Negative electrode sheet and preparation method therefor, battery cell, and battery

Abstract

A negative electrode sheet and a preparation method therefor, a battery cell, and a battery. The negative electrode sheet comprises a current collector and negative electrode active layers arranged on two opposite sides of the current collector. Each negative electrode active layer comprises at least two sub-active layers which are sequentially stacked, and the expansion performance of the sub-active layers gradually increases from inside to outside. After the negative electrode sheet is rolled and rebounded during manufacturing, the outer sub-active layer exhibits high expansion, and the inner sub-active layer exhibits low expansion, so that a porosity distribution that decreases from the surface layer to the bottom layer can be formed, thereby improving a lithium-ion transport channel and improving battery cell performance. The special structure of an electrode and reasonable porosity distribution facilitate lithium-ion migration within a thick electrode, and the requirements of fast charging and high energy density are simultaneously considered.

Description

Negative electrode sheet and preparation method thereof, battery cell and battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure claims priority to application number 202410266113X filed with the China Patent Office on March 8, 2024, entitled “Negative electrode sheet and preparation method thereof, battery cell and battery,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to the technical field of battery materials, and in particular to a negative electrode sheet and a preparation method thereof, a battery cell and a battery. Background Art

[0004] Based on the current demand for high energy density of lithium batteries, the demand for electrode thickness is also increasing. However, currently, excessive electrode thickness will lead to increased polarization of the battery cell, low utilization of active materials, slower charging of the battery cell, and increased risk of lithium plating.

[0005] Currently, traditional coating methods can only apply a single layer of the same formula and cannot construct a gradient microstructure on the electrode.

[0006] With the progress of the energy revolution, the demand for high-energy-density lithium-ion batteries is growing. Currently, the design of high-energy cells focuses on two key aspects: 1. Selecting high-gram-capacity active materials; 2. Using thickly coated electrode sheets. The former significantly increases costs and significantly reduces their lifespan. Thickly coated electrode sheets are prone to processing problems during production, such as cracking, bulging, and roller breakage. Furthermore, thickly coated electrode sheets significantly increase internal resistance, negatively impacting the cycle life of the battery cell.

[0007] During the charging process of a lithium-ion battery, lithium ions are released from the positive electrode active material, passing through the electrolyte and the separator into the negative electrode active material. Electrons, on the other hand, travel in the opposite direction of lithium ions, releasing from the positive electrode active material, following the external circuit, passing through the negative electrode current collector, and reentering the negative electrode active material. As a result, the lithium ion concentration in the negative electrode active material is higher near the separator, while the electron concentration is higher near the current collector. Therefore, it is necessary to improve the lithium ion transmission pathway and increase the lithium ion transmission speed near the separator.

[0008] In view of this, the present disclosure is proposed. Summary of the Invention

[0009] The purpose of the present disclosure is to provide a negative electrode sheet and a preparation method thereof, a battery cell and a battery.

[0010] The present disclosure is achieved as follows:

[0011] In a first aspect, the present disclosure provides a negative electrode sheet, comprising: a current collector and a negative electrode active layer disposed on opposite sides of the current collector;

[0012] The negative electrode active layer includes at least two sub-active layers stacked in sequence, and the expansion performance of the sub-active layers gradually increases from the inside to the outside.

[0013] In an optional embodiment, the expansion performance of each sub-active layer is characterized by an expansion parameter, and the expansion parameter x satisfies the formula: x=k*b*lg 100a, k>0, wherein a is the proportion of the binder in the sub-active layer, and b is the elastic modulus of the binder, in MPa.

[0014] Specifically, the larger the value of the expansion parameter x corresponding to the active layer is, the lower the expansion performance is, the lower the expansion rate of the active layer is, and the lower the porosity of the active layer is.

[0015] In an optional embodiment, the number of sub-active layers is two, which are respectively a first sub-active layer and a second sub-active layer from the inside to the outside, and one side of the first sub-active layer is connected to one side of the current collector;

[0016] The binder in the first sub-active layer is a first binder;

[0017] The binder in the second sub-active layer is a second binder;

[0018] The first binder accounts for a1 in the first sub-active layer, the second binder accounts for a2 in the second sub-active layer, the elastic modulus of the first binder is b1, and the elastic modulus of the second binder is b2;

[0019] The relationship among a1, a2, b1 and b2 is as follows:

[0020] a1>a2;

[0021] Or, a1=a2,b1>b2;

[0022] Or, a1<a2, b1>b2.

