Negative plate, battery monomer and electric vehicle

Abstract

The utility model provides a negative plate, a battery cell and an electric vehicle. The negative plate comprises a first negative active material layer, a second negative active material layer and a third negative active material layer which are arranged along a preset direction, the second negative electrode active material layer is arranged between the first negative electrode active material layer and the third negative electrode active material layer; a hole array is also arranged in the second negative electrode active material layer; the expansion rate of the second negative electrode active material layer is smaller than that of the first negative electrode active material layer; and the expansion rate of the second negative electrode active material layer is smaller than that of the third negative electrode active material layer. The hole array is arranged in the second negative electrode active material layer of the negative electrode plate, the porosity of the second negative electrode active material layer is improved through the hole array, the lithium ion transmission distance is shortened, the lithium ion transmission dynamics is improved, and the lithium separation risk is avoided, so that the cycling stability and the safety performance are improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a negative electrode sheet, a battery cell and an electric vehicle. Background Art

[0002] During the charging process of lithium-ion batteries, when the negative electrode has insufficient lithium insertion space and Li + The resistance of embedding negative electrode is too large, Li + When the amount of positive electrode deintercalation is higher than the amount of negative electrode intercalation, the Li + It can only gain electrons on the surface of the negative electrode, thus forming a silvery-white metallic lithium element, which leads to lithium deposition on the negative electrode sheet.

[0003] At the same time, during the cycle of lithium-ion battery cells, they are affected by temperature and expansion force (the negative electrode is in the Li + The volume change during the embedding process of the negative electrode leads to uneven polarization distribution of the negative electrode sheet and difficulty for the electrolyte to flow back to the middle of the negative electrode sheet, causing lithium precipitation, which in turn affects the battery capacity, cycle life and safety performance. Utility Model Content

[0004] The present application is made in view of the above-mentioned problems, and an object of the present application is to provide a negative electrode sheet having good cycle performance.

[0005] In order to achieve the above-mentioned object, the first aspect of the present application provides a negative electrode sheet, comprising a first negative electrode active material layer, a second negative electrode active material layer and a third negative electrode active material layer arranged along a preset direction;

[0006] The second negative electrode active material layer is disposed in the middle of the first negative electrode active material layer and the third negative electrode active material layer; the second negative electrode active material layer is also provided with a hole array;

[0007] The expansion rate of the second negative electrode active material layer is smaller than the expansion rate of the first negative electrode active material layer;

[0008] The expansion rate of the second negative electrode active material layer is smaller than the expansion rate of the third negative electrode active material layer.

[0009] Therefore, in the present application, the expansion rate of the first negative electrode active material layer and the third negative electrode active material layer is greater than the expansion rate of the second negative electrode active material layer; thereby, the expansion stress of the second negative electrode active material layer can be reduced; the extrusion amount of electrolyte in the second negative electrode active material layer is reduced, thereby increasing the electrolyte retention amount of the second negative electrode active material layer; at the same time, a hole array is also provided in the second negative electrode active material layer, and the porosity of the second negative electrode active material layer is improved through the hole array, thereby shortening the lithium ion transmission distance, improving the lithium ion transmission kinetics, avoiding the risk of lithium plating, and thus improving the cycle stability and safety performance.

[0010] In the present application, the second negative electrode active material layer is arranged in the middle of the first negative electrode active material layer and the third negative electrode active material layer, that is, the risk of lithium plating in the middle area is reduced by the above arrangement.

[0011] Optionally, the hole array includes one of a conical hole array, a cylindrical hole array and a U-shaped hole array.

[0012] Optionally, the spacing between adjacent holes in the hole array is 200 μm to 3000 μm.

[0013] If the spacing between holes is too large, the number of holes per unit volume will be small and the porosity improvement rate will be limited; if the spacing between holes is too small, the proportion of negative electrode active material per unit volume will be reduced, thus affecting the capacity and other electrical properties of the negative electrode sheet; by controlling the spacing between adjacent holes within the above range, it is beneficial to further improve the cycle performance and safety performance.

[0014] Optionally, the ratio of the depth of a single hole in the hole array to the thickness of the second negative electrode active material layer is between (0.05-1):1.

