A lithium-ion battery and a method for preventing lithium-ion battery cycle failure.

Abstract

This disclosure provides a lithium-ion battery and a method for preventing cycle failure of lithium-ion batteries, relating to the field of lithium-ion battery cycle failure technology. The method includes assembling a pouch cell, wherein the lithium-ion battery includes a negative electrode, a positive electrode, a separator, and an electrolyte. The negative electrode is prepared by coating a negative electrode slurry, comprising a negative electrode active material, a conductive agent, and a binder, onto the surface of a negative electrode current collector, drying it to form a negative electrode active material layer, thus obtaining the negative electrode. The pouch cell must satisfy: K*M*L≥0.36, where K is the cell expansion rate, M is the graphite electrode strength, and L is a compensation coefficient. This disclosure comprehensively considers the negative electrode expansion rate, binder content, powder OI value, electrode peel strength, and coating temperature, which can prevent the lithium-ion battery from easily failing during cycling.

Description

Technical Field

[0001] This disclosure relates to the field of lithium-ion battery cycle failure technology, specifically to a lithium-ion battery and a method for preventing lithium-ion battery cycle failure. Background Technology

[0002] The statements in this section are merely background information relating to this disclosure and do not necessarily constitute prior art.

[0003] Lithium battery failures are mainly classified into two categories: performance failure and safety failure. Performance failure (cycle failure) refers to the lithium battery's performance failing to meet usage requirements, mainly including capacity decay, rapid capacity loss, poor performance, poor consistency, high K-value, and poor high and low temperature performance. Safety failure refers to failures that pose certain safety risks to lithium batteries due to improper use or abuse, mainly including thermal runaway, gas expansion, leakage, lithium plating, short circuit, and expansion deformation.

[0004] Failure analysis is a technical and managerial activity that identifies product failure modes, analyzes the causes of failure, and predicts or prevents failure phenomena. In other words, failure analysis involves finding the root causes of failure in defective products, summarizing all the unusual phenomena that occur during the product's lifespan, and then applying these lessons to new products.

[0005] Failure phenomena and their causes are not a simple one-to-one correspondence; the same failure phenomenon may be caused by different failure causes. Existing methods all use a single failure cause to describe and analyze whether a lithium battery has failed, lacking a quantitative analysis perspective to examine the influence weight and priority relationship of multiple failure causes at a certain stage. This makes it impossible to accurately assess failed batteries and propose reasonable targeted measures. Summary of the Invention

[0006] To address the aforementioned problems, this disclosure proposes a lithium-ion battery and a method for preventing lithium-ion battery cycle failure. During the battery cell manufacturing process, the expansion rate of the negative electrode sheet, the binder content, the powder OI value, the electrode sheet peel strength, and the coating temperature are comprehensively considered to ensure that the lithium-ion battery does not easily fail during cycling.

[0007] According to some embodiments, the present disclosure adopts the following technical solutions:

[0008] A method for preventing cycle failure of lithium-ion batteries includes: during the preparation of the battery cell, comprehensively considering the expansion rate of the negative electrode sheet, the binder content, the OI value of the powder, the cell expansion rate, and the strength of the graphite electrode sheet, so that they satisfy the following relationship: K*M*L≥0.36; where K=∈*b*OI; ∈ is the electrode sheet expansion rate, b is the binder content, OI is the OI value of the powder, ∈ is the electrode sheet expansion rate, the smaller ∈ is, the more stable the electrode sheet is; the larger ∈ is, the less stable the electrode sheet is; K is the cell expansion rate, M is the strength of the graphite electrode sheet, and L is the compensation coefficient.

[0009] Furthermore, M = n * t; n is the peel strength of the negative electrode sheet, and t is the highest temperature on one side during negative electrode coating.

[0010] Furthermore, the value of ∈ is 3% to 8%, the value of b is 2.5% to 3.5%, and the value of OI is 2 to 10.

[0011] Furthermore, n takes the value ≥8N / m, t takes the value ≥60℃, and L takes the value 0.5~2.

