Negative pole piece, battery cell and preparation method and application of negative pole piece

Abstract

The invention belongs to the field of batteries, and relates to a negative pole piece, a battery cell and a preparation method and application thereof. The technical problems that in the prior art, due to the fact that the electrode thickness of a lithium ion battery cell is increased, the overall energy density of the battery cell is reduced, and the cycle performance is reduced are solved. The invention provides a negative pole piece. The negative pole piece comprises a main material, an auxiliary material and a high polymer material, in parts by mass, the main material accounts for 90-95 parts; the auxiliary material comprises a conductive agent and a binder, and accounts for 7-9 parts; the high polymer material is swelling type high polymer and accounts for 1-3 parts, and the swelling coefficient range is 1000%-3000%. Pores are formed in the adhesion area of the swelling type polymer; in the direction parallel to the current collector, when the negative pole piece is divided into a plurality of parts, the average size of pores in each part is gradually increased in the direction far away from the current collector. The invention provides the preparation method of the negative pole piece, the slurry mixing, coating and rolling processes are adopted, the cost is low, the operation is convenient and fast, and the controllability is high. Meanwhile, the invention further provides a battery cell and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary battery preparation, and specifically relates to a negative electrode sheet, a battery cell, and their preparation methods and applications. Background Art

[0002] With the acceleration of the technological innovation of power batteries, demands such as higher energy density, higher rate performance, and longer cycle performance have become the main development directions of lithium-ion batteries at the present stage. In addition to the material upgrade of the active main materials, the thick electrode technology in the battery cell system design is also the key to developing high-rate and high-energy density battery cells.

[0003] The design concept of the thick electrode technology is to greatly increase the loading of the electrode active material by reducing the ratio of non-active components, thereby improving the overall energy density of the lithium-ion battery. However, with the increase in the electrode thickness, the battery cell electrical performance will face severe challenges, including but not limited to slow charge kinetics and electrode mechanical instability. Solving these challenges can be said to be the core technical bottleneck for upgrading conventional battery cells to high-rate and high-energy density battery cells.

[0004] For example, Chinese Patent Application Publication No. CN119092794A, with an application date of August 6, 2024, and an invention title of "A Lithium-Ion Battery Cell with Ultra-High Energy Density and Its Preparation Method", discloses a lithium-ion battery cell with ultra-high energy density. The negative electrode of which uses raw materials with the following mass fractions: 90% - 95% graphite, 2% - 7% silicon carbide, 0.5% - 1.5% conductive carbon black, 1.0% - 2.5% polyacrylic acid, 1.0% - 2.5% styrene-butadiene rubber, and 0.02% - 0.15% single-walled carbon nanotubes. The preparation method includes the following steps: powder dry-mix graphite, silicon carbide, and conductive carbon black to obtain a first mixed powder. At the same time, carboxymethyl cellulose powder is highly dispersed with deionized water; the first mixed powder is wetted with deionized water to obtain a second mixed powder. At the same time, carboxymethyl cellulose powder and polyacrylic acid are highly dispersed to obtain a third mixed powder; the third mixed powder and single-walled carbon nanotubes are highly dispersed to obtain a fourth mixed powder. Further, a part of the fourth mixed powder and the second mixed powder are kneaded to obtain a fifth mixed powder; the remaining part of the fourth mixed powder and the fifth mixed powder are homogenized and stirred with deionized water to obtain a first slurry; the first slurry is viscosity-adjusted with deionized water to obtain a second slurry; styrene-butadiene rubber is added to the second slurry to obtain a third slurry. In this technical solution, single-walled carbon nanotubes are added. The dispersibility and compatibility of single-walled carbon nanotubes in most solvents and matrix materials are poor. Due to the strong van der Waals force between carbon nanotubes, they are prone to agglomeration and it is difficult to be uniformly dispersed in the matrix material; at the same time, it is also relatively cumbersome and requires obtaining the slurry through five times of mixed powders.

