Roll core and battery

Abstract

The invention relates to the technical field of batteries, and discloses a roll core and a battery. The roll core comprises a positive plate, a negative plate and a diaphragm, a groove is formed in a positive active layer of the positive plate, and the groove is at least formed in an arc section, closest to the winding center, of the positive plate, so that the thickness of at least partial region on the arc section of the positive plate is reduced, and the risk that active particles on the positive plate pierce the diaphragm is reduced; according to the present invention, by limiting the ratio p1 / H1 between the thickness p1 of the functional layer of the diaphragm and the depth H1 of the groove to be in the range of 0.02-2, the p1 is in the range of 0.3-10 [mu] m, and the H1 is in the range of 3-40 [mu] m, such that the battery can be reduced to the preset charging cut-off current during the charging process, and the self-discharge rate of the battery can be reduced. And on the basis that the battery can reach a fully-charged state, the liquid retention capacity of the battery can be improved, the cycle performance of the battery is improved, and the battery is ensured to have relatively high volume energy density.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a winding core and a battery. Background Technology

[0002] Lithium-ion batteries, also known as lithium batteries, are rechargeable batteries widely used in consumer products, digital products, power products, medical devices, and security applications. How to charge lithium batteries is one of the key technologies in their application. Current technologies generally employ a two-stage charging method: constant current (CC) charging and constant voltage (CV) charging. First, a constant current is used to charge the lithium battery until the cell voltage reaches the cell's charging limit voltage. Then, the cell's charging limit voltage is used for constant voltage charging, during which the charging current gradually decreases. When the charging current decreases to the charging cutoff current, charging ends, and the lithium battery cell is fully charged.

[0003] In the prior art, the negative electrode active layer of the negative electrode sheet of the battery core often uses silicon-based composite materials to improve the energy density of the battery. However, batteries with silicon-based composite materials for the negative electrode active layer often have the problem of difficulty in reducing the current to the preset charging cutoff current during the charging process, making it difficult for the battery to reach a fully charged state, that is, the battery has the problem of difficulty in being fully charged. Summary of the Invention

[0004] In view of this, the present invention provides a core and a battery to solve the problem that batteries with silicon-based composite materials for the negative electrode active layer are difficult to reduce to a preset charging cutoff current during charging, making it difficult for the battery to be fully charged.

[0005] In a first aspect, the present invention provides a wound core, comprising: a positive electrode sheet, a negative electrode sheet, and a separator, wherein the wound core is formed by winding the positive electrode sheet, the separator, and the negative electrode sheet sequentially stacked; the positive electrode sheet includes a positive current collector and a positive active layer located on the surface of the positive current collector; along the winding direction of the wound core, the positive electrode sheet includes a straight section and an arc section, and a groove is provided on the positive active layer of the positive electrode sheet on the side facing the winding center of the wound core, the groove being located at least on one of the arc sections of the positive electrode sheet closest to the winding center, and the depth of the groove being H1; the negative electrode sheet includes a negative current collector. The separator comprises a substrate layer and a negative electrode active layer located on the surface of the negative electrode current collector, the negative electrode active layer comprising a silicon-based material; the separator comprises a substrate layer and a functional layer, the functional layer covering the side of the substrate layer facing the positive electrode sheet, the functional layer comprising a ceramic material, the thickness of the functional layer comprising the ceramic material being p1, wherein p1 and H1 satisfy the following relationship: 0.02≤p1 / H1≤2; the value range of H1 is 3μm≤H1≤40μm, preferably 5μm≤H1≤25μm; the value range of p1 is 0.3μm≤p1≤10μm, preferably 0.5μm≤p1≤8μm.

[0006] Beneficial effects: By setting grooves on the positive electrode active layer of the positive electrode sheet, with the grooves at least located on an arc segment closest to the winding center, the thickness of at least a portion of the arc segment of the positive electrode sheet can be reduced, decreasing the accumulated thickness of the positive electrode active layer at the arc segment. This also increases the effective distance between the grooves on the positive electrode sheet and the separator, thereby reducing the degree of compression of the active particles in the arc segment during winding. It also prevents the active particles on the positive electrode active layer at the arc segment from being excessively compressed and falling off, reducing the risk of active particles on the positive electrode sheet puncturing the separator. Simultaneously, the ceramic material on the separator has good pressure resistance and wear resistance. The functional layer of the ceramic material covering the side of the substrate layer facing the positive electrode sheet prevents the harder active material inside the positive electrode sheet from expanding and compressing the separator during cycling, thus reducing the risk of active particles on the positive electrode sheet puncturing the separator and preventing battery defects. Internal micro-short circuits reduce battery self-discharge and prevent the battery from failing to reach the preset charging cutoff current during charging, thus ensuring the battery reaches a fully charged state. Simultaneously, by limiting the ratio p1 / H1 between the thickness p1 of the functional layer and the depth H1 of the groove 121 to a range of 0.02 to 2, with p1 ranging from 0.3μm to 10μm and H1 ranging from 3μm to 40μm, the risk of active particles on the positive electrode puncturing the separator is reduced. This also prevents active particles on the positive electrode active layer at the arc segment from being excessively compressed during cycling, causing them to fall off or break. This ensures the battery reaches the preset charging cutoff current during charging, allowing it to reach a fully charged state. Furthermore, it increases the battery's liquid retention, improves cycle performance, and ensures a high volumetric energy density.

[0007] In one optional embodiment, the air permeability of the diaphragm is G, and the value of G is in the range of 80s / 100cc≤G≤400s / 100cc, preferably 90s / 100cc≤G≤300s / 100cc, and the relationship between H1 and G is satisfied by the formula: 0.016≤H1 / G≤0.5, preferably 0.017-0.45.

[0008] Beneficial effects: It can further avoid the problem of lithium ions easily becoming dead lithium and precipitating during the migration of lithium ions from the positive electrode to the negative electrode due to the grooves made on the positive electrode. It can reduce the resistance encountered by lithium ions during migration, reduce the occurrence of dead lithium, and ensure the strength of the separator itself, prevent the separator from being damaged by the positive and negative electrodes, and improve the safety of the battery.

[0009] In one optional embodiment, the positive electrode sheet has intersecting first and second directions, the positive electrode sheet is wound along the second direction, and the size of the groove along the second direction is W1, the value of W1 is 3mm≤W1≤10mm;

[0010] And / or, along the second direction, the size of the groove is larger than the size of the arc segment in which it is located;

[0011] And / or, the distance by which the groove extends beyond one side of the arc segment is L1, and the value of L1 is in the range of 0.1mm≤L1≤5mm;

[0012] And / or, along the first direction, the distance between the groove and the edge of the positive electrode is L2, and the value of L2 is in the range of 0.5mm≤L2≤15mm;

[0013] And / or, the thickness of the positive electrode active layer is H2, and H1 and H2 satisfy the relationship: 0.05≤H1 / H2≤0.75.

[0014] Beneficial effects: By setting the size of the groove along the second direction to be within the range of 3mm to 10mm, the groove is limited to a reasonable size. This ensures that the groove can effectively reduce the thickness of the positive electrode active layer at the arc segment, effectively reducing the risk of active particles on the positive electrode damaging the separator, thereby reducing the possibility of CV non-cutoff phenomenon in the battery. It can also avoid removing too much active material from the positive electrode active layer, thereby ensuring that the battery has sufficient capacity and thus ensuring the volumetric energy density of the battery.

[0015] And / or, by limiting the size of the groove along the second direction to be larger than the size of the arc segment in which it is located, it can be ensured that the groove covers and extends beyond the range on the arc segment along the second direction, thereby minimizing the risk of active particles on the arc segment being squeezed off, further reducing the possibility of CV non-cutoff phenomenon during battery charging, and improving battery reliability.

[0016] And / or, by limiting the distance of the groove beyond the arc segment on one side to within the range of 0.1mm to 5mm, it can prevent the active particles near the junction of the arc segment and the straight segment from being squeezed and falling off, thereby avoiding puncturing the separator and further reducing the battery CV non-cutoff phenomenon. It can also reduce the active material on the positive electrode sheet participating in the charge and discharge reaction in the arc area of ​​the core, improve the CB value of the positive and negative electrodes in this area, reduce the probability of lithium plating, and avoid removing too much positive electrode active material, ensuring that the battery has sufficient capacity and energy density.

[0017] And / or, by limiting the distance between the groove and the edge of the positive electrode sheet along the first direction to a value between 0.5mm and 15mm, it can prevent active material particles at the edge of the positive electrode sheet from falling off or leaking foil during the groove processing, thereby avoiding short circuits and thermal runaway and improving battery safety. It can also ensure that the groove has sufficient size along the first direction, thereby effectively reducing the thickness of the positive electrode active layer at the arc section, reducing the risk of active particles on the positive electrode sheet puncturing the separator, and ensuring that the battery can reach a fully charged state.

[0018] And / or, by setting the ratio H1 / H2 to be within the range of 0.05 to 0.75, it is possible to ensure that the groove can effectively reduce the thickness of the positive electrode active layer at the arc segment, thereby effectively reducing the risk of active particles on the positive electrode damaging the separator and improving the CV non-cutoff phenomenon of the battery. It can also prevent the positive electrode current collector from being exposed, thereby preventing the positive electrode current collector from contacting the active material layer of the negative electrode and causing a short circuit, and preventing the exposed positive electrode current collector from undergoing side reactions with the electrolyte, thereby further ensuring the safety of the core and ensuring the electrolyte retention. It can also prevent excessive loss of active material on the positive electrode active layer, thereby ensuring the energy density of the battery.

[0019] In one optional embodiment, the surface of the positive electrode sheet is further provided with a textured area, the textured area including a plurality of recesses and protrusions corresponding to the recesses, the recesses being provided on the surface of the positive electrode sheet facing the winding center of the winding core, and the protrusions being provided on the surface of the positive electrode sheet away from the winding center of the winding core.

[0020] The recessed depth along the third direction is H4, and H4 and H1 satisfy the relationship: 0.25≤H1 / H4≤8. The value range of H4 is 2μm≤H4≤40μm, preferably 3μm≤H4≤20μm.

[0021] And / or, the extension dimension of the recess along the first direction and / or the second direction is D2, wherein the value of D2 is in the range of 0.5mm≤D2≤10mm;

[0022] And / or, along the first direction, the shortest distance between the recess and the edge of the positive electrode is L3, and the value of L3 is in the range of 2mm≤L3≤15mm.

[0023] Beneficial effects: By setting a textured area on the surface of the positive electrode, the recesses in the textured area can provide space for the electrolyte, thereby increasing the electrolyte storage capacity in the area with the recesses, improving the lithium-ion transport rate, and reducing side reactions and lithium plating problems caused by electrolyte deficiency. In particular, it further improves the lithium plating problem at the arc. By limiting the H1 / H4 value to the range of 0.25 to 8, and the recess depth of the recesses to the range of 2μm to 40μm, it can be ensured that the recesses can effectively increase the electrolyte storage capacity in the area with the recesses, thereby improving the lithium-ion transport rate, improving the lithium plating problem, and improving the expansion problem. At the same time, it can also avoid the negative electrode current collector corresponding to the recesses being exposed due to excessive recess depth, thereby improving battery safety and ensuring battery capacity.

[0024] And / or, by setting the extension dimension of the recess along the first direction and / or the second direction to be within the range of 0.5 mm to 10 mm, the liquid storage capacity of the area with the recess can be effectively increased, thereby increasing the lithium ion transport rate and improving the lithium plating problem. It can also avoid excessive loss of active material on the positive electrode active layer, thereby ensuring that the battery has sufficient capacity.

[0025] And / or, by limiting the shortest distance along the first direction between the recess and the edge of the positive electrode to between 2 mm and 15 mm, it is possible to avoid the positive electrode being pressed into a corrugated sheet, thereby ensuring the fit between the positive electrode and the separator and improving the lithium plating problem, and to effectively increase the liquid storage capacity in the area where the recess is provided, thereby effectively improving the lithium plating problem.

[0026] In one optional embodiment, along the winding direction of the core, the positive electrode sheet includes a first fold to an Nth fold connected in sequence, each fold of the positive electrode sheet includes a straight segment and an arc segment, and the groove is disposed at the position of the arc segment on the first fold to the nth fold of the positive electrode sheet, wherein N and n are positive integers, n < N, and n ≤ 3;

[0027] And / or, the number of the grooves is at least one, and along a third direction, the projected area of ​​a single groove on the positive current collector is S1, where S1 ranges from 20 mm. 2 ≤S1≤1500mm 2 ;

[0028] And / or, along a third direction, the total area of ​​the orthogonal projection of the groove onto the positive current collector is S2, and the total area of ​​the orthogonal projection of the positive active layer onto the positive current collector is S3, and S2 and S3 satisfy the relationship: 0.001≤S2 / S3≤0.1.

