Negative plate, battery cell and battery

Abstract

The utility model discloses a negative plate, a battery cell and a battery, the negative plate is used for the battery cell, and the negative plate comprises a negative current collector and a negative active material layer; the negative current collector is suitable for being connected with a negative tab; the negative electrode active material layer is laminated on the negative electrode current collector, the negative electrode active material layer comprises a first region and a second region, the first region is closer to the negative electrode lug than the second region, the negative electrode capacity per unit volume of the first region is N1, the negative electrode capacity per unit volume of the second region is N2, and N1 is greater than N2. The negative plate provided by the utility model can effectively improve the charge-discharge capacity of the edge of the negative plate and reduce lithium precipitation at the edge of the negative plate.

Description

Technical Field

[0001] The utility model relates to the technical field of batteries, and in particular to a negative electrode sheet, a battery core and a battery. Background Art

[0002] The edge area of ​​the lithium-ion battery's electrode will experience lithium deposition due to poor charging and discharging capabilities after multiple fast-charging cycles. The continuous accumulation of deposited lithium will cause the diaphragm to be punctured, posing a serious safety hazard to the lithium-ion battery. Utility Model Content

[0003] The utility model aims to provide a negative electrode sheet, a battery cell and a battery, which can solve the problem of lithium deposition caused by poor charging and discharging capacity at the edge of the negative electrode sheet.

[0004] In order to achieve the purpose of the utility model, the utility model provides the following technical solutions:

[0005] In a first aspect, the utility model provides a negative electrode sheet for a battery cell, comprising:

[0006] A negative electrode current collector, suitable for connecting to the negative electrode ear;

[0007] A negative electrode active material layer is stacked on the negative electrode current collector, the negative electrode active material layer includes a first region and a second region, the first region is closer to the negative electrode ear than the second region, the unit volume capacity of the first region is N1, the unit volume capacity of the second region is N2, and the following is satisfied: N1>N2.

[0008] In one embodiment, a portion of the negative electrode current collector corresponding to the first region has a first edge, and the first edge is suitable for arranging the negative electrode ear.

[0009] In one embodiment, the first area and the second area are arranged along a first direction, wherein the first area includes a second edge and a third edge opposite to each other in the first direction, the third edge is connected to the second area, and in the first direction, the distance between the second edge and the third edge is d1, satisfying: 1mm≤d1≤5mm.

[0010] In one embodiment, the first area has a second edge, and in a first direction, the first edge and the second edge are arranged relative to each other, wherein the distance between the first edge and the second edge is d2, satisfying: 0mm≤d2≤5mm, and the first direction is the arrangement direction of the first area and the second area.

[0011] In one implementation, the capacity per unit area of ​​the first region is M1, and the capacity per unit area of ​​the second region is M2, satisfying: M1>M2.

[0012] In one embodiment, the surface density of the material in the first region is a1, and the surface density of the material in the second region is a2, satisfying: a1>a2.

[0013] In one implementation, the following condition is also satisfied: a1 / a2≥102%.

[0014] In one implementation, the following condition is also satisfied: a1 / a2≤110%.

[0015] In one embodiment, the compaction density of the material in the first region is b1, and the compaction density of the material in the second region is b2, satisfying: b1>b2.

[0016] In one implementation, the following condition is also satisfied: b1 / b2≥102%.

[0017] In one implementation, the following condition is also satisfied: b1 / b2≤110%.

[0018] In one embodiment, the first region includes a first material, and the second region includes a second material, the average particle size of the second material is greater than the average particle size of the first material, and / or the carbon content of the second material is less than the carbon content of the first material, and / or the conductivity of the first region along the second direction is less than the conductivity of the second region along the second direction, the second direction is the stacking direction of the negative electrode current collector and the negative electrode active material layer, and / or the porosity of the first region is greater than the porosity of the second region.

[0019] In one embodiment, the battery cell further includes a positive electrode sheet, the negative electrode sheet includes an overlapping region and an overhang region, the overlapping region overlaps with the positive electrode active material layer of the positive electrode sheet, and the overhang region includes at least a portion of the first region.

[0020] In one embodiment, the negative electrode active material layer further includes a third region, the third region is disposed at one end of the second region away from the first region, and the negative electrode capacity per unit volume of the third region is N3, satisfying: N2<N3.

[0021] In a second aspect, the utility model provides a battery cell, comprising a positive electrode sheet, a separator and a negative electrode sheet as described in any embodiment of the first aspect, wherein the positive electrode sheet, the separator and the negative electrode sheet are stacked, and in the orthographic projection of the positive electrode sheet on the negative electrode sheet, the edge of the positive electrode active material layer of the positive electrode sheet close to the negative electrode ear falls in the first area.

