Battery cell and battery

Abstract

The invention provides a battery cell and a battery, the battery cell comprises a positive plate, a negative plate and diaphragms arranged between the positive plate and the negative plate at intervals, and the positive plate, the negative plate and the diaphragms are stacked and then wound; the positive plate comprises a first current collector and a first active material layer arranged on the surface of the first current collector, and the first active material layer comprises a lithium iron phosphate material; the negative plate comprises a second current collector and second active material layers arranged on two opposite surfaces of the second current collector, and a groove is formed in the surface of the negative plate; the thickness of the first active material layer is Hc, the thickness of the second active material layer is Ha, and Hc / Ha is more than 1 and less than or equal to 1.5; along the length direction of the negative plate, the winding starting end of the second current collector is provided with a negative electrode single-side area, the negative electrode single-side area is provided with a concave structure, and the concave structure comprises a plurality of concave parts. The invention is used for improving the liquid retention capacity of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of battery energy storage, and in particular to a battery cell and a battery. Background Art

[0002] Lithium-ion batteries have been widely used in the battery industry due to their advantages of high safety, long life, wide temperature adaptability and relatively low cost, especially in electric vehicles and energy storage systems.

[0003] Because the current positive electrode materials are limited by the characteristics of small particles, large specific surface area and small compaction, the electrode sheets made are relatively thick. Therefore, under the same volume, the electrolyte consumption in the circulation process is relatively large, so the battery liquid retention requirement is higher. If the electrolyte volume is insufficient, the battery's electrical performance and life will be attenuated.

[0004] Therefore, it is urgent to increase the liquid retention of the battery cell. Summary of the invention

[0005] The invention provides a battery core and a battery for improving the liquid retention capacity of the battery.

[0006] In order to achieve the above object, the present invention provides a battery cell, comprising: a positive electrode sheet, a negative electrode sheet, and a separator arranged between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet, the negative electrode sheet and the separator are stacked and wound;

[0007] The positive electrode sheet includes a first current collector and a first active material layer disposed on the surface of the first current collector, wherein the first active material layer includes lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate or a ternary material;

[0008] The negative electrode sheet comprises a second current collector and a second active material layer disposed on two opposite surfaces of the second current collector, and a surface of the negative electrode sheet has a groove;

[0009] The thickness of the first active material layer is Hc, the thickness of the second active material layer is Ha, and 1<Hc / Ha≤1.5 is satisfied;

[0010] Along the length direction of the negative electrode sheet, the winding starting end of the second current collector has a negative electrode single-sided area, in which the second active material layer is provided on the first side surface of the second current collector and the second active material layer is not provided on the second side surface of the second current collector, and the negative electrode single-sided area is provided with a recessed structure, which includes a plurality of recessed portions.

[0011] A battery cell provided by the present invention has the characteristics of small particles, large specific surface area and small compaction of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate or ternary material, so that the thickness of the positive electrode active material layer of the positive electrode sheet is greater than the thickness of the active material layer of the negative electrode sheet. In order to ensure the normal lithium deintercalation of the positive electrode active material layer, more electrolyte is required and a sufficiently high liquid retention coefficient is required. By arranging grooves on the surface of the second active material layer of the negative electrode sheet and forming a concave structure on the single-sided area of ​​the negative electrode sheet, the grooves can provide more liquid storage space for electrolyte infiltration and rapid ion transmission, thereby accommodating the electrolyte, increasing the liquid retention capacity of the battery, and improving the rate performance and cycle life.

[0012] In addition, the concave structure can hold the electrolyte, which helps to store more electrolyte and improve the wetting effect of the electrode. Furthermore, forming a groove in the negative electrode single-sided area can enhance the deformation ability of the negative electrode single-sided area, thereby preventing the negative electrode single-sided area of ​​the negative electrode sheet from wrinkling or folding during the winding process.

[0013] In a possible implementation, a plurality of the grooves are arranged at intervals on the surface of the second active material layer; and / or,

[0014] The depth D of the groove satisfies 3 μm≤D≤50 μm; and / or,

[0015] The width L of the groove satisfies 30 μm≤L≤180 μm; and / or,

[0016] The distance S between two adjacent grooves satisfies 500 μm ≤ S ≤ 2500 μm; and / or,

[0017] The recessed structure is recessed from the second side surface of the second current collector toward the first side surface of the second current collector.

[0018] In a possible implementation, along the winding direction of the battery cell, the negative electrode single-sided area includes a first bent section, a first straight section, a second bent section, and a second straight section, and the recessed structure located in the first straight section and the recessed structure located in the second straight section are arranged opposite to each other;

[0019] In a possible implementation, the recess includes an indented portion located at a center of the recess and an outdented portion located at an outer edge of the indented portion.

