Lithium battery, lithium battery negative electrode sheet and preparation method thereof

Abstract

The present invention relates to a lithium battery, a negative electrode sheet of a lithium battery and a preparation method thereof. The preparation method of the negative electrode sheet of a lithium battery comprises: coating a negative electrode slurry on a current collector, drying and rolling three times in sequence to obtain a negative electrode sheet, wherein the thickness after the first rolling is H1, the thickness after the second rolling is H2, the target thickness of the negative electrode sheet is H3, H3 / H1=A1, H3 / H2=A2, A1 is 60%~90%, and the difference between A2 and A1 is 5%~30%. The preparation method of the negative electrode sheet provided by the present invention, through three rolling processes with a specific roller ratio, is not only conducive to improving the uniformity of the rolling process of the negative electrode sheet, avoiding the rupture and pulverization of the active material in the negative electrode sheet, and effectively improving the stability of the solid electrolyte interface film, but also can effectively reduce the rebound rate of the negative electrode sheet, ensure the compaction density and thickness of the negative electrode sheet, thereby improving the high temperature storage performance of the lithium battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a lithium battery, a lithium battery negative electrode sheet and a preparation method thereof. Background Art

[0002] With the vigorous development of new energy vehicles and the increasing demand for portable electronic devices, lithium-ion batteries will face the challenge of high temperature environment. When stored at high temperature, lithium batteries will have a fast voltage drop rate, poor charge retention ability and poor cycle performance, which will affect the electrical performance and safety performance of the battery.

[0003] The negative electrode sheet has an important influence on the high-temperature storage performance of lithium batteries. The preparation process of the negative electrode sheet generally includes slurrying, coating, drying and rolling. However, the uniformity of the rolling process is poor, which easily leads to the breakage and pulverization of the active material particles, thereby affecting the high-temperature storage performance of lithium batteries. Therefore, a method for improving the high-temperature storage performance of lithium batteries is needed. Summary of the invention

[0004] Based on this, it is necessary to provide a lithium battery, a lithium battery negative electrode sheet and a preparation method thereof to address the above problems. The preparation method of the lithium battery negative electrode sheet provided by the present invention is conducive to reducing the cracking and pulverization problems of the active material in the negative electrode sheet, effectively improving the stability of the solid electrolyte interface film, and at the same time reducing the rebound rate of the negative electrode sheet, ensuring the compaction density and thickness of the negative electrode sheet, thereby improving the high temperature storage performance of the lithium battery.

[0005] The present invention provides a method for preparing a negative electrode sheet of a lithium battery, comprising: coating a negative electrode slurry on a current collector, drying and then rolling three times in sequence to obtain a negative electrode sheet, wherein the thickness after the first rolling is H1, the thickness after the second rolling is H2, the target thickness of the negative electrode sheet is H3, H3 / H1=A1, H3 / H2=A2, A1 is 60%~90%, and the difference between A2 and A1 is 5%~30%.

[0006] In one embodiment, when the compaction density of the negative electrode sheet is 1.2 g / cm 3 When A1 is 60% to 70%, the difference between A2 and A1 is 15% to 30%, and the compaction density of the negative electrode sheet increases by 0.2 g / cm 3 , A1 increases by 1%~20%, and the difference between A2 and A1 decreases by 1%~5%.

[0007] In one embodiment, when the compaction density of the negative electrode sheet is greater than or equal to 1.2 g / cm 3 And less than 1.4g / cm 3 When A1 is 60%~70%, A2 is 75%~90%.

[0008] In one embodiment, when the compaction density of the negative electrode sheet is greater than or equal to 1.4 g / cm 3 And less than 1.6g / cm 3 When A1 is 70% to 80%, A2 is 85% to 95%.

[0009] In one embodiment, the compaction density of the negative electrode sheet is greater than or equal to 1.6 g / cm 3 When A1 is 80% to 90%, A2 is 95% to 98%.