[0022] In a third aspect, the utility model provides a battery, comprising a housing and a battery core as described in any one of the embodiments of the second aspect, wherein the battery core is accommodated in the housing.

[0023] By setting the negative electrode active material layer as the second region and the first region, the second region is closer to the negative electrode ear than the first region, wherein the unit volume negative electrode capacity N2 of the second region is smaller than the unit volume negative electrode capacity N1 of the first region, so that when the unit volume positive electrode capacity P of the positive electrode sheet remains unchanged, N1 / P of the first region is greater than N2 / P of the second region, and the first region has a better capacity for accommodating lithium ions than the second region, thereby avoiding the accumulation and precipitation of lithium ions at the edge of the negative electrode during high-rate charge and discharge, alleviating the edge lithium plating effect caused by lithium ion migration and cycle accumulation, and effectively solving the battery capacity diving and safety problems caused by edge lithium plating. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the implementation methods of the utility model or the technical solutions in the prior art, the drawings required for use in the implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some implementation methods of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 is a top view of a negative electrode sheet of an embodiment;

[0026] Figure 2 is a cross-sectional view of a negative electrode sheet of an embodiment;

[0027] Figure 3 is a cross-sectional view of a battery cell of an embodiment.

[0028] Description of reference numerals:

[0029] 10-negative electrode sheet, 11-negative electrode current collector, 111-first edge, 112-fourth edge, 113-fifth edge, 114-sixth edge, 12-negative electrode active material layer, 121-first region, 1211-second edge, 1212-third edge, 122-second region, 123-third region, 1231-seventh edge, 1232-eighth edge;

[0030] 20 - positive electrode sheet, 21 - positive electrode current collector, 22 - positive electrode active material layer, 30 - separator, X - first direction. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0032] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there can be a central component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there can be a central component at the same time.

[0033] Unless otherwise defined, all technical and scientific terms used in this utility model have the same meaning as those commonly understood by technicians in the technical field of this utility model. The terms used in the specification of this utility model are only for the purpose of describing specific embodiments and are not intended to limit this utility model. The term "and / or" used in this utility model includes any and all combinations of one or more related listed items.

[0034] In conjunction with the accompanying drawings, some embodiments of the present invention are described in detail below. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0035] For reference Figure 1 and Figure 2 The utility model provides a negative electrode sheet 10, and the negative electrode sheet 10 is used for a battery cell, and the battery cell also includes a positive electrode sheet 20 stacked with the negative electrode sheet 10. The negative electrode sheet 10 includes a negative electrode collector 11 and a negative electrode active material layer 12. The negative electrode collector 11 is suitable for connecting to a negative electrode ear (not shown in the figure). The negative electrode active material layer 12 is stacked on the negative electrode collector 11, and the negative electrode active material layer 12 includes a second region 122 and a first region 121, and the first region 121 is closer to the negative electrode ear than the second region 122, and the unit volume negative electrode capacity of the first region 121 is N1, and the unit volume negative electrode capacity of the second region 122 is N2, satisfying: N1>N2.

[0036] The negative electrode current collector 11 includes, but is not limited to, any one of copper foil, composite copper foil or carbon-coated copper foil.

[0037] The negative electrode active material layer 12 includes a silicon negative electrode material, a carbon-based negative electrode material, a conductive agent and a binder. The conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 (carbon 60) and carbon nanotubes, without limitation. The types of binders include polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan and chitosan derivatives, without limitation. The carbon-based negative electrode material includes at least one of a graphite material and a non-graphite material, without limitation. The graphite material includes at least one of natural graphite or artificial graphite, without limitation. The non-graphite material includes at least one of a hard carbon material or a soft carbon material, without limitation.

[0038] Optionally, the first region 121 is closer to the edge of the negative electrode current collector 11 connected to the negative electrode ear than at least part of the second region 122. For example, the first region 121 and the second region 122 are both rectangular, and the length of the first region 121 in the vertical first direction X is the same as the length of the second region 122 in the vertical first direction X, then the first region 121 is closer to the edge of the negative electrode current collector 11 connected to the negative electrode ear than the second region 122 as a whole, wherein the first direction X is the arrangement direction of the first region and the second region, for example, the first direction X can be the length direction of the negative electrode sheet, and the first direction X can also be the width direction of the negative electrode sheet; or, when the minimum distance from the edge of part of the second region 122 to the edge of the negative electrode current collector 11 connected to the negative electrode ear is the same as the minimum distance from the first region 121 to the edge of the negative electrode current collector 11 connected to the negative electrode ear, the first region 121 is arranged opposite to the negative electrode ear in the first direction X, the second region 122 is in a "concave" shape, and the second region 122 surrounds the outer periphery of the first region 121.