[0023] In an optional embodiment, the first binder and / or the second binder is / are selected from at least one of styrene-butadiene rubber, hydroxymethyl cellulose, polytetrafluoroethylene and polyacrylate.

[0024] In an optional embodiment, a1>a2, b1=b2, the first adhesive and the second adhesive are of the same type, and the crosslinking degree of the first adhesive and the second adhesive is also the same; or, the first adhesive and the second adhesive are of different types.

[0025] In an optional embodiment, the adhesive accounts for 0.5 to 15% of the sub-active layer; and the elastic modulus of the adhesive in the sub-active layer is 1 to 6 MPa.

[0026] In an optional implementation manner, when k=1, the value range of x is 1.19 to 1.96.

[0027] In a second aspect, the present disclosure provides a method for preparing a negative electrode sheet according to any one of the aforementioned embodiments, comprising: sequentially disposing at least two sub-active layers on opposite sides of a current collector by coating and then rolling.

[0028] In a third aspect, the present disclosure provides a battery cell comprising a negative electrode sheet according to any one of the aforementioned embodiments.

[0029] In a fourth aspect, the present disclosure provides a battery comprising the battery cell according to the aforementioned embodiment.

[0030] The present disclosure has the following beneficial effects:

[0031] The negative electrode sheet provided by the embodiment of the present disclosure has a negative electrode active layer including at least two sub-active layers, and the expansion performance of the sub-active layers gradually increases from the inside to the outside. Since the expansion performance of the outer sub-active layer is higher than that of the inner sub-active layer, after the electrode sheet is rolled and rebounded, the expansion rate of the outer sub-active layer is higher than that of the inner sub-active layer, which will form a porosity distribution from large to small from the surface to the bottom layer. In this way, the lithium ion transmission channel can be improved and the battery cell performance can be enhanced. Therefore, setting a special electrode structure and a reasonable porosity distribution is conducive to the migration of lithium ions inside the thick electrode, taking into account the requirements of fast charging and high energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0033] FIG1 is a schematic structural diagram of a negative electrode sheet provided in an embodiment of the present disclosure.

[0034] Icon: 100 - negative electrode sheet; 110 - current collector; 121 - first sub-active layer; 122 - second sub-active layer. DETAILED DESCRIPTION

[0035] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0036] To balance the demands of high energy and longevity, the present disclosure proposes a negative electrode with a gradient microstructure based on the carrier distribution within the cell electrode. To address this issue, the present disclosure proposes a gradient setting on the electrode, so that the surface layer of the electrode near the diaphragm has a high porosity and stronger liquid absorption and retention capacity, while the porosity is low on the side of the electrode near the current collector. Ultimately, the transmission path of lithium ions in the thick-coated electrode is shortened, the transmission resistance is reduced, the overall fast charging capability is enhanced, and the energy density of the battery cell is less affected.

[0037] There are many factors that influence the porosity of the electrode, but existing technologies generally use active materials or conductive agents with different porosities to directly influence the porosity of the electrode. However, this disclosure focuses on the selection of binders to control the porosity distribution of the upper and lower layers.

[0038] The inventors discovered that different elastic moduli of the binder can cause different rebounds in the electrode during processing or later use. The larger the elastic modulus, the smaller the expansion, resulting in a smaller porosity in the electrode. Therefore, the present disclosure selects the appropriate binder to configure the electrode structure based on the difference in elastic modulus.

[0039] The negative electrode sheet 100 for a lithium-ion battery cell, its preparation method, and the battery cell provided in the embodiments of the present disclosure are described in detail below.

[0040] As shown in FIG1 , an embodiment of the present disclosure provides a negative electrode sheet 100 , comprising: a current collector 110 and negative electrode active layers disposed on opposite sides of the current collector 110 ;

[0041] The negative electrode active layer includes at least two sub-active layers stacked in sequence, and the expansion performance of the sub-active layers gradually increases from the inside to the outside.

[0042] The negative electrode sheet provided in the disclosed embodiments comprises at least two sub-active layers, each with increasing expansion properties from the inside out. This results in a porosity distribution from the surface to the bottom, improving lithium ion transport and enhancing battery cell performance. This unique electrode structure and a reasonable porosity distribution facilitate lithium ion migration within thick electrodes, balancing the requirements of fast charging and high energy density.

