A positive electrode sheet and a lithium ion battery

Abstract

This invention provides a positive electrode sheet and a lithium-ion battery. The positive electrode sheet includes a current collector and a positive electrode material composited on the current collector; the positive electrode material includes a positive electrode active material; the positive electrode active material is selected from lithium manganese iron phosphate; the D90 particle size of the lithium manganese iron phosphate particles, the tensile strength σ of the positive electrode sheet, and the compaction density PD of the positive electrode sheet satisfy the relationship in equation (I): 1600 <D90 / PD×σ<4800(I)。

Description

[0001] This application is a divisional application of the invention entitled "A positive electrode sheet and a lithium-ion battery", filed on October 15, 2024, with application number 202411436264.1. Technical Field

[0002] This invention belongs to the field of lithium-ion battery positive electrode technology, and relates to a positive electrode and a lithium-ion battery, particularly to a lithium manganese iron phosphate positive electrode and a lithium-ion battery. Background Technology

[0003] In lithium manganese iron phosphate (LMP) materials, high electron and ion transport impedance leads to poor conductivity and kinetic properties. Solid-phase diffusion of lithium ions within LMP is a key factor limiting its kinetics. Therefore, reducing the primary particle size to shorten the lithium-ion diffusion path can help improve the kinetic performance of LMP materials. However, reducing the primary particle size to a certain extent results in excessively large particle surface areas. This increases the amount of solvent and binder required for uniform particle dispersion during the slurry mixing process, further reducing the solid content of the slurry. This makes the slurry prone to cracking during thick electrode coating, resulting in low coating surface density and hindering the improvement of cell energy density.

[0004] Therefore, how to design a more suitable lithium manganese iron phosphate cathode to solve the above-mentioned problems of existing lithium manganese iron phosphate cathodes has become one of the focuses of attention for many technical personnel in the industry. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a positive electrode sheet and its preparation method, a lithium-ion battery, and in particular a lithium manganese iron phosphate positive electrode sheet. The lithium manganese iron phosphate positive electrode sheet provided by the present invention satisfies a specific relationship, and by controlling the tensile strength of the lithium manganese iron phosphate particles, the tensile strength of the positive electrode sheet, and the compaction density of the positive electrode sheet, the performance of the lithium manganese iron phosphate positive electrode sheet is further improved.

[0006] The first aspect of the present invention provides a positive electrode sheet, the positive electrode sheet comprising a current collector and a positive electrode material composited on the current collector;

[0007] The positive electrode material includes a positive electrode active material;

[0008] The positive electrode active material is selected from lithium iron manganese phosphate;

[0009] The D90 particle size of the lithium manganese iron phosphate particles, the tensile strength σ of the positive electrode, and the compaction density PD of the positive electrode satisfy the relationship described in equation (I):

[0010] 1600 <D90 / PD×σ<4800 (I);

[0011] Where D90 is measured in μm, σ in MPa, and PD in g / cm³. 3 .

[0012] Preferably, in formula (I), 2000 <D90 / PD×σ<4000。

[0013] Preferably, the lithium manganese iron phosphate particles specifically include secondary lithium manganese iron phosphate particles.

[0014] Preferably, the D90 particle size of the lithium manganese iron phosphate particles is 10~50μm.

[0015] Preferably, the D90 particle size of the lithium manganese iron phosphate particles is 15~40μm.

[0016] Preferably, the compaction density PD is 2.0~2.5 g / cm³. 3 .

[0017] Preferably, the tensile strength σ is 100~500MPa.

[0018] Preferably, the compaction change rate ΔPD of the positive electrode sheet and the tensile strength σ of the positive electrode sheet satisfy the relationship described in equation (II):

[0019] 0 < σ × △PD < 95 (II);

[0020] Where σ is in MPa, △PD = (PD max -PD) / PD, PD max This represents the maximum compaction density.

[0021] The maximum compaction density is the compaction density corresponding to the positive electrode sheet after secondary rolling and folding to transmit light.

[0022] Preferably, the range of △PD is 4% to 25%.

[0023] A second aspect of the present invention also provides a lithium-ion battery, including a positive electrode sheet;

[0024] The positive electrode sheet is any one of the positive electrode sheets described in the above technical solutions.

[0025] The present invention provides a positive electrode sheet, which includes a current collector and a positive electrode material compounded on the current collector; the positive electrode material includes a positive electrode active material; the positive electrode active material is selected from lithium iron manganese phosphate; the D90 particle size of the lithium iron manganese phosphate particles, the tensile strength σ of the positive electrode sheet, and the tap density PD of the positive electrode sheet satisfy the relational expression of formula (I): 1600 < D90 / PD × σ < 4800 (I). Compared with the prior art, the positive electrode sheet of the present invention balances the D90 particle size of the lithium iron manganese phosphate particles, the tensile strength σ of the positive electrode sheet, and the tap density PD of the positive electrode sheet, so that the positive electrode sheet has excellent fast charging performance and energy density at the same time. Description of the Drawings

[0026] Figure 1 It is a 1000X SEM photo of the lithium iron manganese phosphate electrode sheet provided by the present invention after rolling;

[0027] Figure 2 It is a 3000X SEM photo of the lithium iron manganese phosphate electrode sheet provided by the present invention after rolling. Detailed Embodiments

[0028] In order to further understand the present invention, the preferred implementation modes of the present invention will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention rather than limiting the claims of the present invention.

[0029] There is no particular limitation on the sources of all raw materials of the present invention, and they can be purchased on the market or prepared by conventional methods well-known to those skilled in the art.

[0030] There is no particular limitation on the purity of all raw materials of the present invention. The present invention preferably uses analytically pure or the conventional purity requirements in the field of lithium ion battery positive electrode sheet material preparation.

[0031] All raw materials of the present invention, their trade names and abbreviations all belong to the conventional trade names and abbreviations in the field. Each trade name and abbreviation is clear and definite in the field of its related uses. Those skilled in the art can purchase or prepare them by conventional methods according to the trade name, abbreviation and corresponding uses.

[0032] The processes used in the present invention, their abbreviations all belong to the conventional abbreviations in the field. The specific steps and conventional parameters of each abbreviation are clear and definite in the related field. Those skilled in the art can implement them by conventional methods according to the abbreviations.

