Roll core and battery

Abstract

The utility model relates to the technical field of battery energy, in particular to a roll core and a battery. The roll core comprises a positive plate, a diaphragm and a negative plate, the positive plate, the diaphragm and the negative plate are sequentially stacked and wound to form a straight section and an arc section, and the positive plate comprises a positive current collector, a first positive active layer and a second positive active layer; the positive electrode current collector exceeds the first positive electrode active layer and the second positive electrode active layer, the distance between the tail end of the first positive electrode active layer and the adjacent arc section is L1, the distance between the tail end of the second positive electrode active layer and the adjacent arc section is L2, and the width of the roll core is W. L1, L2 and W meet the conditions that L1 is larger than or equal to 5 mm, and L1 / W is larger than or equal to 6% and smaller than or equal to 65%, and / or L2 is larger than or equal to 5 mm, and L2 / W is larger than or equal to 6% and smaller than or equal to 65%. By controlling the distance between the positive electrode paste and the arc area, the tensile stress is borne by the contact position of the positive electrode termination adhesive and the positive electrode aluminum foil, the problem that the pole piece is broken at the contact position of the positive electrode termination adhesive and the positive electrode paste is solved, and the safety of the roll core is improved.

Description

Technical Field

[0001] The present application relates to the field of battery energy technology, and in particular to a winding core and a battery. Background Art

[0002] With the rapid development of battery technology, people have put forward higher requirements for battery energy density, fast charging capability and charge and discharge rate. High energy density fast charging batteries are also the development trend of consumer batteries. At present, when manufacturing some battery cells, the positive electrode sheet, diaphragm and negative electrode sheet are stacked together, and then wound from the head to the tail with the head of the negative electrode sheet as the center. The battery cell has a winding arc area. Usually, for the flatness of the battery, when the core is wound, the distance between the positive electrode paste and the arc area should be controlled below 3mm, and the thickness difference should be shortened as much as possible.

[0003] However, in order to improve the energy density of the battery, the pole piece is gradually developing towards high compaction and thick electrodes, that is, the core tends to be thicker and thicker. However, the battery has a breathing effect. The thick core, especially the thick and narrow core, will stretch and shrink in the thickness and width of the core due to the "breathing" of the pole piece during the cycle charge and discharge process. Among them, the tensile stress in the width direction of the core will cause the positive termination glue at the end to break at the contact point with the positive paste, that is, the problem of pole piece breakage, which brings safety hazards. Utility Model Content

[0004] Based on this, the present application provides a winding core and a battery to solve the problem of electrode breakage at the end in the related art, which affects the safety of the battery.

[0005] On the one hand, the present application provides a winding core, comprising a positive electrode sheet, a separator and a negative electrode sheet, wherein the positive electrode sheet, the separator and the negative electrode sheet are sequentially stacked and wound to form a straight section and arc sections located on both sides of the straight section, and the positive electrode sheet comprises a positive electrode current collector and a first positive electrode active layer and a second positive electrode active layer respectively located on both side surfaces thereof;

[0006] Along the winding direction, the positive electrode current collector exceeds the first positive electrode active layer and the second positive electrode active layer, the distance between the tail end of the first positive electrode active layer and the adjacent arc segment is L1, the distance between the tail end of the second positive electrode active layer and the adjacent arc segment is L2, and the width of the winding core is W, wherein L1, L2 and W satisfy: L1≥5mm and 6%≤L1 / W≤65%, and / or, L2≥5mm and 6%≤L2 / W≤65%.

[0007] In a possible implementation, L1 and L2 satisfy: 5 mm ≤ L1 ≤ 20 mm, 5 mm ≤ L2 ≤ 20 mm.

[0008] In a possible implementation, in the thickness direction of the winding core, there is a gap between the orthographic projection of the tail end of the first positive electrode active layer and the orthographic projection of the tail end of the second positive electrode active layer; and / or

[0009] L1 and L2 satisfy: 0<|L1-L2|≤5mm.

[0010] In a possible implementation, the tail end of the separator is located in the arc segment, and along the winding direction of the winding core, the tail end of the separator exceeds the tail end of the negative electrode sheet; and / or

[0011] The dimension of the tail end of the diaphragm exceeding the tail end of the negative electrode sheet is X, the thermal shrinkage rate of the diaphragm is s, and X and s satisfy: 0.9≤X / s≤150.

[0012] In a possible implementation, the positive electrode current collector includes a polymer film and two aluminum foil layers, and the two aluminum foil layers are respectively located on opposite sides of the polymer film in a thickness direction; and / or

[0013] The ratio of the thickness of the polymer film to the thickness of the positive electrode current collector is e, and the value range of e is 0.5-0.95.

[0014] In a possible implementation, the positive electrode sheet further includes a ceramic layer, and a ceramic layer is provided on a surface of the positive electrode current collector extending beyond the first positive electrode active layer and / or beyond the second positive electrode active layer, and the thickness of the ceramic layer is m, and e and m satisfy: 3≤e*m≤30.

[0015] In a possible implementation, the tail end of the first positive electrode active layer covers the head end of the ceramic layer, and / or the tail end of the second positive electrode active layer covers the head end of the ceramic layer.

[0016] In one possible implementation, the negative electrode sheet includes a negative electrode current collector and a second active material layer respectively located on the two side surfaces thereof, a groove is provided on the second active material layer, the groove extends along the width direction of the negative electrode sheet, the width of the groove is Y, and the tensile strength of the negative electrode current collector along the length direction of the negative electrode sheet is S, and Y and S satisfy: 4000≤S*Y≤80000.

[0017] In a possible implementation, at the tail end of the negative electrode sheet, along the winding direction, the negative electrode current collector extends beyond the second active material layer, and the length of the extension is greater than or equal to 1 mm and less than or equal to 5 mm.

[0018] In a possible implementation, the second active material layer includes graphite doped with silicon, and the width of the groove is greater than or equal to three times the particle size of the graphite particles, or greater than or equal to three times the particle size of the silicon particles.