[0039] The negative electrode tab may partially overlap with the negative electrode current collector 11 , or may only be connected to the edge of the negative electrode current collector 11 , without limitation.

[0040] The second region 122 and the first region 121 may be spaced apart, that is, a transition region is provided between the second region 122 and the first region 121 , and the negative electrode capacity per unit volume of the transition region is smaller than the negative electrode capacity per unit volume of the first region 121 .

[0041] The negative electrode ear can be in the form of full-pole ear, multi-pole ear or single-pole ear, etc. The output electrode ear can be in the form of same-side output electrode ear, different-side output electrode ear, symmetrical output electrode ear or asymmetrical output electrode ear, etc.

[0042] The negative electrode ear can be a flattened ear or a die-cut ear, without limitation. The ear of the negative electrode sheet 10 can be made of nickel or copper-nickel material. The negative electrode ear of the negative electrode sheet 10 is mainly used to connect the positive and negative electrodes of the battery, realize the transmission of current, and guide the current of the positive electrode to the negative electrode to realize the charging and discharging process of the battery. At the same time, the negative electrode ear of the negative electrode sheet 10 also plays a role in fixing the internal structure of the lithium battery.

[0043] The negative electrode ear may further include a protective adhesive, which may be used to strengthen the fixation between the negative electrode ear and the negative electrode current collector 11 .

[0044] The negative electrode capacity per unit volume of the first region 121 is greater than the negative electrode capacity per unit volume of the second region 122, so that the current density of the first region 121 is greater than the current density of the second region 122, that is, in the same time, more charges in the first region 121 pass through the tab of the negative electrode sheet 10. The first region 121 is closer to the tab than the second region 122, which can make the current reasonably distributed on the negative electrode sheet 10, which is beneficial to improving the cycle life and performance of the battery.

[0045] A high negative electrode capacity per unit volume generally means that the negative electrode active material has a higher specific surface area and more reaction sites, which is conducive to the diffusion of lithium ions between the solid electrolyte and the negative electrode active material. By setting the negative electrode active material layer 12 as the second region 122 and the first region 121, the second region 122 is closer to the first edge 111 of the negative electrode collector 11 than the first region 121, and the first region 121 is suitable for corresponding to the edge of the positive electrode active material layer 22 of the positive electrode sheet 20 close to the negative electrode ear, and the negative electrode capacity per unit volume N2 of the second region 122 is less than the negative electrode capacity per unit volume N1 of the first region 121, so that when the positive electrode capacity per unit volume P of the positive electrode sheet 20 remains unchanged, N1 / P of the first region is greater than N2 / P of the second region, and the first region 121 has a better capacity to accommodate lithium ions than the second region 122, thereby avoiding the accumulation and precipitation of lithium ions at the edge of the negative electrode during high-rate charge and discharge, alleviating the edge lithium precipitation effect caused by lithium ion migration and cycle accumulation, and effectively solving the battery capacity diving and safety problems caused by edge lithium precipitation.

[0046] For reference Figure 1 In one embodiment, the portion of the negative electrode current collector 11 corresponding to the first region 121 has a first edge 111, and the first edge 111 is suitable for arranging a negative electrode ear.

[0047] For reference Figure 1In one embodiment, the first region 121 includes a second edge 1211 and a third edge 1212 that are opposite to each other in the first direction X, the first edge 111 is located on the side of the second edge 1211 that is opposite to the third edge 1212 in the first direction X, and the third edge 1212 is connected to the second region 122, wherein the first direction X is the arrangement direction of the first region 121 and the second region 122, for example, the first direction X can be the length direction of the negative electrode sheet, and the first direction X can also be the width direction of the negative electrode sheet. Optionally, the second edge 1211 and the third edge 1212 can be a straight line, a curve, etc., without limitation. The second edge 1211 and / or the third edge 1212 can be flush with the edge of the negative electrode collector 11 in the first direction X perpendicular to the first direction X, or there can be a gap between the edge of the negative electrode collector 11 in the first direction X perpendicular to the first direction X, without limitation.

[0048] The negative electrode current collector 11 , the second region 122 and the first region 121 are all rectangular.