[0029] Beneficial effects: By setting grooves at the arc segments on the first to nth folds of the positive electrode sheet, where n is less than or equal to 3, the problem of severe compression of active particles at the arc segments can be effectively improved, thereby effectively improving the battery CV non-cutoff phenomenon and avoiding excessive reduction of battery capacity.

[0030] And / or, by defining the orthographic projection area of ​​a single groove along a third direction in the range of 20 mm. 2 Up to 1500mm 2 Taking values ​​within the range can ensure that after the electrode is wound, the groove can cover the arc area of ​​the core, thereby preventing the active particles on the positive electrode from piercing the separator and improving the phenomenon of non-cut-off of CV in the battery. It can also prevent excessive loss of active material particles on the positive electrode, thereby ensuring that the battery has sufficient capacity.

[0031] And / or, by limiting the values ​​of S2 / S3 to the range of 0.001 to 0.1, it is possible to improve the liquid retention of the battery, improve the CV non-cutoff phenomenon and cycle performance of the battery, and ensure that the battery has sufficient capacity, while solving the problem of the separator 30 being punctured by active material particles.

[0032] In one optional embodiment, the positive electrode active layer is further provided with a pit region, the pit region is provided at the position of the arc segment of at least one of the (n+1)th to Nth folds of the positive electrode sheet, the pit region is located on the side of the arc segment facing the winding center of the core, and the pit region includes a plurality of pits.

[0033] The depth of the pit is H3, and H3 and H1 satisfy the relationship: 0.3≤H1 / H3≤1, and the value range of H3 is 5μm≤H3≤30μm;

[0034] And / or, the extension dimension of the pit along the first direction and / or the second direction is D1, and the value of D1 is in the range of 50μm≤D1≤200μm;

[0035] And / or, the distance between two adjacent pits is W2, and the value of W2 is in the range of 100μm≤W2≤3mm;

[0036] And / or, the area of ​​the pit region projected onto the positive current collector along a third direction is S4, and S4 and S1 satisfy the relationship: 0.2≤S1 / S4≤1.

[0037] Beneficial effects: By adding pits to the positive electrode active layer, and setting the pits at the arc segment of at least one fold other than the fold with grooves, the pits can hold electrolyte, thereby increasing the electrolyte retention in the arc area of ​​the core, reducing the occurrence of side reactions and lithium plating problems caused by electrolyte loss, and also providing a buffer space for battery cycle expansion. By limiting H1 / H3 to the range of 0.3 to 1, and the pit depth H3 to the range of 5mm to 30mm, it can be ensured that the setting of the pits can effectively increase the electrolyte retention in the arc area of ​​the core, avoid excessive expansion rate after battery cycle, and ensure that the battery has a high volumetric energy density.

[0038] And / or, by setting the size of the pit along the first direction and / or the second direction to be within the range of 50μm to 200μm, it can be ensured that the pit can effectively increase the liquid retention of the core arc area, and that too much active material on the positive electrode active layer is avoided, thereby ensuring that the battery has sufficient capacity.

[0039] And / or, by setting the spacing between two adjacent pits to a value between 100μm and 3mm, it is possible to avoid excessive removal of active material on the positive electrode active layer, thereby ensuring that the battery has sufficient capacity, and to effectively increase the liquid retention in the arc area of ​​the core, thereby improving battery performance.

[0040] And / or, by setting S1 / S4 to a value in the range of 0.5 to 1, the area of ​​a single groove is less than or equal to the area of ​​the region where the pit is set on a single arc segment, and greater than or equal to half the area of ​​the region where the pit is set on a single arc segment. This can effectively improve the liquid retention of the arc area of ​​the core and avoid excessive capacity loss.

[0041] In one optional embodiment, the dimension of the recessed area closest to the end of the positive electrode winding along the second direction is W3, and the dimension of the arc segment corresponding to the recessed area closest to the end of the positive electrode winding along the second direction is W4. W3 and W4 satisfy the relationship: 1≤W3 / W4≤1.5.

[0042] Beneficial effects: By setting W3 / W4 to a value between 1 and 1.2, it can prevent the setting area of ​​the pit from not being able to completely cover the width of the arc segment due to process fluctuations, thus ensuring that the setting of the pit can effectively improve the liquid retention of the arc area of ​​the core, and also avoid the pit setting area being too wide, which would lead to excessive loss of active particles, thereby ensuring the battery capacity.

[0043] In one optional embodiment, the diaphragm further includes a first adhesive layer disposed on the side of the substrate layer opposite to the functional layer, wherein the coverage of the first adhesive layer relative to the substrate layer is μ, and the value of μ ranges from 20% to μ to 100%.

[0044] Beneficial effects: By setting the coverage μ of the first adhesive layer on the substrate layer to a value within the range of 20%-100%, the coverage of the first adhesive layer 33 is controlled to have a reasonable value range. This ensures both the air permeability of the separator and the adhesion between the negative electrode sheet and the separator within a suitable range. It reduces the risk of poor adhesion between the negative electrode and the separator due to negative electrode expansion during battery cycling, reduces the risk of lithium plating on the negative electrode, and thus improves the safety of the core.

[0045] In one optional embodiment, in the arc segment where the groove is provided, the peel strength between the functional layer and the positive electrode is F1; in the straight segment, the peel strength between the functional layer and the positive electrode is F2, wherein F1 is less than F2.

[0046] Secondly, the present invention also provides a battery, comprising: a casing, and the aforementioned winding core. Since the battery includes a winding core and has the same effects as a winding core, further details are omitted here. Attached Figure Description

[0047] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0048] Figure 1 This is a schematic cross-sectional view of a winding core according to an embodiment of the present invention;

[0049] Figure 2 for Figure 1 A partially enlarged schematic diagram of the winding core shown;

[0050] Figure 3 This is a top view of the first type of positive electrode sheet in the unfolded state according to an embodiment of the present invention;

[0051] Figure 4 This is a bottom view of the first type of positive electrode sheet in the unfolded state according to an embodiment of the present invention;

[0052] Figure 5 This is a cross-sectional view of the first type of positive electrode sheet in the unfolded state according to an embodiment of the present invention;

[0053] Figure 6This is a cross-sectional view of the first type of diaphragm in the unfolded state according to an embodiment of the present invention;

[0054] Figure 7 This is a cross-sectional view of the second type of diaphragm in the unfolded state according to an embodiment of the present invention;

[0055] Figure 8 This is a top view of the second type of positive electrode sheet in the unfolded state according to an embodiment of the present invention;

[0056] Figure 9 This is a bottom view of the second type of positive electrode sheet in the unfolded state according to an embodiment of the present invention;

[0057] Figure 10 This is a cross-sectional view of the second type of positive electrode sheet in the unfolded state according to an embodiment of the present invention;

[0058] Figure 11 This is a top view of the third type of positive electrode sheet in the unfolded state according to an embodiment of the present invention;

[0059] Figure 12 This is a bottom view of the third type of positive electrode sheet in the unfolded state according to an embodiment of the present invention;

[0060] Figure 13 This is a cross-sectional view of the third type of positive electrode sheet in the unfolded state according to an embodiment of the present invention.

[0061] Explanation of reference numerals in the attached figures:

[0062] 10. Positive electrode plate; 101. Straight section; 102. Arc section; 11. Positive electrode current collector; 12. Positive electrode active layer; 121. Groove; 122. Pits; 123. Concave part; 124. Pits area; 125. Protrusion;

[0063] 20. Negative electrode sheet; 21. Negative electrode current collector; 22. Negative electrode active layer;

[0064] 30. Separator; 31. Substrate layer; 32. Functional layer; 321. Ceramic layer; 322. Second adhesive layer; 33. First adhesive layer;

[0065] X—First direction; Y—Second direction; Z—Third direction; V—Wounding direction. Detailed Implementation

[0066] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0067] Lithium-ion batteries are a common type of rechargeable battery. How to charge lithium batteries is one of the key technologies in their application. In existing technologies, lithium battery charging generally employs a two-stage charging method: constant current (CC) charging and constant voltage (CV) charging. First, a constant current is used to charge the lithium battery until the cell voltage reaches the cell's charging limit voltage. Then, the cell's charging limit voltage is used for constant voltage charging, during which the charging current gradually decreases. When the charging current decreases to the charging cutoff current, charging ends, and the lithium battery cell is fully charged. In existing battery cores, the negative electrode active layer often uses silicon-based composite materials to improve the battery's energy density. However, when the above charging method is applied to silicon-doped cores, batteries with silicon-based composite negative electrode active layers often encounter the problem of difficulty in reducing the current to the preset charging cutoff current during charging, making it difficult for the battery to reach a fully charged state; that is, the battery has a problem of not being able to fully charge.

[0068] To address the aforementioned technical issues, research revealed that the primary cause is the highest winding stress experienced by the inner ring of the core. Furthermore, the bending radius of the first bending zone of the positive electrode sheet (the side facing the core's center line) is too small, approaching 180 degrees. The two straight sections on the inner side of the positive electrode sheet are nearly folded together, causing the positive electrode particles to be squeezed out. Simultaneously, the silicon-based material of the silicon-doped negative electrode sheet is also quite hard, and it expands significantly during charging and discharging. The separator is simultaneously subjected to pressure from both the hard silicon-based material and the positive electrode particles, resulting in excessive stretching of the separator. This leads to a thinner separator at that point, the ceramic layer being squeezed off, the pores in the separator being deformed, or even the pores being enlarged. Positive electrode particles that have been severely squeezed out or the positive active material particles on the inner side puncture the separator and come into contact with the negative electrode sheet, causing numerous localized micro-short circuits and increasing the K-value. Consequently, the battery struggles to reduce its current to the preset charging cutoff during charging, making it difficult to reach a fully charged state. The K value refers to the voltage drop of the battery per unit time. It is an indicator used to measure the self-discharge rate of lithium batteries. The smaller the K value, the lower the self-discharge rate of the battery and the better the battery performance.

[0069] The following is combined Figures 1 to 13 The following describes embodiments of the present invention.

[0070] According to an embodiment of the present invention, a winding core is provided, comprising: a positive electrode sheet 10, a negative electrode sheet 20, and a separator 30, wherein the winding core is formed by winding the positive electrode sheet 10, the separator 30, and the negative electrode sheet 20 sequentially stacked; the positive electrode sheet 10 includes a positive current collector 11 and a positive active layer 12 located on the surface of the positive current collector 11; along the winding direction of the winding core, the positive electrode sheet 10 includes a straight section 101 and an arc section 102, and a groove 121 is provided on the positive active layer 12 of the positive electrode sheet 10 facing the winding center of the winding core, the groove 121 being located at least on one arc section 102 of the positive electrode sheet 10 closest to the winding center, and the depth of the groove 121 being H1; the negative electrode sheet... 20 includes a negative electrode current collector 21 and a negative electrode active layer 22 located on the surface of the negative electrode current collector 21, the negative electrode active layer 22 including a silicon-based material; the separator 30 includes a substrate layer 31 and a functional layer 32, the functional layer 32 covering the side of the substrate layer 31 facing the positive electrode 10, the functional layer 32 including a ceramic material, the thickness of the functional layer 32 including the ceramic material is p1, wherein p1 and H1 satisfy the relationship: 0.02≤p1 / H1≤2; the value range of H1 is 3μm≤H1≤40μm, preferably 5μm≤H1≤25μm; the value range of p1 is 0.3μm≤p1≤10μm, preferably 0.5μm≤p1≤8μm.

[0071] The winding direction refers to Figures 3 to 4 , Figures 8 to 9 and Figures 11 to 12 The "V" direction indicated by the middle arrow is obtained by stacking the positive electrode 10, the separator 30, and the negative electrode 20 and then winding them along the winding direction V. Figure 1 The core shown has an elliptical cross-section. The straight section 101 of the positive electrode 10 corresponds to the straight section of the elliptical structure, and the arc section 102 is a bent section. During the bending process of the arc section 102, the inner circle of the positive electrode active layer 12 is compressed. Along the winding direction, the starting end of the positive electrode 10 is located close to the center of the core. The positive electrode 10 has several straight sections 101, arc sections 102, ... connected in sequence. The arc section 102 closest to the winding center on the positive electrode 10 is the arc section 102 closest to its winding starting end. It should be noted that the positive electrode 10 is coated with a positive electrode active layer 12 on both sides, and the groove 121 is set on the positive electrode active layer 12 on the side of the positive electrode 10 facing the center of the core, that is, the groove 121 is set in the inner circle of the arc section 102.