[0019] In a possible implementation, the winding core further includes a first termination tape and a second termination tape, the first termination tape is connected to the tail end of the first positive electrode active layer, and the size of the connection area is n1, the second termination tape is connected to the tail end of the second positive electrode active layer, and the size of the connection area is n2, and the tail area of ​​the negative electrode sheet is provided with a glue containing groove, the glue containing groove is provided on the second active material layer, and the length of the glue containing groove is L3;

[0020] L3 satisfies: L1+n1≤L3, and L2+n2≤L3; and / or

[0021] The depth of the glue containing groove is h, and h satisfies: h≥10μm.

[0022] On the other hand, the present application provides a battery, comprising a shell and the above-mentioned winding core, wherein the winding core is located in the shell.

[0023] The winding core and battery provided in the present application control the distance between the positive electrode paste and the arc segment when the winding core is wound, so that the ratio of the distance between the tail end of the first positive electrode active layer and the arc segment and the distance between the tail end of the second positive electrode active layer and the arc segment to the width dimension of the winding core satisfies L1≥5mm and 6%≤L1 / W≤65%, and / or, L2≥5mm and 6%≤L2 / W≤65%, so that the position where the positive electrode termination glue contacts the positive electrode paste is as far away from the arc segment as possible, and the tensile stress in the width direction can be borne by the contact position between the positive electrode termination glue and the positive electrode aluminum foil. Since the tensile strength of the contact between the positive electrode termination glue and the positive electrode aluminum foil is much higher than the tensile strength of the contact between the positive electrode finishing paste and the positive electrode termination glue, the problem of electrode sheet breakage at the contact position between the positive electrode termination glue and the positive electrode paste is reduced, thereby improving the safety of the winding core. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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 paying any creative work.

[0025] Figure 1 A schematic diagram of the structure of the winding core provided in an embodiment of the present application;

[0026] Figure 2 A schematic diagram of the structure of the winding core tail area provided in an embodiment of the present application.

[0027] Description of reference numerals:

[0028] 100-winding core; 10-positive electrode sheet; 11-positive electrode current collector; 12-first active material layer; 121-first positive electrode active layer; 122-second positive electrode active layer; 13-double-sided area; 14-single-sided area; 15-empty foil area; 16-ceramic layer; 20-diaphragm; 30-negative electrode sheet; 31-negative electrode current collector; 32-second active material layer; 33-glue storage tank; 40-positive electrode ear; 50-negative electrode ear; 60-first electrode ear tape; 70-first termination tape; 80-second termination tape; 200-arc segment; 300-straight segment. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the embodiment of the present application will be described in more detail below in conjunction with the drawings in the preferred embodiments of the present application. In the drawings, the same or similar reference numerals throughout represent the same or similar parts or parts with the same or similar functions. The described embodiments are part of the embodiments of the present application, not all of the embodiments. The embodiments described below with reference to the drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limitations on the present application. 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 the present application. The embodiments of the present application are described in detail below in conjunction with the drawings.

[0030] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, or it can be an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0031] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are orientations or positional relationships based on the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0032] The terms "first", "second" and "third" (if any) in the specification and claims of this application and the above drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0033] In addition, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, for example, a process, method, system, product, or display comprising a series of steps or elements is not necessarily limited to those steps or elements explicitly listed, but may include other steps or elements not explicitly listed or inherent to such process, method, product, or display.

[0034] At present, in the prior art, the core is formed by stacking the positive electrode sheet, the diaphragm and the negative electrode sheet together, and then winding from the head to the tail with the head of the negative electrode sheet as the center. Therefore, there will be arc areas and straight sections on the core that bend during winding. Usually, for the sake of battery flatness, when the core is wound, the distance between the positive electrode paste and the arc area should be controlled to be less than 3mm, and the thickness difference should be shortened as much as possible. However, in order to improve the energy density of the battery, the pole piece gradually develops in the direction of high compaction and thick electrode, that is, the core tends to be thicker and thicker. However, there is a breathing effect in the battery. Thick cores, especially thick and narrow cores, will stretch and shrink in the thickness and width of the core due to the "breathing" effect of the pole piece during the cyclic charge and discharge process. Among them, the tensile stress in the width direction of the core will cause the positive termination glue at the end to contact the positive electrode paste. The position is broken, that is, the problem of pole piece breakage, which brings safety hazards.

[0035] After repeated thinking and verification, the inventor found that if at the end of the winding core, the distance between the positive electrode paste and the arc segment is controlled, and the position where the positive electrode termination glue contacts the positive electrode paste is as far away from the arc segment as possible, the tensile stress in the width direction can be borne by the contact position between the positive electrode termination glue and the positive electrode aluminum foil. Since the tensile strength of the contact between the positive electrode termination glue and the positive electrode aluminum foil is much higher than the tensile strength of the contact between the positive electrode finishing paste and the positive electrode termination glue, the problem of electrode breakage at the contact position between the positive electrode termination glue and the positive electrode paste can be reduced, thereby improving the safety of the winding core.

[0036] In view of this, the present application provides a winding core, comprising 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 in sequence to form a straight section and arc sections on both sides of the straight section, the positive electrode sheet comprises a positive electrode collector and a first positive electrode active layer and a second positive electrode active layer respectively located on the surfaces of both sides thereof; along the winding direction, the positive electrode collector exceeds the first positive electrode active layer and the second positive electrode active layer, the distance between the tail end of the first positive electrode active layer and the adjacent arc section is L1, the distance between the tail end of the second positive electrode active layer and the adjacent arc section is L2, and the width of the winding core is W, wherein L1, L2 and W satisfy: L1≥5mm and 6%≤L1 / W≤65%, and / or, L2≥5mm and 6%≤L2 / W≤65%.