[0049] Due to the existence of process errors, the angle between any two sides of the first edge 111, the second edge 1211 and the third edge 1212 can be 1°-3°, without limitation. Optionally, the first edge 111, the second edge 1211 and the third edge 1212 are parallel, so that the second region 122 has the same effect of improving the charge and discharge capacity of the edge of the negative electrode sheet 10 in the direction along the first edge 111, which is beneficial to the charge and discharge of the battery.

[0050] The negative electrode current collector 11 further includes a fourth edge 112 and a fifth edge 113 opposite to each other. The fourth edge 112 and the fifth edge 113 are respectively located on both sides of the first edge 111 .

[0051] The fourth edge 112 and the fifth edge 113 may be straight lines or curves without limitation; the edges corresponding to the second area 122 and the first area 121 may also be straight lines or curves without limitation.

[0052] For reference Figure 1 In one embodiment, in the first direction X, the distance from any position of the second edge 1211 to the corresponding position of the third edge 1212 is d1, satisfying: 1mm≤d1≤5mm.

[0053] Optionally, d1 can be 1mm, 2mm, 3mm, 4mm, or 5mm without limitation.

[0054] d1 limits the size of the first region 121 so that the first region 121 corresponds to the edge region of the negative electrode sheet 10. If d1 is less than 1 mm, the second region 122 has little effect on improving the charge and discharge capacity at the edge of the negative electrode sheet 10. If d1 is greater than 5 mm, the ratio of the first region 121 to the negative electrode active material layer 12 is too large, which lengthens the diffusion path of lithium ions in the negative electrode material, slows down the migration rate of lithium ions during the charge and discharge process, reduces the discharge capacity and rate performance, and affects the charge and discharge capacity of the battery.

[0055] For reference Figure 1 In one embodiment, in the first direction X, the distance from any position of the first edge 111 to the corresponding position of the second edge 1211 is d2, satisfying: 0mm≤d2≤5mm.

[0056] Optionally, d2 can be 0mm, 1mm, 2mm, 3mm, 4mm, or 5mm without limitation.

[0057] If d2>5mm, the area of ​​the negative electrode active material layer 12 is too small, which wastes space and reduces the battery capacity. d2 is set so that the positive projection of the second region 122 is located in the negative electrode current collector 11, and the second region 122 is spaced from the edge of the negative electrode current collector 11, which facilitates the coating of the second region 122 and the first region 121 during the production process.

[0058] In one embodiment, the capacity per unit area of ​​the first region 121 is M1, and the capacity per unit area of ​​the second region 122 is M2, satisfying: M1>M2. Specifically, in order to satisfy that the negative electrode capacity per unit volume N1 of the first region 121 is greater than the negative electrode capacity per unit volume N2 of the second region 122, the capacity per unit area of ​​the first region 121 can be adjusted to M1 greater than the capacity per unit area M2 of the second region 122 while maintaining the overall thickness of the negative electrode sheet.

[0059] In one embodiment, the surface density of the material of the first region 121 is a1, and the surface density of the material of the second region 122 is a2, satisfying: a1>a2. Specifically, in order to satisfy that the negative electrode capacity per unit volume N1 of the first region 121 is greater than the negative electrode capacity per unit volume N2 of the second region 122, the surface density of the first region 121 can be adjusted to a1 and the surface density of the second region 122 can be adjusted to satisfy a1>a2, so that the current density of the first region 121 is greater than the current density of the second region 122, that is, in the same time, more charges in the first region 121 pass through the tab of the negative electrode sheet 10. The first region 121 is closer to the tab than the second region 122, so that the current is reasonably distributed on the negative electrode sheet 10, which is beneficial to improving the cycle life and performance of the battery.

[0060] In one embodiment, a1 / a2≥102%. In one embodiment, a1 / a2≤110%. The surface density of the negative electrode active material layer 12 of the negative electrode sheet 10 mainly refers to the mass of the negative electrode active material per unit volume.

[0061] Optionally, a1 / a2 can be 102%, 104%, 106%, 108%, 110%, etc. without limitation.

[0062] When a1 / a2 is less than 102%, the difference in surface density between the materials in the first region 121 and the second region 122 is too small to increase the ratio of the negative electrode surface capacity to the positive electrode surface capacity at the edge, thereby failing to effectively improve the edge lithium deposition problem of the negative electrode sheet 10; when a1 / a2 is greater than 110%, the surface density of the material in the first region 121 is too large, which may lead to expansion and contraction of the material between the negative electrode material particles, particle rupture and inactivation, etc.; when 102%≤a1 / a2≤110%, the higher surface density of the material in the first region 121 may increase the capacity of the negative electrode sheet 10, so that the battery can accommodate more charge during the charge and discharge process, thereby extending the cycle life of the battery, and the first region 121 with a higher surface density may accommodate more lithium ions during the charge and discharge process, thereby avoiding the accumulation and precipitation of lithium ions at the edge of the negative electrode during high-rate charge and discharge, alleviating the edge lithium deposition effect caused by lithium ion migration and cycle accumulation, and effectively solving the battery capacity dive and safety problems caused by edge lithium deposition.