[0072] By applying the winding core of this embodiment, by providing grooves 121 on the positive active layer 12 of the positive electrode sheet 10, and with the grooves 121 being provided on at least one arc segment 102 of the positive electrode sheet 10 closest to the winding center, the thickness of at least a portion of the arc segment 102 of the positive electrode sheet 10 can be reduced, the stacking thickness of the positive active layer 12 at the arc segment 102 can be reduced, and the effective distance between the grooves 121 and the separator 30 on the positive electrode sheet 10 can be increased. This reduces the degree of compression of the active particles in the arc segment 102 during winding, and also prevents the active particles on the positive active layer 12 at the arc segment 102 from being excessively compressed and falling off, thereby reducing the negative electrode thickness. The risk of active particles on the positive electrode 10 puncturing the separator 30 is reduced. At the same time, the ceramic material on the separator has good pressure resistance and wear resistance. The functional layer 32 of the ceramic material covers the side of the substrate layer 31 facing the positive electrode 10. This can prevent the harder active material inside the positive electrode 10 from expanding and squeezing the separator 30 during cycling, thus preventing the separator 30 from deforming or thinning. This reduces the risk of active particles on the positive electrode 10 puncturing the separator, avoids micro-short circuits inside the battery, reduces battery self-discharge, and prevents the battery from failing to reduce to the preset charging cutoff current during charging, thereby ensuring that the battery can reach a fully charged state.

[0073] It should also be noted that the depth H1 of the groove 121 refers to the depth of the groove 121 along the thickness direction of the diaphragm 30, specifically the depth of the groove 121 along... Figure 5 The central arrow indicates the depth of the indentation in the Z-direction; the thickness of the functional layer 32 refers to the dimension of the functional layer 32 along the thickness direction of the diaphragm 30, specifically the dimension of the functional layer 32 along... Figure 6 or Figure 7The dimension in the Z-direction indicated by the middle arrow. Increasing the thickness of the functional layer 32 can improve the compressibility of the separator 30 and reduce the risk of the separator 30 becoming thinner. Meanwhile, setting the groove 121 on the positive electrode 10 can reduce the degree of compression between the positive electrode active particles on the positive electrode 10. If p1 / H1 is less than 0.02, the thickness of the functional layer 32 is too small relative to the depth of the groove 121. If the thickness of the functional layer 32 is too small, the compressibility of the separator 30 is poor, and the separator 30 cannot provide sufficient mechanical strength to resist the compression of the positive electrode active particles, making the separator 30 easily punctured. If p1 / H1... If the value is greater than 2, the thickness of the functional layer 32 is too large relative to the depth of the groove 121, and the depth of the groove 121 is too small. This cannot effectively reduce the degree of compression between the active particles on the arc segment 102 of the positive electrode 10, nor can it reduce the compressive deformation stress experienced by the arc segment 102 of the positive electrode 10 during winding. There is still a high risk that the active particles on the positive electrode 10 will puncture the separator 30, or the risk of the active layer falling off due to excessive stress on the arc segment 102 of the positive electrode 10 can be reduced, causing a micro-short circuit. The increased K value worsens the problem of CV not being cut off. Here, the units of p1 and H1 in p1 / H1 are both μm.

[0074] Furthermore, if H1 is less than 3 μm, the depth of the groove 121 is too small, making it difficult to reduce the thickness of the positive electrode active layer 12 at the arc segment 102. There is still a risk that the active particles will damage the separator 30. In addition, the groove 121 can also provide space for the electrolyte, which is beneficial to improve the electrolyte retention of the battery and thus improve the cycle performance of the battery. If the depth of the groove 121 is too small, there is still a possibility that the battery cannot be reduced to the preset charging cutoff current during charging, and the electrolyte storage space cannot be effectively increased, thus failing to effectively improve the cycle performance of the battery. If H1 is greater than 40 μm, the depth of the groove 121 is too large. During the formation of the groove 121, it is easy to cause foil leakage or damage to the strength of the positive electrode sheet. Moreover, the loss of active material on the positive electrode active layer 12 caused by the groove 121 is too large, resulting in an excessive reduction in the actual capacity of the battery and an excessively low actual energy density of the battery. If p1 is less than 0.3 μm, the thickness of the functional layer 32 is too small, the compressibility of the separator 30 is too poor, the separator 30 is easily damaged, and there is still a risk that the separator 30 will be punctured by the positive electrode active particles; if p1 is greater than 10 μm, the thickness of the functional layer 32 is too large, the volume of the separator 30 is large, the volume of the active material on the electrode in the battery is relatively reduced, and the volume energy density of the battery is affected.

[0075] Therefore, by limiting the ratio p1 / H1 between the thickness p1 of the functional layer 32 and the depth H1 of the groove 121 to a value in the range of 0.02 to 2, and p1 to a value in the range of 0.3 μm to 10 μm, and H1 to a value in the range of 3 μm to 40 μm, the risk of active particles on the positive electrode sheet 10 puncturing the separator 30 can be reduced. At the same time, it can also prevent the active particles on the positive electrode active layer 12 at the arc segment 102 from being excessively squeezed during the cycle and falling off or breaking. This ensures that the battery can be reduced to the preset charging cutoff current during the charging process, so that the battery can reach a fully charged state. It can also improve the liquid retention of the battery, improve the cycle performance of the battery, and ensure that the battery has a high volumetric energy density.

[0076] Optionally, p1 / H1 can take any value from 0.02, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.8, 2, or a value between any two values.

[0077] Optionally, the depth H1 of the groove 121 can be any value selected from 3μm, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 25μm, 30μm, 35μm, and 40μm, or a value between any two of these values. Preferably, the range of H1 is: 5μm ≤ H1 ≤ 25μm.

[0078] Optionally, the thickness p1 of the functional layer 32 can be any value or a value between any two of the following: 0.3μm, 0.5μm, 1μm, 1.5μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, and 10μm. Preferably, the value of p1 is in the range of 0.5μm ≤ p1 ≤ 8μm.

[0079] It should be noted that the thickness of the positive current collector 11 ranges from 4 μm to 20 μm. Optionally, the positive current collector is aluminum foil.

[0080] It should be noted that the diaphragm 30 includes a substrate layer 31 and a functional layer 32 covering one side of the substrate layer 31. The functional layer 32 can be shaped as follows: Figure 6 As shown in the layered configuration, functional layer 32 includes a ceramic layer 321 and a second adhesive layer 322. The ceramic layer 321 directly covers the surface of the substrate layer 31, and the second adhesive layer 322 covers the surface of the ceramic layer 321 away from the substrate layer 31. In this case, the thickness p1 of functional layer 32 refers to the total thickness of the ceramic layer 321 and the second adhesive layer 322 along the Z direction. Functional layer 32 can also be arranged as follows: Figure 7In the single-layer form shown, the functional layer 32 is a coating layer applied to the surface of the substrate layer 31 after the ceramic material and adhesive are mixed. At this time, the thickness p1 of the functional layer 32 is the thickness of the functional layer 32 coated after the ceramic material and adhesive are mixed along the Z direction.

[0081] In some embodiments, the air permeability of the diaphragm 30 is G, and the value of G ranges from 80s / 100cc ≤ G ≤ 400s / 100cc, preferably 90s / 100cc ≤ G ≤ 300s / 100cc. The relationship between H1 and G is: 0.016 ≤ H1 / G ≤ 0.5, and H1 / G is preferably 0.017-0.45. Here, H1 / G is only a numerical relationship and does not involve units. It should be noted that setting the groove 121 on the positive electrode 10 can improve the CV non-cutoff phenomenon of the battery (i.e., the phenomenon that the battery cannot reduce to the preset charging cutoff current during charging). However, in the area where the groove 121 is located, the contact between the positive and negative electrodes becomes worse, which slows down the migration speed of lithium ions from the positive electrode 10 to the negative electrode 20. As a result, the lithium ions that come off the positive electrode 10 may become dead lithium due to the excessively long migration path. Dead lithium is prone to precipitation along the thickness direction of the electrode, puncturing the separator and causing a short circuit between the positive and negative electrodes, affecting the battery safety performance. Therefore, it is necessary to control the ratio between the depth H1 of the groove 121 at this location and the air permeability G of the separator within a reasonable range. The air permeability of the separator can be appropriately increased according to the depth of the groove 121 set on the bending area of ​​the positive electrode 10 to reduce the resistance encountered by lithium ions during migration, reduce the occurrence of dead lithium, and improve the safety of the battery. If H1 / G is less than 0.016, which is below the lower limit of the above range, it will not only fail to improve the CV non-cutoff problem, but also, due to the shallow depth of the groove 121, the separator 30 will be more easily subjected to excessive compression during cycling, leading to the destruction of the polymer chain orientation of the separator 30, a decrease in tensile strength, and rupture of the separator 30, causing a short circuit. If H1 / G is greater than 0.5, which is above the upper limit of the above range, the depth of the groove 121 will be too large, the lithium ion migration path will be too large, and the permeability of the separator 30 will be too small, making it difficult for lithium ions to embed into the negative electrode, which will easily increase dead lithium and increase the precipitation of lithium dendrites in this area, causing short circuit safety problems. In addition, the higher the air permeability G value of the separator 30, the better the air permeability, which is more conducive to the transport of lithium ions in the electrolyte. However, the strength of the separator 30 will decrease, and the separator 30 will be easily damaged. If G is less than 80s / 100cc, the air permeability of the separator 30 is too poor, which seriously affects the smooth transport of lithium ions. If G is greater than 400s / 100cc, the air permeability of the separator 30 is too high, the strength of the separator 30 is too low, the resistance to deformation is poor, and it is easily damaged by the positive and negative electrodes.

[0082] Therefore, by limiting the ratio H1 / G between the depth H1 of the groove 121 and the air permeability G of the separator to a value within the range of 0.016 to 0.5, and G to a value within the range of 80s / 100c to 400cs / 100cc, the problem of lithium ions easily becoming dead lithium deposits during the migration process from the positive electrode 10 to the negative electrode 20 due to the groove 121 on the positive electrode 10 can be further avoided. This reduces the resistance encountered by lithium ions during migration, reduces the occurrence of dead lithium, and ensures the strength of the separator 30 itself, preventing the separator 30 from being damaged by the positive and negative electrodes, thereby improving the safety of the battery.

[0083] Optionally, the value of G can be any value selected from 80s / 100cc, 100s / 100cc, 150s / 100cc, 200s / 100cc, 250s / 100cc, 300s / 100cc, 350s / 100cc, and 400s / 100cc, or a value between any two of these. Preferably, the range of G is: 90s / 100cc ≤ G ≤ 300s / 100cc.

[0084] Optionally, the value of H1 / G can be any value selected from 0.016, 0.02, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, and 0.5, or a value between any two values. Preferably, the value of H1 / G is in the range of 0.017 to 0.45.

[0085] In some embodiments, further combined Figure 6 and Figure 7As shown, the separator 30 also includes a first adhesive layer 33, which is disposed on the side of the substrate layer 31 opposite to the functional layer 32. The coverage of the first adhesive layer 33 relative to the substrate layer 31 is μ, and the value of μ ranges from 20% to μ to 100%. It should be noted that, along the thickness direction of the separator 30, the first adhesive layer 33 is coated on the side of the substrate layer 31 opposite to the functional layer 32. The substrate layer 31 is a polymer material with a certain porous structure, providing ion transport channels for lithium ions in the electrolyte. The first adhesive layer 33 is a functional material coated on the surface of the substrate layer 31, typically containing a polymer binder, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene modified polyvinylidene fluoride and its copolymers, polyacrylonitrile, polymethyl methacrylate, polyacrylic acid, styrene-butadiene rubber (SBR), polyvinyl alcohol and its copolymerized polyvinyl alcohol, polyvinyl acetate, polyacrylamide, and phenolic resin. The material is at least one of resin, epoxy resin, etc. The material of the first adhesive layer 33 can be the same as that of the second adhesive layer 322, or they can be different in one embodiment. The coverage of the first adhesive layer 33 relative to the substrate layer 31 is equal to the area covered by the adhesive layer / the total area of ​​the substrate layer. If the coverage is too small, some areas of the substrate layer 31 will not be protected by the first adhesive layer 33, which will affect the mechanical strength, air permeability, and bonding strength between the separator and the negative electrode of the diaphragm 30. The separator 30 is easily punctured by active material particles, causing the positive electrode 10 to come into contact with the negative electrode 20. If the coverage is too large, it will affect the ion transport efficiency and easily lead to lithium plating on the negative electrode.

[0086] Therefore, by setting the coverage μ of the first adhesive layer 33 on the substrate layer 31 to a value between 20% and 100%, the coverage of the first adhesive layer 33 is controlled to have a reasonable value range. This ensures both the air permeability of the separator 30 and the adhesion between the negative electrode sheet and the separator within a suitable range. This reduces the risk of poor adhesion between the negative electrode and the separator due to negative electrode expansion during battery cycling, reduces the risk of lithium plating on the negative electrode, and thus improves the safety of the core.

[0087] Optionally, μ can take any value from 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or a value between any two values.

