Negative electrode sheet, wound battery cell and lithium-ion battery

Abstract

This application relates to a negative electrode sheet, a wound battery cell, and a lithium-ion battery. The negative electrode sheet includes 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; the first active coating is the active coating that is wrapped by the positive electrode sheet when the negative electrode sheet is wound, and the areal density of the first active coating is greater than that of the second active coating; the first active coating and the second active coating 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; the outer active coating includes a first negative electrode active material, and the inner active coating 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 areal density of the outer active coating is less than that of the inner active coating. The solution provided by this application can effectively prevent the phenomenon of lithium deposition in the arc area of the negative electrode sheet of the lithium-ion battery and improve the cycle performance of the lithium-ion battery.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and particularly 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 lithium-ion batteries with high energy density.

[0003] Silicon-carbon negative electrode materials have attracted much attention as the mainstream development materials for improving the energy density of lithium-ion batteries at present. In the high-energy-density market of 3C consumer products, most of the battery cells of related technology lithium-ion batteries use a wound structure. However, in the wound structure, due to the inconsistent tensions in the flat area and the arc area, stress concentration occurs in the arc area, which easily causes creases and lithium deposition in the wound core, greatly affecting the service life of the product. This phenomenon is more obvious in lithium-ion batteries with a silicon-doped system. Since the contact area between the negative electrode sheet in the arc area and the corresponding positive electrode sheet decreases after bending in the wound structure, the decrease in the contact area causes the N / P value (the ratio of the negative electrode capacity to the positive electrode capacity of the battery) in the arc area to decrease significantly, resulting in the N / P value in the arc area being lower than that in the flat area. When the silicon doping amount of the negative electrode sheet increases, the slight change in the areal density of the negative electrode sheet has a more obvious impact on the N / P value, and the N / P value in the arc area decreases sharply, making it easier to cause lithium deposition in the arc area and reducing the cycle performance of the lithium-ion battery; the stress in the arc area is large, which easily reduces the contact between the positive and negative electrode sheets and the separator, easily increases the lithium-ion transmission path and polarization, and at the same time, the large stress in the arc area also causes insufficient infiltration of the electrolyte between the positive and negative electrode sheets, making it easier to precipitate lithium metal and also reducing the cycle performance of the lithium-ion battery.

[0004] Therefore, in the high-silicon development direction of related technology lithium-ion batteries, how to solve the problems of easy lithium deposition and reduced cycle performance in the arc area of wound lithium-ion batteries has become a major difficulty. Summary of the Invention

[0005] To solve or partially solve the problems existing in the related technology, the present application provides a negative electrode sheet, a wound battery cell, and a lithium-ion battery, which can effectively prevent the phenomenon of lithium deposition in the arc area of the negative electrode sheet of the lithium-ion battery and improve the cycle performance of the lithium-ion battery.

[0006] The first aspect of the present application provides a negative electrode sheet, which includes 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,

[0007] The first active coating is the active coating that is wrapped by the positive electrode sheet when the negative electrode sheet is wound, and the areal density of the first active coating is greater than that of the second active coating;

[0008] The first active coating and the second active coating 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;

[0009] The outer active coating includes a first negative electrode active material, the inner active coating 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;

[0010] The areal density of the outer active coating is less than that of the inner active coating.

[0011] Preferably, the mass percentage of silicon element in the silicon-carbon negative electrode material in the negative electrode plate is M Si , where 3% ≤ M Si ≤ 20%.

[0012] 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.

[0013] Preferably, the first negative electrode active material includes one or more of graphite, hard carbon, and soft carbon.

[0014] Preferably, the ratio of the areal density of the outer active coating to the areal density of the inner active coating is R σ , where (1 / 4) ≤ R σ ≤ (2 / 3).

[0015] Preferably, the difference in areal density between the first active coating and the second active coating is , where .

[0016] Preferably, the first active coating includes at least one first type of groove, and the second active coating includes at least one second type of groove.

[0017] Preferably, the groove depth of the first type of groove is greater than that of the second type of groove; and / or,

[0018] the groove pitch of the first type of groove is less than that of the second type of groove.

[0019] Preferably, the groove depth of the first type of groove is D A , where 20%*H 负 ≤ D A ≤ 40%*H 负 , H 负 is the total thickness of the negative electrode plate after double-rolling;

[0020] The groove depth of the second type of wire groove is D B , where 20%*H 负 ≤D B ≤30%*H 负 .

[0021] Preferably, the groove depth of the first type of wire groove is D A , where D A <(6 / 7)*H 负-A , H 负-A is the total thickness of the first active coating after the opposed rollers;

[0022] The groove depth of the second type of wire groove is D B , where D B <(6 / 7)*H 负-B , H 负-B is the total thickness of the second active coating after the opposed rollers.

[0023] Preferably, the groove pitch of the first type of wire groove is I A , where 0.5 mm ≤ I A ≤ 2 mm;

[0024] The groove pitch of the second type of wire groove is I B , where 1.5 mm ≤ I B ≤ 3 mm.

[0025] In a second aspect of the present application, a wound electric core is provided. The wound electric core includes a positive electrode tab, a separator, and a negative electrode tab as described above. After being stacked, the positive electrode tab, the separator, and the negative electrode tab are wound to form the wound electric core.

[0026] Preferably, the separator includes a porous ceramic layer.

[0027] In a third aspect of the present application, a lithium ion battery is provided. The lithium ion battery includes the wound electric core as described above, or includes the negative electrode tab as described above.

