Negative pole piece and battery

Abstract

The invention relates to the technical field of batteries, in particular to a negative pole piece and a battery. The provided negative pole piece comprises: a current collector, wherein the current collector comprises a plurality of straight parts; the straight part comprises a first area and a plurality of second areas, and the second areas are located at the four corners of the straight part respectively; the first active coating is arranged on the first area and the second area on at least one side of the straight part; the second active coating is arranged on the first active coating in the first area; the third active coating is arranged on the first active coating in the second area; wherein the porosity of the first active coating is A1, the porosity of the second active coating is A2, and the porosity of the third active coating is A3; a1, A2 and A3 satisfy the following formula: A3lt; a1lt; a2. The negative pole piece provided by the invention can enhance the structural stability of the four corners so as to reduce the risk of physical damage; and meanwhile, electrolyte can fully permeate the main body part to improve the battery performance.

Description

Technical Field

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

[0002] The pole piece of lithium battery is designed by coating, and the microscopic design of the pole piece coating can effectively improve the overall performance of the battery. For example, by using a double-layer coating design on the negative electrode, with a high binder content in the lower coating and a low binder content in the upper coating, the fast charging capability and rate performance of the battery can be improved.

[0003] However, during the use of the battery, the upper coating will easily fall off due to its low strength. In addition, as the space utilization of the battery cell increases, the design of the pole piece becomes larger and larger. During the winding process of the pole piece, the stress on the edge of the bending part will also increase, causing wrinkles and deformation of the winding core, which in turn affects the charge and discharge performance and cycle performance of the battery. Summary of the invention

[0004] In view of this, the present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, the present invention provides a negative electrode plate and a battery, which can enhance the mechanical strength of the plate corners and the four corners of the straight part of the plate, prevent wrinkles and deformation, reduce physical damage to the plate, and make the active material on the plate not easy to fall off, thereby improving the cycle performance and charge and discharge performance of the battery.

[0005] In order to solve the above-mentioned technical problems, the present invention is achieved as follows: According to one aspect of the present invention, an embodiment of the present invention provides a negative electrode plate, comprising: A current collector, the current collector comprising a plurality of straight portions; the straight portion comprising a first region and a plurality of second regions, the plurality of second regions being respectively located at four corners of the straight portion; a first active coating, the first active coating being disposed on the first region and the second region on at least one side of the straight portion; a second active coating disposed on the first active coating located in the first region; a third active coating layer, the third active coating layer being disposed on the first active coating layer located in the second region; The porosity of the first active coating is A1, the porosity of the second active coating is A2, the porosity of the third active coating is A3, and A1, A2 and A3 satisfy: A3 <A1<A2。

[0006] In some embodiments, the A1 is 15% to 45%; And / or, A2 is 20% to 50%; And / or, the A3 is 10%~30%.

[0007] In some embodiments, the length of the straight portion in the x-axis direction is L, and the length in the y-axis direction is H; the length of any second region in the x-axis direction is L1, and the length in the y-axis direction is H1, and A1, A2, A3 and L, H, L1, and H1 satisfy: A3*2L1*H1 / (L*H)+ A2*(1-2L1*H1 / (L*H))≥A1.

[0008] In some embodiments, a ratio L1 / L of a length L1 of the second region in the x-axis direction to a length L of the straight portion in the x-axis direction is 0.1 to 0.5; And / or, a ratio H1 / H of a length H1 of the second region in the y-axis direction to a length H of the straight portion in the y-axis direction is 0.1-0.5.

[0009] In some of the embodiments, the current collector further comprises at least one bend; The first active coating is disposed on at least one side of the bent portion and is on the same side as the first active coating on the straight portion; At least the third active coating is disposed on the first active coating located at the bending portion.

[0010] In some of the embodiments, the bending portion includes a third region and a fourth region; The third region is located between the second regions adjacent to the straight portions, and the fourth region is located between the first regions adjacent to the straight portions; the first active coating is disposed on the third region and the fourth region; The third active coating is disposed on the first active coating located in the third region, and the second active coating is disposed on the first active coating located in the fourth region; Alternatively, the third active coating is disposed on both the first active coating located in the third region and the first active coating located in the fourth region.

[0011] In some embodiments, the first active coating, the second active coating and the third active coating all include a negative electrode active material, a conductive agent and a binder; Wherein, the negative electrode active material comprises a carbon-based material and / or a silicon-based material; and / or, The conductive agent includes at least one of conductive carbon black, carbon nanotubes or graphene; and / or, The binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, or polyacrylic acid.

[0012] In some embodiments thereof, the third active coating further includes a thermosetting polymer; the thermosetting polymer includes a resin.

[0013] In some embodiments thereof, the thermosetting polymer includes at least one of phenolic resin, urea-formaldehyde resin, melamine resin, unsaturated polyester resin, epoxy resin, silicone resin, or polyurethane; and / or, the mass content of the thermosetting polymer in the third active coating is 0.5% - 3%.

[0014] According to another aspect of the present invention, an embodiment of the present invention provides a battery, including: a positive electrode sheet, a separator, and the negative electrode sheet in any one of the embodiments of one aspect of the embodiments of the present invention.