[0088] In some embodiments, when the overall thickness of the diaphragm 30 is greater than or equal to 4 μm and less than or equal to 15 μm, the diaphragm needle penetration strength is required to be greater than 100 gf. This reduces the risk of the diaphragm 30 being punctured.

[0089] In some embodiments, further combined Figure 3 and Figure 5As shown, the positive electrode 10 has intersecting first direction X and second direction Y. The positive electrode 10 is wound along the second direction Y, and the dimension of the groove 121 along the second direction Y is W1, where W1 ranges from 3mm ≤ W1 ≤ 10mm. Here, the first direction refers to... Figure 3 The direction indicated by the middle arrow is the "X"; the second direction refers to... Figure 3 and Figure 5 The direction indicated by the middle arrow "Y" is parallel to the second direction Y, where the winding direction V is parallel to the second direction Y. When the electrode is in the unfolded state, the second direction Y is the length direction of the electrode, and the first direction X is the width direction of the electrode. It should be noted that the setting of the groove 121 will reduce the mass of active material on the positive electrode active layer 12, thereby reducing the battery capacity. If W1 is greater than 10mm, the size of the groove 121 along the second direction Y is too large, resulting in too much reduction in the mass of active material and a significant reduction in battery capacity. If W1 is less than 3mm, the size of the groove 121 along the second direction Y is insufficient, and during winding, the active particles of the arc segment 102 on the positive electrode 1 are still subject to considerable compression, making it difficult to reduce the thickness of the positive electrode active layer 12 at the arc segment 102. Therefore, by setting the size of the groove 121 along the second direction Y to be within the range of 3mm to 10mm, the groove 121 is limited to a reasonable size. This ensures that the setting of the groove 121 can effectively reduce the stacking thickness of the positive electrode active layer 12 at the arc segment 102, effectively reducing the risk of active particles on the positive electrode sheet 10 damaging the separator 30, thereby reducing the possibility of CV non-cutoff phenomenon in the battery. It can also avoid removing too much active material from the positive electrode active layer 12, thereby ensuring that the battery has sufficient capacity and thus ensuring the volumetric energy density of the battery.

[0090] Optionally, the dimension W1 of the groove 121 along the second direction can be any value of 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, or 10mm, or a value between any two of these values.

[0091] In some embodiments, further combined Figure 3 , Figure 8 and Figure 11 As shown, along the second direction Y, the size of the groove 121 is larger than the size of the arc segment 102 in which it is located. It should be noted that the junction between the straight segment 101 and the arc segment 102 is as follows... Figure 3 , Figure 7 and Figure 10 As shown by the dotted line, after winding, the arc segment 102 forms... Figures 1 to 2In the bent shape, the active material on the side of the entire arc segment 102 facing the winding center of the core will be squeezed. By limiting the size of the groove 121 along the second direction Y to be larger than the size of the arc segment 102, it can be ensured that the groove 121 covers and extends beyond the area on the arc segment 102 along the second direction, thereby minimizing the risk of active particles on the arc segment 102 being squeezed off, further reducing the possibility of CV non-cutoff phenomenon during battery charging, and improving battery reliability.

[0092] In some embodiments, further combined Figure 1 As shown, the distance by which the groove 121 extends beyond the arc segment 102 on one side is L1, and the value of L1 is in the range of 0.1mm≤L1≤5mm. If L1 is less than 0.1mm, the edge of the groove 121 is too close to the boundary line between the straight section 101 and the arc section 102. In the vicinity of the arc section 102, the amount of powder remaining in the positive electrode active layer 12 after removing the groove 121 is too large. After the core is wound and the arc section 102 is bent, the active particles near the junction of the arc section 102 and the straight section 101 will still be subjected to relatively severe compression. The positive electrode active layer 12 has the risk of powder shedding. Moreover, when participating in the charge and discharge reaction, the mass of the positive electrode active material on the positive electrode sheet 10 is more than the mass of the negative electrode active material on the negative electrode sheet 20. The CB (Capacity Balance) value in this area is too small, and the mass difference between the positive and negative electrode active materials is large, which has the risk of lithium plating. If L1 is greater than 5mm, the amount of positive electrode active material removed by the groove 121 is too large, which affects the battery capacity and ED (Energy Density).

[0093] Therefore, by limiting the distance L1 of the groove 121 extending beyond the arc segment 102 to within the range of 0.1mm to 5mm, it is possible to prevent the active particles near the junction of the arc segment 102 and the straight segment 101 from being squeezed and falling off, thereby avoiding puncturing the separator 30 and further reducing the battery CV non-cutoff phenomenon. It can also reduce the active material on the positive electrode sheet 10 participating in the charge and discharge reaction in the arc area of ​​the core, improve the CB value of the positive and negative electrodes in this area, reduce the probability of lithium plating, and avoid removing too much positive electrode active material, ensuring that the battery has sufficient capacity and energy density.

[0094] Optionally, L1 can be any value among 0.1mm, 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, and 5mm, or a value between any two of these values.

[0095] In some embodiments, further combined Figure 3 , Figure 8 and Figure 11As shown, along the first direction X, the distance between the groove 121 and the edge of the positive electrode 10 is L2, and the value of L2 ranges from 0.5mm to 15mm. It should be noted that the groove 121 is processed after the positive electrode 10 is cut; the cutting position is... Figure 3 , Figure 8 and Figure 11 The paste at the cutting position on both sides of the positive electrode 10 along the first direction X is relatively loose. If L2 is less than 0.5mm, the groove 121 is too close to the edge of the positive electrode 10 along the first direction X. During the processing of the groove 121 by laser or other mechanical means, the laser or other mechanical means may easily sweep the edge of the positive electrode 10, which may cause active material particles to fall off or even foil leakage. The falling off of particles will cause a short circuit with the negative electrode. After foil leakage, the exposed positive current collector 11 will come into contact with the negative active material on the negative electrode 20, which will cause thermal runaway. If L2 is greater than 15mm, the groove 121 is too far from the edge of the positive electrode 10 along the first direction X. Correspondingly, the size of the groove 121 along the first direction X is too small, which is not enough to effectively reduce the thickness of the positive active layer 12 at the arc segment 102. It cannot effectively avoid the problem of CV non-cutoff of the battery and it is difficult to ensure that the battery can reach a fully charged state.

[0096] Therefore, by limiting the distance between the groove 121 and the edge of the positive electrode 10 along the first direction to a value between 0.5 mm and 15 mm, it is possible to avoid the active material particles at the edge of the positive electrode 10 falling off or the foil leaking during the processing of the groove 121, thereby avoiding short circuits and thermal runaway and improving battery safety. At the same time, it is possible to ensure that the groove 121 has sufficient size along the first direction X, thereby effectively reducing the stacking thickness of the positive electrode active layer 12 at the arc segment 102, reducing the risk of active particles on the positive electrode 10 puncturing the separator 30, and ensuring that the battery can reach a fully charged state.

[0097] Optionally, L2 can be any value among 0.5mm, 1mm, 2mm, 5mm, 8mm, 10mm, 12mm, 14mm, and 15mm, or a value between any two of these values.

[0098] In some embodiments, the thickness of the positive electrode active layer 12 is H2 μm, where H1 and H2 satisfy 0.05 ≤ H1 / H2 ≤ 0.75. The thickness of the positive electrode active layer 12 refers to the thickness of one side of the positive electrode active layer 12 along... Figure 5The dimension in the third direction Z is indicated by the middle arrow. If H1 / H2 is less than 0.05, the depth of the groove 121 is too small relative to the thickness of the positive electrode active layer 12, making it difficult to reduce the compression of the active particles in the arc segment 102 and reduce the stacking thickness of the positive electrode active layer 12 at the arc segment 102. If H1 / H2 is greater than 0.75, the depth of the groove 121 is too large relative to the thickness of the positive electrode active layer 12, making it easy for foil leakage to occur during the formation of the groove 121. The exposed positive electrode current collector 11 may come into contact with the active material layer of the negative electrode sheet 20, posing a risk of short circuit, and may also undergo side reactions with the electrolyte, reducing the electrolyte content. Furthermore, the excessive loss of active material on the positive electrode active layer 12 caused by the groove 121 leads to an excessive reduction in the actual capacity of the battery and an excessively low actual energy density. Here, the positive electrode current collector 11 is the foil in the positive electrode sheet 10, and optionally, the positive electrode current collector 11 is aluminum foil.

[0099] Therefore, by setting the ratio H1 / H2 to be within the range of 0.05 to 0.75, it is possible to ensure that the groove 121 can effectively reduce the thickness of the positive electrode active layer 12 at the arc segment 102, thereby effectively reducing the risk of active particles on the positive electrode sheet 10 damaging the separator 30 and improving the CV non-cutoff phenomenon of the battery. It is also possible to avoid the positive electrode current collector 11 being exposed, thereby avoiding the positive electrode current collector 11 contacting the active material layer of the negative electrode sheet 20 and causing a short circuit, and avoiding the exposed positive electrode current collector 11 reacting with the electrolyte, thereby further ensuring the safety of the core and ensuring the electrolyte retention. It is also possible to avoid excessive loss of active material on the positive electrode active layer 12, thereby ensuring the energy density of the battery.

[0100] Optionally, H1 / H2 can be any value from 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, or a value between any two values.

[0101] In some embodiments, the groove 121 is a surface-scanned groove, specifically processed by laser surface scanning, which is convenient to process, has high processing accuracy, and is easy to control processing dimensions; it can also be achieved by mechanical grinding or scraping with a scraper.

[0102] In some embodiments, the value of H2 is in the range of 40μm≤H2≤80μm. If H2 is less than 40μm, the thickness of the positive electrode active layer 12 is too small, affecting the battery capacity, and foil leakage is likely to occur during the processing of the groove 121; if H2 is greater than 80μm, the thickness of the positive electrode active layer 12 is too large, the degree of compression of the active particles in the arc segment 102 is too large during the winding process, and the stacking thickness of the positive electrode active layer 12 at the arc segment 102 is too large, causing the harder active material inside the positive electrode sheet 10 to severely compress the separator 30, and the active particles on the positive electrode active layer 12 are squeezed and fall off, which poses a risk that the active particles on the positive electrode sheet 10 will damage the separator 30. Therefore, by setting H2 to a value within the range of 40μm to 80μm, the positive electrode active layer 12 is limited to a reasonable thickness. This ensures that the battery has sufficient capacity and that the positive electrode active layer 12 has sufficient thickness to support the processing of the groove 121, thus avoiding the exposure of the positive electrode current collector 11 after the groove 121 is processed. It also avoids the positive electrode active layer 12 from being too thick, thereby preventing the active particles on the positive electrode sheet 10 from piercing the separator 30, and thus further ensuring the safety of the core.

[0103] Optionally, the value of H2 can be any value among 40μm, 45μm, 48μm, 50μm, 52μm, 55μm, 57μm, 60μm, 62μm, 65μm, 67μm, 70μm, 72μm, 75μm, 78μm, and 80μm, or a value between any two of these values.

[0104] Preferably, the value of H2 is in the range of 45μm≤H2≤75μm.

[0105] In some embodiments, further combined Figures 8 to 10 As shown, the surface of the positive electrode 10 is also provided with a textured area, and a partial enlarged cross-sectional schematic diagram of the textured area is shown below. Figure 10 As shown, the textured area includes several recesses 123 and corresponding protrusions 125. The recesses 123 are disposed on the surface of the positive electrode sheet 10 facing the winding center of the winding core, and the protrusions 125 are disposed on the surface of the positive electrode sheet 10 away from the winding center of the winding core. The recess depth of the recesses 123 along the third direction Z is H4, and H4 and H1 satisfy the relationship: 0.25≤H1 / H4≤8. The value range of H4 is 2μm≤H4≤40μm, preferably 3μm≤H4≤20μm. The recess depth of the recesses 123 refers to the depth of the recesses 123 along the third direction Z. Figure 10The recess size in the "Z" direction indicated by the middle arrow. By setting a textured region on the surface of the positive electrode 10, the recesses 123 in the textured region can provide space for the electrolyte, thereby increasing the electrolyte storage capacity in the area where the recesses 123 are located, improving the lithium-ion transport rate, and reducing side reactions and lithium plating problems caused by electrolyte deficiency, especially further improving the lithium plating problem at the arc. If H1 / H4 is less than 0.25, or H4 is less than 2μm, the recess depth of the recesses 123 is too small, and the space formed by the recesses 123 to accommodate the electrolyte is limited, which cannot effectively increase the electrolyte storage capacity in the area where the recesses 123 are located, resulting in poor battery cycle performance. If H1 / H4 is greater than 8, or H4 is greater than 40μm, then... If the recess 123 is too deep, foil leakage is likely to occur during the formation of the recess 123, and the battery capacity will be reduced. Therefore, by limiting the value of H1 / H4 to the range of 0.25 to 8, and setting the recess 123 to the range of 2μm to 40μm, it can be ensured that the recess 123 can effectively increase the liquid storage capacity of the area where the recess 123 is provided, thereby improving the lithium ion transport rate, improving the lithium plating problem, and improving the expansion problem. At the same time, it can also avoid the positive electrode current collector 11 corresponding to the recess 123 being exposed due to the excessive recess depth of the recess 123, thereby improving the battery safety and ensuring the battery capacity.