[0020] In a possible implementation, the negative electrode single-sided region further includes an extension segment, the extension segment is connected to one end of the first bent segment away from the first straight segment, and the second active material layer of the extension segment partially overlaps with the second active material layer of the first straight segment;

[0021] Along the length direction of the positive electrode sheet, the winding starting end of the positive electrode sheet at the innermost circle of the battery cell does not exceed the extension section.

[0022] In a possible implementation, a height distance between a bottom wall of the recessed portion and a second side surface of the second current collector is H1, wherein 5 μm≤H1≤30 μm; and / or

[0023] A height distance between the top of the outer protrusion and the second side surface of the second current collector is H2, wherein 5 μm≤H2≤30 μm.

[0024] In one possible implementation, the negative electrode sheet includes a negative electrode double-sided region, in which the second active material layer is provided on two opposite side surfaces of the second current collector, and the groove is provided on the second active material layer in the negative electrode double-sided region and / or the negative electrode single-sided region.

[0025] In a possible implementation, in the thickness direction of the negative electrode sheet, a projection of the groove located in the negative electrode single-sided area does not overlap with a projection of the recessed portion.

[0026] In a possible implementation, the thickness Hc of the first active material layer, the depth D of the groove, and the width L of the groove satisfy: 0.05≤Hc / D×L≤0.26.

[0027] In a possible implementation, the thickness Hc of the first active material layer, the depth D of the groove, and the width L of the groove satisfy: 0.08≤Hc / D×L≤0.15.

[0028] In one possible implementation, the first active material layer is provided on two opposite surfaces of the first current collector, a first pole tab groove is provided in the first active material layer, the first current collector is exposed from the first pole tab groove, a first pole tab is provided in the first pole tab groove, and the first pole tab is connected to the first current collector.

[0029] In a possible implementation, the first active material layer is provided with an avoidance groove, a step is formed between the avoidance groove and the edge of the corresponding first pole tab groove, and pole tab glue is provided in each of the avoidance grooves, and the pole tab glue covers the connection position between the first pole tab and the first current collector.

[0030] In a possible implementation, the depth Dc of the avoidance groove and the thickness Ht of the tab glue satisfy: Dc≥Ht; and / or,

[0031] The first electrode tab is welded to the first current collector, and along the thickness direction of the positive electrode sheet, the thickness of the welding trace formed by the welding position of the first electrode tab and the first current collector is Hs, which satisfies: Hs≤40 μm;

[0032] And / or, along the thickness direction of the positive electrode sheet: the thickness Hp of the first electrode tab, the thickness Hs of the welding trace formed by the welding position of the first electrode tab and the first current collector, the thickness Ht of the electrode tab glue, and the thickness Hc of the first active material layer satisfy:

[0033] Hp+Hs+2×Ht≤2×Hc.

[0034] In one possible implementation, the diaphragm includes a substrate layer, an adhesive layer arranged on one side surface of the substrate layer, and a ceramic layer arranged on the other side surface of the substrate layer, the ceramic layer is arranged on the side of the substrate layer facing the positive electrode sheet; the adhesive layer is arranged on the side of the substrate layer facing the negative electrode sheet.

[0035] In a possible implementation, the ceramic layer includes nano-aluminum oxide material; and / or,

[0036] The porosity e of the substrate layer satisfies 35%≤e≤80%; and / or,

[0037] The porosity of the ceramic layer is greater than the porosity of the bonding layer; and / or,

[0038] The air permeability f of the diaphragm satisfies: 40sec / 100cc≤f≤200sec / 100cc; and / or,

[0039] The adhesive layer includes at least one of water-based PVDF and water-based PMMA, polyacrylic acid, polytetrafluoroethylene, epoxy resin, chloroprene rubber, and methyl methacrylate.

[0040] In a possible implementation, the second active material layer located in the single-sided region of the negative electrode includes a plurality of protrusions, and the protrusions are arranged corresponding to the recesses.

[0041] In a possible implementation, the circumscribed circle diameter R of the protrusion satisfies 300 μm≤R≤2000 μm; and / or,

[0042] The depth Sd of the concave portion satisfies: 3 μm ≤ Sd ≤ 30 μm; and / or,

[0043] The distance W between the centers of the circumscribed circles of two adjacent protrusions satisfies: 1000 μm≤W≤5000 μm.

[0044] In a possible implementation, along the width direction of the negative electrode sheet: the spacing between the recessed structure and the two side edges of the negative electrode sheet are S1 and S2 respectively, wherein 0.5 mm≤S1≤6 mm, and / or 0.5 mm≤S2≤6 mm.

[0045] In a possible implementation, the negative electrode sheet further includes a hollow foil area and a double-sided coating area. Along the length direction of the negative electrode sheet, the negative electrode single-sided area is connected between the hollow foil area and the double-sided coating area. Along the length direction of the negative electrode sheet:

[0046] The distance S3 between the recessed structure and the empty foil area satisfies 1mm≤S3≤10mm; and / or,

[0047] The distance S4 between the recessed structure and the double-sided coating area satisfies 0.5 mm≤S4≤5 mm.