[0015] The larger depth of a single hole helps to further shorten the transmission distance of lithium ions, thereby further improving the transmission kinetics and further improving the cycle stability and safety.

[0016] Optionally, the volume of the second negative electrode active material layer accounts for 0.1% to 40% of the volume of the negative electrode active material layer.

[0017] When the expansion rate of the second negative electrode active material layer is small, the volume of the second negative electrode active material layer is further controlled to ensure that the first negative electrode active material layer and the third negative electrode active material layer are in close contact with the positive electrode sheet, reducing the Gap, thereby reducing the risk of lithium plating in the first negative electrode active material layer and the third negative electrode active material layer.

[0018] Optionally, the expansion rate of the second negative electrode active material layer is between 10% and 45%.

[0019] By controlling the expansion rate of the second negative electrode active material layer within the above range, the thickness of the second negative electrode active material layer can be controlled during the cycle, and excessive thickness changes will not occur, thereby affecting the stability of the negative electrode sheet.

[0020] Optionally, the difference in expansion rate between the second negative electrode active material layer and the first negative electrode active material layer is between 1% and 8%.

[0021] By controlling the expansion rate difference within a certain range, the thickness difference between the second negative electrode active material layer and the first negative electrode active material layer during the cycle is further controlled, the expansion force on the second negative electrode active material layer is reduced, the electrolyte retention in the second negative electrode active material layer is increased, and the risk of lithium plating is reduced.

[0022] Optionally, the negative electrode sheet further includes a current collector; the first negative electrode active material layer, the second negative electrode active material layer and / or the third negative electrode material layer are arranged on at least one side of the current collector.

[0023] The current collector can carry active substances, and can also collect and output the current generated by the negative electrode active materials, which is beneficial to reduce the internal resistance of the battery and improve the coulombic efficiency, cycle stability and rate performance of the battery.

[0024] The first negative electrode active material layer, the second negative electrode active material layer and / or the third negative electrode active material layer are arranged on both sides of the current collector, so as to better improve the structural stability of the negative electrode sheet.

[0025] Optionally, the first negative electrode active material layer is located on one side edge of the current collector along the width direction of the negative electrode sheet and / or along the length direction of the negative electrode sheet.

[0026] Arranging the first negative electrode active material layer at the edge of the negative electrode sheet (in the width direction and / or the length direction) is beneficial to further improving the utilization rate of the current collector.

[0027] A second aspect of the present application provides a battery cell, comprising the negative electrode sheet of the first aspect of the present application.

[0028] A third aspect of the present application provides an electric vehicle, comprising the negative electrode sheet of the first aspect of the present application;

[0029] And / or, the battery cell of the second aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present drawings or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present drawings. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0031] Figure 1 Schematic diagram of the cross-sectional structure of the negative electrode sheet in Example 1.

[0032] Figure 2 Schematic diagram of the top view of the negative electrode sheet in Example 1.

[0033] Description of Figure Numbers:

[0034] 100, negative electrode active material layer; 101, current collector;

[0035] 1001, first negative electrode active material layer; 1002, second negative electrode active material layer; 1003, hole array; 1004, third negative electrode active material layer.

[0036] The purpose, features and advantages of this figure will be further described in conjunction with the embodiments with reference to the accompanying drawings. DETAILED DESCRIPTION

[0037] Hereinafter, the negative electrode sheet, battery cell, battery, electrical equipment and electric vehicle of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0038] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0039] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0040] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0041] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0042] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0043] If not specifically stated, in this application, the term "or" is 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 both A and B are true (or exist).

[0044] During the cycle of lithium-ion battery cells, lithium ions are embedded in the negative electrode, causing the negative electrode active material to expand, generating expansion force; at the same time, the battery temperature will rise during the cycle; under the influence of expansion force and temperature, the polarization distribution of the electrode is uneven and the electrolyte has difficulty flowing back to the middle of the electrode, causing lithium precipitation, which in turn affects the battery capacity, cycle life and safety performance.