[0012] According to some embodiments, the present disclosure adopts the following technical solutions:

[0013] A lithium-ion battery includes: a cell satisfying: K*M*L≥0.36; where K=∈*b*OI; ∈ is the electrode expansion rate, b is the binder content, OI is the powder OI value, ∈ is the electrode expansion rate, the smaller ∈ is, the more stable the electrode; the larger ∈ is, the less stable the electrode; K is the cell expansion rate, M is the graphite electrode strength, and L is the compensation coefficient.

[0014] Furthermore, the lithium-ion battery includes a negative electrode, a positive electrode, a separator, and an electrolyte;

[0015] The negative electrode preparation process is as follows: a negative electrode slurry including a negative electrode active material, a conductive agent and a binder is coated on the surface of a negative electrode current collector, and after drying, a negative electrode active material layer is formed to obtain a negative electrode sheet.

[0016] Furthermore, the negative electrode active material includes at least one of artificial graphite, natural graphite, silicon carbide, hard carbon, and soft carbon.

[0017] Furthermore, the particle size D50 of the negative electrode active material powder is 10-20 μm, the specific surface area of ​​the negative electrode active material powder is 1-3 m2 / g, and the compaction density of the negative electrode sheet is 1.5 g / cm3-1.7 g / cm3.

[0018] Furthermore, the lithium-ion battery preparation includes the following steps: graphite, conductive agent, binder and water are mixed into a slurry through a slurry mixing process, coated onto the current collector, and baked to form a negative electrode sheet; lithium iron phosphate, conductive agent, binder and NMP are mixed into a slurry through a slurry mixing process, coated onto the current collector, and baked to form a positive electrode sheet.

[0019] Furthermore, the battery cells are finally manufactured through processes such as rolling, slitting, die cutting, stacking, hot pressing, welding, packaging, electrolyte injection, formation, and capacity testing.

[0020] Compared with the prior art, the beneficial effects of this disclosure are as follows:

[0021] This disclosure discloses a lithium-ion battery and a method for preventing lithium-ion battery cycle failure. In the battery cell preparation process, the expansion rate of the negative electrode sheet, the binder content, the powder OI value, the electrode sheet peel strength, and the coating temperature are comprehensively considered. A quantitative analysis method is used to ensure that when K*M*L≥0.36, the lithium-ion battery will not easily fail during the cycle.

[0022] This disclosure discloses a lithium-ion battery and a method for preventing lithium-ion battery cycle failure. This method can avoid cell failure caused by electrode processing, thereby discovering problems during the trial production process, identifying problems in advance, and solving problems, thus improving the safe performance of the battery. Attached Figure Description

[0023] The accompanying drawings, which form part of this disclosure, are used to provide a further understanding of this disclosure. The illustrative embodiments of this disclosure and their descriptions are used to explain this disclosure and do not constitute an undue limitation of this disclosure.

[0024] Figure 1 This is a schematic diagram of a prototype battery cell according to an embodiment of this disclosure;

[0025] Figure 2 This is a disassembled photograph of a battery cell after 500 cycles, fully charged, according to an embodiment of this disclosure.

[0026] Figure 3 This is a disassembled photograph of the battery cell after 500 cycles in Comparative Example 4 of this disclosure, showing it fully charged.

[0027] Figure 4 This is a photograph of the battery cell after being fully charged and disassembled in Comparative Example 6 of this disclosure after 500 cycles.

[0028] Figure 5 This is a battery curve graph for all groups in the embodiments of this disclosure after 500 cycles. Detailed Implementation

[0029] The present disclosure will be further described below with reference to the accompanying drawings and embodiments.

[0030] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this disclosure. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0031] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this disclosure. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0032] Example 1

[0033] One embodiment of this disclosure provides a method for preventing cycle failure of lithium-ion batteries. In the preparation process of the battery cell, the expansion rate of the negative electrode sheet, the binder content, the OI value of the powder, the peel strength of the electrode sheet, and the temperature during coating are comprehensively considered to make the cell satisfy: K*M*L≥0.36, where K is the cell expansion rate, M is the graphite electrode sheet strength, and L is the compensation coefficient.

[0034] Where K = ∈ * b * OI; ∈ is the electrode expansion rate, b is the binder content, and OI is the powder OI value. The three factors affecting the value of K must satisfy the following: ∈ is 3% to 8%, b is 2.5% to 3.5%, and OI is 2 to 10; L is 0.5 to 2.