[0005] For example, the Chinese invention patent application publication number is CN115663113A, the application date is November 18, 2022, and the name of the invention is "A negative electrode sheet and its preparation method, lithium-ion battery assembly method". It discloses a negative electrode sheet, including active material, poly 1,4-bis(2,2,6,6-tetramethyl-4-hydroxy-1-oxyl free radical piperidine) butadiyne, conductive agent and binder in a mass ratio of 6 to 9: 0.1 to 1: 0.5 to 1.5: 0.5 to 1.5. The preparation method includes the following steps: taking active material, poly 1,4-bis(2,2,6,6-tetramethyl-4-hydroxy-1-oxygen free radical piperidine) butadiyne, conductive agent, and binder according to the mass ratio, mixing them evenly and then ball milling to obtain a mixed powder; taking copper foil and mixed powder and placing them into a mold in turn, placing the mold into a magnetic field for treatment, the direction of the magnetic field is from the surface of the active layer to the copper foil, and the intensity of the magnetic field gradually weakens along the direction of the magnetic field; hot pressing and calcining the mixed powder and copper foil treated with the magnetic field to obtain a negative electrode sheet. This technical solution applies a magnetic field to the mixture, so that the concentration of the magnetic pore-forming agent gradually increases in the direction away from the current collector, and decomposes to leave pores during calcination to form a porosity gradient. The operation is relatively complicated, and the magnetic pore-forming agent will cause the internal structure of the electrode material to be unstable, especially in the long cycle process, which is easy to cause volume expansion and affect the cycle performance of the battery. Summary of the invention

[0006] 1. Problems to be solved

[0007] In view of the technical problem that when the thickness of the electrode increases, the overall energy density of the battery cell decreases and the cycle performance decreases, the present application provides a negative electrode sheet to improve the transmission rate of lithium ions. Furthermore, the present application provides a method for preparing the negative electrode sheet.

[0008] At the same time, the present application also provides a battery cell and its application.

[0009] 2. Technical solution

[0010] In order to achieve the above purpose, the technical solution provided is:

[0011] The negative electrode plate comprises a main material, auxiliary materials and a polymer material; in terms of weight percentage, the main material accounts for 90 to 95 parts; the auxiliary materials include a conductive agent and a binder, accounting for 7 to 9 parts; the polymer material is a swelling polymer, accounting for 1 to 3 parts, and the swelling coefficient of the polymer material ranges from 1000% to 3000%.

[0012] Preferably, the main material comprises a carbon material.

[0013] Furthermore, the polymer material is one or both of hydrogenated nitrile rubber and / or polyacrylate.

[0014] Furthermore, the main material is one or more of graphite, hard carbon, and / or silicon carbon.

[0015] Furthermore, the conductive agent is one or more of conductive carbon black, conductive graphite, and / or graphene, and the binder is one or more of carboxymethyl cellulose, styrene-butadiene rubber latex, and / or polyacrylic acid.

[0016] Furthermore, the swelling-type polymer forms pores in the area where it adheres; in the direction parallel to the current collector, when the negative electrode plate is divided into several parts, the average size of the pores on each part gradually increases in the direction away from the current collector.

[0017] A method for preparing a negative electrode plate, wherein the raw materials of the negative electrode plate include a main material, an auxiliary material, and a polymer material; by mass, the main material accounts for 90 to 95 parts; the auxiliary material includes a conductive agent and a binder, accounting for 7 to 9 parts; the polymer material is a swelling-type polymer, accounting for 1 to 3 parts, and the swelling coefficient ranges from 1000% to 3000%.

[0018] The raw materials are subjected to slurry mixing, coating, and rolling to obtain the negative electrode plate.

[0019] Preferably, the raw materials are subjected to slurry mixing, coating, rolling, baking, and electrolyte immersion to obtain the negative electrode plate.

[0020] Preferably, the slurry mixing process is double planetary slurry mixing.

[0021] A battery cell comprising the negative electrode plate according to any one of the above.

[0022] Furthermore, it further includes a positive electrode plate; the main material of the positive electrode is a polyanion system, and the raw materials of the polyanion system contain one or several of lithium iron manganese phosphate, lithium iron phosphate, or sodium composite phosphate iron.

[0023] Furthermore, the double-sided surface density of the positive electrode plate ≥ 400 g / m 2 , and the double-sided surface density of the negative electrode plate ≥ 140 g / m 2 .

[0024] Application of the battery cell, the application of the battery cell according to any one of the above in the preparation of new energy vehicles, electronic products, or energy storage systems.

