Roll core and battery

Abstract

The embodiment of the invention provides a roll core. And the negative plate comprises a negative current collector and a negative active material layer arranged on at least one side surface of the negative current collector. The negative electrode active material layer contains silicon element. A first foil exposing groove is formed in the surface of the negative plate; a part of the negative current collector is exposed out of the bottom wall of the first foil exposing groove. The first foil exposing groove is arranged close to the second arc section, and a negative electrode active material layer is arranged on the peripheral side of the first foil exposing groove. The negative plate further comprises a negative tab and first protection glue, and part of the negative tab is located in the first foil exposing groove and electrically connected with the negative current collector. And the first protection glue covers part of the negative pole lug in the first foil exposing groove. In the second direction, gaps are formed between the two side edges of the first protection glue and the two opposite side walls of the first foil exposing groove respectively. On the side close to the second arc section, a first gap m is formed between the side edge of the first protection glue and the side wall of the first foil exposing groove, and a second distance n is formed between the side wall of the first foil exposing groove and the second arc section. The ratio of m to n satisfies 1 < = n / m < = 20.

Description

Technical Field

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

[0002] Lithium-ion batteries have the advantages of high energy density, low self-discharge rate and long life, and are widely used in various electronic devices such as smartphones, laptops and electric vehicles.

[0003] With the rapid development of battery technology, the energy density of lithium-ion batteries is increasingly required. In order to improve the energy density of lithium-ion batteries, silicon is usually added to the negative electrode active material layer.

[0004] However, after doping with silicon, there is a problem that the pole piece is easy to break. Summary of the invention

[0005] In view of this, an embodiment of the present application provides a winding core and a battery having the same, so as to improve the energy density of the battery and reduce the risk of electrode breakage.

[0006] In a first aspect, an embodiment of the present application provides a winding core. The winding core comprises a negative electrode sheet, a separator and a positive electrode sheet stacked and wound in sequence. The winding core comprises a straight section and a first arc section and a second arc section respectively located on both sides of the straight section. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector. The negative electrode active material layer contains silicon. A first foil-exposed groove is disposed on the surface of the negative electrode sheet, and a portion of the negative electrode current collector is exposed from the bottom wall of the first foil-exposed groove. The first foil-exposed groove is disposed near the second arc section, and a negative electrode active material layer is disposed on the circumference of the first foil-exposed groove. The negative electrode sheet further comprises a negative electrode tab and a first protective glue, a portion of the negative electrode tab is disposed in the first foil-exposed groove and is electrically connected to the negative electrode current collector, and the negative electrode tab extends along a first direction and exceeds a first edge of the negative electrode sheet. The first protective glue covers a portion of the negative electrode tab in the first foil-exposed groove. Along the second direction, two side edges of the first protective glue respectively have gaps with two opposite side walls of the first foil-exposed groove, and the second direction is perpendicular to the first direction. On the side close to the second arc segment, the side edge of the first protective glue and the side wall of the first foil stripping groove have a first gap m, and the side wall of the first foil stripping groove and the second arc segment have a second distance n. The ratio of m to n satisfies: 1≤n / m≤20.

[0007] Additionally or alternatively, the ratio of m to n satisfies: 2.5≤n / m≤7.5.

[0008] Additionally or alternatively, the winding core further comprises a third protective adhesive which covers the outer side of the second arc segment and extends to the straight segment, and along the fourth direction, the orthographic projection of the third protective adhesive at least partially overlaps with the orthographic projection of the first gap m.

[0009] Additionally or alternatively, the dimensions of the third protective glue on the straight sections on both sides of the arc section on the non-tailing side of the winding core are L3 and L4 respectively; the values ​​of L3 and L4 satisfy: 0mm<L3≤8mm, 0mm<L4≤8mm, and / or, the thickness of the winding core is H, and the ratios of L3 and L4 to H satisfy: 0.1≤L3 / H≤3.5, 0.1≤L4 / H≤3.5 respectively.

[0010] Additionally or alternatively, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes graphite and a silicon-carbon material. The silicon content in the silicon-carbon material is f, wherein 35wt%≤f≤70wt%; and / or the silicon content in the negative electrode active material layer is e, wherein e satisfies: 0.35wt%≤e≤35wt%.

[0011] In addition or alternatively, the negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer stacked in sequence. The first negative electrode active material layer is located on a side of the second negative electrode active material layer away from the negative electrode current collector. The silicon content in the first negative electrode active material layer is greater than the silicon content in the second negative electrode active material layer, and the silicon content in the second negative electrode active material layer is greater than or equal to 0.

[0012] Additionally or alternatively, the thickness ratio of the first negative electrode active material layer to the negative electrode active material layer is y, and e and y satisfy: 0.05%≤e*y≤20%.

[0013] Additionally or alternatively, a recessed groove portion is provided on the negative electrode active material layer, and the recessed groove portion includes a plurality of recessed grooves arranged at intervals; along the width direction of the negative electrode sheet, a gap between the bottom wall of the first foil-exposed groove and the recessed groove is G1, and the value of G1 satisfies: 0mm<G1≤5mm, and / or, along the length direction of the negative electrode sheet, gaps between the side walls on both sides of the first foil-exposed groove and the recessed groove are respectively G2, and the value of G2 satisfies: 0mm<G2≤5mm, and / or, along the width direction of the negative electrode sheet, a gap between the recessed groove and the edge of the negative electrode sheet is G3, and the value of G3 satisfies: 0mm<G3≤5mm.

[0014] Additionally or alternatively, the ratio of the strength S of the negative electrode current collector to the depth h of the recessed groove satisfies: 3≤S / h≤120; and the value range of h is 3μm to 35μm, and / or the value range of S is 100MPa to 650MPa.

[0015] In addition or alternatively, the positive electrode sheet includes a positive electrode active material layer and a positive electrode current collector. A stepped groove is provided in the projection area of ​​the negative electrode tab on the positive electrode sheet, and a second protective glue is provided in the stepped groove. Along the third direction, the stepped groove includes a first groove and a second groove arranged in sequence. The first groove has a width L1 and a depth h1. The second groove has a width L2 and a depth h2. L1 is greater than or equal to the width of the second protective glue. The width of the negative electrode tab is W3, and L2≥W3. The width of the first foil groove is W1, and the width of the second protective glue is greater than or equal to W1. The thickness of the second protective glue is ≤h1≤h2. h1+h2≤the thickness of the positive electrode active material layer. The third direction is perpendicular to the first direction and the second direction.

[0016] In a second aspect, an embodiment of the present application further provides a battery, comprising the above-mentioned winding core.

[0017] According to the winding core provided in the embodiment of the present application, by controlling n / m within the above range, on the first hand, the empty foil area on the right side of the first foil dew groove can be kept at an appropriate distance from the second arc segment, that is, at an appropriate distance from the place where stress concentration is serious, thereby alleviating the stress concentration phenomenon.

[0018] Secondly, the tension / compression conditions of the copper foil on the left side of the exposed foil groove with weaker strength and the copper foil on the right side with stronger expansion stress are made consistent, that is, the stress conditions of the exposed copper foil on both sides of the exposed foil groove are similar. In this way, the phenomenon of the copper foil being squeezed or stretched in different directions due to the unbalanced force on the copper foil on both sides of the exposed foil groove is effectively reduced, and the probability of fatigue fracture of the copper foil on both sides of the exposed foil groove is reduced.

[0019] On the third aspect, the distance between the first exposed foil groove 24 and the second arc segment 101b can be reasonably adjusted according to the size of m, which can better alleviate the fracture problem of silicon-doped batteries near the negative pole ear 23. When n / m is too small, it is too close to the place where stress is concentrated, and it cannot effectively alleviate the fracture problem of silicon-doped batteries near the negative pole ear. At the same time, due to process errors, the first exposed foil groove may be partially or completely located in the bending section with greater stress. When n / m is too large, the negative pole ear is closer to the center of the battery cell, and the electrolyte corrosion rate of the copper foil on the left side of the exposed foil is faster, making it easier to break. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the three-dimensional structure of a winding core according to an embodiment of the present application.

[0021] Figure 2 for Figure 1 Cross-sectional view of the middle winding core along BB.

[0022] Figure 3 for Figure 2 A partial enlarged view of the middle C area.

[0023] Figure 4 for Figure 3 An enlarged schematic diagram of the middle negative electrode tab and its surrounding structures.

[0024] Figure 5 for Figure 4 Top view of the middle negative electrode tab and its surrounding structures.

[0025] Figure 6 Schematic diagram of a negative electrode tab and its surrounding structures according to another embodiment of the present application.

[0026] Figure 7 for Figure 6 Top view of the middle negative electrode tab and its surrounding structures.

[0027] Figure 8 for Figure 1 Right view of .

[0028] Fig. 9 for Figure 1 Left view of .

[0029] Fig.10 Schematic diagram of a negative electrode sheet structure according to an embodiment of the present application.

[0030] Fig.11 for Fig.10 Schematic diagram of the local structure of area D in the middle.

[0031] Fig.12 for Fig.10 Schematic diagram of the local structure at both ends.

[0032] Fig.13 1 is a cross-sectional view of a negative electrode sheet according to one embodiment of the present application.

[0033] Fig.14 Schematic diagram of a battery structure according to an embodiment of the present application.

[0034] Fig.15 Schematic diagram of a battery structure according to another embodiment of the present application.

[0035] Reference numerals:

[0036] 1000. Battery;

[0037] 100, winding core; 101, arc segment; 101a, first arc segment; 101b, second arc segment; 102, straight segment;

[0038] 10. positive electrode sheet; 11. positive electrode active material layer; 12 / 12', stepped groove; 121 / 121', first groove; 122 / 122', second groove; 13. positive electrode current collector; 14. positive electrode tab; 15. second foil-exposing groove;

[0039] 20, negative electrode sheet; 21, negative electrode active material layer; 211, first negative electrode active material layer; 212, second negative electrode active material layer; 22, negative electrode current collector; 23, negative electrode tab; 24 / 24', first foil-exposing groove; 25 / 25', third groove; 26, straight portion; 27, arc portion; 28, concave groove portion; 281 concave groove;

[0040] 30 / 30', first protective glue; 40 / 40', second protective glue; 50, third protective glue; 60, fourth protective glue; 70, fifth protective glue;

[0041] 80. Finishing protective glue; 90. Diaphragm;

[0042] 200. Shell. DETAILED DESCRIPTION

[0043] Improving energy density is the continuous improvement direction of lithium-ion batteries. At present, adding silicon to the negative electrode active material layer is a technical means that can be mass-produced and effectively improve the energy density of lithium-ion batteries. However, there is a risk of electrode breakage caused by silicon expansion.