[0035] After a battery cell fails, analysis of the causes of the failure reveals that the parameters mentioned above during the trial production process can affect the quality of the battery cell, thus leading to its failure.

[0036] As one example, ∈ represents the electrode expansion rate. The smaller ∈ is, the more stable the electrode is, which is beneficial for lithium ion insertion and extraction and can prevent the battery from becoming too thick. The larger ∈ is, the less stable the electrode is, which is not conducive to cell cycling and can lead to battery failure due to water pressure.

[0037] As one embodiment, M = n*t; n is the peel strength of the negative electrode sheet, and t is the highest temperature on one side during negative electrode coating. The value of n is ≥8N / m, the value of t is ≥60℃, and the value of L is 0.5~2.

[0038] Where b represents the binder content. Too much binder will reduce the proportion of active material and make the electrode more brittle. Too little binder will result in low electrode peel strength, even die-cutting loss, increased side reactions, and also increased battery short-circuit rate.

[0039] OI refers to the powder's OI value, where VOI = C004 / C110, where C004 is the peak area of ​​the 004 characteristic diffraction peak in the X-ray diffraction pattern of the negative electrode active material powder, and C110 is the peak area of ​​the 110 characteristic diffraction peak in the X-ray diffraction pattern of the negative electrode active material powder. A higher OI value indicates worse kinetic performance, reducing the charging rate of the material and battery, and making lithium plating more likely under high-rate conditions, affecting safety performance. A lower OI value indicates better isotropy and kinetic performance, but it also results in poor adhesion and deviations in high-temperature performance.

[0040] n represents the peel strength of the negative electrode sheet. The greater the peel strength of the electrode sheet, the better the bond between the binder and the material, and the better the bond between the slurry and the current collector. High peel strength is beneficial to battery cycle.

[0041] t represents the highest temperature on one side during negative electrode coating. When the coating temperature is too low, the coated electrode may become wet, causing roller sticking or even coating delamination (the upper layer is dry and the lower layer is wet), leading to cycle powder removal failure. When the coating temperature is too high, the coated electrode may crack.

[0042] As an example, electrode expansion rate, binder content, powder OI value, electrode peel strength, and coating temperature can all significantly affect battery performance and lead to battery failure.

[0043] In the design disclosed herein, the expansion rate of the negative electrode sheet, the binder content, the powder OI value, the electrode sheet peel strength, and the coating temperature are taken into account. When K*M*L≥0.36, the lithium-ion battery can be prevented from easily failing during cycling.

[0044] In some embodiments, the particle size D50 of the negative electrode active material powder is 10-20 μm, the specific surface area is 1-3 m² / g, and the compaction density of the negative electrode sheet is 1.5 g / cm³ to 1.7 g / cm³. Regarding particle size D50, if it is too small, it will reduce the compaction density; if the particle size is too large, the compaction density will increase, resulting in higher impedance of the material and affecting rate performance. Regarding specific surface area, if it is too small, there will be fewer active sites, reducing the lithium-ion diffusion coefficient; if it is too large, the compaction density will decrease, which is beneficial to rate and cycle performance but will reduce high-temperature performance. Regarding compaction density, if it is too low, the electrode sheet will be too thick, affecting the material's diffusion coefficient and reducing energy density; if the compaction density is too high, a "crushing" phenomenon may occur, leading to lithium plating.

[0045] Example 2

[0046] One embodiment of this disclosure provides a lithium-ion battery, wherein the lithium-ion battery is assembled into a pouch cell, and the lithium-ion battery includes a negative electrode, a positive electrode, a separator, and an electrolyte.

[0047] The negative electrode preparation process is as follows: a negative electrode slurry including a negative electrode active material, a conductive agent and a binder is coated on the surface of a negative electrode current collector, and after drying, a negative electrode active material layer is formed to obtain a negative electrode sheet.

[0048] As one embodiment, the particle size D50 of the negative electrode active material powder is 10-20 μm, the specific surface area of ​​the negative electrode active material powder is 1-3 m2 / g, and the compaction density of the negative electrode sheet is 1.5 g / cm3-1.7 g / cm3.

[0049] As one embodiment, the negative electrode active material includes at least one of artificial graphite, natural graphite, silicon carbide, hard carbon, and soft carbon.