[0028] The technical solution provided by the present application may include the following beneficial effects:

[0029] In the technical solution of this application, a first active coating is applied to one side of the negative electrode current collector of the negative electrode sheet, and a second active coating is applied to the other side; the first active coating is the active coating that is wrapped by the positive electrode sheet when the negative electrode sheet is wound, and the areal density of the first active coating is greater than that of the second active coating; the first active coating and the second active coating 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; the outer active coating includes a first negative electrode active material, and the inner active coating 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 areal density of the outer active coating is less than that of the inner active coating; it can improve the kinetics of the lithium-ion battery, increase the energy density of the lithium-ion battery, and meet the capacity performance of the lithium-ion battery; it can effectively alleviate the decrease in the N / P value caused by the reduction of the contact surface due to the bending of the negative electrode sheet in the arc area after winding, reduce the difference between the N / P value in the arc area and the N / P value in the flat area of the negative electrode sheet after winding, can effectively prevent the phenomenon of lithium deposition in the arc area of the negative electrode sheet 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.

[0030] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit this application. Brief Description of the Drawings

[0031] By describing the exemplary embodiments of the present application in more detail in conjunction with the drawings, the above and other objects, features, and advantages of the present application will become more apparent. Among them, in the exemplary embodiments of the present application, the same reference numerals generally represent the same components.

[0032] Figure 1 It is a partial schematic cross-sectional view of the negative electrode sheet shown in the embodiment of the present application;

[0033] Figure 2 It is a partial schematic view of the wound negative electrode sheet, separator, and positive electrode sheet shown in the embodiment of the present application;

[0034] Figure 3 It is a schematic structural view of the cross-section in the height direction of the wound battery cell of the negative electrode sheet, separator, and positive electrode sheet shown in the embodiment of the present application;

[0035] Figure 4 It is a partial schematic cross-sectional view in the width direction of the separator shown in the embodiment of the present application. Detailed Description of the Embodiments

[0036] Embodiments of the present application will be described in more detail below with reference to the accompanying drawings. Although embodiments of the present application are shown in the drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth 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.

[0037] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit the present application. The singular forms "a", "the", and "said" used in this application and the appended claims are also intended to include the plural forms unless the context clearly dictates otherwise. It should also be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0038] It should be understood that although the terms "first", "second", "third", etc. may be used in this application to describe various information, such 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 with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of this application, "a plurality" means two or more unless otherwise specifically defined.

[0039] An embodiment of the present application provides a negative electrode tab, which can effectively prevent the phenomenon of lithium deposition in the arc area of the negative electrode tab of a lithium-ion battery and improve the cycling performance of the lithium-ion battery.

[0040] The technical solutions of the embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0041] Figure 1 is a partial schematic view of the cross-section of the negative electrode tab shown in an embodiment of the present application; Figure 2 is a partial schematic view of the negative electrode tab, the separator, and the positive electrode tab after winding.

[0042] See Figure 1 , a negative electrode tab 1, comprising a negative current collector 13, a first active coating 11 coated on one side of the negative current collector 13, and a second active coating 12 coated on the other side of the negative current collector 13.

[0043] In one embodiment, the first active coating 11 and the second active coating 12 include an inner active coating 111 close to the negative current collector 13, and an outer active coating 112 coated on the surface of the inner active coating 111.

[0044] In one embodiment, the first active coating 11 includes an inner active coating 111 adjacent 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 adjacent 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.

[0045] 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.

[0046] 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.

[0047] See Figure 2 , the first active coating 11 is the active coating covered by the positive electrode sheet 2 when the negative electrode sheet 1 is wound, and the areal density of the first active coating 11 is greater than that of the second active coating 12.

[0048] 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 covered by the separator 3 and the positive electrode sheet 2 in sequence in the direction from the center of the wound battery cell to the edge of the wound battery cell.

[0049] In one embodiment, the areal density of the outer active coating 112 is less than that of the inner active coating 111.

[0050] The negative electrode sheet of the embodiment of the present application includes 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 the active coating covered by the positive electrode sheet when the negative electrode sheet is wound, and the areal density of the first active coating is greater than that of the second active coating; the first active coating and the second active coating 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; the outer active coating includes a first negative electrode active material, and the inner active coating 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 areal density of the outer active coating is less than that of the inner active coating; it can improve the kinetics of the lithium-ion battery, increase the energy density of the lithium-ion battery, and meet the capacity performance of the lithium-ion battery; it can effectively alleviate the decrease in the N / P value caused by the reduction of the contact surface due to the bending of the negative electrode sheet in the arc area after winding, reduce the difference between the N / P value in the arc area and the N / P value in the flat area of the negative electrode sheet after winding, can effectively prevent the phenomenon of lithium deposition in the arc area of the negative electrode sheet 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.

[0051] See Figure 2 , a negative electrode sheet 1, including 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 the active coating covered by the positive electrode sheet 2 when the negative electrode sheet 1 is wound, and the areal density of the first active coating 11 is greater than that of the second active coating 12.

[0052] See 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. Wherein, the areal density of the outer active coating 112 is less than that of the inner active coating 111.

[0053] 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.

[0054] In one embodiment, the silicon-carbon negative electrode material and the first negative electrode active material can 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.

[0055] In one embodiment, the mass percentage of silicon element in the silicon-carbon negative electrode material in the negative electrode sheet is M Si , wherein, 3% ≤ M Si ≤ 20%.

[0056] 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.

[0057] In one embodiment, the first negative electrode active material may include one or more of graphite, hard carbon, and soft carbon.

[0058] In one embodiment, the graphite may be green coke graphite.