[0043] Specifically, the expansion performance of each sub-active layer is characterized by an expansion parameter, and the expansion parameter x satisfies the formula: x=k*b*lg100a, k>0, wherein a is the proportion of the binder in the sub-active layer, and b is the elastic modulus of the binder, in MPa.

[0044] Specifically, the larger the value of the expansion parameter x corresponding to the active layer is, the lower the expansion performance is, the lower the expansion rate of the active layer is, and the lower the porosity of the active layer is.

[0045] It should be noted that k in the above formula is a coefficient, and its value can be any value greater than zero. The function of this formula is only to compare the expansion parameters of each sub-active layer, and there is no need to impose other restrictions on its value.

[0046] Furthermore, the number of sub-active layers is 2, which are respectively a first sub-active layer 121 and a second sub-active layer 122 from the inside to the outside, and one side of the first sub-active layer 121 is connected to one side of the current collector 110;

[0047] The binder in the first sub-active layer 121 is a first binder, and the binder in the second sub-active layer 122 is a second binder;

[0048] The first binder accounts for a1 in the first sub-active layer 121 , and the second binder accounts for a2 in the second sub-active layer 122 . The elastic modulus of the first binder is b1, and the elastic modulus of the second binder is b2.

[0049] The relationship among a1, a2, b1 and b2 is as follows:

[0050] a1>a2,b1=b2 or b1>b2 or b1<b2;

[0051] Or, a1=a2,b1>b2;

[0052] Or, a1<a2, b1>b2.

[0053] When the proportion of binder in the two sub-active layers is the same, the elastic modulus of the added first binder is greater than the elastic modulus of the second binder. In this way, during the processing and use of the battery cell, the electrode on the diaphragm side expands greatly, the porosity is large, and the electrolyte absorption capacity is strong. Therefore, the ion transmission path of the electrode in this section is short, the transmission rate is fast, and the transmission resistance is reduced; on the side close to the current collector 110, the elastic modulus of the first binder is large, the electrode expands less, and the overall energy density is improved. The elastic modulus is positively correlated with the degree of cross-linking. A larger elastic modulus usually results in a higher degree of cross-linking. After the electrode is shelled, the two layers with different degrees of cross-linking have different absorption capacities for the electrolyte, resulting in inconsistent porosity between the upper and lower layers of the electrode, thereby increasing the transmission rate of lithium ions on the surface of the electrode and reducing the overall DCR of the electrode. When the elastic modulus of the binder used in the two-layer structure is the same, the proportion of binder in the first sub-active layer 121 is higher than that in the second negative electrode active layer. In this way, after rolling, the rebound expansion of the inner and outer layers of the electrode is inconsistent. The less binder in the second negative electrode active layer, the greater the rebound of the electrode, the greater the porosity, and the shorter the ion transmission path, which can also achieve the effect of improving the lithium ion transmission rate.

[0054] Optionally, the first binder and / or the second binder is / are selected from at least one of styrene-butadiene rubber, hydroxymethyl cellulose, polytetrafluoroethylene and polyacrylate.

[0055] Preferably, to ensure that the negative electrode sheet has better electrochemical performance, the binder accounts for 0.5-15% of the sub-active layer; and the elastic modulus of the binder in the sub-active layer is 1-6 MPa.

[0056] In some optional embodiments of the present disclosure, specific configurations of the sub-active layer include the following:

[0057] (1) a1=a2=0.5-15%, the first binder and the second binder are of the same type, and the crosslinking degree of the first binder is greater than that of the second binder.

[0058] (2) a1=a2=0.5-15%, the first adhesive and the second adhesive are of different types, and the elastic modulus of the first adhesive is greater than the elastic modulus of the second adhesive.

[0059] (3) a1>a2, b1=b2, a1 is 0.5~15%, a2 is 0.5~15%;

[0060] The first adhesive and the second adhesive are of the same type, and the cross-linking degree of the first adhesive and the second adhesive is also the same, that is, the first adhesive and the second adhesive are the same adhesive;

[0061] Alternatively, the first adhesive and the second adhesive are of different types, but have the same elastic modulus.

[0062] (4) a1>a2, b1<b2, a1 is 0.5~15%, a2 is 0.5~15%;

[0063] That is, the proportion of the first binder is greater than that of the second binder, the elastic modulus of the first binder is smaller than that of the second binder, but the expansion parameter x1 of the first sub-active layer 121 is greater than the expansion parameter x2 of the second sub-active layer 122 .

