大于1％。
  9. 根据权利要求7所述的正极极片，其特征在于，所述第一混合活性材料层相比所述第二混合活性材料层更靠近所述集流体，所述T2-T1的值小于所述T2’-T1’的值。
  10. 根据权利要求6所述的正极极片，其特征在于，相邻设置的两层所述子层中的一层为所述混合活性材料层，另一层为单活性材料层，所述单活性材料层的正极活性材料包括所述第一正极活性材料或所述第二正极活性材料。
  11. 根据权利要求10所述的正极极片，其特征在于，所述单活性材料层比所述混合活性材料层更靠近所述集流体。
  12. 根据权利要求10所述的正极极片，其特征在于，所述单活性材料层的正极活性材料包括所述第一正极活性材料。
  13. 根据权利要求6所述的正极极片，其特征在于，所述混合活性材料层中含有线性导电剂；可选地，所述混合活性材料层中，长度≥1μm的所述线性导电剂的质量占比为0.2％～1％；可选地，所述线性导电剂包括碳纳米管、碳纤维和线状石墨烯中的至少一种。
  14. 根据权利要求6所述的正极极片，其特征在于，相邻的两层所述子层中，远离所述集流体一侧的所述子层的孔隙率≥30％，邻近所述集流体一侧的所述子层的孔隙率≥50％；
    可选地，远离所述集流体一侧的所述子层的孔隙率≥50％，邻近所述集流体一侧的所述子层的孔隙率≥60％。
  15. 一种电池，其特征在于，包括如权利要求1～14任一项所述的正极极片组成的电芯。
  16. 一种用电装置，其特征在于，包括根据权利要求15所述的电池。
PCT/CN2023/095341 2023-05-19 2023-05-19 正极极片、电池及用电装置 Ceased WO2024239157A1 (zh)

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