[0059] In one embodiment, the first negative electrode active material may be graphite, and the second negative electrode active material may be an active material in which the first negative electrode active material and the silicon-carbon negative electrode material are uniformly mixed. For example, an active material in which the silicon-carbon negative electrode material (SiC) and graphite are uniformly mixed.

[0060] The outer active coating 112 adopts a graphite high Loading (coating weight, which refers to the mass of the active substance coated per unit area or unit volume) parameter formula, including 97wt% - 99wt% of graphite, 0.8wt% - 1.5wt% of SBR (styrene-butadiene rubber), 0.8wt% - 1.5wt% of CMCLi (lithium carboxymethyl cellulose), and 0.8wt% - 1.5wt% of NMP (N-methylpyrrolidone).

[0061] The inner active coating 111 adopts a silicon-carbon low Loading parameter formula, including 95wt% - 97.8wt% of the silicon-carbon negative electrode material and graphite blended active material, 0.8%wt - 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-based binder).

[0062] The outer active coating 112 of the negative electrode sheet in the embodiment of the present application adopts a graphite-based negative electrode active material, and the inner active coating 111 adopts a high-silicon-based negative electrode active material. The graphite-based negative electrode active material has an insignificant influence on the change in the areal density of the first active coating 11 and the second active coating 12. For the change in the CB value caused by the change in the areal density, it is much smaller than the change in the CB value caused by the high-silicon-based negative electrode active material. The outer active coating 112 adopts a graphite-based negative electrode active material, which can reduce the change in the N / P value in the arc area after the negative electrode sheet is wound. The combination of the high-silicon-based negative electrode active material of the inner active coating 111 and the graphite-based negative electrode active material of the outer active coating 112 can improve the kinetic performance of the lithium-ion battery.

[0063] In one embodiment, an outer coating slurry of the outer active coating 112 can be prepared according to the graphite high Loading parameter formula of the outer active coating 112; an inner coating slurry of the inner active coating 111 can be prepared according to the silicon-carbon low Loading parameter formula of the inner active coating 111; by using a double-layer coating process and a positive-negative side coating process, the outer coating slurry and the inner coating slurry are coated on one side of the negative current collector 13 (for example, a copper foil) to form a first active coating 11, and the outer coating slurry and the inner coating slurry are coated on the other side of the negative current collector 13 (for example, a copper foil) to form a second active coating 12, and then through drying and cold pressing, the negative electrode plate 1 is obtained.

[0064] In one embodiment, during the double-layer coating process of the outer coating slurry and the inner coating slurry, the greater the silicon content in the inner coating slurry of the inner active coating 111, the more serious the gas generation of the slurry. Therefore, within 10 hours after the preparation of the inner coating slurry, the coating should be completed.

[0065] The solid contents of the graphite high Loading parameter formula of the outer active coating 112 and the silicon-carbon low Loading parameter formula of the inner active coating 111 in the embodiments of the present application are close, avoiding the problem that too large a difference in the solid contents of the outer coating slurry and the inner coating slurry is likely to cause coating cracking.

[0066] In one embodiment, due to too much conductive agent content, side reactions increase and the high-temperature performance deteriorates severely. Therefore, the conductive agents SWCNT (single-walled carbon nanotubes) and conductive carbon black SP in the outer active coating 112 and the inner active coating 111 should not be too much, and the ratio and content of the conductive agents SWCNT and conductive carbon black SP need to be strictly controlled. The conductive agent SWCNT is difficult to disperse in the slurry. During 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 at a rotation speed of 2000 r / min to 2500 r / min (revolutions per minute) in the dispersion stage.

[0067] In one embodiment, both the first active coating 11 and the second active coating 12 of the negative electrode plate 1 respectively include the outer active coating 112 and the inner active coating 111. If the areal density of the inner active coating 111 is too small, the advantages of the graphite-based negative active material of the outer active coating 112 are not obvious; if the areal density of the inner active coating 111 is too large, it will lead to a low total capacity of the negative electrode and the swelling of the negative electrode plate cannot be suppressed. Therefore, the ratio of the areal density of the outer active coating 112 to the areal density of the inner active coating 111 of the negative electrode plate in the embodiments of the present application is R σ , where, (1 / 4) ≤ R σ ≤ (2 / 3).

[0068] In one embodiment, the areal density of the outer active coating 112 is σ 上 and the areal 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-based anode active material of the outer active coating 112 can greatly improve the high-temperature performance of the lithium-ion battery; the high-silicon-based anode active material of the inner active coating 111 can meet the requirement of the designed capacity of the lithium-ion battery, give full play to the advantages of the graphite-based anode active material of the outer active coating 112, and meet the total capacity requirement of the anode of the lithium-ion battery.

[0069] After the negative electrode tab is wound, the areal density of the negative electrode tab in the arc area changes, resulting in a change in the N / P value in the arc area. The change in the areal density of the first active coating covered by the positive electrode tab during the winding of the negative electrode tab in the arc area is more obvious, resulting in a more obvious lithium plating effect of the first active coating in the arc area. Therefore, the areal density of the first active coating 11 of the negative electrode tab in the embodiment of the present application is greater than the areal density of the second active coating 12. When the difference between the areal density of the first active coating 11 and the areal density of the second active coating 12 is too large, it is easy to cause deterioration of the high-temperature performance of the lithium-ion battery.

