Negative pole piece, winding battery cell and lithium ion battery

Abstract

The invention relates to a negative pole piece, a winding battery cell and a lithium ion battery. The negative pole piece comprises a first active coating coated on one side of a negative current collector and a second active coating coated on the other side of the negative current collector, the first active coating is an active coating coated by the positive pole piece when the negative pole piece is wound, and the surface density of the first active coating is greater than that of the second active coating; the first active coating and the second active coating comprise an inner side active coating close to the negative electrode current collector and an outer side active coating coated on the surface of the inner side active coating; the outer active coating comprises a first negative electrode active material, the inner active coating comprises a second negative electrode active material, and the second negative electrode active material comprises a silicon-carbon negative electrode material and the first negative electrode active material; and the surface density of the outer active coating is smaller than that of the inner active coating. According to the scheme provided by the invention, the lithium precipitation phenomenon in the arc region of the negative electrode plate of the lithium ion battery can be effectively prevented, and the cycle performance of the lithium ion battery is improved.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a negative electrode sheet, a wound battery cell and a lithium-ion battery. Background Art

[0002] With the continuous development of lithium-ion battery technology, the usage rate of lithium-ion batteries in daily life is getting higher and higher, and the consumer market has higher and higher requirements for high-energy-density lithium-ion batteries.

[0003] Silicon-carbon negative electrode materials have attracted much attention as the mainstream development materials for improving the energy density of lithium-ion batteries. In the 3C consumer high-energy density market, the cells of related lithium-ion batteries mostly use a winding structure. However, due to the inconsistent tension between the straight area and the arc area, the stress concentration in the arc area can easily cause lithium precipitation in the core crease, greatly affecting the service life of the product. This phenomenon is more obvious in silicon-doped lithium-ion batteries. After the negative electrode sheet in the arc area of ​​the winding structure is bent, the contact area with the corresponding positive electrode sheet is reduced. The reduction in contact area will significantly reduce the N / P value (the ratio of the battery negative electrode capacity to the positive electrode capacity) in the arc area, resulting in the N / P value in the arc area being lower than the N / P value in the straight area. When the silicon doping content of the negative electrode plate increases, the slight change in the surface density of the negative electrode plate has a more obvious effect on the N / P value, and the N / P value of the arc zone decreases sharply, which is more likely to cause lithium precipitation in the arc zone, reducing the cycle performance of the lithium-ion battery; the stress in the arc zone is high, which can easily reduce the contact between the positive and negative electrode plates and the diaphragm, increase the lithium ion transmission path, and increase polarization. At the same time, the high stress in the arc zone will also cause insufficient electrolyte infiltration of the positive and negative electrode plates, making it easier to precipitate lithium metal, and also reduce the cycle performance of the lithium-ion battery.

[0004] Therefore, in the development of high-silicon lithium-ion batteries with related technology, how to solve the problem of lithium deposition in the arc area of ​​wound-structure lithium-ion batteries and reduced cycle performance has become a major difficulty. Summary of the invention

[0005] In order to solve or partially solve the problems existing in the related art, the present application provides a negative electrode plate, a wound battery cell and a lithium-ion battery, which can effectively prevent lithium deposition in the arc area of ​​the negative electrode plate of the lithium-ion battery and improve the cycle performance of the lithium-ion battery.

[0006] In a first aspect, the present application provides a negative electrode plate, the negative electrode plate comprising a negative electrode current collector, a first active coating coated on one side of the negative electrode current collector, and a second active coating coated on the other side of the negative electrode current collector; wherein, The first active coating is an active coating that is coated by the positive electrode sheet when the negative electrode sheet is wound, and the surface density of the first active coating is greater than the surface density of the second active coating; The first active coating layer and the second active coating layer include an inner active coating layer close to the negative electrode current collector and an outer active coating layer coated on the surface of the inner active coating layer; The outer active coating layer includes a first negative electrode active material, the inner active coating layer includes a second negative electrode active material, and the second negative electrode active material includes a silicon-carbon negative electrode material and the first negative electrode active material; The surface density of the outer active coating layer is smaller than the surface density of the inner active coating layer.

[0007] Preferably, the mass percentage of silicon in the silicon-carbon negative electrode material in the negative electrode plate is M Si , where 3%≤M Si ≤20%.

[0008] Preferably, the silicon-carbon negative electrode material includes one or more of a coated silicon-carbon negative electrode material, a supported silicon-carbon negative electrode material, and a dispersed silicon-carbon negative electrode material.

[0009] Preferably, the first negative electrode active material includes one or more of graphite, hard carbon and soft carbon.

[0010] Preferably, the surface density ratio of the surface density of the outer active coating to the surface density of the inner active coating is R σ , where (1 / 4) ≤ R σ ≤(2 / 3).

[0011] Preferably, the surface density difference between the surface density of the first active coating and the surface density of the second active coating is ,in, .

[0012] Preferably, the first active coating includes at least one first type wire groove, and the second active coating includes at least one second type wire groove.

[0013] Preferably, the groove depth of the first type of wire trough is greater than the groove depth of the second type of wire trough; and / or, The wire slot spacing of the first type of wire slots is smaller than the wire slot spacing of the second type of wire slots.

[0014] Preferably, the depth of the first type of wire trough is D A , of which 20%*H 负 ≤D A ≤40%*H 负 , H 负 is the total thickness of the negative electrode sheet after rolling; The depth of the second type of wire trough is D B , of which 20%*H 负 ≤D B≤30%*H 负 .

[0015] Preferably, the depth of the first type of wire trough is D A , where D A <(6 / 7)*H 负-A , H 负-A is the total thickness of the first active coating after rolling; The depth of the second type of wire trough is D B , where D B <(6 / 7)*H 负-B , H 负-B It is the total thickness of the second active coating after rolling.

[0016] Preferably, the spacing between the first type of wire troughs is I A , where 0.5mm≤I A ≤2mm; The spacing between the second type of wire troughs is I B , where 1.5mm≤I B ≤3mm.

[0017] A second aspect of the present application provides a wound battery cell, which includes a positive electrode sheet, a separator and the negative electrode sheet as described above, and the positive electrode sheet, the separator and the negative electrode sheet are stacked and wound to form the wound battery cell.

[0018] Preferably, the diaphragm comprises a porous ceramic layer.

[0019] A third aspect of the present application provides a lithium-ion battery, wherein the lithium-ion battery comprises the wound battery cell as described above, or comprises the negative electrode plate as described above.

