Positive electrode sheet and preparation method therefor, and lithium-ion battery

Abstract

The present invention relates to the technical field of lithium-ion batteries, and particularly provides a positive electrode sheet and a preparation method therefor, and a lithium-ion battery comprising the positive electrode sheet. The positive electrode sheet comprises a positive electrode active material layer, and the positive electrode active material layer comprises a positive electrode material, a negative thermal expansion material, a conductive agent, and a binder, wherein the characteristic value J of the positive electrode sheet satisfies: 0.001≤J≤0.005, wherein J=R(F) / ρ, R(F) represents the peak intensity ratio between the main peak (F) of the negative thermal expansion material and the (003) characteristic peak of the positive electrode material in the XRD pattern of the positive electrode plate, and ρ represents the surface density of the positive electrode sheet, with a unit of mg / cm2. The provided positive electrode sheet has low volume expansion, high structural stability, and high temperature stability at the same time. In addition, the lithium-ion battery comprising the positive electrode sheet has excellent capacity performance, rate capability, cycle performance, and energy density.

Description

Positive electrode sheet and preparation method thereof, and lithium-ion battery

[0001] Priority information

[0002] This application claims priority to and the benefits of patent application 202311735942.X filed on December 15, 2023 with the State Intellectual Property Office of China, and incorporates the entire text of this application herein by reference. Technical Field

[0003] The present invention relates to the technical field of lithium-ion batteries, and in particular to a positive electrode sheet and a preparation method thereof, and a lithium-ion battery containing the positive electrode sheet. Background Art

[0004] Lithium-ion batteries, a new type of green secondary battery developed in the 1990s, have seen rapid growth in recent years as people pursue green energy. Their applications have expanded from small digital devices to power tools, electric vehicles, and energy storage power stations. Achieving high energy density, high voltage, long cycle life, and high safety in lithium-ion batteries has become a key goal in this field.

[0005] The positive electrode sheet has an important influence on the performance of lithium-ion batteries. The positive electrode sheet includes a positive current collector and a positive active material layer arranged on the surface of the current collector. The positive active material layer is a thin film formed by coating the positive active material on the surface of the current collector. It is composed of a lithium-containing layered compound positive electrode material, a conductive agent and a binder, of which the positive electrode material accounts for the majority. The positive electrode active material layer needs to have high conductivity and high durability. For the positive electrode material, the insertion and extraction of lithium ions during the charge and discharge process will cause the unit cell volume to change, affecting the contact between the positive electrode particles. At the same time, heat will be released during the charge and discharge cycle of the lithium-ion battery. The thermal expansion and contraction of the current collector and the positive active material layer will generate stress and deformation, causing expansion, leading to deformation of the electrode sheet, fragmentation of the positive electrode particles, and destruction of the contact between the positive electrode and the current collector. This will cause the battery discharge performance to continue to decline, accelerate the battery cycle life attenuation, and cause safety hazards.

[0006] CN109728275A utilizes the negative thermal expansion properties of scandium fluoride (ScF3 phase) to improve the high-temperature stability of the material. However, after the surface of the positive electrode material is coated with scandium fluoride, the coating layer will affect the transmission performance of lithium ions on the surface of the positive electrode material, affecting the capacity of the corresponding positive electrode material after the electrode is made, resulting in a significant reduction in the capacity of the lithium battery, and thus adversely affecting the rate and energy density. Therefore, it is necessary to utilize the good properties of the negative thermal expansion material to improve the electrical performance from the perspective of optimizing the performance of the electrode.

[0007] Therefore, it is of great significance to propose a positive electrode sheet with good high-temperature stability and good electrochemical properties such as capacity, rate and cycle.

[0008] Summary of the Invention

[0009] The purpose of the present invention is to overcome the above-mentioned technical problems and provide a positive electrode plate and a preparation method thereof and a lithium-ion battery, wherein the positive electrode plate has low volume expansion, high structural stability and high temperature stability; at the same time, the lithium-ion battery containing the positive electrode plate has excellent capacity performance, rate performance, cycle performance and energy density.

[0010] In order to achieve the above-mentioned object, the present invention provides a positive electrode sheet in a first aspect, wherein the positive electrode sheet comprises a positive electrode active material layer, wherein the positive electrode active material layer comprises a positive electrode material, a negative thermal expansion material, a conductive agent and a binder;

[0011] Wherein, the characteristic value J of the positive electrode sheet satisfies: 0.001≤J≤0.005;

[0012] Wherein, J=R(F) / ρ, R(F) represents the peak intensity ratio of the main peak (F) of the negative thermal expansion material and the (003) characteristic peak of the positive electrode material in the XRD spectrum of the positive electrode; ρ represents the surface density of the positive electrode, mg / cm 2 .

[0013] The inventors of the present invention have discovered that by adding a negative thermal expansion material to the positive electrode active material layer, the negative thermal expansion material can absorb heat in situ during the positive electrode material cycle, reducing its volume and providing space for the volume expansion of the positive electrode active material, thereby relieving stress and avoiding material deformation. Furthermore, by compounding the negative thermal expansion material with the positive electrode material in the positive electrode active material layer, the negative thermal expansion material maintains its original material structure and is evenly distributed in the positive electrode active material layer, forming inter-particle contact with the positive electrode material. This ensures that the negative thermal expansion material can optimally neutralize the volume expansion of the positive electrode active material layer caused by the thermal expansion of the positive electrode material during the charge and discharge cycles at the positive electrode plate level. Because the lattice parameters of positive electrode materials (especially lithium nickel cobalt manganese oxide positive electrode materials) vary within a certain range through different doping modifications, the heat generation during charge and discharge after application to the plate also varies.

[0014] At the same time, when the same formula is used to process the positive electrode sheet for the same positive electrode material, the internal resistance of the electrode sheet will be different due to the different coating surface density, which will lead to different heat generation of the electrode sheet during the charge and discharge cycle.

[0015] Therefore, the present invention realizes a positive electrode sheet with a positive electrode material composited with a negative thermal expansion material by reasonably controlling the characteristic value J of the positive electrode sheet, that is, by reasonably controlling the composition of the positive electrode active material layer in the positive electrode sheet, while not affecting the lithium ion transmission performance and conductivity performance, effectively alleviating the deformation of the positive electrode sheet caused by thermal volume expansion during the charge and discharge cycle.