[0048] In one possible implementation, the first current collector includes aluminum foil, and the tensile strength cf of the first current collector satisfies: 200 MPa≤Cf.

[0049] The present invention further provides a battery, comprising a shell and the above-mentioned battery cell, wherein a receiving cavity is formed inside the shell, and the battery cell is arranged in the receiving cavity.

[0050] In addition to the technical problems solved by the embodiments of the present invention described above, the technical features that constitute the technical solutions, and the beneficial effects brought about by the technical features of the technical solutions, other technical problems that can be solved by a battery cell and a battery provided by the embodiments of the present invention, other technical features included in the technical solutions, and the beneficial effects brought about by these technical features will be further described in detail in the specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0052] Figure 1 A schematic diagram of a three-dimensional structure of a battery cell provided in an embodiment of the present invention;

[0053] Figure 2 A partial structural cross-sectional view of a battery cell at the first electrode tab position provided by an embodiment of the present invention;

[0054] Figure 3 A schematic diagram of the structure of a negative electrode sheet of a battery cell provided in an embodiment of the present invention;

[0055] Figure 4 A cross-sectional view of a negative electrode sheet of a battery cell provided in an embodiment of the present invention;

[0056] Figure 5 A partial structural diagram of the negative electrode sheet of the battery cell provided by an embodiment of the present invention after laser etching;

[0057] Figure 6 A cross-sectional view of a groove of a negative electrode sheet of a battery cell provided in an embodiment of the present invention;

[0058] Figure 7 A cross-sectional view of a diaphragm of a battery cell provided by an embodiment of the present invention;

[0059] Figure 8 for Figure 4 A magnified view of the structure at B;

[0060] Fig. 9 Another structural schematic diagram of a concave structure provided in the negative electrode single-side region of the negative electrode sheet of the battery cell provided in an embodiment of the present invention;

[0061] Fig.10 for Figure 8 A top view of

[0062] Fig.11 Another structural schematic diagram of the concave structure of the negative electrode sheet of the battery cell provided by an embodiment of the present invention;

[0063] Fig.12 A schematic structural diagram of the inner ring of a battery cell provided in an embodiment of the present invention;

[0064] Fig.13 for Figure 1 A magnified view of the structure at A;

[0065] Fig.14 A thickness curve diagram of different positions of the battery cell provided by an embodiment of the present invention when the paste is folded on the A / C surface of the negative electrode sheet;

[0066] Fig.15 The thickness curve diagram of the battery cell provided by the embodiment of the present invention at different positions when the paste is not folded on the A / C surface of the negative electrode sheet.

[0067] Description of reference numerals:

[0068] 10- positive electrode;

[0069] 11- first current collector;

[0070] 12- first active material layer;

[0071] 13- Avoidance slot;

[0072] 14-first pole lug slot;

[0073] 15-ear glue;

[0074] 20- negative electrode sheet;

[0075] 21- second fluid collector;

[0076] 22- second active material layer;

[0077] 221-groove;

[0078] 23 - empty foil area;

[0079] 24-negative electrode single-sided area;

[0080] 241-first bending section;

[0081] 242-first straight section;

[0082] 243- second bending section;

[0083] 244- the second straight section;

[0084] 245-extension section;

[0085] 25- double-sided coating area;

[0086] 30 - diaphragm;

[0087] 311- base material layer;

[0088] 312-ceramic layer;

[0089] 32-adhesive layer;

[0090] 40-depression structure;

[0091] 41- convex;

[0092] 42-inner concave cavity;

[0093] 43-concave;

[0094] 431- invagination;

[0095] 432-external convex part;

[0096] 50-first pole lug;

[0097] 60- Second pole lug. DETAILED DESCRIPTION

[0098] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0099] Indicators of battery performance include cycle performance, which indicates how many times a battery can undergo a complete charge and discharge process before the battery fails or begins to lose capacity. High cycle performance can help improve the range and service life of the electrical device containing the battery. Currently, in order to improve the cycle performance of the battery, the active material content and the amount of electrolyte in the battery are usually increased.

[0100] In lithium-ion batteries, the electrolyte plays a role in conducting ions between the positive and negative electrodes. The degree of electrolyte penetration in the battery directly affects the energy density and life of the battery. Due to the characteristics of small particles, large specific surface area, and small compaction of the current positive electrode materials, the pole pieces made are relatively thick. Therefore, under the same volume, the consumption of electrolyte in the circulation process is relatively large, and the thickness of the positive electrode paste is greater than that of the negative electrode. Therefore, the electrolyte that penetrates the pole piece and is consumed in the circulation is relatively high, and there is a problem of insufficient electrolyte content, which affects the performance and life of the battery.