[0070] In one embodiment, the mass percentage M Si of silicon element in the silicon-carbon anode material in the negative electrode tab is the average silicon doping amount of the silicon element in the silicon-carbon anode material in the first active coating and the second active coating. The silicon doping amount of the second anode active material of the first active coating and the second active coating can be calculated according to the mass percentage M Si of silicon element in the silicon-carbon anode material in the negative electrode tab, and the areal density ratio R σ of the areal density of the outer active coating and the areal density of the inner active coating of the negative electrode tab; according to the silicon doping amount of the second anode active material, the masses of the silicon-carbon anode material and the first anode active material of the inner active coating are calculated respectively; the second anode active material of the inner active coating is prepared according to the masses of the silicon-carbon anode material and the first anode active material.

[0071] In one embodiment, according to the areal density ratio R σ of the areal density of the outer active coating 112 and the areal density of the inner active coating 111 of the negative electrode tab, and the mass percentage M Si of silicon element in the silicon-carbon anode material in the negative electrode tab, on the premise that the mass percentage M Si of silicon element in the silicon-carbon anode material in the negative electrode tab is determined, the areal density ratio R σThe smaller (the larger the proportion of the second negative electrode active material), the smaller the mass percentage of silicon element in the inner active coating of the silicon-carbon negative electrode material, and the surface density ratio R σ The larger (the smaller the proportion of the second negative electrode active material), the larger the mass percentage of silicon element in the inner active coating of the silicon-carbon negative electrode material.

[0072] In one embodiment, the larger the mass percentage of silicon element in the inner active coating of the silicon-carbon negative electrode material, the larger 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 and the inner active coating 111 of the negative electrode plate σ , and the mass percentage M of silicon element in the silicon-carbon negative electrode material in the negative electrode plate Si .

[0073] In one embodiment, the surface density difference between the surface density of the first active coating 11 and the surface density of the second active coating 12 is , where . The surface density of the first active coating 11 and the surface density of the second active coating 12 differ by 2 g / m 2 ~4 g / m 2 , which can significantly improve the lithium deposition phenomenon at the crease in the arc area 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 performance of the lithium-ion battery is not obvious.

[0074] See Figure 1 , the first active coating 11 includes at least one first type of wire groove 110, and the second active coating 12 includes at least one second type of wire groove 120. The wire groove parameters of the first type of wire groove 110 and the second type of wire groove 120 include the wire groove depth 1101, the wire groove spacing 1102, and the wire groove width 1103.

[0075] In one embodiment, the wire groove depth of the first type of wire groove 110 is greater than the wire groove depth of the second type of wire groove 120.

[0076] In one embodiment, the wire groove depth of the first type of wire groove is D A , where 20%*H 负 ≤D A ≤40%*H 负 , H 负 is the total thickness of the negative electrode plate after double rolling; the wire groove depth of the second type of wire groove is D B , where 20%*H 负 ≤D B ≤30%*H 负 .

[0077] In one embodiment, the wire groove depth of the first type of wire groove is D A , where D A<(6 / 7)*H 负-A , H 负-A is the total thickness of the first active coating after the pair of rollers; the groove depth of the second type of wire groove is D B , where D B <(6 / 7)*H 负-B , H 负-B is the total thickness of the second active coating after the pair of rollers.

[0078] In one embodiment, the total thickness H of the negative electrode tab after the pair of rollers 负 = the total thickness H of the first active coating after the pair of rollers 负-A + the total thickness H of the second active coating after the pair of rollers 负-B + the thickness of the negative electrode current collector.

[0079] In one embodiment, the groove pitch of the first type of wire groove 110 is less than the groove pitch of the second type of wire groove 120.

[0080] In one embodiment, the groove pitch of the first type of wire groove is I A , where 0.5 mm ≤ I A ≤ 2 mm; the groove pitch of the second type of wire groove is I B , where 1.5 mm ≤ I B ≤ 3 mm.

[0081] In one embodiment, the groove width of the wire groove is corresponding to the groove depth of the wire groove and shows a linear growth relationship. The deeper the groove depth of the wire groove, the larger the groove width. When the groove depth of the wire groove is 20%*H 负 , the corresponding groove width is 73 microns to 80 microns; when the groove depth of the wire groove is 30%*H 负 , the corresponding groove width is 88 microns to 95 microns; when the groove depth of the wire groove is 40%*H 负 , the corresponding groove width is 103 microns to 110 microns.

[0082] In one embodiment, laser etching technology can be used to laser etch the negative electrode tab after the pair of rollers. According to the groove depth and groove pitch of the first type of wire groove 110, a plurality of first type of wire grooves 110 are laser etched on the first active coating 11 of the negative electrode tab 1; according to the groove depth and groove pitch of the second type of wire groove 120, a plurality of second type of wire grooves 120 are laser etched on the second active coating 12 of the negative electrode tab 1. The plurality of first type of wire grooves 110 of the first active coating 11 and the plurality of second type of wire grooves 120 of the second active coating 12 can store part of the electrolyte and improve the cycling performance of the lithium-ion battery.

[0083] In one embodiment, the groove depth and groove spacing of the first type of wire grooves 110 and the second type of wire grooves 120 can be calculated based on the target CB (Cell Balance) value of the negative electrode plate and the positive electrode plate after laser etching (referring to the margin by which the negative electrode capacity exceeds the positive electrode capacity within the same stage and under the same conditions, which can also be referred to as the N / P value).