[0016] A second aspect of the present invention provides a method for preparing a positive electrode sheet, the method comprising the following steps:

[0017] (1) mixing a positive electrode material, a negative thermal expansion material, a conductive agent, a binder, and a solvent to obtain a positive electrode slurry;

[0018] (2) coating the positive electrode slurry on the surface of the positive electrode current collector, drying and rolling the slurry in sequence to load the positive electrode active material layer on the surface of the positive electrode current collector to obtain a positive electrode sheet;

[0019] Wherein, the positive electrode material is a lithium-containing layered compound; the negative thermal expansion material has a composition shown in formula II: Q a Q' b O c (II); wherein a, b and c are each independently selected from a natural number of 1-15; Q and Q' are each independently selected from at least one element of Zr, W, Hf, Al, Sc, In, Y, Mo, V, Sn, Ti, and P, and Q and Q' are different elements.

[0020] A third aspect of the present invention provides a lithium-ion battery, which comprises the positive electrode sheet provided by the first aspect, or the positive electrode sheet prepared by the preparation method provided by the second aspect.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The positive electrode provided by the present invention combines a negative thermal expansion material into the positive electrode, and combined with a specific characteristic value J, achieves good rate performance and capacity performance under the premise of ensuring that the transmission of lithium ions from the bulk phase to the surface of the positive electrode material in the positive electrode active material layer is not restricted; at the same time, due to the combination of the negative thermal expansion material and the positive electrode material, the expansion of the positive electrode is suppressed during the cycle, avoiding the influence of the expansion of the positive electrode on the electrical performance, improving the structural stability, thermal stability and cycle life of the positive electrode, and at the same time improving the safety of the battery;

[0023] (2) The positive electrode provided by the present invention, by adding a specific amount of negative thermal expansion material, not only has little effect on the discharge capacity, but also has a certain improvement in high-rate performance. This is because under high rate and high current, the volume thermal expansion effect of the positive electrode material can be partially neutralized by the volume contraction of the negative thermal expansion material;

[0024] (3) The preparation method provided by the present invention has the advantages of simple process, green and pollution-free preparation process and low production cost, and is convenient for large-scale industrial production;

[0025] (4) The positive electrode provided by the present invention is applied to lithium-ion batteries, which can effectively improve the electrochemical performance of lithium-ion batteries, especially the capacity performance, rate performance and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG1 is an XRD spectrum of the positive electrode sheet S1 prepared in Example 1.

[0027] Detailed Description of the Invention

[0028] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0029] A first aspect of the present invention provides a positive electrode plate, the positive electrode plate comprising a positive electrode active material layer, the positive electrode active material layer comprising a positive electrode material, a negative thermal expansion material, a conductive agent and a binder;

[0030] Wherein, the characteristic value J of the positive electrode sheet satisfies: 0.001≤J≤0.005;

[0031] Wherein, J=R(F) / ρ, R(F) represents the peak intensity ratio of the main peak (F) of the negative thermal expansion material and the (003) characteristic peak of the positive electrode material in the XRD spectrum of the positive electrode; ρ represents the surface density of the positive electrode, mg / cm 2 .

[0032] In the present invention, the range of J=R(F) / ρ is selected from 0.001-0.005, which is limited to when the unit of the surface density ρ of the positive electrode sheet is mg / cm 2 When the positive electrode sheet has a certain value, the other parameter needs to be within a suitable range to obtain the positive electrode sheet of the present invention.

[0033] In the present invention, unless otherwise specified, the positive electrode sheet further comprises: a positive electrode current collector, wherein the positive electrode active material layer is disposed on the surface of the positive electrode current collector. In the present invention, the positive electrode current collector includes but is not limited to aluminum foil.

[0034] In some embodiments of the present invention, the characteristic value J of the positive electrode plate satisfies: 0.001≤J≤0.005, for example, 0.001, 0.00125, 0.0015, 0.0018, 0.002, 0.0023, 0.0025, 0.003, 0.0035, 0.004, 0.005, and any value in the range of any two values, preferably 0.00125≤J≤0.004.

[0035] In the present invention, by reasonably controlling the characteristic value J of the positive electrode plate, the transmission of lithium ions from the bulk to the surface of the positive electrode material in the positive electrode active material layer is guaranteed to be unrestricted, thereby achieving good rate performance and capacity performance; at the same time, due to the composite of the negative thermal expansion material and the positive electrode material, the expansion of the positive electrode plate is suppressed during the cycle, avoiding the influence of the positive electrode plate expansion on the electrical performance, improving the high-temperature stability and cycle life of the positive electrode plate, and at the same time improving the safety of the battery.

[0036] In some embodiments of the present invention, preferably, R(F)=I(F) / I(003), wherein I(F) and I(003) respectively represent the peak intensities of the main peak (F) of the negative thermal expansion material and the (003) characteristic peak of the positive electrode material in the XRD spectrum of the positive electrode sheet.

[0037] In the present invention, unless otherwise specified, I(003) represents the peak intensity of the (003) characteristic peak of the positive electrode material near 2θ=18°±2; I(F) represents the peak intensity of the (F) main peak of the negative thermal expansion material.

[0038] In the present invention, the high-temperature performance and cycling stability of the electrode can be improved by regulating the peak intensity ratio (R(F)) of the main peak I(F) of the negative thermal expansion material to the peak intensity ratio (I(003)) of the positive electrode material in the positive electrode. A low R(F) value indicates that the negative thermal expansion material in the processed positive electrode has failed to maintain its original crystal structure, and its thermal contraction and cold expansion properties cannot be fully utilized. However, a high R(F) value indicates that the amount of negative thermal expansion material added is too large, which will affect the capacity of the positive electrode.

[0039] In some embodiments of the present invention, preferably, 0.005≤R(F)≤0.1, for example, 0.005, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.08, 0.1, and any value in the range consisting of any two numerical values, further preferably, 0.02≤R(F)≤0.05.

[0040] In the present invention, the R(F) value that meets the above range, especially the R(F) value that meets the preferred range, on the one hand, can indicate that the negative thermal expansion material used has good crystallinity and can maintain its structure in the electrode, thereby appearing a characteristic peak (F) in the XRD diffraction spectrum; on the other hand, it shows that the proportion of the negative thermal expansion material that can play a negative thermal expansion role in the active layer of the positive electrode material can match the electrode process to achieve the best effect.