[0101] In view of this, the present invention provides a battery cell, which provides grooves and concave structures on the surface of the second active material layer of the negative electrode sheet. The grooves can provide more liquid storage space for electrolyte infiltration and rapid ion transmission, so that the electrolyte can be accommodated and the liquid retention of the battery can be increased. The increase in liquid retention helps to improve the rate performance and cycle life. The concave structure can increase the liquid retention of the battery and improve the storage capacity of the electrolyte.

[0102] The following describes a cell and a battery provided by an embodiment of the present invention with reference to the accompanying drawings.

[0103] refer to Figure 1 As shown, the present invention provides a battery cell, comprising: a positive electrode sheet 10, a negative electrode sheet 20, and a separator 30 arranged between the positive electrode sheet 10 and the negative electrode sheet 20, wherein the positive electrode sheet 10, the negative electrode sheet 20 and the separator 30 are stacked and wound; Figure 2 and Figure 3 As shown, the positive electrode sheet 10 includes a first current collector 11 and a first active material layer 12 arranged on the surface of the first current collector 11, and the first active material layer 12 includes lithium iron phosphate material, lithium manganese iron phosphate, lithium manganese phosphate or ternary; the negative electrode sheet 20 includes a second current collector 21 and a second active material layer 22 arranged on the surface of the second current collector 21, and the surface of the second active material layer 22 has a groove 221.

[0104] refer to Figure 4 As shown, the negative electrode sheet 20 includes a second current collector 21 and a second active material layer 22 disposed on two opposite surfaces of the second current collector 21, and the surface of the negative electrode sheet 20 has a groove 221; the thickness of the first active material layer 12 is Hc, the thickness of the second active material layer 22 is Ha, and 1<Hc / Ha≤1.5 is satisfied;

[0105] Along the length direction of the negative electrode sheet 20, the winding starting end of the second current collector 21 has a negative electrode single-sided area 24, in which the first side surface of the second current collector 21 is provided with a second active material layer 22 and the second side surface of the second current collector 21 is not provided with the second active material layer 22, and the negative electrode single-sided area 24 is provided with a recessed structure 40, and the recessed structure 40 includes a plurality of recesses 43.

[0106] In a battery cell provided by the present invention, due to the characteristics of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate or ternary materials having small particles, large specific surface area and small compaction, the thickness of the first active material layer 12 of the positive electrode sheet 10 is greater than the thickness of the second active material layer 22 of the negative electrode sheet 20. In order to ensure the normal lithium deintercalation of the first active material layer 12, i.e., the positive electrode active material layer, more electrolyte is required, and a sufficiently high liquid retention coefficient is required. By providing a groove 221 on the surface of the second active material layer 22 of the negative electrode sheet 20, the groove 221 can provide more liquid storage space for electrolyte infiltration and rapid ion transmission, so as to accommodate the electrolyte, increase the liquid retention of the battery, and improve the rate performance and cycle life. By providing a recessed structure 40 in the negative electrode single-sided area 24, the liquid retention of the battery can be increased, and the infiltration effect of the electrode sheet can be improved. Furthermore, forming the groove in the negative electrode single-sided area 24 can enhance the deformation ability of the negative electrode sheet single-sided area, thereby preventing the negative electrode single-sided area 24 of the negative electrode sheet 20 from wrinkling or folding during the rolling and winding process.

[0107] The first current collector 11 can carry the first active material layer 12, and can also collect and output the current generated by the active material in the first active material layer 12, which is beneficial to reducing the internal resistance of the lithium ion battery. The second current collector 21 can carry the second active material layer 22, and can also collect and output the current generated by the active material in the second active material layer 22, which is beneficial to reducing the internal resistance of the lithium ion battery.

[0108] refer to Figure 3 and Figure 5As shown in the figure, the groove 221 can be formed by using the negative electrode wire-punching technology, and etching the surface of the negative electrode sheet 20 with a laser in a direction perpendicular to the surface of the second current collector 21. The negative electrode wire-punching technology helps lithium ions to diffuse quickly in the thicker positive electrode sheet, reduces the polarization of the electrode sheet under high current charging conditions, increases the battery's liquid retention, and improves the battery's cycle performance under fast charging conditions. It is understandable that the groove 221 can also be formed by laser drilling or mechanical pore making or embossing.

[0109] The groove 221 may extend along the width direction of the negative electrode sheet 20 , which is beneficial for the electrolyte to pass through the groove 221 more quickly, thereby significantly improving the wetting consistency of the electrolyte in the width direction and thickness direction of the battery cell.

[0110] In one possible implementation, reference Figure 2 and Figure 6 As shown, the thickness of the first active material layer 12 is Hc, and the thickness of the second active material layer 22 is Ha; when 1<Hc / Ha≤1.5, there are multiple grooves 221, and the multiple grooves 221 are arranged at intervals on the surface of the second active material layer 22. The multiple grooves 221 can be arranged in a matrix.