[0045] In order to solve at least one aspect of the above problems, a first aspect of an embodiment of the present application provides a negative electrode sheet, comprising a first negative electrode active material layer, a second negative electrode active material layer and a third negative electrode active material layer arranged along a preset direction;

[0046] The second negative electrode active material layer is disposed in the middle of the first negative electrode active material layer and the third negative electrode active material layer; the second negative electrode active material layer is also provided with a hole array;

[0047] The expansion rate of the second negative electrode active material layer is smaller than the expansion rate of the first negative electrode active material layer;

[0048] The expansion rate of the second negative electrode active material layer is smaller than the expansion rate of the third negative electrode active material layer.

[0049] Therefore, in the present application, the expansion rate of the first negative electrode active material layer and the third negative electrode active material layer is greater than the expansion rate of the second negative electrode active material layer; thereby, the expansion stress of the second negative electrode active material layer can be reduced; the extrusion amount of electrolyte in the second negative electrode active material layer is reduced, thereby increasing the electrolyte retention amount of the second negative electrode active material layer; at the same time, a hole array is also provided in the second negative electrode active material layer, and the porosity of the second negative electrode active material layer is improved through the hole array, thereby shortening the lithium ion transmission distance, improving the lithium ion transmission kinetics, avoiding the risk of lithium plating, and thus improving the cycle stability and safety performance.

[0050] In the present application, the second negative electrode active material layer is arranged in the middle of the first negative electrode active material layer and the third negative electrode active material layer, that is, the risk of lithium plating in the middle area is reduced by the above arrangement.

[0051] In some embodiments, the hole array includes one of a conical hole array, a cylindrical hole array, and a U-shaped hole array.

[0052] In the embodiment, no special configuration is made to the structure of a single hole, and it is only required to shorten the lithium ion transmission distance.

[0053] In some embodiments, the bottom width of a single conical hole in the conical hole array is 30 μm to 700 μm.

[0054] In some embodiments, the bottom width of a single cylindrical hole in the cylindrical hole array is 30 μm to 700 μm.

[0055] In some embodiments, a single U-shaped hole in the U-shaped hole array is composed of a cylindrical segment and a hemispherical segment.

[0056] In some embodiments, the bottom width of the cylindrical segment in the U-shaped hole array is 30 μm to 700 μm.

[0057] By controlling the bottom width of a single hole, the transport dynamics of lithium ions are controlled; if the bottom width is too small, it becomes more difficult for lithium ions to enter; and if the bottom width is too large, the relative amount of negative electrode active material is reduced, thus affecting the electrical properties of the negative electrode sheet.

[0058] In some embodiments, the tapered hole array includes one of a circular tapered hole array and a square tapered hole array.

[0059] In some embodiments, the square pyramid hole array includes one of a triangular pyramid hole array, a quadrangular pyramid hole array, and a pentagonal pyramid hole array.

[0060] In some embodiments, the cylindrical hole array includes one of a cylindrical hole array and a prismatic hole array.

[0061] In some embodiments, the prism hole array includes one of a triangular prism hole array, a quadrangular prism hole array, a pentagonal prism hole array, and a hexagonal prism hole array.

[0062] In some embodiments, the spacing between adjacent holes in the hole array is 200 μm to 3000 μm.

[0063] If the spacing between holes is too large, the number of holes per unit volume will be small and the porosity improvement rate will be limited; if the spacing between holes is too small, the proportion of negative electrode active material per unit volume will be reduced, thus affecting the capacity and other electrical properties of the negative electrode sheet; by controlling the spacing between adjacent holes within the above range, it is beneficial to further improve the cycle performance and safety performance.

[0064] In some embodiments, the ratio of the depth of a single hole in the hole array to the thickness of the second negative electrode active material layer is between (0.05-1):1.

[0065] The larger depth of a single hole helps to further shorten the transmission distance of lithium ions, thereby further improving the transmission kinetics and further improving the cycle stability and safety.

[0066] In some embodiments, the volume of the first negative electrode active material layer accounts for 0.1% to 40% of the volume of the negative electrode active material layer.

[0067] When the expansion rate of the second negative electrode active material layer is small, the volume of the second negative electrode active material layer is further controlled to ensure that the first negative electrode active material layer and the third negative electrode active material layer are in close contact with the positive electrode sheet, reducing the Gap, thereby reducing the risk of lithium plating in the first negative electrode active material layer and the third negative electrode active material layer.

[0068] In some embodiments, the volume of the second negative electrode active material layer accounts for 0.1% to 40% of the volume of the negative electrode active material layer.