[0064] (5) a1>a2, b1<b2, a1 is 0.5~15%, a2 is 0.5~15%;

[0065] That is, the proportion of the first binder is smaller than that of the second binder, the elastic modulus of the first binder is greater than that of the second binder, but the expansion parameter x1 of the first sub-active layer 121 is greater than the expansion parameter x2 of the second sub-active layer 122 .

[0066] Furthermore, the material of the current collector 110 is copper. For example, the current collector 110 may be a copper composite current collector.

[0067] The embodiment of the present disclosure further provides a method for preparing the negative electrode sheet 100 , comprising: sequentially disposing at least two sub-active layers on two opposite sides of the current collector 110 by coating and then rolling.

[0068] The embodiments of the present disclosure also provide a battery cell, comprising the negative electrode sheet provided in the embodiments of the present disclosure.

[0069] In some optional embodiments of the present disclosure, the battery cell further includes a positive electrode sheet, a separator and an electrolyte.

[0070] The embodiments of the present disclosure also provide a battery, comprising the battery cell provided in the embodiments of the present disclosure.

[0071] The features and performance of the present disclosure are further described in detail below with reference to the embodiments. In the provided embodiments, k=1 is used as an example for illustration.

[0072] Example 1

[0073] The negative electrode sheet 100 provided in this embodiment includes a current collector 110 and negative electrode active layers disposed on opposite sides of the current collector 110 . The negative electrode active layers include an inner first sub-active layer 121 and an outer second sub-active layer 122 .

[0074] In this embodiment, the binder content in the two sub-active layers is the same, and the binders are of different types with different elastic moduli.

[0075] The slurry preparation for the first sub-active layer 121 is as follows: 95 parts by weight of negative electrode active material (graphite), 1 part by weight of conductive agent (conductive carbon black), and 4 parts by weight of first binder (SBR). The elastic modulus of the first binder is 3 MPa.

[0076] The expansion parameter x of the first active sub-layer 121 is 1.81.

[0077] The slurry for the second sub-active layer 122 is prepared as follows: 95 parts by weight of negative electrode active material (graphite), 1 part by weight of conductive agent (conductive carbon black), and 4 parts by weight of second binder (PAA). The elastic modulus of the second binder is 2 MPa.

[0078] The expansion parameter x of the second active sub-layer 122 is 1.20.

[0079] The current collector 110 is a copper foil;

[0080] The slurry of the first sub-active layer 121 is coated on one side of a copper foil through a double-layer die head and dried in an oven. The other side of the copper foil is then coated, dried, and then roll-formed to prepare the negative electrode sheet 100 .

[0081] Example 2

[0082] The negative electrode sheet 100 provided in this embodiment includes a current collector 110 and negative electrode active layers disposed on opposite sides of the current collector 110 . The negative electrode active layers include an inner first sub-active layer 121 and an outer second sub-active layer 122 .

[0083] In this embodiment, the two sub-active layers have different binder proportions, the binder types are the same, and the cross-linking degrees are the same, so the elastic moduli are the same.

[0084] The slurry for the first sub-active layer 121 is prepared as follows: 95 parts by weight of negative electrode active material (graphite), 0.5 parts by weight of conductive agent (carbon black), and 4.5 parts by weight of first binder (SBR). The elastic modulus of the first binder is 3 MPa.

[0085] The expansion parameter x of the first active sub-layer 121 is 1.96.

[0086] The slurry preparation for the second sub-active layer 122 is as follows: 95 parts by weight of negative electrode active material (graphite), 1 part by weight of conductive agent (carbon black), and 4 parts by weight of second binder (SBR). The elastic modulus of the second binder is 3 MPa.

[0087] The expansion parameter x of the second active sub-layer 122 is 1.81.

[0088] The current collector 110 is a copper foil;

[0089] The slurry of the first sub-active layer 121 is coated on one side of a copper foil through a double-layer die head and dried in an oven. The other side of the copper foil is then coated, dried, and then roll-formed to prepare the negative electrode sheet 100 .

[0090] Example 3

[0091] The negative electrode sheet 100 provided in this embodiment includes a current collector 110 and negative electrode active layers disposed on opposite sides of the current collector 110 . The negative electrode active layers include an inner first sub-active layer 121 and an outer second sub-active layer 122 .