[0041] In the present invention, the areal density parameter of the positive electrode plate affects its performance. The lower the areal density of the positive electrode plate, the thinner the positive electrode plate, and the lower the internal resistance of the battery. This reduces the changes in the plate structure caused by the continuous insertion and removal of lithium-ion batteries during the charge and discharge cycle, facilitating lithium ion migration and minimizing thermal expansion of the plate. A higher areal density of the positive electrode plate lengthens the migration path of the lithium-ion battery, increases the internal resistance of the battery, and increases thermal expansion of the plate.

[0042] In the present invention, if the areal density ρ of the positive electrode sheet is too low, it means that there is little active material in the battery for fast charging, the gram capacity of the positive electrode sheet is lower, and the positive electrode active particles are easily broken during the processing of the positive electrode sheet, which affects the battery life. If the areal density ρ of the positive electrode sheet is too high, it will not only affect the stability of the positive electrode active material layer and the surface quality of the positive electrode sheet, but also increase the charge transfer impedance and polarization degree, resulting in an increase in the battery internal resistance, reducing the discharge specific capacity, and affecting the rate performance and cycle life. Therefore, rationally controlling the areal density of the positive electrode sheet is of great significance to battery performance.

[0043] In some embodiments of the present invention, preferably, the surface density of the positive electrode sheet satisfies: 8 mg / cm 2 ≤ρ≤25mg / cm 2 , for example, 8 mg / cm 2 、10mg / cm 2 , 12mg / cm 2 , 14mg / cm 2 、16mg / cm 2 , 20mg / cm 2 , 25mg / cm 2 , and any value in the range of any two values, preferably 10 mg / cm 2 ≤ρ≤16mg / cm 2 .

[0044] In the present invention, unless otherwise specified, the areal density ρ of the positive electrode sheet refers to the coating weight of the positive electrode active material layer per unit area of ​​the battery sheet. The areal density ρ parameter of the positive electrode sheet is measured using the following method: areal density ρ = coating weight m of the positive electrode active material layer / coating area S, where the coating weight m of the positive electrode active material layer can be obtained by weighing the weight of the coated positive electrode sheet and subtracting the weight of the positive electrode current collector (aluminum foil); the coating area S is the area of ​​the positive electrode current collector corresponding to the positive electrode sheet, that is, the area of ​​the circular aluminum foil, which can be calculated based on the diameter of the aluminum foil.

[0045] In the present invention, since the crystal structure of the positive electrode material has a strong orientation, it appears in the XRD spectrum as independent and distinct diffraction peaks appearing within a certain angle range, such as the (003) characteristic peak and the (101) characteristic peak of the positive electrode material, which correspond to 2θ = 18° ± 2 and 2θ = 37° ± 2, respectively, and no peaks of other positive electrode materials appear between the two peaks.

[0046] In some embodiments of the present invention, preferably, in the XRD pattern of the positive electrode sheet, the positive electrode material has a (003) characteristic peak and a (101) characteristic peak at 2θ=18°±2 and 2θ=37°±2, respectively.

[0047] In the present invention, for the positive electrode active material layer modified with a negative thermal expansion material, the negative thermal expansion material existing in its original crystal structure can display a corresponding graph in the XRD diffraction pattern of the positive electrode plate, and the graph will appear between the (003) characteristic peak and the (101) characteristic peak of the positive electrode material. One or more characteristic peaks of the negative thermal expansion material may appear in this interval, among which the peak with the highest peak intensity is defined as the main peak (F), and its XRD main peak intensity is defined as I(F).

[0048] In some embodiments of the present invention, preferably, in the XRD pattern of the positive electrode sheet, the main peak (F) of the negative thermal expansion material is located between the (003) characteristic peak and the (101) characteristic peak of the positive electrode material. Meeting these characteristics indicates that the negative thermal expansion material compounded within the positive electrode sheet can maintain its original structure and exhibit good negative thermal expansion performance.

[0049] In a specific embodiment of the present invention, in the XRD pattern of the positive electrode sheet, the diffraction peaks of the negative thermal expansion material, especially the main peak (F), are distributed between the (003) characteristic peak and the (101) characteristic peak of the positive electrode material, that is, between 2θ=18° and 2θ=37°.

[0050] In some embodiments of the present invention, preferably, the average particle size D of the negative thermal expansion material 50 (F) Satisfaction: D 50 (F)≤0.42D50 , D 50 is the average particle size of the positive electrode material, μm. In the present invention, an appropriate D 50 The negative thermal expansion material (F) helps to fill the gaps in the positive electrode material in the positive electrode sheet to better function.

[0051] In some embodiments of the present invention, preferably, the average particle size D of the positive electrode material is 50 It is selected from 1-20 μm, for example, 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 15 μm and 20 μm, and any value in a range consisting of any two values, preferably 1-10 μm.

[0052] In some embodiments of the present invention, preferably, the average particle size D of the negative thermal expansion material 50 (F) is selected from 0.1-10 μm, for example, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 5 μm and 10 μm, and any value in a range consisting of any two values, preferably 0.1-3 μm.

[0053] In some embodiments of the present invention, preferably, the positive electrode material is a lithium-containing layered compound.

[0054] In the present invention, there is a wide range of selection for the type of the positive electrode material. Preferably, the positive electrode material has a composition shown in Formula I: Li 1+α Ni x Co y Mn z M m M′ n O2(I); wherein, -0.5≤α≤0.4, 0<x<1, 0≤y<1, 0≤z<1, 0≤m≤0.1, 0≤n≤0.1, x+y+z+m+n=1; M and M′ are each independently selected from at least one element of Al, Y, Ti, Zr, V, Nb, Ta, Cr, Mo, W, La, Ce, Er, Mg, Sr, Ba, P and B.

[0055] In some specific embodiments of the present invention, in Formula I, -0.5≤α≤0.4, for example, -0.5, -0.2, -0.1, 0, 0.02, 0.03, 0.05, 0.1, 0.2, 0.4, and any value in the range consisting of any two values, preferably 0≤α≤0.1.

[0056] In some specific embodiments of the present invention, in Formula I, 0<x<1, for example, 0.2, 0.5, 0.6, 0.7, 0.8, 0.83, 0.9, 0.95, and any value in the range consisting of any two values, preferably 0.6≤x≤0.9.

[0057] In some specific embodiments of the present invention, in Formula I, 0≤y<1, for example, 0, 0.01, 0.05, 0.1, 0.11, 0.15, 0.2, 0.3, 0.4, and any value in the range consisting of any two values, preferably 0.01≤y≤0.2.