[0106] Optionally, H1 / H4 can be any value from 0.25, 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8, or a value between any two values.

[0107] Optionally, the value of H4 can be any value selected from 2μm, 5μm, 10μm, 15μm, 25μm, 30μm, and 40μm, or a value between any two of these values. Preferably, the value range of H4 is 3μm ≤ H4 ≤ 20μm.

[0108] In some embodiments, further combined Figure 10As shown, the protrusion height of the protrusion 125 is H5, and H5 and H1 satisfy the relationship: 0.25≤H1 / H5≤8, where the value of H5 is in the range of 2μm≤H5≤40μm. The protrusion 125 increases the contact area between the positive and negative electrode sheets, reserving space for the expansion of the negative electrode during battery use. If H1 / H5 is less than 0.25, the protrusion height of the protrusion 125 is too large relative to the depth of the groove 121, resulting in poor adhesion between the positive electrode sheet 10 and the separator 30, affecting the compactness of the core, and hindering the transport of lithium ions between the positive and negative electrodes, posing a risk of lithium plating. If H1 / H5 is greater than 8, the protrusion height of the protrusion 125 is too small relative to the depth of the groove 121, failing to provide sufficient space for the expansion of the negative electrode. While leaving sufficient space may not effectively mitigate expansion, the expansion of the negative electrode may still compress the separator, leading to separator blockage and further electrolyte extrusion. Therefore, by limiting H1 / H5 to the range of 0.25 to 8, and H5 to the range of 2μm to 40μm, sufficient space can be reserved for the expansion of the negative electrode during battery use. This avoids short circuits caused by the negative electrode compressing the separator after expansion, and also reduces the risk of lithium plating, thereby further improving the battery's charge / discharge performance and safety.

[0109] Alternatively, the protrusion height H5 of the protrusion 125 can be equal to the recess depth H4 of the recess 123.

[0110] It should be noted that the textured area is formed by embossing the surface of the positive electrode 10 using an embossing roller. After the embossing roller rolls the positive electrode 10, a recess 123 is formed on one side of the surface of the positive electrode 10, and a protrusion 125 is formed on the other side of the surface of the positive electrode 10. Optionally, the shape of a single recess 123 can be circular, square, rhomboid, or elliptical, etc., preferably circular. Optionally, the textured area and the groove 121 are spaced apart, that is, along the winding direction, the textured area is located downstream of the arc segment 102 where the groove 121 is provided. It can be understood that, as an alternative embodiment, the recess 123 and the protrusion 125 can also be provided in the area where the groove 121 is provided, that is, the recess 123 and the protrusion 125 can overlap with the groove 121.

[0111] In some embodiments, the extension dimension of the recess 123 along the first direction X and / or the second direction Y is D2, and the value of D2 is in the range of 0.5mm ≤ D2 ≤ 10mm. If D2 is less than 0.5mm, the size of the recess 123 is too small, which is not conducive to the entry of electrolyte, and thus not conducive to increasing the electrolyte storage capacity in the area where the recess 123 is provided; if D2 is greater than 10mm, the size of the recess 123 is too large, and the amount of active material lost on the positive electrode active layer 12 due to the recess 123 is too large, affecting the battery capacity. Therefore, by setting the extension dimension of the recess 123 along the first direction X and / or the second direction Y to be in the range of 0.5mm to 10mm, the electrolyte storage capacity in the area where the recess 123 is provided can be effectively increased, thereby increasing the lithium ion transport rate and improving the lithium plating problem, while avoiding excessive loss of active material on the positive electrode active layer 12, thus ensuring that the battery has sufficient capacity.

[0112] Optionally, D2 is any value among 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, and 10mm, or a value between any two values.

[0113] Preferably, the opening shape of the recess 123 is circular, which is convenient for processing; of course, the opening shape of the recess 123 is not limited to a circle, but can also be a triangular hole, a quadrilateral hole, a pentagonal hole or other polygonal hole, or an elliptical hole or other shapes.

[0114] In some embodiments, the distance between two adjacent recesses 123 along the second direction Y is W5, where W5 satisfies: 0.5×D2≤W≤1.2×D2. This distance between two adjacent recesses 123 is related to the size of the recesses 123, ensuring a reasonable distance between them. This ensures the density in the area where the recesses 123 are located. This ensures that the recesses 123 can sufficiently increase the electrolyte capacity, thereby effectively increasing the residual electrolyte content in the area where the recesses 123 are located and improving battery performance. It also avoids excessive loss of active material on the positive electrode active layer 12 due to excessive density of the recesses 123, thus ensuring that the battery has sufficient capacity.

[0115] In some embodiments, further combined Figure 8As shown, along the first direction X, the shortest distance between the recess 123 and the edge of the positive electrode 10 is L3, and the value of L3 is in the range of 2mm ≤ L3 ≤ 15mm. Here, the edge of the positive electrode 10 refers to the edges on both sides of the positive electrode 10 along the first direction X; along the first direction X, there are multiple recesses 123, and the shortest distance L3 refers to the distance between the recess 123 closest to the edge of the positive electrode 10 and the edge of the positive electrode 10. It should be noted that the recess 123 is formed by embossing rollers pressing the positive electrode sheet 10. The pressure during the embossing process is relatively large. If L3 is less than 2mm, the shortest distance between the recess 123 and the edge of the positive electrode sheet 10 along the first direction X is too small. Along the first direction X, the edge of the embossing roller is too close to the edge of the positive electrode sheet 10, which will cause the positive electrode sheet 10 to be pressed into a wavy sheet, affecting the adhesion between the positive electrode sheet 10 and the separator 30, and thus affecting the compactness of the core and the transmission of lithium ions. If L3 is greater than 15mm, the shortest distance between the recess 123 and the edge of the positive electrode sheet 10 along the first direction X is too large. There is insufficient space on the positive electrode sheet 10 along the first direction X for setting the recess 123, which cannot effectively increase the liquid storage capacity, and thus cannot effectively improve the lithium plating problem.

[0116] Therefore, by limiting the shortest distance along the first direction between the recess 123 and the edge of the positive electrode 10 to between 2 mm and 7 mm, it is possible to avoid the positive electrode 10 being pressed into a corrugated sheet, thereby ensuring the fit between the positive electrode 10 and the separator 30, and to effectively increase the liquid storage capacity in the area where the recess 123 is provided, thereby effectively improving the lithium plating problem.

[0117] Optionally, the value of L3 is any one of 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, or a value between any two of these values.

[0118] It should be noted that, along the first direction X, the shortest distance between the convex portion 125 and the edge of the positive electrode 10 is equal to the shortest distance between the concave portion 123 and the edge of the positive electrode 10.

[0119] In some embodiments, L3 and L2 satisfy the relationship: L3 > L2. By limiting the shortest distance L3 between the recess 123 and the edge of the positive electrode 10 along the first direction X to be greater than the distance L2 between the groove 121 and the edge of the positive electrode 10 along the first direction X, it is ensured that the recess 123 closest to the edge of the positive electrode 10 has a sufficient distance to the edge of the positive electrode 10 along the first direction X, thereby preventing the positive electrode 10 from being pressed into a wavy sheet by the embossing roller and ensuring the compactness of the core.

[0120] In some embodiments, along the winding direction of the core, the positive electrode sheet 10 includes a first to an Nth fold connected in sequence. Each fold of the positive electrode sheet 10 includes a straight segment 101 and an arc segment 102. A groove 121 is disposed at the position of the arc segment 102 on the first to nth folds of the positive electrode sheet 10, wherein N and n are positive integers, n < N, and n ≤ 3. Further combined with... Figure 1 As shown in the schematic diagram of the cross-section of the core, the first fold of the positive electrode sheet 10 is close to a 180-degree bend. Therefore, the active particles on the positive electrode active layer 12 at the first arc segment 102 are subjected to the most severe compression, and the active particles are easily squeezed off. Furthermore, the problems of powder shedding from the positive electrode sheet 10 and puncture of the separator 30 mainly occur in the first three folds. In addition, the presence of grooves 121 reduces the amount of active material on the positive electrode sheet 10, affecting battery capacity. Therefore, while improving the separator puncture problem, the number of grooves 121 should be minimized. By placing grooves 121 at the arc segments 102 on the first to nth folds of the positive electrode sheet 10, where n is less than or equal to 3, the problem of severe compression of active particles at the arc segments 102 can be effectively improved. This can effectively improve the battery CV non-cutoff phenomenon and avoid excessive reduction in battery capacity. Optionally, n=1, a groove 121 is provided on the first arc segment 102 of the positive electrode 10, and the number of grooves 121 is one; or, n=2, a groove 121 is provided on the first two arc segments 102 of the positive electrode 10, and the number of grooves 121 is two; or, n=3, a groove 121 is provided on the first three arc segments 102 of the positive electrode 10, and the number of grooves 121 is three.

[0121] In some embodiments, the number of grooves 121 is at least one, and the projected area of ​​a single groove 121 on the positive current collector 11 along the third direction Z is S1, where S1 ranges from 20 mm. 2 ≤S1≤1500mm 2 Among them, "third party to Z" refers to... Figure 5 The direction indicated by the middle arrow, "Z," is perpendicular to the XY plane in the third direction. It should be noted that there can be one or more grooves 121; if the orthographic projection area of ​​a single groove 121 along the third direction is less than 20 mm²... 2 If the area is too small, due to process fluctuations during the winding process, the groove 121 may not be able to cover the arc area, thus failing to solve the problem of active particles on the positive electrode 10 piercing the separator 30; if the projected area of ​​a single groove 121 along a third direction is greater than 1500 mm², the problem may occur. 2 If the area is too large, the loss of active material particles on the positive electrode 10 will be too great, affecting the battery capacity. Therefore, the positive projection area of ​​a single groove 121 along a third direction is limited to 20 mm². 2 Up to 1500mm 2The range of values ​​ensures that after the electrode is wound, the groove 121 can cover the arc area of ​​the core, thereby preventing the active particles on the positive electrode 10 from piercing the separator 30 and improving the phenomenon of non-cut-off of CV in the battery. It also prevents excessive loss of active material particles on the positive electrode 10, thereby ensuring that the battery has sufficient capacity.

[0122] Optionally, S1 is 20mm 2 50mm 2 100mm 2 200mm 2 500mm 2 1000mm 2 1500mm 2 It can be any value in the range or the value between any two values.

[0123] In some embodiments, along the third direction Z, the total area of ​​the orthographic projection of the groove 121 onto the positive current collector 11 is S2, and the total area of ​​the orthographic projection of the positive active layer 12 onto the positive current collector 11 is S3. S2 and S3 satisfy the relationship: 0.001 ≤ S2 / S3 ≤ 0.1. It should be noted that when there is only one groove 121, S2 equals S1; when there are two or more grooves 121, S2 is the total area of ​​the orthographic projection of all grooves 121 along the third direction, and S2 equals the product of S1 and the number of grooves 121. The orthographic projection of the groove 121 along the third direction refers to the orthographic projection of the groove 121 along the third direction Z onto the XY plane; the orthographic projection of the positive electrode sheet 10 along the third direction refers to the orthographic projection of the positive electrode sheet 10 along the third direction Z onto the XY plane. If S2 / S3 is less than 0.001, the total area of ​​the groove 121 is too small relative to the total area of ​​the positive electrode 10. The insufficient area of ​​the groove 121 cannot effectively reduce the thickness of the positive active layer 12 at the arc segment 102, thus failing to effectively prevent the separator 30 from being punctured by active material particles. Furthermore, the positive active layer 12 compresses the space, resulting in a low liquid retention capacity of the battery, affecting the battery's cycle performance and posing a risk of lithium plating. If S2 / S3 is greater than 0.1, the total area of ​​the groove 121 is too large relative to the total area of ​​the positive electrode 10, resulting in excessive loss of active material particles on the positive electrode 10 and affecting the battery's capacity.

[0124] Therefore, by limiting the values ​​of S2 / S3 to the range of 0.001 to 0.1, it is possible to improve the liquid retention of the battery, improve the CV non-cutoff phenomenon and cycle performance of the battery, and ensure that the battery has sufficient capacity, while solving the problem of the separator 30 being punctured by active material particles.

[0125] Optionally, S2 / S3 can be any value from 0.001, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a value between any two values.