[0015] Implementing the technical solution of the present invention has at least the following beneficial effects: 1. In the embodiment of the present invention, the provided negative electrode sheet is provided with a first region on the straight portion of the current collector and a second region at the four corners of the straight portion, a second active coating is provided on the first region, a third active coating is provided on the third region, and the porosity A1 of the first active coating, the porosity A2 of the second active coating, and the porosity A3 of the third active coating satisfy A3 < A1 < A2; the negative electrode sheet provided by the embodiment of the present application enhances the mechanical strength of the corners and the four corners of the straight portion, prevents wrinkles and deformation, reduces the physical damage of the electrode sheet, and thus improves the cycle performance and charge-discharge performance of the battery.

[0016] 2. In the preferred embodiment of the embodiment of the present invention, by using a thermosetting material disposed in the third active coating of the electrode sheet, a hard protective layer is formed outside the battery core, which is more helpful to resist physical stress during the use of the battery, reduce the physical deformation of the battery during long-term cycling, and further slow down the attenuation of the comprehensive performance of the battery.

[0017] The additional aspects and advantages of the present invention will be partially given in the following description, partially become apparent from the following description, or be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present invention, and are used together with the specification to explain the principles of the present invention.

[0019] Figure 1 The following shows a schematic structure of a negative electrode sheet provided by an embodiment of the present invention Figure 1 .

[0020] Figure 2 Shown is a schematic diagram of a cross-sectional structure of a negative electrode sheet provided in an embodiment of the present invention.

[0021] Figure 3 The figure shows a schematic diagram of a negative electrode plate structure provided by an embodiment of the present invention. Figure 2 .

[0022] Figure 4 The figure shows a schematic diagram of a negative electrode plate structure provided by an embodiment of the present invention. Figure 3 .

[0023] Figure 5 The figure shows a schematic diagram of a negative electrode plate structure provided by an embodiment of the present invention. Figure 4 .

[0024] Figure 6 The figure shows a schematic diagram of a negative electrode plate structure provided by an embodiment of the present invention. Figure 5 .

[0025] Figure 7 The figure shows a schematic diagram of a negative electrode plate structure provided by an embodiment of the present invention. Figure 6 .

[0026] Figure 8 Shown is a schematic diagram of a battery cell structure provided by an embodiment of the present invention.

[0027] Figure structure description: 100——current collector; 110——straight part; 120——bend part; 111——first area; 112——second area; 121——third area; 122——fourth area; 200——first active coating; 300——second active coating; 400——third active coating.

[0028] The above drawings have shown clear embodiments of the present invention, which will be described in more detail below. These drawings and text descriptions are not intended to limit the scope of the present invention in any way, but to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0029] The present application is further described below in conjunction with specific embodiments. It should be understood that these embodiments of the present application are only used to illustrate the present application and are not used to limit the scope of the present application.

[0030] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0031] If not otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form a new technical solution.

[0032] Unless otherwise specified, all technical features and optional technical features of the present invention can be combined with each other to form a new technical solution.

[0033] If not otherwise specified, all steps of the present invention may 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.

[0034] If there is no special explanation, the "include" and "comprising" mentioned in the present invention represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent 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.

[0035] refer to Figure 8 The battery cell is usually obtained by winding the pole piece and the diaphragm. During the winding process, the stress on the straight part of the pole piece at the four corners becomes greater and greater, which causes wrinkles and deformation at the four corners of the straight part of the pole piece in the battery cell, which can easily affect the battery capacity, charge and discharge performance, and cycle performance.

[0036] Based on this, an embodiment of the present invention provides a negative electrode plate, which is divided into a first area and multiple second areas on the current collector, and the second area is set at the four corners of the current collector. Different active coatings are then set on the first area and the second area. When the electrode plate is wound, the coating structure at the four corners of the straight part of the electrode plate is stable, thereby reducing physical damage to the electrode plate, so that the obtained battery cell in the battery can be fully penetrated by the electrolyte, thereby improving the cycle performance and charge and discharge performance of the battery.

[0037] like Figure 1As shown, an embodiment of the present invention provides a negative electrode plate, which includes: a current collector 100, the current collector 100 includes a plurality of straight portions 110; the straight portion 110 includes a first region 111 and a plurality of second regions 112, and the plurality of second regions 112 are respectively located at the four corners of the straight portion 110.

[0038] refer to Figure 1 , a plurality of straight portions 110 are arranged on the current collector 100, the straight portions 110 are divided into first regions 111, and a plurality of second regions 112 are divided at the four corners of the straight portions 110. The first region 111 is located between the plurality of second regions 112, wherein the first region 111 is a main region; preferably, the area of ​​the first region 111 may be greater than the area of ​​the plurality of second regions 112. Exemplarily, the shape of the second region 112 may be a right triangle, wherein the two right-angled sides respectively overlap with the long side and the wide side of the straight portion 110, and the hypotenuse corresponding to the right angle of the second region 112 may be a straight line or a curve.

[0039] refer to Figure 2 and Figure 3 The negative electrode sheet further includes a first active coating 200, which is disposed on the first region 111 and the second region 112 on at least one side of the straight portion 110. The first active coating 200 may be disposed on a single side surface of the current collector 100 along the thickness direction, or may be disposed on both side surfaces of the current collector 100 along the thickness direction, that is, the first active coating 200 may be disposed on a single side surface or on both side surfaces of the straight portion 110.

