Roll core and battery

Abstract

The utility model provides a roll core and a battery, relates to the technical field of batteries, and is used for solving the technical problems of low safety and low energy density of the roll core in the related art. The roll core is characterized in that a positive electrode winding starting section of a positive electrode plate and a negative electrode winding starting section of a negative electrode plate respectively extend towards different directions along a first direction; the inner side of the positive electrode winding starting section along the second direction is directly opposite to the inner side of the negative electrode winding starting section along the second direction; in the second direction, the negative plate comprises a first surface and a second surface which are oppositely arranged, a first diaphragm is arranged between the first surface and the positive plate, and a second diaphragm is arranged between the second surface and the positive plate; the first diaphragm and the second diaphragm extend out of the negative plate from the negative winding starting section; and the negative winding starting section, the first diaphragm and the second diaphragm are compounded to form a composite region. And the negative electrode double-sided coating design is adopted, and the composite area is arranged at the end part of the negative electrode sheet at the innermost ring of the roll core, so that the negative electrode sheet is prevented from being exposed due to diaphragm shrinkage, and the short circuit of the battery is avoided.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a winding core and a battery. Background Art

[0002] Lithium-ion batteries are increasingly used. As portable devices become more intelligent and multifunctional, they require higher energy density. In related technologies, the negative electrode on the innermost coil of the core is single-sided, with the innermost two folds being single-sided, leaving a large area without active material, limiting the battery's energy density. Furthermore, during use, the separator can shrink, exposing the negative electrode. This can cause a short circuit between the positive and negative electrodes, compromising battery safety. Utility Model Content

[0003] In view of the above problems, embodiments of the present application provide a winding core and a battery to solve the problems of low safety and low energy density of winding cores in related technologies.

[0004] In order to achieve the above objectives, the embodiments of the present application provide the following technical solutions:

[0005] An embodiment of the present application provides a winding core, which includes: a positive electrode sheet and a negative electrode sheet, along a first direction, the positive electrode winding starting section of the positive electrode sheet and the negative electrode winding starting section of the negative electrode sheet extend in different directions respectively, and the inner side of the positive electrode winding starting section along a second direction is directly opposite to the inner side of the negative electrode winding starting section along the second direction; along the second direction, the negative electrode sheet includes a first surface and a second surface arranged opposite to each other, a first separator is arranged between the first surface and the positive electrode sheet, and a second separator is arranged between the second surface and the positive electrode sheet, the first separator and the second separator both extend from the negative electrode winding starting section to the negative electrode sheet, and the negative electrode winding starting section, the first separator and the second separator are combined to form a composite area; wherein, the first direction is perpendicular to the second direction.

[0006] In one embodiment of the present application, the composite region includes a first composite region, and the first composite region includes the first separator, the negative electrode winding starting section, and the second separator sequentially arranged along the second direction.

[0007] In one embodiment of the present application, the composite region includes a second composite region, and the second composite region includes the first separator and the second separator extending from the negative electrode sheet from the negative electrode winding starting section.

[0008] In one embodiment of the present application, in the first direction, the first composite region has a first length M1, and the first length M1 is ≤25 mm.

[0009] In one embodiment of the present application, in the first direction, the second composite region has a second length M2, and the second length M2 is ≤10 mm.

[0010] In one embodiment of the present application, the negative electrode sheet includes a first negative electrode bend portion, and the length of the first negative electrode bend portion from the negative electrode winding starting section is a third length M3; the relationship between the first length M1 and the third length M3 is: M1≤0.5xM3.

[0011] In one embodiment of the present application, a texture structure is provided on the first diaphragm and / or the second diaphragm in the first composite area; and / or a texture structure is provided on the first diaphragm and / or the second diaphragm in the second composite area; the texture structure includes text, letters or geometric figures composed of lines, etc.

[0012] In one embodiment of the present application, the positive electrode sheet includes a first positive electrode bending portion, the first positive electrode bending portion is provided with an insulating layer, and a groove is provided on the positive electrode active layer on the side of the first positive electrode bending portion close to the negative electrode winding starting section, and at least part of the insulating layer is located in the groove; the length of the part of the insulating layer located outside the groove in the first direction is a third length Y1, and the third length Y1 is ≥0.2 mm.

