CN110556538B - Positive plate and lithium ion battery - Google Patents

Positive plate and lithium ion battery Download PDF

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Publication number
CN110556538B
CN110556538B CN201810558165.9A CN201810558165A CN110556538B CN 110556538 B CN110556538 B CN 110556538B CN 201810558165 A CN201810558165 A CN 201810558165A CN 110556538 B CN110556538 B CN 110556538B
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positive electrode
equal
positive
active material
lithium ion
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CN110556538A (en
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孟焕平
杜锐
柳娜
闫传苗
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Contemporary Amperex Technology Co Ltd
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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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • 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
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/665—Composites
    • H01M4/667—Composites in the form of layers, e.g. coatings
    • 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

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  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
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  • Composite Materials (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Secondary Cells (AREA)

Abstract

The application provides a positive plate and a lithium ion battery. The positive plate comprises a positive current collector and a positive diaphragm, wherein the positive diaphragm is arranged on the positive current collector and comprises a first positive material layer and a second positive material layer. The first positive electrode material layer is arranged on the positive electrode current collector and comprises a first positive electrode active material, and the first positive electrode active material is a ternary positive electrode material; the second positive electrode material layer is arranged on the first positive electrode material layer and comprises a second positive electrode active material, and the second positive electrode active material is selected from one or more of olivine lithium-containing phosphate and spinel lithium manganate. The total reversible capacity of the first positive electrode active material is a in unit area of the positive electrode diaphragm, the total reversible capacity of the second positive electrode active material is b in unit area of the positive electrode diaphragm, and a/b is more than or equal to 1 and less than or equal to 30. The high-temperature cycle performance and the safety performance of the lithium ion battery can be improved, and the lithium ion battery is ensured to have higher energy density.

Description

Positive plate and lithium ion battery
Technical Field
The application relates to the field of batteries, in particular to a positive plate and a lithium ion battery.
Background
Energy crisis and haze cause new energy car's demand and development more and more urgent for too littly, pure electric new energy car replaces traditional gasoline car gradually and becomes the inevitable trend of developing now, and the new energy car is also more and more prominent to the high requirement of power battery yet. For example, a high-quality new energy vehicle requires a lithium ion battery to have higher energy density, so that the new energy vehicle is ensured to have longer cruising mileage; the high-quality new energy vehicle also requires that the lithium ion battery has better cycle performance so as to ensure that the new energy vehicle has longer service life; the requirement of high-quality new energy vehicles on safety performance is more severe, and thermal runaway of lithium ion batteries during abuse needs to be avoided; lithium ion batteries are also expected to have lower manufacturing costs for high quality new energy vehicles.
The positive active material has attracted general attention of research and development workers as one of key factors influencing the energy density of the lithium ion battery, and currently, lithium iron phosphate is widely used as the positive active material in the market, but the energy density of the lithium iron phosphate cannot meet the requirements of new energy vehicles, so that research and development of the positive active material with high capacity, long service life, safety and low cost is not only necessary but also urgent.
When the ternary cathode material is used for improving the energy density of the lithium ion battery, a high-voltage electrolyte matched with the ternary cathode material needs to be developed at the same time, the cost of a relatively high-voltage-resistant organic solvent and an electrolyte additive in the market is high, and the potential safety hazard of the lithium ion battery under high voltage is greatly improved. Another method for improving the energy density of the lithium ion battery is to improve the nickel (Ni) content of the ternary cathode material, but the high-nickel ternary cathode material inevitably has the problems of high cost, serious gas generation, high potential safety hazard and the like. In order to improve the safety performance of the high-nickel ternary cathode material, a generally applicable method is also used for mixing a low-nickel ternary cathode material or a high-nickel ternary material with a cathode active material with good relative safety such as lithium iron phosphate and the like, but the method can achieve the purpose of improving the safety performance of the lithium ion battery only by mixing a high-content low-nickel ternary cathode material or lithium iron phosphate. Meanwhile, the lithium iron phosphate can also reduce the working voltage of the lithium ion battery, so that the energy density of the lithium ion battery is greatly reduced; the relatively high cobalt (Co) content of low-nickel ternary cathode materials increases the manufacturing cost of lithium ion batteries.
Disclosure of Invention
In view of the problems in the background art, an object of the present application is to provide a positive electrode sheet and a lithium ion battery, which can improve the high-temperature cycle performance and the safety performance of the lithium ion battery, and ensure that the lithium ion battery using the positive electrode sheet has a higher energy density.
In order to achieve the above object, in a first aspect of the present application, the present application provides a positive plate, which includes a positive current collector and a positive diaphragm, wherein the positive diaphragm is disposed on the positive current collector and includes a first positive material layer and a second positive material layer. The first positive electrode material layer is arranged on the positive electrode current collector and comprises a first positive electrode active material, and the first positive electrode active material is a ternary positive electrode material; the second positive electrode material layer is arranged on the first positive electrode material layer and comprises a second positive electrode active material, and the second positive electrode active material is selected from one or more of olivine lithium-containing phosphate and spinel lithium manganate. The total reversible capacity of the first positive electrode active material is a in unit area of the positive electrode diaphragm, the total reversible capacity of the second positive electrode active material is b in unit area of the positive electrode diaphragm, and a/b is more than or equal to 1 and less than or equal to 30.
In a second aspect of the present application, there is provided a lithium ion battery comprising the positive electrode sheet according to the first aspect of the present application.