[0037] By controlling the distance between the positive electrode paste and the arc segment when the core is wound, the distance between the tail end of the first positive electrode active layer and the arc segment and the distance between the tail end of the second positive electrode active layer and the arc segment, and the ratio of the width of the core satisfying L1≥5mm and 6%≤L1 / W≤65%, and / or, L2≥5mm and 6%≤L2 / W≤65%, the position where the positive electrode termination glue contacts the positive electrode paste can be as far away from the arc segment as possible, and the tensile stress in the width direction can be borne by the contact position between the positive electrode termination glue and the positive electrode aluminum foil. Since the tensile strength of the contact between the positive electrode termination glue and the positive electrode aluminum foil is much higher than the tensile strength of the contact between the positive electrode termination paste and the positive electrode termination glue, the problem of electrode sheet breakage at the contact position between the positive electrode termination glue and the positive electrode paste is reduced, thereby improving the safety of the core.

[0038] The contents of the present application will be described in detail below in conjunction with the accompanying drawings so that those skilled in the art can understand the contents of the present application more clearly and in detail.

[0039] Figure 1 A schematic diagram of the structure of the winding core provided in an embodiment of the present application. Figure 2 A schematic diagram of the structure of the winding core tail area provided in an embodiment of the present application.

[0040] like Figure 1 and Figure 2 As shown, the winding core 100 provided in the embodiment of the present application includes a wound positive electrode sheet 10, a separator 20 and a negative electrode sheet 30. The positive electrode sheet 10 and the negative electrode sheet 30 have opposite polarities, and the separator 20 is located between the adjacent positive electrode sheet 10 and the negative electrode sheet 30 to avoid contact short circuit between the positive electrode sheet 10 and the negative electrode sheet 30.

[0041] Specifically, the winding core 100 is formed by stacking the positive electrode sheet 10, the separator 20 and the negative electrode sheet 30 in sequence, and then winding the negative electrode sheet 30 from one side of the longitudinal direction to the other side along the longitudinal direction of the electrode sheet, with a partial area on one side of the longitudinal direction of the negative electrode sheet 30 as the center.

[0042] Therefore, the winding core 100 has a winding head and a winding tail. The winding head is the middle part of the winding core 100, and the winding tail is the part where the outer side of the winding core 100 ends. The positive electrode sheet 10, the separator 20, the negative electrode sheet 30, etc. have a head and a tail along the length direction. Among them, the head of the negative electrode sheet 30 is one side of the length direction of the negative electrode sheet 30, and the tail of the negative electrode sheet 30 is the other side of the length direction of the negative electrode sheet 30. The positive electrode sheet 10, the separator 20, and the negative electrode sheet 30 are wound from the head to the tail to form the winding core 100. The length direction of the positive electrode sheet 10, the separator 20, and the negative electrode sheet 30 is the direction in which the winding occurs, that is, the winding direction of the winding core 100 is the positive electrode sheet 10, the separator 20, and the negative electrode sheet 30 from the head in the length direction to the tail in the length direction.

[0043] Since the winding core 100 is formed by winding, the winding core 100 has an arc segment 200. It can be understood that the arc segment 200 is the area where the positive electrode sheet 10, the separator 20 and the negative electrode sheet 30 are bent when they are wound. Figure 1 and Figure 2 As shown in FIG. 1 , both ends of the winding core 100 in the left-right direction are arc segments 200. The winding core 100 also includes a straight segment 300 connected to the arc segment 200. The thickness direction of the winding core 100, i.e. Figure 1 The A direction is the width direction of the winding core 100, that is, Figure 1 Direction B shown.

[0044] In a possible implementation, the positive electrode sheet 10 uses aluminum foil as the positive electrode current collector 11 , and the negative electrode sheet 30 uses copper foil as the negative electrode current collector 31 .

[0045] The winding core 100 further includes a positive electrode tab 40 , a negative electrode tab 50 and a first electrode tab adhesive tape 60 . The positive electrode tab 40 is disposed on the positive electrode sheet 10 , the negative electrode tab 50 is disposed on the negative electrode sheet 30 , and the first electrode tab adhesive tape 60 is disposed on the positive electrode sheet 10 , and the first electrode tab adhesive tape 60 covers the positive electrode tab 40 .

[0046] like Figure 2 As shown, the positive electrode sheet 10 includes a positive electrode current collector 11 and two first active material layers 12. The two first active material layers 12 are respectively located on opposite sides of the thickness direction of the positive electrode current collector 11. The negative electrode sheet 30 includes a negative electrode current collector 31 and two second active material layers 32. The two second active material layers 32 are respectively located on opposite sides of the thickness direction of the negative electrode current collector 31.

[0047] Specifically, the two first active material layers 12 are respectively a first positive electrode active layer 121 and a second positive electrode active layer 122. Along the winding direction, the positive electrode current collector 11 exceeds the first positive electrode active layer 121 and the second positive electrode active layer 122, and the first positive electrode active layer 121 exceeds the second positive electrode active layer 122.

[0048] The positive electrode sheet 10 includes a double-sided area 13, a single-sided area 14 and an empty foil area 15. The double-sided area 13 is an area where the first active material layer 12 exists on both sides of the positive electrode current collector 11, that is, the first positive electrode active layer 121 and the second positive electrode active layer 122 exist at the same time. The single-sided area 14 is an area where the first active material layer 12 exists on only one side of the positive electrode current collector 11, that is, only the first positive electrode active layer 121 exists. The empty foil area 15 is an area where only the positive electrode current collector 11 exists.

[0049] Among them, along the length direction of the positive electrode sheet 10 , the double-sided area 13 , the single-sided area 14 and the empty foil area 15 are connected in sequence, so that the winding tail end of the positive electrode sheet 10 ends with the empty foil area 15 .

[0050] Along the width direction of the winding core 100, the distance between the tail end of the single-sided area 14 (the tail end of the first positive electrode active layer 121, that is, the end of the single-sided area 14 close to the empty foil area 15) and the adjacent arc segment 200 is L1, the distance between the tail end of the double-sided area 13 (the tail end of the second positive electrode active layer 122, that is, the end of the double-sided area 13 close to the single-sided area 14) and the adjacent arc segment 200 is L2, and the width dimension of the winding core 100 is W.