[0069] In some embodiments, the volume of the third negative electrode active material layer accounts for 0.1% to 45% of the volume of the negative electrode active material layer.

[0070] In some embodiments, the expansion rate of the first negative electrode active material layer is between 10% and 45%.

[0071] In some embodiments, the expansion rate of the second negative electrode active material layer is between 10% and 45%.

[0072] By controlling the expansion rate of the second negative electrode active material layer within the above range, the thickness of the second negative electrode active material layer can be controlled during the cycle, and excessive thickness changes will not occur, thereby affecting the stability of the negative electrode sheet.

[0073] In some embodiments, the expansion rate of the third negative electrode active material layer is between 10% and 45%.

[0074] In some embodiments, the difference in expansion rate between the second negative electrode active material layer and the first negative electrode active material layer is between 1% and 8%.

[0075] By controlling the expansion rate difference within a certain range, the thickness difference between the second negative electrode active material layer and the first negative electrode active material layer during the cycle is further controlled, the expansion force on the second negative electrode active material layer is reduced, the electrolyte retention in the second negative electrode active material layer is increased, and the risk of lithium plating is reduced.

[0076] By controlling the expansion rate difference within a certain range, the expansion difference between the second negative electrode active material layer and the first negative electrode active material layer is further controlled, thereby avoiding side edge ridges.

[0077] In some embodiments, the difference in expansion rate between the second negative electrode active material layer and the third negative electrode active material layer is between 1% and 8%.

[0078] By controlling the expansion rate difference within a certain range, the thickness difference between the second negative electrode active material layer and the third negative electrode active material layer during the cycle is further controlled, the expansion force on the second negative electrode active material layer is reduced, the electrolyte retention in the second negative electrode active material layer is increased, and the risk of lithium plating is reduced.

[0079] By controlling the expansion rate difference within a certain range, the expansion difference between the second negative electrode active material layer and the third negative electrode active material layer is further controlled, thereby avoiding side edge ridge formation.

[0080] In some embodiments, the difference in expansion rate between the second negative electrode active material layer and the first negative electrode active material layer is between 1% and 7.9%.

[0081] In some embodiments, the difference in expansion rate between the second negative electrode active material layer and the third negative electrode active material layer is between 1% and 7.9%.

[0082] In some embodiments, the raw materials for preparing the negative electrode active material layer include a negative electrode active material, a binder, and a conductive agent.

[0083] In some embodiments, the negative electrode active material includes at least one of a graphite material and a silicon-based material.

[0084] In some embodiments, the graphite material includes at least one of artificial graphite, natural graphite, mesophase carbon microsphere graphite, soft carbon and hard carbon.

[0085] In some embodiments, the silicon-based material includes at least one of a silicon anode, a silicon oxygen anode, a pre-lithiation silicon oxygen anode, a silicate anode, a silicon alloy anode and a silicon carbon anode.

[0086] In some embodiments, the adhesive includes at least one of styrene-butadiene rubber and hydroxymethyl cellulose salt.

[0087] In some embodiments, the conductive agent includes at least one of conductive carbon black and carbon nanotubes.

[0088] In some embodiments, the hole array is formed by mechanical punching or laser drilling.

[0089] The method of forming the hole array is not limited to the above two methods, and also includes other hole forming methods similar to the above two methods.

[0090] In some embodiments, the negative electrode sheet further includes a current collector; the first negative electrode active material layer, the second negative electrode active material layer and / or the third negative electrode material layer are disposed on at least one side of the current collector.

[0091] The current collector can carry active substances, and can also collect and output the current generated by the negative electrode active materials, which is beneficial to reduce the internal resistance of the battery and improve the coulombic efficiency, cycle stability and rate performance of the battery.

[0092] The first negative electrode active material layer, the second negative electrode active material layer and / or the third negative electrode active material layer are arranged on both sides of the current collector, which can better improve the structural stability of the negative electrode sheet. In some embodiments, the current collector is a copper current collector.

[0093] In some embodiments, the first negative electrode active material layer is located on one side edge of the current collector along the width direction of the negative electrode sheet and / or along the length direction of the negative electrode sheet.

[0094] Arranging the first negative electrode active material layer at the edge of the negative electrode sheet (in the width direction and / or the length direction) is beneficial to further improving the utilization rate of the current collector.