[0111] In one possible implementation, reference Figure 6 As shown in FIG. 1 , the depth D of the groove 221 satisfies 8 μm≤D≤50 μm. The depth D of the groove 221 may be, for example, 8 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 30 μm, 40 μm or 50 μm.

[0112] In a possible implementation, the width L of the groove 221 satisfies 30 μm≤L≤180 μm. For example, the width L of the groove 221 may be 30 μm, 50 μm, 60 μm, 80 μm, 90 μm, 100 μm, 120 μm, 130 μm, 150 μm, 160 μm or 180 μm.

[0113] In a possible implementation, the distance S between two adjacent grooves 221 satisfies 500 μm≤S≤2500 μm. For example, the distance S between two adjacent grooves 221 may be 500 μm, 800 μm, 1000 μm, 1200 μm, 1500 μm, 1800 μm, 2000 μm, 2300 μm or 2500 μm.

[0114] In one possible implementation, the recessed structure 40 is formed by being recessed from the second side surface of the second current collector 21 toward the first side surface of the second current collector 21, that is, the recessed structure 40 is formed by being recessed from the second side surface of the recessed structure 40 of the negative electrode sheet 20 close to the center of the winding core toward the first side surface away from the center of the winding core. This implementation can improve the deformation capacity of the negative electrode single-sided area 24 while preventing the second active material layer 22 from falling off due to uneven stress in the negative electrode single-sided area 24 when embossing the second active material layer 22 in the negative electrode single-sided area 24 during the formation of the recessed structure 40.

[0115] The thicker the thickness of the positive electrode sheet 10 is, the greater the depth and width of the groove 221 of the negative electrode sheet 20 is required to be, that is, the greater the volume of the groove 221 is required to account for the volume of the second active material layer 22, so that the groove 221 can store enough electrolyte to ensure that the thicker first active material layer 12, i.e., the positive electrode active material layer, can be fully infiltrated; however, if the volume of the groove 221 is too large, the weight loss rate of the negative electrode sheet 20 will be too high, affecting the ratio of the positive and negative active materials, reducing the CB value, and causing the problem of lithium precipitation during the cycle. The volume of the negative electrode sheet 20 is controlled according to the width and depth of the groove 221 per unit area to improve the electrolyte infiltration efficiency and the uniformity of the infiltration effect.

[0116] In a possible implementation, when the distance S between two adjacent grooves 221 satisfies 500 μm ≤ S ≤ 2500 μm, the thickness Hc of the first active material layer 12, the depth D of the groove 221, and the width L of the groove 221 satisfy: 0.05 ≤ Hc / D×L ≤ 0.26. The purpose is to provide more liquid storage space while preventing the negative electrode sheet 20 from having an excessively high weight loss rate.

[0117] The depth D of the groove 221 and the width L of the groove 221 are too large, and Hc / D×L is likely to exceed the specified range. The liquid retention amount is increased, but the negative electrode weight loss rate is too high, resulting in a decrease in the ratio of positive and negative electrode active materials, which is prone to the problem of negative electrode cycle lithium deposition and a reduced cycle retention rate.

[0118] In one possible implementation, Hc / D×L may be, for example, 0.05, 0.08, 0.1, 0.12, 0.13, 0.15, 0.18, 0.2, 0.23 or 0.26.

[0119] In a possible implementation, the thickness Hc of the first active material layer 12, the depth D of the groove 221, and the width L of the groove 221 satisfy: 0.08≤Hc / D×L≤0.15. This allows the liquid storage space provided by the groove 221 to be optimized while preventing the negative electrode sheet 20 from having an excessively high weight loss rate, thereby ensuring sufficient infiltration of the positive electrode active material layer of the positive electrode sheet.

[0120] In one possible implementation, reference Fig.12 As shown, the negative electrode single-sided area 24 includes a first bending section 241, a first straight section 242, a second bending section 243 and a second straight section 244, and the concave structure located in the first straight section 242 and the concave structure located in the second straight section 244 are arranged relative to each other. It can be seen that the winding stress and the extrusion stress at the inner layer of the winding core are the largest, so the inner circle area is most likely to have the problem of insufficient electrolyte. The concave structure 40 located in the first straight section 242 and the concave structure 40 located in the second straight section 244 are arranged relative to each other, that is, the concave structures 40 in the inner layer of the battery cell are relative, and the relative concave structures 40 can form a larger liquid storage space in the inner layer of the battery cell, improve the liquid storage capacity, help increase the liquid retention of the inner layer of the battery, and improve the wetting effect of the pole piece located in the inner layer of the battery cell.

[0121] In one possible implementation, reference Fig.11 As shown, the recessed portion 43 includes a recessed portion 431 located at the center of the recessed portion 43 and a convex portion 432 located at the outer edge of the recessed portion 431. The convex portion 432 can block the electrolyte stored in the recessed structure 40 from flowing away, thereby improving the electrolyte storage effect of the recessed structure 40 and providing liquid retention. The recessed portion 431 is used to store electrolyte.