[0020] The technical solution provided by this application may have the following beneficial effects: The technical solution of the present application comprises a first active coating coated on one side of the negative electrode current collector of the negative electrode plate and a second active coating coated on the other side; the first active coating is an active coating coated by the positive electrode plate when the negative electrode plate is wound, and the surface density of the first active coating is greater than the surface density of the second active coating; the first active coating and the second active coating comprise an inner active coating close to the negative electrode current collector, and an outer active coating coated on the surface of the inner active coating; the outer active coating comprises a first negative electrode active material, the inner active coating comprises a second negative electrode active material, and the second negative electrode active material comprises a silicon-carbon negative electrode The invention discloses a first negative electrode material, a first negative electrode active material; the surface density of the outer active coating is less than the surface density of the inner active coating; the dynamics of the lithium-ion battery can be improved, the energy density of the lithium-ion battery can be increased, and the capacity of the lithium-ion battery can be fully utilized; the N / P value reduction caused by the reduction in contact area due to the bending of the negative electrode sheet in the arc area after winding can be effectively alleviated, and the difference between the N / P value of the arc area of ​​the negative electrode sheet and the N / P value of the straight area after winding can be reduced, and the lithium precipitation phenomenon in the arc area of ​​the negative electrode sheet of the lithium-ion battery can be effectively prevented, which greatly improves the high temperature performance of the lithium-ion battery and improves the cycle performance of the lithium-ion battery.

[0021] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other objects, features and advantages of the present application will become more apparent by describing in more detail exemplary embodiments of the present application in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the present application.

[0023] Figure 1 is a partial schematic diagram of a cross section of a negative electrode sheet shown in an embodiment of the present application; Figure 2 It is a partial schematic diagram of the winding of the negative electrode sheet, the separator and the positive electrode sheet shown in the embodiment of the present application; Figure 3 It is a schematic structural diagram of a cross section in the height direction of a wound battery cell after a negative electrode sheet and a separator and a positive electrode sheet are wound, as shown in an embodiment of the present application; Figure 4 It is a partial schematic diagram of a width-direction cross section of the diaphragm shown in an embodiment of the present application. DETAILED DESCRIPTION

[0024] The embodiments of the present application will be described in more detail below with reference to the accompanying drawings. Although the embodiments of the present application are shown in the accompanying drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to make the present application more thorough and complete, and to fully convey the scope of the present application to those skilled in the art.

[0025] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The singular forms of "a", "said" and "the" used in this application and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0026] It should be understood that although the terms "first", "second", "third", etc. may be used in this application to describe various information, this information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of this application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0027] The embodiment of the present application provides a negative electrode plate, which can effectively prevent lithium deposition in the arc region of the negative electrode plate of a lithium-ion battery and improve the cycle performance of the lithium-ion battery.

[0028] The technical solution of the embodiments of the present application is described in detail below with reference to the accompanying drawings.

[0029] Figure 1 is a partial schematic diagram of a cross section of a negative electrode sheet shown in an embodiment of the present application; Figure 2 It is a partial schematic diagram of the negative electrode sheet, the separator and the positive electrode sheet after winding according to the embodiment of the present application.

[0030] See also Figure 1 A negative electrode sheet 1 includes a negative electrode current collector 13, a first active coating 11 coated on one side of the negative electrode current collector 13, and a second active coating 12 coated on the other side of the negative electrode current collector 13.

[0031] In one embodiment, the first active coating layer 11 and the second active coating layer 12 include an inner active coating layer 111 close to the negative electrode current collector 13 , and an outer active coating layer 112 coated on the surface of the inner active coating layer 111 .

[0032] In one embodiment, the first active coating 11 includes an inner active coating 111 close to the negative electrode current collector 13, and an outer active coating 112 coated on the surface of the inner active coating 111 and away from the negative electrode current collector 13. The second active coating 12 includes an inner active coating 111 close to the negative electrode current collector 13, and an outer active coating 112 coated on the surface of the inner active coating 111 and away from the negative electrode current collector 13.

[0033] In one embodiment, the outer active coating 112 includes a first negative electrode active material, and the inner active coating 111 includes a second negative electrode active material, and the second negative electrode active material includes a silicon-carbon negative electrode material and the first negative electrode active material.

[0034] In one embodiment, the second negative electrode active material of the inner active coating 111 may be a first negative electrode active material doped with silicon, and the silicon-carbon negative electrode material and the first negative electrode active material may be uniformly mixed to form the second negative electrode active material.

[0035] See also Figure 2 The first active coating 11 is an active coating that is covered by the positive electrode sheet 2 when the negative electrode sheet 1 is wound. The surface density of the first active coating 11 is greater than the surface density of the second active coating 12 .

[0036] In one embodiment, after the negative electrode sheet 1, the positive electrode sheet 2 and the separator 3 are wound, the first active coating 11 of the negative electrode sheet 1 is sequentially covered by the separator 3 and the positive electrode sheet 2 from the center of the wound battery cell to the edge of the wound battery cell.

[0037] In one embodiment, the area density of the outer active coating layer 112 is smaller than the area density of the inner active coating layer 111 .

[0038] The negative electrode sheet of the embodiment of the present application comprises a first active coating coated on one side of the negative electrode current collector of the negative electrode sheet and a second active coating coated on the other side; the first active coating is an active coating coated by the positive electrode sheet when the negative electrode sheet is wound, and the surface density of the first active coating is greater than the surface density of the second active coating; the first active coating and the second active coating comprise an inner active coating close to the negative electrode current collector, and an outer active coating coated on the surface of the inner active coating; the outer active coating comprises a first negative electrode active material, the inner active coating comprises a second negative electrode active material, and the second negative electrode active material comprises silicon carbon Negative electrode material, first negative electrode active material; the surface density of the outer active coating is less than the surface density of the inner active coating; it can improve the dynamics of lithium-ion batteries, increase the energy density of lithium-ion batteries, and meet the capacity of lithium-ion batteries; it can effectively alleviate the reduction in N / P value caused by the reduction in contact area caused by the bending of the negative electrode pole piece in the arc area after winding, and reduce the difference between the N / P value of the arc area of ​​the negative electrode pole piece and the N / P value of the straight area after winding, and can effectively prevent lithium precipitation in the arc area of ​​the negative electrode pole piece of the lithium-ion battery, greatly improve the high temperature performance of the lithium-ion battery, and improve the cycle performance of the lithium-ion battery.