[0095] In some embodiments, the third negative electrode active material layer is located on the other side edge of the current collector along the width direction of the negative electrode sheet and / or along the length direction of the negative electrode sheet.

[0096] Providing the third negative electrode active material layer at the edge of the negative electrode sheet (in the width direction and / or the length direction) is beneficial to further improve the utilization rate of the current collector.

[0097] In some embodiments, the first negative electrode active material layer is located on one edge of the current collector along the width direction of the negative electrode sheet;

[0098] The third negative electrode active material layer is located on the other side edge of the current collector along the width direction of the negative electrode sheet.

[0099] In some embodiments, the first negative electrode active material layer is located on one edge of the current collector along the length direction of the negative electrode sheet;

[0100] The third negative electrode active material layer is located on the other side edge of the current collector along the length direction of the negative electrode sheet.

[0101] The length direction of the negative electrode sheet refers to the long side direction of the negative electrode sheet, and the width direction of the negative electrode sheet refers to the short side direction of the negative electrode sheet.

[0102] In some embodiments, the first negative electrode active material layer has a hole array disposed therein.

[0103] In some embodiments, the pore array in the first negative electrode active material layer is the same as or different from the pore array in the second negative electrode active material layer.

[0104] In some embodiments, the third negative electrode active material layer has a hole array disposed therein.

[0105] In some embodiments, the pore array in the third negative electrode active material layer is the same as or different from the pore array in the second negative electrode active material layer.

[0106] A second aspect of the embodiments of the present application provides a battery cell, comprising the negative electrode sheet of the first aspect of the embodiments of the present application.

[0107] A third aspect of the embodiments of the present application provides a battery, comprising the negative electrode sheet of the first aspect of the embodiments of the present application or the battery cell of the second aspect of the embodiments of the present application.

[0108] A fourth aspect of the embodiments of the present application provides an electrical device, including the negative electrode sheet of the first aspect of the embodiments of the present application, the battery cell of the second aspect of the embodiments of the present application, or the battery of the third aspect of the embodiments of the present application.

[0109] A fifth aspect of the embodiments of the present application provides an electric vehicle, comprising the negative electrode sheet of the first aspect of the embodiments of the present application, the battery cell of the second aspect of the embodiments of the present application, or the battery of the third aspect of the embodiments of the present application.

[0110] In order to further illustrate the influence of negative electrode active material layers with different expansion rates on the performance of negative electrode sheets, in the embodiments of the present application, graphite materials and / or silicon oxide materials with different expansion rates are selected to form negative electrode active material layers with different expansion rates, and the performance of negative electrode sheets is tested after being made; for specific settings, please refer to the following embodiments and comparative examples.

[0111] Among them, the expansion rate is equal to the test thickness of the electrode when it is charged (using a fully charged battery cell electrode) divided by the thickness of the electrode during rolling. Generally, the expansion rate of a graphite electrode when fully charged is between 10% and 30% (in the embodiments and comparative examples of the present application, the graphite materials selected are Gr1, Gr2 and Gr3 ((expansion rate Gr3>Gr2>Gr1)); the expansion rate of a silicon oxide electrode is between 10% and 180%; technicians in this field can make a choice based on actual conditions, which will not be elaborated here.

[0112] Example 1

[0113] This embodiment is a negative electrode sheet, such as Figures 1-2 As shown, it includes a current collector 101,

[0114] Negative electrode active material layers 100 are disposed on both sides of the current collector 101;

[0115] The negative electrode active material layer 100 is composed of a first negative electrode active material layer 1001 , a second negative electrode active material layer 1002 and a third negative electrode active material layer 1004 ;

[0116] The second negative electrode active material layer 1002 is also provided with a hole array 1003 ( Figure 1 not shown).

[0117] The first negative electrode active material layer 1001 is made of a negative electrode active material (graphite (Gr1) and silicon oxide mixed, the mass fraction of silicon oxide is 5%), conductive carbon black, styrene-butadiene rubber and sodium hydroxycellulose (CMC) in a mass ratio of 94:1.5:3:1.5, and the expansion rate is 26%;

[0118] The volume ratio of the first negative electrode active material layer 1001 to the negative electrode active material layer 100 is 0.35.