[0013] In one embodiment of the present application, the first separator and the second separator bonded to each other in the second composite region are folded back in a direction opposite to the winding direction of the negative electrode sheet to form a folded segment, and the length of the folded segment is ≤10 mm.

[0014] In one embodiment of the present application, in the first direction, a distance between an end portion of the insulating layer outside the groove and an end portion of the folded segment is a first distance Y2, and the first distance Y2 is ≥0.1 mm.

[0015] In one embodiment of the present application, in the first direction, the distance between the end of the folded segment and the edge of the groove is a second distance Y3, and the second distance Y3 is ≥0.1 mm.

[0016] In one embodiment of the present application, in the first direction, the distance between the end of the negative electrode winding starting section in the first composite region and the edge of the groove is a third distance Y4, and the third distance Y4 is ≥0.2 mm.

[0017] In one embodiment of the present application, in the first direction, the distance between the end of the negative electrode winding starting section in the first composite region and the first positive electrode bending portion is a fourth distance Y5, and the fourth distance Y5 is ≥1.5 mm.

[0018] An embodiment of the present application further provides a battery, which includes the winding core described above.

[0019] The present application provides a winding core and a battery, the winding core comprising: a positive electrode sheet and a negative electrode sheet. Along a first direction, the positive electrode winding starting section of the positive electrode sheet and the negative electrode winding starting section of the negative electrode sheet extend in different directions, and the inner side of the positive electrode winding starting section along a second direction is directly opposite the inner side of the negative electrode winding starting section along the second direction. Along a second direction, the negative electrode sheet comprises a first surface and a second surface disposed opposite each other, a first separator disposed between the first surface and the positive electrode sheet, and a second separator disposed between the second surface and the positive electrode sheet. The first separator and the second separator both extend from the negative electrode winding starting section to the negative electrode sheet, and the negative electrode winding starting section, the first separator, and the second separator are combined to form a composite region. The first and second directions are perpendicular. A double-sided negative electrode coating design is employed to mitigate lithium plating issues caused by insufficient compaction in a single-sided arrangement. Furthermore, the relative positioning of the positive electrode winding starting section and the negative electrode winding starting section of the winding core can reduce the thickness of the innermost circle of the winding core, thereby improving the space utilization of the battery. A composite area is also provided at the end of the negative electrode sheet of the innermost circle of the winding core, which composites the "negative electrode sheet-diaphragm" and "diaphragm-diaphragm" together to protect the end of the negative electrode sheet and prevent the negative electrode sheet from being exposed due to the shrinkage of the diaphragm during the use of the battery cell, thereby avoiding battery short circuit and improving battery safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0021] Figure 1 A schematic diagram of the structure of the negative electrode sheet of the winding core provided in an embodiment of the present application;

[0022] Figure 2 A schematic diagram of the structure of the winding core provided in an embodiment of the present application;

[0023] Figure 3 Schematic diagram of the structure of the end of the negative electrode sheet of the winding core provided in the embodiment of the present application Figure 1 ;

[0024] Figure 4 Schematic diagram of the structure of the end of the negative electrode sheet of the winding core provided in the embodiment of the present application Figure 2 ;

[0025] Figure 5 Schematic diagram of the local structure of the innermost circle of the winding core provided in the embodiment of the present application Figure 1 ;

[0026] Figure 6 Schematic diagram of the local structure of the innermost circle of the winding core provided in the embodiment of the present application Figure 2 ;

[0027] Figure 7 Schematic diagram of the local structure of the innermost circle of the winding core provided in the embodiment of the present application Figure 3 ;

[0028] Figure 8 A schematic diagram of a winding core in the related art;

[0029] Figure 9 This is a comparison chart of the energy density of the control group and the experimental group provided in the examples of this application.