[0039] See also Figure 2 A negative electrode sheet 1 includes a negative electrode current collector 13, a first active coating 11 coated on one side of the negative electrode current collector 13, and a second active coating 12 coated on the other side of the negative electrode current collector 13; wherein the first active coating 11 is an active coating coated by the positive electrode sheet 2 when the negative electrode sheet 1 is wound, and the surface density of the first active coating 11 is greater than the surface density of the second active coating 12.

[0040] See also Figure 1 and Figure 2 The first active coating 11 and the second active coating 12 include an inner active coating 111 close to the negative electrode current collector 13 and an outer active coating 112 coated on the surface of the inner active coating 111. The surface density of the outer active coating 112 is less than that of the inner active coating 111.

[0041] In one embodiment, the outer active coating 112 includes a first negative electrode active material, and the inner active coating 111 includes a second negative electrode active material, and the second negative electrode active material includes a silicon-carbon negative electrode material and the first negative electrode active material.

[0042] In one embodiment, the silicon-carbon negative electrode material and the first negative electrode active material may be uniformly mixed to form a silicon-doped first negative electrode active material, and the silicon-doped first negative electrode active material is used as the second negative electrode active material.

[0043] In one embodiment, the mass percentage of silicon in the negative electrode sheet of the silicon-carbon negative electrode material is M Si , where 3%≤M Si ≤20%.

[0044] In one embodiment, the silicon-carbon negative electrode material may include one or more of a coated silicon-carbon negative electrode material, a supported silicon-carbon negative electrode material, and a dispersed silicon-carbon negative electrode material.

[0045] In one embodiment, the first negative electrode active material may include one or more of graphite, hard carbon, and soft carbon.

[0046] In one embodiment, the graphite may be green graphite.

[0047] In one embodiment, the first negative electrode active material may be graphite, and the second negative electrode active material may be an active material obtained by uniformly mixing the first negative electrode active material and a silicon-carbon negative electrode material, for example, an active material obtained by uniformly mixing a silicon-carbon negative electrode material (SiC) and graphite.

[0048] The outer active coating 112 adopts a graphite high loading (coating weight, which refers to the mass of active material coated per unit area or unit volume) parameter formula, including 97wt%~99wt% graphite, 0.8wt%~1.5wt% SBR (styrene butadiene rubber), 0.8wt%~1.5wt% CMCLi (carboxymethyl cellulose lithium), 0.8wt%~1.5wt% NMP (N-methylpyrrolidone).

[0049] The inner active coating 111 adopts a silicon-carbon low loading parameter formula, including 95wt%~97.8wt% of silicon-carbon negative electrode material and graphite blended active material, 0.8wt%~2.5wt% of SBR, 0.8wt%~2.0wt% of CMCLi, 0.2wt%~1.0wt% of NMP, and 1.0wt%~2.5wt% of PAA (polyacrylic acid, PAA-type binder).

[0050] The outer active coating 112 of the negative electrode plate of the embodiment of the present application adopts a graphite system negative electrode active material, and the inner active coating 111 adopts a high-silicon system negative electrode active material. The graphite system negative electrode active material has little effect on the change of the surface density of the first active coating 11 and the second active coating 12, and the change of the CB value caused by the change of the surface density is much smaller than the change of the CB value caused by the high-silicon system negative electrode active material. The outer active coating 112 adopts the graphite system negative electrode active material, which can reduce the change of the N / P value of the arc area after the negative electrode plate is wound. The high-silicon system negative electrode active material of the inner active coating 111 and the graphite system negative electrode active material of the outer active coating 112 can improve the kinetic performance of the lithium-ion battery.

[0051] In one embodiment, the outer coating slurry of the outer active coating 112 can be prepared according to the high loading parameter formula of graphite of the outer active coating 112; the inner coating slurry of the inner active coating 111 can be prepared according to the low loading parameter formula of silicon carbon of the inner active coating 111; the outer coating slurry and the inner coating slurry are coated on one side of the negative electrode collector 13 (for example, copper foil) to form a first active coating 11 by a double-layer coating process and a positive and negative surface coating process, and the outer coating slurry and the inner coating slurry are coated on the other side of the negative electrode collector 13 (for example, copper foil) to form a second active coating 12, and then dried and cold pressed to obtain the negative electrode sheet 1.

[0052] In one embodiment, during the double-layer coating process of the outer coating slurry and the inner coating slurry, the greater the silicon content of the inner coating slurry of the inner active coating 111, the more serious the slurry gas generation. Therefore, after the inner coating slurry is prepared, the coating should be completed within 10 hours.

[0053] The solid content of the high-loading parameter formula of graphite in the outer active coating 112 of the embodiment of the present application is close to that of the low-loading parameter formula of silicon-carbon in the inner active coating 111, thereby avoiding the problem of coating cracking caused by a large difference in solid content between the outer coating slurry and the inner coating slurry.

[0054] In one embodiment, due to excessive content of the conductive agent, the side reaction increases and the high temperature performance deteriorates seriously. Therefore, the conductive agent SWCNT (single-walled carbon nanotube) and the conductive agent carbon black SP of the outer active coating 112 and the inner active coating 111 should not be too much, and the ratio and content of the conductive agent SWCNT and the conductive agent carbon black SP should be strictly controlled. The conductive agent SWCNT is difficult to disperse in the slurry. In the slurry preparation process, the conductive agent SWCNT should be placed in front to increase the dispersion effect. The outer coating slurry and the inner coating slurry can be prepared by turning on the vacuum revolution and the speed of 2000r / min~2500 r / min (revolutions / minute) in the dispersion link. In one embodiment, the first active coating 11 and the second active coating 12 of the negative electrode plate 1 respectively include an outer active coating 112 and an inner active coating 111. If the surface density of the inner active coating 111 is too small, the advantages of the graphite system negative electrode active material of the outer active coating 112 will not be obvious; if the surface density of the inner active coating 111 is too large, the total capacity of the negative electrode will not be high, and the expansion of the negative electrode plate cannot be suppressed. Therefore, the surface density ratio of the surface density of the outer active coating 112 to the surface density of the inner active coating 111 of the negative electrode plate of the embodiment of the present application is R σ , where (1 / 4) ≤ R σ ≤(2 / 3).