[0025] 3. Beneficial effects

[0026] Adopting the technical solution provided by the present invention, compared with the existing well-known technologies, it has the following beneficial effects:

[0027] (1) The negative electrode sheet of the present invention comprises a main material, an auxiliary material and a polymer material; calculated by mass fraction, the proportion of the main material is 90 parts to 95 parts; the auxiliary material comprises a conductive agent and a binder, with a proportion of 7 parts to 9 parts; the polymer material is a swelling polymer, with a proportion of 1 part to 3 parts, and the swelling coefficient ranges from 1000% to 3000%. By introducing a swelling polymer of a suitable type and proportion into the negative electrode sheet, different gradient pore structures are created due to the different swelling coefficients of the polymer in the electrolyte from that of the binder, etc., and the closed pores existing in the electrode sheet can also be opened. After the swelling polymer is soaked in the electrolyte, pores are formed in the area where it adheres, and the distribution of the pores is consistent with the area where the polymer is located, and it is evenly dispersed at various positions of the coating. In the direction parallel to the current collector, when the negative electrode sheet is divided into several parts, the average size of the pores on each part gradually increases in the direction away from the current collector, that is, in the direction perpendicular to the current collector from bottom to top, the pores gradually increase. It can effectively reduce the ohmic impedance of the thick electrode, which is beneficial to the performance of the battery rate and cycle performance; and it makes the originally isolated pores communicate with each other, further expand evenly, form a more connected channel, reduce the tortuosity of the pores of the electrode sheet, make the lithium ion transmission path more direct, and thus improve the lithium ion transmission rate; at the same time, the proportion of the polymer used in the whole electrode sheet is very small, so this swelling pore expansion does not significantly increase the rebound of the electrode sheet and damage the bonding network of the electrode sheet.

[0028] (2) The preparation method of the negative electrode sheet of the present invention adopts a slurry mixing, coating and rolling process, which has low cost, convenient operation and high controllability.

[0029] (3) For the battery cell of the present invention, the double-sided surface density of the negative electrode sheet is 200 g / m 2 , and the compaction density is 1.5 g / cm 3 . The double-sided surface density of the positive electrode sheet is 400 g / m 2 , and the compaction density is 2.3 g / cm 3 . When charging at a rate of 1.2C, the lithium deposition SOC of the negative electrode of the high energy density battery cell is greatly improved, from 70% of the basic group to 96%, and the cycle performance of the battery cell is also significantly improved.

[0030] (4) The application of the battery cell of the present invention is in the preparation of new energy vehicles, electronic products or energy storage systems. The battery cell of the present invention can provide a longer cruising range for new energy vehicles, a longer usage time for electronic products (such as laptop computers, tablet computers, mobile phone power banks, etc.) and improve the cycle service life of energy storage batteries due to its larger capacity and higher energy density. Description of the Drawings

[0031] Figure 1 It is the core mechanism diagram of the design of the modified group negative electrode sheet in the embodiment of the present invention;

[0032] Figure 2 In the embodiment of the present invention, it is the microscopic SEM morphology diagram of the cross-section of the modified group negative electrode sheet and the basic group negative electrode sheet;

[0033] Figure 3 In Example 1 of the present invention, it is the negative electrode lithium deposition potential diagram of the prepared battery cell and the conventional battery cell at a 1.2C rate in a three-electrode system;

[0034] Figure 4 In Example 1 of the present invention, it is the charge and discharge cycle performance diagram of the prepared battery cell and the conventional battery cell. Detailed Embodiments

[0035] To further understand the content of the present invention, the present invention will be described in detail in combination with the embodiments.

[0036] Example 1

[0037] The negative electrode sheet, battery cell, and their preparation methods and applications in this embodiment include the following steps:

[0038] (1) Basic group: Taking the graphite negative electrode formula of a lithium-ion battery as a control group,

[0039] The main material used in the basic group of this embodiment is graphite; the auxiliary materials are carboxymethyl cellulose, styrene-butadiene rubber, and conductive carbon black; the solvent is water.

[0040] The raw materials of the negative electrode formula of the basic group include, by mass:

[0041]

[0042] After double planetary slurry mixing, coating, rolling, baking, and electrolyte soaking, the negative electrode sheet of the basic group is obtained. The electrolyte soaking step is completed in the liquid injection process of battery preparation.

[0043] (2) Modified group: Introducing swelling-type polymer hydrogenated nitrile rubber (HNBR) into the graphite negative electrode formula of a lithium-ion battery as the modified group,

[0044] The main material used in the modified group of this embodiment is graphite; the auxiliary materials are carboxymethyl cellulose, styrene-butadiene rubber, and conductive carbon black; the polymer material is hydrogenated nitrile rubber; the solvent is water.

[0045] The negative electrode formula of the modified group includes, by mass:

[0046]

[0047] After double-planet slurry mixing, coating, rolling, baking, and electrolyte soaking, the negative electrode sheets of the modified group are obtained. The electrolyte soaking step is completed during the electrolyte injection process in battery preparation.