[0126] In some embodiments, the value of S2 ranges from 20 mm. 2 ≤S2≤4500mm 2 This design ensures that the groove 121 has a sufficient total area, allowing enough active material to be removed from the positive electrode active layer 12 at the arc segment 102 of the positive electrode 10, thus preventing the active particles on the positive electrode 10 from piercing the separator 30 and improving the CV non-cutoff phenomenon of the battery. It also avoids excessive loss of active material particles on the positive electrode 10, thus ensuring that the battery has sufficient capacity and a high volumetric energy density.

[0127] Optionally, S2 is 20mm 2 50mm 2 100mm 2 200mm 2 500mm 2 1000mm 2 1500mm 2 2000mm 2 2500mm 2 3000mm 2 3500mm 2 4000mm 2 4500mm 2 It can be any value in the range or the value between any two values.

[0128] In some embodiments, the positive electrode active layer 12 is further provided with a pit region 124. The pit region 124 is located at the position of at least one arc segment 102 in the (n+1)th to Nth fold of the positive electrode sheet 10. The pit region 124 is located on the side of the arc segment 102 facing the winding center of the core. The pit region 124 includes a plurality of pits 122. The depth of the pit 122 is H3, and H3 and H1 satisfy the relationship: 0.3≤H1 / H3≤1, and the value range of H3 is 5μm≤H3≤30μm. Further combined with Figures 11 to 13As shown, the recess 122 is disposed at at least one of the arc segments 102 of the positive electrode sheet 10, excluding the fold with groove 121. The recess 122 is formed by a portion of the surface of the positive electrode active layer 12 facing away from the positive electrode current collector 11. By adding the recess 122 to the positive electrode active layer 12, and disposing of the recess 122 at at least one of the arc segments 102 other than the fold with groove 121, the recess 122 can contain electrolyte, thereby increasing the electrolyte retention in the arc area of ​​the core, reducing the occurrence of side reactions and lithium plating problems caused by electrolyte deficiency, and also providing buffer space for battery cycle expansion.

[0129] It should be noted that if the depth of the groove 121 is too large, it will affect the battery capacity. The purpose of setting the area of ​​the pit 122 is mainly to improve the liquid retention of the arc area of ​​the core. Increasing the depth of the pit 122 is beneficial to improving the liquid retention. Therefore, the depth of the pit 122 should be greater than or equal to the depth of the groove 121, that is, H1 / H3≤1, and the depth of the groove 121 is less than or equal to the depth of the pit 122. If H1 / H3 is greater than 1, the depth of the pit 122 is relatively too small, the liquid retention of the core is poor, and the expansion rate of the battery after cycling is large. If H1 / H3 is less than 0.3, the depth of the pit 122 is too large relative to the depth of the groove 121. In this case, foil leakage is likely to occur during the formation of the pit 122, and the loss of active material on the positive electrode active layer 12 caused by the pit 122 is too large, resulting in a significant reduction in the actual capacity of the battery and a low actual energy density. The recess 122 is a blind hole, and its depth is less than the thickness of the positive electrode active layer 12. If H3 is less than 5 μm, the depth of the recess 122 is too shallow, and the space provided by the recess 122 is too small, which cannot effectively improve the liquid retention of the arc area of ​​the core, nor can it provide sufficient buffer space for battery cycle expansion. If H3 is greater than 30 μm, the depth of the recess 122 is too large, which can easily lead to foil leakage during the formation of the recess 122 and reduce the battery capacity. Therefore, by limiting the value of H1 / H3 to the range of 0.3 to 1, and the depth of the recess 122 to the range of 5 mm to 30 mm, it is possible to ensure that the setting of the recess 122 can effectively improve the liquid retention of the arc area of ​​the core, avoid excessive expansion rate after battery cycle, and ensure that the battery has a high volumetric energy density.

[0130] Optionally, the value of H1 / H3 can be any one of 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a value between any two values.

[0131] Optionally, the value of H3 is any one of 5μm, 6μm, 8μm, 9μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, 22μm, 24μm, 26μm, 28μm, 30μm, or a value between any two of these values.

[0132] Optionally, the positive electrode 10 may only have a groove 121 and a textured area; or, the positive electrode 10 may only have a groove 121 and a pit area 124; or, the positive electrode 10 may simultaneously have a groove 121, a textured area, and a pit area 124.

[0133] In some embodiments, further combined Figure 13 As shown, the extension dimension of the recess 122 along the first direction X and / or the second direction Y is D1, and the value of D1 is in the range of 50μm≤D1≤200μm. If D1 is less than 50μm, the size of the recess 122 is too small, which is not conducive to the entry of electrolyte, thus not conducive to improving the electrolyte retention. If D1 is greater than 200μm, the size of the recess 122 is too large, and the amount of active material reduced on the positive electrode active layer 12 due to the recess 122 is too large, affecting the battery capacity. Therefore, by setting the extension dimension of the recess 122 along the first direction X and / or the second direction Y to be in the range of 50μm to 200μm, it can be ensured that the recess 122 can effectively improve the electrolyte retention in the arc area of ​​the core, and it can also avoid excessive removal of active material on the positive electrode active layer 12, thereby ensuring that the battery has sufficient capacity.

[0134] Optionally, the value of D1 is any one of 50μm, 60μm, 80μm, 100μm, 120μm, 140μm, 150μm, 160μm, 180μm, 200μm or a value between any two of these values.

[0135] Preferably, the recess 122 is a circular countersunk hole, which is convenient for processing, and D1 is the diameter of the circular hole. Of course, the recess 122 is not limited to a circular hole, but can also be a triangular hole, a quadrilateral hole, a pentagonal hole or other polygonal hole, or an elliptical hole or other shapes.

[0136] In some embodiments, further combined Figure 13As shown, the distance between two adjacent pits 122 is W2, and the value of W2 ranges from 100μm ≤ W2 ≤ 3mm. It should be noted that each arc segment 102 with pits 122 has several pits 122 to form a pit region 124. If W2 is less than 100μm, the distance between two adjacent pits 122 is too small, the density of the pit region 124 is too high, excessive removal of active material from the positive electrode active layer 12, and excessive loss of battery capacity. If W2 is greater than 3mm, the distance between two adjacent pits 122 is too large, the density of the pit region 124 is too low, and the liquid retention in the arc region of the core cannot be effectively improved. Therefore, by setting the distance between two adjacent pits 122 to a value between 100μm and 3mm, excessive removal of active material from the positive electrode active layer 12 can be avoided, thus ensuring sufficient battery capacity, while effectively improving the liquid retention in the arc region of the core, thereby improving battery performance.

[0137] Optionally, the value of W2 is any one of 100μm, 200μm, 500μm, 800μm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, or a value between any two of these values.

[0138] Further integration Figure 11 and Figure 12 As shown, the positive electrode 10 has pits 122 on both sides along the third direction Z, which can further improve the liquid retention of the arc area of ​​the core.

[0139] In some embodiments, the orthogonal projection area of ​​the pit region 124 along the third direction Z onto the positive current collector 11 is S4, and S4 satisfies the relationship between S1 and S1: 0.2 ≤ S1 / S4 ≤ 1. The pit region 124 is the area composed of all the pits 122 on a single arc segment 102, as shown in the figure. Figure 11 The area enclosed by the dashed box is shown in the diagram. It should be noted that the dashed lines are for illustrative purposes only and do not represent actual locations. Both the groove 121 and the pit 122 contribute to the loss of active particles on the positive electrode active layer 12. For areas of the same size, the amount of active particle loss corresponding to the groove 121 is 2-5 times that corresponding to the pit 122. Therefore, by setting S1 / S4 to values ​​between 0.5 and 1, the area of ​​a single groove 121 is less than or equal to the area of ​​the area where the pit 122 is located on a single arc segment 102, and greater than or equal to half the area of ​​the area where the pit 122 is located on a single arc segment 102. This effectively improves the liquid retention capacity of the core arc area while preventing excessive capacity loss.

[0140] Optionally, the value of S1 / S4 is any one of 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a value between any two values.

[0141] In some embodiments, the value range of S4 is: 40mm 2 ≤S4≤3000mm 2 This ensures that the area where the pit 122 is set on a single arc segment 102 (i.e., the pit area) has sufficient area, thereby effectively improving the liquid retention of the arc area of ​​the core, and also avoids excessive capacity loss of the battery due to an excessively large pit area.

[0142] Optionally, S4 is 40mm 2 70mm 2 100mm 2 200mm 2 300mm 2 500mm 2 800mm 2 1000mm 2 1500mm 2 2000mm 2 2500mm 2 3000mm 2 3000mm 2 It can be any value in the range or the value between any two values.

[0143] In some embodiments, further combined Figures 11 to 12 As shown, the dimension of the recessed area 124 closest to the winding end of the positive electrode 10 along the second direction Y is W3, and the dimension of the corresponding arc segment 102 along the second direction is W4. W3 and W4 satisfy the relationship: 1≤W3 / W4≤1.5. If W3 / W4 is less than 1, that is, the width of the last recessed area 122 on the positive electrode 10 along the winding direction of the core is less than the width of the corresponding arc segment 102, then due to process fluctuations during the winding process, the recessed area 122 cannot completely cover the width of the arc segment 102, thus failing to effectively improve the liquid retention of the arc area of ​​the core; however, if W3 / W4 is greater than 1.2, then the width of the last recessed area 122 is too large relative to the width of the last arc segment 102, resulting in excessive loss of active particles and insufficient battery capacity. Therefore, by setting W3 / W4 to a value within the range of 1 to 1.2, it is possible to prevent the setting area of ​​the pit 122 from not being able to completely cover the width of the arc segment 102 due to process fluctuations, thereby ensuring that the setting of the pit 122 can effectively improve the liquid retention of the arc area of ​​the core, and also to avoid the pit 122 setting area being too wide, which would lead to excessive loss of active particles, thereby ensuring the battery capacity.

[0144] Optionally, W3 / W4 can be any value from 1, 1.02, 0.04, 1.06, 1.08, 1.1, 1.12, 1.14, 1.16, 1.18, 1.2 or a value between any two values.

[0145] In some embodiments, in the arc segment 102 with the groove 121, the peel strength between the functional layer 32 and the positive electrode 10 is F1; in the straight segment 101, the peel strength between the functional layer 32 and the positive electrode 10 is F2, where F1 is less than F2. It should be noted that the groove 121 causes some damage to the surface structure of the positive electrode 10, resulting in a weakened bond between the functional layer 32 and the arc segment 102 of the positive electrode 10; the straight segment 101 does not have the groove 121, and its structure is relatively complete, therefore the bond between the functional layer 32 and the straight segment 101 of the positive electrode 10 is stronger.

[0146] The test method for the peel strength between the positive electrode and the separator in the arc section and the straight section includes: dissecting the battery, selecting separator and positive electrode samples of the same length and width in the arc section and the straight section respectively, attaching the positive electrode to the steel plate with 3M tape, and placing the separator and the positive electrode at a 180-degree angle on a universal tensile testing machine at a speed of 100 mm / min and a test displacement of 50 mm. The test result is recorded as the adhesive strength between the separators (unit: N / m).

[0147] In some embodiments, the negative electrode 20 includes a negative electrode current collector 21 and a negative electrode active layer 22 located on the surface of the negative electrode current collector 21, wherein both surfaces of the negative electrode current collector 21 are coated with the negative electrode active layer 22; the negative electrode active layer 22 includes a silicon-based material, which includes silicon-carbon composite material and / or silicon-oxygen composite material; the silicon-carbon composite material includes a porous carbon matrix, silicon grains located in the pores of the porous carbon matrix, and a carbon layer located on the surface of the porous carbon matrix. It should be noted that silicon-carbon composite material has advantages such as high specific capacity and high safety. Specifically, silicon grains can be deposited in the pores of the porous carbon matrix. By placing the silicon grains in the pores and forming a carbon layer on the surface of the porous carbon matrix, the carbon layer can be shaped carbon or amorphous carbon. When silicon grains expand, the interior of the porous carbon matrix can provide sufficient expansion space, thereby preventing the overall structural deformation of the silicon-carbon composite material. Furthermore, the carbon layer can constrain the outward expansion force of the porous carbon matrix during silicon expansion, ensuring the structural strength of the silicon-carbon material. This avoids problems such as cracking, pulverization, and shedding of the negative electrode active layer, and improves the cycle performance and rate performance of the battery.

[0148] The carbon layer includes openings that correspond to the pores of the porous carbon matrix. The openings in the carbon layer improve the wettability of the electrolyte to the negative electrode 20 and reduce the expansion properties of the silicon-based material, thereby reducing the battery impedance and improving the battery's cycle performance and rate performance.