[0055] In one embodiment, the surface density of the outer active coating 112 is σ上 , the surface density of the inner active coating 111 is σ 下 , R σ =σ 上 / σ 下 , where (2 / 8) ≤ R σ ≤(4 / 6); the graphite system negative electrode active material of the outer active coating 112 can greatly improve the high temperature performance of the lithium-ion battery; the high silicon system negative electrode active material of the inner active coating 111 can meet the design capacity of the lithium-ion battery, give full play to the advantages of the graphite system negative electrode active material of the outer active coating 112, and can meet the total capacity requirement of the negative electrode of the lithium-ion battery.

[0056] After the negative electrode sheet is wound, the surface density of the negative electrode sheet in the arc area changes, causing the N / P value of the arc area to also change. When the negative electrode sheet is wound, the surface density of the first active coating coated by the positive electrode sheet changes more obviously in the arc area, causing the lithium precipitation effect of the first active coating in the arc area to be more obvious. Therefore, the surface density of the first active coating 11 of the negative electrode sheet of the embodiment of the present application is greater than the surface density of the second active coating 12. When the surface density of the first active coating 11 differs too much from the surface density of the second active coating 12, it is easy to cause the high temperature performance of the lithium-ion battery to deteriorate.

[0057] In one embodiment, the mass percentage of silicon in the negative electrode sheet of the silicon-carbon negative electrode material is M Si , is the average silicon content of the silicon element in the first active coating and the second active coating in the silicon-carbon negative electrode material. Si , and the surface density ratio R of the surface density of the outer active coating of the negative electrode sheet to the surface density of the inner active coating σ , calculate the silicon doping amount of the second negative electrode active material of the first active coating and the second active coating; according to the silicon doping amount of the second negative electrode active material, respectively calculate the mass of the silicon-carbon negative electrode material of the inner active coating and the first negative electrode active material; prepare the second negative electrode active material of the inner active coating according to the mass of the silicon-carbon negative electrode material and the first negative electrode active material.

[0058] In one embodiment, according to the surface density ratio R of the surface density of the outer active coating 112 of the negative electrode plate to the surface density of the inner active coating 111 σ , and the mass percentage M of silicon in the negative electrode sheet in the silicon-carbon negative electrode material Si , the mass percentage of silicon in the negative electrode sheet in the silicon-carbon negative electrode material is M Si Under the premise of determining the surface density ratio R σ The smaller the second negative electrode active material is (the larger the proportion), the smaller the mass percentage of silicon in the inner active coating of the silicon-carbon negative electrode material is, and the surface density is R σThe larger it is (the smaller the proportion of the second negative electrode active material), the greater the mass percentage of silicon element in the inner active coating of the silicon-carbon negative electrode material.

[0059] In one embodiment, the greater the mass percentage of silicon in the inner active coating of the silicon-carbon negative electrode material, the greater the expansion rate of the negative electrode plate. Therefore, it is necessary to comprehensively consider the surface density ratio R of the surface density of the outer active coating 112 of the negative electrode plate to the surface density of the inner active coating 111. σ , and the mass percentage M of silicon in the negative electrode sheet in the silicon-carbon negative electrode material Si .

[0060] In one embodiment, the difference between the surface density of the first active coating 11 and the surface density of the second active coating 12 is ,in, The difference between the surface density of the first active coating 11 and the surface density of the second active coating 12 is 2 g / m 2 ~4 g / m 2 , which can significantly improve the lithium deposition phenomenon in the arc fold of the negative electrode plate 1 and effectively prevent the lithium deposition phenomenon in the arc area of ​​the negative electrode plate 1, while the deterioration of other performances of the lithium-ion battery is not obvious.

[0061] See also Figure 1 The first active coating 11 includes at least one first type wire groove 110, and the second active coating 12 includes at least one second type wire groove 120. The wire groove parameters of the first type wire groove 110 and the second type wire groove 120 include a wire groove depth 1101, a wire groove spacing 1102, and a wire groove width 1103.

[0062] In one embodiment, the groove depth of the first type of wire groove 110 is greater than the groove depth of the second type of wire groove 120 . In one embodiment, the depth of the first type of wire trough is D A , of which 20%*H 负 ≤D A ≤40%*H 负 , H 负 is the total thickness of the negative electrode sheet after rolling; the depth of the second type of wire groove is D B , of which 20%*H 负 ≤D B ≤30%*H 负 .

[0063] In one embodiment, the depth of the first type of wire trough is D A , where D A <(6 / 7)*H 负-A , H 负-A is the total thickness of the first active coating behind the roller; the groove depth of the second type of groove is D B, where D B <(6 / 7)*H 负-B , H 负-B It is the total thickness of the second active coating after the roll.

[0064] In one embodiment, the total thickness H of the negative electrode sheet after rolling is 负 = Total thickness of the first active coating after the roller H 负-A +Total thickness of the second active coating after the roller H 负-B +Thickness of negative electrode current collector.

[0065] In one embodiment, the spacing between the first type of cable ducts 110 is smaller than the spacing between the second type of cable ducts 120 .

[0066] In one embodiment, the spacing between the first type of wire troughs is I A , where 0.5mm≤I A ≤2mm; the spacing between the second type of wire trough is I B , where 1.5mm≤I B ≤3mm.

[0067] In one embodiment, the width of the wire trough corresponds to the depth of the wire trough, and there is a linear growth relationship. The deeper the wire trough is, the larger the width of the wire trough is. When the wire trough depth is 20%*H 负 , the corresponding wire slot width is 73 microns ~ 80 microns; when the wire slot depth is 30%*H 负 , the corresponding wire slot width is 88 microns ~ 95 microns; when the wire slot depth is 40%*H 负 The corresponding wire slot width is 103 microns ~ 110 microns.

[0068] In one embodiment, laser etching technology can be used to laser etch the negative electrode sheet after rolling. According to the groove depth and groove spacing of the first groove 110, multiple first-type grooves 110 are laser etched in the first active coating 11 of the negative electrode sheet 1; according to the groove depth and groove spacing of the second-type grooves 120, multiple second-type grooves 120 are laser etched in the second active coating 12 of the negative electrode sheet 1. The multiple first-type grooves 110 of the first active coating 11 and the multiple second-type grooves 120 of the second active coating 12 can store part of the electrolyte and improve the cycle performance of the lithium-ion battery.

[0069] In one embodiment, the groove depth and groove spacing of the first type of grooves 110 and the second type of grooves 120 can be calculated based on the target CB (Cell Balance) values ​​of the negative electrode sheets and the positive electrode sheets after laser etching (referring to the margin of the negative electrode capacity exceeding the positive electrode capacity in the same stage and under the same conditions, which can also be called N / P value).