[0122] In one possible implementation, the negative electrode single-sided area 24 also includes an extension segment 245, which is connected to one end of the first bending segment 241 away from the first straight segment 242, and the second active material layer 22 of the extension segment 245 and the second active material layer 22 of the first straight segment 242 partially overlap, that is, the extension segment 245 is bent inward in a direction close to the center of the winding core, and the extension segment 245 and the first straight segment 242 partially overlap; along the length direction of the positive electrode sheet 10, the starting end of the winding of the positive electrode sheet 10 at the innermost circle of the battery cell does not exceed the extension segment 245, that is, the head of the positive electrode sheet 10 is folded, thereby preventing lithium deposition at the position of the negative electrode sheet 20 corresponding to the starting end of the winding of the positive electrode sheet 10.

[0123] In addition, the head folded paste of the positive electrode material layer of the positive electrode sheet 10, plus the partial overlap of the epitaxial section 245 and the first straight section 242, form a negative electrode folded paste, thereby avoiding lithium deposition and filling the gap formed by the head folded paste of the positive electrode sheet 10, thereby improving the flatness of the battery cell, making the battery interface uniform after formation, the expansion degree of the battery cell uniform, the pressure applied consistent, and the overall electrolyte distribution uniform inside the battery cell, thereby reducing the problem of black spot lithium deposition caused by excessive accumulation of electrolyte during the cycle, improving the cycle life of the battery, and solving the problem of ridges on the side of the battery.

[0124] In a possible implementation, a height distance between a bottom wall of the recessed portion 431 and the second side surface of the second current collector 21 is H1, wherein 5 μm≤H1≤30 μm.

[0125] In a possible implementation, a height distance H1 between a bottom wall of the recessed portion 431 and the second side surface of the second current collector 21 may be, for example, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm or 30 μm.

[0126] In a possible implementation, a height distance between the top of the outer protrusion 432 and the second side surface of the second current collector 21 is H2, wherein 5 μm≤H2≤30 μm.

[0127] In a possible implementation, a height H2 between the top of the outer protrusion 432 and the second side surface of the second current collector 21 may be, for example, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm or 30 μm.

[0128] In one possible implementation, the negative electrode sheet 20 includes a negative electrode double-sided area, in which the second active material layer 22 is provided on the opposite side surfaces of the second current collector 21, and grooves 221 are provided on the second active material layer 22 of the negative electrode double-sided area and / or the negative electrode single-sided area 24.

[0129] In one possible implementation, in the thickness direction of the negative electrode sheet 20, the projection of the groove 221 located in the negative electrode single-sided area 24 does not overlap with the projection of the recess 43, thereby preventing the laser wire punching or mechanical pore making process and the embossing process from the collector direction from being performed simultaneously at the same position of the negative electrode single-sided area 24 of the negative electrode sheet 20, thereby avoiding the problem of the second active material layer 22, i.e., the negative electrode active material layer falling off or the second active material layer 22 breaking due to uneven force on the negative electrode single-sided area 24.

[0130] In one possible implementation, reference Figure 2 As shown, the first active material layer 12 is provided on two opposite surfaces of the first current collector 11, a first pole lug groove 14 is opened in the first active material layer, the first current collector 11 is exposed from the first pole lug groove 14, a first pole lug 50 is provided in the first pole lug groove 14, and the first pole lug 50 is connected to the first current collector 11.

[0131] In one possible implementation, the first active material layer 12 is provided with an avoidance groove 13, and a step is formed between the avoidance groove 13 and the edge of the corresponding first pole ear groove 14. The pole ear glue 15 is provided in the avoidance groove 13, and the pole ear glue 15 covers the connection position between the first pole ear 50 and the first current collector 11.

[0132] In the present application, since the first active material layer 12 includes lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate or a ternary material, the thickness of the first active material layer 12 is thicker than that of a conventional active material layer. By opening an avoidance groove 13 in the first active material layer 12, the thickness of the first active material layer 12 is reduced at the position of the avoidance groove 13. Therefore, the ear glue 15 is arranged in the avoidance groove 13, which can prevent the positive electrode sheet 10 from being thicker at the position of the ear glue 15, and will not cause the coating area of ​​the first active material layer 12 on the positive electrode sheet 10 to be reduced.

[0133] In one possible implementation, the thickness of the first pole tab 50 is less than the sum of the thicknesses of the first active material layer 12 on two opposite surfaces of the first current collector 11, thereby reducing the thickness difference between the position where the first pole tab 50 is located and other areas, and ensuring the thickness uniformity of the battery cell. In other possible implementations, the sum of the thicknesses of the first pole tab 50 and the pole tab glue 15 is less than the sum of the thicknesses of the first active material layer 12 on two opposite surfaces of the first current collector 11, further improving the thickness consistency of the battery cell.