[0058] In some specific embodiments of the present invention, in Formula I, 0≤z<1, for example, 0, 0.01, 0.05, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, 0.4, and any value in the range consisting of any two values ​​is preferably 0.01≤z≤0.3.

[0059] In some specific embodiments of the present invention, in Formula I, 0≤m≤0.1, for example, 0, 0.001, 0.002, 0.005, 0.01, 0.018, 0.05, 0.06, 0.08, 0.1, and any value in the range consisting of any two numerical values; 0≤n≤0.1, for example, 0, 0.001, 0.002, 0.005, 0.01, 0.018, 0.05, 0.06, 0.08, 0.1, and any value in the range consisting of any two numerical values; preferably, 0.001≤m+n≤0.1, for example, 0.001, 0.006, 0.01, 0.02, 0.05, 0.06, 0.08, 0.09, 0.1, and any value in the range consisting of any two numerical values.

[0060] In some specific embodiments of the present invention, in Formula I, M and M' are each independently selected from at least one element of Al, Y, Ti, Zr, V, Nb, Ta, Cr, Mo, W, La, Ce, Er, Mg, Sr, Ba, P and B; preferably, M and M' are different elements; further preferably, M is selected from at least one element of Al, Y, Ti, Zr, La, Sr and B, and M' is selected from at least one element of Nb, Mo, W and P.

[0061] In a specific embodiment of the present invention, the positive electrode material includes but is not limited to Li 1.02 Ni 0.9 Co 0.05 Mn 0.05 O2、Li 1.03 Ni 0.83 Co 0.11 Mn 0.06 O2、Li 1.03 Ni 0.6 Co 0.1 Mn 0.3 O2、Li 1.02 Ni 0.9Co 0.05 Mn 0.05 Al 0.018 W 0.002 O2、Li 1.03 Ni 0.83 Co 0.104 Mn 0.06 Zr 0.005 Nb 0.001 O2, etc.

[0062] In some embodiments of the present invention, preferably, the negative thermal expansion material has a composition shown in Formula II: Q a Q' b O c (II); wherein a, b and c are each independently selected from a natural number of 1-15; Q and Q' are each independently selected from at least one element of Zr, W, Hf, Al, Sc, In, Y, Mo, V, Sn, Ti, and P, and Q and Q' are different elements.

[0063] In some embodiments of the present invention, further preferably, the negative thermal expansion material is selected from at least one of tungstate, molybdate, vanadate and pyrophosphate.

[0064] In a specific embodiment of the present invention, when the negative thermal expansion material is selected from tungstate, the tungstate includes but is not limited to ZrW2O8, HfW2O8, Al2W3O 12 Sc2W3O 12 、In2W3O 12 、Y2W3O 12 wait.

[0065] In a specific embodiment of the present invention, when the negative thermal expansion material is selected from molybdate, the molybdate includes but is not limited to ZrMo2O8, HfMo2O8 and the like.

[0066] In a specific embodiment of the present invention, when the negative thermal expansion material is selected from vanadate, the vanadate includes but is not limited to ZrV2O7, HfV2O7, SnV2O7, TiV2O7 and the like.

[0067] In a specific embodiment of the present invention, when the negative thermal expansion material is selected from pyrophosphate, the pyrophosphate includes but is not limited to ZrP2O7, HfP2O7, SnP2O7 and TiP2O7.

[0068] In some embodiments of the present invention, preferably, the thickness of the positive electrode active material layer is 20-85 μm, for example, 20 μm, 25 μm, 30 μm, 40 μm, 50 μm, 60 μm, 75 μm, 85 μm, and any value in the range of any two values, preferably 25-60 μm.

[0069] In the present invention, for the positive electrode plate, the thickness of the positive electrode active material layer is related to the properties, weight and rolling pressure of the coated active material. The active material refers to a mixture formed by the positive electrode material, the negative thermal expansion material, the conductive agent and the binder; the active material coating weight is large, the compaction performance of the positive electrode plate is low, and the rolling pressure during the processing is small, which will lead to a thicker active material layer, increase the charge transfer path, have an adverse effect on the charge transfer, cause an increase in impedance, and make the thermal effect during the charge and discharge process more significant, which has an adverse effect on the cycle.

[0070] In the present invention, in order to achieve the optimal electrical performance of the positive electrode, the presence of negative thermal expansion material in the positive electrode also requires matching the surface density of the positive electrode. Positive electrode sheets with low surface density, low positive electrode material content, low calorific value, and poor processing performance need to reduce the content of negative thermal expansion material in the positive electrode to match the thermal expansion of the positive active material layer on the electrode. Positive electrode sheets with high surface density and high positive electrode material content generate high calorific value. During processing, the crystal structure of the negative thermal expansion material in the positive electrode sheet needs to be maintained intact, and more negative thermal expansion material is required to neutralize the volume expansion of the electrode during charging and discharging.

[0071] In some embodiments of the present invention, preferably, based on the total weight of the positive electrode active material layer, the content of the positive electrode material is 85.5-94.52 wt%, preferably 90-94.5 wt%; the content of the negative thermal expansion material is 0.48-9.5 wt%, preferably 0.5-5 wt%.

[0072] In some embodiments of the present invention, further preferably, based on the total weight of the positive electrode active material layer, the content of the conductive agent is 2-4 wt%, preferably 2.5-3.5 wt%; the content of the binder is 1-3 wt%, preferably 1.5-2.5 wt%.

[0073] In the present invention, the conductive agent includes but is not limited to acetylene black, carbon fiber, carbon nanotube, graphite, Ketjen black, etc.; the binder includes but is not limited to PVDF, etc.

[0074] The positive electrode plate provided by the present invention has the characteristic of low internal resistance. An impedance test is performed on the positive electrode plate, and it is measured that the initial discharge impedance value of the positive electrode plate is R(d)≤20Ω, preferably R(d)≤18Ω.

[0075] A second aspect of the present invention provides a method for preparing a positive electrode sheet, the method comprising the following steps:

[0076] (1) mixing a positive electrode material, a negative thermal expansion material, a conductive agent, a binder, and a solvent to obtain a positive electrode slurry;

[0077] (2) coating the positive electrode slurry on the surface of the positive electrode current collector, drying and rolling the slurry in sequence to load the positive electrode active material layer on the surface of the positive electrode current collector to obtain a positive electrode sheet;

[0078] Wherein, the positive electrode material is a lithium-containing layered compound; the negative thermal expansion material has a composition shown in formula II: Q a Q' b O c (II); wherein a, b and c are each independently selected from a natural number of 1-15; Q and Q' are each independently selected from at least one element of Zr, W, Hf, Al, Sc, In, Y, Mo, V, Sn, Ti, and P, and Q and Q' are different elements.