[0033] D90 particle size of lithium iron manganese phosphate particles: In the particle size distribution of particles, it is the particle size value corresponding to the cumulative distribution percentage reaching 90% from small to large.

[0034] Tensile strength (σ) of positive electrode: In a tensile test, the maximum tensile stress that the specimen experiences until it breaks is the tensile strength, and the result is expressed in MPa.

[0035] Compaction change rate △PD after re-pressing of positive electrode sheet: The degree of change in compaction of the positive electrode sheet after re-rolling after disassembly, relative to the compaction before rolling, in units of .

[0036] This invention provides a positive electrode sheet, the positive electrode sheet comprising a current collector and a positive electrode material composited on the current collector;

[0037] The positive electrode material includes a positive electrode active material;

[0038] The positive electrode active material is selected from lithium iron manganese phosphate;

[0039] The D90 particle size of the lithium manganese iron phosphate particles, the tensile strength σ of the positive electrode, and the compaction density PD of the positive electrode satisfy the relationship described in equation (I):

[0040] 1600 <D90 / PD×σ<4800 (I);

[0041] Where D90 is measured in μm, σ in MPa, and PD in g / cm³. 3 .

[0042] This invention suggests that while using an agglomerate structure can reduce the solvent and binder content in the slurry mixing process, achieving both primary particle size reduction and thick electrode coating, agglomeration results in larger particle sizes. This makes it difficult to achieve high compaction density during processing, thus hindering the improvement of cell energy density. Therefore, it is necessary to address the issue of improving the compaction density of lithium manganese iron phosphate (LFP) agglomerate electrodes. This invention specifically designs a LFP cathode with a unique structure, where the D90 particle size of the LFP particles, the tensile strength σ of the cathode, and the compaction density PD satisfy a specific relationship. By controlling the LFP particles, the tensile strength of the cathode, and the compaction density of the cathode, this invention further improves the performance of the LFP cathode.

[0043] The tensile strength of the lithium iron manganese phosphate agglomerate electrode in the present invention is comprehensively related to the particle size distribution of the particles and the state of the electrode corresponding to high compaction. Among them, the tensile strength of the electrode is also related to the properties of the current collector (foil), the properties of the active material layer, and the processing technology / equipment. In the present invention, when D90, σ, and PD satisfy the following relational expression (I), at a certain compaction density, using lithium iron manganese phosphate agglomerates with relatively large particle sizes, in coordination with a suitable foil and processing technology, the prepared electrode has a relatively low tensile strength; using lithium iron manganese phosphate agglomerates with relatively small particle sizes, in coordination with a suitable foil and processing technology, the prepared electrode has a relatively high tensile strength; when the particle size is certain, using a relatively large compaction density, in coordination with a suitable foil and processing technology, the prepared electrode has a relatively high tensile strength; using a relatively low compaction density, in coordination with a suitable foil and processing technology, the prepared electrode has a relatively low tensile strength. Further, compared with D50 of the lithium iron manganese phosphate particles, D50 reflects the overall particle size of the particles, while D90 can better reflect the size characteristics of the large particles in the lithium iron manganese phosphate material. When exceeding the upper limit of D90, the particle size is too large, which is likely to cause scratches on the electrode during coating, and the strength requirement for the foil during rolling is relatively high; when exceeding the lower limit of D90, the particle size is too small, more solvents and binders are required during slurry mixing, and the processing performance of the slurry becomes poor, which is not conducive to thick electrode coating.

[0044] Moreover, the tensile strength of the electrode is related to the properties of the current collector (foil) itself, the properties of the active material layer, and the processing technology, especially the foil, the coating amount (surface density) of the active material, and the adhesion between the active material layer and the foil. If the tensile strength σ is too low, it indicates the deterioration of the processing performance of the electrode after rolling, which may lead to negative impacts such as breakage of the electrode during rolling. In addition, there may be some microcracks inside the current collector, affecting electron transport and thus the performance of the battery cell.

[0045] In the present invention, in the relational expression described in formula (I), it can be 2000 < D90 / PD × σ < 4000, or it can be 2500 < D90 / PD × σ < 3500.

[0046] In the present invention, the lithium iron manganese phosphate particles are specifically preferably lithium iron manganese phosphate secondary particles.

[0047] In the present invention, the D90 particle size of the lithium iron manganese phosphate particles is preferably 10 - 50 μm, more preferably 15 - 40 μm, more preferably 20 - 35 μm, and even more preferably 25 - 30 μm.

[0048] In the present invention, the compaction density PD is preferably 2.0 - 2.5 g / cm 3 , more preferably 2.1 - 2.4 g / cm 3 , even more preferably 2.2 - 2.3 g / cm 3 .

[0049] In this invention, the tensile strength σ is preferably 100~500MPa, more preferably 150~450MPa, more preferably 200~400MPa, and even more preferably 250~350MPa.

[0050] In this invention, the compaction change rate ΔPD of the positive electrode sheet and the tensile strength σ of the positive electrode sheet preferably satisfy the relationship described in equation (II):

[0051] 0 < σ × △PD < 95 (II);

[0052] Where σ is in MPa, △PD = (PD max -PD) / PD, PD max This represents the maximum compaction density.

[0053] In this invention, the maximum compaction density is preferably the compaction density corresponding to the time when the positive electrode sheet is folded in half to transmit light after secondary rolling or the compaction density corresponding to the time when the lithium manganese iron phosphate particles are crushed after secondary rolling of the positive electrode sheet.

[0054] In this invention, in formula (II), σ×△PD can also be 5~90, or 15~80, or 35~60.

[0055] In this invention, the range of △PD is preferably 4%~25%, more preferably 5%~23%, more preferably 8%~20%, and even more preferably 10%~18%.

[0056] This invention provides a method for preparing a positive electrode sheet, comprising the following steps:

[0057] 1) After mixing the above-mentioned lithium manganese iron phosphate agglomerate secondary particles, binder, conductive agent and solvent, a positive electrode slurry is obtained;

[0058] 2) Coat the positive electrode slurry obtained in the above steps onto the current collector, and then roll it to obtain the positive electrode sheet.