[0040] The first active coating 200 is disposed on both sides of the current collector 100, such as 200 is disposed on both surfaces of the current collector 100 in the thickness direction, that is, the first active coating 200 is disposed on two opposite surfaces of the current collector 100. The first active coating 200 includes a negative electrode active material, such as graphite, silicon-based material or lithium titanate.

[0041] Continue to refer Figure 2 and Figure 3 , the negative electrode sheet further includes a second active coating 300 and a third active coating 400, the second active coating 300 is disposed on the first active coating 200 located in the first region 111, and the third active coating 400 is disposed on the first active coating 200 located in the second region 112. Similarly, if the first active coating 200 is disposed on one side surface of the current collector 100, the second active coating 300 and the third active coating 400 are disposed on the first active coating 200. If the first active coating 200 is disposed oppositely on two surfaces of the current collector 100 along the thickness direction, the second active coating 300 and the third active coating 400 are disposed on two opposite surfaces of the current collector 100 and the first active coating 200.

[0042] The second active coating 300 includes a negative electrode active material, such as graphite, silicon-based materials, etc., and the third active coating 400 includes a negative electrode active material, such as graphite, silicon-based materials, etc. For example, Figure 2 and Figure 3 A first active coating 200 is disposed on a single side surface of the straight portion 110, and a second active coating 300 and a third active coating 400 are disposed on the first active coating 200, wherein the second active coating 300 is located on the first region 111 of the straight portion 110, and the third active coating 400 is located on the second region 112 of the straight portion 110. The difference between the active materials in the first active coating 200, the second active coating 300, and the third active coating 400 may be different in particle size of the active materials; or different in specific components of the active materials, such as component content ratio; or different coating density, porosity, etc. between the coatings. Exemplarily, the particle sizes of active materials in the first active coating 200, the second active coating 300 and the third active coating 400 are different, wherein the particle size of active materials in the third active coating 400 is smaller than those in the first active coating 200 and the second active coating 300, so that during the winding process of the negative electrode plate, the third active coating 400 located at the four corners of the straight portion 110 is less subject to physical damage, such as wrinkles, coating shedding, etc., so that the battery has higher battery capacity, cycle performance, etc.

[0043] Further, in some embodiments, the porosity of the first active coating 200 is A1, the porosity of the second active coating 300 is A2, and the porosity of the third active coating 400 is A3; A1, A2 and A3 satisfy: A3 <A1<A2。

[0044] The differences between the first active coating 200, the second active coating 300, and the third active coating 400 can also lie in the different porosities between the respective coatings. For example, the porosity of the first active coating 200 is A1, the porosity of the second active coating 300 is A2, and the porosity of the third active coating 400 is A3. Among them, A1, A2, and A3 satisfy: A3 < A1 < A2. In this way, it can ensure that the second active coating 300 located on the second region 112 has better structural stability and avoid physical damage to the electrode during the winding process. Based on the above settings, the porosity A2 of the second active coating 300 is greater than the porosity A1 of the first active coating 200, which can ensure that when the electrode contacts the electrolyte, the electrolyte can quickly and fully penetrate into the second active coating 300 and quickly and fully penetrate from the second active coating 300 to the first active coating 200, thereby improving the capacity, charge-discharge performance, and cycle performance of the battery. At the same time, A3 < A1, which gives the four corners of the straight part 110 of the electrode excellent mechanical strength and protects them from physical damage during bending or winding. If A1 is not less than A2, after the electrolyte contacts the second active coating 300, it cannot quickly penetrate to the first active coating 200 close to the current collector 100, thereby affecting the capacity of the battery. If A3 is not less than A2, the mechanical strength of the third active coating 400 at the four corners of the straight part 110 is too low, and it is easily physically damaged during bending or winding, which also affects the comprehensive performance of the battery.

[0045] An embodiment of the present invention provides a negative electrode, which includes a current collector 100. The current collector 100 includes a plurality of straight parts 110. By dividing the straight part 110 into a first region 111 and a plurality of second regions 112, where the plurality of second regions 112 are respectively located at the four corners of the straight part 110. And a first active coating 200 is provided on at least one side of the first region 111 and the second region 112 of the straight part 110, a second active coating 300 is provided on the first active coating 200 located in the first region 111, and a third active coating 400 is provided on the first active coating 200 located in the second region 112. Among them, the porosity of the first active coating 200 is A1, the porosity of the second active coating 300 is A2, and the porosity of the third active coating 400 is A3, and A1, A2, and A3 satisfy: A3 < A1 < A2. The negative electrode provided by the present invention can enhance the structural stability of the four-corner part to reduce the risk of physical damage; at the same time, ensure that the electrolyte can fully penetrate the main part to improve the battery performance.

[0046] In some embodiments, A1 is 15% - 45%.

[0047] Specifically, A1 can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44% or 45%, etc.; A1 within this range can ensure the contact between the electrolyte and the active material, so that the electrolyte is fully diffused and has an excellent ion migration rate. If A1 is greater than this range, it will cause excessive aggregation of the electrolyte and reduce the contact of the active material; if A1 is less than this range, it will limit the diffusion of the electrolyte and reduce the ion migration rate.