[0084] In one embodiment, the surface density of the outer active coating 112 is small and the outer active coating 112 is thin. According to the groove spacing I of the first type of wire grooves 110 A , the groove depth D of the wire grooves A , where 20%*H 负 ≤D A ≤40%*H 负 , when laser etching the negative electrode plate, the laser passes through the outer active coating 112 and reaches the inner active coating 111. If the groove depth D of the wire grooves A is too large and the distance from the negative electrode current collector copper foil is close, it is easy to cause the risk of micro short circuit. Therefore, the groove depth of the first type of wire grooves is D A , where D A <(6 / 7)*H 负-A , and H 负-A is the total thickness of the first active coating after double rolling.

[0085] In one embodiment, in a system where the surface density of the positive electrode plate of the lithium-ion battery is less than 120 g / m 2 , the negative electrode plate uses double coating. Multiple first type of wire grooves 110 are laser etched on the first active coating 11 of the negative electrode plate and multiple second type of wire grooves 120 are laser etched on the second active coating 12 of the negative electrode plate, and the normal temperature kinetic window of the lithium-ion battery is only improved by 0.1C. In a system where the surface density of the positive electrode plate of the lithium-ion battery is greater than 200 g / m 2 , the negative electrode plate uses double coating. Multiple first type of wire grooves 110 are laser etched on the first active coating 11 of the negative electrode plate and multiple second type of wire grooves 120 are laser etched on the second active coating 12 of the negative electrode plate, and the improvement effect on the normal temperature kinetics of the lithium-ion battery is obvious, and the normal temperature kinetic window of the lithium-ion battery is increased by more than 0.3C.

[0086] In one embodiment, the areal density of the first active coating 11 is greater than that of the second active coating 12. To avoid the phenomenon of lithium plating caused by insufficient N / P value, the groove depth of the first type of wire grooves 110 can be greater than that of the second type of wire grooves 120; and / or, the groove pitch of the first type of wire grooves 110 can be less than that of the second type of wire grooves 120; and / or, the groove width of the first type of wire grooves 110 can be greater than that of the second type of wire grooves 120; so that the areal density loss caused by laser etching multiple first type of wire grooves 110 in the first active coating 11 is larger, and the areal density loss caused by laser etching multiple second type of wire grooves 120 in the second active coating 12 is smaller, such that the total volume (total capacity) of the multiple first type of wire grooves 110 in the first active coating 11 is greater than the total volume (total capacity) of the multiple second type of wire grooves 120 in the second active coating 12.

[0087] For the negative electrode tab of the embodiment of the present application, a first active coating is coated on one side of the negative electrode current collector of the negative electrode tab, and a second active coating is coated on the other side; the first active coating is the active coating that is covered by the positive electrode tab when the negative electrode tab is wound, and the areal density of the first active coating is greater than that of the second active coating; the first active coating and the second active coating 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; the outer active coating includes a first negative electrode active material, and the inner active coating 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 areal density of the outer active coating is less than that of the inner active coating; it can improve the kinetics of the lithium-ion battery, increase the energy density of the lithium-ion battery, and meet the capacity performance of the lithium-ion battery; it can effectively alleviate the reduction of the N / P value caused by the decrease in the contact surface due to the bending of the negative electrode tab in the arc area after winding, reduce the difference between the N / P value in the arc area and the N / P value in the flat area of the negative electrode tab after winding, and can effectively prevent the phenomenon of lithium plating in the arc area of the negative electrode tab of the lithium-ion battery, greatly improving the high-temperature performance of the lithium-ion battery and increasing the cycle performance of the lithium-ion battery.

[0088] Furthermore, for the negative electrode tab of the embodiment of the present application, a double-layer coating is used to construct an outer active coating of a graphite-based negative electrode active material and an inner active coating of a high-silicon-based negative electrode active material. The mass percentage of silicon element in the high-silicon-based negative electrode active material of the inner active coating in the negative electrode tab (the silicon element in the silicon-carbon negative electrode material of the second negative electrode active material of the inner active coating in the negative electrode tab) is M Si , where 3% ≤ M Si≤20%; On the premise of ensuring the high energy density of the lithium-ion battery, it effectively alleviates the reduction of the N / P value caused by the decrease in the contact surface due to the bending of the negative electrode sheet in the winding arc area, significantly improves the lithium deposition phenomenon in the arc area of the negative electrode sheet of the lithium-ion battery, can effectively prevent the lithium deposition phenomenon in the arc area of the negative electrode sheet of the lithium-ion battery, improves the cycle performance of the lithium-ion battery, and provides a direction for solving the lithium deposition problem in the arc area of the high-silicon negative electrode material development direction of the lithium-ion battery.

[0089] Further, the negative electrode sheet of the embodiment of the present application adopts double-layer coating to construct the outer active coating of the graphite-based negative electrode active material and the inner active coating of the high-silicon-based negative electrode active material. 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 reduction of the 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.

[0090] Further, the negative electrode sheet of the embodiment of the present application adopts yin-yang 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 covered 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 , where, ; It can effectively alleviate the reduction of the 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.

[0091] Further, for the negative electrode sheet of the embodiment of the present application, according to the fact that the surface density of the first active coating is greater than the surface density of the second active coating, at least one first type of groove is etched on the first active coating of the negative electrode sheet, and at least one second type of groove is etched on the second active coating of the negative electrode sheet. The liquid retention amount in the arc area is increased through the grooves, and at the same time, more lithium insertion channels are added for the positive electrode, which can effectively improve the lithium deposition phenomenon in the arc area of the negative electrode sheet 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.

[0092] Figure 3 is a schematic structural diagram of the height direction section of the wound battery cell after the negative electrode sheet, the separator and the positive electrode sheet of the embodiment of the present application are wound.