[0059] The present invention first mixes the above-mentioned lithium manganese iron phosphate agglomerate secondary particles, binder, conductive agent and solvent to obtain positive electrode slurry.

[0060] In this invention, the method for preparing the secondary particles of lithium manganese iron phosphate agglomerates preferably includes the following steps:

[0061] (1) After ball milling and mixing manganese source, iron source, carbon source, lithium source and phosphorus source, the precursor powder is obtained after one grinding, one spray drying and one sintering.

[0062] (2) After the precursor powder and carbon source obtained in the above steps are ball-milled and mixed again, they are then subjected to secondary grinding, secondary spraying and secondary sintering to obtain secondary particles of lithium manganese iron phosphate agglomerates.

[0063] In this invention, the sintering process of the secondary particles of lithium manganese iron phosphate agglomerates is specifically carried out under a protective atmosphere.

[0064] In this invention, the pressure of the single spray is preferably 0.1~1.35MPa, more preferably 0.1~1.35MPa, more preferably 0.5~1.3MPa, and even more preferably 1~1.2MPa.

[0065] In this invention, the carbon content of the single spray coating is preferably 0.1%wt to 0.8%wt, more preferably 0.2%wt to 0.7%wt, and even more preferably 0.3%wt to 0.6%wt.

[0066] In this invention, the sintering time for one sintering is preferably 1 to 10 hours, more preferably 3 to 8 hours, and even more preferably 5 to 6 hours.

[0067] In this invention, the temperature of the first sintering is preferably 200~800℃, more preferably 300~700℃, and even more preferably 400~600℃.

[0068] In this invention, the carbon content of the secondary spray coating is preferably 1.0%wt to 3.0%wt, more preferably 1.2%wt to 2.8%wt, and even more preferably 1.5%wt to 2.5%wt.

[0069] In this invention, the pressure of the secondary spray is preferably 0.1~1.35MPa, more preferably 0.1~1.35MPa, more preferably 0.5~1.3MPa, and even more preferably 1~1.2MPa.

[0070] In this invention, the secondary sintering time is 1~10h, more preferably 3~8h, and even more preferably 5~6h.

[0071] In this invention, the temperature of the secondary sintering is 400~800℃, more preferably 450~750℃, and even more preferably 500~700℃.

[0072] In this invention, the secondary spraying specifically involves adding a fluxing agent and a dispersant for secondary spraying;

[0073] In this invention, the amount (mass content) of the fluxing agent is preferably 0.1% to 1.5%, more preferably 0.3% to 1.2%, and even more preferably 0.5% to 1.0%.

[0074] In this invention, the amount (mass content) of dispersant A is preferably 0.1-1.3%, more preferably 0.3%-1.1%, and even more preferably 0.5%-0.8%.

[0075] In this invention, the method for preparing the secondary particles of lithium manganese iron phosphate agglomerates preferably includes the following steps:

[0076] (1) Manganese source, iron source, carbon source, lithium source, phosphorus source and water are ground and mixed once, and then spray dried and sintered to obtain precursor powder;

[0077] (2) Under a protective atmosphere, the precursor powder obtained in the above steps is ball-milled and mixed with carbon source and water again. Under a protective atmosphere, it is then sprayed and sintered twice to obtain secondary particles of lithium manganese iron phosphate agglomerates.

[0078] In this invention, the sintering process of the secondary particles of lithium manganese iron phosphate agglomerates is specifically carried out under a protective atmosphere.

[0079] In this invention, the pressure of the single spray is preferably 0.3~1.25MPa, more preferably 0.5~1.0MPa, and even more preferably 0.7~0.8MPa.

[0080] In this invention, the carbon content of the single spray coating is preferably 0.2%wt to 0.7%wt, more preferably 0.3%wt to 0.6%wt, and even more preferably 0.4%wt to 0.5%wt.

[0081] In this invention, the sintering time for the first sintering is preferably 2-8 hours, more preferably 3-7 hours, and even more preferably 4-6 hours.

[0082] In this invention, the temperature of the first sintering is preferably 300~600℃, more preferably 350~550℃, and even more preferably 400~500℃.

[0083] In this invention, the carbon content of the secondary spray coating is preferably 1.2%wt to 3.0%wt, more preferably 1.5%wt to 2.8%wt, and even more preferably 1.8%wt to 2.5%wt.

[0084] In this invention, the pressure of the secondary spray is preferably 0.3~1.25MPa, more preferably 0.5~1.05MPa, and even more preferably 0.7~0.9MPa.

[0085] In this invention, the secondary sintering time is 2 to 11 hours, more preferably 4 to 9 hours, and even more preferably 6 to 7 hours.

[0086] In this invention, the temperature of the secondary sintering is 500~700℃, more preferably 550~650℃.

[0087] In this invention, the secondary spraying specifically involves adding a fluxing agent and a dispersant for secondary spraying;

[0088] In this invention, the amount (mass content) of the fluxing agent is preferably 0.05% to 1.4%, more preferably 0.3% to 1.2%, and even more preferably 0.5% to 1.0%.

[0089] In this invention, the amount (mass content) of dispersant A is preferably 0.01% to 1.0%, more preferably 0.05% to 0.8%, and even more preferably 0.1% to 0.5%.

[0090] Finally, the positive electrode slurry obtained in the above steps is coated onto the current collector, and then rolled to obtain the positive electrode sheet.

[0091] This invention provides a lithium-ion battery, including a positive electrode sheet;

[0092] The positive electrode sheet is the positive electrode sheet described in any one of the above technical solutions or the positive electrode sheet prepared by the preparation method described in any one of the above technical solutions.

[0093] To complete and refine the overall technical solution and better ensure that the positive electrode sheet satisfies the relationship described in equation (I), the aforementioned lithium manganese iron phosphate positive electrode sheet and its preparation method, as well as the lithium-ion battery, may specifically include the following:

[0094] A battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material, the positive electrode active material includes lithium manganese iron phosphate particles, the particle size of the lithium manganese iron phosphate particles is D90, and the tensile strength (denoted as σ) and compaction (denoted as PD) of the positive electrode sheet are related by the following equation (I): 1600 <D90 / PD×σ<4800。

[0095] In this invention, under a certain compaction density, the larger the D90, the more large particles there are. Large particles can cause damage to foil materials during the rolling process. The tensile strength of the electrode sheet made under a certain compaction condition is low. Therefore, it is necessary to improve the tensile strength of the electrode sheet by taking into account other conditions to avoid the electrode sheet from breaking during subsequent processes such as winding.