[0048] In some embodiments, A2 is 20% to 50%.

[0049] Specifically, A2 can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49% or 50%, etc.; A2 within this range can strengthen the structure of the coating and reduce the risk of active coating material falling off; at the same time, it can also ensure the effective diffusion of the electrolyte and improve the battery charging and discharging performance. If A2 is greater than this range, it may weaken the structure of the active coating and increase the risk of active material falling off; if A2 is less than this range, it may reduce the effective diffusion of the electrolyte and affect the charging and discharging performance.

[0050] In some embodiments, A3 is 10% to 30%.

[0051] Specifically, A3 can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30%, etc.; A3 within this range can make the active coating more solid and not easily damaged under mechanical stress, and provide an effective channel for the electrolyte to penetrate, thereby ensuring the performance of the battery. If A3 is greater than this range, the structure may be too fragile and easily damaged under mechanical stress; if A3 is less than this range, it may not be sufficient to provide the necessary channels for the electrolyte to penetrate effectively, affecting the battery performance.

[0052] In some embodiments, the length of the straight portion 110 in the x-axis direction is L, and the length in the y-axis direction is H; the length of any second region 112 in the x-axis direction is L1, and the length in the y-axis direction is H1, and A1, A2, A3 and L, H, L1, H1 satisfy: A3*2L1*H1 / (L*H)+A2*(1-2L1*H1 / (L*H))≥A1.

[0053] refer to Figure 1 , assuming that the long side of the straight portion 110 on the current collector 100 is the x-axis, and the wide side of the straight portion 110 is the y-axis; then the length of the straight portion 110 in the x-axis direction is L, and the length in the y-axis direction is H; the second region 112 located at any one of the four corners of the straight portion 110 has a length L1 in the x-axis and a length H1 in the y-axis direction, that is, the two right-angled sides of the second region 112 have a length L1 in the x-axis and a length H1 in the y-axis direction. A1, A2, A3 and L, H, L1, H1 satisfy: A3*2L1*H1 / (L*H)+A2*(1-2L1*H1 / (L*H))≥A1, which can make the porosity of the active coating close to the current collector 100 smaller than the porosity of the active coating far from the current collector 100, thereby ensuring the active coating located in the second region 112, i.e., the four corners of the straight portion 110, enhancing the toughness of the active material in the active coating, so that the active coating can provide sufficient support under mechanical stress without affecting the overall porosity, ensuring the effective penetration of the electrolyte, and improving the overall performance of the battery. If A1, A2, A3 and L, H, L1, H1 are not within this range, such as the average porosity of the upper layer is too small, there is not enough space for lithium ions to reach the current collector smoothly, or it is easy to cause powdering and collapse during charge and discharge overcharge, which will affect the overall performance of the battery.

[0054] In some embodiments, a ratio L1 / L of a length L1 of the second region 112 in the x-axis direction to a length L of the straight portion 110 in the x-axis direction is 0.1-0.5.

[0055] The ratio of L1 / L can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5; when the ratio of L1 / L is within this range, the active coating at the four corners of the straight portion 110 can have a certain mechanical strength, and the mechanical strength will not be too strong to affect the flexibility of the pole piece, so that the pole piece can be wound. If the ratio of L1 / L is greater than this range, the mechanical strength of the four corners of the straight portion 110 will be too strong, affecting the overall flexibility of the battery; if the ratio of L1 / L is less than this range, the reinforcement effect of the four corners of the straight portion 110 is insufficient and cannot effectively resist mechanical stress.

[0056] In some embodiments, a ratio H1 / H of a length H1 of the second region 112 in the y-axis direction to a length H of the straight portion 110 in the y-axis direction is 0.1-0.5.

[0057] The ratio of H1 / H can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5, etc. When the ratio of H1 / H is within this range, the four corners of the straight portion 110 have sufficient mechanical strength and flexibility, and will not affect the curling of the pole piece. If the ratio of H1 / H is greater than this range, it will also lead to excessive strengthening of the four corners, which may affect the flexibility of battery curling or shape adjustment; if the ratio of H1 / H is less than this range, it is not enough to protect the structural integrity of the edge when subjected to external forces.

[0058] In some embodiments, the current collector 100 also includes at least one bend 120; a first active coating 200 is disposed on at least one side of the bend 120 and is on the same side as the first active coating 200 on the straight portion 110; and at least a third active coating 400 is also disposed on the first active coating 200 located on the bend 120.

[0059] refer to Figure 1 and Figure 4 The current collector 100 also includes a bending portion 120, which is located between any two straight portions 110. The first active coating 200 is disposed on a single side surface of the bending portion 120 on the same side as the first active coating 200 on the straight portion 110, and a third active coating 400 is disposed on the first active coating 200, or a second active coating 300 and a third active coating 400 are disposed, wherein the third active coating 400 is disposed at the upper and lower edges of the bending portion 120, and the second active coating 300 is disposed between the third active coatings 400; the second active coating 300 in the middle has a porosity of A2, which provides the battery with necessary active materials and electrolyte channels; and the third active coatings 400 at the upper and lower edges have a porosity of A3, which enhances the mechanical strength and structural stability of the bending portion.