[0010] In one embodiment, the speeds of the three rolling processes are independently selected from 10 m / min to 30 m / min;

[0011] And / or, the pressures of the three rolling processes are independently selected from 10 tons to 60 tons.

[0012] In one embodiment, the pressure of the first rolling is 10 tons to 30 tons;

[0013] And / or, the pressure of the second rolling is 20 tons to 50 tons;

[0014] And / or, the pressure of the third rolling is 30 tons to 60 tons.

[0015] In one embodiment, the coating surface density of the negative electrode slurry is 12 mg / cm 2 ~18mg / cm 2 .

[0016] The above-mentioned preparation method of the negative electrode sheet, through three rolling processes with a specific rolling roller ratio, is not only beneficial to improving the uniformity of the rolling process of the negative electrode sheet, avoiding the rupture and pulverization of the active material in the negative electrode sheet, and effectively improving the stability of the solid electrolyte interface film, but also can effectively reduce the rebound rate of the negative electrode sheet, ensure the compaction density and thickness of the negative electrode sheet, thereby improving the high temperature storage performance of the lithium battery.

[0017] The present invention also provides a negative electrode sheet prepared by the above-mentioned method for preparing a negative electrode sheet for a lithium battery.

[0018] The above-mentioned negative electrode sheet has less breakage and pulverization of active material particles and a high uniformity of pore size distribution. The negative electrode sheet has a high yield and consistency. When used in lithium batteries, it can effectively improve the high-temperature storage performance and safety of lithium batteries.

[0019] The present invention also provides a lithium battery, comprising the negative electrode sheet as described above.

[0020] The above-mentioned lithium battery has excellent high-temperature storage performance and safety and has broad application prospects. DETAILED DESCRIPTION

[0021] For ease of understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by technicians in the technical field of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments or embodiments, and are not intended to limit the present invention. The optional range of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of related listed items, and the arbitrary and all combinations include any two related listed items, any more related listed items, or all related listed items. If not specifically stated, in the present invention, the terms "or" and "or" are inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or A and B are both true (or exist). If not specifically stated, in the present invention, "one or more" or "at least one" refers to any one, any two or more of the listed items. Among them, "several" refers to any two or more than two. If there is no special explanation, in the present invention, "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0023] In the present invention, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0024] The preparation method of the negative electrode sheet of the lithium battery provided by the present invention includes: coating the negative electrode slurry on the current collector, and sequentially performing three roll pressings after drying to obtain the negative electrode sheet. Among them, the thickness after the first roll pressing is H1, the thickness after the second roll pressing is H2, and the target thickness of the negative electrode sheet is H3. H3 / H1 = A1, H3 / H2 = A2, A1 is 60% - 90%, and the difference between A2 and A1 is 5% - 30%.

[0025] It can be understood that A1 < A2, and A2 < 100%. A1 includes but is not limited to any point value or the range value between any two of 60%, 62%, 63%, 65%, 70%, 73%, 75%, 80%, 85%, 90%. The difference between A2 and A1 includes but is not limited to any point value or the range value between any two of 5%, 6%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%.

[0026] The above preparation method of the negative electrode sheet, through three roll pressings with a specific roll press ratio, not only helps to improve the uniformity of the roll pressing treatment of the negative electrode sheet, avoid the rupture and pulverization of the active substances in the negative electrode sheet, effectively improve the stability of the solid electrolyte interface film, but also can effectively reduce the rebound rate of the negative electrode sheet, ensure the compaction density and thickness of the negative electrode sheet, thereby improving the high-temperature storage performance and cycling performance of the lithium battery, being able to provide stable and reliable energy support for high-temperature special equipment, having good safety. At the same time, the preparation method of the present invention is applicable to large-scale production and has great popularization value.

[0027] It can be understood that when the active substances rupture and pulverize, it will cause the decomposition of the solid electrolyte interface film, and the repair of the solid electrolyte interface film will continuously consume active lithium ions, resulting in poor charge retention ability, and further affecting the high-temperature storage performance of the lithium battery.