[0119] The second negative electrode active material layer 1002 is made of a negative electrode active material (graphite (Gr1)), conductive carbon black, styrene-butadiene rubber and sodium hydroxycellulose (CMC) in a mass ratio of 96:1:1.8:1.2, and the expansion rate is 18%;

[0120] The volume ratio of the second negative electrode active material layer 1002 to the negative electrode active material layer 100 is 0.3.

[0121] The hole array 1003 is composed of a plurality of conical holes; the width of the conical holes is 100 μm, the spacing between adjacent conical holes is 2000 μm, and the ratio of the depth of the conical holes to the thickness of the second negative electrode active material layer 1002 is 70%.

[0122] The third negative electrode active material layer 1004 is made of a negative electrode active material (graphite (Gr1) and silicon oxide mixed, the mass fraction of silicon oxide is 5%), conductive carbon black, styrene-butadiene rubber and sodium hydroxycellulose (CMC) in a mass ratio of 94:1.5:3:1.5, and the expansion rate is 26%;

[0123] The volume ratio of the third negative electrode active material layer 1004 to the negative electrode active material layer 100 is 0.35;

[0124] The first negative electrode active material layer 1001 , the second negative electrode active material layer 1002 and the third negative electrode active material layer 1004 have the same length;

[0125] The thicknesses of the first negative electrode active material layer 1001 , the second negative electrode active material layer 1002 , and the third negative electrode active material layer 1004 are the same.

[0126] Example 2

[0127] This embodiment is a negative electrode sheet, which is different from the embodiment 1 in that:

[0128] The first negative electrode active material layer is mixed with negative electrode active material (graphite (Gr2)), conductive carbon black, styrene-butadiene rubber and sodium hydroxycellulose (CMC) in a mass ratio of 96:1:1.8:1.2, and the expansion rate is 20%;

[0129] The third negative electrode active material layer is formed by mixing negative electrode active material (graphite (Gr2)), conductive carbon black, styrene-butadiene rubber and sodium hydroxycellulose (CMC) in a mass ratio of 96:1:1.8:1.2, and the expansion rate is 20%.

[0130] Example 3

[0131] This embodiment is a negative electrode sheet, which is different from the embodiment 1 in that:

[0132] The first negative electrode active material layer is mixed with negative electrode active material (graphite (Gr3)), conductive carbon black, styrene-butadiene rubber and sodium hydroxycellulose (CMC) in a mass ratio of 96:1:1.8:1.2, and the expansion rate is 24%;

[0133] The third negative electrode active material layer is a mixture of negative electrode active material (graphite (Gr3)), conductive carbon black, styrene-butadiene rubber and sodium hydroxycellulose (CMC) in a mass ratio of 96:1:1.8:1.2, and the expansion rate is 24%;

[0134] The first negative electrode active material layer and the third negative electrode active material layer are also provided with hole arrays, and the parameters of the hole arrays are the same as those in the second negative electrode active material layer.

[0135] Comparative Example 1

[0136] This comparative example is a negative electrode sheet, which differs from Example 1 in that:

[0137] The first negative electrode active material layer is formed by mixing the negative electrode active material (graphite (Gr1)), conductive carbon black, styrene-butadiene rubber and sodium hydroxycellulose (CMC) in a mass ratio of 96:1:1.8:1.2, and the expansion rate is 18%;

[0138] The second negative electrode active material layer is not provided with array holes;

[0139] The third negative electrode active material layer is formed by mixing the negative electrode active material (graphite (Gr1)), conductive carbon black, styrene-butadiene rubber and sodium hydroxycellulose (CMC) in a mass ratio of 96:1:1.8:1.2, and the expansion rate is 18%.