[0060] In some embodiments, the bending portion 120 includes a third region 121 and a fourth region 122; the third region 121 is located between the second regions 112 of adjacent straight portions 110, and the fourth region 122 is located between the first regions 111 of adjacent straight portions 110; a first active coating 200 is disposed on the third region 121 and the fourth region 122; a third active coating 400 is disposed on the first active coating 200 located in the third region 121, and a second active coating 300 is disposed on the first active coating 200 located in the fourth region 122. The width and length of the third region 121 along the y-axis may be the same as or different from those of the second region 112, and the corresponding length of the third active coating 400 located on the third region 121 along the y-axis may be the same as or different from the length of the third active coating 400 located on the second region 112. Similarly, the width and length of the fourth region 122 along the y-axis may be the same as or different from the length of the first region 111.

[0061] refer to Figures 4 to 6 , the bending portion 120 is divided into a third region 121 and a fourth region 122; the third region 121 is located between two second regions 112 of adjacent straight portions 110, and the fourth region 122 is located between two first regions 111 of adjacent straight portions 110, wherein the boundary line between the third region 121 and the fourth region 122 can be a straight line or a curve. A first active coating 200 is provided on the single-side surface of the bending portion 120 of the current collector 100 in the third region 121 and the fourth region 122, a third active coating 400 is provided on the first active coating 200 located in the third region 121, and a second active coating 300 is provided on the first active coating 200 located in the fourth region 122. The negative electrode plate in this embodiment can not only make the plate located at the edge of the bending region have a certain mechanical strength, but also have a certain flexibility, so as to ensure that the bending portion 120 of the plate can be bent arbitrarily when being bent and wound, and the material in the active coating will not fall off, thereby improving the comprehensive performance of the battery.

[0062] In some embodiments, the third active coating layer 400 is disposed on both the first active coating layer 200 located in the third region 121 and the first active coating layer 200 located in the fourth region 122 .

[0063] refer to Figure 7 A first active coating 200 is provided on a single side surface of the bending portion 120, and a third active coating 400 is provided on the first active coating 200. The pole piece in this embodiment has good and appropriate strength and flexibility, and can allow the electrolyte to fully penetrate, thereby improving the overall performance of the battery.

[0064] In some embodiments, the first active coating 200 , the second active coating 300 , and the third active coating 400 all include a negative electrode active material, a conductive agent, and a binder; wherein the negative electrode active material includes a carbon-based material and / or a silicon-based material.

[0065] The ratios of the negative electrode active material, the conductive agent and the binder in the first active coating layer 200 , the second active coating layer 300 and the third active coating layer 400 may be ratios known to those skilled in the art, and will not be described in detail herein.

[0066] The negative electrode active materials in the first active coating 200, the second active coating 300 and the third active coating 400 can be the same or different; preferably, the negative electrode active materials, conductive agents and binders of the same category can make the negative electrode sheet preparation process simpler and faster. At the same time, the porosity of each active coating can be better controlled, so that the electrolyte can fully penetrate and improve the performance of the battery.

[0067] The negative electrode active material includes carbon-based materials, such as graphite, amorphous carbon, carbon nanotubes, etc.; or silicon-based materials, such as single crystal silicon, polycrystalline silicon or silicon oxide, etc.; in a preferred embodiment, the carbon-based material includes artificial graphite, natural graphite, soft carbon or hard carbon. Among them, the negative electrode active material can be one or several of the carbon-based materials in any proportion, or one or several of the silicon-based materials in any proportion; it can also be carbon-based materials and silicon-based materials in any proportion.

[0068] Furthermore, the conductive agent includes but is not limited to any one or any ratio of conductive carbon black, carbon nanotubes or graphene.

[0069] Furthermore, the binder includes but is not limited to any one or any ratio of polyvinylidene fluoride, styrene butadiene rubber or polyacrylic acid.

[0070] In one embodiment of the present invention, the third active coating 400 further includes a thermosetting polymer; the thermosetting polymer includes a resin.

[0071] Furthermore, the thermosetting polymer includes but is not limited to at least one of phenolic resin, urea-formaldehyde resin, melamine resin, unsaturated polyester resin, epoxy resin, silicone resin or polyurethane.

[0072] A thermosetting polymer is added to the third active coating 400. When heated, the thermosetting polymer undergoes a cross-linking reaction to solidify. For example, in the battery manufacturing process, after the pole pieces are coated and rolled and the anode and cathode separators are paired, there is a step of hot pressing, that is, through pressure and high temperature, the positive and negative pole pieces are more closely combined together, which is helpful for the shaping of the battery cell and improving the uniformity. After the hot pressing process is combined, the bonding force between the pole pieces of the battery cell is enhanced, which plays a role in curing the battery cell, further enhancing the mechanical strength of the negative pole piece, and thus improving the overall performance of the battery.

[0073] In another embodiment of the present invention, the mass content of the thermosetting polymer in the third active coating 400 is 0.5% to 3%.

[0074] Specifically, the mass content of the thermosetting polymer in the third active coating 400 is 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.7%, 2.8%, 2.9% or 3%; within this range, the thermosetting polymer can enhance the mechanical strength of the negative electrode sheet to a certain extent, so that the positive and negative electrode sheets are better bonded together. If it is less than this range, it will not meet the requirements for enhancing the mechanical strength of the electrode sheet; if it is greater than this range, it will cause the mechanical strength to be too high, which is not conducive to the curling and bending of the electrode sheet.