[0028] To further improve the uniformity of the roll pressing, avoid the rupture and pulverization of the active substances in the negative electrode sheet, and at the same time, reduce the rebound rate of the negative electrode sheet, ensure the compaction density and thickness of the negative electrode sheet. When the compaction density of the negative electrode sheet is 1.2 g / cm 3 ³, A1 is preferably 60% - 70%, including but not limited to any point value or the range value between any two of 60%, 62%, 65%, 68%, 70%. The difference between A2 and A1 is 15% - 30%, including but not limited to any point value or the range value between any two of 15%, 18%, 20%, 25%, 30%. And for every 0.2 g / cm 3, A1 is preferably increased by 1% to 20%, including but not limited to any value among 1%, 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20% or any range between two values, and the difference between A2 and A1 is preferably reduced by 1% to 5%, including but not limited to any value among 1%, 2%, 3%, 4%, 5% or any range between two values.

[0029] It can be understood that when the compaction density of the negative electrode sheet increases by 0.2 g / cm 3 When the compaction density of the negative electrode sheet is 1.4 g / cm 3 When A1 is preferably 61% to 90%, the difference between A2 and A1 is preferably 10% to 29%.

[0030] In one embodiment, when the compaction density of the negative electrode sheet is greater than or equal to 1.2 g / cm 3 And less than 1.4g / cm 3 In order to further improve the uniformity of rolling, prevent the problem of cracking and pulverization of active materials, and make the pore size distribution in the pole piece more uniform, thereby promoting the infiltration of electrolyte, the A1 is preferably 60%~70%, including but not limited to any point value of 60%, 62%, 65%, 68%, 70% or any range value between two of them, and the A2 is preferably 75%~90%, including but not limited to any point value of 75%, 78%, 83%, 87%, 90% or any range value between two of them.

[0031] In another embodiment, when the compaction density of the negative electrode sheet is greater than or equal to 1.4 g / cm 3 And less than 1.6g / cm 3 When the compaction density increases, in order to reduce the rebound rate of the negative electrode sheet and ensure the compaction density and thickness of the negative electrode sheet, the A1 is preferably 70% to 80%, including but not limited to any point value of 70%, 72%, 75%, 78%, 80% or any range value between two of them, and the A2 is preferably 85% to 95%, including but not limited to any point value of 85%, 88%, 90%, 92%, 95% or any range value between two of them.

[0032] In another embodiment, the compaction density of the negative electrode sheet is greater than or equal to 1.6 g / cm 3When the compaction density is high and close to the upper limit of material compaction, in order to further reduce the rebound rate of the negative electrode sheet, avoid the expansion of the negative electrode sheet, and improve the yield and consistency of the negative electrode sheet, the A1 is preferably 80%~90%, including but not limited to any point value among 80%, 82%, 85%, 88%, 90% or any range value between two of them, and the A2 is preferably 95%~98%, including but not limited to any point value among 95%, 96%, 97%, 98% or any range value between two of them.

[0033] It should be noted that the present invention has no special restriction on the speed of the negative electrode sheet during the roller pressing process. Those skilled in the art can select and adjust it according to the actual production situation, product requirements or quality requirements. In order to ensure the rolling effect, improve production efficiency, and be more suitable for industrial production, the speeds of the three roller pressing processes are independently selected from 10m / min~30m / min.

[0034] In one embodiment, the pressures of the three rolling processes are independently selected from 10 tons to 60 tons.

[0035] It can be understood that the pressure of the first rolling, the pressure of the second rolling and the pressure of the third rolling can be the same or different.

[0036] Preferably, the pressure of the first rolling is 10 tons to 30 tons.

[0037] Preferably, the second rolling pressure is 20 tons to 50 tons.

[0038] Preferably, the pressure of the third rolling is 30 tons to 60 tons.

[0039] In one embodiment, the three roller pressing processes are performed in a cold pressing mode.