[0048] The positive electrode sheets of both the basic group and the modified group contain lithium iron phosphate. By mass fraction,

[0049] 94 parts of lithium iron phosphate (LFP);

[0050] 3 parts of polyvinylidene fluoride (PVDF);

[0051] 3 parts of conductive carbon black (SP).

[0052] The electrode sheets of the basic group and the modified group are respectively made into 3 Ah soft-pack lithium-ion battery cells.

[0053] The core mechanism of the design of the negative electrode sheet of the modified group: As Figure 1 shown, after electrolyte soaking, the original pores in the electrode sheet are swollen by the swelling-type polymer dispersed in the electrode sheet and then further uniformly expanded to form more connected channels. This swelling pore expansion reduces the tortuosity of the pores in the electrode sheet, thereby improving the lithium-ion transport rate.

[0054] The double-sided areal density of the negative electrode sheet in this embodiment is 200 g / m 2 , and the tap density is 1.5 g / cm 3 . The double-sided areal density of the positive electrode sheet is 400 g / m 2 , and the tap density is 2.3 g / cm 3 .

[0055] Test the pore distribution of the negative electrode sheet of the basic group and the negative electrode sheet of the modified group before and after electrolyte soaking:

[0056] The electrolyte used in the present invention is a conventional electrolyte in the field of lithium-ion batteries. Specifically, the electrolyte can be selected from various electrolyte systems widely used in lithium-ion batteries in the prior art, such as, but not limited to, organic solvent electrolyte systems containing lithium salts (such as lithium hexafluorophosphate, lithium tetrafluoroborate, etc.). Those skilled in the art can select a suitable electrolyte according to actual needs to meet the basic functional requirements of lithium-ion batteries.

[0057] Before electrolyte immersion, there was basically no obvious difference in the pore structure of the cross-sectional SEM images of the negative electrode plates in the basic group (i.e., conventional negative electrode plates) and the modified group. Both showed a trend of being affected by rolling pressure, with the pores getting smaller from bottom to top perpendicular to the current collector. This trend is disadvantageous for electrolyte infiltration and lithium-ion diffusion. After electrolyte immersion and drying, there was no obvious difference in the basic group of negative electrode plates before and after immersion. However, there were obvious changes in the pore structure of the modified group of negative electrode plates. In the direction parallel to the current collector, when the negative electrode plate was divided into several parts, the average size of the pores on each part gradually increased in the direction away from the current collector, that is, in the direction from bottom to top perpendicular to the current collector, the pores gradually increased, and the gradient structure was obvious (as Figure 2 shown).

[0058] The reason for this effect is that the ultra-high swelling type polymer selected in this embodiment basically maintains the same physical properties as the conventional binder when the modified negative electrode plate is not immersed in the electrolyte and will be evenly distributed on the surface of the particles in the electrode coating and between the particles. However, after immersion in the electrolyte, its swelling ratio can be as high as more than 2000%, creating larger pores in the area where it adheres. The distribution of these pores is consistent with the area where the polymer is located and is evenly dispersed at various positions in the coating. Also, because the overall structure of the battery cell negative electrode plate is dense, after electrolyte infiltration and swelling, the expansion stress of the negative electrode plate will be released from the inside to the outside and finally relax near the separator section, spontaneously forming this pore structure with larger pores at the top and smaller pores at the bottom. In addition, the proportion of the polymer used in the entire negative electrode plate is very small, so this swelling and pore expansion will not significantly increase the rebound of the negative electrode plate and damage the bonding network of the negative electrode plate.

[0059] The difference in the fast charging performance of the negative electrode was evaluated through a three-electrode test:

[0060] Table 1. Data table of the lithium plating boundary of the modified group and the basic group of negative electrode plates in Example 1

[0061]

[0062] As shown in Table 1, it can be seen that as the charging rate increases, the lithium plating SOC of the negative electrode plates in the basic group shows an obvious downward trend, but the SOC of the negative electrode plates in the modified group changes little and basically remains above 90%. As Figure 3 shown, when charging at a rate of 1.2C, the modified group was tested twice in parallel (i.e., modified group 1 and modified group 2), and the lithium plating SOC of the negative electrode plates in the modified group increased significantly, from 70% of the negative electrode plates in the basic group to 96%.