[0079] In some embodiments of the present invention, preferably, in step (1), the mass ratio of the positive electrode material, the negative thermal expansion material, the conductive agent, and the binder is (85.5-94.52):(0.48-9.5):(2-4):(1-3), preferably (90-94.5):(0.5-5):(2.5-3.5):(1.5-2.5).

[0080] In some embodiments of the present invention, preferably, in step (1), the cathode material has a composition shown in formula I: Li 1+α Ni x Co y Mn z M m M′ n O2(I); wherein, -0.5≤α≤0.4, 0<x<1, 0≤y<1, 0≤z<1, 0≤m≤0.1, 0≤n≤0.1, x+y+z+m+n=1; M and M′ are each independently selected from at least one element of Al, Y, Ti, Zr, V, Nb, Ta, Cr, Mo, W, La, Ce, Er, Mg, Sr, Ba, P and B.

[0081] In some embodiments of the present invention, preferably, in Formula I, 0≤α≤0.1, 0.6≤x≤0.9, 0.01≤y≤0.2, 0.01≤z≤0.3, m and n are not 0 at the same time, and 0.001≤m+n≤0.1.

[0082] In some embodiments of the present invention, preferably, in Formula I, M and M' are different elements; further preferably, in Formula I, M is selected from at least one element of Al, Y, Ti, Zr, La, Sr and B, and M' is selected from at least one element of Nb, Mo, W and P.

[0083] In some embodiments of the present invention, preferably, in step (1), the average particle size D of the negative thermal expansion material 50 (F) Satisfaction: D 50 (F) ≤0.42D 50 , D 50 is the average particle size of the positive electrode material, μm; further preferably, the average particle size D of the positive electrode material 50 The average particle size D of the negative thermal expansion material is selected from 1-20 μm, preferably 1-10 μm; 50 (F) is selected from 0.1-10 μm, preferably 0.1-3 μm.

[0084] In the present invention, in step (1), the solvent is used to uniformly mix the positive electrode material, negative thermal expansion material, conductive agent and binder. The solvent includes but is not limited to NMP, methanol, ethanol, etc.

[0085] In some embodiments of the present invention, preferably, in step (1), the mixing conditions include: temperature of 15-40°C, preferably 20-30°C; time of 10-120 min, preferably 20-60 min; rotation speed of 500-2000 rpm, preferably 800-1500 rpm.

[0086] In some embodiments of the present invention, preferably, the solid content of the positive electrode slurry is 40-60 wt %.

[0087] In the present invention, in step (2), the coating is to uniformly coat the positive electrode slurry on the surface of the positive electrode current collector to form a positive electrode slurry coating layer; the drying is to remove the solvent in the positive electrode slurry coating layer to form a positive electrode active material layer. Preferably, the drying is to remove the positive electrode slurry. The drying temperature is 80-150°C, preferably 120-150°C.

[0088] In some embodiments of the present invention, preferably, the rolling pressure P is selected from 5-20 T. In the present invention, the rolling operation is generally performed in a roller press, and the rolled product is cut to obtain a positive electrode sheet.

[0089] The preparation method of the positive electrode provided by the present invention can balance the volume expansion of the material during the charge and discharge process by mixing and compounding the negative thermal expansion material into the positive electrode material particles, thereby improving the cycle stability of the electrode; specifically, by regulating the type, addition amount and D50 , the type, amount and D of negative thermal expansion material 50 (F), and the rolling pressure P, thereby regulating the characteristic value J of the positive electrode sheet, so that the positive electrode sheet has low volume expansion, high structural stability and high temperature stability.

[0090] A third aspect of the present invention provides a lithium-ion battery, which comprises the positive electrode sheet provided by the first aspect, or the positive electrode sheet prepared by the preparation method provided by the second aspect.

[0091] In a specific embodiment of the present invention, the lithium-ion battery comprises the positive electrode sheet and the negative electrode sheet provided by the present invention, a separator disposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte.

[0092] The present invention will be described in detail below through examples.

[0093] The process parameters for preparing the positive electrode sheets in the examples and comparative examples, as well as the physical properties of the prepared positive electrode sheets are listed in Table 1.

[0094] Example 1

[0095] (1) The positive electrode material (Li 1.02 Ni 0.9 Co 0.05 Mn 0.05 O2, D 50 3.5μm), negative thermal expansion materials (ZrW2O8, D 50 (F) is 0.4 μm), a conductive agent (acetylene black), a binder (PVDF) and a solvent (NMP) are mixed (temperature is 25° C., rotation speed is 1000 rpm, time is 40 min) to obtain a positive electrode slurry with a solid content of 40 wt%;

[0096] The mass ratio of the positive electrode material, negative thermal expansion material, conductive agent and binder is 91.2:3.8:3:2;

[0097] (2) The positive electrode slurry is coated on the surface of the positive electrode current collector aluminum foil to coat the positive electrode slurry coating on the surface of the aluminum foil. After drying at 135°C, a roller press is used to roll (with a pressure of 15T) to set a positive electrode active material layer on the surface of the aluminum foil to obtain a positive electrode sheet S1.

[0098] The XRD spectrum of the positive electrode S1 is shown in FIG1 . As can be seen from FIG1 , the positive electrode materials have 2θ=18 ° and 2θ = 37 ° The (003) characteristic peak and the (101) characteristic peak at the cathode material are located between the (003) characteristic peak and the (101) characteristic peak at the cathode material, and the main peak (F) of the negative thermal expansion material is located between the (003) characteristic peak and the (101) characteristic peak at the cathode material.

[0099] Examples 2-6

[0100] According to the method of Example 1, the difference is that

[0101] In step (1), the mass ratios of the positive electrode material, negative thermal expansion material, conductive agent, and binder are adjusted based on the data in Table 1;

[0102] The other conditions are the same, and positive electrode sheets S2-S6 are obtained respectively.

[0103] Examples 7-11

[0104] According to the method of Example 1, the difference is that

[0105] In step (1), the type and D of the positive electrode material are adjusted based on the data in Table 1. 50 , Types of negative thermal expansion materials and D 50 (F), and the mass ratio of the above-mentioned positive electrode material, negative thermal expansion material, conductive agent and binder;

[0106] In step (2), the roller pressure is adjusted based on the data in Table 1;

[0107] The other conditions were the same, and positive electrode sheets S7-S11 were obtained respectively.