[0051] L1 and L2 satisfy: L1 ≥ 5 mm and 6% ≤ L1 / W ≤ 65%, and / or, L2 ≥ 5 mm and 6% ≤ L2 / W ≤ 65%.

[0052] Preferably, L1 and L2 satisfy: 5mm≤L1≤20mm, 5mm≤L2≤20mm.

[0053] The ratio range of L1, L2 and W is controlled within a range of 6%-65%. At this time, the tail end of the single-sided area 14 and the tail end of the double-sided area 13 can be kept as far away from the arc segment 200 as possible, so that the position where the termination glue connecting the positive electrode finishing paste contacts the positive electrode finishing paste is kept away from the arc segment 200. In this way, during the stress release process in the width direction, the stress is borne by the contact position between the positive electrode termination glue and the positive electrode collector 11 (usually aluminum foil). Since the tensile strength of the contact between the positive electrode termination glue and the aluminum foil is much higher than the tensile strength of the contact between the positive electrode finishing paste and the positive electrode termination glue, the problem of electrode sheet breakage at the contact position between the positive electrode termination glue and the positive electrode paste can be reduced, thereby improving the safety of the winding core.

[0054] Specifically, the positive electrode termination paste includes a first termination tape 70 and a second termination tape 80. The first termination tape 70 is connected to the tail end of the single-sided area 14. The second termination tape 80 is connected to the tail end of the double-sided area 13. The position where the positive electrode finishing paste contacts the positive electrode termination paste is the connection area between the first termination tape 70 and the single-sided area 14 and the connection area between the second termination tape 80 and the double-sided area 13.

[0055] Along the width direction of the roll core 100 , the size of the connection area between the first terminating adhesive tape 70 and the tail end of the single-sided area 14 is n1 , and the size of the connection area between the second terminating adhesive tape 80 and the tail end of the double-sided area 13 is n2 .

[0056] In a possible implementation, a glue containing groove 33 is provided in the tail region of the negative electrode sheet 30 . The glue containing groove 33 is provided on the second active material layer 32 .

[0057] Two adhesive grooves 33 are provided, and they are respectively opposite to the first stop tape 70 and the second stop tape 80 , that is, in the end area of ​​the negative electrode sheet 30 , adhesive grooves 33 are provided on the second active material layer 32 on both sides of the negative electrode current collector 31 .

[0058] The glue holding groove 33 is used to accommodate the thickness of the positive electrode termination glue, thereby reducing the thickness difference on the straight section 300 caused by setting the positive electrode termination glue, improving the flatness of the winding core 100, thereby reducing the appearance of interface gaps, and reducing the impact of thickness stacking on energy density.

[0059] Along the width direction of the winding core 100 , the length of the glue containing groove is L3 , and the depth of the glue containing groove is h .

[0060] Preferably, L3 satisfies: the larger one of L1+n1 and L2+n2 is less than or equal to L3, that is, L1+n1≤L3, and L2+n2≤L3, Figure 2 , the size difference L4≥0.

[0061] By making the length of L3 greater than L1+n1 and L2+n2, the positive electrode termination glue in the straight section 300 can be contained in the glue containing groove 33, thereby further reducing the thickness difference and improving the flatness of the winding core 100.

[0062] Preferably, h satisfies: h≥10 μm.

[0063] Since the thickness of the positive electrode termination glue is at least 10 μm, by setting the depth of the glue containing groove 33 to be at least greater than the thickness of the positive electrode termination glue, it is possible to prevent the straight section 300 from having thickness stacking at this point, thereby affecting the energy density.

[0064] In a possible implementation, there is a gap between the orthographic projection of the tail end of the double-sided area 13 (the tail end of the second positive electrode active layer 122) in the thickness direction of the winding core 100 and the orthographic projection of the tail end of the single-sided area 14 (the tail end of the first positive electrode active layer 121) in the thickness direction of the winding core 100, that is, on the positive electrode sheet 10, the paste ends on both sides are not flush. In terms of size, it is shown as L1≠L2.

[0065] The uneven finishing of the paste coating on the positive electrode sheet 10 can alleviate the sudden drop in thickness on the straight section 300 caused by the finishing of the positive electrode paste coating, thereby improving the flatness of the winding core 100.

[0066] Preferably, L1 and L2 satisfy: 0<|L1-L2|≤5mm.

[0067] In a possible implementation, the positive electrode current collector 11 includes a polymer film and two aluminum foil layers. The two aluminum foil layers are located on opposite sides of the polymer film in the thickness direction. The positive electrode current collector 11 uses a composite current collector, which can effectively inhibit the growth of lithium dendrites, block the current during puncture, and prevent thermal runaway, so it has the advantage of high safety.

[0068] Preferably, the ratio of the thickness of the polymer film to the thickness of the positive electrode current collector 11 is e, and the value range of e is 0.5-0.95.

[0069] It should be noted that e can be any value among 0.5, 0.6, 0.7, 0.8, 0.9, and 0.95.

[0070] When L1 and / or L2 exceed the length in the prior art, the tail end of the positive current collector is prone to breakage due to the presence of a long empty foil area in the straight area, resulting in greater stress. By limiting the thickness ratio e of the polymer film to the entire positive current collector 11, the toughness and structural strength of the positive current collector can be improved, thereby effectively avoiding the breakage of the core winding tail end, and the toughness and structural strength of the positive current collector can be further improved as the e value increases.

[0071] In addition, since the e-value is increased, that is, the content of insulating material in the positive electrode current collector is increased, it can further improve the pass rate of the battery cell in the puncture test and improve the safety of the battery.

[0072] In a possible implementation, the positive electrode sheet 10 further includes a ceramic layer 16. The ceramic layer 16 is disposed on at least one side of the surface of the end region of the positive electrode sheet 10, that is, the surface of the positive electrode current collector 11 that extends beyond the first positive electrode active layer 121 and / or beyond the second positive electrode active layer 122 is provided with the ceramic layer 16.