[0063] The electrolyte infiltration speed and adsorption effect of the modified group and the basic group of negative electrode plates were evaluated:

[0064] Table 2. Electrolyte Wetting Performance Table of the Anode Plates of the Modified Group and the Anode Plates of the Basic Group in Example 1

[0065] Group Liquid absorption rate Liquid retention rate Contact angle Basic group 17.87％ 16.93％ 10.1 Modified group 17.30％ 15.06％ 6.2

[0066] As shown in Table 2, it can be seen that there is no difference in this performance between the anode plates of the modified group and the anode plates of the basic group. From this, it can be known that the mechanism for the improvement in fast charging performance in this application lies in the optimization of the pore structure, rather than the improvement of liquid retention and infiltration effects by other similar strategies.

[0067] The cycle performance of the cells of the basic group (conventional cells) and the cells of the modified group (prepared cells) was tested.

[0068] As Figure 4 shown, it can be seen that in the early stage, the cycle performance of the cells of the modified group is significantly better than that of the basic group.

[0069] Example 2

[0070] The anode plate, cell, and their preparation methods and applications in this example include the following steps:

[0071] (1) Basic group: Using the graphite anode formula of a lithium-ion battery as the control group,

[0072] The main material used in the basic group of this example is graphite; the auxiliary materials are carboxymethyl cellulose, styrene-butadiene rubber, and conductive carbon black; the solvent is water.

[0073] The raw materials of the basic group anode formula, calculated by mass fraction, include:

[0074]

[0075] After double planetary slurry mixing, coating, rolling, baking, and electrolyte immersion, the basic group anode plate is obtained. The electrolyte immersion step is completed in the liquid injection process of battery preparation.

[0076] (2) Modified group: A graphite anode formula with 30% silicon-carbon mixed in a lithium-ion battery, and introducing swelling-type polymer hydrogenated nitrile rubber as the modified group.

[0077] The main material used in the modified group of this example is graphite mixed with 30% silicon-carbon; the auxiliary materials are carboxymethyl cellulose, polyacrylic acid, styrene-butadiene rubber, and conductive carbon black; the polymer material is hydrogenated nitrile rubber; the solvent is water.

[0078] The raw materials of the modified group anode formula, calculated by mass fraction, include:

[0079]

[0080] After double-planet slurry mixing, coating, rolling, baking, and electrolyte immersion, the modified group's negative electrode sheets are obtained. The electrolyte immersion step is completed during the electrolyte injection process in battery preparation.

[0081] The positive electrode sheets of both the basic group and the modified group contain lithium iron phosphate. By mass fraction,

[0082] 94 parts of lithium iron phosphate (LFP);

[0083] 3 parts of polyvinylidene fluoride (PVDF);

[0084] 3 parts of conductive carbon black (SP).

[0085] The electrode sheets of the basic group and the modified group are respectively made into 3 Ah soft-pack battery cells.

[0086] The double-sided areal density of the negative electrode sheet in this example is 140 g / m 2 , and the tap density is 1.5 g / cm 3 . The double-sided areal density of the positive electrode sheet is 400 g / m 2 , and the tap density is 2.3 g / cm 3 .

[0087] The difference in the fast charging performance of the negative electrode is evaluated through a three-electrode test:

[0088] Table 3. Data table of the lithium deposition boundary of the modified group's negative electrode sheet and the basic group's negative electrode sheet in Example 2

[0089]

[0090] As shown in Table 3, through the three-electrode test, it is found that the lithium deposition potential of the modified group has also increased significantly compared with that of the basic group.

[0091] The cycle performance of the battery cells of the basic group and the modified group is tested. As can be seen from Table 4, the cycle performance of the modified group is better than that of the basic group.

[0092] Table 4. Charge and discharge cycle performance data of the modified group's battery cells and the basic group's battery cells in Example 2

[0093]

[0094] Example 3

[0095] The negative electrode sheet, battery cell, and its preparation method and application in this example include the following steps:

[0096] (1) Basic group: Using the graphite negative electrode formula of a lithium-ion battery as a control group,

[0097] The main material used in the base group of this embodiment is graphite; the auxiliary materials are carboxymethyl cellulose, styrene-butadiene rubber, and conductive carbon black; the solvent is water.

[0098] The raw materials of the negative electrode formula of the base group include, by mass:

[0099]

[0100] After double planetary slurry mixing, coating, rolling, baking, and electrolyte soaking, the negative electrode sheet of the base group is obtained. Among them, the electrolyte soaking step is completed in the liquid injection process of battery preparation.