[0040] In one embodiment, the negative electrode slurry includes graphite, a conductive agent, a binder and a solvent.

[0041] It should be noted that the negative electrode slurry of the present invention adopts conventional slurry in the art, and the present invention has no special restrictions on the components, proportions and preparation methods of the slurry.

[0042] Specifically, the graphite is selected from at least one of artificial graphite and natural graphite.

[0043] Specifically, the conductive agent is selected from at least one of carbon black, carbon nanotubes and conductive graphite.

[0044] Specifically, the binder is selected from at least one of sodium hydroxymethyl cellulose and polyvinylidene fluoride.

[0045] Specifically, the solvent is selected from water or N-methylpyrrolidone (NMP).

[0046] In one embodiment, the negative electrode slurry has a viscosity of 2500 mPa·s to 6500 mPa·s, and a solid content of 40% to 55%.

[0047] In one embodiment, the surface density of the negative electrode slurry coating is 12 mg / cm 2 ~18mg / cm 2 , including but not limited to 12 mg / cm 2 、13mg / cm 2 、14mg / cm 2 、15mg / cm 2 、16mg / cm 2 、17mg / cm 2 、18mg / cm 2 Any point value in or any range of values ​​between them.

[0048] The present invention also provides a negative electrode sheet prepared by the method for preparing a negative electrode sheet for a lithium battery as described above, wherein the active material particles in the negative electrode sheet are less likely to be broken and pulverized, and the pore size distribution is highly uniform, the yield and consistency of the negative electrode sheet are high, and the use of the negative electrode sheet in lithium batteries can effectively improve the high-temperature storage performance and safety of the lithium batteries.

[0049] The present invention also provides a lithium battery, comprising the negative electrode sheet as described above, wherein the lithium battery has excellent high-temperature storage performance and safety, and has broad application prospects.

[0050] Specifically, the lithium-ion battery further comprises a positive electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet, the separator and the electrolyte can be any commercially available medium-low nickel ternary material, a ceramic-coated separator and a wide-temperature electrolyte, which is not limited in the present invention.

[0051] It should be noted that the preparation method of the lithium battery adopts the above-mentioned preparation method of the negative electrode sheet to prepare the negative electrode sheet, and the preparation methods of the positive electrode sheet and the lithium battery cell etc. all adopt the existing methods in the art, and the present invention has no special restrictions on this.

[0052] It should be noted that the positive electrode sheet and the separator of the present invention are made of conventional materials in the art, and the present invention has no special restrictions on this.

[0053] Hereinafter, the lithium battery, the lithium battery negative electrode sheet and the preparation method thereof will be further described through the following specific examples.

[0054] Example 1

[0055] Premix in a slurry tank according to the ratio of graphite: conductive agent: binder = 95.5:2:2.5, where the negative electrode active material is artificial graphite, the conductive agent is carbon black SP, and the binder is carboxymethyl cellulose (CMC) glue. After premixing, add styrene butadiene rubber (SBR) emulsion and the remaining CMC glue, stir and disperse evenly to obtain negative electrode slurry. Mix the negative electrode slurry at 13mg / cm 2 The negative electrode slurry was coated on the copper foil, dried in an oven and rolled three times to obtain the negative electrode sheet. The compaction density of the negative electrode sheet was 1.3g / cm 3 Among them, the speed of the negative electrode sheet is 10m / min, the pressure of the first rolling is 13 tons, the pressure of the second rolling is 20 tons, and the pressure of the third rolling is 32 tons. A1 is 60%, A2 is 80%, and the difference between A2 and A1 is 20%.

[0056] Example 2

[0057] The negative electrode slurry of Example 1 was prepared at 15 mg / cm 2 The negative electrode slurry is coated on the copper foil, dried in an oven and rolled three times to obtain the negative electrode sheet. The compaction density of the negative electrode sheet is 1.5g / cm 3 Among them, the speed of the negative electrode sheet is 20m / min, the pressure of the first rolling is 21 tons, the pressure of the second rolling is 38 tons, and the pressure of the third rolling is 45 tons. A1 is 75%, A2 is 90%, and the difference between A2 and A1 is 15%.