[0063] In one embodiment, the compaction density of the material of the first region 121 is b1, and the compaction density of the material of the second region 122 is b2, satisfying: b1>b2. Specifically, the compaction density b1 of the material of the first region 121 can be adjusted to be greater than the compaction density b2 of the material of the second region 122, so that the unit volume negative electrode capacity N1 of the first region 121 is greater than the unit volume negative electrode capacity N2 of the second region 122.

[0064] In one embodiment, the following is also satisfied: b1 / b2≥102%. In one embodiment, the following is also satisfied: b1 / b2≤110%.

[0065] Optionally, b1 / b2 can be 102%, 104%, 106%, 108%, 110%, etc. without limitation.

[0066] When b1 / b2 is less than 102%, the difference in compaction density between the materials in the first region 121 and the second region 122 is too small to increase the ratio of the negative electrode surface capacity to the positive electrode surface capacity at the edge, thereby failing to effectively improve the lithium deposition problem at the edge of the negative electrode sheet 10; when b1 / b2 is greater than 110%, the compaction density of the material in the first region 121 is too large, which will increase the degree of extrusion between the negative electrode material particles and reduce the porosity of the electrode sheet, making it difficult for the electrolyte to infiltrate the interior of the negative electrode sheet 10, resulting in insufficient electrolyte infiltration, which directly affects the specific capacity of the negative electrode sheet 10, and increases polarization and internal resistance during the cycle; when 102%≤b1 / b2≤110%, while increasing the ratio of the negative electrode surface capacity to the positive electrode surface capacity at the edge, the electrolyte can infiltrate the interior of the negative electrode sheet 10.

[0067] Optionally, a multi-layer coating technology is used to achieve that the compaction density b2 of the material in the second region 122 is smaller than the compaction density b1 of the material in the first region 121 .

[0068] Optionally, when coating is performed multiple times only on the first region 121 , the second region 122 is coated during the last coating, and then the pole piece is rolled.

[0069] Optionally, the second area 122 and the first area 121 may be uniformly coated first, and then only the first area 121 may be coated multiple times.

[0070] Optionally, the second area 122 may be coated once or multiple times, without any specific limitation.

[0071] Optionally, the coating times of the first region 121 is one or more times greater than the coating times of the second region 122 , without any specific limitation.

[0072] During coating, the coating direction is the extending direction of the first edge 111 .

[0073] By changing the compaction density through multi-layer coating, the unit volume negative electrode capacity of the second region 122 is achieved to be smaller than the unit volume negative electrode capacity of the first region 121, so that the first region 121 has a better capacity to accommodate lithium ions, thereby reducing the accumulation and precipitation of lithium ions at the edge, helping to inhibit the formation of lithium dendrites and improving the safety and cycle stability of the battery.

[0074] In addition, other means may be used to achieve that the negative electrode capacity per unit volume of the first region 121 is greater than the negative electrode capacity per unit volume of the second region 122. Specifically, in one embodiment, the first region 121 includes a first material, the second region 122 includes a second material, the average particle size of the second material is greater than the average particle size of the first material, and / or the carbon content of the second material is less than the carbon content of the first material, and / or the conductivity of the first region 121 along the second direction is less than the conductivity of the second region 122 along the second direction, the second direction being the stacking direction of the negative electrode current collector 11 and the negative electrode active material layer 12, and / or the porosity of the first region 121 is less than the porosity of the second region 122.

[0075] The fact that the average particle size of the second material is greater than that of the first material indicates that the first material can accommodate more active substances in the same volume, thereby increasing the energy density of the battery. At the same time, the first material with a smaller average particle size has a larger specific surface area, which helps to increase the contact area with the electrolyte, accelerate the transmission of lithium ions between the solid phase and the liquid phase, and avoid the accumulation and precipitation of lithium ions at the edge of the negative electrode during high-rate charge and discharge, thereby improving the charge and discharge performance of the battery.