[0149] In some embodiments, the silicon content of the negative electrode active layer 22 is less than or equal to 50 wt%. It should be noted that silicon-carbon composite materials have advantages such as high specific capacity and high safety, and can improve battery cycle performance and charge / discharge efficiency. However, during battery charging and discharging, the silicon in the silicon-carbon composite material undergoes significant volume expansion and contraction. Excessive expansion of the silicon-based material, together with the harder positive electrode active material particles on the positive electrode sheet 10, can compress the separator 30, causing the separator 30 to deform or thin, thus posing a higher risk of the separator 30 being punctured by the active material particles. Therefore, by limiting the silicon content of the negative electrode active layer 22 to less than or equal to 50 wt%, excessive expansion of the silicon-based material within the negative electrode sheet 20 can be prevented, and the harder active material on the positive electrode sheet 10 can be prevented from compressing the separator 30 together with the expanded silicon-based particles, thereby avoiding deformation or thinning of the separator 30 and preventing the active particles on the positive electrode active layer from puncturing the separator 30.

[0150] Preferably, the silicon content of the negative electrode active layer 22 ranges from 1.5 wt% to 40 wt%, ensuring a reasonable range. This avoids both excessively low silicon content leading to a low specific capacity of the negative electrode sheet 20, thus affecting the battery capacity, and excessive silicon content causing over-expansion of the negative electrode sheet 20 during charging and discharging, which could compress the separator 30. This approach effectively utilizes the high specific capacity of silicon-based materials to improve battery capacity while preventing the separator 30 from being deformed, thinned, or punctured, thereby enhancing battery safety. Optionally, the silicon content of the negative electrode active layer 22 can be any value from 1.5 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, and 40 wt%, or a value between any two of these.

[0151] The mass percentage of silicon in the negative electrode active material layer was determined using thermogravimetric analysis (TGA). The specific method was as follows: After discharging the lithium-ion secondary battery to 0% SOC, the negative electrode was disassembled and removed. It was then soaked in dimethyl carbonate (DMC) solvent for 12 hours, followed by rinsing with DMC to remove attached lithium salts. After drying, the electrode was subjected to high-temperature treatment at 400℃ in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active material layer could then be peeled off from the current collector, and the negative electrode active material was collected. For silicon content testing, a thermogravimetric analyzer (e.g., a TGA550 thermogravimetric analyzer) was used. The sample size was 5–15 mg. Under an air or oxygen atmosphere, the temperature was increased from room temperature to 900℃ at a rate of 10℃ / min, and held at 900℃ for 40 minutes. This allowed the non-silicon components in the active layer of the negative electrode material to volatilize while the silicon was fully oxidized to silicon dioxide. The weight percentage at the end of the entire test process is the ash content of the negative electrode active material layer; divide the ash value by the molar mass of silicon dioxide (60) and then multiply it by the molar mass of silicon (28) to obtain the percentage content of silicon in the negative electrode active material layer.

[0152] According to an embodiment of the present invention, another aspect provides a battery comprising: a housing and the aforementioned winding core. The winding core is disposed within the housing, and the housing further contains an electrolyte that wets the winding core.

[0153] In this embodiment, the battery uses the aforementioned winding core. The groove 121 can effectively reduce the thickness of the positive electrode active layer 12 at the arc segment 102 and the degree of compression of the active particles in the arc segment 102. This can effectively prevent the harder active material inside the positive electrode sheet 10 from squeezing the separator 30 during the winding process, avoid the separator 30 from deforming or thinning due to compression, reduce the risk of the separator 30 being punctured, avoid micro-short circuits inside the battery, reduce the battery's self-discharge rate, and prevent the battery from failing to reduce to the preset charging cutoff current during charging, thereby ensuring that the battery can reach a fully charged state.

[0154] The battery of this application will be described in detail below through specific embodiments. The specific differences of the batteries are shown in Table 1.

[0155] Example 1

[0156] The battery fabrication in this embodiment includes the following steps:

[0157] 1. Negative electrode preparation:

[0158] 1) Negative electrode slurry

[0159] Artificial graphite as the negative electrode active material, conductive carbon black as the conductive agent, styrene-butadiene rubber as the binder, and sodium carboxymethyl cellulose as the thickener are added to a mixing tank in a mass ratio of 96.9:1.5:1.3:13. Deionized water solvent is added, and the mixture is thoroughly stirred according to a known batching process. The mixture is then passed through a 150-mesh sieve to prepare a negative electrode slurry with a solid content of 40% to 45%.

[0160] 2) Negative electrode coating

[0161] The negative electrode paste is coated onto copper foil using a coating machine according to a known coating method. The foil is then dried at 100°C. Subsequently, the negative electrode sheet is rolled and slit to obtain the negative electrode sheet of the required size.

[0162] 2. Preparation of positive electrode sheet:

[0163] 1) Positive electrode slurry

[0164] Lithium cobalt oxide, conductive agent, and binder are added to a mixing tank in a mass ratio of 97.2:1.5:1.3. NMP solvent is added, and the mixture is thoroughly stirred according to a known batching process. The mixture is then passed through a 200-mesh sieve to prepare a positive electrode slurry with a solid content of 70% to 75%.

[0165] 2) Positive electrode coating

[0166] The positive slurry is coated onto aluminum foil using a coating machine according to a known coating method. The foil is then dried at 120°C. Subsequently, the positive electrode sheet is rolled and slit to obtain a positive electrode sheet of the required size. The thickness H2 of the positive active material layer in the positive electrode sheet is 60 μm, and the ratio H1 / H2 between the depth H1 of the groove 121 and the thickness H2 of the positive active material layer is 0.167.

[0167] On the positive electrode active material layer on the side of the positive electrode sheet facing the center of the core, and at the position corresponding to the three-fold arc area of ​​the core, a laser surface scan is performed to form a groove 121. The depth H1 of the groove 121 is 10μm, and the distance L2 between the groove and the edge of the positive electrode sheet 10 is 5mm.

[0168] Embossing is performed on the straight section 101 and the arc section 102 of the positive electrode sheet, except for the groove 121. An embossing roller is used to emboss the positive electrode sheet to form a textured area, so that a recess 123 is formed on the side of the positive electrode sheet 10 facing the center of the core and a protrusion 125 corresponding to the recess 123 is formed on the side of the positive electrode sheet 10 away from the center of the core. The depth H4 of the recess 123 is 10 μm, the shortest distance L3 between the protrusion 125 and the edge of the positive electrode sheet 10 is 10 mm, the extension dimension D2 of the recess 123 along the first direction X and the second direction Y is 2 mm, and the ratio H1 / H4 between the depth H1 of the groove 121 and the depth H4 of the recess 123 is 1.0.

[0169] Laser drilling is performed on the positive electrode active layer of the positive electrode sheet, except for the grooves 121 and textured areas, to form a pit region 124 composed of a number of pits 122. The depth H3 of the pits 122 is 15 μm, the size D1 of the pits 122 along the first direction X and / or the second direction Y is 60 μm, and the distance W2 between two adjacent pits 122 is 100 μm.

[0170] 3. Preparation of diaphragm 30:

[0171] The membrane base is made of polyethylene with a thickness of 5μm, coated with alumina ceramic on one side and PVDF polymer adhesive layer on both sides; the areal density of the paste coating on the surface of the membrane 30 is 3.5g / m³. 2 The functional layer 32 on the diaphragm 30 has a thickness p1 of 2 μm, a p1 / H1 ratio of 0.200, an air permeability G of the diaphragm 30 of 200 s / 100 cc, and a ratio H1 / G between the depth H1 of the groove 121 and the air permeability G of the diaphragm 30 of 0.05.

[0172] 4. Electrolyte preparation:

[0173] LiPF6 was added to a solvent containing propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a weight ratio of approximately 1:1:0.5:1 and mixed thoroughly. The concentration of LiPF6 was approximately 1 mol / L. The resulting electrolyte was obtained.

[0174] 5. Assembly:

[0175] The prepared positive and negative electrode sheets and separator 30 are wound together to form a core, packaged in aluminum-plastic film, baked to remove moisture, and then injected with electrolyte. A hot-pressing formation process is then used to obtain the battery. During winding, the side of the separator 30 coated with alumina ceramic faces the positive electrode sheet, and the other side faces the negative electrode sheet.

[0176] The data for Examples 2 to 30 are shown in Table 1.

[0177] Comparative Example 1

[0178] In Comparative Example 1, the positive electrode 10 does not have a groove 121, and other parameters are set in accordance with Example 1.

[0179] Comparative Example 2

[0180] Comparative Example 2 is carried out with reference to Example 1, except that the ratio of the thickness p1 of the functional layer 32 to the depth H1 of the groove 121 is 0.018, which is less than 0.02 and is not within the scope of this application.

[0181] Comparative Example 3

[0182] Comparative Example 3 is carried out with reference to Example 1, except that the ratio of the thickness p1 of the functional layer 32 to the depth H1 of the groove 121 is 2.250, which is greater than 2 and is not within the scope of this application.

[0183] Comparative Example 4

[0184] Comparative Example 4 was carried out with reference to Example 1, except that the thickness p1 of the functional layer 32 was 12 μm, which is greater than 10 μm and is not within the scope of this application.

[0185] Comparative Example 5

[0186] Comparative Example 5 was carried out with reference to Example 1, except that the thickness p1 of the functional layer 32 was 0.28 μm, which is greater than 0.3 μm and is not within the scope of this application.

[0187] Comparative Example 6

[0188] Comparative Example 6 was carried out with reference to Example 1, except that the depth H1 of the groove 121 was 45 μm, which is greater than 40 μm and is not within the scope of this application.

[0189] Comparative Example 7

[0190] Comparative Example 7 was carried out with reference to Example 1, except that the depth H1 of the groove 121 was 2.9 μm, which is less than 3 μm and is not within the scope of this application.

[0191] Table 1

[0192]

[0193]

[0194] The relevant performance of the batteries in the above embodiments and comparative examples was tested, and the test results are recorded in Table 2. The test methods are as follows:

[0195] 1. Cut-off current test after the predetermined charging time

[0196] At an ambient temperature of 25℃, the charging regime was 1.8C constant current and constant voltage charging to 4.48V, followed by constant current charging for 4 hours. The final cutoff current was then observed. A cutoff current less than 0.08C is defined as a normal battery, while a cutoff current greater than 0.08C indicates that the battery is experiencing CV non-cutoff.

[0197] 2. Capacity retention test

[0198] At room temperature (25℃), the battery was charged at 1C to 4.5V, with a cutoff current of 0.025C, and discharged at 0.5C to 3.0V. A cycle test was then performed for 1000 cycles, and the battery capacity after each cycle was recorded. Capacity retention rate = (Remaining capacity after 1000 cycles / Initial capacity) × 100%.

[0199] 3. Battery thickness expansion rate test

[0200] During the battery cycle test, the battery thickness was measured after every 100 cycles, and the expansion rate was calculated as (expanded volume - initial volume) / initial volume × 100%.

[0201] 4. Volumetric energy density test

[0202] The volume of the battery is V, the actual capacity of the battery is C when tested at room temperature (25℃), and the average discharge voltage of the battery is U. Then the volumetric energy density is C×U / V.

[0203] 5. Lithium plating on the negative electrode

[0204] After conducting battery expansion rate tests on the batteries obtained in the above embodiments and comparative examples, the batteries obtained in the above embodiments and comparative examples were fully charged and disassembled in a dry room environment to observe the lithium plating on the negative electrode. If a gray or dark yellow area appears on the surface of the negative electrode, it is considered lithium plating; if a golden yellow area appears on the surface of the negative electrode, it is considered no lithium plating.

[0205] Table 2

[0206]

[0207]

[0208] As can be seen from Tables 1 and 2, for the batteries of Examples 1 to 13, the ratio of the thickness p1 of the functional layer 32 to the depth H1 of the groove 121, p1 / H1, is within the range of 0.02 to 2 as defined in this application. After testing, the cutoff current after the predetermined charging time is less than 0.08C, meaning that the battery does not exhibit CV non-cutoff, and the battery can reach a fully charged state, indicating good battery performance. Furthermore, the capacity retention rate of the batteries after cycling is not less than 94.41%, the battery thickness expansion rate does not exceed 8.25%, and lithium plating does not occur. It is evident that the batteries have high capacity retention rate and low battery thickness expansion rate after cycling tests, indicating good cycle performance and high safety performance.

[0209] Furthermore, for the batteries of Examples 2 to 6, p1 gradually increases while H1 remains constant. It should be noted that when p1 changes, the air permeability G of the separator 30 remains constant by controlling the distribution density of the functional layer 32 on the substrate layer 31 and the size of the ceramic particles. The batteries of Examples 2 to 6 are used to verify the effect of the change of p1 within the range defined in this application on battery performance. It can be seen that: as p1 increases, the charging cut-off current of the battery decreases slightly, indicating that increasing p1 is more conducive to improving the CV non-cut-off phenomenon of the battery; as p1 increases, the battery thickness expansion rate after cycling gradually increases, and the volumetric energy density gradually decreases, indicating that increasing p1 is not conducive to improving the cycle performance and increasing the volumetric energy density of the battery.