[0101] (2) Modified group: A swelling-type polymer polyacrylate is introduced into the graphite negative electrode formula of the lithium-ion battery as the modified group.

[0102] The main material used in the modified group of this embodiment is graphite; the auxiliary materials are carboxymethyl cellulose, styrene-butadiene rubber, and conductive carbon black; the polymer material is polyacrylate; the solvent is water.

[0103] The raw materials of the negative electrode formula of the modified group include, by mass:

[0104]

[0105] After double planetary slurry mixing, coating, rolling, baking, and electrolyte soaking, the negative electrode sheet of the modified group is obtained. Among them, the electrolyte soaking step is completed in the liquid injection process of battery preparation.

[0106] The positive electrode sheets of both the base group and the modified group use lithium iron phosphate. By mass,

[0107] 94 parts of lithium iron phosphate (LFP)

[0108] 3 parts of polyvinylidene fluoride (PVDF);

[0109] 3 parts of conductive carbon black (SP).

[0110] The electrode sheets of the base group and the modified group are respectively made into 3 Ah soft-pack battery cells.

[0111] The double-sided areal density of the negative electrode sheet in this embodiment is 200 g / m 2 , and the tap density is 1.5 g / cm 3 . The double-sided areal density of the positive electrode sheet is 400 g / m 2 , and the tap density is 2.3 g / cm 3 .

[0112] The difference in the fast charging performance of the negative electrode is evaluated through a three-electrode test:

[0113] Table 5 Data table of the lithium plating boundary of the negative electrode sheets of the modified group and the base group in Example 3

[0114]

[0115] As shown in Table 5, it can be seen that with the increase of the charging rate, the lithium plating SOC of the basic group shows an obvious downward trend, but the SOC of the modified group changes little and remains above 90%.

[0116] The above-described embodiments only represent the preferred embodiments of the present invention, and the description thereof is relatively specific and detailed. However, it should not be construed as a limitation to the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations, improvements and substitutions can be made, 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 appended claims.

Claims

1. A negative electrode sheet, characterized in that: It comprises main material, auxiliary material and polymer material; in terms of weight percentage, the main material accounts for 90 to 95 parts; the auxiliary material comprises a conductive agent and a binder, accounting for 7 to 9 parts; the polymer material is a swelling type polymer, accounting for 1 to 3 parts, and the swelling coefficient of the polymer material ranges from 1000% to 3000%.

2. The negative electrode sheet according to claim 1, characterized in that: The polymer material is one or both of hydrogenated nitrile rubber and / or polyacrylate.

3. The negative electrode sheet according to claim 1, characterized in that: The main material is one or more of graphite, hard carbon and / or silicon carbon.

4. The negative electrode plate according to claim 1, characterized in that: The conductive agent is one or more of conductive carbon black, conductive graphite and / or graphene, and the binder is one or more of carboxymethyl cellulose, styrene-butadiene rubber latex and / or polyacrylic acid.

5. The negative electrode sheet according to any one of claims 1 to 4, characterized in that: The swelling polymer forms pores in the area where it is attached; in a direction parallel to the current collector, when the negative electrode sheet is divided into several parts, the average size of the pores on each part gradually increases in the direction away from the current collector.

6. A method for preparing a negative electrode sheet, characterized in that: The raw materials of the negative electrode plate include main materials, auxiliary materials and polymer materials; in terms of weight percentage, the main materials account for 90 to 95 parts; the auxiliary materials include conductive agents and binders, accounting for 7 to 9 parts; the polymer material is a swelling polymer, accounting for 1 to 3 parts, and the swelling coefficient of the polymer material ranges from 1000% to 3000%; The raw materials are mixed, coated and rolled to obtain a negative electrode sheet.

7. A battery cell, characterized in that: A negative electrode sheet comprising the negative electrode sheet according to any one of claims 1 to 5.

8. The battery cell according to claim 7, characterized in that: It also includes a positive electrode plate; the main material of the positive electrode is a polyanion system, and the raw materials of the polyanion system contain one or more of lithium manganese iron phosphate, lithium iron phosphate or composite sodium iron phosphate.

9. The battery cell according to claim 7 or 8, characterized in that: The double-sided surface density of the positive electrode sheet is ≥400g / m 2 The double-sided surface density of the negative electrode sheet is ≥140g / m 2 .

10. Application of battery cells, characterized by: Use of the battery cell described in any one of claims 7 to 9 in the preparation of new energy vehicles, electronic products or energy storage systems.

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