[0058] Example 3

[0059] The negative electrode slurry of Example 1 was prepared at 17 mg / cm 2 The negative electrode slurry was coated on the copper foil, dried in an oven and rolled three times to obtain the negative electrode sheet. The compaction density of the negative electrode sheet was 1.7 g / cm 3 Among them, the speed of the negative electrode sheet is 30m / min, the pressure of the first rolling is 28 tons, the pressure of the second rolling is 46 tons, and the pressure of the third rolling is 55 tons. A1 is 85%, A2 is 95%, and the difference between A2 and A1 is 10%.

[0060] Comparative Example 1

[0061] The difference between Comparative Example 1 and Example 1 is that the negative electrode slurry is coated on the copper foil, and then rolled once after being dried in an oven, with A1 being 100% and the pressure being 40 tons, to obtain a negative electrode sheet.

[0062] Comparative Example 2

[0063] The difference between Comparative Example 2 and Example 1 is that the negative electrode slurry is coated on the copper foil, and then rolled twice after being dried in an oven. The pressure after the first rolling is 25 tons, and the pressure after the second rolling is 36 tons. A1 is 80%, and A2 is 100%.

[0064] Comparative Example 3

[0065] The difference between Comparative Example 3 and Example 1 is that the pressure after the first rolling is 10 tons, the pressure after the second rolling is 13 tons, and the pressure after the third rolling is 35 tons, A1 is 40%, A2 is 50%, and the difference between A2 and A1 is 10%.

[0066] Comparative Example 4

[0067] The difference between Comparative Example 4 and Example 3 is that the pressure after the first rolling is 28 tons, the pressure after the second rolling is 32 tons, and the pressure after the third rolling is 37 tons. A1 is 92%, A2 is 98%, and the difference between A2 and A1 is 6%.

[0068] Comparative Example 5

[0069] The difference between Comparative Example 5 and Example 1 is that the pressure after the first rolling is 13 tons, the pressure after the second rolling is 30 tons, and the pressure after the third rolling is 36 tons, A1 is 60%, A2 is 98%, and the difference between A2 and A1 is 38%.

[0070] Application Examples

[0071] The positive electrode active material, conductive agent and binder are mixed in a mass ratio of 96:2.5:1.5, wherein the positive electrode active material is NCM111, the conductive agent is SP, and the binder is polyvinylidene fluoride (PVDF) glue. After being stirred and dispersed in a homogenizer, they are coated on aluminum foil at a certain surface density, and then rolled and cut to obtain the positive electrode sheet.

[0072] The negative electrode sheet, positive electrode sheet and separator are wound and assembled to obtain the finished battery cell, and the pre-charging and capacity composition process of the rear stage of the battery cell remains consistent.

[0073] The 18650 lithium battery cells prepared in all application examples and application comparison examples were subjected to performance tests, and the test indicators and test methods are as follows:

[0074] 85℃ high temperature storage performance test: First, fully charge the battery cell at room temperature with standard charge and discharge, and calculate the initial capacity by standard discharge to 2.75V. The battery cell is charged to 4.1V with 0.5C constant current and constant voltage (cut-off current is 0.02C), then stored in an 85℃ constant temperature box for 1000h and the voltage is measured. After standing at room temperature for 5h, standard discharge is performed to calculate the retention capacity, and standard charge is performed to calculate the recovery capacity. Ten battery cells are randomly selected for testing, and the results are averaged.

[0075] The performance test results of 18650 lithium battery cells prepared in all application examples and application comparison examples are shown in Table 1.