[0073] The ceramic layer 16 is beneficial for absorbing heat and reducing the overall temperature rise of the battery.

[0074] In some embodiments, a ceramic layer 16 is coated on the aluminum foil in the tail region of the positive electrode sheet 10, wherein the ceramic layer 16 may be coated on both sides or on one side. That is, in the single-sided region 14, a ceramic layer 16 is provided on the side of the positive electrode current collector 11 away from the first active material layer 12, and in the empty foil region 15, a ceramic layer 16 may be provided on both opposite sides of the positive electrode current collector 11.

[0075] In a possible implementation, at the tail end of the single-sided area 14 or the tail end of the double-sided area 13, part of the first active material layer 12 covers the ceramic layer 16, that is, the tail end of the first positive electrode active layer 121 covers the head of the ceramic layer 16, and / or the tail end of the second positive electrode active layer 122 covers the head of the ceramic layer 16. The ceramic layer 16 overlaps with the first active material layer 12 to prevent foil leakage.

[0076] Preferably, the thickness of the ceramic layer 16 is m, and e and m satisfy: 3≤e*m≤30.

[0077] It should be noted that e*m can also be any value among 5, 7, 11, 15, 19, 23, and 27.

[0078] In this way, the rupture of the positive electrode current collector due to stress stretching can be effectively avoided, and its safety during needle puncture and heavy object impact can be improved.

[0079] The adhesive containing groove 33 is also used to accommodate the thickness of the ceramic layer 16 , thereby reducing the thickness difference on the straight section 300 and improving the flatness of the winding core 100 .

[0080] The provision of the ceramic layer 16 also helps to improve the safety of the winding core 100 against needle puncture and heavy object impact.

[0081] At least one groove is formed on the second active material layer 32 , and the groove extends along the width direction of the negative electrode sheet 30 .

[0082] By opening a groove on the second active material layer 32, when the second active material layer 32 expands during "breathing", the groove can accommodate the expansion amount during "breathing", thereby reducing the tensile stress on the negative electrode sheet 30 caused by the expansion during the "breathing" process and alleviating the stress of the negative electrode sheet 30 in the width direction of the winding core 100.

[0083] Preferably, the groove may be a linear groove.

[0084] Alternatively, the groove may be a blind hole or a countersunk hole, etc., and a plurality of grooves are arranged in an array on the second active material layer 32 .

[0085] The grooves can also store electrolyte, improve the wetting performance of the electrolyte on the electrode, reduce the impedance of the negative electrode side, improve the kinetic performance of the negative electrode side, and improve the problems of edge lithium deposition and arc lithium deposition.

[0086] The grooves can be formed on the negative electrode sheet 30 by laser marking.

[0087] In a possible implementation, when the groove is a linear groove, the width of the groove is Y (unit μm), along the length direction of the negative electrode sheet 30, the tensile strength of the negative electrode collector 31 is S (unit MPa), and Y and S satisfy: 4000≤S*Y≤80000.

[0088] The larger the width of the groove is, the more space there is to accommodate the expanded particles when the paste (i.e., the second active material layer 32) on the negative electrode sheet 30 expands. When the width of the groove is small or not formed, the expansion of the paste will cause the negative electrode current collector 31 to stretch, and the negative electrode sheet 30 is easily broken due to tensile stress.

[0089] In a possible implementation, the second active material layer 32 includes graphite doped with silicon, and the width of the groove should be greater than or equal to three times the particle size of the graphite particles, or greater than or equal to three times the particle size of the silicon particles.

[0090] Under normal circumstances, the expansion of silicon-based particles does not exceed 300%, so the width of the groove needs to ensure that there is still space to accommodate the silicon-based particles when they expand to the maximum, so as to prevent the paste from causing the negative electrode current collector 31 to stretch.

[0091] In a possible implementation, the tail end of the negative electrode sheet 30 only has the negative electrode current collector 31 , that is, along the winding direction, the negative electrode current collector 31 exceeds the second active material layer 32 , and the tail section of the negative electrode sheet 30 is the negative electrode current collector 31 (empty foil) that does not contain the second active material layer 32 .

[0092] The negative electrode sheet 30 ends with an empty foil, which can improve the safety of the end side. According to the way the electrode sheet is short-circuited, it can be known that the heat generated by the contact between the second active material layer 32 of the negative electrode sheet 30 and the positive electrode current collector 11 of the empty foil area 15 of the positive electrode sheet 10 is much greater than the heat generated by the contact between the negative electrode current collector 31 and the positive electrode current collector 11 of the empty foil area 15. Therefore, the end section of the negative electrode sheet 30 ends with the negative electrode current collector 31 that does not contain the second active material layer 32. Even if a short circuit such as needle puncture or tearing of the positive electrode sheet occurs here, the voltage of the core 100 can be quickly reduced with less heat generation, thereby ensuring the safety of the battery cell.

[0093] The tail end of the negative electrode current collector 31 may be located on the arc segment 200 , but may not go beyond the arc segment 200 to the straight segment 300 .

[0094] Preferably, the length of the negative electrode current collector 31 at the tail end of the negative electrode sheet 30 beyond the second active material layer 32 is greater than or equal to 1 mm and less than or equal to 5 mm.

[0095] In a possible implementation, the tail end of the diaphragm 20 is located in the arc segment 200 , that is, the diaphragm 20 does not exceed the arc segment 200 , does not overlap with the straight segment 300 , and does not increase the thickness of the straight segment 300 .

[0096] The arc segment 200 at the end of the diaphragm 20 increases the thickness of the arc segment 200 (compared to the straight segment 300), so that in the subsequent hot pressing process, the force on the arc segment 200 is more uniform, the interface gap is reduced, and the combination is tighter, thereby solving the problem of poor adhesion between the diaphragm 20 and the positive and negative electrodes in the arc segment 200 and improving the long cycle life of the battery.