[0134] In one possible implementation, the pole ear glue 15 can be a pole ear glue paper, which plays an insulating and protective role and protects the connection position between the first pole ear 50 and the first current collector 11. Especially when the first pole ear 50 and the first current collector 11 are connected by welding, the pole ear glue 15 can effectively block the burrs formed by welding and avoid the problem of short circuit caused by the exposure of the burrs formed by welding.

[0135] A battery cell provided by the present invention adopts a structure in which the pole ear is placed in the middle. Considering that the thickness of the pole ear glue 15 at the welding position is relatively thick, an avoidance groove 13 is opened in the first active material layer 12, and the first pole ear 50 is connected to the first pole ear groove 14. The pole ear glue 15 is located in the avoidance groove 13, which helps to reduce the thickness of the position where the pole ear glue 15 is welded and improve the uniformity of the battery cell thickness.

[0136] In one possible implementation, reference Figure 2 As shown, the depth Dc of the avoidance groove 13 and the thickness Ht of the tab glue 15 satisfy: Dc≥Ht. This ensures that the tab glue 15 is located in the avoidance groove 13, preventing the tab glue 15 from protruding from the surface of the positive electrode sheet 10, causing the surface of the positive electrode sheet 10 to be uneven.

[0137] In one possible implementation, the first electrode tab 50 is welded to the first current collector 11 , and along the thickness direction of the positive electrode sheet 10 , a welding mark (not shown in the figure) formed at the welding position of the first electrode tab 50 and the first current collector 11 has a thickness Hs that satisfies: Hs≤40 μm.

[0138] In a possible implementation, Hs may be, for example, 20 μm, 25 μm, 30 μm, 34 μm or 40 μm.

[0139] In one possible implementation, reference Figure 2 As shown, along the thickness direction of the positive electrode sheet 10: the thickness Hp of the first pole tab 50, the thickness Hs of the welding mark formed at the welding position of the first pole tab 50 and the first current collector 11, the thickness Ht of the pole tab glue 15, and the thickness Hc of the first active material layer 12 satisfy: Hp+Hs+2×Ht≤2×Hc. The purpose is to avoid protrusion of the positive electrode sheet 10 at the welding position of the first pole tab 50 due to welding the first pole tab 50, improve the flatness of the welding position of the first pole tab 50, and thus improve the thickness consistency and volume energy density of the battery.

[0140] The first pole ear 50 is relatively flat, which is beneficial to improving the flatness of the battery cell, making the expansion degree of the battery cell uniform, the pressure applied to the battery cell consistent, and the overall electrolyte distribution inside the battery cell uniform, thereby reducing the problem of black spots and lithium precipitation caused by excessive electrolyte accumulation during the cycle process, and improving the cycle life of the battery.

[0141] In one possible implementation, reference Figure 7 As shown, the diaphragm 30 includes a substrate layer 311, an adhesive layer 32 arranged on one side surface of the substrate layer 311, and a ceramic layer 312 arranged on the other side surface of the substrate layer 311, the ceramic layer 312 is arranged on the side of the substrate layer 311 facing the positive electrode sheet 10; the adhesive layer 32 is arranged on the side of the substrate layer 311 facing the negative electrode sheet 20; the ceramic layer 312 includes an aluminum oxide material.

[0142] Alumina material has good liquid absorption and retention capabilities, has a certain pore size and porosity, ensures low resistance and high ion conductivity, has good permeability to lithium ions, helps to evenly distribute the electrolyte, and ensures smooth battery charging and discharging. The ceramic layer 312 faces the positive electrode sheet 10, which is a positive electrode sheet, which is conducive to storing more electrolyte on the side of the negative electrode sheet facing the positive electrode sheet. When the first active material layer 12 includes lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate or ternary material, and the positive electrode sheet 10 is thick, the electrolyte has a uniform infiltration effect on the positive electrode sheet 10.

[0143] In a possible implementation, the porosity e of the substrate layer 311 satisfies 35%≤e≤80%. When the porosity e of the substrate layer 311 is greater than 35%, the substrate layer 311 is defined as a high-porosity base membrane. In the present application, the substrate layer 311 is a high-porosity base membrane with a high porosity, and the existing pores can store more electrolyte.

[0144] In a possible implementation, the porosity e of the substrate layer 311 may be, for example, 35%, 40%, 50%, 60%, 70% or 80%.

[0145] In a possible implementation, the air permeability f of the diaphragm 30 satisfies: 40 sec / 100 cc≤f≤200 sec / 100 cc.

[0146] In a possible implementation, the air permeability f of the diaphragm 30 may be, for example, 40 sec / 100 cc, 80 sec / 100 cc, 100 sec / 100 cc, 160 sec / 100 cc, or 200 sec / 100 cc.

[0147] The high porosity of the substrate layer 311 makes the diaphragm 30 have good air permeability, fast electrolyte absorption efficiency, increased electrolyte absorption, increased ion conduction rate and battery cycle life, and prevents pore blockage in the adhesive layer.