[0030] Reference numerals:

[0031] 100: negative electrode current collector;

[0032] 110: negative electrode sheet; 120: positive electrode sheet; 111: negative electrode winding starting section; 121: positive electrode winding starting section;

[0033] 200: negative electrode coating;

[0034] 301: first diaphragm; 302: second diaphragm;

[0035] 400: grain structure;

[0036] 500: positive electrode current collector;

[0037] 600: positive electrode coating;

[0038] 700: groove;

[0039] 800: insulation layer;

[0040] A: composite area; A1: first composite area; A2: second composite area. DETAILED DESCRIPTION

[0041] In order to make the above-mentioned purposes, features and advantages of the embodiments of the present application more obvious and easy to understand, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0042] refer to Figure 1 、 Figure 2 and Figure 5 , Figure 1 This is a schematic diagram of the structure of the negative electrode sheet of the winding core provided in an embodiment of the present application. Figure 2 This is a schematic diagram of the structure of the winding core provided in the embodiment of the present application. Figure 5 Schematic diagram of the local structure of the innermost circle of the winding core provided in the embodiment of the present application Figure 1 ; The winding core provided in the embodiment of the present application includes: a positive electrode sheet 120 and a negative electrode sheet 110, the positive electrode sheet 120 includes a positive electrode collector 500, and the front and back sides of the positive electrode collector 500 are both provided with a positive electrode coating 600; the negative electrode sheet 110 includes a negative electrode collector 100, and the front and back sides of the negative electrode collector 100 are both provided with a negative electrode coating 200.

[0043] Both the positive electrode sheet 120 and the negative electrode sheet 110 have a head and a tail. The positive and negative electrode sheets of the core are wound from the inside out. The innermost circle of the core is the first circle where the positive and negative electrode sheets start to be wound. For the core, the heads of the positive electrode sheet 120 and the negative electrode sheet 110 are both arranged at the innermost circle of the core; the positive electrode sheet 120 has a positive electrode winding starting section 121, and the negative electrode sheet 110 has a negative electrode winding starting section 111. The positive electrode winding starting section 121 refers to the head of the positive electrode sheet 120, and the negative electrode winding starting section 111 refers to the head of the negative electrode sheet 110.

[0044] Along the first direction, the positive electrode winding starting section 121 and the negative electrode winding starting section 111 extend in different directions respectively, and the inner side of the positive electrode winding starting section 121 along the second direction is directly opposite to the inner side of the negative electrode winding starting section 111 along the second direction, so that the innermost circle of the winding core forms a pole piece plug-in structure.

[0045] For the positive electrode sheet 120 and the negative electrode sheet 110, the first direction refers to the length direction of the positive electrode sheet 120 and the negative electrode sheet 110, that is, Figure 1 and Figure 2 For the core, the first direction refers to the width direction of the core, which is also the X direction. Figure 2 and Figure 5 The X direction shown in .

[0046] For the positive electrode sheet 120 and the negative electrode sheet 110, the second direction refers to the thickness direction of the positive electrode sheet 120 and the negative electrode sheet 110, that is, Figure 1 and Figure 2 For the core, the second direction refers to the thickness direction of the core, that is, Figure 2 and Figure 5 In the Y direction shown in , the second direction is perpendicular to the first direction.

[0047] Along the second direction, the negative electrode sheet 110 includes a first surface and a second surface arranged opposite to each other, a first separator 301 is arranged between the first surface and the positive electrode sheet 120, and a second separator 302 is arranged between the second surface and the positive electrode sheet 120; that is, the front and back sides of the negative electrode sheet 110 are respectively provided with the first separator 301 and the second separator 302, and the negative electrode coating 200 on the front and the negative electrode coating 200 on the back are respectively provided with the first separator 301 and the second separator 302.

[0048] The positive electrode sheet 120 includes multiple bends arranged sequentially from the inside out. The first positive bend of the positive electrode sheet 120 is located at the innermost circle of the winding core and is the first bend of the positive electrode sheet 120. The negative electrode winding starting section 111 is opposite the first positive bend of the positive electrode sheet 120 and extends into the first positive bend. Similarly, the negative electrode sheet 110 includes multiple bends arranged sequentially from the inside out. The first negative bend of the negative electrode sheet 110 is located at the innermost circle of the winding core and is the first bend of the negative electrode sheet 110. The positive electrode winding starting section 121 is opposite the first negative bend of the negative electrode sheet 110 and extends into the first negative bend. This creates a pole piece interleaving structure at the innermost circle of the winding core.