Compared with the prior art, the invention at least comprises the following beneficial effects:
the utility model provides an anode plate regards ternary cathode material as the inlayer of anode diaphragm, contain the outer of lithium phosphate and/or spinel type lithium manganate as the anode diaphragm with olivine type, and carry out the capacity matching through the total reversible capacity to first anode active material and second anode active material on the unit area of anode diaphragm, utilize the characteristics that second anode active material stable in structure is high, the security is good, can be under the prerequisite that does not influence lithium ion battery high capacity demand, play and effectively improve the problem that first anode active material oxidability is strong, the thermal stability is poor, the easy thermal runaway of extreme condition (especially in the nail penetration, overcharge), and full play the advantage of first anode active material high energy density.
The positive plate carries out capacity matching through the total reversible capacity of the first positive active material and the second positive active material on the unit area of the positive plate, and can also ensure that the heat generated by the first positive active material in the using process can be effectively isolated, so that the high-temperature cycle performance and the safety performance of the lithium ion battery are well improved.
According to the lithium ion battery positive plate, the first positive active material and the second positive active material are subjected to particle size collocation and component collocation, and the positive plate with higher compaction density and higher safety can be obtained, so that the energy density of the lithium ion battery is further improved, and the high-temperature cycle performance and the safety performance of the lithium ion battery are further improved.
Detailed Description
The positive electrode sheet and the lithium ion battery according to the present application will be described in detail below.
The positive electrode sheet according to the first aspect of the present application is first explained.
The positive plate according to the first aspect of the present application includes a positive current collector and a positive diaphragm, the positive diaphragm set up in on the positive current collector and including a first positive material layer and a second positive material layer. The first positive electrode material layer is arranged on the positive electrode current collector and comprises a first positive electrode active material, and the first positive electrode active material is a ternary positive electrode material; the second positive electrode material layer is arranged on the first positive electrode material layer and comprises a second positive electrode active material, and the second positive electrode active material is selected from one or more of olivine lithium-containing phosphate and spinel lithium manganate. The total reversible capacity of the first positive electrode active material is a in unit area of the positive electrode diaphragm, the total reversible capacity of the second positive electrode active material is b in unit area of the positive electrode diaphragm, and a/b is more than or equal to 1 and less than or equal to 30.
In the positive plate according to the first aspect of the present application, the olivine lithium-containing phosphate and/or spinel lithium manganate is used as the outer layer of the positive plate, and the ternary positive material is used as the inner layer of the positive plate, so that the direct contact between the electrolyte and the ternary positive material can be isolated, the thermal stability of the whole positive plate can be improved, the side reaction between the electrolyte and the ternary positive material can be reduced, and the advantage of high energy density of the ternary positive material can be fully exerted; the olivine lithium-containing phosphate or spinel lithium manganate has high thermal stability and structural stability, has small volume change in the using process, can bear higher cold pressing pressure when used as the outer layer of the anode diaphragm, and then the obtained anode diaphragm not only has better thermal stability and structural stability but also has higher compaction density, and the lithium ion battery also can have higher energy density. In addition, through reasonably controlling the relation between the total reversible capacity a of the first anode active material and the total reversible capacity b of the second anode active material on the unit area of the anode diaphragm, the heat generated by the ternary anode material in the using process can be effectively isolated, and the lithium ion battery is further ensured to have higher safety performance and longer cycle service life.
Wherein the total reversible capacity a of the first positive electrode active material per unit area of the positive electrode membrane is the reversible gram capacity of the first positive electrode active material x the total mass of the first positive electrode active material per unit area of the positive electrode membrane; the total reversible capacity b of the second positive electrode active material per unit area of the positive electrode sheet is equal to the reversible gram capacity of the second positive electrode active material × the total mass of the second positive electrode active material per unit area of the positive electrode sheet.
Preferably, 1. ltoreq. a/b. ltoreq.12.
In the positive electrode sheet according to the first aspect of the present application, the ternary positive electrode material is selected from Lix1Ni1-y1-z1- a1Coy1Mnz1M1a1O2、Lix2Ni1-y2-z2-a2Coy2Alz2M2a2O2And one or more of composite materials obtained by coating and modifying the materials. Wherein x1 is more than or equal to 0.95 and less than or equal to 1.05, y1 is more than 0 and less than or equal to 0.2, z1 is more than or equal to 0 and less than or equal to 0.2, a1 is more than or equal to 0 and less than or equal to 0.05, and M1 is selected from one or more of Ti, Al, Zr, Mg, Zn, Ba, Mo and B; x2 is more than or equal to 0.95 and less than or equal to 1.05, y2 is more than 0 and less than or equal to 0.1, z2 is more than 0 and less than or equal to 0.1, a2 is more than or equal to 0 and less than or equal to 0.05, and M2 is selected from one or more of Ti, Mn, Zr, Mg, Zn, Ba, Mo and B.
Preferably, 0 < y1+ z1+ a1 ≦ 0.4, 0 < y2+ z2+ a2 ≦ 0.4.
The surface of the ternary cathode material is coated and modified, the coating layer can further play a role in isolating the direct contact between the electrolyte and the ternary cathode material, the side reaction between the electrolyte and the ternary cathode material can be reduced to a great extent, and transition metal is reducedDissolving out, and improving the electrochemical stability of the ternary cathode material. The coating layer can be a carbon layer, a graphene layer, an oxide layer, an inorganic salt layer or a conductive polymer layer. Preferably, the oxide can be an oxide formed by one or more elements of Al, Ti, Mn, Zr, Mg, Zn, Ba, Mo and B; the inorganic salt may be Li2ZrO3、LiNbO3、Li4Ti5O12、Li2TiO3、Li3VO4、LiSnO3、Li2SiO3、LiAlO2One or more of the above; the conductive polymer may be polypyrrole (PPy), poly 3, 4-ethylenedioxythiophene (PEDOT) or Polyamide (PI).