[0108] Example 12

[0109] According to the method of Example 1, the difference is that

[0110] In step (1), the type and D of the positive electrode material are adjusted based on the data in Table 1. 50 , and the mass ratio of the above-mentioned positive electrode material, negative thermal expansion material, conductive agent and binder;

[0111] In step (2), the roller pressure is adjusted based on the data in Table 1;

[0112] The other conditions are the same, and the positive electrode sheet S12 is obtained.

[0113] Example 13

[0114] The method of Example 12 is followed, except that

[0115] In step (1), the D of the negative thermal expansion material is adjusted based on the data in Table 1. 50 (F);

[0116] The remaining conditions are the same, and the positive electrode sheet S13 is obtained.

[0117] Example 14

[0118] According to the method of Example 1, the difference is that

[0119] In step (1), the type of the positive electrode material is adjusted based on the data in Table 1;

[0120] The remaining conditions are the same, and the positive electrode sheet S14 is obtained.

[0121] Example 15

[0122] The method of Example 14 is followed, except that

[0123] In step (2), the roller pressure is adjusted based on the data in Table 1;

[0124] The other conditions are the same, and the positive electrode sheet S15 is obtained.

[0125] Example 16

[0126] The method of Example 14 is followed, except that

[0127] In step (1), the type of the negative thermal expansion material is adjusted based on the data in Table 1;

[0128] The other conditions are the same, and the positive electrode sheets S16 are obtained respectively.

[0129] Example 17

[0130] The method of Example 7 is followed, except that

[0131] Adjust the type of the above-mentioned positive electrode material based on the data in Table 1;

[0132] The remaining conditions are the same, and the positive electrode sheet S17 is obtained.

[0133] Comparative Example 1

[0134] According to the method of Example 1, the difference is that

[0135] In step (1), the mass ratio of the positive electrode material, negative thermal expansion material, conductive agent and binder is adjusted based on the data in Table 1;

[0136] The other conditions are the same, and the positive electrode sheet DS1 is obtained.

[0137] Comparative Example 2

[0138] According to the method of Example 1, the difference is that

[0139] In step (1), the D of the negative thermal expansion material is adjusted based on the data in Table 1. 50 (F), make D 50 (F)>0.42D 50 ;

[0140] The other conditions are the same, and the positive electrode sheet DS2 is obtained.

[0141] Comparative Example 3

[0142] According to the method of Example 1, the difference is that

[0143] In step (2), the roller pressure is adjusted based on the data in Table 1 and replaced with 4T;

[0144] The other conditions are the same, and the positive electrode sheet DS3 is obtained.

[0145] Table 1

[0146] Note: When the D of negative thermal expansion material 50 (F)≤0.42D 50 , recorded as √; otherwise, recorded as ×;

[0147] *-Mass ratio of positive electrode material, negative thermal expansion material, conductive agent and binder.

[0148] Table 1

[0149] Table 1

[0150] Note: Peak intensity ratio R(F) = I(F) / I(003), i.e., the peak intensity ratio of the main peak (F) of the negative thermal expansion material and the (003) characteristic peak of the positive electrode material; characteristic value J = R(F) / ρ.

[0151] Test Case

[0152] The positive electrode sheets prepared in the above examples and comparative examples were evaluated using 2025 button batteries. The assembly process was as follows:

[0153] Battery Assembly: In an argon-filled glove box with water and oxygen contents less than 5 ppm, the aforementioned positive electrode, separator, negative electrode, and electrolyte were assembled into 2025-type button cells and allowed to rest for 6 hours. The negative electrode consisted of a 16 mm diameter, 0.5 mm thick lithium metal sheet; the separator was a 25 μm thick polyethylene porous membrane (Celgard 2325); and the electrolyte was a mixture of equal parts ethylene carbonate (EC) and diethyl carbonate (DEC) containing 1 mol / L LiPF6.

[0154] The electrochemical performance of the 2025 button batteries assembled in the above embodiments and comparative examples was tested using a Shenzhen Xinweier battery testing system. The test results are listed in Tables 1 and 2.

[0155] (1) Initial impedance test method: The button cell was fixed at 25°C and 0.1C (when the nickel content of the positive electrode material in the positive electrode sheet is ≥80 mol%, the charge and discharge current density at 0.1C during the test is 20 mA / g; when the nickel content of the positive electrode material in the positive electrode sheet is <80 mol%, the charge and discharge current density at 0.1C during the test is 18 mA / g). After 10 minutes of storage, the cell was charged to 4.35 V at 0.33C constant current and constant voltage, and then stored for 10 minutes; the cell was discharged to 3.0 V at 0.33C constant current, and then stored for 10 minutes; the cell after the fixed capacity was taken and charged and discharged again to 50% DOD, and after 3 minutes of storage, the cell was discharged at 1C constant current for 18 seconds. The voltage and current before and after the discharge process were recorded, and the impedance value was calculated.

[0156] (2) 0.1C first charge and discharge specific capacity and first charge and discharge efficiency test: At 25°C, the button battery was charged and discharged at 0.1C. When the nickel content of the positive electrode material in the positive electrode sheet was ≥80 mol%, the charge and discharge current density at 0.1C during the test was 20 mA / g, and the charge and discharge voltage range was controlled to be 3-4.3 V; when the nickel content of the positive electrode material in the positive electrode sheet was <80 mol%, the charge and discharge current density at 0.1C during the test was 18 mA / g, and the charge and discharge voltage range was controlled to be 3.0-4.4 V.

[0157] (3) Cycling performance test: Control the charge and discharge voltage range to 3-4.3V, at a constant temperature of 45°C, charge and discharge the button battery at 0.1C for 2 cycles, and then charge and discharge for 80 cycles at 1C;

[0158] (4) Rate performance test: Control the charge and discharge voltage range to 3.0-4.3V. At 25°C, charge and discharge the button battery twice at 0.1C, and then charge and discharge once at 0.2C, 0.33C, 0.5C, 1C, and 2C respectively. The rate performance of the multi-element positive electrode material is evaluated by the ratio of the 0.1C first discharge specific capacity to the 2C discharge specific capacity; among which, the 0.1C first discharge specific capacity is the discharge specific capacity of the button battery in the first cycle, and the 2C discharge specific capacity is the discharge specific capacity of the button battery in the seventh cycle.