[0093] See Figure 2 and Figure 3, an embodiment of the present application provides a wound battery cell 40, which includes a positive electrode tab 2, a separator 3, and the negative electrode tab 1 described above. After the positive electrode tab 2, the separator 3, and the negative electrode tab 1 are stacked, they are wound to form a wound battery cell 40. The wound battery cell 40 includes an arc region 401 and a flat region 402.

[0094] Figure 4 It is a partial schematic diagram of the width direction section of the separator shown in the embodiment of the present application.

[0095] See Figure 4 , the separator 3 is an oil-based roll-coated separator with a porous ceramic and an oil-based coating, and includes a polymer layer 301, a porous ceramic layer 302, and a base film layer 303.

[0096] In one embodiment, the porous ceramic layer 302 includes porous ceramic, and the porous ceramic can be porous alumina (Al 2 O 3 ) ceramic.

[0097] In one embodiment, the base film layer 303 includes a porous PP (polypropylene) base film, and the polymer layer 301 is an oil-based coating that contacts the electrode tab face to face.

[0098] In one embodiment, after the positive electrode tab 2, the separator 3, and the negative electrode tab 1 are stacked and wound, the bending curvature of the negative electrode tab 1 and the positive electrode tab 2 in the arc region of the wound battery cell 40 is relatively large, the stress increases, the liquid retention amount is less, and the porous ceramic layer 302 of the separator 3 can effectively increase the liquid retention amount of the negative electrode tab 1 and the positive electrode tab 2, and can effectively improve the lithium deposition phenomenon in the arc region of the negative electrode tab of the lithium-ion battery.

[0099] In one embodiment, after the positive electrode tab 2, the separator 3, and the negative electrode tab 1 are stacked and wound, the adhesion force between the positive electrode tab 2 and the negative electrode tab 1 in the arc region is weak. After chemical forming and hot pressing, the oil-based coating of the polymer layer 301 melts, which can increase the viscosity, significantly improve the adhesion between the positive electrode tab and the negative electrode tab in the arc region, reduce the contact gap between the positive electrode tab and the negative electrode tab, shorten the lithium ion diffusion distance, the porous base film improves the lithium ion transmission rate, and the porous ceramic can improve the liquid retention performance and the safety of the battery cell in the arc region, can effectively improve the lithium deposition phenomenon in the arc region of the negative electrode tab of the lithium-ion battery, and improve the comprehensive performance of the lithium-ion battery.

[0100] An embodiment of the present application also provides a lithium-ion battery, which includes the wound battery cell described above, or includes the negative electrode tab described above.

[0101] The present invention will be further described below through embodiments.

[0102] Example 1:

[0103] Example 1 is used to illustrate the battery and its preparation method according to the embodiments of the present application, including the following steps:

[0104] 1) Preparation of the positive electrode sheet:

[0105] Positive electrode formula: The positive electrode active material lithium cobalt oxide (LCO) is 94wt% - 97.2%, carbon nanotubes (CNT) is 0.05wt% - 0.25wt%, conductive carbon black (SP) is 0.5wt% - 1.1wt%, and polyvinylidene fluoride (PVDF) is 1.0wt% - 1.7wt%.

[0106] Mix the positive electrode active material lithium cobalt oxide: carbon nanotubes: conductive carbon black: polyvinylidene fluoride in a weight ratio of 98.2:0.3:0.6:0.9 in N-methylpyrrolidone solvent (NMP) to form a uniform positive electrode slurry; coat the positive electrode slurry on the positive electrode current collector Al (aluminum) foil, dry it, and cold press it to obtain the positive electrode sheet.

[0107] 2) Preparation of the negative electrode sheet:

[0108] Graphite and silicon-carbon negative electrode material are stirred and mixed in corresponding proportions to a capacity of 400mAh / g - 650mAh / g. The specific capacity of graphite is 360mAh / g, and the specific capacity of the silicon-carbon negative electrode material is 1800mAh / g. PAA:SBR:CMC-Li:CNT:SP = 1.5%:1.2%:1.0%:0.1%:0.2% by mass ratio are dispersed in deionized water to form a uniform outer coating slurry and inner coating slurry; using a double-layer coating process and a positive-negative side coating process, coat the outer coating slurry and the inner coating slurry on one side of the copper foil to form a first active coating, and coat the outer coating slurry and the inner coating slurry on the other side of the copper foil to form a second active coating, and then through drying and cold pressing, the negative electrode sheet is prepared.

[0109] 3) Fabrication of the battery:

[0110] Stack the positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator in the middle of the positive electrode sheet and the negative electrode sheet to play an isolation role, and then wind it into a bare battery cell. Place the bare battery cell in an outer packaging bag, dry it at high temperature, inject the corresponding electrolyte, and complete the preparation of the lithium-ion battery through processes such as vacuum packaging, standing, formation, and shaping, and obtain the lithium-ion battery in sequence.

[0111] The lithium-ion batteries and their preparation methods in Examples 2 - 29 include most of the operation steps in Example 1. For the specific differences, please refer to the specific parameters in Tables 1 - 6.

[0112] The silicon doping amount in Tables 1 - 6 is the mass percentage of silicon element in the negative electrode sheet of the lithium-ion battery, which is the mass percentage M of silicon element in the silicon-carbon negative electrode material of the inner active coating in the negative electrode sheet.Si .

[0113] The double-coated layers in Tables 1 - 6 indicate that the first and second active coatings of the negative electrode plate 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.

[0114] The outer layer graphite in Tables 1 - 6 indicates that the negative electrode active material (the first negative electrode active material) of the outer active coating of the first and second active coatings of the negative electrode plate of the lithium-ion battery is graphite.