[0044] During the charge and discharge process, the maximum expansion of silicon can reach about 300%, which is hundreds of times that of graphite. And because silicon has a cubic structure, stress is released in all directions during expansion, which may bring problems that lithium-ion batteries with pure graphite negative electrode active material layers have never experienced before, such as electrode fracture.

[0045] Taking a lithium-ion battery with a rolled core as an example, the inventors found that the negative electrode sheet is more likely to break at or near the tab.

[0046] In view of this situation, the inventor conducted research and analysis, which are described in detail as follows.

[0047] The winding core comprises a positive electrode sheet, a negative electrode sheet and a separator which are stacked. The positive electrode sheet and the negative electrode sheet are wound through the separator to form a winding core having a straight section and arc sections on both sides of the straight section.

[0048] As is known, the metal conductor that leads the positive and negative electrodes out of the battery cell, i.e., the tab, is usually fixed to the current collector by welding. Taking the negative electrode sheet as an example, before welding the negative electrode tab, the negative electrode active material layer on the tab welding area on the negative electrode sheet is usually removed by laser or scraper to expose the negative electrode current collector and form a foil groove for welding the tab.

[0049] On the side of the electrode welding area, in order to avoid short circuits between the positive and negative electrodes caused by contact between the electrodes and short circuits between the positive and negative electrodes caused by welding burrs piercing the diaphragm, protective glue is usually attached to the negative electrode. In order to simplify the processing of the exposed foil groove and facilitate the attachment of the protective glue, the exposed foil groove is usually processed once to form a through groove, and a gap is left between the attached protective glue and the two sides of the exposed foil groove. However, the exposed metal foil (such as copper foil) is in direct contact with the electrolyte and is prone to oxidation / corrosion, which reduces the strength of this area.

[0050] During the winding process of the battery cell, it is necessary to tighten and turn the arc sections on both sides, resulting in the tension of the arc section being greater than the tension of the straight section in the middle. Therefore, the compression and fit of the arc section is greater than that of the straight section, and the closer the compression force is to the arc section on the straight section, the greater the compression force is. At the junction of the straight section and the arc section, the stress is the largest and there is stress concentration. Moreover, there is a pulling force between the straight section and the arc section. The closer the area on the straight section is to the arc section, the greater the pulling force is. The junction of the two is subjected to opposite pulling forces on both sides, which is a stress concentration area. The above factors cause the cross section of the battery cell to be basically an elliptical shape under the action of force, that is, the middle of the straight section is raised and gradually lowered towards the arc sections on both sides. Therefore, the gap between the pole pieces in the middle area of ​​the straight section of the winding core is larger, and the gap between the pole pieces close to the arc sections on both sides gradually decreases (the cross section of the gap is similar to a normal distribution curve), and the storage capacity of the electrolyte is smaller as it approaches the arc sections on both sides.

[0051] In addition, in order to improve the energy density of the battery, silicon is usually added to the negative active material layer of the negative electrode sheet. Silicon is easy to expand during the charging process. During the charging process, as mentioned above, due to the small storage capacity of the electrolyte and the corresponding poor reaction kinetics, the lithium deintercalation speed of the negative active material layer of the straight section on the right side of the exposed foil groove on the negative electrode sheet (the side close to the arc section) is not as fast as the deintercalation speed of the negative active material layer of the straight section close to the middle area of ​​the negative electrode sheet (i.e., the deintercalation speed of the negative active material layer in the area on the left side of the negative electrode tab). Therefore, the expansion speed of the straight section on the right side of the exposed foil groove on the negative electrode sheet is slow, and the speed of recovery from the expansion state is also slow. The stress generated by the inconsistent volume changes on both sides further aggravates the stress concentration on the side of the exposed foil groove close to the arc section, especially the stress concentration at the junction of the arc section and the straight section. In multiple charge and discharge cycles, stress fatigue fracture is prone to occur there.

[0052] Then, during the charging process, as mentioned above, the gap between the electrodes in the straight section of the negative electrode sheet on the right side of the exposed foil groove (the side close to the arc section) is smaller, resulting in less space to relieve the expansion of silicon during charging, which also aggravates the stress concentration in this area.

[0053] In addition, when welding the negative electrode tab in the exposed foil groove, the surface of the area will become uneven and there will be certain welding stress.

[0054] In addition, the arc section of the winding core and the area bordering the straight section are themselves locations where structural stress is concentrated.

[0055] In addition, along the width direction of the battery cell, due to the different sizes of the gaps on both sides of the foil groove, the electrolyte is on the side of the foil groove close to the arc segment (i.e. Figure 3 The accumulation on the right side of the battery cell is greater than that on the side close to the center of the battery cell (i.e. Figure 3 Moreover, the fluidity of the electrolyte on the right side of the foil slot is stronger than that on the left side, resulting in the electrolyte corrosion rate on the copper foil on the right side of the foil slot being weaker than that on the left side, that is, the strength of the copper foil on the right side of the foil slot is stronger than that on the left side. As the number of charge and discharge cycles of the battery cell increases, the electrolyte in the battery cell is gradually consumed, and the amount of electrolyte accumulated on the side of the foil slot close to the arc segment will gradually decrease to approach zero, that is, the reaction corrosion rate of the same electrolyte on the copper foil on the right side of the foil slot is weaker than that on the left side, that is, the strength of the copper foil on the right side of the foil slot is stronger than that on the left side.

[0056] Based on the above research and analysis, it can be concluded that the copper foil on the right side of the exposed foil groove is stronger than the copper foil on its left side, and the stress of the copper foil on the right side of the exposed foil groove is more concentrated. The strength and / or stress state of the two after corrosion do not match, resulting in excessive differences in the tensile and / or compressive conditions of the empty foil areas on both sides of the negative electrode tab during the charge and discharge cycle of the battery cell, making it easier to break.

[0057] In order to solve the above problems, the present application embodiment provides a winding core 100 and a battery 1000. Figures 1 to 15 , the core 100 and the battery 1000 are described.

[0058] It should be understood that there may be many ways to implement the present application, and it should not be construed as being limited to the embodiments described herein. The embodiments described herein are merely for a more thorough and clear understanding of the present disclosure.

[0059] It should be noted that in the embodiment of the present application, the winding center of the core 100 may refer to its winding axis. It is understood that in the winding process, the positive electrode sheet 10, the negative electrode sheet 20 and the separator 90 are wound around the winding axis into the above-mentioned flat structure. The flat structure here means that the thickness of the core 100 is less than the length of the core 100. It is understood that the positive electrode sheet 10 and the negative electrode sheet 20 have a starting end and a tail end. In the winding process, the positive electrode sheet 10 and the negative electrode sheet 20 are wound from the starting end to the tail end.

[0060] For the convenience of explanation, the embodiments of the present application mention the "width direction", "thickness direction" and "length direction" of the winding core 100. The width direction of the winding core 100 refers to the direction from one arc segment 101 to another arc segment 101, that is, the length direction of the positive and negative electrode sheets, which is indicated by the arrow U in the figure; the length direction of the winding core 100 refers to the direction parallel to the winding axis A, which is indicated by the arrow R in the figure; the thickness direction (fourth direction) of the winding core 100 refers to the direction perpendicular to both the width direction and the length direction, which is indicated by the arrow V in the figure.

[0061] In addition, this article will also mention the length direction (second direction), width direction (first direction) and thickness direction (third direction) of each pole piece. The length direction of the pole piece refers to the direction from the starting end of the winding to the end of the winding, which is indicated by the arrow X in the figure; the width direction of the pole piece is the direction perpendicular to the length direction, that is, the direction from one edge of the pole piece to the other edge of the pole piece, which is indicated by the arrow Y in the figure; the thickness direction of the pole piece is the direction perpendicular to both the length direction and the width direction, which is indicated by the arrow Z in the figure. After the pole piece is wound, its length direction is the winding direction.

[0062] Exemplary core

[0063] See 1 to Fig.13 The winding core 100 may include a negative electrode sheet 20, a separator 90, and a positive electrode sheet 10 stacked in sequence. The winding core formed by winding the positive electrode sheet 10 and the negative electrode sheet 20 with the separator 90 interposed therebetween has a straight section 102 and arc sections 101 located on both sides of the straight section 102. The arc section 101 may include a first arc section 101a and a second arc section 101b distributed on opposite sides of the straight section 102 along the width direction.

[0064] The positive electrode sheet 10 may include a positive electrode current collector 13 and a positive electrode active material layer 11 disposed thereon. The two positive electrode active material layers 11 may be located at opposite sides of the positive electrode current collector 13 in the thickness direction.

[0065] The negative electrode sheet 20 may include a negative electrode current collector 22 and a negative electrode active material layer 21 disposed on at least one side of the negative electrode current collector 22. Exemplarily, two negative electrode active material layers 21 are disposed on at least part of the negative electrode current collector 22, and they may be located on opposite sides of the thickness direction of the negative electrode current collector 22. The negative electrode active material layer 21 contains silicon.

[0066] It can be understood that, along the length direction, the negative electrode sheet 20 includes a plurality of straight portions 26 and a plurality of arc portions 27, and the plurality of straight portions 26 and the plurality of arc portions 27 are arranged alternately. After winding, the arc portion 27 of the negative electrode sheet 20 is located in the arc segment 101 of the winding core 100, and the straight portion 26 of the negative electrode sheet 20 is located in the straight segment 102 of the winding core 100.

[0067] By way of example only, the positive electrode current collector 13 may be a strip of metal foil, and the positive electrode active material layer 11 may include a positive electrode active material that can reversibly absorb and release charge carriers. In addition, they may further include conductive materials, adhesives, and various additives. By way of example only, the metal foil mentioned here may be aluminum foil, the positive electrode active material mentioned may be a lithium transition metal composite oxide such as lithium nickel cobalt manganese composite oxide, the conductive material mentioned may be a carbon material such as acetylene black, and the adhesive mentioned may be polyvinylidene fluoride. The positive electrode active material layer 11 is provided on the upper and lower sides of the positive electrode current collector 13, respectively.