[0050] As one embodiment, a method for preparing a lithium-ion battery is provided, comprising the following steps: preparing a slurry by combining graphite, a conductive agent, a binder, and water through a slurry mixing process, coating it onto a current collector, and baking it to form a negative electrode sheet; preparing a slurry by combining lithium iron phosphate, a conductive agent, a binder, and NMP through a slurry mixing process, coating it onto a current collector, and baking it to form a positive electrode sheet.

[0051] Finally, the battery cells are manufactured through processes such as rolling, slitting, die cutting, stacking, hot pressing, welding, packaging, electrolyte injection, formation, and capacity testing.

[0052] Specifically, such as Figure 1 As shown, the soft-pack lithium-ion battery in this embodiment has a capacity of 3Ah;

[0053] As one embodiment, the preparation of a lithium-ion battery includes the following steps:

[0054] 1. Graphite, conductive agent, binder, water, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the negative electrode sheet; lithium iron phosphate, conductive agent, binder, NMP, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the positive electrode sheet; then, through processes such as rolling, slitting, die-cutting, stacking, hot pressing, welding, packaging, liquid injection, formation, and capacity testing, the battery cell is manufactured.

[0055] 2. Among them, after the negative electrode sheet is left to stand for 24 hours, the electrode sheet with a rebound rate of about 5% is selected. Its powder OI value is 5, the binder content is 3%, the peel force is 18N / m, the single-sided baking temperature is 60℃ during coating, and other influencing factors are around 1.5 during the trial production process.

[0056] 3. The obtained battery was subjected to a cycle test at 25°C, with a cycle voltage of 2.5V-3.65V.

[0057] As one embodiment, the soft-pack lithium-ion battery in this embodiment has a specification of 3Ah; compared with the above embodiment, the difference lies in the change of parameters;

[0058] A lithium-ion battery includes the following steps:

[0059] 1. Graphite, conductive agent, binder, water, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the negative electrode sheet; lithium iron phosphate, conductive agent, binder, NMP, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the positive electrode sheet; then, through processes such as rolling, slitting, die-cutting, stacking, hot pressing, welding, packaging, liquid injection, formation, and capacity testing, the battery cell is manufactured.

[0060] 2. Among them, after the negative electrode sheet is left to stand for 24 hours, the electrode sheet with a rebound rate of about 8% is selected. Its powder OI value is 2, the binder content is 2.5%, the peel force is 8N / m, the single-sided baking temperature is 60℃ during coating, and other influencing factors are around 1.5 during the trial production process.

[0061] 3. The obtained battery was subjected to a cycle test at 25°C, with a cycle voltage of 2.5V-3.65V.

[0062] As one embodiment, the soft-pack lithium-ion battery in this embodiment has a specification of 3Ah; compared with the above embodiment, the difference lies in the change of parameters;

[0063] A lithium-ion battery includes the following steps:

[0064] 1. Graphite, conductive agent, binder, water, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the negative electrode sheet; lithium iron phosphate, conductive agent, binder, NMP, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the positive electrode sheet; then, through processes such as rolling, slitting, die-cutting, stacking, hot pressing, welding, packaging, liquid injection, formation, and capacity testing, the battery cell is manufactured.

[0065] 2. Among them, after the negative electrode sheet is left to stand for 24 hours, the electrode sheet with a rebound rate of about 3% is selected. Its powder OI value is 10, the binder content is 3.5%, the peel force is 25N / m, and the single-sided baking temperature is 60℃ during coating. During the trial production process, other influencing factors are around 1.5.

[0066] 3. The obtained battery was subjected to a cycle test at 25°C, with a cycle voltage of 2.5V-3.65V.

[0067] Simulation comparison

[0068] Comparative Example 1: The soft-pack lithium-ion battery in Comparative Example 1 has a specification of 3Ah; compared with the example, the difference lies in the changes in steps and parameters.

[0069] A lithium-ion battery includes the following steps:

[0070] 1. Graphite, conductive agent, binder, water, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the negative electrode sheet; lithium iron phosphate, conductive agent, binder, NMP, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the positive electrode sheet; then, through processes such as rolling, slitting, die-cutting, stacking, hot pressing, welding, packaging, liquid injection, formation, and capacity testing, the battery cell is manufactured.