[0097] In a possible implementation, along the winding direction of the winding core 100 , the tail end of the separator 20 exceeds the tail end of the negative electrode sheet 30 .

[0098] The separator 20 is longer than the negative electrode 30 to prevent the separator 20 from shrinking due to heat and causing the electrode short circuit problem.

[0099] Along the winding direction of the winding core 100 , the dimension of the tail end of the separator 20 exceeding the tail end of the negative electrode sheet 30 is X (unit: mm), and the thermal shrinkage rate of the separator 20 at 130° C. is s (unit: %).

[0100] In a possible implementation, X and s satisfy: 0.9≤X / s≤150.

[0101] The more severely the diaphragm 20 shrinks, the larger the size of the diaphragm 20 that exceeds the negative electrode sheet 30 should be to prevent a short circuit; however, the excess size should not be too large, as this will affect the energy density of the battery.

[0102] The winding core 100 provided in the embodiment of the present application includes a positive electrode sheet 10, a separator 20 and a negative electrode sheet 30, which are stacked and wound in sequence to form a straight section 300 and arc sections 200 located on both sides of the straight section 300. The positive electrode sheet 10 includes a positive electrode collector 11 and a first positive electrode active layer 121 and a second positive electrode active layer 122 located on both side surfaces thereof respectively; along the winding direction, the positive electrode collector 11 exceeds the first positive electrode active layer 121 and the second positive electrode active layer 122, the tail end of the first positive electrode active layer 121 is at a distance L1 from the adjacent arc section 200, the tail end of the second positive electrode active layer 122 is at a distance L2 from the adjacent arc section 200, and the width of the winding core is W, wherein L1, L2 and W satisfy: L1≥5mm and 6%≤L1 / W≤65%, and / or, L2≥5mm and 6%≤L2 / W≤65%. By controlling the distance between the positive electrode paste and the arc segment 200 when the winding core 100 is wound, the distance between the tail end of the first positive electrode active layer 121 and the arc segment 200 and the distance between the tail end of the second positive electrode active layer 122 and the arc segment 200 are controlled to satisfy the ratio of L1≥5mm and 6%≤L1 / W≤65% to the width of the winding core, and / or, L2≥5mm and 6%≤L2 / W≤65%. This allows the position where the positive electrode termination glue contacts the positive electrode paste to be as far away from the arc segment 200 as possible, and allows the tensile stress in the width direction to be borne by the contact position between the positive electrode termination glue and the positive electrode aluminum foil. Since the tensile strength of the contact between the positive electrode termination glue and the positive electrode aluminum foil is much higher than the tensile strength of the contact between the positive electrode finishing paste and the positive electrode termination glue, the problem of electrode sheet breakage at the contact position between the positive electrode termination glue and the positive electrode paste is reduced, thereby improving the safety of the winding core.

[0103] In addition, the embodiment of the present application further provides a battery, including a battery housing and a winding core 100. The winding core 100 is located in the battery housing.

[0104] The battery is not limited to lithium batteries, and in the future this technology may be applied to sodium batteries, etc. In the present application, lithium-ion batteries are preferred.

[0105] The specific structure, working principle and function of the winding core 100 have been described in detail in the above embodiments and will not be repeated here. It should be noted that the preparation process of the lithium-ion battery is as follows:

[0106] Step 1: Preparation of positive electrode sheet 10: Use a gravure roller or a jump coating roller to coat a ceramic layer 16 with a thickness of 10 μm on the composite current collector according to a predetermined size, wherein the aluminum layer of the composite current collector is 3 μm thick (two layers), and the middle polymer film layer is 7 μm thick. Prepare a positive electrode active layer slurry, and apply the positive electrode active layer slurry on the surface of the positive electrode collector 11 (the paste and the ceramic layer overlap by 1mm-5mm to prevent foil exposure). After baking and rolling, a positive electrode sheet 10 is obtained. A certain position of the positive electrode sheet 10 has a slot of fixed size, and a first pole ear 40 with a thickness of 100 μm is welded in this slot by laser or ultrasonic welding, and a first pole ear adhesive tape 60 with a thickness of 12 μm is respectively attached to both sides of the slot pole piece.

[0107] Step 2: Preparation of negative electrode sheet 30: Prepare negative electrode active layer slurry; wherein, the negative electrode active material includes graphite and silicon carbon, and the mass ratio of silicon carbon to graphite (silicon doping amount) is 10%. The negative electrode active layer slurry is coated on a carbon-coated copper foil (the tensile strength of the copper foil used in the length direction is 200Mpa), and the negative electrode sheet 30 is obtained after baking and rolling. A certain position of the negative electrode sheet 30 has a slot of fixed size, and the second pole ear 50 is welded in this slot by laser or ultrasonic welding, and a 12μm thick adhesive tape is attached to both sides of the slot pole piece; in addition, the second active material layer 32 on both sides of the negative electrode sheet 30 is cleaned to form a glue groove 33 with a length of L3=13mm, and the depth of the glue groove 33 is 10μm; the negative electrode sheet 30 is punched with a linear groove using a laser, and the groove depth is 15μm and the width is 80μm;

[0108] Step 3: After the positive and negative electrode sheets are cut and sliced, they are wound with the separator 20 to obtain a winding core 100. During winding, the distance between the paste coating at the tail of the positive electrode sheet and the arc segment 200 is L1=10mm, L2=8mm. The positive electrode termination glue is 10μm green adhesive paper, and the termination glue cover paste n1=n2=2mm.

[0109] Step 4: After packaging, baking, liquid injection, formation, secondary sealing, sorting and OCV (open circuit voltage) testing, a lithium-ion battery is obtained.

[0110] The electrolyte is a commercially available conventional electrolyte, and the lithium salt therein is LiFP6.

[0111] It should be noted that the following is a table comparing the cycle test data of batteries prepared in multiple groups of embodiments and comparative examples.