[0049] The first separator 301 and the second separator 302 both extend from the negative electrode winding starting section 111 to the negative electrode sheet 110 and are bonded to each other, forming a composite area A in the negative electrode winding starting section 111. The composite area A includes: the negative electrode winding starting section 111, the first separator 301 and the second separator 302; that is, the first separator 301 and the second separator 302 extending from the negative electrode sheet 110 are used to wrap the negative electrode winding starting section to prevent the negative electrode sheet 110 from being exposed.

[0050] The winding core provided in the embodiment of the present application includes a positive electrode sheet 120 and a negative electrode sheet 110. Along the first direction, the positive electrode winding starting section 121 of the positive electrode sheet 120 and the negative electrode winding starting section 111 of the negative electrode sheet 110 extend in different directions respectively, and the inner side of the positive electrode winding starting section 121 along the second direction is directly opposite to the inner side of the negative electrode winding starting section 111 along the second direction; along the second direction, the negative electrode sheet 110 includes a first surface and a second surface arranged opposite to each other, a first separator 301 is arranged between the first surface and the positive electrode sheet 120, and a second separator 302 is arranged between the second surface and the positive electrode sheet 120; the first separator 301 and the second separator 302 both extend from the negative electrode winding starting section 111 to the negative electrode sheet 110, and the negative electrode winding starting section 111, the first separator 301 and the second separator 302 form a composite area A. The double-sided coating design of the negative electrode mitigates the lithium plating problem caused by insufficient compaction in a single-sided design. It also reduces thickness (eliminating one layer of copper foil and three layers of separator), improving battery space utilization. A composite area is also provided at the end of the negative electrode sheet on the innermost coil to protect the end of the negative electrode sheet 110, preventing it from being exposed due to separator shrinkage during use. This prevents short circuits and improves battery safety.

[0051] Continue to refer Figure 1 In the embodiment of the present application, the composite area A includes a first composite area A1, and the first composite area A1 includes a Figure 1 The negative electrode winding starting section 111, the first separator 301 and the second separator 302 are sequentially arranged (in the X direction shown in FIG), and the "negative electrode sheet-separator" is composited together to protect the end of the negative electrode sheet 110.

[0052] In an embodiment of the present application, the composite area A also includes a second composite area A2, and the second composite area A2 includes a first diaphragm 301 and a second diaphragm 302 extending from the negative electrode sheet 110 from the negative electrode winding starting section 111; wherein, the first diaphragm 301 and the second diaphragm 302 extending from the negative electrode sheet 110 include: a first diaphragm 301 and a second diaphragm 302 with a certain distance, and a first diaphragm 301 and a second diaphragm 302 that are bonded to each other; the "diaphragm-diaphragm" is composited together to protect the end of the negative electrode sheet 110 from direct contact with the positive electrode, while preventing the diaphragm from folding or thermal shrinkage causing a short circuit between the positive and negative electrodes.

[0053] Continue to refer Figure 1 In the embodiment of the present application, in the first direction ( Figure 1 In the X direction shown in FIG, the first composite region A1 has a first length M1, and the first length M1 is ≤ 25 mm. This is to avoid excessive tension on the outer side of the negative electrode sheet 110 causing deformation and affecting battery performance.

[0054] Continue to refer Figure 1 In the embodiment of the present application, in the first direction ( Figure 1 In the X direction shown in FIG, the second composite region A2 has a second length M2, and the second length M2 is ≤ 10 mm. This is to prevent the second composite region A2 from being too long and extending between the positive and negative electrode sheets, thereby preventing the presence of multiple layers of separators between the positive and negative electrode sheets and causing lithium deposition.