[0096] In this invention, if the lower limit of the relation is exceeded, D90 becomes too small, resulting in an excessively large specific surface area, poor slurry processability, and excessive interfacial side reactions. This leads to accelerated capacity decay and DCR growth during long-term cycling or storage, or the tensile strength of the electrode becomes too low to meet processing requirements, or the electrode compaction becomes too large, causing cracking of the agglomerate material and poor conductivity between primary particles, affecting the battery's kinetic performance. If the upper limit of the relation is exceeded, D90 becomes too large, making it easy to cause electrode scratches during coating and requiring higher foil strength during rolling. Alternatively, if the electrode compaction is too low, the battery's energy density will be low, and the ohmic contact between agglomerate particles will be poor, affecting the battery's kinetic performance. Or, if the tensile strength of the electrode is too high, higher requirements will be placed on the foil strength.

[0097] Specifically, the lithium manganese iron phosphate is an agglomerate comprising multiple primary particles.

[0098] Specifically, the D90 range of lithium manganese iron phosphate particles is 10~50μm.

[0099] Specifically, the PD range is 2.0~2.5. The larger the PD, the higher the energy density of the battery. However, if the PD is too large, the agglomerate particles will be crushed, and the conductivity between the primary particles will be poor, which is not conducive to the dynamic performance. At the same time, the current collector will be over-pressed, and the rolled electrode sheet will be prone to breakage, which is not conducive to processing. If the PD is too small, the energy density of the battery will be low. At the same time, the contact resistance between the agglomerate particles will be large, and the electronic conductivity will be low, which is also not conducive to the dynamic performance.

[0100] Specifically, the tensile strength σ of the positive electrode sheet ranges from 100 to 500 MPa.

[0101] Specifically, the compaction change rate ΔPD (the degree of change in compaction after the positive electrode sheet is rolled again after disassembly, relative to the compaction before rolling) and the tensile strength σ of the positive electrode sheet satisfy the following relationship (II):

[0102] 0 < σ × △PD < 95. Equation (II) reflects the matching of particle strength / agglomeration degree.

[0103] In this invention, the tensile strength σ is the tensile strength of the electrode under the initial compaction conditions, in MPa, △PD is the maximum compaction change rate of the electrode, △PD=(PDmax-PD) / PD, PDmax is the maximum compaction value corresponding to the first fold of light transmission after the electrode is rolled again, or the agglomerate particles are broken, and particle breakage is defined as the original positive electrode particle D90 change rate decreasing by more than 20%.

[0104] The larger the value of △PD, the higher the particle strength of the electrode, and the higher the strength and toughness of the electrode / aluminum foil.

[0105] Specifically, the compaction change rate ΔPD after the positive electrode is repressurized ranges from 4% to 25%.

[0106] In this invention, PD, PD max The detection method for σ specifically includes the following steps:

[0107] PD:

[0108] 1. Actual surface density a before electrode rolling.

[0109] 2. Based on the material powder compaction b, calculate the corresponding electrode thickness c = a / (b+0.1) + foil thickness under the corresponding compaction gradient according to the design compaction. After adjusting the appropriate pressure of the roller press machine according to the calculated electrode thickness under different compaction conditions, the electrode is rolled by the roller press.

[0110] With the same folding force, after folding the electrode sheet in both directions once, if no light passes through the folded area when compared to a bright light source, then increase the number of folds. After two folds, if light passes through one fold, this indicates that the electrode sheet is actually compacted. Actual compaction d = Electrode sheet density after roller pressing / (Electrode sheet thickness after roller pressing - Foil thickness).

[0111] △PD = (PD) max -PD) / PD, PD max This represents the maximum compaction density.

[0112] In this invention, the maximum compaction density PD max This refers to the compaction density of the positive electrode sheet when it is folded in half and exposed to light once after being rolled twice.

[0113] Specific test conditions: After the positive electrode sheet undergoes a normal single rolling process, the compacted PD of the positive electrode sheet under the single rolling process is obtained. Then, the positive electrode sheet is subjected to a second rolling process to obtain the maximum compacted PD of the positive electrode sheet under the second rolling process. max The specific constraint is that the positive electrode sheet must not break under the secondary rolling pressure.

[0114] The specific test conditions are shown in Table 1.

[0115] σ:

[0116] 1. Cut a 50cm positive electrode sheet using a utility knife.

[0117] 2. Place the positive electrode sheet on the thin film sample preparation machine and cut it into several strips with a length of 100 mm and a width of 150 mm along the MD and TD directions.

[0118] 3. Clamp the positive electrode strip onto the pneumatic fixture of the universal testing machine. At this time, the gauge distance between the fixtures is 100mm.

[0119] 4. The universal testing machine was used to perform tensile testing at a tensile speed of 100 mm / min.

[0120] 5. After the universal testing machine stops, open the pneumatic clamp, clean the diaphragm debris, and readjust the gauge length to the initial length.

[0121] 6. Record the tensile strength and elongation at break results displayed on the instrument program.

[0122] 7. Repeat steps 1 to 6, and take the arithmetic mean of the results, keeping one decimal place.

[0123] See Figure 1, Figure 1 The image is a 1000X SEM image of the lithium manganese iron phosphate electrode sheet after rolling, provided by the present invention.

[0124] See Figure 2 , Figure 2 The SEM image of the lithium manganese iron phosphate electrode sheet after rolling is shown at 3000X.

[0125] This invention also provides a method for preparing a lithium-ion battery made of lithium manganese iron phosphate, comprising the following steps:

[0126] 1) Preparation of cathode material: Manganese source, iron source, carbon source, lithium source and phosphorus source are mixed, ball-milled evenly (the manganese-iron ratio of the agglomerates is adjusted according to the molar ratio of manganese source and iron source), and spray-dried to obtain precursor powder;

[0127] Precursor powder, carbon source, dopant source (additives can also be added) are mixed, ball milled twice, the material is sprayed once and sintered at high temperature for a period of time, and then sprayed twice and sintered twice (the particle size is controlled by the sintering temperature) to obtain lithium manganese iron phosphate agglomerate particles.