[0076] Optionally, the carbon content of the second material is 0.5%-1%, and the carbon content of the first material is 1.5%-2%, satisfying that the carbon content of the second material is less than that of the first material, so that the first material has a higher specific capacity, and the unit volume negative electrode capacity of the first region 121 having the first material is higher than the unit volume negative electrode capacity of the second region 122. The first region 121 has a better capacity for accommodating lithium ions than the second region 122, avoiding the accumulation of lithium ions at the edge of the negative electrode during high-rate charge and discharge, alleviating the edge lithium plating effect caused by lithium ion migration and cycle accumulation, and effectively solving the battery capacity diving and safety problems caused by edge lithium plating.

[0077] The conductivity of the first region 121 along the second direction is lower than the conductivity of the second region 122 along the second direction, indicating that the current transmission speed in the first region 121 close to the negative electrode ear is slow, which suppresses the conductivity of the edge of the negative electrode sheet 10, reduces its current, and thus reduces the temperature rise in the edge area, which can reduce the temperature difference between the edge and the middle of the negative electrode sheet 10, reduce lithium plating, and extend the service life of the battery cell.

[0078] The porosity of the first region 121 is less than that of the second region 122 , which means that the first region 121 has more pores and can accommodate more lithium ions, thereby reducing lithium deposition at the edge of the negative electrode sheet 10 and extending the service life of the battery cell.

[0079] In one embodiment, the negative electrode sheet 10 includes an overlap region and an overhang region, the overlap region overlaps with the positive electrode active material layer 22 of the positive electrode sheet 20, and the overhang region includes at least a portion of the first region 121. The overhang region may exceed the overlap region in a first direction X, or may exceed the overlap region in a third direction, and the third direction has an angle with the first direction X, that is, the overhang region may be arranged around the overlap region. The third direction is the extension direction of the first edge 111.

[0080] In the first direction X, the size of the overhang area is 1 mm-3 mm, and optionally, the size of the overhang area is 1 mm, 2 mm, 3 mm, etc., without limitation. The overhang area can prevent lithium deposition on the negative electrode sheet 10 and improve the safety of the battery cell.

[0081] For reference Figure 1 and Figure 2 In one embodiment, the negative electrode active material layer 12 further includes a third region 123 , which is disposed at one end of the second region 122 away from the first region 121 , and a negative electrode capacity per unit volume of the third region 123 is N3 , satisfying: N2<N3.

[0082] Optionally, the overhang area also includes at least part of the third area 123. The size of the third area 123 that exceeds the positive electrode active material layer 22 of the positive electrode sheet 20 in the first direction X is 1 mm-3 mm. The overhang area can also exceed the overlap area in the second direction, that is, the overhang area can be arranged around the overlap area.

[0083] The overhang area of ​​the third area 123 corresponding to the overhang area of ​​the first area 121 can also prevent lithium deposition on the negative electrode sheet 10, thereby improving the safety of the battery cell.

[0084] Optionally, a first pole ear and a second pole ear are provided on the negative electrode sheet 10, and the first region 121 is closer to the edge of the negative electrode current collector 11 connected to the first pole ear than at least a portion of the second region 122, and the third region 123 is closer to the edge of the negative electrode current collector 11 connected to the second pole ear than at least a portion of the second region 122. For example, the third region 123 and the second region 122 are both rectangular, and the length of the third region 123 in the perpendicular first direction X is the same as the length of the second region 122 in the perpendicular first direction X, then the third region 123 is closer to the edge of the negative electrode current collector 11 connected to the second pole ear than the second region 122 as a whole; or, when the minimum distance from a portion of the edge of the second region 122 to the edge of the negative electrode current collector 11 connected to the second pole ear is the same as the minimum distance from the third region 123 to the edge of the negative electrode current collector 11 connected to the second pole ear, the third region 123 is arranged opposite to the second pole ear in the first direction X, the second region 122 is in a "concave" shape, and the second region 122 surrounds the outer periphery of the third region 123.

[0085] The negative electrode current collector 11 further includes a fourth edge 112 opposite to the first edge 111. Optionally, the negative electrode current collector 11 further includes a sixth edge 114, which is arranged opposite to the first edge 111. The third region 123 includes a seventh edge 1231 and an eighth edge 1232 opposite to each other, the sixth edge 114 is located on the side of the seventh edge 1231 opposite to the eighth edge 1232, and the eighth edge 1232 is connected to the second region 122.

[0086] Optionally, the sixth edge 114 , the seventh edge 1231 , and the eighth edge 1232 are parallel.

[0087] With reference to d1, in the first direction X, the distance from any position of the seventh edge 1231 to the corresponding position of the eighth edge 1232 is d3, which satisfies: 1mm≤d3≤5mm. Optionally, d3 can be 1mm, 2mm, 3mm, 4mm, or 5mm, without limitation.