[0070] In one embodiment, the surface density of the outer active coating 112 is small, and the outer active coating 112 is thin. A , Wire duct depth D A , of which 20%*H 负 ≤D A ≤40%*H 负 When the negative electrode is laser-etched, the laser passes through the outer active coating 112 and reaches the inner active coating 111. The groove depth D A If the diameter is too large, the distance to the negative electrode current collector copper foil will be close, which may cause a micro short circuit risk. Therefore, the depth of the first type of wire slot is D A , where D A <(6 / 7)*H 负-A , H 负-A It is the total thickness of the first active coating after rolling.

[0071] In one embodiment, the surface density of the positive electrode sheet of the lithium-ion battery is less than 120 g / m 2 The negative electrode plate adopts double-layer coating, and multiple first-type line grooves 110 are laser-etched on the first active coating 11 of the negative electrode plate and multiple second-type line grooves 120 are laser-etched on the second active coating 12 of the negative electrode plate. The room temperature kinetic window of the lithium-ion battery is only improved by 0.1C. The surface density of the positive electrode plate of the lithium-ion battery is greater than 200g / m 2 In the system, the negative electrode plate adopts double-layer coating, and multiple first-type line grooves 110 are laser-etched on the first active coating layer 11 of the negative electrode plate, and multiple second-type line grooves 120 are laser-etched on the second active coating layer 12 of the negative electrode plate, which has a significant effect on improving the room-temperature kinetics of the lithium-ion battery, and the room-temperature kinetics window of the lithium-ion battery is increased by more than 0.3C.

[0072] In one embodiment, the surface density of the first active coating 11 is greater than the surface density of the second active coating 12. To avoid lithium precipitation caused by insufficient N / P value, the groove depth of the first type of grooves 110 can be greater than the groove depth of the second type of grooves 120; and / or the groove spacing of the first type of grooves 110 is smaller than the groove spacing of the second type of grooves 120; and / or the groove width of the first type of grooves 110 is greater than the groove width of the second type of grooves 120; so that the surface density loss caused by laser etching of multiple first type grooves 110 in the first active coating 11 is large, and the surface density loss caused by laser etching of multiple second type grooves 120 in the second active coating 12 is small, so that the total volume (total capacity) of the multiple first type grooves 110 of the first active coating 11 is greater than the total volume (total capacity) of the multiple second type grooves 120 of the second active coating 12.

[0073] The negative electrode sheet of the embodiment of the present application comprises a first active coating coated on one side of the negative electrode current collector of the negative electrode sheet and a second active coating coated on the other side; the first active coating is an active coating coated by the positive electrode sheet when the negative electrode sheet is wound, and the surface density of the first active coating is greater than the surface density of the second active coating; the first active coating and the second active coating comprise an inner active coating close to the negative electrode current collector, and an outer active coating coated on the surface of the inner active coating; the outer active coating comprises a first negative electrode active material, the inner active coating comprises a second negative electrode active material, and the second negative electrode active material comprises silicon carbon Negative electrode material, first negative electrode active material; the surface density of the outer active coating is less than the surface density of the inner active coating; it can improve the dynamics of lithium-ion batteries, increase the energy density of lithium-ion batteries, and meet the capacity of lithium-ion batteries; it can effectively alleviate the reduction in N / P value caused by the reduction in contact area caused by the bending of the negative electrode pole piece in the arc area after winding, and reduce the difference between the N / P value of the arc area of ​​the negative electrode pole piece and the N / P value of the straight area after winding, and can effectively prevent lithium precipitation in the arc area of ​​the negative electrode pole piece of the lithium-ion battery, greatly improve the high temperature performance of the lithium-ion battery, and improve the cycle performance of the lithium-ion battery.

[0074] Furthermore, the negative electrode plate of the embodiment of the present application adopts a double-layer coating to construct an outer active coating of a graphite system negative electrode active material and an inner active coating of a high-silicon system negative electrode active material, and the mass percentage of silicon in the high-silicon system negative electrode active material of the inner active coating in the negative electrode plate (the mass percentage of silicon in the silicon-carbon negative electrode material of the second negative electrode active material of the inner active coating in the negative electrode plate) is M Si , where 3%≤M Si ≤20%; Under the premise of ensuring the high energy density of lithium-ion batteries, it effectively alleviates the reduction in N / P value caused by the reduction in contact area caused by the bending of the negative electrode piece in the winding arc area, and significantly improves the lithium deposition phenomenon in the arc area of ​​the negative electrode piece of the lithium-ion battery. It can effectively prevent the lithium deposition phenomenon in the arc area of ​​the negative electrode piece of the lithium-ion battery, improve the cycle performance of the lithium-ion battery, and provide direction for solving the problem of lithium deposition in the arc area in the development direction of high-silicon negative electrode materials for lithium-ion batteries.

[0075] Furthermore, the negative electrode sheet of the embodiment of the present application adopts double-layer coating to construct an outer active coating of a graphite system negative electrode active material and an inner active coating of a high silicon system negative electrode active material, and the surface density ratio of the outer active coating to the surface density of the inner active coating is R σ , where (1 / 4) ≤ R σ ≤(2 / 3), which can effectively alleviate the decrease of N / P value in the arc area caused by the winding and bending of the negative electrode sheet and the positive electrode sheet, and significantly and effectively improve the lithium deposition phenomenon in the arc area of ​​the negative electrode sheet of the lithium-ion battery.

[0076] Furthermore, the negative electrode sheet of the embodiment of the present application adopts positive and negative surface coating, a first active coating is coated on one side of the negative electrode current collector, and a second active coating is coated on the other side of the negative electrode current collector, the first active coating is the active coating coated by the positive electrode sheet when the negative electrode sheet is wound, the surface density of the first active coating is greater than the surface density of the second active coating, and the surface density difference between the surface density of the first active coating and the surface density of the second active coating is ,in, It can effectively alleviate the decrease of N / P value in the arc area caused by the winding and bending of the negative electrode sheet and the positive electrode sheet, and significantly and effectively improve the lithium deposition phenomenon in the arc area of ​​the negative electrode sheet of the lithium-ion battery.