[0128] Cathode material preparation 2: Manganese source, iron source, carbon source, lithium source and phosphorus source are added to deionized water, mixed, dried and pulverized to obtain a precursor. The precursor is sprayed once and sintered under a nitrogen atmosphere to obtain a sintered sample. The sintered sample, carbon source and deionized water are mixed, ball-milled, dried and pulverized, sprayed a second time and sintered a second time under a nitrogen atmosphere. After pulverization, lithium manganese iron phosphate agglomerate particles are obtained.

[0129] 2) Preparation of positive electrode sheet: The above-mentioned lithium manganese iron phosphate agglomerates are used as the main material and mixed evenly with binder PVDF, conductive agent SP and conductive agent according to the mass ratio (94~97.5:1.5~4.0:0.8~1.2:0.2~0.8). The mixture is dispersed in a solvent to obtain positive electrode slurry. The positive electrode slurry is coated on aluminum foil to obtain double-sided coated positive electrode sheet. Then it is rolled and cut to obtain positive electrode sheet.

[0130] 3) Negative electrode preparation: Natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon, and SiO2 are used. x Silicon-carbon, Li4Ti5O 12 One or more of the ingredients are mixed evenly with conductive agent SP, binder CMC and binder in a certain mass ratio, and dispersed in deionized water to obtain a negative electrode slurry; the negative electrode slurry is coated on copper foil to obtain a single-sided coated electrode sheet; then it is rolled and cut to obtain a negative electrode sheet.

[0131] 4) Preparation of electrolyte

[0132] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, thoroughly dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. (The specific electrolyte solvent should be adjusted according to actual conditions.)

[0133] 5) Preparation of the separating membrane

[0134] The separator film is selected from PP, PE, or PP / PF. (The selection of the separator film can also be adjusted according to the actual situation.)

[0135] 6) Assembly and formation

[0136] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The cells are then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0137] The present invention provides a lithium manganese iron phosphate (LMP) cathode sheet and its preparation method, as well as a lithium-ion battery. The LMP cathode sheet with a specific structure designed in this invention satisfies a specific relationship between the D90 particle size of the LMP particles, the tensile strength σ of the cathode sheet, and the compaction density PD of the cathode sheet. By controlling the LMP particles, the tensile strength of the cathode sheet, and the compaction density of the cathode sheet, the present invention further improves the performance of the LMP cathode sheet.

[0138] This invention relates the tensile strength of lithium manganese iron phosphate (LFP) agglomerate electrodes to the particle size distribution and the electrode state corresponding to high compaction. The tensile strength is further related to the properties of the current collector (foil), the performance of the active material layer, and the processing technology / equipment. Under the condition that D90 and σ, PD satisfy the relationship (I), at a certain compaction density, using LFP agglomerates with relatively large particle sizes, combined with suitable foil and processing technology, results in electrodes with lower tensile strength; conversely, using LFP agglomerates with relatively small particle sizes, combined with suitable foil and processing technology, results in electrodes with higher tensile strength. With a fixed particle size, to obtain a higher compaction density, using suitable foil and processing technology results in electrodes with higher tensile strength; conversely, at a lower compaction density, using suitable foil and processing technology results in electrodes with lower tensile strength. However, when the lower limit of the relationship is exceeded, the tensile strength of the electrode is too low to meet processing requirements. Furthermore, compared to D50, which reflects the overall particle size of lithium manganese iron phosphate particles, D90 better reflects the size characteristics of large particles in lithium manganese iron phosphate materials. Exceeding the upper limit of D90 results in excessively large particle sizes, which can easily cause scratches on the electrode sheet during coating and places higher demands on the foil strength during rolling. Conversely, exceeding the lower limit of D90 results in excessively small particle sizes, requiring more solvent and binder during slurry preparation, leading to poorer slurry processing performance and hindering thick electrode coating.

[0139] Furthermore, the tensile strength of the electrode is related to the properties of the current collector (foil) itself, the properties of the active material layer, and the processing technology, especially the foil, the amount of active material coating (areal density), and the adhesion between the active material layer and the foil. A low tensile strength σ indicates a deterioration in the processability of the electrode after rolling, which may lead to negative effects such as electrode breakage during rolling. In addition, there may be some microcracks inside the current collector, affecting electron transport and thus impacting cell performance.

[0140] Furthermore, this invention also provides equation (II), where the compaction change rate ΔPD reflects the particle strength and agglomeration of lithium manganese iron phosphate particles. Simultaneously controlling ΔPD and tensile strength σ helps achieve the desired battery energy density while maintaining good processability. If the upper limit of the equation is exceeded, ΔPD is too large, indicating that the initial compaction is too low, which is detrimental to achieving high battery energy density, or that the electrode tensile strength is too high, placing excessive demands on the aluminum foil. Moreover, a certain ΔPD indicates that the lithium manganese iron phosphate particles have suitable agglomeration; too high a ΔPD indicates low particle strength, making the agglomerates easily crushed under high pressure; too low a ΔPD indicates that the lithium manganese iron phosphate particles are close to their ultimate compaction limit, resulting in insufficient electrode flexibility or near-fracture of the particles.

[0141] To further illustrate the present invention, the following describes in detail a positive electrode sheet and its preparation method, as well as a lithium-ion battery, provided by the present invention, with reference to embodiments. However, it should be understood that these embodiments are implemented under the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. They are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention. The scope of protection of the present invention is not limited to the following embodiments.