[0068] By way of example only, the negative electrode current collector 22 may be a strip of metal foil, and its active material layer may include a negative electrode active material that can reversibly absorb and release charge carriers, a binder, a dispersant, and various additives. By way of example only, the metal foil mentioned here may be copper foil, the negative electrode active material mentioned may be a carbon material such as graphite doped with silicon, the binder mentioned may be a rubber such as styrene-butadiene rubber, and the dispersant mentioned may be a cellulose such as carboxymethyl cellulose. Negative electrode active material layers 21 are provided on the upper and lower sides of the negative electrode current collector 22, respectively.

[0069] The separator 90 is a member that insulates the positive electrode sheet 10 and the negative electrode sheet 20. As some examples, the separator 90 may be a porous belt made of a polyolefin resin such as polyethylene or polypropylene. Of course, the separator 90 may be made of other materials.

[0070] refer to Figures 1 to 13 A first foil-exposing groove 24 may be provided on the surface of the negative electrode sheet 20, and a portion of the negative electrode current collector 22 is exposed at the bottom wall of the first foil-exposing groove 24. Exemplarily, the first foil-exposing groove 24 is provided close to the second arc segment 101b, and the negative electrode active material layer 21 is provided around the first foil-exposing groove 24.

[0071] The negative electrode sheet 20 may further include a negative electrode tab 23 and a first protective adhesive 30. A portion of the negative electrode tab 23 is located in the first foil-extracting groove 24 and is electrically connected to the negative electrode current collector 22. For example, a portion of the negative electrode tab 23 may be welded in the first foil-extracting groove 24. The first protective adhesive 30 may cover a portion of the negative electrode tab 23 in the first foil-extracting groove 24. The negative electrode tab 23 may extend along a first direction and beyond a first edge of the negative electrode sheet 20.

[0072] Along the second direction (the length direction of the negative electrode sheet 20 ), two side edges of the first protective glue 30 may have gaps with two opposite side walls of the first foil-exposing groove 24 . The second direction is perpendicular to the first direction.

[0073] In some examples, along the first direction (the width direction of the negative electrode sheet 20 ), a gap may exist between the bottom edge of the first protective glue 30 and the bottom wall of the first foil-depositing groove 24 away from the first edge.

[0074] On the side close to the second arc segment 101b, the side edge of the first protective glue 30 and the side wall of the first foil stripping groove 24 have a first gap m, and the side wall of the first foil stripping groove 24 and the second arc segment 101b have a second distance n. The ratio of m to n satisfies: 1≤n / m≤20.

[0075] For example, m satisfies 0mm<m≤6mm, for example, 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, etc.

[0076] For example, n satisfies 0mm<n≤30mm, for example, 1mm, 2mm, 3mm, 5mm, 7mm, 9mm, 12mm, 15mm, 18mm, 20mm, 22mm, 25mm, 28mm, etc.

[0077] It should be noted that the negative electrode tab 23 can also be arranged in the first foil groove 24 in other ways, for example, integrally formed with the negative electrode current collector 22; the negative electrode sheet 20 has a first edge and a second edge in the extended width direction, and the first edge and the second edge are the two longer sides of the negative electrode sheet 20, which is not limited in the present application.

[0078] By controlling n / m within the above range, firstly, the empty foil area on the right side of the first foil-exposing groove 24 can be kept at an appropriate distance from the second arc segment 101b, that is, kept at an appropriate distance from the place where stress concentration is serious, so that the stress concentration phenomenon can be alleviated. Secondly, the tension / compression conditions of the left copper foil with weaker strength of the foil-exposing groove and the right copper foil with stronger expansion stress are made consistent, that is, the stress conditions of the exposed copper foil on both sides of the foil-exposing groove are similar. In this way, the phenomenon of the copper foil being squeezed or stretched in different directions due to the unbalanced force on the copper foil on both sides of the foil-exposing groove is effectively reduced, and the probability of fatigue fracture of the copper foil on both sides of the foil-exposing groove is reduced.

[0079] On the third aspect, the distance between the first exposed foil groove 24 and the second arc segment 101b can be reasonably adjusted according to the size of m, which can better alleviate the fracture problem of silicon-doped batteries near the negative pole ear 23. When n / m is too small, it is too close to the place where stress is concentrated, and it cannot effectively alleviate the fracture problem of silicon-doped batteries near the negative pole ear. At the same time, due to process errors, the first exposed foil groove may be partially or completely located in the bending section with greater stress. When n / m is too large, the negative pole ear is closer to the center of the battery cell, and the electrolyte corrosion rate of the copper foil on the left side of the exposed foil is faster, making it easier to break.

[0080] Meanwhile, the first protective adhesive 30 is accommodated in the first foil stripping groove 24, which can avoid increasing the invalid thickness. The molding process of the first foil stripping groove 24 is simple, and the pasting process of the first protective adhesive 30 is simple.

[0081] Preferably, 2.5≤n / m≤7.5.

[0082] The ratio of n to m is controlled within this range, that is, the exposed copper foils on both sides of the foil groove are placed on the side close to the arc section, so that the ratio of the distance between the exposed copper foils on both sides of the foil groove and the arc section in the width of the entire straight section is within 0.35, that is, the second half of the right side of the normal distribution curve with smooth curvature. In this part, the difference in the corrosion conditions of the exposed copper foils on both sides of the foil groove will not be too large, that is, the strength difference of the exposed copper foils on both sides of the foil groove is low (close), which can better alleviate the fracture problem of silicon-doped batteries near the negative electrode tab 23.

[0083] Optionally, n / m can also be any value of 3, 3.5, 4, 4.5, 5, 5.5, 6 or 7, without further limitation herein.

[0084] Exemplarily, a first foil stripping groove 24' is also provided at a position corresponding to the first foil stripping groove 24 on the negative electrode active material layer 21 on the other side of the negative electrode sheet. Accordingly, a first protective adhesive 30' is also provided in the first foil stripping groove 24' to make the stress states on the upper and lower sides of the negative electrode sheet in this area nearly consistent.

[0085] Similarly, the first protective glue 30' in the first foil stripping groove 24' can be completely contained in the first foil stripping groove 24', which can avoid the entire first protective glue 30' on this side protruding above the negative electrode active material layer 21 to cause invalid thickness and reduce the energy density of the battery. Generally, the thickness of the first protective glue 30' is relatively thin, and the remaining space of the first foil stripping groove 24' on this side can be used to absorb silicon expansion and reduce stress concentration. In addition, the first protective glue 30, 30' is respectively arranged in the two first foil stripping grooves 24, 24', so that the stress states on both sides of the welding area of ​​the negative electrode tab 12 can be close, and the fracture of the negative electrode sheet 20 caused by stress mutation superposition and silicon expansion can be avoided.

[0086] Next reference Figures 3 to 5 The projection area of ​​the negative electrode tab 23 on the positive electrode sheet 10 may be provided with a stepped groove 12, and a second protective glue 40 may be provided in the stepped groove 12. Exemplarily, the stepped groove is located on the positive electrode active material layer 11 on the positive electrode sheet 10 close to the negative electrode sheet 20 side.

[0087] Along the third direction (the thickness direction of the positive electrode sheet 10), the stepped groove 12 may include a first groove 121 and a second groove 122 arranged in sequence, the first groove 121 may have a width L1, a depth h1, and the second groove 122 may have a width L2, a depth h2. Here, L1 is greater than or equal to the width of the second protective glue 40. The width of the first foil groove is W1. The width of the negative electrode tab is W3, L2≥W3. The width of the second protective glue 40 is greater than or equal to W1, and the thickness of the second protective glue 40 is ≤h1≤h2, h1+h2≤the thickness of the positive electrode active material layer. The third direction is perpendicular to the first direction and the second direction.

[0088] Exemplarily, the projection area of ​​the negative electrode tab 23 on the positive electrode sheet 10 may also be provided with a stepped groove 12', and a second protective glue 40' may be provided in the stepped groove 12. Exemplarily, the stepped groove 12' is located on the positive electrode active material layer 11 on the positive electrode sheet 10 away from the negative electrode sheet 20.

[0089] The second protective glue 40, 40' is arranged in the first groove 121, 121' arranged in the projection area of ​​the negative electrode tab 23 on the positive electrode sheet 10, and the width of the second protective glue 40, 40' is less than or equal to the width of the first groove 121, 121', and the thickness thereof is less than or equal to the depth of the first groove 121, 121', which can avoid the second protective glue 40, 40' protruding from the positive electrode active material layer and increasing the volume of the battery 1000, and can improve the energy density of the battery 1000. In addition, the reduction of the N / P ratio of the region caused by the provision of the first leakage foil groove 24, 24' can be alleviated. The width of the second groove 122 arranged in sequence with the first groove 121 is greater than or equal to the width of the negative electrode tab 23, so that the high point of the welding area of ​​the negative electrode tab 23 can be accommodated in the second groove 122, thereby avoiding the increase of the invalid volume of the battery 1000, and further improving the energy density of the battery 1000, and can also avoid the high point of the welding area of ​​the negative electrode tab 23 piercing the diaphragm 90 to cause a positive and negative short circuit. Moreover, when the second grooves 122, 122' penetrate the bottom of the positive electrode active material layer, the second protective glue 40, 40' can directly contact the negative electrode current collector 22, so that the second protective glue 40, 40' is firmly bonded to the positive electrode sheet 10, and the second protective glue 40, 40' can be prevented from falling off.

[0090] Return to reference Figure 2 , and also refer to Figure 8 and Fig. 9 The winding core 100 may further include a third protective adhesive 50 , and the third protective adhesive 50 covers the outer side surface of the second arc segment 101 b .

[0091] The arc segment 101 of the winding core 100 is a stress concentration area. The greater its thickness and the larger the size of the arc segment 101, the larger the stress concentration area. In particular, the outermost pole piece of the arc segment 101 is subjected to greater tensile stress when the winding core 100 expands, and is more likely to break at this position. Providing a third protective glue 50 on the outer side of the arc segment 101 on the non-ending side of the winding core 100 can improve the overall strength of this area, better resist the tensile stress when the battery cell expands, and thus reduce the risk of the outermost pole piece of the arc segment 101 breaking.

[0092] In one example, a third protective glue 50 can be provided on the outer side of the arc segment 101 of the winding core 100, that is, the third protective glue 50 can extend to a certain distance from the adjacent straight segment 102. In this way, the overall strength of this area can be better improved, the tensile stress when the winding core 100 expands can be better resisted, and the risk of fracture of the outermost pole piece of the arc segment 101 can be better reduced.