[0112] Table 1 is a data table of multiple groups of examples and comparative examples cycle test

[0113]

[0114]

[0115]

[0116]

[0117] Among them, the difference between the comparative example and Example 1 is that the surface of the negative electrode sheet 30 of the comparative example has not been laser-marked, has no grooves, has no glue holding groove 33 in the tail area of ​​the negative electrode sheet 30, the positive electrode current collector is a pure aluminum foil non-composite current collector, has no ceramic layer 16 at the tail of the positive electrode, and the distance between the paste coating at the tail of the positive electrode sheet and the arc is L1=2mm, L2=1mm.

[0118] The difference between Example 2 and Example 1 is that the distance between the paste coating at the tail of the positive electrode sheet and the arc is L1=2mm, L2=1mm, and L3=5mm.

[0119] The difference between Example 3 and Example 1 is that the groove width is 30 μm.

[0120] The difference between Example 4 and Example 3 is that the tensile strength of the copper foil is 100 MPa.

[0121] The difference between Example 5 and Example 1 is that the thickness of the positive electrode tail ceramic layer 16 is 5 μm, and the thickness ratio of the positive electrode composite current collector polymer film is e=0.5.

[0122] The difference between Example 6 and Example 1 is that the thickness ratio of the positive electrode composite current collector polymer film is e=0.5.

[0123] The difference between Example 7 and Example 1 is that the thickness ratio of the positive electrode composite current collector polymer film is e=0.95.

[0124] The difference between Example 8 and Example 1 is that the thickness of the positive electrode tail ceramic layer 16 is 5 μm, and the thickness ratio of the positive electrode composite current collector polymer film is e=0.95.

[0125] The difference between Example 9 and Example 1 is that the thickness of the positive electrode tail ceramic layer 16 is 30 μm, and the thickness ratio of the positive electrode composite current collector polymer film is e=0.95.

[0126] The difference between Example 10 and Example 1 is that the length L3 of the glue containing groove 33 in the negative electrode tailing area is 10 mm.

[0127] The difference between Example 11 and Example 1 is that the thermal shrinkage rate of the separator is 3.5%.

[0128] The difference between Example 12 and Example 1 is that the thermal shrinkage rate of the separator is 0.2%, and the dimension of the tail end of the separator 20 exceeding the tail end of the negative electrode sheet 30 is 30 mm.

[0129] The difference between Example 13 and Example 1 is that the thermal shrinkage rate of the separator is 0.2%, and the dimension of the tail end of the separator 20 exceeding the tail end of the negative electrode sheet 30 is 35 mm.

[0130] Among them, the test method of the cycle test is:

[0131] 1. Cycle 50T at 25℃: In a 25℃ constant temperature room, use the charge and discharge method specified in the specification to cycle 50T, then disassemble the fully charged battery and observe the winding core;

[0132] 2. End-side acupuncture: Before acupuncture, perform 5 normal temperature cycles (1C constant current and constant voltage charging to the upper limit voltage, 0.05C cut-off, 0.5C discharge), and complete the acupuncture test within 2 days after the cycle. The test is carried out within 24 hours after the battery cell is fully charged (1C constant current and constant voltage charging to the upper limit voltage, 0.05C cut-off); use a 4mm diameter iron nail to pierce the left, center and right positions of the battery cell respectively, with a needle speed of 30mm / s. The nail is left in the battery for 1min and then taken out, and 5pcs of battery cells are tested.

[0133] The judgment criteria are: no explosion and no fire.

[0134] The test method for the thermal shrinkage rate of the diaphragm adopts the standard: GB / T 13519-2016 Polyethylene heat shrinkable film for packaging.

[0135] As shown in Table 1, the comparison between the comparative example and the embodiment shows that a groove is provided on the second active material layer 32; a glue holding groove 33 is provided in the tail area of ​​the negative electrode sheet 30; a composite current collector is used; a ceramic layer 16 is provided at the tail of the positive electrode; and the paste at the tail of the positive electrode sheet is kept as far away from the arc segment 200 as possible, which can reduce the problem of the electrode sheet breaking at the position where the positive electrode termination glue contacts the positive electrode paste, thereby improving safety.

[0136] Comparison between Example 1 and Example 2 shows that the tail paste of the positive electrode sheet is kept as far away from the arc segment 200 as possible so that the tensile stress in the width direction is borne by the contact position between the positive electrode termination glue and the positive electrode aluminum foil. Since the tensile strength of the contact between the positive electrode termination glue and the positive electrode aluminum foil is much higher than the tensile strength of the contact between the positive electrode termination paste and the positive electrode termination glue, the problem of electrode sheet breakage at the contact position between the positive electrode termination glue and the positive electrode paste can be reduced, thereby improving safety.

[0137] Comparison between Example 1 and Example 3 shows that the width of the grooves formed on the second active material layer 32 is small, which is not conducive to accommodating the expansion of the negative electrode sheet, thereby making the winding core susceptible to the tensile stress of the expansion and prone to breakage.

[0138] Comparison between Example 3 and Example 4 shows that the tensile strength of the negative electrode current collector is reduced, so that the winding core is easily broken due to the tensile stress when expanding.

[0139] Comparison between Example 1 and Example 5, between Example 7 and Example 8, and between Example 8 and Example 9 show that the thickness of the ceramic layer at the end of the positive electrode is reduced, making it easy for the winding core to be punctured when it is punctured by a needle or impacted by a heavy object, thereby causing a short circuit between the positive and negative electrodes, resulting in fire or explosion.

[0140] Comparison between Example 1 and Example 6, and between Example 1 and Example 7 show that the high proportion of the thickness of the positive electrode composite current collector polymer film is beneficial to improving the safety of the positive electrode sheet, can inhibit the growth of lithium dendrites, can block the current when punctured, and prevent thermal runaway caused by short circuit.