[0075] An embodiment of the present invention further provides a battery, which includes: a positive electrode sheet, a separator, and a negative electrode sheet in any of the above embodiments.

[0076] The positive electrode sheet in the embodiment of the present invention comprises a current collector and a positive electrode active material, wherein the positive electrode active material includes but is not limited to LiCoO 2 (lithium cobalt oxide), LiNiO 2 (Lithium Nickel Oxide), LiMnO 2 (Lithium manganate), LiFePO 4 (lithium iron phosphate), NMC (lithium nickel cobalt manganese oxide), NCA (lithium nickel cobalt aluminum oxide), LiMn 2 O 4 (Lithium manganate), LiNi 0 . 5 Mn 1 . 5 O 4 (lithium nickel manganese oxide), LiFePO 4 (lithium iron phosphate), LiMnPO 4 (Lithium manganese phosphate), Li 3 V 2 (PO 4 ) 3 (lithium trivanadium phosphate) or LiTi 2 (PO 4 ) 3 (lithium titanate phosphate) one or more of them in any proportion.

[0077] The diaphragm in this embodiment is a diaphragm used in the art and is not particularly limited herein. All solvents and substances in the present invention can be purchased from the market.

[0078] Since the battery provided in the embodiment of the present invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

[0079] The present application is described in detail below with reference to the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. The following embodiments are only partial embodiments of the present application and are not limitations of the present application.

[0080] Example 1 1. Preparation of raw materials: (1) Negative electrode slurry A1: 400 g of artificial graphite, 8 g of styrene-butadiene rubber, 4 g of sodium carboxymethyl cellulose, and 4 g of carbon black were mixed in 60 g of deionized water.

[0081] (2) Negative electrode slurry A2: 400 g of artificial graphite (more small particles), 8 g of styrene-butadiene rubber, 4 g of sodium carboxymethyl cellulose, and 4 g of carbon black are mixed in 60 g of deionized water. Note: Increasing the processing time of graphite can make the graphite particles smaller, so that the porosity of the graphite is smaller, and vice versa.

[0082] (3) Negative electrode slurry A3: 400 g of artificial graphite (more large particles), 8 g of styrene-butadiene rubber, 4 g of sodium carboxymethyl cellulose, and 4 g of carbon black, mixed in 60 g of deionized water.

[0083] (4) Positive electrode slurry: 950 g of lithium iron phosphate, 20 g of conductive agent, and 30 g of binder are mixed in 600 g of NMP solution and stirred to form a positive electrode slurry.

[0084] (5) 250 g electrolyte: lithium hexafluorophosphate (LiPF 6 ) was dissolved in a mixed solvent consisting of ethylene carbonate (EC), dimethyl carbonate (DEC) and ethyl methyl carbonate (EMC) (the mass ratio of the three was 1:1:1) to obtain an electrolyte.

[0085] (6) Diaphragm: A 7 μm thick PE diaphragm (polyethylene) was coated on both sides with a 3 μm ceramic layer and a 3 μm polyvinylidene fluoride (PVDF) layer.

[0086] 2. Battery assembly: (1) Preparation of positive electrode: The positive electrode slurry obtained above is coated on the current collector to prepare a positive electrode sheet.

[0087] (2) Preparation of negative electrode sheet: The negative electrode slurry A1 is coated on the current collector to obtain a first active coating, and the porosity A1 of the first active coating is 20%; the second active coating and the third active coating are respectively coated on the first active coating corresponding to the first region and the second region, and A2 is 30% and A3 is 15%, to prepare a negative electrode sheet.

[0088] In this embodiment 1, the length L of the straight portion of the current collector along the x-axis is 100 mm, and the length H along the y-axis is 50 mm; wherein the length L1 of the second region along the x-axis is 20 mm, and the length H1 along the y-axis is 10 mm.

[0089] The positive electrode sheet, negative electrode sheet and separator are assembled, and the electrolyte is injected to make a battery.

[0090] Example 2 The battery of Example 2 was prepared according to the above Example 1, except that: In the preparation of the negative electrode sheet, 4 g of urea-formaldehyde resin was also added to the negative electrode slurry A3.

[0091] Example 3 The battery of Example 3 was prepared according to the above Example 1, except that: In the preparation of the negative electrode sheet, the porosity A1 of the first active coating layer is adjusted to 35%.

[0092] Example 4 The battery of Example 4 was prepared according to the above Example 1, except that: In the preparation of the negative electrode sheet, the porosity A1 of the first active coating layer is adjusted to 15%.

[0093] Example 5 The battery of Example 5 was prepared according to the above Example 1, except that: In the preparation of the negative electrode sheet, the porosity A3 of the third active coating layer is adjusted to 30%.

[0094] Example 6 The battery of Example 6 was prepared according to the above Example 1, except that: In the preparation of the negative electrode sheet, the porosity A3 of the third active coating layer is adjusted to 10%.

[0095] Example 7 The battery of Example 7 was prepared according to the above Example 1, except that: In the preparation of the negative electrode sheet, the porosity A2 of the second active coating is adjusted to 50%.