In the positive electrode sheet according to the first aspect of the present application, the olivine-type lithium-containing phosphate has a general formula of LiFe1-x3-y3Mnx3M’y3PO4X3 is more than or equal to 0 and less than or equal to 1, y3 is more than or equal to 0 and less than or equal to 0.1, x3+ y3 is more than or equal to 0 and less than or equal to 1, and M' is selected from one or more of transition metal elements except Fe and Mn and non-transition metal elements.
Preferably, the olivine-type lithium-containing phosphate is selected from LiFePO4、LiMnPO4、LiMn1-x3Fex3PO40 < x3 < 1.
In the positive electrode sheet according to the first aspect of the present application, the first positive electrode active material is a mixture of a ternary positive electrode material having a single crystal particle structure and a ternary positive electrode material having a secondary particle structure, the olivine-type lithium-containing phosphate has a single crystal particle structure, and the spinel-type lithium manganate has a single crystal particle structure.
The ternary anode material has higher specific discharge capacity and is the first choice of the high-energy-density lithium ion battery. The ternary positive electrode material with the secondary particle structure has low direct current impedance and good cycle performance, but the bonding force between primary particles agglomerated into secondary particles is not strong, and the primary particles are easy to break in the cold pressing process of the positive electrode plate, so that the performance exertion of the lithium ion battery is influenced. The ternary cathode material with the single crystal particle structure has a complete crystal structure, the crushing resistance strength and the thermal stability of the particles are superior to those of the ternary cathode material with the secondary particle structure, and the average size of the single crystal particles of the ternary cathode material is usually lower than that of the secondary particles, so that when the ternary cathode material with the secondary particle structure and the ternary cathode material with the single crystal particle structure are mixed for use, gaps among the secondary particles in the cold pressing process of the cathode plate can be occupied by the single crystal particles, the compaction density of the cathode plate is greatly improved, and the energy density of the lithium ion battery is improved. Meanwhile, under the same cold pressing pressure, the pressure born by the mixed secondary particles and single crystal particles is smaller than that born by the single use of the secondary particles or the single crystal particles, and then each particle can have a relatively larger volume expansion space in the high-temperature circulation process, so that the lithium ion battery has higher thermal stability and better high-temperature circulation performance.
The olivine type lithium-containing phosphate has a single crystal particle structure, and compared with a polycrystalline particle structure, the olivine type lithium-containing phosphate has a more stable crystal structure, higher stability of lithium ions during the process of extraction and insertion, and smaller resistance of the lithium ions during the process of extraction and insertion, and can improve the safety performance of the lithium ion battery on the basis of not influencing the dynamic performance of the lithium ion battery. In addition, the lithium-containing phosphate having a single crystal grain structure has a smaller grain size than that of the lithium-containing phosphate having a polycrystalline grain structure, and thus formation of a miscible diffusion layer described later is facilitated.
Spinel type lithium manganate is also a single crystal particle structure, and compared with a polycrystalline particle structure, the lithium manganate crystal structure of single crystal particles is more stable, the stability of lithium ions during extraction and insertion is higher, and the resistance of the lithium ions during extraction and insertion is smaller, so that the safety performance of the lithium ion battery can be improved on the basis of not influencing the dynamic performance of the lithium ion battery. In addition, the lithium manganate with a single crystal particle structure has a smaller particle size than that of the lithium manganate with a polycrystalline particle structure, so that the formation of a mutual soluble diffusion layer described later is facilitated.
Preferably, the mass ratio of the ternary cathode material with the single-crystal particle structure to the ternary cathode material with the secondary particle structure is 1: 9-5: 5.
Preferably, the particle size D50 of the ternary cathode material with the single crystal particle structure is 1-5 μm.
Preferably, the particle diameter D50 of the ternary cathode material with the secondary particle structure is 5-20 μm.
Preferably, the particle size D50 of the olivine lithium-containing phosphate is 0.5 to 2 μm.
Preferably, the particle size D50 of the spinel type lithium manganate is 0.5-2 μm.
Preferably, the morphology of the ternary cathode material with the secondary particle structure can be spherical or spheroidal.
In the positive electrode sheet according to the first aspect of the present application, in order to avoid the delamination of the first positive electrode material layer and the second positive electrode material layer during coating and cold pressing, it is preferable that the particle size D50 of the olivine lithium-containing phosphate is smaller than the particle size D50 of the single crystal grain structured ternary positive electrode material, and the particle size D50 of the spinel lithium manganate is smaller than the particle size D50 of the single crystal grain structured ternary positive electrode material.
In the positive electrode sheet according to the first aspect of the present application, the positive electrode sheet further includes a mutual solution diffusion layer, which is disposed between the first positive electrode material layer and the second positive electrode material layer, and is formed by mutual solution diffusion between the first positive electrode material layer and the second positive electrode material layer. The existence of the mutual soluble diffusion layer can obviously improve the compatibility between the first anode material layer and the second anode material layer, improve the binding force between the first anode material layer and the second anode material layer, and avoid the second anode material layer from falling off from the first anode material layer, thereby further improving the performance of the lithium ion battery. However, if the proportion of the mutual soluble diffusion layer to the total thickness of the positive plate is too high, the thickness of the second positive electrode material layer containing only the high-stability second positive electrode active material is reduced, and under the conditions of nailing, overcharging and the like, the heat generated by the first positive electrode active material in the recycling process cannot be effectively isolated, so that the effects of inhibiting the side reaction of the electrolyte on the surface of the positive plate and controlling the temperature rise are not obvious.