[0055] Continue to refer Figure 1 and Figure 2 In the embodiment of the present application, the negative electrode sheet 110 includes a plurality of bent portions arranged sequentially from the inside to the outside. The first negative electrode bent portion is arranged at the innermost circle of the winding core and is the first bent portion of the negative electrode sheet 110. The length from the first negative electrode bent portion of the negative electrode sheet 110 to the negative electrode winding starting section 111 is a third length M3.

[0056] The relationship between the first length M1 and the third length M3 of the first composite area A1 is: M1≤0.5×M3. This prevents the first composite area A1 from being too long, which may cause excessive tension on the outer side of the negative electrode sheet 110 and deformation, thereby affecting battery performance.

[0057] refer to Figure 3 and Figure 4 , Figure 3 Schematic diagram of the structure of the end of the negative electrode sheet of the winding core provided in the embodiment of the present application Figure 1 , Figure 4 Schematic diagram of the structure of the end of the negative electrode sheet of the winding core provided in the embodiment of the present application Figure 2 ; In an embodiment of the present application, a texture structure 400 is provided on the first diaphragm 301 in the first composite area A1, or a texture structure 400 is provided on the second diaphragm 302 in the first composite area A1, or a texture structure 400 is provided on both the first diaphragm 301 and the second diaphragm 302 in the first composite area A1; the texture structure 400 may include text, letters or geometric figures composed of lines, etc., which can enhance the bonding strength of the first composite area A1.

[0058] Similarly, a textured structure 400 is provided on the first diaphragm 301 in the second composite area A2, or a textured structure 400 is provided on the second diaphragm 302 in the second composite area A2, or a textured structure 400 is provided on both the first diaphragm 301 and the second diaphragm 302 in the second composite area A2; the textured structure 400 may include text, letters, or geometric figures composed of lines, etc., and the textured structure 400 can enhance the bonding strength of the second composite area A2.

[0059] Optionally, the texture structure 400 may be provided on both the membranes of the first composite area A1 and the second composite area A2, or the texture structure 400 may be provided on at least one membrane of the first composite area A1 and the second composite area A2.

[0060] Continue to refer Figure 5In the embodiment of the present application, the first separator 301 and the second separator 302 in the second composite area A2 are adhered to each other and folded back in a direction opposite to the winding direction of the negative electrode sheet 110 to form a folded section 130; the folded back first separator 301 and the second separator 302 can make the negative electrode sheet 110 go deeper into the first positive electrode bending portion of the positive electrode sheet 120, thereby improving the internal space utilization.

[0061] The length of the folded section 130 is ≤10 mm. If the folded section 130 is too long, it may easily cause wrinkles, resulting in too many separator layers between the positive and negative electrodes, and too long a lithium ion migration path, which may lead to lithium deposition.

[0062] Continue to refer Figure 5 In the embodiment of the present application, an insulating layer 800 is provided on the inner side of the first positive electrode bend portion close to the negative electrode winding starting section 111, and a groove 700 is provided on the positive electrode active layer on the side of the first positive electrode bend portion close to the negative electrode winding starting section 111. At least part of the insulating layer 800 is provided in the groove 700, and the part of the insulating layer 800 located outside the groove 700 is in the first direction ( Figure 5 The length in the X direction (shown in FIG) is a third length Y1, and the third length Y1 is ≥ 0.2 mm. This ensures that the insulating layer 800 extends beyond the groove 700, preventing the insulating layer 800 from falling off and causing lithium deposition, thereby improving the safety performance of the battery cell.

[0063] It should be noted that the groove 700 is made on the positive electrode active layer by using a laser cleaning or scraper process, and to facilitate the making of the groove 700 , a portion of the positive electrode active material is retained at the bottom of the groove 700 .

[0064] The depth of the groove 700 may range from 5 to 30 microns or from 5 to 40 microns; and the depth of the groove 700 is greater than or equal to the thickness of the insulating layer 800, so that at least part of the insulating layer 800 can be embedded in the groove 700, reducing the thickness of this part.

[0065] Continue to refer Figure 5 In the embodiment of the present application, in the first direction ( Figure 5 In the X direction shown in FIG, the distance between the end of the portion of insulating layer 800 outside the groove 700 and the end of the folded segment 130 is a first distance Y2, and the first distance Y2 is ≥ 0.1 mm. This ensures that the folded segment 130 does not extend beyond the insulating layer 800, thereby preventing the presence of multiple separators between the positive and negative electrodes and causing lithium deposition.