[0141] Comparison between Example 1 and Example 10 shows that the length of the adhesive holding groove 33 in the negative electrode finishing area is too short, which may easily lead to the inability to completely accommodate the thickness of the positive electrode termination adhesive, resulting in an increase in the thickness of the winding core, which is not conducive to improving the energy density of the battery.

[0142] Comparison between Example 1 and Example 11 shows that when the heat shrinkage rate of the diaphragm is increased, it is not conducive for the diaphragm to cover the tail end of the negative electrode, so that when the winding core is punctured by a needle or impacted by a heavy object, the tail end of the negative electrode is easily exposed, which can easily cause a short circuit between the positive and negative electrodes, resulting in fire or explosion.

[0143] Comparison between Example 1 and Example 12, and between Example 12 and Example 13, shows that when the thermal shrinkage rate of the diaphragm is reduced and the size of the tail end of the super-negative electrode at the tail of the diaphragm is increased too much, it will not further prevent the problem of short circuit between the positive and negative electrodes. On the contrary, the increase in the size of the diaphragm will cause the thickness of the core to increase, which is not conducive to improving the energy density of the battery.

[0144] The battery provided in the embodiment of the present application controls the distance between the positive electrode paste and the arc segment 200 when the winding core 100 is finished, so that the ratio of the distance between the tail end of the first positive electrode active layer 121 and the arc segment 200 and the distance between the tail end of the second positive electrode active layer 122 and the arc segment 200 to the width of the winding core satisfies L1≥5mm and 6%≤L1 / W≤65%, and / or, L2≥5mm and 6%≤L2 / W≤65%, so that the position where the positive electrode termination glue contacts the positive electrode paste is as far away from the arc segment 200 as possible, and the tensile stress in the width direction can be borne by the contact position between the positive electrode termination glue and the positive electrode aluminum foil. Since the tensile strength of the contact between the positive electrode termination glue and the positive electrode aluminum foil is much higher than the tensile strength of the contact between the positive electrode termination paste and the positive electrode termination glue, the problem of fracture of the electrode sheet at the contact position between the positive electrode termination glue and the positive electrode paste is reduced, thereby improving the safety of the winding core.

[0145] 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 it. 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 replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A winding core, 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 sequentially stacked and wound to form a straight section and arc sections located on both sides of the straight section, and the positive electrode sheet comprises a positive electrode current collector and a first positive electrode active layer and a second positive electrode active layer respectively located on both side surfaces thereof; Along the winding direction, the positive current collector exceeds the first positive active layer and the second positive active layer, the distance between the tail end of the first positive active layer and the adjacent arc segment is L1, the distance between the tail end of the second positive active layer and the adjacent arc segment is L2, and the width of the winding core is W, wherein L1, L2 and W satisfy: L1≥5mm and 6%≤L1 / W≤65%, and / or, L2≥5mm and 6%≤L2 / W≤65%.

2. The winding core according to claim 1, characterized in that: L1, L2 meet: 5mm≤L1≤20mm; and / or, 5mm≤L2≤20mm; and / or, 0<|L1-L2|≤5mm.

3. The winding core according to claim 1, characterized in that: The tail end of the separator is located at the arc segment, and along the winding direction of the winding core, the tail end of the separator exceeds the tail end of the negative electrode sheet; and / or The dimension of the tail end of the separator exceeding the tail end of the negative electrode sheet is X, the thermal shrinkage rate of the separator is s, and X and s satisfy: 0.9≤X / s≤150.

4. The winding core according to claim 1, characterized in that: The positive electrode current collector comprises a polymer film and two aluminum foil layers, and the two aluminum foil layers are respectively located on opposite sides of the polymer film in the thickness direction; The ratio of the thickness of the polymer film to the thickness of the positive electrode current collector is e, and the value range of e is 0.5-0.

95.

5. The winding core according to claim 4, characterized in that: The positive electrode sheet further includes a ceramic layer. The ceramic layer is disposed on a surface of the positive electrode current collector that extends beyond the first positive electrode active layer and / or beyond the second positive electrode active layer. The thickness of the ceramic layer is m, and e and m satisfy: 3≤e*m≤30.

6. The winding core according to claim 5, characterized in that: Along the winding direction, the tail end of the first positive electrode active layer covers the head of the ceramic layer, and / or the tail end of the second positive electrode active layer covers the head of the ceramic layer.

7. The winding core according to claim 1, characterized in that: The negative electrode sheet includes a negative electrode current collector and a second active material layer respectively located on the two side surfaces thereof. A groove is provided on the second active material layer. The groove extends along the width direction of the negative electrode sheet. The width of the groove is Y. Along the length direction of the negative electrode sheet, the tensile strength of the negative electrode current collector is S, and Y and S satisfy: 4000≤S*Y≤80000.

8. The winding core according to claim 7, characterized in that: At the tail end of the negative electrode sheet, along the winding direction, the negative electrode current collector extends beyond the second active material layer, and the length of the excess is greater than or equal to 1 mm and less than or equal to 5 mm.

9. The winding core according to claim 7, characterized in that: The second active material layer includes graphite doped with silicon, and the width of the groove is greater than or equal to three times the particle size of the graphite particles, or greater than or equal to three times the particle size of the silicon particles.

10. The winding core according to claim 7, characterized in that: The winding core further includes a first termination adhesive tape and a second termination adhesive tape, wherein the first termination adhesive tape is connected to the tail end of the first positive electrode active layer, and the size of the connection area is n1, and the second termination adhesive tape is connected to the tail end of the second positive electrode active layer, and the size of the connection area is n2, and a glue containing groove is provided in the tail area of ​​the negative electrode sheet, and the glue containing groove is provided on the second active material layer, and the length of the glue containing groove is L3; L3 satisfies: L1+n1≤L3, and L2+n2≤L3; and / or The depth of the glue containing groove is h, and h satisfies: h≥10μm.

11. A battery, characterized in that: It comprises a shell and a winding core as claimed in any one of claims 1 to 10, wherein the winding core is located in the shell.

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