Preferably, the thickness of the mutual soluble diffusion layer is 1/2000-1/12 of the total thickness of the positive electrode plate.
More preferably, the thickness of the miscible diffusion layer is 1/200-1/30 of the total thickness of the positive electrode sheet.
In the positive electrode sheet according to the first aspect of the present application, the first positive electrode material layer further includes a conductive agent and a binder, and the types of the conductive agent and the binder are not particularly limited and may be selected according to actual needs. Preferably, the conductive agent can be selected from one or more of conductive graphite, carbon black, carbon nanotubes and graphene, and the binder can be selected from polyvinylidene fluoride.
In the positive electrode sheet according to the first aspect of the present application, the second positive electrode material layer further includes a conductive agent and a binder, and the types of the conductive agent and the binder are not particularly limited and may be selected according to actual needs. Preferably, the conductive agent can be selected from one or more of conductive graphite, carbon black, carbon nanotubes and graphene, and the binder can be selected from polyvinylidene fluoride.
The types of the conductive agent and the binder in the first positive electrode material layer and the types of the conductive agent and the binder in the second positive electrode material layer may be the same or different, and may be selected according to actual needs.
Next, a lithium ion battery according to a second aspect of the present application will be described.
A lithium ion battery according to a second aspect of the present application includes the positive electrode sheet according to the first aspect of the present application.
In the lithium ion battery according to the second aspect of the present application, the lithium ion battery further includes a negative electrode sheet, a separator, an electrolyte solution, and the like. The types of the negative electrode sheet, the separator and the electrolyte are not particularly limited and may be selected according to actual requirements.
The present application is further illustrated below with reference to examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present application.
Example 1
(1) Preparation of positive plate
LiNi of secondary particle structure0.8Co0.12Mn0.08O2And LiNi of single crystal grain structure0.8Co0.12Mn0.08O2A second one formed by mixing according to the mass ratio of 7:3Uniformly mixing a positive electrode active material, a binding agent polyvinylidene fluoride (PVDF) and a conductive agent conductive carbon (Super-P), adding a solvent N-methylpyrrolidone (NMP), and uniformly stirring to obtain a first positive electrode slurry. Wherein the solid mass ratio of the first positive electrode active material, Super-P and PVDF is 95:2.5:2.5, and LiNi is in a secondary particle structure0.8Co0.12Mn0.08O2Has a particle diameter of 11 μm and has a single crystal grain structure0.8Co0.12Mn0.08O2Has a particle diameter of 3 μm, and the solid content of the first positive electrode slurry was 70%.
Olivine-type lithium iron phosphate (LiFePO)4) Uniformly mixing the anode slurry with a binder polyvinylidene fluoride (PVDF) and a conductive agent conductive carbon (Super-P), adding a solvent N-methylpyrrolidone (NMP), and uniformly stirring to obtain a second anode slurry. Wherein LiFePO4The mass ratio of the solids of the Super-P and the PVDF is 95:2.5:2.5, the solid content of the second anode slurry is 70%, and the LiFePO is4Particle diameter of (3) is 1.5. mu.m.
And simultaneously coating the first positive electrode slurry and the second positive electrode slurry on an aluminum foil current collector with the thickness of 16 microns in a one-step coating mode, standing, drying, cold pressing and cutting into pieces to obtain the positive plate.
Wherein the compaction density of the positive plate is 3.14g/cm3And by controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry, the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material in unit area of the final positive electrode membrane is 3.2:1, and the standing time, the drying temperature and the cold pressing pressure of the first positive electrode slurry and the second positive electrode slurry are reasonably controlled, so that the thickness of the mutual soluble diffusion layer is 1/105 of the total thickness of the positive electrode membrane.
(2) Preparation of negative plate
Fully stirring and dispersing graphite serving as a negative electrode active material, a conductive agent Super-P, sodium carboxymethyl cellulose serving as a thickening agent and styrene butadiene rubber serving as an adhesive in solvent purified water, uniformly mixing to obtain negative electrode slurry, uniformly coating the negative electrode slurry on a copper foil current collector, and baking, cold pressing and cutting into pieces to obtain a negative electrode piece, wherein the mass ratio of the graphite to the Super-P to the sodium carboxymethyl cellulose to the styrene butadiene rubber is 96:1.2:1.2: 1.6.
(3) Preparation of the electrolyte
The organic solvent is a mixed solution of Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and diethyl carbonate (DEC), wherein the volume ratio of EC, EMC and DEC is 20:20: 60. At water content<In a 10ppm argon atmosphere glove box, a well dried lithium salt (LiPF)6) Dissolving in the organic solvent, and mixing to obtain electrolyte, wherein the electrolyte contains LiPF6The concentration of (2) is 1 mol/L.
(4) Preparation of the separator
A single layer Polyethylene (PE) film was selected as the barrier film.
(5) Preparation of lithium ion battery
And (3) preparing the positive plate, the negative plate and the isolating membrane into a battery cell in a winding mode, then filling the battery cell into an aluminum-plastic bag, removing a solvent through hot-pressing reshaping and baking, then injecting an electrolyte, welding and sealing, and then carrying out formation and aging processes to obtain the lithium ion battery.
Example 2
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
The first positive electrode active material is composed of LiNi of a secondary particle structure0.8Co0.12Mn0.08O2And LiNi of single crystal grain structure0.8Co0.12Mn0.08O2Mixing according to the mass ratio of 8: 2;
the compacted density of the positive plate is 3.11g/cm3；
Controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry to enable the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material to be 3.2:1 in unit area of the final positive electrode membrane;
and reasonably controlling the standing time, the drying temperature and the cold pressing pressure of the first anode slurry and the second anode slurry to enable the thickness of the mutual soluble diffusion layer to be 1/110 of the total thickness of the anode plate.