[0092] In this embodiment, the two sub-active layers have different binder proportions, different binder types, and different elastic moduli.

[0093] The slurry preparation for the first sub-active layer 121 is as follows: 95 parts by weight of negative electrode active material (graphite), 1 part by weight of conductive agent (conductive carbon black), and 4 parts by weight of first binder (SBR). The elastic modulus of the first binder is 3 MPa.

[0094] The expansion parameter x of the first active sub-layer 121 is 1.81.

[0095] The slurry preparation for the second sub-active layer 122 is as follows: 95 parts by weight of negative electrode active material (graphite), 0.5 parts by weight of conductive agent (conductive carbon black), and 4.5 parts by weight of second binder (PAA). The elastic modulus of the second binder is 2 MPa.

[0096] The expansion parameter x of the second active sub-layer 122 is 1.31.

[0097] The current collector 110 is a copper foil;

[0098] The slurry of the first sub-active layer 121 is coated on one side of a copper foil through a double-layer die head and dried in an oven. The other side of the copper foil is then coated, dried, and then roll-formed to prepare the negative electrode sheet 100 .

[0099] Example 4

[0100] The negative electrode sheet 100 provided in this embodiment includes a current collector 110 and negative electrode active layers disposed on opposite sides of the current collector 110 . The negative electrode active layers include an inner first sub-active layer 121 and an outer second sub-active layer 122 .

[0101] In this embodiment, the binder ratio in the first active sub-layer 121 is greater than that in the second active sub-layer 122 , the elastic modulus of the first binder is smaller than that of the second binder, but the expansion parameter of the first active sub-layer 121 is greater than that of the second active sub-layer 122 .

[0102] The slurry preparation for the first sub-active layer 121 is as follows: 95 parts by weight of negative electrode active material (graphite), 1 part by weight of conductive agent (conductive carbon black), and 4 parts by weight of first binder (PAA). The elastic modulus of the first binder is 2.4 MPa.

[0103] The expansion parameter x of the first active sub-layer 121 is 1.44.

[0104] The slurry preparation for the second sub-active layer 122 is as follows: 96 parts by weight of negative electrode active material (graphite), 1 part by weight of conductive agent (conductive carbon black), and 3 parts by weight of second binder (SBR). The elastic modulus of the second binder is 2.5 MPa.

[0105] The expansion parameter x of the second active sub-layer 122 is 1.19.

[0106] The current collector 110 is a copper foil;

[0107] The slurry of the first sub-active layer 121 is coated on one side of a copper foil through a double-layer die head and dried in an oven. The other side of the copper foil is then coated, dried, and then roll-formed to prepare the negative electrode sheet 100 .

[0108] Comparative Example 1

[0109] This comparative example is basically the same as Example 1, except that: the negative electrode sheet structure of this comparative example is: a negative electrode active layer is provided on both opposite sides of the current collector;

[0110] The negative electrode active layer in Comparative Example 1 is prepared at one time using the first sub-active layer 121 , and its thickness is approximately equal to the sum of the first sub-active layer 121 and the second sub-active layer 122 in Example 1.

[0111] Comparative Example 2

[0112] This comparative example is basically the same as Example 1, except that: the negative electrode sheet structure of this comparative example is: a negative electrode active layer is provided on both opposite sides of the current collector;

[0113] The negative electrode active layer is prepared at one time using the second sub-active layer 122 , and its thickness is approximately equal to the sum of the first sub-active layer 121 and the second sub-active layer 122 in Example 1.

[0114] Experimental example

[0115] The negative electrode sheets prepared in each example and comparative example were assembled with lithium iron phosphate electrodes to form 50Ah square aluminum batteries, and their electrochemical performance was tested. The test results are recorded in Table 1.

[0116] Table 1 Statistics of electrochemical performance of various embodiments and comparative examples

[0117] It can be seen from the above table that the negative electrode sheets prepared in various embodiments have good electrochemical performance after being assembled into batteries.

[0118] Comparing Examples 1-4 with Comparative Examples 1-2, the cycle performance of Examples 1-4 is significantly better, indicating that when the negative electrode active layer is set to two layers and the expansion parameter of the inner layer is greater than that of the outer layer, the battery cell can obtain better cycle performance.

[0119] In summary, the negative electrode active layer is set to be multi-layer, and the expansion parameters of the sub-active layer gradually increase from the inside to the outside. In this way, after the electrode is rolled and rebounded, the outer sub-active layer expands more and the inner active layer expands less, forming a porosity distribution from large to small from the surface to the bottom layer, thereby improving the lithium ion transmission channel and enhancing the performance of the battery cell.