[0142] Example 1

[0143] 1) Preparation of cathode material: Manganese acetate, ferric acetate, sucrose / polyvinyl alcohol, lithium carbonate, and ammonium dihydrogen phosphate are mixed in a ratio of n(manganese acetate + ferric acetate), n(lithium carbonate), and n(ammonium dihydrogen phosphate) = 1:1:1, where n(manganese acetate):n(ferric acetate) satisfies a ratio of 3:1. The mixture is ground once to achieve uniformity, followed by a single spray drying and sintering to obtain precursor powder. The precursor powder is then mixed with sucrose / polyvinyl alcohol, magnesium chloride, and calcium chloride, and subjected to a second ball milling. The material is then sprayed twice and sintered at high temperature for a period of time. Finally, a second spraying and sintering process is performed to obtain lithium manganese iron phosphate agglomerate particles. The spraying equipment pressure before the first and second sintering is 0.4 MPa. The amount of flux (potassium carbonate) added during the second spray drying before the second sintering is 0.1%, and the amount of dispersant (polyester polyether) is 0.05%.

[0144] 2) Preparation of positive electrode sheet: The above-mentioned lithium manganese iron phosphate agglomerates are used as the main material according to the mass ratio (94:3:1:2), and are mixed evenly with binder PVDF, conductive agent SP and conductive agent, and dispersed in solvent to obtain positive electrode slurry; the positive electrode slurry is coated on aluminum foil to obtain double-sided coated positive electrode sheet; then it is rolled and cut to obtain positive electrode sheet.

[0145] 3) Preparation of negative electrode sheet: Artificial graphite is mixed evenly with conductive agent SP 4% and binder 4% at a mass ratio of 92%, and dispersed in deionized water to obtain negative electrode slurry; the negative electrode slurry is coated on copper foil to obtain single-sided coated electrode sheet; then it is rolled and cut to obtain negative electrode sheet.

[0146] 4) Preparation of electrolyte

[0147] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0148] 5) The separator is made of PP.

[0149] 6) Assembly and formation

[0150] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The cells are then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0151] Example 2

[0152] 1) Preparation of cathode material: Manganese acetate, ferric acetate, sucrose / polyvinyl alcohol, lithium carbonate, and ammonium dihydrogen phosphate were mixed in a ratio of n(manganese acetate + ferric acetate), n(lithium carbonate), and n(ammonium dihydrogen phosphate) = 1:1:1, where the ratio of n(manganese acetate):n(ferric acetate) satisfies 3:1. The mixture was ball-milled until homogeneous and then spray-dried to obtain precursor powder. The precursor powder was then mixed with sucrose / polyvinyl alcohol, magnesium chloride, and calcium chloride, and ball-milled a second time. After the material was sprayed once and sintered at high temperature for a period of time, it underwent a second spraying and a second sintering to obtain lithium manganese iron phosphate agglomerates. The spraying equipment pressure before the first and second sintering was 0.9 MPa. The amount of flux (potassium carbonate) added during the second spray drying before the second sintering was 1.32%, and the amount of dispersant (polyester polyether) was 0.4%.

[0153] 2) The preparation of the positive electrode is the same as in Example 1.

[0154] 3) The negative electrode preparation is the same as in Example 1.

[0155] 4) The preparation of the electrolyte is the same as in Example 1.

[0156] 5) The release liner is made of PE.

[0157] 6) Assemble and process as in Example 1.

[0158] Example 3

[0159] 1) Preparation of cathode material: Manganese acetate, ferric acetate, sucrose / polyvinyl alcohol, lithium carbonate, and ammonium dihydrogen phosphate were mixed in a ratio of n(manganese acetate + ferric acetate), n(lithium carbonate), and n(ammonium dihydrogen phosphate) = 1:1:1, where the ratio of n(manganese acetate):n(ferric acetate) satisfies 3:1. The mixture was ball-milled until homogeneous and then spray-dried to obtain precursor powder. The precursor powder was then mixed with sucrose / polyvinyl alcohol, magnesium chloride, and calcium chloride, and ball-milled a second time. After the material was sprayed once and sintered at high temperature for a period of time, it underwent a second spraying and a second sintering to obtain lithium manganese iron phosphate agglomerate particles. The spraying equipment pressure before the first and second sintering was 0.65 MPa. The amount of flux (potassium carbonate) added during the second spray drying before the second sintering was 0.3%, and the amount of dispersant (polyester polyether) was 0%.

[0160] 2) The preparation of the positive electrode is the same as in Example 1.

[0161] 3) The negative electrode is prepared in the same way as in Example 1.

[0162] 4) The preparation of the electrolyte is the same as in Example 1.

[0163] 5) The separator is selected from PP / PF.

[0164] 6) Assemble and process as in Example 1.

[0165] Example 4

[0166] 1) Preparation of cathode material: Manganese acetate, ferric acetate, sucrose / polyvinyl alcohol, lithium carbonate, and ammonium dihydrogen phosphate were mixed with deionized water at a ratio of n(manganese acetate + ferric acetate), n(lithium carbonate), n(ammonium dihydrogen phosphate) = 1:1:1, where n(manganese acetate):n(ferric acetate) satisfies a ratio of 3:1. The mixture was dried and pulverized to obtain a precursor. The precursor was sprayed once and sintered under a nitrogen atmosphere to obtain a first-burned sample. The first-burned sample, carbon source, and deionized water were mixed, ball-milled, dried, pulverized, sprayed a second time, and sintered a second time under a nitrogen atmosphere. After pulverization, lithium manganese iron phosphate agglomerates were obtained. The spraying equipment pressure before the first and second burns was 1.05 MPa. The amount of flux (potassium carbonate) added during the second spray drying before the second burn was 1.28%, and the amount of dispersant (polyester polyether) was 0.3%. The amount of flux and dispersant added was based on the mass of lithium manganese iron phosphate powder after the first burn.

[0167] 2) The preparation of the positive electrode is the same as in Example 1.

[0168] 3) The negative electrode is prepared in the same way as in Example 1.

[0169] 4) The preparation of the electrolyte is the same as in Example 1.

[0170] 5) Preparation of the separator: PP is selected as the separator.

[0171] 6) Assemble and process as in Example 1.