[0076] Table 1

[0077]

[0078] According to the test results in Table 1, under the same test conditions, the average voltage drop of the battery cells of all application embodiments after being stored at 85°C for 1000h is lower than 145mV, and the range after storage is lower than 7mV, and the capacity retention rate of the battery cells of all application embodiments after being stored at 85°C for 1000h reaches more than 92.60%, while before the battery cells are stored, the voltage drop range is similar, and the average voltage drop and the voltage drop range of all application comparison examples after being stored at 85°C for 1000h are significantly higher than those of all embodiments, and the capacity retention rate of the battery cells of the application comparison examples after being stored at 85°C for 1000h is higher than that ... The capacity retention rate of the battery cell after storage is lower than that of all the application examples. This is mainly because the negative electrode sheet pressing roller method of the comparative example easily leads to the rupture and pulverization of the active material particles, which causes the solid electrolyte interface membrane to rupture and decompose at high temperature. The repair of the solid electrolyte interface membrane after decomposition will continuously consume active lithium ions, resulting in poor charge retention ability. In addition, the difference in capacity recovery rate of the battery cells of the application example and the comparative example after storage at 85°C for 1000 hours is not as significant as the capacity retention rate, indicating that most of the capacity loss is reversible.

[0079] In summary, the negative electrode sheet preparation method of the present invention is not only beneficial to improving the uniformity of the negative electrode sheet rolling process, avoiding the rupture and pulverization of the active material in the negative electrode sheet, and effectively improving the stability of the solid electrolyte interface film, but also can effectively reduce the rebound rate of the negative electrode sheet, ensure the compaction density and thickness of the negative electrode sheet, thereby improving the high temperature storage performance of the lithium battery, so that the battery has better high temperature charge retention ability and cycle performance, can provide stable and reliable energy support for high temperature special equipment, and has good safety. At the same time, the preparation method of the present invention is suitable for large-scale production and has great promotion value.

[0080] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0081] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a negative electrode sheet for a lithium battery, characterized in that: The preparation method comprises: coating the negative electrode slurry on the current collector, drying and rolling three times in sequence to obtain a negative electrode sheet, wherein the thickness after the first rolling is H1, the thickness after the second rolling is H2, the target thickness of the negative electrode sheet is H3, H3 / H1=A1, H3 / H2=A2, A1 is 60%~90%, and the difference between A2 and A1 is 5%~30%; When the compaction density of the negative electrode sheet is 1.2 g / cm 3 When A1 is 60% to 70%, the difference between A2 and A1 is 15% to 30%, and the compaction density of the negative electrode sheet increases by 0.2 g / cm 3 , A1 increases by 1%~20%, and the difference between A2 and A1 decreases by 1%~5%.

2. The preparation method according to claim 1, characterized in that: When the compaction density of the negative electrode sheet is greater than or equal to 1.2 g / cm 3 And less than 1.4g / cm 3 When A1 is 60%~70%, A2 is 75%~90%.

3. The preparation method according to claim 1, characterized in that: When the compaction density of the negative electrode sheet is greater than or equal to 1.4 g / cm 3 And less than 1.6g / cm 3 When A1 is 70% to 80%, A2 is 85% to 95%.

4. The preparation method according to claim 1, characterized in that: The compaction density of the negative electrode sheet is greater than or equal to 1.6 g / cm 3 When A1 is 80% to 90%, A2 is 95% to 98%.

5. The preparation method according to claim 1, characterized in that: The speeds of the three rolling processes are independently selected from 10 m / min to 30 m / min; And / or, the pressures of the three rolling processes are independently selected from 10 tons to 60 tons.

6. The preparation method according to claim 5, characterized in that: The pressure of the first rolling is 10 tons to 30 tons; And / or, the pressure of the second rolling is 20 tons to 50 tons; And / or, the pressure of the third rolling is 40 tons to 60 tons.

7. The preparation method according to claim 1, characterized in that: The coating surface density of the negative electrode slurry is 12 mg / cm 2 ~18mg / cm 2 .

8. A negative electrode sheet made by the method for making a negative electrode sheet for a lithium battery according to any one of claims 1 to 7.

9. A lithium battery, characterized in that: The lithium battery comprises the negative electrode sheet as claimed in claim 8.

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