[0066] refer to Figure 6 , Figure 6 Schematic diagram of the local structure of the innermost circle of the winding core provided in the embodiment of the present application Figure 2 In the embodiment of the present application, when the insulating layer 800 is not provided in the groove 700, in the first direction ( Figure 6In the X direction shown in FIG, the distance between the end of the folded segment 130 and the edge of the groove 700 is a second distance Y3, and the second distance Y3 is ≥ 0.1 mm. This ensures that there are no multiple layers of separators between the positive and negative electrodes, which may cause lithium deposition.

[0067] Continue to refer Figure 6 In the embodiment of the present application, when the insulating layer 800 is not provided in the groove 700, in the first direction ( Figure 6 In the X direction (shown in FIG), the distance between the end of the negative electrode winding starting section 111 in the first composite area A1 and the edge of the groove 700 is a third distance Y4, and the third distance Y4 is ≥ 0.2 mm. This ensures that the negative electrode winding starting section 111 of the negative electrode sheet 110 extends into the groove 700 of the positive electrode sheet 120, improving electrode sheet coverage, preventing lithium deposition, and enhancing safety performance.

[0068] refer to Figure 7 , Figure 7 Schematic diagram of the local structure of the innermost circle of the winding core provided in the embodiment of the present application Figure 3 ; In the embodiment of the present application, when the first diaphragm 301 and the second diaphragm 302 in the second composite area A2 do not have a fold back, and a groove 700 is provided on the positive electrode active layer on the side of the first positive electrode bending portion close to the negative electrode winding starting section 111, the distance between the end of the negative electrode winding starting section 111 in the first composite area A1 and the first positive electrode bending portion is a fourth distance Y5, and the fourth distance Y5 is ≥1.5mm, ensuring that the second composite area A2 has sufficient size to avoid the negative electrode sheet 110 from being exposed, thereby improving the safety performance of the battery.

[0069] refer to Figure 8 , Figure 8 A schematic diagram of a winding core in the related art is shown in FIG. Figure 8 The roll core in is used as a comparison group, and the roll core provided in the embodiment of the present application is used as an experimental group, and the roll core provided in the embodiment of the present application is further explained.

[0070] The negative electrode sheets in the control group were coated in a normal manner. The electrode sheets included a single-sided coating area and a blank foil area. After winding was completed, the innermost layer of the core was the blank foil and the single-sided coating area.

[0071] The negative electrode sheets in the experimental group were coated continuously, eliminating the single-sided coated and bare foil areas. The negative electrode sheets were completely double-sided coated. The coating was removed from a specific area in the center of the sheet, exposing the current collector for tab welding. After winding, a composite area A was placed on the innermost end of the winding core. Composite area A consists of two parts: the first composite area A1 (negative electrode-separator) and the second composite area A2 (separator-separator).

[0072] It should be noted that the formation of the composite area A can be achieved by applying a certain pressure to the negative electrode sheet and the separator at a certain temperature, so that a certain bonding force is generated between the separators or between the separator and the negative electrode sheet through a thermal composite process to form a composite area.

[0073] Among them, the length M2 of the second composite area A2 "diaphragm-diaphragm" is 15 mm, the length M1 of the first composite area A1 "negative electrode-diaphragm" is 3 mm, and a grid-like texture structure is set on the first composite area A1 "negative electrode-diaphragm". The presence of the grid-like texture structure can increase the adhesion between the diaphragms in this area and prevent them from separation.

[0074] A groove is placed at the first positive bend of the positive electrode sheet on the innermost coil of the winding core. This is to remove a portion of the positive electrode sheet's coating. An insulating layer is then placed over the groove, extending 0.5mm beyond it to ensure it completely covers the groove.