[0172] Example 5

[0173] Cathode material preparation: Manganese acetate, ferric acetate, sucrose / polyvinyl alcohol, lithium carbonate, and ammonium dihydrogen phosphate were mixed with deionized water at a ratio of n(manganese acetate + ferric acetate), n(lithium carbonate), and n(ammonium dihydrogen phosphate) of 1:1:1, where the ratio of n(manganese acetate):n(ferric acetate) satisfies 3:1. The mixture was dried and pulverized to obtain a precursor. The precursor was then sprayed once and sintered under a nitrogen atmosphere to obtain a first-burned sample. The first-burned sample, carbon source, and deionized water were mixed, ball-milled, dried, pulverized, sprayed a second time, and then sintered a second time under a nitrogen atmosphere. The pulverized sample yielded lithium manganese iron phosphate agglomerates. The spraying equipment pressure before the first and second burns was 0.82 MPa. The amount of flux (potassium carbonate) added during the second spray drying before the second burn was 1.4%, and the amount of dispersant (polyester polyether) was 0.8%.

[0174] 2) The preparation of the positive electrode is the same as in Example 1.

[0175] 3) The negative electrode preparation is the same as in Example 1.

[0176] 4) The preparation of the electrolyte is the same as in Example 1.

[0177] 5) Preparation of the separator: PE is selected as the separator.

[0178] 6) Assemble and process as in Example 1.

[0179] Example 6

[0180] 1) Manganese acetate, ferric acetate, sucrose / polyvinyl alcohol, lithium carbonate, and ammonium dihydrogen phosphate were mixed with deionized water at a ratio of n(manganese acetate + ferric acetate), n(lithium carbonate), and n(ammonium dihydrogen phosphate) = 1:1:1, where the ratio of n(manganese acetate) to n(ferric acetate) was 3:1. The mixture was dried and pulverized to obtain a precursor. The precursor was sprayed once and then sintered under a nitrogen atmosphere to obtain a first-burned sample. The first-burned sample, carbon source, and deionized water were mixed, ball-milled, dried, pulverized, sprayed a second time, and then sintered a second time under a nitrogen atmosphere. After pulverization, lithium manganese iron phosphate agglomerate particles were obtained. The spraying equipment pressure before the first and second burns was 0.6 MPa. The amount of flux (potassium carbonate) added during the second spray drying before the second burn was 0.4%, and the amount of dispersant (polyester polyether) was 0.25%.

[0181] 2) The preparation of the positive electrode is the same as in Example 1.

[0182] 3) The negative electrode preparation is the same as in Example 1.

[0183] 4) The preparation of the electrolyte is the same as in Example 1.

[0184] 5) Preparation of the separator: PP / PF is selected as the separator.

[0185] 6) Assemble and process as in Example 1.

[0186] Comparative Example 1

[0187] 1) Preparation of cathode material: Manganese acetate, ferric acetate, sucrose / polyvinyl alcohol, lithium carbonate, and ammonium dihydrogen phosphate were mixed with deionized water at a ratio of n(manganese acetate + ferric acetate), n(lithium carbonate), n(ammonium dihydrogen phosphate) = 1:1:1, where the ratio of n(manganese acetate):n(ferric acetate) satisfies 3:1. The mixture was dried and pulverized to obtain a precursor. The precursor was sprayed once and sintered under a nitrogen atmosphere to obtain a first-burned sample. The first-burned sample, carbon source, and deionized water were mixed, ball-milled, dried, pulverized, sprayed a second time, and sintered a second time under a nitrogen atmosphere to obtain lithium manganese iron phosphate agglomerates. The spraying equipment pressure before the first and second burns was 1.12 MPa. The amount of flux (potassium carbonate) added during the second spray drying before the second burn was 0.25%, and the amount of dispersant (polyester polyether) was 0.15%. The first and second burn temperatures were 570℃ and 720℃, respectively, and the sintering times were 9 and 10 hours, respectively.

[0188] 2) The preparation of the positive electrode is the same as in Example 1.

[0189] 3) The negative electrode preparation is the same as in Example 1.

[0190] 4) The preparation of the electrolyte is the same as in Example 1.

[0191] 5) Preparation of the separator: PE is selected as the separator.

[0192] 6) Assemble and process as in Example 1.

[0193] Comparative Example 2

[0194] 1) Preparation of cathode material: Manganese acetate, ferric acetate, sucrose / polyvinyl alcohol, lithium carbonate, and ammonium dihydrogen phosphate were mixed with deionized water at a ratio of n(manganese acetate + ferric acetate), n(lithium carbonate), n(ammonium dihydrogen phosphate) = 1:1:1, where the ratio of n(manganese acetate):n(ferric acetate) satisfies 3:1. The mixture was dried and pulverized to obtain a precursor. The precursor was sprayed once and sintered under a nitrogen atmosphere to obtain a first-burned sample. The first-burned sample, carbon source, and deionized water were mixed, ball-milled, dried, pulverized, sprayed a second time, and sintered a second time under a nitrogen atmosphere to obtain lithium manganese iron phosphate agglomerates. The spraying equipment pressure before the first and second burns was 0.35 MPa. The amount of flux (potassium carbonate) added during the second spray drying before the second burn was 0.13%, and the amount of dispersant (polyester polyether) was 0.2%. The first and second burn temperatures were 450℃ and 665℃, respectively, and the sintering times were 10h and 9h, respectively.

[0195] 2) The preparation of the positive electrode is the same as in Example 1.

[0196] 3) The negative electrode preparation is the same as in Example 1.

[0197] 4) The preparation of the electrolyte is the same as in Example 1.

[0198] 5) Preparation of the separator: PE is selected as the separator.

[0199] 6) Assemble and process as in Example 1.

[0200] Other testing methods:

[0201] D90:

[0202] After turning the sample inside the self-sealing bag upside down 2-3 times, weigh out about 0.04-0.06g of the sample and put it into a 50ml beaker;

[0203] Add 10 ml of 1% NP-40 sample dispersant to a beaker, stirring with a glass rod during the addition process. Then, ultrasonically disperse the sample at 40 kHz for 3 minutes. Quickly pour the dispersed sample into the sample cell of the particle size analyzer. Rinse the beaker with a wash bottle and pour all the rinsing solution into the sample cell. Set the sample refractive index and absorptivity in the instrument, and the laser intensity ≥75%. Start the test. After the test is completed, the computer connected to the particle size analysis software will automatically output the particle size D90 data.