Example 3
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
The first positive electrode active material is composed of LiNi of a secondary particle structure0.8Co0.12Mn0.08O2And LiNi of single crystal grain structure0.8Co0.12Mn0.08O2Mixing according to the mass ratio of 9: 1;
the compacted density of the positive plate is 3.00g/cm3；
Controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry to enable the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material to be 3.2:1 in unit area of the final positive electrode membrane;
and reasonably controlling the standing time, the drying temperature and the cold pressing pressure of the first anode slurry and the second anode slurry to enable the thickness of the mutual soluble diffusion layer to be 1/200 of the total thickness of the anode plate.
Example 4
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
The first positive electrode active material is composed of LiNi of a secondary particle structure0.8Co0.12Mn0.08O2And LiNi of single crystal grain structure0.8Co0.12Mn0.08O2Mixing according to the mass ratio of 6: 4;
the compacted density of the positive plate is 3.18g/cm3；
Controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry to enable the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material to be 3.2:1 in unit area of the final positive electrode membrane;
and reasonably controlling the standing time, the drying temperature and the cold pressing pressure of the first anode slurry and the second anode slurry to enable the thickness of the mutual soluble diffusion layer to be 1/150 of the total thickness of the anode plate.
Example 5
The first positive electrode active material is composed of LiNi of a secondary particle structure0.8Co0.12Mn0.08O2And single crystal grain structureLiNi of (2)0.8Co0.12Mn0.08O2Mixing according to the mass ratio of 5: 5;
the compacted density of the positive plate is 3.20g/cm3；
Controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry to enable the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material to be 3.2:1 in unit area of the final positive electrode membrane;
and reasonably controlling the standing time, the drying temperature and the cold pressing pressure of the first anode slurry and the second anode slurry to enable the thickness of the mutual soluble diffusion layer to be 1/100 of the total thickness of the anode plate.
Example 6
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
The first positive electrode active material is composed of LiNi of a secondary particle structure0.8Co0.12Mn0.07Zr0.01O2And LiNi of single crystal grain structure0.8Co0.12Mn0.07Zr0.01O2Mixing according to the mass ratio of 7: 3;
the compacted density of the positive plate is 3.20g/cm3；
Controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry to enable the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material to be 3.2:1 in unit area of the final positive electrode membrane;
and reasonably controlling the standing time, the drying temperature and the cold pressing pressure of the first anode slurry and the second anode slurry to enable the thickness of the mutual soluble diffusion layer to be 1/90 of the total thickness of the anode plate.
Example 7
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
The first positive electrode active material is composed of a secondary particle structure, Al2O3Coated LiNi0.8Co0.12Mn0.07Zr0.01O2And single crystal grain structure、Al2O3Coated LiNi0.8Co0.12Mn0.07Zr0.01O2Mixing according to the mass ratio of 7: 3;
the compacted density of the positive plate is 3.30g/cm3；
Controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry to enable the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material to be 3.2:1 in unit area of the final positive electrode membrane;
and reasonably controlling the standing time, the drying temperature and the cold pressing pressure of the first anode slurry and the second anode slurry to enable the thickness of the mutual soluble diffusion layer to be 1/90 of the total thickness of the anode plate.
Example 8
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
The first positive electrode active material is composed of a secondary particle structure, Al2O3Coated LiNi0.8Co0.12Mn0.07Zr0.01O2And single crystal grain structure, Al2O3Coated LiNi0.8Co0.12Mn0.07Zr0.01O2Mixing according to the mass ratio of 7: 3;
the compacted density of the positive plate is 2.77g/cm3；
Controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry to enable the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material to be 1.4:1 in unit area of the final positive electrode membrane;
and reasonably controlling the standing time, the drying temperature and the cold pressing pressure of the first anode slurry and the second anode slurry to enable the thickness of the mutual soluble diffusion layer to be 1/90 of the total thickness of the anode plate.
Example 9
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
The first positive electrode active material is composed of a secondary particle structure, Al2O3Coated LiNi0.8Co0.12Mn0.07Zr0.01O2And single crystal grain structure, Al2O3Coated LiNi0.8Co0.12Mn0.07Zr0.01O2Mixing according to the mass ratio of 7: 3;
the compacted density of the positive plate is 3.30g/cm3；
Controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry to enable the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material to be 12:1 in unit area of the final positive electrode membrane;
and reasonably controlling the standing time, the drying temperature and the cold pressing pressure of the first anode slurry and the second anode slurry to enable the thickness of the mutual soluble diffusion layer to be 1/90 of the total thickness of the anode plate.
Example 10
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
Replacing olivine-type lithium iron phosphate with spinel-type lithium manganate;
the compacted density of the positive plate is 3.25g/cm3；
Controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry to enable the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material on the unit area of the final positive electrode membrane to be 3.7: 1;
and reasonably controlling the standing time, the drying temperature and the cold pressing pressure of the first anode slurry and the second anode slurry to enable the thickness of the mutual soluble diffusion layer to be 1/90 of the total thickness of the anode plate.