[0088] With reference to d2, in the first direction X, the distance from any position of the sixth edge 114 to the corresponding position of the seventh edge 1231 is d4, which satisfies: 0mm≤d4≤5mm. Optionally, d4 can be 0mm, 1mm, 2mm, 3mm, 4mm, or 5mm, without limitation.

[0089] Due to the existence of process errors, the angle between any two sides of the sixth edge 114, the seventh edge 1231 and the eighth edge 1232 may be 1°-3° without limitation.

[0090] The third region 123 is provided, and at the same time, the negative electrode capacity N3 per unit volume of the third region 123 is greater than the negative electrode capacity N2 per unit volume of the second region 122, so that N1 / P of the first region 121 and N3 / P of the third region 123 on both sides of the second region 122 are greater than N2 / P of the second region 122, so that the lithium ion capacity of the corresponding region is increased, and the accumulation and precipitation of lithium ions at the edge of the negative electrode during high-rate charge and discharge is avoided. Compared with only providing the first region 121 on one side of the second region 122, the improvement of the charge and discharge capacity of the edge of the negative electrode sheet 10 is more obvious, and the battery capacity diving and safety problems caused by edge lithium precipitation are effectively solved.

[0091] For reference Figure 3 The utility model provides a battery cell, comprising a positive electrode sheet 20, a separator 30 and a negative electrode sheet 10 as described in any of the aforementioned embodiments, wherein the positive electrode sheet 20, the separator 30 and the negative electrode sheet 10 are stacked, and in the orthographic projection of the positive electrode sheet 20 on the negative electrode sheet 10, the edge of the positive electrode active material layer 22 of the positive electrode sheet 20 close to the negative electrode ear falls in the first area 121.

[0092] Optionally, the edge of the positive electrode active material layer 22 of the positive electrode sheet 20 away from the negative electrode ear falls in the third region 123 .

[0093] The positive electrode sheet 20 includes a positive electrode current collector 21 and a positive electrode active material layer 22, and the positive electrode active material layer 22 is arranged on the positive electrode current collector 21. The positive electrode current collector 21 includes but is not limited to any one of aluminum foil, composite aluminum foil or carbon-coated aluminum foil. The positive electrode active material layer 22 includes components such as positive electrode material, conductive agent, binder, etc. The utility model does not specifically limit these materials, and suitable materials can be selected according to actual application requirements. The positive electrode active material can be a phosphate positive electrode active material and a ternary positive electrode active material. In a specific embodiment, it includes one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium phosphate, fluoro vanadium lithium phosphate, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide. The conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 and carbon nanotubes, and the content of the conductive agent in the positive electrode active layer is 3wt%-5wt%. The types of binders include one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethylcellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan and chitosan derivatives.

[0094] Optionally, the positive electrode current collector 21 may have the same size as the positive electrode active material layer 22 , or may be larger than the positive electrode active material layer 22 , without limitation.

[0095] Optionally, the separator 30 may be any one of a woven membrane, a non-woven membrane (non-woven fabric), a microporous membrane, a composite membrane, a rolled membrane, etc., without limitation.

[0096] In the orthographic projection of the positive electrode sheet 20 on the negative electrode sheet 10, that is, the projection of the positive electrode sheet 20 in the overlapping direction of the positive electrode sheet 20, the diaphragm 30 and the negative electrode sheet 10, the edge of the positive electrode sheet 20 falls on the first area 121, realizing the structure of the negative electrode sheet 10 wrapping the positive electrode sheet 20, and the negative electrode sheet 10 provided by the utility model can alleviate the edge lithium plating effect caused by lithium ion migration and cycle accumulation, effectively solve the battery capacity diving and safety problems caused by edge lithium plating, the battery cell life can be extended, and the safety is good.

[0097] The utility model provides a battery, comprising a shell and a battery core as described in any one of the above embodiments, wherein the battery core is accommodated in the shell.

[0098] The battery may be a square shell battery, a cylindrical battery, or other types such as a prismatic battery, without limitation.

[0099] The shell is a material with high structural strength, specifically metal materials, high-strength plastics, ceramics, etc. Metal materials such as aluminum, aluminum alloys, magnesium alloys, iron and iron alloys, etc. The shell includes a bottom plate and side plates. The shell can be an integrated structure, that is, the bottom plate and the side plates are an integrated structure made by an integrated molding process. The integrated molding process can be specifically stamping, casting, etc., without limitation. The shell can also be a split structure, and the side plate and the bottom plate can be connected and fixed by welding, bonding, clamping, screwing, etc. The wall thickness of the shell can be roughly uniform everywhere, that is, the thickness of the side plate can be roughly uniform, and the thickness of the bottom plate and the side plate can also be roughly the same.