[0093] In one example, along the fourth direction (the thickness direction of the winding core 100), the orthographic projection of the third protective glue 50 may at least partially overlap with the orthographic projection of the first gap m. For example, the orthographic projection of the third protective glue 50 in the fourth direction partially covers the first gap m, or the orthographic projection of the third protective glue 50 in the fourth direction completely covers the first gap m.

[0094] In this way, while improving the overall strength of the area covered by the third protective glue 50, the structural strength at the gap m can be appropriately improved to avoid fracture at this location.

[0095] Continue to refer Figure 2 , Figure 8 and Fig. 9 The dimensions of the third protective adhesive 50 on the straight section 102 on both sides of the arc section 101 on the non-end side of the winding core 100 are L3 and L4 respectively. The values ​​of L3 and L4 respectively satisfy: 0mm<L3≤8mm (for example, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, etc.), 0mm<L4≤8mm (for example, 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, etc.).

[0096] The thickness of the core 100 is H, and the ratios of L3 and L4 to H respectively satisfy: 0.1≤L3 / H≤3.5 (for example, 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, 2.0, 2.5, 3, 3.4, etc.), 0.1≤L4 / H≤3.5 (for example, 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, 2.0, 2.5, 3, 3.4, etc.).

[0097] In one example, it can be simultaneously satisfied that: the third protective glue 50 is disposed on the arc segment 101 (e.g., the second arc segment 101b) and the partial straight segment 102 on the non-end side of the winding core 100, and the dimensions of the third protective glue 50 on the straight segments 102 on both sides of the arc segment 101 on the non-end side of the winding core 100 are L3 and L4 respectively. The values ​​of L3 and L4 respectively satisfy: 0mm<L3≤8mm, 0mm<L4≤8mm, the thickness of the winding core 100 is H, and the ratios of L3 and L4 to H respectively satisfy: 0.1≤L3 / H≤3.5, 0.1≤L4 / H≤3.5.

[0098] According to the thickness of the winding core 100, the portion of the third protective glue 50 extending to the straight section 102 is controlled within the above range, which can well improve the overall strength of the area where the third protective glue 50 is applied. At the same time, the energy reduction caused by the increase in the ineffective volume of the battery cell due to the application of the third protective glue 50 can be avoided.

[0099] Return to reference Figure 1 A finishing protective glue 80 may be provided at the end portion of the winding core 100 to prevent the winding core 100 from spreading out, and a fourth protective glue 60 and a fifth protective glue 70 may be respectively affixed on both sides of the empty foil area of ​​the finishing portion of the positive electrode sheet 10. The fourth protective glue 60 and the fifth protective glue 70 may be partially extended onto the positive electrode active material layer 11 to prevent the foil from short-circuiting with the negative electrode active material layer 21 and generating heat, thereby affecting the performance of the battery 1000.

[0100] In the embodiment of the present application, the negative electrode active material of the negative electrode active material layer 21 may include graphite and silicon-carbon material. The content of Si in the negative electrode active material layer 21 is e, 0.35wt%≤e≤35wt%. For example, 0.5wt%, 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, etc.).

[0101] In the present application, the mass percentage of Si element in the negative electrode active material layer 21 can be obtained by testing by conventional methods in the art. For example, after the battery is discharged to 0% SOC, the negative electrode sheet is disassembled and taken out. Then, the negative electrode sheet is soaked in DMC solvent for 12 hours, and then rinsed with DMC solvent to remove the lithium salt attached to the negative electrode sheet, and dried. Then the negative electrode sheet is treated at a high temperature of 400°C in an inert atmosphere for 2 hours (for example, in a tubular furnace, under a nitrogen or argon atmosphere), and the negative electrode active material layer can be peeled off from the negative electrode current collector. Collect the negative electrode active material layer as a test sample. Using a thermogravimetric analyzer (for example, a TGA 550 thermogravimetric analyzer), the test sample amount is 5mg to 15mg. In an air or oxygen atmosphere, the temperature is raised from room temperature (25°C) to 900°C at a heating rate of 10°C / min, and kept at 900°C for 40min, so that the non-silicon components in the negative electrode active material layer are volatilized, and silicon is fully oxidized to silicon dioxide. The remaining substance is the ash of the negative electrode active material layer. The mass content of element Si in the negative electrode active coating can be calculated according to the mass of the ash, and the calculation formula is as follows: mass content of element Si in the negative electrode active coating = (molecular weight of silicon / molecular weight of silicon dioxide) * (1-mass of ash / mass of test sample) = (7 / 15) * (1-mass of ash / mass of test sample).

[0102] The silicon content in the silicon-carbon material is f, and f satisfies: 35wt% to 70wt%. Exemplarily, the silicon-carbon material is granular silicon formed by graphite and silicon. The silicon content in the granular silicon is f, and f satisfies: 35wt% to 70wt% (e.g., 38wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, etc.), and the granular silicon can be formed by coating graphite particles with silicon.

[0103] By controlling the content of granular silicon in the negative active material within the above range, the energy density of the battery 1000 can be increased by silicon doping while keeping the silicon content within a low range, thereby minimizing the impact of silicon expansion.

[0104] In addition, the granular silicon has the characteristics of high silicon content at the edges of the particles and low silicon content in the middle of the particles, which can improve the energy density of the battery 1000 and the charging rate of the battery 1000, while helping to reduce the expansion of the granular silicon, thereby alleviating the overall expansion and contraction rate in the first gap.

[0105] refer to Fig.13The negative electrode active material layer 21 may include a first negative electrode active material layer 211 and a second negative electrode active material layer 212 stacked in sequence, and the first negative electrode active material layer 211 is located on a side of the second negative electrode active material layer 212 away from the negative electrode current collector 22. The silicon content in the first negative electrode active material layer 211 is greater than the silicon content in the second negative electrode active material layer 212, and the silicon content in the second negative electrode active material layer 212 is greater than or equal to 0.

[0106] Granular silicon expands greatly, and when it expands, it will drive the surrounding graphite particles and thus drive the overall extension of the current collector. The silicon content in the first negative electrode active material layer 211 is greater than the silicon content in the second negative electrode active material layer 212, which can reduce the effect of the expansion of granular silicon on the negative electrode current collector 22, reduce the extension of the negative electrode sheet 20 and the resulting stress concentration that causes the breakage of the negative electrode current collector 22. In addition, the stress generated by the expansion of granular silicon will squeeze the graphite in all directions, and at the same time, the granular silicon and the surrounding graphite particles will form pores, which will cause the expansion of the entire electrode sheet and generate stress. The silicon content in the first negative electrode active material layer 211 is greater than the silicon content in the second negative electrode active material layer 212, and the lower graphite in contact with the granular silicon is reduced, which can reduce the impact on the lower graphite, thereby reducing the impact of silicon expansion on graphite, so as to appropriately alleviate the expansion of the electrode sheet and reduce the stress generated thereby.

[0107] In one example, granular silicon is doped in the first negative electrode active material layer 21 .

[0108] As mentioned above, placing granular silicon on the upper layer of the negative electrode sheet 20 can better reduce the impact of the expansion of granular silicon on the negative electrode current collector 22, reduce the extension of the negative electrode sheet 20 and the resulting stress concentration that causes the breakage of the negative electrode current collector 22. At the same time, it can better alleviate the expansion of the electrode sheet and further reduce the stress generated thereby.

[0109] The thickness ratio of the first negative electrode active material layer 21 to the negative electrode active material layer 21 is y, and the ratio of e to y satisfies: 0.05%≤e*y≤20%

[0110] In this way, the content of silicon-carbon material in the negative electrode active material layer 21 can be more reasonably regulated according to the thickness of the negative electrode active material layer 21, so as to avoid the silicon-carbon material content being too low to effectively provide the energy density of the battery, or the content being too high to cause serious expansion during charging.

[0111] refer to Figures 10 to 12 The negative electrode current collector active material layer 21 may be provided with a recessed groove portion 28 , and the recessed groove portion 28 includes a plurality of recessed grooves 281 that are spaced apart.

[0112] For example, the extending direction of the recessed groove portion 28 may be perpendicular to the length direction of the negative electrode current collector 22 .

[0113] Along the width direction of the negative electrode sheet 20 , the gap between the bottom wall of the first foil-exposing groove 24 and the recessed groove 281 is G1 , and the value of G1 satisfies: 0mm<G1≤5mm, for example, 0.5mm, 0.8mm, 1.2mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, etc.

[0114] Along the length direction of the negative electrode sheet 20, the gaps between the side walls of the first foil-exposing groove 24 and the recessed groove 281 are respectively G2, and the value of G2 satisfies: 0mm<G2≤5mm, for example 0.5mm, 0.8mm, 1.2mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, etc.

[0115] Along the width direction of the negative electrode sheet, the gap between the recessed groove and the edge of the negative electrode sheet is G3, and the value of G3 satisfies: 0mm<G3≤5mm, for example, 0.5mm, 0.8mm, 1.2mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, etc.

[0116] In one example, the following conditions can be satisfied at the same time: along the width direction of the negative electrode sheet 20, the gap between the bottom wall of the first foil-exposing groove 24 and the recessed groove 281 is G1, and the value of G1 satisfies: 0mm<G1≤5mm. Along the length direction of the negative electrode sheet 20, the gaps between the side walls of the first foil-exposing groove 24 and the recessed groove 281 are G2, respectively, and the value of G2 satisfies: 0mm<G2≤5mm. Along the width direction of the negative electrode sheet, the gap between the recessed groove and the edge of the negative electrode sheet is G3, and the value of G3 satisfies: 0mm<G3≤5mm.

[0117] The recessed groove 28 is provided on the negative electrode active material layer 21 of the negative electrode sheet 20, so that the storage capacity of the electrolyte can be increased, so that the lithium ions from the positive electrode can be better received, so as to improve the reaction kinetics of the negative electrode, so that the negative electrode can have better reaction kinetics to receive lithium ions and improve the lithium precipitation problem, and improve the energy density of the battery 1000. However, when the recessed groove 28 is formed by laser, the heat affected range is large, the strength of the negative electrode current collector 22 will decrease under the influence of heat, and the passivation layer of the negative electrode current collector 22 may be damaged, for example, the passivation layer of the copper foil may be damaged.

[0118] A certain gap is reserved in the area near the first foil-exposing groove 24 and the two ends of the negative electrode sheet 20 (i.e., the edges in the length direction of the negative electrode active material layer 21) without setting the recessed groove portion 28, which can prevent the electrolyte from entering the first foil-exposing groove 24, and can prevent the copper foil from being corroded by the electrolyte after the passivation layer is damaged, and the silicon expansion stress is superimposed and the copper foil is prevented from being broken.