[0071] 2. Among them, after the negative electrode sheet is left to stand for 24 hours, the electrode sheet with a rebound rate of about 5% is selected. Its powder OI value is 5, the binder content is 3%, the peel force is 6N / m, the single-sided baking temperature is 60℃ during coating, and other influencing factors are around 1.5 during the trial production process.

[0072] 3. The obtained battery was subjected to a cycle test at 25°C, with a cycle voltage of 2.5V-3.65V.

[0073] Comparative Example 2: The soft-pack lithium-ion battery in Comparative Example 2 has a capacity of 3Ah; the difference from the Example is that the parameters have changed.

[0074] A lithium-ion battery includes the following steps:

[0075] 1. Graphite, conductive agent, binder, water, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the negative electrode sheet; lithium iron phosphate, conductive agent, binder, NMP, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the positive electrode sheet; then, through processes such as rolling, slitting, die-cutting, stacking, hot pressing, welding, packaging, liquid injection, formation, and capacity testing, the battery cell is manufactured.

[0076] 2. Among them, after the negative electrode sheet is left to stand for 24 hours, the electrode sheet with a rebound rate of about 10% is selected. Its powder OI value is 5, the binder content is 3%, the peel force is 18N / m, the single-sided baking temperature is 60℃ during coating, and other influencing factors are around 1.5 during the trial production process.

[0077] 3. The obtained battery was subjected to a cycle test at 25°C, with a cycle voltage of 2.5V-3.65V.

[0078] Comparative Example 3: The soft-pack lithium-ion battery in Comparative Example 3 has a capacity of 3Ah; the difference from the Example is that the parameters have changed.

[0079] A lithium-ion battery includes the following steps:

[0080] 1. Graphite, conductive agent, binder, water, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the negative electrode sheet; lithium iron phosphate, conductive agent, binder, NMP, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the positive electrode sheet; then, through processes such as rolling, slitting, die-cutting, stacking, hot pressing, welding, packaging, liquid injection, formation, and capacity testing, the battery cell is manufactured.

[0081] 2. Among them, after the negative electrode sheet is left to stand for 24 hours, the electrode sheet with a rebound rate of about 2% is selected. Its powder OI value is 5, the binder content is 3%, the peel force is 18N / m, the single-sided baking temperature is 60℃ during coating, and other influencing factors are around 1.5 during the trial production process.

[0082] 3. The obtained battery was subjected to a cycle test at 25°C, with a cycle voltage of 2.5V-3.65V.

[0083] Comparative Example 4: The soft-pack lithium-ion battery in Comparative Example 4 has a capacity of 3Ah; the difference from the Example is that the parameters have changed.

[0084] A lithium-ion battery includes the following steps:

[0085] 1. Graphite, conductive agent, binder, water, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the negative electrode sheet; lithium iron phosphate, conductive agent, binder, NMP, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the positive electrode sheet; then, through processes such as rolling, slitting, die-cutting, stacking, hot pressing, welding, packaging, liquid injection, formation, and capacity testing, the battery cell is manufactured.

[0086] 2. Among them, after the negative electrode sheet is left to stand for 24 hours, the electrode sheet with a rebound rate of about 5% is selected. Its powder OI value is 5, the binder content is 2.3%, the peel force is 18N / m, the single-sided baking temperature is 60℃ during coating, and other influencing factors are around 1.5 during the trial production process.

[0087] 3. The obtained battery was subjected to a cycle test at 25°C, with a cycle voltage of 2.5V-3.65V.

[0088] Comparative Example 5: The soft-pack lithium-ion battery in Comparative Example 5 has a capacity of 3Ah; the difference from the Example is that the parameters have changed.

[0089] A lithium-ion battery includes the following steps:

[0090] 1. Graphite, conductive agent, binder, water, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the negative electrode sheet; lithium iron phosphate, conductive agent, binder, NMP, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the positive electrode sheet; then, through processes such as rolling, slitting, die-cutting, stacking, hot pressing, welding, packaging, liquid injection, formation, and capacity testing, the battery cell is manufactured.

[0091] 2. Among them, after the negative electrode sheet is left to stand for 24 hours, the electrode sheet with a rebound rate of about 5% is selected. Its powder OI value is 5, the binder content is 4%, the peel force is 18N / m, the single-sided baking temperature is 60℃ during coating, and other influencing factors are around 1.5 during the trial production process.