[0100] The battery provided by the utility model uses the negative electrode sheet 10 in the embodiment of the utility model, which can alleviate the edge lithium plating effect caused by lithium ion migration and cycle accumulation, effectively solve the battery capacity diving and safety problems caused by edge lithium plating, and the battery life can be extended with good safety.

[0101] In the description of the embodiments of the present invention, it should be noted that the orientation or positional relationship of terms such as "center", "up", "down", "left", "right", "vertical", "horizontal", "inside" and "outside" are based on the orientation or positional relationship described in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0102] The above disclosure is only a preferred embodiment of the present invention, and certainly cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. A negative electrode sheet for a battery cell, characterized in that: include: A negative electrode current collector, suitable for connecting to the negative electrode ear; A negative electrode active material layer is stacked on the negative electrode current collector, the negative electrode active material layer includes a first region and a second region, the first region is closer to the negative electrode ear than the second region, the unit volume capacity of the first region is N1, the unit volume capacity of the second region is N2, and the following is satisfied: N1>N2.

2. The negative electrode sheet according to claim 1, characterized in that: The portion of the negative electrode current collector corresponding to the first region has a first edge, and the first edge is suitable for arranging the negative electrode tab.

3. The negative electrode sheet according to claim 1, characterized in that: The first area and the second area are arranged along a first direction, wherein the first area includes a second edge and a third edge opposite to each other in the first direction, the third edge is connected to the second area, and in the first direction, a distance between the second edge and the third edge is d1, satisfying: 1mm≤d1≤5mm.

4. The negative electrode sheet according to claim 2, characterized in that: The first area has a second edge, and in a first direction, the first edge and the second edge are arranged opposite to each other, wherein the distance between the first edge and the second edge is d2, satisfying: 0mm≤d2≤5mm, and the first direction is the arrangement direction of the first area and the second area.

5. The negative electrode sheet according to claim 1, characterized in that: The capacity per unit area of ​​the first region is M1, and the capacity per unit area of ​​the second region is M2, satisfying: M1>M2.

6. The negative electrode sheet according to claim 1, characterized in that: The surface density of the material in the first region is a1, and the surface density of the material in the second region is a2, satisfying: a1>a2.

7. The negative electrode sheet according to claim 6, characterized in that: Also meets: a1 / a2≥102%.

8. The negative electrode sheet according to claim 7, characterized in that: Also meets: a1 / a2≤110%.

9. The negative electrode sheet according to claim 1, characterized in that: The compaction density of the material in the first region is b1, and the compaction density of the material in the second region is b2, satisfying: b1>b2.

10. The negative electrode sheet according to claim 9, characterized in that: Also meets: b1 / b2≥102%.

11. The negative electrode sheet according to claim 10, characterized in that: Also meets: b1 / b2≤110%.

12. The negative electrode sheet according to claim 1, characterized in that: The first region includes a first material, and the second region includes a second material, the average particle size of the second material is larger than the average particle size of the first material, and / or the carbon content of the second material is smaller than that of the first material, and / or the conductivity of the first region along a second direction is smaller than the conductivity of the second region along the second direction, and the second direction is the stacking direction of the negative electrode current collector and the negative electrode active material layer, and / or the porosity of the first region is smaller than the porosity of the second region.

13. The negative electrode sheet according to claim 1, characterized in that: The battery cell further includes a positive electrode sheet, the negative electrode sheet includes an overlapping region and an overhang region, the overlapping region overlaps with the positive electrode active material layer of the positive electrode sheet, and the overhang region includes at least a portion of the first region.

14. The negative electrode sheet according to any one of claims 1 to 13, characterized in that: The negative electrode active material layer further includes a third region, which is disposed at one end of the second region away from the first region, and the negative electrode capacity per unit volume of the third region is N3, satisfying: N2<N3.

15. A battery cell, characterized in that: It comprises a positive electrode sheet, a separator and a negative electrode sheet as described in any one of claims 1 to 14, wherein the positive electrode sheet, the separator and the negative electrode sheet are stacked, and in the orthographic projection of the positive electrode sheet on the negative electrode sheet, the edge of the positive electrode active material layer of the positive electrode sheet close to the negative electrode ear falls in the first area.

16. A battery, characterized in that: It comprises a shell and the battery core as claimed in claim 15, wherein the battery core is accommodated in the shell.

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