[0120] The above are merely preferred embodiments of the present disclosure and are not intended to limit the present disclosure. Those skilled in the art will readily appreciate that various modifications and variations of the present disclosure are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present disclosure shall be included within the scope of protection of the present disclosure. Industrial Applicability

[0121] The negative electrode sheet disclosed herein features a decreasing porosity distribution of the negative electrode active layer from the surface to the bottom, improving lithium ion transport and enhancing battery cell performance. Therefore, the unique electrode structure and optimal porosity distribution facilitate lithium ion migration within the thick electrode, balancing fast charging and high energy density requirements.

Claims

1. A negative electrode sheet, characterized in that: include: a current collector and a negative electrode active layer disposed on opposite sides of the current collector; The negative electrode active layer includes at least two sub-active layers stacked in sequence, and the expansion performance of the sub-active layers gradually increases from the inside to the outside.

2. The negative electrode sheet according to claim 1, characterized in that: The expansion performance of each sub-active layer is characterized by an expansion parameter x, and the expansion parameter x satisfies the formula: x=k*b*lg 100a, k>0, where a is the proportion of the binder in the sub-active layer, and b is the elastic modulus of the binder, in MPa.

3. The negative electrode sheet according to claim 2, characterized in that: There are two sub-active layers, which are respectively a first sub-active layer and a second sub-active layer from the inside to the outside, and one side of the first sub-active layer is connected to one side of the current collector; The binder in the first sub-active layer is a first binder; The binder in the second sub-active layer is a second binder; The first binder accounts for a1 in the first sub-active layer, the second binder accounts for a2 in the second sub-active layer, the elastic modulus of the first binder is b1, and the elastic modulus of the second binder is b2; The relationship among a1, a2, b1 and b2 is as follows: a1>a2; Or, a1=a2,b1>b2; Or, a1<a2, b1>b2.

4. The negative electrode sheet according to claim 3, characterized in that: The first binder and / or the second binder is / are selected from at least one of styrene-butadiene rubber, hydroxymethyl cellulose, polytetrafluoroethylene and polyacrylate.

5. The negative electrode sheet according to claim 3, characterized in that: When a1>a2, b1=b2, the first adhesive and the second adhesive are of the same type, and the crosslinking degrees of the first adhesive and the second adhesive are also the same; or, the first adhesive and the second adhesive are of different types.

6. The negative electrode sheet according to claim 3, characterized in that: a1=a2, the first binder and the second binder are of the same type, and the cross-linking degree of the first binder is greater than that of the second binder.

7. The negative electrode sheet according to claim 3, characterized in that: a1=a2, the first adhesive and the second adhesive are of different types, and the elastic modulus of the first adhesive is greater than that of the second adhesive.

8. The negative electrode sheet according to claim 3, characterized in that: a1>a2, b1<b2, the proportion of the first binder is greater than that of the second binder, the elastic modulus of the first binder is smaller than the elastic modulus of the second binder, and the expansion parameter of the first sub-active layer is greater than the expansion parameter of the second sub-active layer.

9. The negative electrode sheet according to claim 3, characterized in that: a1>a2, b1<b2, the proportion of the first binder is smaller than that of the second binder, the elastic modulus of the first binder is greater than the elastic modulus of the second binder, and the expansion parameter of the first sub-active layer is greater than the expansion parameter of the second sub-active layer.

10. The negative electrode sheet according to claim 1, characterized in that: The material of the current collector is copper.

11. The negative electrode sheet according to any one of claims 2 to 10, characterized in that: The adhesive in the sub-active layer accounts for 0.5 to 15%; the elastic modulus of the adhesive in the sub-active layer is 1 to 6 MPa.

12. The negative electrode sheet according to any one of claims 2 to 10, characterized in that: When k=1, the value of x ranges from 1.19 to 1.

96.

13. A method for preparing a negative electrode sheet according to any one of claims 1 to 12, characterized in that: include: The at least two sub-active layers are sequentially arranged on two opposite sides of the current collector by coating and then rolling.

14. A battery cell, characterized in that: The negative electrode sheet comprises the negative electrode sheet according to any one of claims 1 to 12.

15. A battery, characterized in that: Comprising the battery cell as claimed in claim 14.