[0075] In the innermost circle of the winding core, the ends of the positive and negative electrode sheets are respectively located on both sides of the width direction of the winding core. At this time, the length of the first negative electrode bend portion from the starting section of the negative electrode winding of the negative electrode sheet is 65mm; the diaphragm of the first composite area A1 "negative electrode-diaphragm" is folded back, and its folding direction is opposite to the winding direction of the electrode sheet. The distance between the end of the insulating layer and the end of the folded section is 1.0mm, ensuring that the diaphragm is completely "hidden" in the insulating layer after folding back, avoiding the appearance of multiple layers of diaphragms between the positive and negative electrodes, which leads to an increase in lithium ion transmission paths, and then leads to lithium plating.

[0076] like Figure 9 As shown, after the winding of the control group and the experimental group was completed, the batteries circulated normally. After capacity division, the battery size was tested and the energy density of the battery cells was calculated. The energy density of the control group was about 761.9Wh / L, and the energy density of the battery cells in the experimental group was about 765.8Wh / L. The energy density of the battery cells in the experimental group increased by about 0.5%. At the same time, after about 800 cycles, it can be seen that the capacity retention rate of the control group is about 75.4%, and the capacity retention rate of the experimental group is about 79.7%.

[0077] The improvement in energy density is mainly due to the structure of the experimental group's battery cells. The innermost circle of the core saves the thickness of 3 layers of diaphragm and 2 layers of copper foil, which in turn improves the energy density. After disassembly after the cycle, it was found that lithium deposition occurred in the single-sided coating area of ​​the comparison group's battery cells. This is mainly because the single-sided coating area has relatively small compaction after rolling, which causes the lithium ion conduction path to become longer during the cycle expansion process. The experimental group has no single-sided coating area design and has better compaction consistency.

[0078] An embodiment of the present application further provides a battery, which includes the winding core described above.

[0079] In summary, an embodiment of the present application provides a winding core and a battery, wherein the winding core includes a positive electrode sheet 120 and a negative electrode sheet 110. Along the first direction, the positive electrode winding starting section 121 of the positive electrode sheet 120 and the negative electrode winding starting section 111 of the negative electrode sheet 110 extend in different directions respectively, and the inner side of the positive electrode winding starting section 121 along the second direction is directly opposite to the inner side of the negative electrode winding starting section 111 along the second direction; along the second direction, the negative electrode sheet 110 includes a first surface and a second surface arranged opposite to each other, a first separator 301 is arranged between the first surface and the positive electrode sheet 120, and a second separator 302 is arranged between the second surface and the positive electrode sheet 120; the first separator 301 and the second separator 302 both extend from the negative electrode winding starting section 111 to the negative electrode sheet 110, and the negative electrode winding starting section 111, the first separator 301 and the second separator 302 form a composite area A. The double-sided negative electrode coating design mitigates the lithium plating problem caused by insufficient compaction in single-sided coating. It also reduces thickness (eliminating one layer of copper foil and three layers of separator), improving battery space utilization. A composite area is also provided at the end of the negative electrode sheet on the innermost coil, combining the "negative electrode sheet-separator" and "separator-separator" layers. This protects the negative electrode sheet's end and prevents the negative electrode sheet from being exposed due to separator shrinkage during battery use, thereby preventing short circuits and improving battery safety.

[0080] In this specification, each embodiment or example is described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referenced to each other.

[0081] It should be noted that references in this specification to "one embodiment," "an embodiment," "an exemplary embodiment," "some embodiments," and the like indicate that the described embodiment may include a particular feature, structure, or characteristic, but not necessarily every embodiment includes that particular feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in conjunction with an embodiment, it is within the knowledge of those skilled in the art to implement such feature, structure, or characteristic in conjunction with other embodiments, whether explicitly described or not.

[0082] Generally speaking, terms should be understood, at least in part, based on the context in which they are used. For example, as used herein, the term "one or more" can be used to describe any feature, structure, or characteristic in the singular sense, or can be used to describe a combination of features, structures, or characteristics in the plural sense, depending at least in part on the context. Similarly, terms such as "a," "an," or "the" can also be understood to convey either singular or plural usage, depending at least in part on the context.