Example 11
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
LiNi of secondary particle structure0.8Co0.12Mn0.08O2Has a particle diameter of 19.5 μm;
LiNi of single crystal grain structure0.8Co0.12Mn0.08O2The particle diameter of (D) is 4.5 mu m;
the compacted density of the positive plate is 3.22g/cm3；
Controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry to enable the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material to be 3.2:1 in unit area of the final positive electrode membrane;
and reasonably controlling the standing time, the drying temperature and the cold pressing pressure of the first anode slurry and the second anode slurry to enable the thickness of the mutual soluble diffusion layer to be 1/12 of the total thickness of the anode plate.
Example 12
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
LiNi of secondary particle structure0.8Co0.12Mn0.08O2The particle diameter of (2) is 5 μm;
LiNi of single crystal grain structure0.8Co0.12Mn0.08O2The particle diameter of (2.5) mu m;
the compacted density of the positive plate is 3.00g/cm3；
Controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry to enable the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material to be 3.2:1 in unit area of the final positive electrode membrane;
and reasonably controlling the standing time, the drying temperature and the cold pressing pressure of the first anode slurry and the second anode slurry to enable the thickness of the mutual soluble diffusion layer to be 1/2000 of the total thickness of the anode plate.
Example 13
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
LiNi of secondary particle structure0.8Co0.12Mn0.08O2Has a particle diameter of 10 μm;
LiNi of single crystal grain structure0.8Co0.12Mn0.08O2The particle diameter of (A) is 1.5 μm;
the compacted density of the positive plate is 3.12g/cm3；
Controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry to enable the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material to be 3.2:1 in unit area of the final positive electrode membrane;
and reasonably controlling the standing time, the drying temperature and the cold pressing pressure of the first anode slurry and the second anode slurry to enable the thickness of the mutual soluble diffusion layer to be 1/15 of the total thickness of the anode plate.
Example 14
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
LiNi of secondary particle structure0.8Co0.12Mn0.08O2Has a particle diameter of 10 μm;
LiNi of single crystal grain structure0.8Co0.12Mn0.08O2The particle diameter of (A) is 1.5 μm;
LiFePO4the particle diameter of (2) is 0.5 μm;
the compacted density of the positive plate is 3.25g/cm3；
Controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry to enable the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material to be 3.2:1 in unit area of the final positive electrode membrane;
and reasonably controlling the standing time, the drying temperature and the cold pressing pressure of the first anode slurry and the second anode slurry to enable the thickness of the mutual soluble diffusion layer to be 1/12 of the total thickness of the anode plate.
Example 15
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
LiFePO4The particle diameter of (2.0) mu m;
the compacted density of the positive plate is 3.11g/cm3；
Controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry to enable the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material to be 3.2:1 in unit area of the final positive electrode membrane;
and reasonably controlling the standing time, the drying temperature and the cold pressing pressure of the first anode slurry and the second anode slurry to enable the thickness of the mutual soluble diffusion layer to be 1/120 of the total thickness of the anode plate.
Comparative example 1
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
LiNi in secondary particle structure0.8Co0.12Mn0.08O2Uniformly mixing the positive electrode active material serving as a positive electrode active material with a binder polyvinylidene fluoride (PVDF) and conductive carbon (Super-P), adding a solvent N-methylpyrrolidone (NMP), and uniformly stirring to obtain a positive electrode slurry, wherein LiNi is0.8Co0.12Mn0.08O2The solid mass ratio of Super-P to PVDF is 95:2.5:2.5, LiNi in secondary particle structure0.8Co0.12Mn0.08O2Has a particle diameter D50 of 11 μm and a solid content of the positive electrode slurry of 70%. And then coating the positive electrode slurry on an aluminum foil current collector with the thickness of 16 microns, baking in an oven to completely volatilize the solvent, and then cold pressing and cutting into pieces to obtain the positive electrode piece. Wherein the compaction density of the positive plate is 3.45g/cm3。
Comparative example 2
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
LiNi in single crystal grain structure0.8Co0.12Mn0.08O2Uniformly mixing the positive electrode active material serving as a positive electrode active material with a binder polyvinylidene fluoride (PVDF) and conductive carbon (Super-P), adding a solvent N-methylpyrrolidone (NMP), and uniformly stirring to obtain a positive electrode slurry, wherein LiNi is0.8Co0.12Mn0.08O2The solid mass ratio of Super-P to PVDF is 95:2.5:2.5, LiNi in a single crystal grain structure0.8Co0.12Mn0.08O2Has a particle diameter D50 of 3 μm and is used as a positive electrode slurryThe content is 70%. And then coating the positive electrode slurry on an aluminum foil current collector with the thickness of 16 microns, baking in an oven to completely volatilize the solvent, and then cold pressing and cutting into pieces to obtain the positive electrode piece. Wherein the compaction density of the positive plate is 3.30g/cm3。
Comparative example 3
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
LiNi in secondary particle structure0.8Co0.12Mn0.08O2And LiNi of single crystal grain structure0.8Co0.12Mn0.08O2Mixing the positive active material, a binder polyvinylidene fluoride (PVDF) and a conductive agent conductive carbon (Super-P) according to a mass ratio of 7:3, uniformly mixing, adding a solvent N-methyl pyrrolidone (NMP), and uniformly stirring to obtain positive slurry. Wherein the solid mass ratio of the positive electrode active material, the Super-P and the PVDF is 95:2.5:2.5, and the LiNi with a secondary particle structure0.8Co0.12Mn0.08O2Has a particle diameter of 11 μm and has a single crystal grain structure0.8Co0.12Mn0.08O2The particle diameter of (2) was 3 μm, and the solid content of the positive electrode slurry was 70%. And then coating the positive electrode slurry on an aluminum foil current collector with the thickness of 16 microns, baking in an oven to completely volatilize the solvent, and then cold pressing and cutting into pieces to obtain the positive electrode piece. Wherein the compaction density of the positive plate is 3.50g/cm3。
Comparative example 4
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
With LiFePO4Uniformly mixing the active material serving as the positive electrode with polyvinylidene fluoride (PVDF) serving as a binder and conductive carbon (Super-P) serving as a conductive agent, adding N-methylpyrrolidone (NMP) serving as a solvent, and uniformly stirring to obtain positive electrode slurry. Wherein LiFePO4The mass ratio of the solids of Super-P and PVDF is 95:2.5:2.5, LiFePO4The particle diameter of (D) was 1.5. mu.m. Then coating the positive electrode slurry on an aluminum foil current collector with the thickness of 16 mu m, and then baking the aluminum foil current collector in an oven to completely volatilize the solventAnd then cold pressing and cutting into pieces to obtain the positive plate. Wherein the compaction density of the positive plate is 2.45g/cm3。
Comparative example 5
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
The compacted density of the positive plate is 2.50g/cm3；
Controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry to enable the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material to be 0.5:1 in unit area of the final positive electrode membrane;
and reasonably controlling the standing time, the drying temperature and the cold pressing pressure of the first anode slurry and the second anode slurry to enable the thickness of the mutual soluble diffusion layer to be 1/120 of the total thickness of the anode plate.