[0096] Example 8 The battery of Example 8 was prepared according to the above Example 1, except that: In the preparation of the negative electrode sheet, the porosity A2 of the second active coating is adjusted to 20%.

[0097] Example 9 The battery of Example 9 was prepared according to the above Example 1, except that: During the preparation of the negative electrode sheet, the length L1 of the second region along the x-axis direction is adjusted to 40 mm.

[0098] Example 10 The battery of Example 10 was prepared according to the above Example 1, except that: During the preparation of the negative electrode sheet, the length L1 of the second region along the x-axis direction is adjusted to 10 mm.

[0099] Embodiment 11 The battery of Example 11 was prepared according to the above Example 1, except that: During the preparation of the negative electrode sheet, the length H1 of the second region along the y-axis direction is adjusted to 20 mm.

[0100] Example 12 The battery of Example 12 was prepared according to the above Example 1, except that: During the preparation of the negative electrode sheet, the length H1 of the second region along the y-axis direction is adjusted to 5 mm.

[0101] Comparative Example 1 The battery of Comparative Example 1 was prepared according to the above Example 1, except that: In the preparation of the negative electrode sheet, the porosity A1 of the first active coating layer is adjusted to 50%.

[0102] Comparative Example 2 The battery of Comparative Example 2 was prepared according to the above Example 1, except that: In the preparation of the negative electrode sheet, the porosity A1 of the first active coating layer was adjusted to 10%, and the length H1 of the second region along the y-axis direction was adjusted to 11 mm.

[0103] Comparative Example 3 The battery of Comparative Example 3 was prepared according to the above Example 1, except that: In the preparation of the negative electrode sheet, the porosity A2 of the second active coating layer was adjusted to 55%, and the length H1 of the second region along the y-axis direction was adjusted to 11 mm.

[0104] Comparative Example 4 The battery of Comparative Example 4 was prepared according to the above Example 1, except that: In the preparation of the negative electrode sheet, the porosity A2 of the second active coating layer was adjusted to 10%, and the length H1 of the second region along the y-axis direction was adjusted to 11 mm.

[0105] Comparative Example 5 The battery of Comparative Example 5 was prepared according to the above Example 1, except that: In the preparation of the negative electrode sheet, the porosity A3 of the third active coating layer was adjusted to 40%, and the length H1 of the second region along the y-axis direction was adjusted to 11 mm.

[0106] Comparative Example 6 The battery of Comparative Example 6 was prepared according to the above Example 1, except that: In the preparation of the negative electrode sheet, the porosity A3 of the third active coating layer was adjusted to 5%, and the length H1 of the second region along the y-axis direction was adjusted to 11 mm.

[0107] Performance Testing Test 1: 25℃ cycle test Place the battery in a 25°C environment, charge it at a current rate of 1C to the charge cut-off voltage, then let it stand for 30 minutes. Discharge it at a current rate of 1C to the discharge cut-off voltage, and let it stand for 30 minutes. This process is one cycle. Repeat this process, record the discharge capacity Cn of each cycle, the first discharge capacity C0, the capacity retention rate of the nth cycle Cn / C0, and record the number of cycles to achieve 80% capacity retention rate.

[0108] Test 2: The test method for porosity is gas adsorption method: place the sample in a vacuum environment and gradually introduce an inert gas (such as nitrogen) with a known volume and pressure. The gas molecules will gradually fill the pores of the material. By monitoring the amount of gas adsorption at different pressures, the pore volume can be calculated. The porosity is calculated by combining the total mass and volume information of the sample. This method usually requires specialized instruments such as BET analyzers to complete.

[0109] Test 3: Extreme extrusion safety test: 1) Extrusion of the large surface: Fully charge the finished battery at 25°C, use a cylinder with a radius of 75mm, and extrude it toward the large surface at a speed of 5mm / s. Maintain the deformation for 1min for every 1% deformation, and stop extrusion when the voltage reaches 0V. Record the deformation at the final failure of the battery cell.

[0110] 2) Extrusion of the top: Fully charge the finished battery at 25°C, use a cylinder with a radius of 75mm, and extrude it toward the top at a speed of 5mm / s. Maintain the deformation for 1min for every 1% deformation until the voltage reaches 0V and stop extrusion. Record the deformation at the final failure of the battery cell.

[0111] The test results are shown in Table 1.

[0112] Table 1. Test results Table 1 continued. Note: The “large surface” in Table 1 means Figure 8The middle cell is located in the xy-axis plane. The maximum extrusion deformation represents the deformation amount of the plane located in the xy-axis and extruded along the z-axis direction. The "top" represents the deformation amount of the plane located in the xy-axis and extruded along the z-axis direction. Figure 8 The battery cell is located in the plane of the xz axis, and the "limited extrusion large surface deformation" refers to the deformation amount extruded along the y-axis direction in the plane located on the xz axis.