[0083] It should be readily understood that “on,” “above,” and “over” in this disclosure should be interpreted in the broadest manner, such that “on” means not only “directly on something,” but also includes “on something” with intervening features or layers therebetween, and “above” or “over” includes not only the meaning of “above” or “over,” but also includes “above” or “over” with no intervening features or layers therebetween (i.e., directly on something).

[0084] Additionally, spatially relative terms, such as "below," "beneath," "beneath," "above," and the like, may be used herein for ease of description to describe the relationship of one element or feature relative to other elements or features as shown in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The device may be in other orientations (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein should be interpreted accordingly.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A winding core, characterized in that: include: Positive and negative electrodes, Along the first direction, the positive electrode winding starting section of the positive electrode sheet and the negative electrode winding starting section of the negative electrode sheet extend in different directions respectively, and the inner side of the positive electrode winding starting section along the second direction is directly opposite to the inner side of the negative electrode winding starting section along the second direction; Along the second direction, the negative electrode sheet includes a first surface and a second surface opposite to each other, a first separator is provided between the first surface and the positive electrode sheet, and a second separator is provided between the second surface and the positive electrode sheet, and both the first separator and the second separator extend from the negative electrode winding starting section to the negative electrode sheet; The negative electrode winding starting section, the first separator and the second separator are combined to form a composite area; The first direction and the second direction are perpendicular.

2. The winding core according to claim 1, characterized in that The composite region includes a first composite region, and the first composite region includes the first separator, the negative electrode winding starting section, and the second separator sequentially arranged along the second direction.

3. The winding core according to claim 2, characterized in that The composite region includes a second composite region, and the second composite region includes the first separator and the second separator extending from the negative electrode sheet from the negative electrode winding starting section.

4. The winding core according to claim 2, characterized in that In the first direction, the first composite region has a first length M1, and the first length M1 is ≤25 mm.

5. The winding core according to claim 3, characterized in that In the first direction, the second composite region has a second length M2, and the second length M2 is ≤10 mm.

6. The winding core according to claim 4, characterized in that The negative electrode sheet includes a first negative electrode bend portion, and the length of the first negative electrode bend portion from the end of the negative electrode winding starting section is a third length M3; The relationship between the first length M1 and the third length M3 is: M1≤0.5M3.

7. The winding core according to claim 3, characterized in that The first diaphragm and / or the second diaphragm in the first composite area is provided with a texture structure; and / or, A texture structure is provided on the first diaphragm and / or the second diaphragm in the second composite area; The texture structure includes text, letters or geometric figures composed of lines.

8. The winding core according to claim 3, characterized in that The positive electrode sheet includes a first positive electrode bend, the first positive electrode bend is provided with an insulating layer, and a groove is provided on the positive electrode active layer on the side of the first positive electrode bend close to the negative electrode winding starting section, at least part of the insulating layer is located in the groove; A length of a portion of the insulating layer outside the groove in the first direction is a third length Y1 , and the third length Y1 is ≥ 0.2 mm.

9. The winding core according to claim 8, characterized in that The first separator and the second separator bonded to each other in the second composite region are folded back in a direction opposite to the winding direction of the negative electrode sheet to form a folded segment, and the length of the folded segment is ≤10 mm.

10. The winding core according to claim 9, characterized in that In the first direction, a distance between an end portion of the insulating layer outside the groove and an end portion of the folded segment is a first distance Y2, and the first distance Y2 is ≥0.1 mm.

11. The winding core according to claim 9, characterized in that In the first direction, the distance between the end of the folded segment and the edge of the groove is a second distance Y3, and the second distance Y3 is ≥0.1 mm.

12. The winding core according to claim 8, characterized in that In the first direction, a distance between an end of the negative electrode winding starting section in the first composite region and an edge of the groove is a third distance Y4, and the third distance Y4 is ≥0.2 mm.

13. The winding core according to claim 8, characterized in that In the first direction, the distance between the end of the negative electrode winding starting section in the first composite region and the first positive electrode bending portion is a fourth distance Y5, and the fourth distance Y5 is ≥1.5 mm.

14. A battery, characterized in that: The winding core comprises the winding core according to any one of claims 1 to 13.

Images