[0077] Furthermore, in the negative electrode plate of the embodiment of the present application, according to the surface density of the first active coating being greater than the surface density of the second active coating, at least one first type of groove is etched in the first active coating layer of the negative electrode plate, and at least one second type of groove is etched in the second active coating layer of the negative electrode plate. The grooves increase the liquid retention capacity in the arc area, and at the same time, more lithium insertion channels are added to the positive electrode, which can effectively improve the lithium plating phenomenon in the arc area of ​​the negative electrode plate of the lithium-ion battery, effectively improve the kinetic performance of the lithium-ion battery, and enhance the comprehensive performance of the lithium-ion battery.

[0078] Figure 3 It is a structural schematic diagram of the cross-section in the height direction of the wound battery cell after the negative electrode sheet and the separator and the positive electrode sheet are wound in the embodiment of the present application.

[0079] See also Figure 2 and Figure 3 The embodiment of the present application provides a wound battery cell 40, comprising a positive electrode sheet 2, a separator 3 and the above-mentioned negative electrode sheet 1, wherein the positive electrode sheet 2, the separator 3 and the negative electrode sheet 1 are stacked and wound to form the wound battery cell 40. The wound battery cell 40 comprises an arc region 401 and a straight region 402.

[0080] Figure 4 It is a partial schematic diagram of a width-direction cross section of the diaphragm shown in an embodiment of the present application.

[0081] See also Figure 4 The diaphragm 3 is an oil-based roller-coated diaphragm having a coating layer of porous ceramic and an oily coating, and includes a polymer layer 301 , a porous ceramic layer 302 , and a base film layer 303 .

[0082] In one embodiment, the porous ceramic layer 302 includes porous ceramic, which may be porous aluminum oxide (Al 2 O 3 )ceramics.

[0083] In one embodiment, the base film layer 303 includes a porous PP (polypropylene) base film, and the polymer layer 301 is an oily coating in face-to-face contact with the pole piece.

[0084] In one embodiment, after the positive electrode sheet 2, the separator 3 and the negative electrode sheet 1 are stacked and wound, the bending curvature of the negative electrode sheet 1 and the positive electrode sheet 2 in the arc area of ​​the wound battery cell 40 is large, the stress is increased, and the liquid retention amount is small. The porous ceramic layer 302 of the separator 3 can effectively increase the liquid retention amount of the negative electrode sheet 1 and the positive electrode sheet 2, and can effectively improve the lithium plating phenomenon in the arc area of ​​the negative electrode sheet of the lithium-ion battery.

[0085] In one embodiment, after the positive electrode sheet 2, the separator 3 and the negative electrode sheet 1 are stacked and wound, the adhesion between the positive electrode sheet 2 and the negative electrode sheet 1 in the arc area is weak. After hot pressing, the oily coating of the polymer layer 301 melts, which can increase the viscosity, significantly improve the adhesion between the positive electrode sheet and the negative electrode sheet in the arc area, reduce the contact gap between the positive electrode sheet and the negative electrode sheet, shorten the lithium ion diffusion distance, and the porous base film improves the lithium ion transmission rate. The porous ceramic can improve the liquid retention performance and battery cell safety in the arc area, and can effectively improve the lithium precipitation phenomenon in the arc area of ​​the negative electrode sheet of the lithium ion battery, thereby improving the comprehensive performance of the lithium ion battery.

[0086] An embodiment of the present application further provides a lithium-ion battery, which includes the above-mentioned wound battery cell, or includes the above-mentioned negative electrode plate.

[0087] The present invention is further described below by way of examples.

[0088] Embodiment 1: Example 1 is used to illustrate the battery and the preparation method thereof of the present application, comprising the following steps: 1) Preparation of positive electrode sheet: Positive electrode formula: positive electrode active material lithium cobalt oxide (LCO) 94wt%~972wt%, carbon nanotubes (CNT) 0.05wt%~0.25wt%, conductive carbon black (SP) 0.5wt%~1.1wt%, polyvinylidene fluoride (PVDF) 1.0wt%~1.7wt%.

[0089] The positive electrode active material lithium cobalt oxide: carbon nanotubes: conductive carbon black: polyvinylidene fluoride are mixed in an N-methylpyrrolidone solvent (NMP) at a weight ratio of 98.2:0.3:0.6:0.9 to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector Al (aluminum) foil, dried, and cold pressed to obtain a positive electrode sheet.

[0090] 2) Preparation of negative electrode sheet: Graphite and silicon-carbon negative electrode materials are stirred and mixed in corresponding proportions to form a capacity of 400Ah / g~650mAh / g, the gram capacity of graphite is 360mAh / g, the gram capacity of silicon-carbon negative electrode material is 1800mAh / g, PAA: SBR: CMC-Li: CNT: SP = 1.5%: 1.2%: 1.0%: 0.1%: 0.2% mass ratio is dispersed in deionized water to form a uniform outer coating slurry and inner coating slurry; a double-layer coating process and a positive and negative surface coating process are adopted to apply the outer coating slurry and the inner coating slurry to one side of the copper foil to form a first active coating, and the outer coating slurry and the inner coating slurry are applied to the other side of the copper foil to form a second active coating, and then after drying and cold pressing, the negative electrode sheet is obtained.

[0091] 3) Battery production: The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then the bare battery cell is wound. The bare battery cell is placed in an outer packaging bag, dried at high temperature, and injected with the corresponding electrolyte. After vacuum packaging, standing, forming, shaping and other processes, the preparation of lithium-ion batteries is completed, and lithium-ion batteries are obtained in turn.

[0092] The lithium-ion batteries and preparation methods thereof of Examples 2 to 29 include most of the operation steps in Example 1. For the specific differences, please refer to the specific parameters in Tables 1 to 6.

[0093] The silicon content in Tables 1 to 6 is the mass percentage of silicon in the negative electrode of lithium-ion batteries, and is the mass percentage of silicon in the negative electrode of the inner active coating silicon-carbon negative electrode material. Si .

[0094] The double-layer coating in Tables 1 to 6 indicates that the first active coating and the second active coating of the negative electrode sheet of the lithium-ion battery include an inner active coating close to the negative electrode current collector and an outer active coating coated on the surface of the inner active coating.

[0095] The outer graphite in Tables 1 to 6 indicates that the negative electrode active material (first negative electrode active material) of the outer active coating of the first active coating and the second active coating of the negative electrode sheet of the lithium-ion battery is graphite.

[0096] The inner silicon carbon in Tables 1 to 6 indicates that the negative electrode active material (second negative electrode active material) of the inner active coating of the first active coating and the second active coating of the negative electrode sheet of the lithium-ion battery is graphite + silicon carbon negative electrode material.