[0115] The inner layer silicon carbide in Tables 1 - 6 indicates that the negative electrode active material (the second negative electrode active material) of the inner active coating of the first and second active coatings of the negative electrode plate of the lithium-ion battery is a graphite + silicon carbide negative electrode material.

[0116] The surface density ratio in Tables 1 - 6 is the surface density ratio R of the surface density of the outer active coating to the surface density of the inner active coating of the first and second active coatings of the negative electrode plate of the lithium-ion battery. σ .

[0117] The surface density difference in Tables 1 - 6 is the surface density difference between the surface density of the first active coating and the surface density of the second active coating of the negative electrode plate of the lithium-ion battery. .

[0118] The groove depth of the A-type grooves in Tables 1 - 6 indicates the groove depth of the first type of grooves of the first active coating of the negative electrode plate of the lithium-ion battery.

[0119] The groove depth of the B-type grooves in Tables 1 - 6 indicates the groove depth of the second type of grooves of the second active coating of the negative electrode plate of the lithium-ion battery.

[0120] The groove pitch of the A-type grooves in Tables 1 - 6 indicates the groove pitch of the first type of grooves of the first active coating of the negative electrode plate of the lithium-ion battery.

[0121] The groove pitch of the B-type grooves in Tables 1 - 6 indicates the groove pitch of the second type of grooves of the second active coating of the negative electrode plate of the lithium-ion battery.

[0122] The lithium-ion batteries of Examples 1 - 29 were subjected to a cycle test, and the capacity (mAh, milliampere-hour), lithium deposition in the circular arc area at 600 cycles, capacity retention rate at 600 cycles at room temperature (25 degrees Celsius), expansion rate at 600 cycles at room temperature, capacity retention rate at 400 cycles at 45 °C (degrees Celsius), expansion rate at 400 cycles at 45 °C, net liquid coefficient (g / mAh), and weighted N / P value of the lithium-ion batteries of Examples 1 - 29 as shown in Tables 1 - 6 were obtained.

[0123] The weighted N / P values in Tables 1 - 6 are the N / P values obtained by averaging the N / P values in the arc region and the straight region, and are the average N / P values of the wound battery cells.

[0124] The net liquid coefficient in Tables 1 - 6 is the mass net liquid coefficient, that is, how many grams of electrolyte correspond to the capacity exerted, which is the gram - capacity value.

[0125] The cycle test includes:

[0126] Step 1: Charge at 0.5C to 4.55V, with a cut - off current of 0.05C, and let it stand for 10 min (minutes);

[0127] Step 2: Discharge at 0.2C to 3.0V, and record the discharge capacity C 0 as the initial capacity;

[0128] Step 3: Charge at 1.0C with constant current and constant voltage to 4.55V, with a cut - off current of 0.05C, and let it stand for 10 min;

[0129] Step 4: Discharge at 0.5C to 3.0V, and let it stand for 10 min;

[0130] Step 5: Repeat Step 3 and Step 4 for 600 times, and record the discharge data as well as the voltage, internal resistance, and thickness at 50 times / 100 times / 200 times / 300 times / 400 times / 600 times.

[0131] Table 1:

[0132]

[0133] Table 2:

[0134]

[0135] Table 3:

[0136]

[0137] Table 4:

[0138]

[0139] Table 5:

[0140]

[0141] Table 6:

[0142]

[0143] According to the data of Example 1 and Example 2 in Table 1, double-layer coating is used for the first active coating and the second active coating, including an inner active coating (inner layer silicon carbide) and an outer active coating (outer layer graphite), which can effectively prevent the phenomenon of lithium deposition in the arc area of the negative electrode sheet 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.

[0144] According to the data of Example 3 and Example 1 in Table 1, increasing the areal density of the outer active coating (outer layer graphite) can effectively prevent the phenomenon of lithium deposition in the arc area of the negative electrode sheet of the lithium-ion battery. However, to ensure the capacity of the lithium-ion battery, the silicon doping amount of the inner active coating needs to be correspondingly increased; when the silicon doping amount of the inner active coating is increased, the expansion rate of the lithium-ion battery will increase sharply, the expansion rate of the lithium-ion battery deteriorates significantly, and the safety of the lithium-ion battery is reduced.

[0145] According to the data of Example 4 and Example 1 in Table 1, the areal density difference between the areal density of the first active coating and the areal density of the second active coating 12 =5g / m 2 , when the areal density difference between the areal density of the first active coating and the areal density of the second active coating is too large, the capacity retention rate at 45°C decreases significantly, the expansion rate at 45°C increases significantly, and the high-temperature performance of the lithium-ion battery deteriorates significantly.

[0146] According to the data of Example 5 and Example 1 in Table 1, the separator of Example 1 is an oil-based roll-coated separator with a porous base film coated with porous ceramics and an oily coating, which can effectively improve the phenomenon of lithium deposition in the arc area of the negative electrode sheet of the lithium-ion battery and enhance the comprehensive performance of the lithium-ion battery; Example 5 uses a separator without porous ceramics, and the capacity retention rate of the corresponding lithium-ion battery in Example 5 decreases, the expansion rate increases significantly, lithium deposition appears in the arc area of the negative electrode sheet of the lithium-ion battery, and the safety of the lithium-ion battery is reduced.

[0147] 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 grooves. Although it can reduce the weighted N / P value of the lithium-ion battery in Example 6, the capacity of the lithium-ion battery in Example 6 is poorly exerted, there is slight lithium deposition, the expansion rate increases significantly, and the performance of the lithium-ion battery in Example 6 decreases.