[0159] Table 2

[0160] Based on the data in Table 1-2, it can be seen that compared with Comparative Examples 1-3, Example 1-17 adjusts the type of positive electrode material and D 50 , Types of negative thermal expansion materials and D 50(F), the mass ratio of the positive electrode material and the negative thermal expansion material, and the rolling pressure, the peak intensity ratio R(F), the surface density ρ and the characteristic value J of the prepared positive electrode plate are within the preferred range, ensuring that the layered active material in the positive electrode plate can exert good electrical properties, its lithium ion intercalation and deintercalation ability is good, and its capacity rate performance is good; at the same time, the addition of the negative thermal expansion material to the plate can neutralize the volume expansion of the plate during the charging and discharging process, so that the volume expansion of the plate during the charging and discharging process is weakened, avoiding the adverse effect of the volume expansion of the plate on the battery performance, thereby ensuring that the battery has good cycle performance; ultimately, the battery has the comprehensive performance of high capacity, good rate and good cycle life.

[0161] In Comparative Example 1, the amount of negative thermal expansion material used is small, and the R(F) value of the positive electrode plate is very small. The surface density ρ of the positive electrode plate is large, and the corresponding plate characteristic value J is small, indicating that the proportion of negative thermal expansion material that can play a negative thermal expansion role in the positive electrode plate is low. During the charge and discharge process, the negative thermal expansion material is not enough to offset the volume change of the positive electrode material. The larger surface density ρ leads to an increase in the internal resistance of the battery, reduces the discharge specific capacity, and affects the rate performance and cycle life. During the charge and discharge process, the volume expansion and thermal effect of the positive electrode particles are high, which makes the cycle performance of the plate worse.

[0162] The negative thermal expansion material used in Comparative Example 2 has a D 50 (F) is too large, there is a mismatch between the negative thermal expansion material and the positive electrode material, and the electrode R(F) value is also small. Although the electrode surface density ρ is moderate, the corresponding electrode characteristic value J is small. This shows that although a certain amount of negative thermal expansion material is added during the electrode production process, due to the mismatch between the negative thermal expansion material and the positive electrode material, the two cannot play a synergistic role after the electrode is made, resulting in a decrease in the electrode capacity. At the same time, the negative thermal expansion material cannot play a role in neutralizing the thermal effect, thereby affecting the rate and cycle performance.

[0163] In Comparative Example 3, the electrode thickness obtained after electrode processing is too high, the surface density is too high, the J value deviates from the optimal range, and the material with negative thermal expansion in the active layer of the positive electrode material cannot fully play its neutralizing role during the cycle, resulting in poor electrode performance.

[0164] Examples 1-13 show the electrical performance of the electrodes made using the preferred design. It can be seen that for different positive electrode materials and negative thermal expansion materials, the electrodes processed under the premise of meeting the electrode characteristic value requirements are made into batteries, and the batteries have good rate and cycle performance. Among them, the amount of negative thermal expansion material added in Example 11 is relatively high, resulting in a certain deviation of the electrode characteristic value J from the preferred range, thereby resulting in a certain reduction in electrical performance.

[0165] Examples 14-15 and Example 17 select preferred positive electrode materials for application in positive electrode plates. By using ternary positive electrode materials that introduce M and M' modifying elements, the stability of the positive electrode material itself is improved. At the same time, by controlling the processing conditions, the obtained positive electrode plates meet the plate characteristic values, thereby improving the cycle performance. In Example 16, a non-preferred negative thermal expansion material is used, and its characteristic value J deviates from the preferred range, which reduces the plate rate and cycle performance.

[0166] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode sheet comprises a positive electrode active material layer, wherein the positive electrode active material layer comprises a positive electrode material, a negative thermal expansion material, a conductive agent and a binder; Wherein, the characteristic value J of the positive electrode sheet satisfies: 0.001≤J≤0.005; Wherein, J=R(F) / ρ, R(F) represents the peak intensity ratio of the main peak (F) of the negative thermal expansion material and the characteristic peak (003) of the positive electrode material in the XRD spectrum of the positive electrode sheet; ρ represents the surface density of the positive electrode sheet, mg / cm 2 .

2. The positive electrode sheet according to claim 1, wherein: The characteristic value J of the positive electrode plate satisfies: 0.00125≤J≤0.

004.

3. The positive electrode sheet according to claim 1 or 2, wherein: R(F)=I(F) / I(003), where I(F) and I(003) respectively represent the peak intensities of the main peak (F) of the negative thermal expansion material and the characteristic peak (003) of the positive electrode material in the XRD spectrum of the positive electrode sheet.

4. The positive electrode sheet according to claim 3, wherein: 0.005≤R(F)≤0.1, preferably 0.02≤R(F)≤0.

05.

5. The positive electrode sheet according to any one of claims 1 to 4, wherein: The surface density of the positive electrode sheet meets the following requirements: 8 mg / cm 2 ≤ρ≤25mg / cm 2 , preferably 10 mg / cm 2 ≤ρ≤16mg / cm 2 .

6. The positive electrode sheet according to any one of claims 1 to 5, wherein: In the XRD spectrum of the positive electrode sheet, the positive electrode material has a (003) characteristic peak and a (101) characteristic peak at 2θ=18°±2 and 2θ=37°±2, respectively.

7. The positive electrode sheet according to any one of claims 1 to 6, wherein: In the XRD spectrum of the positive electrode sheet, the main peak (F) of the negative thermal expansion material is between the (003) characteristic peak and the (101) characteristic peak of the positive electrode material.

8. The positive electrode sheet according to any one of claims 1 to 7, wherein: The average particle size D of the negative thermal expansion material 50 (F) Satisfaction: D 50 (F)≤0.42D 50 , D 50 is the average particle size of the positive electrode material, μm.

9. The positive electrode sheet according to any one of claims 1 to 8, wherein: The average particle size D of the positive electrode material 50 Selected from 1-20 μm, preferably 1-10 μm.

10. The positive electrode sheet according to any one of claims 1 to 9, wherein: The average particle size D of the negative thermal expansion material 50 (F) is selected from 0.1-10 μm, preferably 0.1-3 μm.

11. The positive electrode sheet according to any one of claims 1 to 10, wherein: The positive electrode material is a lithium-containing layered compound.