[0097] The surface density ratios in Tables 1 to 6 are the surface density ratios R of the surface density of the outer active coating of the first active coating and the second active coating of the negative electrode sheet of the lithium ion battery to the surface density of the inner active coating. σ .

[0098] The surface density difference values ​​in Tables 1 to 6 are the surface density differences between the surface density of the first active coating and the surface density of the second active coating of the negative electrode sheet of the lithium-ion battery. .

[0099] The groove depth of the A-type grooves in Tables 1 to 6 represents the groove depth of the first type of grooves in the first active coating layer of the negative electrode sheet of a lithium-ion battery.

[0100] The groove depth of line B in Tables 1 to 6 represents the groove depth of the second type of grooves of the second active coating layer of the negative electrode sheet of the lithium-ion battery.

[0101] The A-type slot spacing in Tables 1 to 6 represents the slot spacing of the first type of slots in the first active coating of the negative electrode sheet of a lithium-ion battery.

[0102] The B groove spacing in Tables 1 to 6 represents the groove spacing of the second type of grooves of the second active coating layer of the negative electrode sheet of a lithium-ion battery.

[0103] The lithium ion batteries of Examples 1 to 29 were subjected to cycle tests to obtain the capacity (mAh, milliampere-hour), 600-cycle arc zone lithium precipitation, 600-cycle capacity retention rate at room temperature (25 degrees Celsius), 600-cycle expansion rate at room temperature, 400-cycle capacity retention rate at 45°C (degrees Celsius), 400-cycle expansion rate at 45°C, net liquid coefficient (g / mAh), and weighted N / P value of the lithium ion batteries of Examples 1 to 29 as shown in Tables 1 to 6.

[0104] The weighted N / P values ​​in Tables 1 to 6 are the average N / P values ​​of the arc area and the N / P values ​​of the straight area, and are the average N / P values ​​of the wound cells.

[0105] The net liquid coefficients in Tables 1 to 6 are mass net liquid coefficients, that is, how many grams of electrolyte corresponds to how much capacity, which is the gram capacity value.

[0106] The cycle test includes: Step 1, 0.5C full charge 4.55V, cut-off current 0.05C, stand for 10 minutes; Step 2, discharge at 0.2C to 3.0V, record the discharge capacity C 0 As initial capacity; Step 3, charge at 1.0C constant current and constant voltage to 4.55V, cut-off current 0.05C, and let stand for 10 minutes; Step 4, discharge at 0.5C to 3.0V and let stand for 10min; Step 5, repeat step 3 and step 4, repeat 600 times, record the discharge data as well as the voltage, internal resistance, and thickness of 50 times / 100 times / 200 times / 300 times / 400 times / 600 times.

[0107] Table 1:

[0108] Table 2:

[0109] Table 3:

[0110] Table 4:

[0111] Table 5:

[0112] Table 6:

[0113] According to the data of Example 1 and Example 2 in Table 1, a double-layer coating is adopted in the first active coating and the second active coating, including an inner active coating (inner silicon carbon) and an outer active coating (outer graphite), which can effectively prevent lithium deposition in the arc area of ​​the negative electrode of the lithium-ion battery, greatly improve the high temperature performance of the lithium-ion battery, and improve the cycle performance of the lithium-ion battery.

[0114] According to the data of Example 3 and Example 1 in Table 1, increasing the surface density of the outer active coating (outer graphite) can effectively prevent lithium deposition in the arc area of ​​the negative electrode of the lithium-ion battery. However, in order to ensure the capacity of the lithium-ion battery, the silicon content of the inner active coating needs to be increased accordingly. Increasing the silicon content of the inner active coating will increase the expansion rate of the lithium-ion battery sharply, and the expansion rate of the lithium-ion battery will deteriorate significantly, thereby reducing the safety of the lithium-ion battery.

[0115] According to the data of Example 4 and Example 1 in Table 1, the difference in surface density between the surface density of the first active coating and the surface density of the second active coating 12 is =5g / m 2 When the difference between the surface density of the first active coating and the surface density of the second active coating is too large, the 45°C capacity retention rate is significantly reduced, the 45°C expansion rate is significantly increased, and the high temperature performance of the lithium-ion battery is significantly deteriorated.

[0116] According to the data of Example 5 and Example 1 in Table 1, the diaphragm of Example 1 adopts an oil-based roller-coated diaphragm in which a porous base film is coated with porous ceramics and an oily coating, which can effectively improve the lithium deposition phenomenon in the arc area of ​​the negative electrode piece of the lithium ion battery and improve the comprehensive performance of the lithium ion battery; Example 5 adopts a diaphragm without porous ceramics, and the capacity retention rate of the lithium ion battery corresponding to Example 5 is reduced, the expansion rate is significantly increased, and lithium deposition occurs in the arc area of ​​the negative electrode piece of the lithium ion battery, which reduces the safety of the lithium ion battery.

[0117] According to the data of Example 6 in Table 2 and Example 1 in Table 1, the second active coating of Example 6 etches more second-type wire grooves, and although the weighted N / P value of the lithium-ion battery of Example 6 can be reduced, the capacity of the lithium-ion battery of Example 6 is low, there is slight lithium deposition, the expansion rate is significantly increased, and the performance of the lithium-ion battery of Example 6 is reduced.

[0118] According to the data of Example 7 in Table 2 and Example 1 in Table 1, the first active coating of Example 7 has more first-type grooves, and the weighted N / P value of the lithium-ion battery of Example 7 is reduced. The performance of the lithium-ion battery of Example 7 has no obvious deterioration, but the capacity loss of the lithium-ion battery of Example 7 is obvious, which affects the gram capacity and increases the expansion rate.

[0119] According to the data of Example 8 in Table 2 and Example 1 in Table 1, the groove depths of the first type of grooves in the first active coating and the second type of grooves in the second active coating are reduced, and the groove depths of the first type of grooves and the second type of grooves are equal, the amount of electrolyte stored in the grooves of Example 8 is reduced, the weighted N / P value of the lithium ion battery of Example 8 is increased, the capacity retention rate is reduced, the expansion rate is significantly increased, and the high temperature performance of the lithium ion battery of Example 8 is reduced.