[0148] According to the data of Example 7 in Table 2 and Example 1 in Table 1, the first active coating of Example 7 etches more first-type grooves. The weighted N / P value of the lithium-ion battery in Example 7 decreases, the performance of the lithium-ion battery in Example 7 does not deteriorate significantly, but the capacity loss of the lithium-ion battery in Example 7 is obvious, which affects the specific capacity exertion, and the expansion rate increases.

[0149] According to the data of Example 8 in Table 2 and Example 1 in Table 1, the groove depths of the first type of wire grooves in the first active coating and the second type of wire grooves in the second active coating are reduced, and the groove depths of the first type of wire grooves and the second type of wire grooves are equal. The amount of electrolyte stored in the wire grooves of Example 8 is reduced, the weighted N / P value of the lithium-ion battery in Example 8 increases, the capacity retention rate decreases, the swelling rate increases significantly, and the high-temperature performance of the lithium-ion battery in Example 8 decreases.

[0150] 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 tab in Example 9 do not adopt double-layer coating. In Example 9, lithium deposition in the arc area of the lithium-ion battery is obvious, the capacity retention rate decreases, and the swelling rate increases significantly. Therefore, the first active coating and the second active coating of the negative electrode tab of the lithium-ion battery adopt double-layer coating, including an inner active coating (inner layer of silicon carbide) and an outer active coating (outer layer of graphite), which can effectively prevent lithium deposition in the arc area of the negative electrode tab 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.

[0151] According to the data of Examples 10-18, although increasing the silicon doping amount of the inner active coating of the first active coating and the second active coating of the negative electrode tab can improve the energy density of the lithium-ion battery, with the increase of the silicon doping amount, the lithium deposition phenomenon in the arc area of the negative electrode tab of the lithium-ion battery becomes gradually serious, the capacity retention rate gradually decreases, and the swelling rate gradually increases.

[0152] According to the data of Examples 19-24, 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 area caused by the winding and bending of the negative electrode tab and the positive electrode tab, significantly and effectively improve the lithium deposition phenomenon in the arc area of the negative electrode tab of the lithium-ion battery, and reduce the swelling rate of the lithium-ion battery.

[0153] According to the data of Examples 25-29, increasing the surface density of the first active coating, with the increase of the surface density difference between the first active coating and the second active coating, can more effectively improve the lithium deposition phenomenon in the arc area of the negative electrode tab of the lithium-ion battery and reduce the swelling rate of the lithium-ion battery. However, if the surface density difference between the first active coating and the second active coating is too large, the capacity retention rate will decrease.

[0154] Therefore, the technical solution of the embodiments of the present application, by adopting yin-yang surface coating, coats the first active coating on one side of the negative electrode current collector and coats the second active coating on the other side of the negative electrode current collector. The first active coating is the active coating covered by the positive electrode tab when the negative electrode tab 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 , wherein, ; a double-layer coating is used to construct an outer active coating for the graphite-based anode active material and an inner active coating for the high-silicon-based anode active material on the first active coating and the second active coating, and the areal density ratio of the outer active coating to the inner active coating is R σ , wherein, (1 / 4) ≤ R σ ≤ (2 / 3); and at least one first type of groove is etched in the first active coating, and at least one second type of groove is etched in the second active coating of the anode electrode sheet; a separator with porous ceramics is used to increase the liquid retention amount in the arc area of the electrode sheet; it can effectively alleviate the decrease of the N / P value in the arc area caused by the winding and bending of the anode electrode sheet and the cathode electrode sheet, increase the liquid retention amount in the arc area, and at the same time add more lithium insertion channels for the cathode, which can effectively improve the lithium deposition phenomenon in the arc area of the anode electrode sheet 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.

[0155] The embodiments of the present application have been described above. The above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technologies in the market, or to enable other ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A wound battery cell, characterized in that: The invention comprises a positive electrode sheet, a separator and a negative electrode sheet, wherein the positive electrode sheet, the separator and the negative electrode sheet are stacked and wound to form the wound battery cell, wherein the negative electrode sheet comprises a negative electrode collector, and a first active coating applied on one side of the negative electrode collector and a second active coating applied on the other side of the negative electrode 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. 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 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, wherein the first negative electrode active material includes one or more of graphite, hard carbon, and soft carbon; The inner active coating comprises a second negative electrode active material, the second negative electrode active material comprises a silicon-carbon negative electrode material and the first negative electrode active material, and the mass percentage of silicon element in the silicon-carbon negative electrode material in the negative electrode sheet is M Si , wherein the mass percentage is the average silicon doping amount of the silicon element in the silicon-carbon negative electrode material in the first active coating and the second active coating, ; The surface density of the outer active coating is less than the surface density of the inner active coating, and the surface density ratio of the outer active coating to the surface density of the inner active coating is ,in, ; The first active coating includes at least one first type of wire groove, and the second active coating includes at least one second type of wire groove, wherein the wire groove depth of the first type of wire groove is greater than the wire groove depth of the second type of wire groove; and / or the wire groove spacing of the first type of wire groove is smaller than the wire groove spacing of the second type of wire groove.

2. The wound battery cell 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.

3. The wound battery cell according to claim 1, 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, .

4. The wound battery cell according to claim 3, 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.

5. The wound battery cell according to claim 1, 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.

6. The wound battery cell according to claim 1, characterized in that: The separator includes a porous ceramic layer.

7. A lithium ion battery, characterized in that: It comprises a wound battery cell as described in any one of claims 1 to 6.

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