[0210] For the batteries in Examples 7 to 11, H1 gradually increases while p1 remains constant. It can be seen that as H1 gradually increases, the charging cutoff current of the battery decreases, indicating that increasing H1 is beneficial to improving the CV non-cutoff phenomenon of the battery. As H1 gradually increases, the battery capacity retention rate gradually increases, the battery thickness expansion rate gradually decreases, and the volumetric energy density gradually decreases. It can be seen that increasing H1 is beneficial to improving the liquid retention of the battery, thereby improving the battery capacity retention rate. It is also beneficial to reserve space for the cyclic expansion of the negative electrode and improve the cycle performance of the battery, but it is not conducive to improving the volumetric energy density of the battery.

[0211] In contrast, the positive electrode 10 of the battery in Comparative Example 1 does not have a groove 121. The cutoff current after the predetermined charging time is 0.3C, which is significantly higher than that in Example 1. The battery in Comparative Example 1 cannot reduce to the preset charging cutoff current (0.08C) after the predetermined charging time, meaning that the battery cannot reach a fully charged state. Furthermore, the capacity retention rate after battery cycling is significantly reduced, the battery thickness expansion rate is significantly increased, and lithium plating occurs on the negative electrode. It can be seen that the battery has a CV non-cutoff phenomenon, cannot reach a fully charged state, and has poor cycle performance, produces lithium plating, and has poor safety performance.

[0212] For the battery of Comparative Example 2, the p1 / H1 value is 0.018, which is less than the lower limit of 0.02 defined in this application. The cutoff current of the battery after the predetermined charging time is 0.09C, which is greater than 0.08C, indicating a failure of CV cutoff. For the battery of Comparative Example 3, the p1 / H1 value is 2.250, which is greater than the upper limit of 2 defined in this application. The cutoff current of the battery after the predetermined charging time is 0.1C, which is greater than 0.08C, indicating a failure of CV cutoff. Furthermore, compared with Example 1, the capacity retention rate of the batteries of Comparative Example 2 and Comparative Example 3 is reduced, the battery thickness expansion rate is increased, the volumetric energy density of the batteries is reduced, and lithium plating and separator wrinkling occur in both. It can be seen that the p1 / H1 values ​​of the batteries of Comparative Example 2 and Comparative Example 3 are not within the range defined in this application, and both exhibit failure of CV cutoff. The batteries cannot reach a fully charged state, and the battery cycle performance is poor, the volumetric energy density is low, the battery separator wrinkles, lithium plating occurs, and the safety performance is poor.

[0213] In Comparative Example 4, the p1 value is 12 μm, which is greater than the upper limit of 10 μm defined in this application. The thickness of the functional layer 32 is too large. The cutoff current of the battery after the predetermined charging time is 0.07C, which is greater than the cutoff current of the battery in Example 1. Therefore, the energy actually charged into the battery is less than that in Example 1, and the battery capacity retention rate decreases, the battery thickness expansion rate increases, and the battery volumetric energy density decreases. In Comparative Example 5, the p1 value is 0.28 μm, which is less than the lower limit of 0.3 μm defined in this application. The thickness of the functional layer 32 is small. The cutoff current of the battery after the predetermined charging time is 0.18C, which is greater than 0.08C. The CV non-cutoff phenomenon occurs, and the battery cannot reach the fully charged state. Furthermore, the battery capacity retention rate after cycling decreases, the battery thickness expansion rate increases, the battery volumetric energy density decreases, and lithium plating occurs on the negative electrode.

[0214] In Comparative Example 6, the value of H1 is 45 μm, which is greater than the upper limit of 40 μm defined in this application. The volumetric energy density of the battery decreases, and the capacity retention rate of the battery decreases due to the damage to the electrode due to the excessively large H1. The battery thickness expansion rate increases, the volumetric energy density decreases, and the ion migration path is long, resulting in lithium plating on the negative electrode. In Comparative Example 7, the value of H1 is 2.9 μm, which is less than the lower limit of 3 μm defined in this application. The cutoff current of the battery after the predetermined charging time is 0.25C, which is greater than 0.08C. The CV non-cutoff phenomenon occurs, and the battery cannot reach the full charge state. Furthermore, the capacity retention rate of the battery decreases after cycling, the battery thickness expansion rate increases, the volumetric energy density decreases, and lithium plating occurs on the negative electrode.

[0215] In summary, it can be seen that when p1 / H1 takes values ​​within the range of 0.02 to 2 as defined in this application, and p1 takes values ​​within the range of 0.3 μm to 10 μm as defined in this application, and H1 takes values ​​within the range of 3 μm to 40 μm as defined in this application, in addition to improving the battery's CV non-cutoff phenomenon, it can also increase the battery's liquid retention, improve the battery's cycle performance, ensure that the battery has a high volumetric energy density, avoid lithium plating, and improve the battery's safety performance.

[0216] For the batteries of Examples 14 to 24, the H1 / G values ​​are all within the range of 0.016 to 0.5 as defined in this application; however, the H1 / G value of the battery of Example 25 is 0.0143, which is less than the lower limit of 0.016 as defined in this application. The cutoff current of the battery of Example 25 after the predetermined charging time is 0.07C, which is larger than the cutoff current of the batteries of Examples 14 to 24, which is not conducive to improving the CV non-cutoff problem of the battery, and the positive electrode active particles slightly squeeze the separator, resulting in lithium plating on the negative electrode; while the H1 / G value of the battery of Example 26 is 0.5250, which is greater than the upper limit of 0.5 as defined in this application. The cutoff current of the battery of Example 26 after the predetermined charging time is 0.06C, which is larger than the cutoff current of the batteries of Examples 14 to 24, which is not conducive to improving the CV non-cutoff problem of the battery, and lithium plating on the negative electrode. It should be noted that in Examples 14 to 18, when G changes, the thickness p1 of the functional layer 32 remains constant by controlling the distribution density of the functional layer 32 on the substrate layer 31 and the size of the ceramic particles. It can be seen that by limiting the ratio H1 / G between the depth H1 of the groove 121 and the air permeability G of the separator to a value within the range of 0.016 to 0.5, and by limiting G to a value within the range of 80s / 100c to 400cs / 100cc, the problem of lithium plating on the negative electrode can be further avoided.

[0217] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A type of winding core, characterized in that, include: A positive electrode (10), a negative electrode (20), and a separator (30) are provided. The core is formed by winding the positive electrode (10), the separator (30), and the negative electrode (20) arranged in sequence. The positive electrode sheet (10) includes a positive current collector (11) and a positive active layer (12) located on the surface of the positive current collector (11); along the winding direction of the core, the positive electrode sheet (10) includes a straight section (101) and an arc section (102), and a groove (121) is provided on the positive active layer (12) of the positive electrode sheet (10) facing the winding center of the core, and the groove (121) is located on at least one of the arc sections (102) of the positive electrode sheet (10) closest to the winding center, and the depth of the groove (121) is H1; The negative electrode sheet (20) includes a negative electrode current collector (21) and a negative electrode active layer (22) located on the surface of the negative electrode current collector (21), wherein the negative electrode active layer (22) includes a silicon-based material; The separator (30) includes a substrate layer (31) and a functional layer (32). The functional layer (32) covers the side of the substrate layer (31) facing the positive electrode (10). The functional layer (32) includes a ceramic material and has a thickness of p1, wherein p1 and H1 satisfy the relationship: 0.02≤p1 / H1≤2. The value of H1 is in the range of 3μm≤H1≤40μm, preferably 5μm≤H1≤25μm; The value of p1 is in the range of 0.3μm≤p1≤10μm, preferably 0.5μm≤p1≤8μm.

2. The winding core according to claim 1, characterized in that, The air permeability of the diaphragm (30) is G, and the value range of G is 80s / 100cc≤G≤400s / 100cc, preferably 90s / 100cc≤G≤300s / 100cc. The relationship between H1 and G is 0.016≤H1 / G≤0.5, preferably 0.017-0.

45.

3. The winding core according to claim 1, characterized in that, The positive electrode (10) has intersecting first direction (X) and second direction (Y). The positive electrode (10) is wound along the second direction (Y). The size of the groove (121) along the second direction (Y) is W1. The value range of W1 is 3mm≤W1≤10mm. And / or, along the second direction (Y), the size of the groove (121) is larger than the size of the arc segment (102) in which it is located; And / or, the distance by which the groove (121) extends beyond the arc segment (102) on one side is L1, and the value of L1 is in the range of 0.1mm≤L1≤5mm; And / or, along the first direction (X), the distance between the groove (121) and the edge of the positive electrode (10) is L2, and the value of L2 is in the range of 0.5mm≤L2≤15mm; And / or, the thickness of the positive electrode active layer (12) is H2, and H1 and H2 satisfy the relationship: 0.05≤H1 / H2≤0.

75.

4. The winding core according to claim 1, characterized in that, The surface of the positive electrode (10) is also provided with a textured area, which includes a plurality of recesses (123) and protrusions (125) corresponding to the recesses (123). The recesses (123) are provided on the surface of the positive electrode (10) facing the winding center of the core, and the protrusions (125) are provided on the surface of the positive electrode (10) away from the winding center of the core. The recess (123) has a recess depth of H4 along the third direction (Z). H4 and H1 satisfy the following relationship: 0.25≤H1 / H4≤8. The value range of H4 is 2μm≤H4≤40μm, preferably 3μm≤H4≤20μm. And / or, the extension dimension of the recess (123) along the first direction (X) and / or the second direction (Y) is D2, wherein the value of D2 is in the range of 0.5mm≤D2≤10mm; And / or, along the first direction (X), the shortest distance between the recess (123) and the edge of the positive electrode (10) is L3, and the value of L3 is in the range of 2mm≤L3≤15mm.

5. The winding core according to claim 1 or 4, characterized in that, Along the winding direction of the core, the positive electrode sheet (10) includes a first fold to the Nth fold connected in sequence. Each fold of the positive electrode sheet (10) includes a straight segment (101) and an arc segment (102). The groove (121) is disposed at the position of the arc segment (102) on the first fold to the nth fold of the positive electrode sheet (10), where N and n are positive integers, n < N, and n ≤ 3. And / or, the number of the grooves (121) is at least one, and along the third direction (Z), the orthographic projection area of ​​a single groove (121) on the positive current collector (11) is S1, and the value of S1 is in the range of 20 mm. 2 ≤S1≤1500mm 2 ; And / or, along the third direction (Z), the total area of ​​the groove (121) projected onto the positive current collector (11) is S2, and the total area of ​​the positive active layer (12) projected onto the positive current collector (11) is S3. S2 and S3 satisfy the relationship: 0.001≤S2 / S3≤0.

1.

6. The winding core according to claim 5, characterized in that, The positive electrode active layer (12) is further provided with a pit area (124), the pit area (124) is provided at the position of the arc segment (102) of at least one of the (n+1)th to Nth folds of the positive electrode sheet (10), the pit area (124) is located on the side of the arc segment (102) facing the winding center of the core, and the pit area (124) includes a plurality of pits (122); The depth of the pit (122) is H3, and H3 and H1 satisfy the relationship: 0.3≤H1 / H3≤1, and the value range of H3 is 5μm≤H3≤30μm; And / or, the extension dimension of the pit (122) along the first direction (X) and / or the second direction (Y) is D1, and the value of D1 is in the range of 50μm≤D1≤200μm; And / or, the distance between two adjacent pits (122) is W2, and the value of W2 is in the range of 100μm≤W2≤3mm; And / or, the projected area of ​​the pit region (124) on the positive current collector (11) along a third direction is S4, and S4 and S1 satisfy the relationship: 0.2≤S1 / S4≤1.

7. The winding core according to claim 6, characterized in that, The dimension of the pit area (124) closest to the end of the positive electrode (10) along the second direction (Y) is W3, and the dimension of the arc segment (102) corresponding to the pit area (124) closest to the end of the positive electrode (10) along the second direction is W4. W3 and W4 satisfy the relationship: 1≤W3 / W4≤1.

5.

8. The winding core according to claim 2, characterized in that, The diaphragm (30) further includes a first adhesive layer (33), which is disposed on the side of the substrate layer (31) away from the functional layer (32). The coverage of the first adhesive layer (33) relative to the substrate layer (31) is μ, and the value of μ is in the range of 20% ≤ μ ≤ 100%.

9. The winding core according to claim 1, characterized in that, In the arc segment (102) where the groove (121) is provided, the peel strength between the functional layer (32) and the positive electrode (10) is F1; in the straight segment (101), the peel strength between the functional layer (32) and the positive electrode (10) is F2, wherein F1 is less than F2.

10. A battery, characterized in that, include: The housing, and the core as described in any one of claims 1-9 above.

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