[0120] According to the data of Example 9 in Table 2 and Example 1 in Table 1, the first active coating and the second active coating of the negative electrode plate of Example 9 are not double-layer coated, and lithium deposition is obvious in the arc area of ​​the lithium ion battery of Example 9, the capacity retention rate is reduced, and the expansion rate is significantly increased. Therefore, the first active coating and the second active coating of the negative electrode plate of the lithium ion battery are double-layer coated, including an inner active coating (inner silicon carbon) and an outer active coating (outer graphite), which can effectively prevent lithium deposition from occurring in the arc area of ​​the negative electrode plate of the lithium ion battery, greatly improve the high temperature performance of the lithium ion battery, and improve the cycle performance of the lithium ion battery.

[0121] According to the data of Examples 10-18, although increasing the silicon content of the inner active coating of the first active coating layer and the second active coating layer of the negative electrode plate can improve the energy density of the lithium-ion battery, as the silicon content increases, the lithium plating phenomenon in the arc area of ​​the negative electrode plate of the lithium-ion battery becomes increasingly serious, the capacity retention rate gradually decreases, and the expansion rate gradually increases.

[0122] According to the data of Examples 19 to 24, increasing the surface density of the outer active coating (graphite-based negative electrode active material) of the first active coating and the second active coating can effectively alleviate the decrease in the N / P value in the arc zone caused by the winding and bending of the negative electrode sheet and the positive electrode sheet, significantly and effectively improve the lithium plating phenomenon in the arc zone of the negative electrode sheet of the lithium-ion battery, and reduce the expansion rate of the lithium-ion battery.

[0123] According to the data of Examples 25 to 29, the surface density of the first active coating is increased. As the surface density difference between the first active coating and the second active coating increases, the lithium plating phenomenon in the arc area of ​​the negative electrode of the lithium-ion battery can be more effectively improved, and the expansion rate of the lithium-ion battery can be reduced. However, if the surface density difference between the first active coating and the second active coating is too large, the capacity retention rate will be reduced.

[0124] Therefore, the technical solution of the embodiment of the present application adopts positive and negative surface coating, and the first active coating is coated on one side of the negative electrode current collector, and the second active coating is coated on the other side of the negative electrode current collector. The first active coating is the active coating that is coated by the positive electrode sheet when the negative electrode sheet is wound. The surface density of the first active coating is greater than the surface density of the second active coating. The surface density difference between the surface density of the first active coating and the surface density of the second active coating is ,in, ; The outer active coating of the graphite system negative electrode active material and the inner active coating of the high silicon system negative electrode active material are constructed by double-layer coating on the first active coating and the second active coating, and the surface density ratio of the outer active coating to the surface density of the inner active coating is R σ , where (1 / 4) ≤ R σ ≤(2 / 3); and etching at least one first type of groove in the first active coating layer, and etching at least one second type of groove in the second active coating layer of the negative electrode plate; using a porous ceramic diaphragm to increase the liquid retention of the arc area plate; can effectively alleviate the decrease in the N / P value of the arc area caused by the winding and bending of the negative electrode plate and the positive electrode plate, increase the liquid retention of the arc area, and at the same time increase more lithium insertion channels for the positive electrode, which can effectively improve the lithium precipitation phenomenon in the arc area of ​​the negative electrode plate of the lithium-ion battery, effectively improve the kinetic performance of the lithium-ion battery, and enhance the comprehensive performance of the lithium-ion battery.

[0125] The embodiments of the present application have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A negative electrode plate, characterized in that: It comprises a negative electrode current collector, a first active coating coated on one side of the negative electrode current collector, and a second active coating coated on the other side of the negative electrode current collector; wherein, The first active coating is an active coating that is coated by the positive electrode sheet when the negative electrode sheet is wound, and the surface density of the first active coating is greater than the surface density of the second active coating; The first active coating layer and the second active coating layer include an inner active coating layer close to the negative electrode current collector and an outer active coating layer coated on the surface of the inner active coating layer; The outer active coating layer includes a first negative electrode active material, the inner active coating layer includes a second negative electrode active material, and the second negative electrode active material includes a silicon-carbon negative electrode material and the first negative electrode active material; The surface density of the outer active coating layer is smaller than the surface density of the inner active coating layer.

2. The negative electrode sheet according to claim 1, characterized in that: The mass percentage of silicon in the silicon-carbon negative electrode material in the negative electrode plate is M Si ,in, 。 3. The negative electrode sheet according to claim 1, characterized in that: The silicon-carbon negative electrode material includes one or more of a coated silicon-carbon negative electrode material, a supported silicon-carbon negative electrode material, and a dispersed silicon-carbon negative electrode material.

4. The negative electrode plate according to claim 1, characterized in that: The first negative electrode active material includes one or more of graphite, hard carbon, and soft carbon.

5. The negative electrode sheet according to claim 1, characterized in that: The surface density ratio of the surface density of the outer active coating layer to the surface density of the inner active coating layer is ,in, 。 6. The negative electrode plate according to claim 1, characterized in that: The difference between the surface density of the first active coating and the surface density of the second active coating is ,in, 。 7. The negative electrode sheet according to claim 1, characterized in that: The first active coating layer includes at least one first type wire groove, and the second active coating layer includes at least one second type wire groove.

8. The negative electrode plate according to claim 7, characterized in that: The depth of the first type of wire trough is greater than the depth of the second type of wire trough; and / or, The wire slot spacing of the first type of wire slots is smaller than the wire slot spacing of the second type of wire slots.

9. The negative electrode sheet according to claim 8, characterized in that: The depth of the first type of wire trough is D A ,in, , H 负 is the total thickness of the negative electrode sheet after rolling; The depth of the second type of wire trough is D B ,in, .

10. The negative electrode sheet according to claim 9, characterized in that: The depth of the first type of wire trough is D A ,in, , H 负-A is the total thickness of the first active coating after rolling; The depth of the second type of wire trough is D B ,in, , H 负-B It is the total thickness of the second active coating after rolling.

11. The negative electrode plate according to claim 8, characterized in that: The spacing between the first type of wire troughs is I A , where 0.5mm≤I A ≤2mm; The spacing between the second type of wire troughs is I B , where 1.5mm≤I B ≤3mm.

12. A wound battery cell, characterized in that: The invention comprises a positive electrode sheet, a separator and the negative electrode sheet according to any one of claims 1 to 11, wherein the positive electrode sheet, the separator and the negative electrode sheet are stacked and wound to form the wound battery cell.

13. The wound battery cell according to claim 12, characterized in that: The separator includes a porous ceramic layer.

14. A lithium ion battery, characterized in that: It comprises a wound battery cell as claimed in claim 12 or 13, or comprises a negative electrode sheet as claimed in any one of claims 1 to 11.

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