Comparative example 6
The lithium ion battery was prepared in the same manner as in example 1, except that,
(1) preparation of positive plate
The compacted density of the positive plate is 3.4g/cm3；
Controlling the coating weight of the first positive electrode slurry and the second positive electrode slurry to enable the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material to be 32:1 in unit area of the final positive electrode membrane;
and reasonably controlling the standing time, the drying temperature and the cold pressing pressure of the first anode slurry and the second anode slurry to enable the thickness of the mutual soluble diffusion layer to be 1/120 of the total thickness of the anode plate.
Figure BDA0001682093060000161
Next, a test procedure of the lithium ion battery is explained.
(1) High temperature cycle performance testing of lithium ion batteries
And (3) carrying out a cyclic charge-discharge test on the lithium ion battery by 1C charge and 1C discharge at the temperature of 45 ℃, wherein the charge-discharge voltage is 2.8V-4.2V, and calculating the capacity retention ratio of the lithium ion battery after 500 cycles at the temperature of 45 ℃.
(2) Safety performance test of lithium ion battery
Fully charging the lithium ion batteries at 1C until the voltage is 4.2V, then using high-temperature-resistant steel nails with the diameters of 3mm to carry out nail penetration test at the speed of 25 +/-5 mm/s, and testing 8 lithium ion batteries in each group to obtain the nail penetration test passing rate of the lithium ion batteries.
TABLE 2 Performance test results of examples 1 to 15 and comparative examples 1 to 6
Figure BDA0001682093060000171
From the analysis of the test results in table 2, it can be seen that:
the lithium ion battery positive plate prepared by the method has the advantages that the compaction density of the comparative example 3 is higher and the cycle performance of the lithium ion battery is slightly better in the positive plate prepared by the method, but the high-temperature cycle performance of the lithium ion battery is poorer and the passing rate of a through-nail test is low in the comparative examples 1-3 because only the ternary positive material with strong oxidizing property and poorer structural stability exists in the positive plate, so that the ternary positive plate prepared by the method only uses the ternary positive material with the secondary particle structure, the comparative example 2 only uses the ternary positive material with the single-crystal particle structure and the comparative example 3 uses the mixed system of the ternary positive material with the secondary particle structure and the ternary positive material with the. Comparative example 4 Using LiFePO alone4The volume of the lithium ion battery is basically unchanged in the high-temperature circulation process, so that the high-temperature circulation performance of the lithium ion battery is better, and meanwhile, the lithium ion battery has better safety performance, but the compaction density of the positive plate is relatively lower, so that the lithium ion battery is unfavorable for improving the energy density of the lithium ion battery.
In embodiments 1 to 15, a ternary cathode material with a single crystal particle structure and a ternary cathode material with a secondary particle structure are mixed and used as an inner layer of a cathode membrane, olivine lithium-containing phosphate and/or spinel lithium manganate is used as an outer layer of the cathode membrane, and by matching total reversible capacities of a first cathode active material and a second cathode active material per unit area of the cathode membrane, the characteristics of stable and high structure and good safety of the second cathode active material are utilized, so that the problems of strong oxidation property, poor thermal stability and easy thermal runaway of the first cathode active material under extreme conditions (especially nail penetration and overcharge) can be effectively improved on the premise of not influencing the high capacity requirement of a lithium ion battery, and the advantage of high energy density of the first cathode active material is fully exerted.
Meanwhile, the positive plate with higher compaction density and higher safety can be obtained by matching the particle size and the components of the first positive active material and the second positive active material, so that the lithium ion battery using the positive plate has higher energy density, and the high-temperature cycle performance and the safety performance of the lithium ion battery are further improved. When the ternary cathode material with the secondary particle structure and the ternary cathode material with the single crystal particle structure are mixed for use, on one hand, gaps among the secondary particles can be occupied by the single crystal particles in the cold pressing process of the cathode plate, so that the compaction density of the cathode plate and the energy density of the lithium ion battery can be further improved, and on the other hand, under the same cold pressing pressure, the pressure borne by each particle in a mixing system is smaller than that when the secondary particles or the single crystal particles are used alone, so that a relatively large volume expansion space exists in the high-temperature circulation process, and the high-temperature circulation performance of the lithium ion battery is better; through further collocation of the second anode active material with a proper particle size, the mutual soluble diffusion layer between the first anode material layer and the second anode material layer is more stable, the compatibility between the first anode material layer and the second anode material layer is better, the binding force is higher, the second anode material layer is greatly prevented from falling off from the first anode material layer, and therefore the high-temperature cycle performance and the safety performance of the lithium ion battery can be further improved.