[0119] In addition, the concave groove 28 maintains a certain distance from the edges on both sides of the negative electrode sheet 20, that is, from the edge in the width direction of the negative electrode active material layer 21, which can improve the negative electrode reaction kinetics while preventing the subsequent negative electrode sheet 20 from falling off and burring during cutting, thereby affecting the K value of the battery cell. Here, the K value refers to the voltage drop of the battery per unit time.

[0120] The ratio of the strength S of the negative electrode current collector 22 to the depth h of the plurality of recessed grooves 281 satisfies: 3≤s / h≤120, for example, 4, 8, 10, 15, 20, 30, 40, 60, 80, 90, 100, 110, etc.

[0121] The value range of h is 3μm to 35μm (for example, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 23μm, 25μm, 28μm, 30μm, 33μm, etc.).

[0122] The value range of s is 100MPa~650MPa (for example, 120MPa, 150MPa, 180MPa, 200MPa, 250MPa, 300MPa, 350MPa, 400MPa, 450MPa, 500MPa, 550MPa, 600MPa, etc.).

[0123] In one example, the following conditions can be satisfied at the same time: the ratio of the strength S of the negative electrode current collector 22 to the depth h of the plurality of recessed grooves 281 satisfies: 3≤s / h≤120. The value range of h is 3 μm to 35 μm. The value range of s is 100 MPa to 650 MPa.

[0124] In this way, the depth of the recessed groove 28 can match the strength S of the negative electrode current collector 22 , thereby preventing the recessed groove 28 from being too shallow to effectively store the electrolyte, and preventing the recessed groove 28 from being too deep to affect the strength of the negative electrode current collector 22 .

[0125] It is understandable that the extension direction of the recessed groove portion 28 can also be set to other directions as needed, for example, the extension direction of the recessed groove portion 28 is parallel to the length direction of the negative electrode current collector 22. In addition, the recessed groove portion 28 can be continuously arranged on the negative electrode active material layer 21, or can be arranged at intervals, that is, a plurality of recessed groove segments are arranged at intervals on the negative electrode active material layer 21.

[0126] As mentioned above, the heat generated during laser forming of the recessed groove 281 will affect the strength of the negative electrode current collector 22. According to the strength of the negative electrode current collector 22, the depth of the recessed groove 281 is controlled within a certain range, and while improving the negative electrode reaction kinetics, the appropriate depth of the recessed groove 281 can be matched to avoid excessive influence on the strength of the negative electrode current collector 22 due to the mismatch between the groove depth and the strength, thereby superimposing the silicon expansion stress and causing the negative electrode sheet 20 to break.

[0127] Continue to refer Figure 6 The embodiment of the present application further provides a winding core 100. The winding core 100 may include a negative electrode 20 sheet, a separator 90 and a positive electrode sheet 30 which are stacked and wound in sequence.

[0128] The winding core 100 has a straight section 102 and a first arc section 101a and a second arc section 101b respectively located on both sides of the straight section 102. The negative electrode sheet 20 includes a negative electrode current collector 22 and a negative electrode active material layer 21 disposed on at least one side of the negative electrode current collector 22. The negative electrode active material layer 21 contains silicon.

[0129] The surface of the negative electrode sheet 20 may be provided with a first foil-exposing groove 24 . The bottom wall of the first foil-exposing groove 24 exposes a portion of the negative electrode current collector 22 . The first foil-exposing groove 24 is arranged close to the second arc segment 101 b , and the negative electrode active material layer 21 is arranged around the first foil-exposing groove 24 .

[0130] The negative electrode sheet 20 further includes a negative electrode tab 23 and a first protective glue 30, a portion of the negative electrode tab 23 is located in the first foil stripping groove 24 and is electrically connected to the negative electrode current collector 22, and the negative electrode tab 23 extends along the first direction and exceeds the first edge of the negative electrode sheet 20. The first protective glue 30 covers a portion of the negative electrode tab 23 in the first foil stripping groove 24. A third groove 25 is provided on the negative electrode active material layer 21 around the first foil stripping groove 24, and a portion of the first protective glue 30 that exceeds the width of the first foil stripping groove 24 is accommodated in the third groove 25. The width of the first protective glue 30 is W3, and the width of the third groove is W4, and W3 and W4 satisfy: W4≥W2.

[0131] In this way, the edge of the first protective glue 30 can be accommodated in the negative electrode active material layer 21 to avoid protruding from the negative electrode active material layer 21 to increase the volume of the battery 1000, thereby improving the energy density of the battery 1000.

[0132] Exemplarily, a first foil strip groove 24' is also provided at a position corresponding to the first foil strip groove 24 on the negative electrode active material layer 21 on the other side of the negative electrode sheet 20, and a third groove 25' is provided around the first foil strip groove 24' on the negative electrode active material layer 21. Accordingly, a first protective adhesive 30' is also affixed in the first foil strip groove 24'. The first protective adhesive 30' covers the first foil strip groove 24'. A third groove 25' is provided around the first foil strip groove 24 on the negative electrode active material layer 21, and a portion of the first protective adhesive 30' that exceeds the width of the first foil strip groove 24' is accommodated in the third groove 25'. The width of the first protective adhesive 30' is W3, and the width of the third groove 25' is W4, and W3 and W4 satisfy: W4 ≥ W2, so that the stress state of the upper and lower sides of the negative electrode sheet in this area is close to the same.

[0133] Similarly, the edge of the first protective glue 30' can be contained in the negative electrode active material layer 21 to avoid protruding from the negative electrode active material layer 21 and causing the volume of the battery 1000 to increase, thereby improving the energy density of the battery 1000. Generally, the thickness of the first protective glue 30' is relatively thin, and the remaining space of the first foil-exposing groove 24' on this side can be used to absorb silicon expansion and reduce stress concentration.

[0134] In addition, the first protective glue 30, 30' is respectively arranged in the two first foil-exposing grooves 24, 24', so that the stress states on both sides of the welding area of ​​the negative electrode tab 12 can be close to each other, and the fracture of the negative electrode sheet 20 caused by stress mutation and silicon expansion can be avoided.

[0135] Next reference Figures 3 to 5 The projection area of ​​the negative electrode tab 23 on the positive electrode sheet 10 may be provided with a stepped groove 12, and a second protective glue 40 may be provided in the stepped groove 12. Exemplarily, the stepped groove is located on the positive electrode active material layer 11 on the positive electrode sheet 10 close to the negative electrode sheet 20 side.

[0136] Along the third direction, the stepped groove 12 may include a first groove 121 and a second groove 122 arranged in sequence, the first groove 121 may have a width L1, a depth h1, and the second groove 122 may have a width L2, a depth h2. Here, L1 is greater than or equal to the width of the second protective glue 40. The width of the first foil-exposing groove is W1. The width of the negative electrode tab is W3, L2≥W3. The width of the second protective glue 40 is greater than or equal to W1, and the thickness of the second protective glue 40 is ≤h1≤h2, h1+h2≤the thickness of the positive electrode active material layer. The third direction is perpendicular to the first direction and the second direction.

[0137] Exemplarily, the projection area of ​​the negative electrode tab 23 on the positive electrode sheet 10 may also be provided with a stepped groove 12', and a second protective glue 40' may be provided in the stepped groove 12. Exemplarily, the stepped groove 12' is located on the positive electrode active material layer 11 on the positive electrode sheet 10 away from the negative electrode sheet 20.

[0138] A second protective glue 40, 40' is arranged in the first groove 121, 121' arranged in the projection area of ​​the negative electrode tab 23 on the positive electrode sheet 10, and the width of the second protective glue 40, 40' is less than or equal to the width of the first groove 121, 121', and the thickness thereof is less than or equal to the depth of the first groove 121, 121', so that the second protective glue 40, 40' can be prevented from protruding from the positive electrode active material layer and increasing the volume of the battery 1000, thereby improving the energy density of the battery 1000.

[0139] In addition, the reduction in the N / P ratio of the region caused by the provision of the first leakage foil groove 24, 24' can be alleviated. The width of the second groove 122 arranged in sequence with the first groove 121 is greater than or equal to the width of the negative electrode tab 23, so that the high point of the welding area of ​​the negative electrode tab 23 can be accommodated in the second groove 122, thereby avoiding the increase of the invalid volume of the battery 1000, and further improving the energy density of the battery 1000. It can also avoid the high point of the welding area of ​​the negative electrode tab 23 piercing the diaphragm 90 to cause a short circuit between the positive and negative electrodes. Moreover, when the second grooves 122, 122' penetrate the bottom of the positive electrode active material layer, the second protective glue 40, 40' can directly contact the negative electrode collector 22, so that the second protective glue 40, 40' is more firmly bonded to the positive electrode sheet 10, and the second protective glue 40, 40' can be prevented from falling off.

[0140] Return to reference Figure 2 , and also refer to Figure 8 and Fig. 9 The winding core 100 may further include a third protective adhesive 50 , and the third protective adhesive 50 at least covers the outer side of the second arc segment 101 b .

[0141] The arc segment 101 of the winding core 100 is a stress concentration area. The greater its thickness and the larger the size of the arc segment 101, the larger the stress concentration area. In particular, the outermost pole piece of the arc segment 101 is subjected to greater tensile stress when the winding core 100 expands, and is more likely to break at this position. Providing a third protective glue 50 on the outer side of the arc segment 101 on the non-ending side of the winding core 100 can improve the overall strength here, better resist the tensile stress when the battery cell expands, and thus reduce the risk of the outermost pole piece of the arc segment 101 breaking.

[0142] In one example, a third protective glue 50 can be provided on the outer side of the arc segment 101 of the winding core 100, that is, the third protective glue 50 can extend to a certain distance from the adjacent straight segment 102. In this way, the overall strength here can be better improved, the tensile stress when the winding core 100 expands can be better resisted, and the risk of fracture of the outermost pole piece of the arc segment 101 can be better reduced.

[0143] Continue to refer Figure 2 , Figure 8 and Fig. 9The third protective glue 50 is arranged on the arc segment 101 (e.g., the second arc segment 101b) and the part of the straight segment 102 on the non-end side of the winding core 100. The dimensions of the third protective glue 50 on the straight segments 102 on both sides of the arc segment 101 on the non-end side of the winding core 100 are L3 and L4 respectively. The values ​​of L3 and L4 satisfy: 0mm<L3≤8mm (e.g., 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, etc.), 0mm<L4≤8mm (e.g., 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, etc.).