[0140] After assembling the negative electrode sheets and the positive electrode sheets (the preparation method of the positive electrode active material layer includes: mixing NCM, conductive carbon black and polyvinylidene fluoride in a mass ratio of 96.5:1.5:2 and then coating) in Examples 1 to 3 and Comparative Example 1 to form a battery, after 200 cycles of 1C / 1C charge and discharge at 25°C (voltage range of 2.8V to 4.35V), the lithium deposition of the negative electrode sheets was observed. The evaluation criteria for the lithium deposition are as follows:

[0141] The degree of lithium precipitation is defined as follows:

[0142] No lithium precipitation: lithium precipitation cannot be observed with the naked eye;

[0143] Slight lithium deposition: the lithium deposition area is less than 10% of the area of ​​the second negative electrode active material layer;

[0144] Moderate lithium deposition: the lithium deposition area is greater than or equal to 10% of the area of ​​the second negative electrode active material layer; and the lithium deposition area is less than 30% of the area of ​​the second negative electrode active material layer;

[0145] Severe lithium deposition: The lithium deposition area is greater than or equal to 30%.

[0146] The lithium plating test results are shown in Table 1.

[0147] Table 1 Test results of lithium precipitation in Examples 1 to 3 and Comparative Example 1

[0148]

[0149] In Examples 1 to 3, the expansion rate of the first negative electrode active material layer is greater than the expansion rate of the second negative electrode active material layer; the expansion rate of the third negative electrode active material layer is greater than the expansion rate of the second negative electrode active material layer, and a hole array is provided in the second negative electrode active material layer; therefore, the lithium precipitation of the negative electrode sheets of Examples 1 to 3 after cycling is greatly alleviated. That is, in Examples 1 to 3, by adjusting the expansion rates of different regions, the electrolyte retention amount of the second negative electrode active material layer is increased, so that the second negative electrode active material layer remains in an infiltrated state, and at the same time, a hole array is provided in the second negative electrode active material layer to increase the porosity of the second negative electrode active material layer, thereby shortening the lithium ion transmission distance and reducing the risk of lithium precipitation.

[0150] The difference in expansion rate in Example 1 is relatively large, which affects the contact between the first negative electrode active layer and the electrolyte in the second negative electrode active material layer, and the contact between the third negative electrode active material layer and the electrolyte in the second negative electrode active material layer; resulting in the risk of bridge breaking of the electrolyte in the three negative electrode active material layers, leading to slight lithium deposition.

[0151] In Comparative Example 1, there is no difference in the expansion rate of the negative electrode active material layer, resulting in a decrease in the amount of electrolyte retained; at the same time, a pore array is not set, the transmission distance of lithium ions becomes longer, and the kinetics becomes worse; therefore, the lithium precipitation in Comparative Example 1 is more serious than in Examples 1 to 3.

[0152] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode sheet, characterized in that: comprising a first negative electrode active material layer, a second negative electrode active material layer and a third negative electrode active material layer arranged along a preset direction; The second negative electrode active material layer is disposed in the middle of the first negative electrode active material layer and the third negative electrode active material layer; The second negative electrode active material layer is also provided with a hole array; The expansion rate of the second negative electrode active material layer is smaller than the expansion rate of the first negative electrode active material layer; The expansion rate of the second negative electrode active material layer is smaller than the expansion rate of the third negative electrode active material layer.

2. The negative electrode sheet according to claim 1, characterized in that: The distance between adjacent holes in the hole array is 200 μm to 3000 μm.

3. The negative electrode sheet according to claim 1, characterized in that: The ratio of the depth of a single hole in the hole array to the thickness of the second negative electrode active material layer is between (0.05 and 1):

1.

4. The negative electrode sheet according to claim 1, characterized in that: The volume of the second negative electrode active material layer accounts for 0.1% to 40% of the volume of the negative electrode active material layer.

5. The negative electrode sheet according to claim 1, characterized in that: The expansion rate of the second negative electrode active material layer is between 10% and 45%.

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The difference in expansion rate between the second negative electrode active material layer and the first negative electrode active material layer is between 1% and 8%.

7. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The negative electrode sheet further includes a current collector; the first negative electrode active material layer, the second negative electrode active material layer and / or the third negative electrode material layer are arranged on at least one side of the current collector.

8. The negative electrode sheet according to claim 7, characterized in that: The first negative electrode active material layer is located on one side edge of the current collector along the width direction of the negative electrode sheet and / or along the length direction of the negative electrode sheet.

9. A battery cell, characterized in that: The invention comprises the negative electrode sheet as claimed in any one of claims 1 to 8.

10. An electric vehicle, characterized in that: A negative electrode sheet comprising any one of claims 1 to 8; And / or, the battery cell as claimed in claim 9.

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