12. The positive electrode sheet according to any one of claims 1 to 11, wherein: The positive electrode material has a composition shown in Formula I: Li 1+α Ni x Co y Mn z M m M′ n O2 (I); Wherein, -0.5≤α≤0.4, 0<x<1, 0≤y<1, 0≤z<1, 0≤m≤0.1, 0≤n≤0.1, x+y+z+m+n=1; M and M′ are each independently selected from at least one element of Al, Y, Ti, Zr, V, Nb, Ta, Cr, Mo, W, La, Ce, Er, Mg, Sr, Ba, P and B; Preferably, in formula I, 0≤α≤0.1, 0.6≤x≤0.9, 0.01≤y≤0.2, 0.01≤z≤0.3, m and n are not 0 at the same time, 0.001≤m+n≤0.1; Preferably, in formula I, M and M' are different elements; More preferably, in Formula I, M is at least one element selected from Al, Y, Ti, Zr, La, Sr and B, and M' is at least one element selected from Nb, Mo, W and P.

13. The positive electrode sheet according to any one of claims 1 to 12, wherein: The negative thermal expansion material has a composition shown in Formula II: a Q' b O c (II); Wherein, a, b and c are each independently selected from natural numbers of 1-15; Q and Q' are each independently selected from at least one element of Zr, W, Hf, Al, Sc, In, Y, Mo, V, Sn, Ti, P, and the elements Q and Q' are different.

14. The positive electrode sheet according to any one of claims 1 to 13, wherein: The negative thermal expansion material is selected from at least one of tungstate, molybdate, vanadate and pyrophosphate; Preferably, the negative thermal expansion material is selected from ZrW2O8, HfW2O8, Al2W3O 12 Sc2W3O 12 、In2W3O 12 、Y2W3O 12 , at least one of ZrMo2O8, HfMo2O8, ZrV2O7, HfV2O7, SnV2O7, TiV2O7, ZrP2O7, HfP2O7, SnP2O7 and TiP2O7.

15. The positive electrode sheet according to any one of claims 1 to 14, wherein: The thickness of the positive electrode active material layer is 20-85 μm, preferably 25-60 μm.

16. The positive electrode sheet according to any one of claims 1 to 15, wherein: Based on the total weight of the positive electrode active material layer, the content of the positive electrode material is 85.5-94.52wt%, preferably 90-94.5wt%; the content of the negative thermal expansion material is 0.48-9.5wt%, preferably 0.5-5wt%.

17. The positive electrode sheet according to any one of claims 1 to 16, wherein: Based on the total weight of the positive electrode active material layer, the content of the conductive agent is 2-4wt%, preferably 2.5-3.5wt%; the content of the binder is 1-3wt%, preferably 1.5-2.5wt%.

18. The positive electrode sheet according to any one of claims 1 to 17, wherein: The initial discharge impedance value of the positive electrode plate is R(d)≤20Ω, preferably R(d)≤18Ω.

19. A method for preparing a positive electrode sheet, characterized in that: The preparation method comprises the following steps: (1) mixing a positive electrode material, a negative thermal expansion material, a conductive agent, a binder and a solvent to obtain a positive electrode slurry; (2) coating the positive electrode slurry on the surface of the positive electrode current collector, drying and rolling in sequence to load a positive electrode active material layer on the surface of the positive electrode current collector to obtain a positive electrode sheet; Wherein, the positive electrode material is a lithium-containing layered compound; the negative thermal expansion material has a composition shown in formula II: Q a Q' b O c (II); wherein a, b and c are each independently selected from a natural number of 1-15; Q and Q' are each independently selected from at least one element of Zr, W, Hf, Al, Sc, In, Y, Mo, V, Sn, Ti, P, and Q and Q' are different elements.

20. The preparation method according to claim 19, wherein: In step (1), The mass ratio of the positive electrode material, the negative thermal expansion material, the conductive agent and the binder is (85.5-94.52):(0.48-9.5):(2-4):(1-3), preferably (90-94.5):(0.5-5):(2.5-3.5):(1.5-2.5).

21. The preparation method according to claim 19 or 20, wherein: The positive electrode material has a composition shown in Formula I: Li 1+α Ni x Co y Mn z M m M′ n O2 (I); Wherein, -0.5≤α≤0.4, 0<x<1, 0≤y<1, 0≤z<1, 0≤m≤0.1, 0≤n≤0.1, x+y+z+m+n=1; M and M′ are each independently selected from at least one element of Al, Y, Ti, Zr, V, Nb, Ta, Cr, Mo, W, La, Ce, Er, Mg, Sr, Ba, P and B; Preferably, in formula I, 0≤α≤0.1, 0.6≤x≤0.9, 0.01≤y≤0.2, 0.01≤z≤0.3, m and n are not 0 at the same time, 0.001≤m+n≤0.1; preferably, in formula I, M and M′ are different elements; further preferably, in formula I, M is selected from at least one element of Al, Y, Ti, Zr, La, Sr and B, and M′ is selected from at least one element of Nb, Mo, W and P.

22. The preparation method according to any one of claims 19 to 21, wherein The average particle size D of the negative thermal expansion material 50 (F) Satisfaction: D 50 (F)≤0.42D 50 , D 50 is the average particle size of the positive electrode material, μm.

23. The preparation method according to any one of claims 19 to 22, wherein: The average particle size D of the positive electrode material 50 Selected from 1-20 μm, preferably 1-10 μm.

24. The preparation method according to any one of claims 19 to 23, wherein The average particle size D of the negative thermal expansion material 50 (F) is selected from 0.1-10 μm, preferably 0.1-3 μm.

25. The preparation method according to any one of claims 19 to 24, wherein The mixing conditions include: temperature of 15-40° C., preferably 20-30° C.; time of 10-120 min, preferably 20-60 min; rotation speed of 500-2000 rpm, preferably 800-1500 rpm.

26. The preparation method according to any one of claims 19 to 25, wherein In step (2), the drying temperature is 80-150°C, preferably 120-150°C.

27. The preparation method according to any one of claims 19 to 26, wherein The rolling pressure P is selected from 5T<P<20T.

28. The preparation method according to any one of claims 19 to 27, wherein In step (1), the mass ratio of the positive electrode material, the negative thermal expansion material, the conductive agent, and the binder is (90-94.5):(0.5-5):(2.5-3.5):(1.5-2.5).

29. A lithium ion battery, characterized in that: The lithium-ion battery contains the positive electrode sheet according to any one of claims 1 to 18, or the positive electrode sheet prepared by the preparation method according to any one of claims 19 to 28.

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