[0144] The thickness of the core 100 is H, and the ratios of L3 and L4 to H respectively satisfy: 0.1≤L3 / H≤3.5 (for example, 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, 2.0, 2.5, 3, 3.4, etc.), 0.1≤L4 / H≤3.5 (for example, 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, 2.0, 2.5, 3, 3.4, etc.).

[0145] In one example, it can be simultaneously satisfied that: the third protective glue 50 is disposed on the arc segment 101 (e.g., the second arc segment 101b) and the partial straight segment 102 on the non-end side of the winding core 100, and the dimensions of the third protective glue 50 on the straight segments 102 on both sides of the arc segment 101 on the non-end side of the winding core 100 are L3 and L4 respectively. The values ​​of L3 and L4 satisfy: 0mm<L3≤8mm, 0mm<L4≤8mm, the thickness of the winding core 100 is H, and the ratios of L3 and L4 to H satisfy: 0.1≤L3 / H≤3.5, 0.1≤L4 / H≤3.5 respectively.

[0146] According to the thickness of the winding core 100, the portion of the third protective glue 50 extending to the straight section 102 is controlled within the above range, which can well improve the overall strength of the area where the third protective glue 50 is applied. At the same time, the energy reduction caused by the increase in the ineffective volume of the battery cell due to the application of the third protective glue 50 can be avoided.

[0147] refer to Figure 6 and Figure 7 In some alternative embodiments, the width of the first leakage foil groove 24 is W1, the width of the first protective glue 30 is W2, the width of the negative electrode tab 23 is W3, and W2>W1>W3. In other words, the first protective glue 30 completely covers the first cleaning tank leakage foil groove 24, and its edge extends from the first cleaning tank leakage foil groove 24 to the negative electrode active material layer 21 to prevent the negative current collector 22 from being exposed and directly oxidized by the electrolyte, causing the negative electrode sheet 20 to break.

[0148] Return to reference Figure 1A finishing protective glue 80 may be provided at the end portion of the winding core 100 to prevent the winding core 100 from spreading out, and a fourth protective glue 60 and a fifth protective glue 70 may be respectively affixed on both sides of the empty foil area of ​​the finishing portion of the positive electrode sheet 10. The fourth protective glue 60 and the fifth protective glue 70 may be partially extended onto the positive electrode active material layer 11 to prevent the foil from short-circuiting with the negative electrode active material layer 21 and generating heat, thereby affecting the performance of the battery 1000.

[0149] In the embodiment of the present application, the negative electrode active material of the negative electrode active material layer 21 may include graphite and silicon-carbon material. The content of Si in the negative electrode active material layer is e, 0.35wt%≤e≤35wt%. For example, the content of silicon in the negative electrode active material is e, 0.35wt%≤e≤35wt% (for example, 0.5wt%, 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, etc.).

[0150] The silicon content in the silicon-carbon material is f, and f satisfies: 35wt% to 70wt%. Exemplarily, the silicon-carbon material is granular silicon formed by graphite and silicon. The silicon content in the granular silicon is f, and f satisfies: 35wt% to 0wt% (e.g., 38wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, etc.), and the granular silicon can be formed by coating graphite particles with silicon.

[0151] By controlling the content of granular silicon in the negative active material within the above range, the energy density of the battery 1000 can be increased by silicon doping while keeping the silicon content within a low range, thereby minimizing the impact of silicon expansion.

[0152] In addition, granular silicon has the characteristics of high silicon content at the edges of the particles and low silicon content in the middle of the particles, which can improve the energy density of battery 1000, increase the charging rate of battery 1000, and at the same time help reduce the expansion of granular silicon.

[0153] refer to Fig.13 The negative electrode active material layer 21 may include a first negative electrode active material layer 211 and a second negative electrode active material layer 212 stacked in sequence, and the first negative electrode active material layer 211 is located on a side of the second negative electrode active material layer 212 away from the negative electrode current collector 22. The silicon content in the first negative electrode active material layer 211 is greater than the silicon content in the second negative electrode active material layer 212, and the silicon content in the second negative electrode active material layer 212 is greater than or equal to 0.

[0154] Granular silicon expands greatly, and when it expands, it will drive the surrounding graphite particles and thus drive the overall extension of the current collector. The silicon content in the first negative electrode active material layer 211 is greater than the silicon content in the second negative electrode active material layer 212, which can reduce the effect of the expansion of granular silicon on the negative electrode current collector 22, reduce the extension of the negative electrode sheet 20 and the resulting stress concentration that causes the breakage of the negative electrode current collector 22. In addition, the stress generated by the expansion of granular silicon will squeeze the graphite in all directions, and at the same time, the granular silicon and the surrounding graphite particles will form pores, which will cause the expansion of the entire electrode sheet and generate stress. The silicon content in the first negative electrode active material layer 211 is greater than the silicon content in the second negative electrode active material layer 212, and the lower graphite in contact with the granular silicon is reduced, which can reduce the impact on the lower graphite, thereby reducing the impact of silicon expansion on graphite, so as to appropriately alleviate the expansion of the electrode sheet and reduce the stress generated thereby.

[0155] In one example, granular silicon is doped in the first negative electrode active material layer 21 .

[0156] As mentioned above, placing granular silicon on the upper layer of the negative electrode sheet 20 can better reduce the impact of the expansion of granular silicon on the negative electrode current collector 22, reduce the extension of the negative electrode sheet 20 and the resulting stress concentration that causes the breakage of the negative electrode current collector 22. At the same time, it can better alleviate the expansion of the electrode sheet and further reduce the stress generated thereby.

[0157] The thickness ratio of the first negative electrode active material layer 21 to the negative electrode active material layer 21 is y, and the ratio of e to y satisfies: 0.05%≤e*y≤20%

[0158] In this way, the content of silicon-carbon material in the negative electrode active material layer 21 can be more reasonably regulated according to the thickness of the negative electrode active material layer 21, so as to avoid the silicon-carbon material content being too low to effectively provide the energy density of the battery, or the content being too high to cause serious expansion during charging.

[0159] refer to Figures 10 to 12 The negative electrode current collector active material layer 21 may be provided with a recessed groove portion 28 , and the recessed groove portion 28 includes a plurality of recessed grooves 281 that are spaced apart.

[0160] For example, the extending direction of the recessed groove portion 28 may be perpendicular to the length direction of the negative electrode current collector 22 .

[0161] Along the width direction of the negative electrode sheet 20 , the gap between the bottom wall of the first foil-exposing groove 24 and the recessed groove 281 is G1 , and the value of G1 satisfies: 0mm<G1≤5mm, for example, 0.5mm, 0.8mm, 1.2mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, etc.

[0162] Along the length direction of the negative electrode sheet 20, the gaps between the side walls of the first foil-exposing groove 24 and the recessed groove 281 are respectively G2, and the value of G2 satisfies: 0mm<G2≤5mm, for example 0.5mm, 0.8mm, 1.2mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, etc.

[0163] Along the width direction of the negative electrode sheet, the gap between the recessed groove and the edge of the negative electrode sheet is G3, and the value of G3 satisfies: 0mm<G3≤5mm, for example, 0.5mm, 0.8mm, 1.2mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, etc.

[0164] In one example, the following conditions can be satisfied at the same time: along the width direction of the negative electrode sheet 20, the gap between the bottom wall of the first foil-exposing groove 24 and the recessed groove 281 is G1, and the value of G1 satisfies: 0mm<G1≤5mm. Along the length direction of the negative electrode sheet 20, the gaps between the side walls of the first foil-exposing groove 24 and the recessed groove 281 are G2, respectively, and the value of G2 satisfies: 0mm<G2≤5mm. Along the width direction of the negative electrode sheet, the gap between the recessed groove and the edge of the negative electrode sheet is G3, and the value of G3 satisfies: 0mm<G3≤5mm.

[0165] The recessed groove 28 is provided on the negative electrode active material layer 21 of the negative electrode sheet 20, so that the storage capacity of the electrolyte can be increased, so that the lithium ions from the positive electrode can be better received, so as to improve the reaction kinetics of the negative electrode, so that the negative electrode can have better reaction kinetics to receive lithium ions and improve the lithium precipitation problem, and improve the energy density of the battery 1000. However, when the recessed groove 28 is formed by laser, the heat affected range is large, the strength of the negative electrode current collector 22 will decrease under the influence of heat, and the passivation layer of the negative electrode current collector 22 may be damaged, for example, the passivation layer of the copper foil may be damaged.

[0166] A certain gap is reserved in the area near the first foil exposure groove 24 and the two ends of the negative electrode sheet 20 (i.e., the edges in the length direction of the negative electrode active material layer 21) without setting the recessed groove portion 28, so as to avoid the copper foil after the passivation layer is damaged by electrolyte immersion corrosion and the superposition of silicon expansion stress and fracture.

[0167] In addition, the concave groove 28 maintains a certain distance from the edges on both sides of the negative electrode sheet 20, that is, from the edge in the width direction of the negative electrode active material layer 21, which can improve the negative electrode reaction kinetics while preventing the subsequent negative electrode sheet 20 from falling off and burring during cutting, thereby affecting the K value of the battery cell. Here, the K value refers to the voltage drop of the battery per unit time.

[0168] The ratio of the strength S of the negative electrode current collector 22 to the depth h of the plurality of recessed grooves 281 satisfies: 3≤s / h≤120, for example, 4, 8, 10, 15, 20, 30, 40, 60, 80, 90, 100, 110, etc.

[0169] The value range of h is 3μm to 35μm (for example, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 23μm, 25μm, 28μm, 30μm, 33μm, etc.).

[0170] The value range of s is 100MPa~650MPa (for example, 120MPa, 150MPa, 180MPa, 200MPa, 250MPa, 300MPa, 350MPa, 400MPa, 450MPa, 500MPa, 550MPa, 600MPa, etc.).

[0171] In one example, the following conditions can be satisfied at the same time: the ratio of the strength S of the negative electrode current collector 22 to the depth h of the plurality of recessed grooves 281 satisfies: 3≤s / h≤120. The value range of h is 3 μm to 35 μm. The value range of s is 100 MPa to 650 MPa.