[0092] 3. The obtained battery was subjected to a cycle test at 25°C, with a cycle voltage of 2.5V-3.65V.

[0093] Comparative Example 6: The soft-pack lithium-ion battery in Comparative Example 6 has a specification of 3Ah; the difference from the Example is that the parameters have changed.

[0094] A lithium-ion battery includes the following steps:

[0095] 1. Graphite, conductive agent, binder, water, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the negative electrode sheet; lithium iron phosphate, conductive agent, binder, NMP, etc. are mixed into a slurry through a slurry-making process, which is then coated onto the current collector and baked to form the positive electrode sheet; then, through processes such as rolling, slitting, die-cutting, stacking, hot pressing, welding, packaging, liquid injection, formation, and capacity testing, the battery cell is manufactured.

[0096] 2. Among them, after the negative electrode sheet is left to stand for 24 hours, the electrode sheet with a rebound rate of about 5% is selected. Its powder OI value is 5, the binder content is 3%, the peel force is 18N / m, the single-sided baking temperature is 55℃ during coating, and other influencing factors are around 1.5 during the trial production process.

[0097] 3. The obtained battery was subjected to a cycle test at 25°C, with a cycle voltage of 2.5V-3.65V.

[0098] Batteries produced according to the above embodiments and comparative examples were randomly selected from each group (3 batteries) for cycling, performing 1C / 1C charge-discharge cycles within a voltage range of (2.5V-3.65V). After 500 cycles, the battery with the best cycle performance from each group was selected, and the battery cycle curve was observed. Figure 5 As shown.

[0099] from Figure 5It can be seen that the battery cell satisfies: K*M*L≥0.36. Among them, the three factors affecting the value of K must satisfy: when ∈ is 3%~8%, b is 2.5%~3.5%, and OI is 2~10, the resulting battery has obvious advantages.

[0100] While the specific embodiments of this disclosure have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of this disclosure. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of this disclosure are still within the scope of protection of this disclosure.

Claims

1. A lithium-ion battery, characterized in that, The battery cells meet the following requirements: Where K is the cell expansion rate. b represents the binder content, with a value ranging from 2.5% to 3.5%; OI represents the powder OI value, with a value ranging from 2 to 10. The electrode expansion rate, The value ranges from 3% to 8%. The smaller the size, the more stable the electrode. The larger the value, the less stable the electrode; M is the graphite electrode strength, M=n*t, n is the negative electrode peel strength, n is ≥8N / m, t is the highest temperature on one side when the negative electrode is coated, t is ≥60℃; L is the compensation coefficient, L is 0.5~2.

2. A lithium-ion battery as described in claim 1, characterized in that, The lithium-ion battery includes a negative electrode, a positive electrode, a separator, and an electrolyte. The negative electrode preparation process is as follows: a negative electrode slurry including a negative electrode active material, a conductive agent and a binder is coated on the surface of a negative electrode current collector, and after drying, a negative electrode active material layer is formed to obtain a negative electrode sheet.

3. A lithium-ion battery as described in claim 2, characterized in that, The negative electrode active material includes at least one of artificial graphite, natural graphite, silicon carbide, hard carbon, and soft carbon.

4. A lithium-ion battery as described in claim 2, characterized in that, The particle size D50 of the negative electrode active material powder is 10~20μm, and the specific surface area of ​​the negative electrode active material powder is... The compaction density of the negative electrode sheet is .

5. A method for preparing a lithium-ion battery according to any one of claims 1-4, characterized in that, The lithium-ion battery is prepared by the following steps: Graphite, conductive agent, binder and water are mixed into a slurry through a slurry mixing process, which is then coated onto the current collector and baked to form a negative electrode sheet; lithium iron phosphate, conductive agent, binder and NMP are mixed into a slurry through a slurry mixing process, which is then coated onto the current collector and baked to form a positive electrode sheet.

6. The method for preparing a lithium-ion battery as described in claim 5, characterized in that, Finally, the battery cells are manufactured through processes such as rolling, slitting, die cutting, stacking, hot pressing, welding, packaging, electrolyte injection, formation, and capacity testing.

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