In addition, the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material on the unit area of the positive electrode diaphragm is controlled within a certain range, and heat generated by the ternary positive electrode material in the using process can be effectively isolated, so that the high-temperature cycle performance and the safety performance of the lithium ion battery are well improved.
If the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material per unit area of the positive electrode membrane is too small, for example, comparative example 5, the compaction density of the positive electrode sheet is affected, and thus the energy density of the lithium ion battery is affected; if the total reversible capacity ratio of the first positive electrode active material to the second positive electrode active material per unit area of the positive electrode membrane is too large, such as in comparative example 6, the safety performance of the lithium ion battery is significantly deteriorated, and the improvement of the high-temperature cycle performance of the lithium ion battery is also disadvantageous.

Claims (14)

1. A positive electrode sheet, comprising:
a positive current collector; and
the positive electrode diaphragm is arranged on the positive electrode current collector;
it is characterized in that the preparation method is characterized in that,
the positive electrode diaphragm includes:
the first positive electrode material layer is arranged on the positive electrode current collector and comprises a first positive electrode active material, and the first positive electrode active material is a ternary positive electrode material; and
the second positive electrode material layer is arranged on the first positive electrode material layer and comprises a second positive electrode active material, and the second positive electrode active material is selected from one or more of olivine lithium-containing phosphate and spinel lithium manganate;
the total reversible capacity of the first positive electrode active material is a in unit area of the positive electrode diaphragm, the total reversible capacity of the second positive electrode active material is b in unit area of the positive electrode diaphragm, and a/b is more than or equal to 1 and less than or equal to 30.
2. The positive electrode sheet according to claim 1, wherein 1. ltoreq. a/b. ltoreq.12.
3. The positive electrode sheet according to claim 1,
the ternary cathode material is selected from Lix1Ni1-y1-z1-a1Coy1Mnz1M1a1O2、Lix2Ni1-y2-z2-a2Coy2Alz2M2a2O2And composite materials obtained by coating and modifying the above materialsWherein x1 is more than or equal to 0.95 and less than or equal to 1.05, y1 is more than 0 and less than or equal to 0.2, z1 is more than 0 and less than or equal to 0.2, a1 is more than or equal to 0 and less than or equal to 0.05, and M1 is selected from one or more of Ti, Al, Zr, Mg, Zn, Ba, Mo and B; x2 is more than or equal to 0.95 and less than or equal to 1.05, y2 is more than 0 and less than or equal to 0.1, z2 is more than 0 and less than or equal to 0.1, a2 is more than or equal to 0 and less than or equal to 0.05, and M2 is selected from one or more of Ti, Mn, Zr, Mg, Zn, Ba, Mo and B.
4. The positive electrode sheet according to claim 3, wherein 0 < y1+ z1+ a1 is 0.4 or less, and 0 < y2+ z2+ a2 is 0.4 or less.
5. The positive electrode sheet according to claim 1, wherein the olivine-type lithium-containing phosphate has a general formula of LiFe1-x3-y3Mnx3M’y3PO4X3 is more than or equal to 0 and less than or equal to 1, y3 is more than or equal to 0 and less than or equal to 0.1, and M' is selected from one or more of transition metal elements except Fe and Mn and non-transition metal elements.
6. The positive electrode sheet according to claim 5, wherein the olivine-type lithium-containing phosphate is selected from LiFePO4、LiMnPO4、LiMn1-x3Fex3PO40 < x3 < 1.
7. The positive electrode sheet according to claim 1,
the ternary cathode material is a mixture of a ternary cathode material with a single crystal particle structure and a ternary cathode material with a secondary particle structure;
the olivine lithium-containing phosphate has a single crystal particle structure;
the spinel type lithium manganate has a single crystal particle structure.
8. The positive electrode sheet according to claim 7, wherein the mass ratio of the ternary positive electrode material having the single crystal grain structure to the ternary positive electrode material having the secondary grain structure is 1:9 to 5: 5.
9. The positive electrode sheet according to claim 7,
the particle size D50 of the ternary cathode material with the single crystal particle structure is 1-5 mu m;
the particle size D50 of the ternary cathode material with the secondary particle structure is 5-20 μm;
the particle size D50 of the olivine lithium-containing phosphate is 0.5-2 μm;
the particle size D50 of the spinel type lithium manganate is 0.5-2 μm.
10. The positive electrode sheet according to claim 7 or 9,
the particle size D50 of the olivine lithium-containing phosphate is smaller than the particle size D50 of the single-crystal grain structure ternary cathode material;
the particle size D50 of the spinel type lithium manganate is smaller than the particle size D50 of the ternary cathode material with the single-crystal particle structure.
11. The positive electrode sheet according to claim 1, wherein the positive electrode sheet further comprises a mutual solution diffusion layer disposed between the first positive electrode material layer and the second positive electrode material layer, and formed by mutual solution diffusion between the first positive electrode material layer and the second positive electrode material layer.
12. The positive electrode sheet according to claim 11, wherein the thickness of the miscible diffusion layer is 1/2000 to 1/12 of the total thickness of the positive electrode sheet.
13. The positive electrode sheet according to claim 12, wherein the thickness of the miscible diffusion layer is 1/200 to 1/30 of the total thickness of the positive electrode sheet.
14. A lithium ion battery comprising the positive electrode sheet according to any one of claims 1 to 13.
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