[0172] In this way, the depth of the recessed groove 28 can match the strength S of the negative electrode current collector 22 , thereby preventing the recessed groove 28 from being too shallow to effectively store the electrolyte, and preventing the recessed groove 28 from being too deep to affect the strength of the negative electrode current collector 22 .

[0173] It is understandable that the extension direction of the recessed groove portion 28 can also be set to other directions as needed, for example, the extension direction of the recessed groove portion 28 is parallel to the length direction of the negative electrode current collector 22. In addition, the recessed groove portion 28 can be continuously arranged on the negative electrode active material layer 21, or can be arranged at intervals, that is, a plurality of recessed groove segments are arranged at intervals on the negative electrode active material layer 21.

[0174] As mentioned above, the heat generated during laser forming of the recessed groove 281 will affect the strength of the negative electrode current collector 22. According to the strength of the negative electrode current collector 22, the depth of the recessed groove 281 is controlled within a certain range, and while improving the negative electrode reaction kinetics, the appropriate depth of the recessed groove 281 can be matched to avoid excessive influence on the strength of the negative electrode current collector 22 due to the mismatch between the groove depth and the strength, thereby superimposing the silicon expansion stress and causing the negative electrode sheet 20 to break.

[0175] Exemplary Batteries

[0176] On the other hand, Fig.14 and 15 As shown, the embodiment of the present application further provides a battery 1000. The battery 1000 includes the winding core 100 mentioned above.

[0177] refer to Fig.14 and 15 The battery 1000 may include a winding core 100 and a shell 200. The shell 200 may be provided with a receiving cavity, and one or more winding cores 100 may be accommodated in the receiving cavity.

[0178] like Fig.14 As shown, in some embodiments, the housing 200 may be square. That is, the battery 1000 may be a square battery 1000. The material of the housing 200 may be the same as that used in the past, and there is no particular limitation. For example, the housing 200 may be made of metal, in particular, may be made of aluminum (alloy) or iron (alloy).

[0179] like Fig.15 As shown, in some embodiments, the housing 200 is flat and made of a relatively soft material, such as an aluminum-plastic film. That is, in this embodiment, the battery 1000 can be a soft-pack battery 1000.

[0180] It is foreseeable that in other examples of the embodiments of the present application, the battery 1000 may also be implemented as other types besides the square battery 1000 and the soft-pack battery 1000 .

[0181] It should be noted that other aspects of the structure of the battery 1000 may be the same as the structure of the conventional battery 1000 , and for the purpose of brevity, this embodiment of the present application will not be described in detail.

[0182] The battery 1000 provided according to the embodiment of the present application has the corresponding effects of the above-mentioned winding core 100. Please refer to the above for details and will not be repeated here.

[0183] In order to further understand and explain the winding core 100 and the battery 1000 of the present application, some examples and comparative examples of the preparation of the winding core 100 are provided below. Accordingly, structural parameters and characterization parameters of the corresponding examples are provided.

[0184] Example 1

[0185] The battery cells were prepared by the following steps.

[0186] Preparation of positive electrode sheet 10: Lithium cobalt oxide, conductive carbon black (Super P, SP) and polyvinylidene fluoride (PVDF) are mixed according to a mass percentage of 97.6:1.4:1, and N-methylpyrrolidone (NMP) is added, stirred evenly, and a positive electrode slurry is prepared. The positive electrode slurry is coated on the front and back surfaces of the aluminum foil, and then baked and rolled in sequence to obtain a positive electrode sheet 10 with a thickness of 80 μm. A second foil stripping groove 15 is provided on the positive electrode sheet 10, and the positive electrode tab is welded in the second foil stripping groove 15 by laser or ultrasonic welding to obtain a positive electrode sheet 1 with a positive electrode tab 13. 0. A fixed scraper is used to clean the stepped groove 12 on the positive electrode sheet 10. The first groove 121 of the stepped groove 12 has a depth h1 of 15 μm and a width L1=22 mm. The second groove 122 has a depth h2 of 21 μm and a width L2=4 mm. The sum of the depths of the first groove 121 and the second groove 122 is 36 μm, which is equal to the thickness of the positive electrode active material layer. The thickness of the positive electrode termination glue (the fourth protective glue 60 and the fifth protective glue 70) is 12 μm and the width is 20 mm. A protective glue is attached to the portion of the positive electrode tab 13 located in the second foil stripping groove 15.

[0187] Preparation of negative electrode sheet 20: The negative electrode active material doped with granular silicon is mixed with SP, carboxymethyl cellulose lithium (CMC-Li) and polyacrylic acid (PAA) in a mass percentage ratio of 97:0.4:0.1:2.5, the silicon content in the granular silicon is 50wt%, and the silicon content in the negative electrode active material layer is 5wt%, and then deionized water is added to prepare a first negative electrode slurry. Graphite is mixed with SP, CMC-Li and styrene butadiene rubber (SBR) in a mass percentage of 97:0.4:0.1:2.5 to prepare a second negative electrode slurry. The second negative electrode slurry is applied on the surface of the negative electrode current collector 22, and the first negative electrode slurry doped with silicon is applied on the surface of the second negative electrode slurry, and then baked and rolled to obtain a negative electrode sheet 20 with a thickness of 95μm. A first foil stripping groove 24, 24' with a width of W1 = 12 mm is provided at a certain position of the negative electrode sheet 20, and a copper-plated nickel electrode tab with a width of 6 mm is welded in the first foil stripping groove 24 by laser or ultrasonic welding. The first protective glue 30, 30' is attached to the surface of the electrode tab and the first foil stripping groove 24, 24'. The width of the first protective glue is 9 mm, and the distance between the edge of the first protective glue 30, 30' (protective glue) and the first foil stripping groove 24 is m = 2 mm, and the distance between the edge of the first foil stripping groove 24 and the arc segment 27 is n = 10 mm. A laser is used to punch a line on the surface of the negative electrode sheet 20 to form a concave groove portion 28, and the punching depth, i.e., the depth of the concave groove 281, is h = 20 μm. The distance G3 between the concave groove portion 28 and the first foil stripping groove 24 and the edge of the negative active material layer 21 along the width direction of the negative electrode sheet 20 is 0.5 mm. Along the length direction of the negative electrode sheet 20, the distance between the concave groove 28 and the two ends of the negative electrode active material layer is 0.5 mm. The gaps G2 between the side walls of the first foil-exposed groove 24 and the concave groove 281 are 0.5 mm, and the gap G1 between the bottom wall of the first foil-exposed groove 24 and the concave groove 281 is 0.5 mm. y is 0.1, and e*y is 0.5%.

[0188] After slitting and sheeting, the positive and negative electrode sheets 20 are wound together with the separator 90 to obtain a winding core 100, wherein a third protective glue 50 is affixed to the non-end side of the winding core 100, and the width of the third protective glue 50 is 15 mm (referring to the length of the third protective glue 50 along the winding direction), and the dimensions L3 and L4 of the third protective glue 50 extending to the straight section 102 are 3 mm.

[0189] Then, the lithium-ion battery 1000 is obtained through packaging, baking, electrolyte injection, formation, secondary sealing, sorting and open circuit voltage (OCV) testing.

[0190] It should be noted that the electrolyte is a conventional electrolyte available on the market, and the lithium salt in the electrolyte is LiFP6. The baking and rolling of the positive electrode sheet 10 and the negative electrode sheet 20, as well as the packaging, baking after packaging, and chemical formation are conventional processes and will not be described in detail here. In addition, the fourth protective glue 60, the fifth protective glue 70, and the final protective glue 80 are affixed in the corresponding process and corresponding parts, which will not be described in detail here.

[0191] Example 2

[0192] The difference between Example 2 and Example 1 is that the projection area of ​​the negative electrode tab 23 on the positive electrode sheet 10 of Example 2 is not provided with a stepped groove 12 .

[0193] Example 3

[0194] The difference between Example 3 and Example 1 is that the width of the first protective glue 30 is greater than the setting mode of the first foil stripping groove 24, a first foil stripping groove 24 with a width W1=9 mm is provided at a certain position of the negative electrode sheet 20, the width of the first protective glue 30 attached to the surface of the negative electrode tab 23 is 12 mm, and a third groove 25 is provided on the negative electrode active material layer 21 around the first foil stripping groove 24, and the width of the third groove is 14 mm.

[0195] Example 4

[0196] The difference between Example 4 and Example 1 is that the value of m is adjusted to 1.5 mm.

[0197] Example 5

[0198] The difference between Example 5 and Example 1 is that the value of m is adjusted to 5 mm.

[0199] Example 6

[0200] The difference between Example 6 and Example 1 is that the n value is adjusted to 20 mm.

[0201] Example 7

[0202] The difference between Example 7 and Example 1 is that the value of m is adjusted to 1 mm.

[0203] Example 8

[0204] The difference between Example 8 and Example 1 is that the value of m is adjusted to 1 mm.

[0205] Example 9

[0206] The difference between Example 9 and Example 1 is that the value of m is adjusted to 3 mm.

[0207] Example 10

[0208] The difference between Example 10 and Example 1 is that the n value is adjusted to 7 mm.

[0209] Embodiment 11

[0210] The difference between Example 11 and Example 1 is that the third protective glue 50 is not provided on the outer side of the arc segment 101 on the non-trailing side of the winding core 100 .

[0211] Example 12

[0212] The difference between Example 12 and Example 1 is that the width of the third protective glue 50 arranged on the outer side of the arc segment 101 on the non-trailing side of the winding core 100 is 42 mm, and the dimensions L3 and L4 of the third protective glue 50 extending to the straight segment 102 are 18 mm.

[0213] Embodiment 13

[0214] The difference between Example 13 and Example 1 is that there is no reserved gap between the recessed groove 28 formed by laser wire-punching and the edge of the first foil-exposing groove 24 , the edge in the width direction of the negative electrode active material layer 21 , and the edge in the length direction of the negative electrode active material layer 21 .

[0215] Embodiment 14

[0216] The difference between Example 14 and Example 1 is that the depth h of the recessed groove 281 of the recessed groove portion 28 formed by laser wire-punching is 30 μm, and the tensile strength of the copper foil is 80 MPa.

[0217] Embodiment 15

[0218] The difference between Example 15 and Example 1 is that the depth h of the depressed groove 281 of the depressed groove portion 28 formed by laser wire-punching in Example 8 is 4 μm, and the tensile strength of the copper foil is 600 MPa.