[0113] It can be seen from Table 1 that if a thermosetting polymer is added, the maximum deformation of the large surface and the top will be greater, and the compressive resistance will be stronger; if the porosity formula is not satisfied, the number of cycles of the battery cell will be affected, and the compressive resistance of the large surface and the top will be weaker; the porosity of A1 is larger, the maximum deformation of the large surface is smaller, the large surface pressure resistance is weaker, the porosity of A1 is smaller, and the number of cycles of the battery cell affected is smaller; the porosity of A2 is larger, the maximum deformation of the large surface is smaller, the large surface pressure resistance is weaker, the porosity of A2 is smaller, and the number of cycles of the battery cell affected is smaller; the porosity of A3 is larger, the maximum deformation of the top is smaller, and the pressure resistance of the top is weaker, the porosity of A3 is smaller, the maximum deformation of the top is larger, the pressure resistance of the top is stronger, but the number of cycles of the battery cell is smaller; when the area of ​​the four corners is larger, the compressive resistance of the large surface and the top is stronger, and when the area of ​​the four corners is smaller, the compressive resistance of the large surface and the top is weaker.

[0114] Parts of the present invention that are not described in detail are well known to those skilled in the art.

[0115] The basic principle of the present invention is described above in conjunction with specific embodiments. However, it should be pointed out that the advantages, strengths, effects, etc. mentioned in the present invention are only examples and not limitations, and it cannot be considered that these advantages, strengths, effects, etc. must be possessed by each embodiment of the present invention. In addition, the specific details disclosed above are only for the purpose of illustration and facilitation of understanding, rather than limitation, and the above details do not limit the present invention to being implemented by adopting the above specific details.

[0116] It should be noted that the term "and / or" or " / " used in this document is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The singular forms of "a", "the" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0117] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A, B are listed, the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, C are listed, the phrase "at least one of A, B, C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode plate, characterized in that: include: A current collector (100), the current collector (100) comprising a plurality of straight portions (110); the straight portion (110) comprising a first region (111) and a plurality of second regions (112), the plurality of second regions (112) being respectively located at four corners of the straight portion (110); A first active coating (200), the first active coating (200) being disposed on the first region (111) and the second region (112) on at least one side of the straight portion (110); a second active coating (300), the second active coating (300) being disposed on the first active coating (200) located in the first region (111); a third active coating (400), the third active coating (400) being disposed on the first active coating (200) located in the second region (112); The porosity of the first active coating (200) is A1, the porosity of the second active coating (300) is A2, the porosity of the third active coating (400) is A3, and A1, A2 and A3 satisfy: A3 <A1<A2。 2. The negative electrode sheet according to claim 1, characterized in that: The A1 is 15% to 45%; And / or, A2 is 20% to 50%; And / or, the A3 is 10%~30%.

3. The negative electrode sheet according to claim 1, characterized in that: The length of the straight portion (110) in the x-axis direction is L, and the length in the y-axis direction is H; the length of any one of the second regions (112) in the x-axis direction is L1, and the length in the y-axis direction is H1, and A1, A2, A3, L, H, L1, and H1 satisfy: A3*2L1*H1 / (L*H)+ A2*(1-2L1*H1 / (L*H))≥A1.

4. The negative electrode sheet according to claim 3, characterized in that: A ratio L1 / L of a length L1 of the second region (112) in the x-axis direction to a length L of the straight portion (110) in the x-axis direction is 0.1 to 0.5; And / or, a ratio H1 / H of a length H1 of the second region (112) in the y-axis direction to a length H of the straight portion (110) in the y-axis direction is 0.1-0.

5.

5. The negative electrode sheet according to claim 1, characterized in that: The current collector (100) further comprises at least one bent portion (120); The first active coating (200) is provided on at least one side of the bent portion (120), and is on the same side as the first active coating (200) on the straight portion (110); At least the third active coating (400) is also provided on the first active coating (200) located at the bending portion (120).

6. The negative electrode sheet according to claim 5, characterized in that: The bent portion (120) comprises a third region (121) and a fourth region (122); The third region (121) is located between the second regions (112) adjacent to the straight portions (110), and the fourth region (122) is located between the first regions (111) adjacent to the straight portions (110); the first active coating (200) is provided on the third region (121) and the fourth region (122); The third active coating (400) is arranged on the first active coating (200) located in the third region (121), and the second active coating (300) is arranged on the first active coating (200) located in the fourth region (122); Alternatively, the third active coating (400) is disposed on both the first active coating (200) located in the third region (121) and the first active coating (200) located in the fourth region (122).

7. The negative electrode sheet according to any one of claims 1 to 6, characterized in that: The first active coating (200), the second active coating (300) and the third active coating (400) all include a negative electrode active material, a conductive agent and a binder; Wherein, the negative electrode active material comprises a carbon-based material and / or a silicon-based material; and / or, The conductive agent includes at least one of conductive carbon black, carbon nanotubes or graphene; and / or, The binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber or polyacrylic acid.

8. The negative electrode sheet according to claim 7, characterized in that: The third active coating (400) further comprises a thermosetting polymer; the thermosetting polymer comprises a resin.

9. The negative electrode sheet according to claim 8, characterized in that: The thermosetting polymer includes at least one of phenolic resin, urea-formaldehyde resin, melamine resin, unsaturated polyester resin, epoxy resin, silicone resin or polyurethane; And / or, the mass content of the thermosetting polymer in the third active coating (400) is 0.5% to 3%.

10. A battery, characterized in that: include: A positive electrode sheet, a separator, and a negative electrode sheet as claimed in any one of claims 1 to 9.

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