[0204] 2C constant current ratio:

[0205] Assemble a positive electrode half-cell using fresh positive electrode sheets. The assembled positive electrode half-cell is then filled with electrolyte, sealed, and subjected to room temperature capacitance testing. The capacitated half-cell is then subjected to a double-charge test in a room temperature chamber. The double-charge test (charge rate is 0.33C / 1 / 2C, constant voltage charging at 4.3V, cutoff current 0.05C, discharge rate is 0.33C) follows these steps: 2C constant rate charging to 4.3V, then constant voltage charging at 4.3V, cutoff current 0.05C, and then 0.33C discharge. The 2C constant current ratio = 2C constant rate charging capacity / total 2C charging capacity. The capacity in the current is taken as the design capacity.

[0206] Energy density: Battery energy density = cell capacity × discharge plateau ÷ cell volume

[0207] See Table 1, which shows the PD and PD of this invention. max Specific test conditions

[0208] Table 1

[0209] Example Primary roller pressure Secondary roller pressure Roller temperature Roller speed Example 1 55bar 182bar 110℃ 8m / min Example 2 55bar 188bar 110℃ 8m / min Example 3 55bar 185 bar 110℃ 8m / min Example 4 55bar 185 bar 110℃ 8m / min Example 5 55bar 189bar 110℃ 8m / min Example 6 55bar 187bar 110℃ 8m / min Comparative Example 1 55bar 178bar 110℃ 8m / min Comparative Example 2 55bar 185 bar 110℃ 8m / min

[0210] See Table 2, which shows some of the experimental parameters in the embodiments and comparative examples of the present invention.

[0211] Table 2

[0212] process parameters First / Second Burn Pre-burning Spray Pressure Flux addition amount before second firing Dosage of dispersant A added in the pre-burning spray section First sintering temperature Sintering time Carbon encapsulation amount in one sintering Secondary sintering temperature Secondary sintering time Secondary sintering carbon coating amount unit MPa % % ℃ h % ℃ h % Example 1 0.4 0.1 0.05 550 8 0.25 640 9 1.8 Example 2 0.9 1.32 0.4 500 3 0.6 720 7 2.6 Example 3 0.65 0.3 0 540 9 0.35 660 8 1.9 Example 4 1.05 1.28 0.3 520 3 0.55 690 6 2.8 Example 5 0.82 1.4 0.8 545 6 0.4 760 7 2.2 Example 6 0.6 0.4 0.25 530 8 0.4 680 7 2.05 Comparative Example 1 1.12 0.25 0.15 570 9 0.58 720 10 3 Comparative Example 2 0.35 0.13 0.2 450 10 0.2 665 9 1.6

[0213] See Table 3, which shows the detection effect data in the embodiments and comparative examples of the present invention.

[0214] Table 3

[0215] D90 PD σ Formula 1 Range △PD Formula 2 range Performance 1 (2C constant current ratio) Performance 2 (Energy Density of Square-Case Battery) micrometer <![CDATA[g / cm 3 ]]> Mpa <![CDATA[micrometer × MPa / (g / cm 3 )]]> % <![CDATA[MPa×(g / cm 3 )]]> % Wh / L Parameter range 10-50 2.0~2.5 100~500 1600-4800 0~25 0-95 Example 1 49 2.05 150 3585 5% 7.50 60% 390 Example 2 11 2.39 400 1841 20% 80.00 56% 400 Example 3 42 2.15 170 3321 12% 20.40 69% 410 Example 4 14 2.32 360 2172 18% 64.80 65% 430 Example 5 25 2.45 420 4592 22% 92.40 59% 415 Example 6 38 2.20 230 4015 14% 32.20 74% 460 Comparative Example 1 12 2.3 300 1565 2.00% 6 46% 340 Comparative Example 2 31 2.15 395 5695 24.8% 97.96 36% 320

[0216] The foregoing has provided a detailed description of the lithium manganese iron phosphate cathode sheet, its preparation method, and the lithium-ion battery provided by this invention. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are merely for the purpose of helping to understand the method and core ideas of this invention, including the best mode, and also to enable any person skilled in the art to practice this invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those skilled in the art, several improvements and modifications can be made to this invention without departing from the principles of this invention, and these improvements and modifications also fall within the protection scope of the claims of this invention. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements that are not different from the textual description of the claims, or if they include equivalent structural elements that are not substantially different from the textual description of the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A positive electrode plate, characterized in that, The positive electrode includes a current collector and a positive electrode material composited on the current collector; The positive electrode material includes a positive electrode active material; The positive electrode active material is selected from lithium manganese iron phosphate; The D90 particle size of the lithium manganese iron phosphate particles, the tensile strength σ of the positive electrode, and the compaction density PD of the positive electrode satisfy the relationship described in equation (I): 1841≤D90 / PD×σ≤4592 (I); Where D90 is measured in μm, σ in MPa, and PD in g / cm³. 3 ; The compaction change rate ΔPD of the positive electrode sheet and the tensile strength σ of the positive electrode sheet satisfy the relationship described in equation (II): 0 < σ × △PD < 95 (II); Where σ is in MPa, △PD = (PD max -PD) / PD, PD max This represents the maximum compaction density. The maximum compaction density is the compaction density corresponding to the positive electrode sheet after secondary rolling and folding to transmit light.

2. The positive electrode sheet according to claim 1, characterized in that, In the formula (I), 2000 <D90 / PD×σ<4000。 3. The positive electrode sheet according to claim 1, characterized in that, The lithium manganese iron phosphate particles specifically include secondary lithium manganese iron phosphate particles.

4. The positive electrode sheet according to claim 1, characterized in that, The D90 particle size of the lithium manganese iron phosphate particles is 10~50μm.

5. The positive electrode sheet according to claim 4, characterized in that, The D90 particle size of the lithium manganese iron phosphate particles is 15~40μm.

6. The positive electrode sheet according to claim 1, characterized in that, The compaction density PD is 2.0~2.5 g / cm³. 3 .

7. The positive electrode sheet according to claim 1, characterized in that, The tensile strength σ is 100~500MPa.

8. The positive electrode sheet according to claim 1, characterized in that, The range of △PD is 4% to 25%.

9. A lithium-ion battery, characterized in that, Including the positive electrode plate; The positive electrode is the positive electrode as described in any one of claims 1 to 8.

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