[0219] Example 16

[0220] The difference between Example 16 and Example 1 is that the silicon content in the silicon particles is 30%, the silicon content e in the negative electrode active material layer is 0.3%, y is 0.17, and e*y is 0.05%.

[0221] Embodiment 17

[0222] The difference between Example 17 and Example 1 is that the silicon content in the granular silicon is 70wt%, the silicon content in the negative electrode active material layer is 35wt%, y is 0.5, and e*y is 17.5%.

[0223] Embodiment 18

[0224] The difference between Example 18 and Example 1 is that the silicon content in the granular silicon is 35%, the silicon content in the negative electrode active material layer is 0.35wt%, and e*y is 0.035%.

[0225] Embodiment 19

[0226] The difference between Example 19 and Example 1 is that the silicon content in the granular silicon is 70wt%, the silicon content in the negative electrode active material layer is 42%, the negative electrode upper layer paste accounts for y of 0.5, and e*y is 21%.

[0227] Embodiment 20

[0228] The difference between Example 20 and Example 1 is that a first foil-exposing groove 24 with a width W1=9 mm is provided at a certain position of the negative electrode sheet 20 , a first protective adhesive 30 with a width W2=12 mm is attached to the surface of the negative electrode tab 23 , and no third groove 25 is provided on the negative electrode active material layer 21 .

[0229] Comparative Example 1

[0230] The difference between the comparative example and the embodiment 1 is that the distance between the side edge of the first protective glue 30 on the negative electrode sheet 20 and the side wall of the first foil stripping groove 24 is m=3 mm, and the distance between the side wall of the first foil stripping groove 24 and the arc segment 27 is n=2 mm.

[0231] The batteries prepared in the examples and comparative examples were tested.

[0232] The test conditions of K value are as follows: after storing the battery at a temperature of 45℃±3℃ (for example, in a high temperature room) for 48h~60h, take out the battery and place it at 25℃±3℃ (for example, in a constant temperature room) for 24h, test the battery voltage V1, and then place it at a constant temperature room of 25℃±3℃ for 72h~96h (for example, 72h), test the voltage V2, wherein the voltage drop (K value) = (V1-V2) / interval between two tests.

[0233] The test conditions for fracture are as follows: 10 batteries (10 pcs) prepared in each embodiment and comparative example are grouped together, and charged to the upper limit voltage at 1C constant current and constant voltage at a temperature of 45°C±3°C (for example, in a constant temperature room), and then cut off at a cutoff current of 0.05C, left to stand for 10 minutes, and then discharged to 3.0V at 0.5C. After 600 cycles of heavy discharge under the above test conditions, 10 pcs of batteries are disassembled. If any 1 pcs of batteries are broken, it is judged as fracture, and if all batteries are not broken, it is judged as no fracture.

[0234] Volumetric energy density (ED): The volumetric energy density of lithium-ion batteries is ED = E / V, where E is the discharge energy of the lithium-ion battery in joules (J) or kilowatt-hours (kWh), and V is the volume of the lithium-ion battery in cubic meters (m 3 ) or liter (L). The test method is to charge the lithium-ion battery to the upper voltage limit at a current of 0.2C, then charge it at a constant voltage until the current drops to 0.02C, and then discharge it at a current of 0.2C to 3.0V. The discharged energy is E. The volume of the lithium-ion battery is obtained by measuring the thickness, width and length of the lithium-ion battery and calculating the product of the three. The calculated E / V is the volume energy density obtained by the test.

[0235] The capacity of a lithium-ion battery refers to the maximum energy that the battery can store and discharge as current under specific conditions, usually expressed in ampere-hours (Ah) or milliampere-hours (mAh). The formula for calculating battery capacity is: capacity (Ah) = current (A) × time (h).

[0236] Specifically, the test method for the capacity of a lithium-ion battery is as follows: charge the lithium-ion battery to an upper voltage limit at a current of 0.2C, then charge at a constant voltage until the current drops to 0.02C, then discharge at a current of 0.2C to 3.0V, and the resulting discharge capacity is the battery capacity.

[0237] Tables 1 and 2 show the relevant parameters, fracture conditions and K values ​​of various embodiments and comparative examples.

[0238] Table 1

[0239]

[0240]

[0241] Table 2

[0242]

[0243]

[0244] It can be seen from Table 1 that by controlling the ratio of n and m, the breakage of the empty foil on both sides of the negative electrode ear can be effectively reduced.

[0245] It should be noted that in the present application, "battery" refers to a storage device that can be repeatedly charged and discharged, which can be interpreted as the concept of "secondary battery". In the embodiments of the present application, the concept of "secondary battery" can include lithium-ion secondary batteries and the like.

[0246] It should be understood that the term "including" and its variations used in the embodiments of the present application are open inclusions, i.e., "including but not limited to". The term "according to" means "at least in part according to". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least another embodiment". The term "plurality" means "more than one", which is intended to cover two, three or more situations.

[0247] It should be understood that although the terms "first" or "second" etc. may be used in the embodiments of the present application to describe various elements, such as the first protective glue and the second protective glue, these elements are not defined by these terms, which are only used to distinguish one element from another.

[0248] The protection scope of the embodiments of the present application is not limited to the above embodiments. Any changes or substitutions that can be imagined by any technician familiar with the technical field within the technical scope disclosed in the embodiments of the present application should be included in the protection scope of the embodiments of the present application. Therefore, the protection scope of the embodiments of the present application should be based on the protection scope of the claims.

Claims

1. A winding core, characterized in that: The winding core comprises a negative electrode sheet, a separator and a positive electrode sheet which are stacked and wound in sequence, wherein the winding core comprises a straight section and a first arc section and a second arc section respectively located on both sides of the straight section; The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer provided on at least one side of the surface of the negative electrode current collector, the negative electrode active material layer contains silicon, a first foil-exposed groove is provided on the surface of the negative electrode sheet, a bottom wall of the first foil-exposed groove exposes a portion of the negative electrode current collector, the first foil-exposed groove is provided close to the second arc segment, and the negative electrode active material layer is provided on the circumference of the first foil-exposed groove; The negative electrode sheet further includes a negative electrode tab and a first protective glue, a portion of the negative electrode tab is located in the first foil-exposing groove and is electrically connected to the negative electrode current collector, and the negative electrode tab extends along a first direction and exceeds a first edge of the negative electrode sheet; The first protective glue covers a portion of the negative electrode tab in the first foil-extracting groove; along a second direction, two side edges of the first protective glue respectively have gaps with two opposite side walls of the first foil-extracting groove, and the second direction is perpendicular to the first direction; as well as On the side close to the second arc segment, a first gap m is formed between the side edge of the first protective glue and the side wall of the first foil stripping groove, and a second distance n is formed between the side wall of the first foil stripping groove and the second arc segment. Among them, the ratio of m to n satisfies: 1≤n / m≤20.

2. The winding core according to claim 1, characterized in that: The ratio of m to n satisfies: 2.5≤n / m≤7.

5.

3. The winding core according to claim 1, characterized in that: Also includes: A third protective glue covers the outer side surface of the second arc segment and extends to the straight segment. Along a fourth direction, an orthographic projection of the third protective glue at least partially overlaps with an orthographic projection of the first gap m.

4. The winding core according to claim 3, characterized in that: The dimensions of the third protective adhesive on the straight sections on both sides of the arc section on the non-tailing side of the winding core are L3 and L4 respectively; The values ​​of L3 and L4 satisfy: 0mm<L3≤8mm, 0mm<L4≤8mm; and / or The thickness of the winding core is H, and the ratios of L3 and L4 to H respectively satisfy: 0.1≤L3 / H≤3.5, 0.1≤L4 / H≤3.

5.

5. The winding core according to claim 1, characterized in that: The negative electrode active material layer comprises a negative electrode active material, wherein the negative electrode active material comprises graphite and a silicon-carbon material, wherein the silicon content in the silicon-carbon material is f, wherein 35wt%≤f≤70wt%; and / or The silicon content in the negative electrode active material layer is e, and e satisfies: 0.35wt%≤e≤35wt%.

6. The winding core according to claim 5, characterized in that: The negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer stacked in sequence, the first negative electrode active material layer is located on a side of the second negative electrode active material layer away from the negative electrode current collector, the silicon content in the first negative electrode active material layer is greater than the silicon content in the second negative electrode active material layer, and the silicon content in the second negative electrode active material layer is greater than or equal to 0.

7. The winding core according to claim 6, characterized in that: The thickness ratio of the first negative electrode active material layer to the negative electrode active material layer is y, and e and y satisfy: 0.05%<e*y<20%.

8. The winding core according to any one of claims 1 to 7, characterized in that: The negative electrode active material layer is provided with a concave groove portion, and the concave groove portion includes a plurality of concave grooves arranged at intervals; Along the width direction of the negative electrode sheet, the gap between the bottom wall of the first foil-exposing groove and the recessed groove is G1, and the value of G1 satisfies: 0mm<G1≤5mm, and / or, Along the length direction of the negative electrode sheet, the gaps between the side walls of both sides of the first foil-exposing groove and the recessed groove are respectively G2, and the value of G2 satisfies: 0mm<G2≤5mm, and / or, Along the width direction of the negative electrode sheet, a gap between the recessed groove and the edge of the negative electrode sheet is G3, and the value of G3 satisfies: 0mm<G3≤5mm.

9. The winding core according to claim 8, characterized in that: The ratio of the strength S of the negative electrode current collector to the depth h of the concave groove satisfies: 3≤S / h≤120; and The value range of h is 3 μm to 35 μm, and / or The value range of S is 100MPa to 650MPa.

10. The winding core according to claim 1, characterized in that: The positive electrode sheet comprises a positive electrode active material layer and a positive electrode current collector, a projected area of ​​the negative electrode tab on the positive electrode sheet is provided with a stepped groove, a second protective glue is provided in the stepped groove, and along the third direction, the stepped groove comprises a first groove and a second groove which are sequentially arranged, the first groove has a width L1 and a depth h1, and the second groove has a width L2 and a depth h2; Wherein, L1 is greater than or equal to the width of the second protective glue; and / or, The width of the negative electrode tab is W3, L2≥W3; and / or, The width of the first leak foil groove is W1, and the width of the second protective glue is greater than or equal to W1; and / or, The thickness of the second protective glue is ≤ h1 ≤ h2; and / or, h1+h2≤thickness of the positive electrode active material layer; The third direction is perpendicular to the first direction and the second direction.

11. A battery, characterized in that: The battery comprises the winding core according to any one of claims 1 to 10.

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