[0148] In a possible implementation, the porosity of the ceramic layer 312 is greater than the porosity of the bonding layer 32. The ceramic layer 312 faces the positive electrode sheet 10, while the bonding layer 32 faces the negative electrode sheet. The liquid storage capacity of the ceramic layer is better than that of the base film, which is beneficial to the electrolyte storage capacity of the thicker positive electrode sheet 10 area.

[0149] In a possible implementation, the adhesive layer 32 includes at least one of water-based polyvinylidene fluoride (PVDF) and water-based polymethyl methacrylate (PMMA), polyacrylic acid, polytetrafluoroethylene, epoxy resin, chloroprene rubber, and methyl methacrylate. It has the advantages of low cost, mature large-scale production, and good bonding effect.

[0150] Because the oil-based adhesive is hydrophobic, the oil-based diaphragm is relatively dry, and the coating of the oil-based diaphragm 30 is fully coated, so that the contact area between the oil-based diaphragm 30 and the roller is larger. By selecting the water-based diaphragm 30 with a water-based adhesive, the friction coefficient of the diaphragm 30 is reduced, and the water-based adhesive is arranged in an array, and the contact area with the electrode is smaller, thereby reducing the static electricity effect.

[0151] In one possible implementation, reference Figure 4 As shown, the negative electrode sheet 20 further includes an empty foil area 23 and a double-sided coating area 25. Along the length direction of the negative electrode sheet 20, the negative electrode single-sided area 24 is connected between the empty foil area 23 and the double-sided coating area 25. In the empty foil area 23, the second active material layer 22 is not provided on both surfaces of the second current collector 21. In the double-sided coating area 25, the second active material layer 22 is provided on both surfaces of the second current collector 21. The empty foil area 23 is located at the innermost circle of the battery cell. Figure 3 and Figure 4 The arrow X indicates the direction.

[0152] In the negative electrode sheet 20 , the double-sided coating area 25 is provided with a second electrode tab 60 , and the second electrode tab 60 serves as a negative electrode tab.

[0153] In one possible implementation, reference Figure 4 and Figure 8 As shown, the second active material layer 22 located in the negative electrode single-sided area 24 includes a plurality of protrusions 41, and the protrusions 41 are arranged corresponding to the recesses 43. The protrusions 41 can be circular protrusions, polygonal protrusions, diamond-shaped protrusions, etc.

[0154] In a possible implementation, the circumscribed circle diameter R of the protrusion 41 satisfies 300μm≤R≤2000μm. For example, the circumscribed circle diameter R of the protrusion 41 may be 300μm, 350μm, 400μm, 450μm, 500μm, 600μm, 700μm or 800, 1000, 2000μm. If the circumscribed circle diameter R of the protrusion 41 is too large, the strength of the protrusion 41 itself will be weakened, resulting in a weakened support effect of the recessed structure 40. If the circumscribed circle diameter R of the protrusion 41 is too small, the protrusion 41 will be too sharp, and the problem of pole piece damage will easily occur.

[0155] In one possible implementation, a concave cavity 42 is formed on the back side of the protrusion 41, and the depth Sd of the concave cavity 42 satisfies: 3μm≤Sd≤30μm. For example, the depth Sd of the concave cavity 42 may be 3, 4, 8, 10μm, 12μm, 15μm, 18μm, 20μm, 25μm or 30μm. The concave cavity 42 may store electrolyte. When the depth Sd of the concave cavity 42 is too large, it is easy to cause damage to the second current collector 21. When the depth Sd of the concave cavity 42 is too small, it is not conducive to increasing the amount of electrolyte.

[0156] In a possible implementation, the spacing W between the centers of the circumscribed circles of two adjacent protrusions 41 satisfies: 1000 μm ≤ W ≤ 2000 μm. For example, the spacing W between the centers of the circumscribed circles of two adjacent protrusions 41 may be 1000 μm, 1200 μm, 1300 μm, 1500 μm, 1600 μm, 1800 μm or 2000 μm. This makes the size distribution of the protrusions 41 reasonable, ensures the structural strength of the recessed structure 40 itself, and can play an effective supporting effect.

[0157] In one possible implementation, reference Figure 8 and Fig.10 As shown, along the width direction of the negative electrode sheet 20: the spacing between the recessed structure 40 and the two side edges of the negative electrode sheet 20 is S1 and S2 respectively, wherein 0.5 mm ≤ S1 ≤ 6 mm, and / or 0.5 mm ≤ S2 ≤ 6 mm. Fig.10 The arrow Y in the figure indicates the direction.

[0158] If S1 or S2 is too large, the proportion of the recessed structure 40 in the negative electrode single-sided area 24 will be reduced, and the supporting function of the recessed structure 40 will be weakened, which is not conducive to increasing the gap between the inner layers of the winding core and the storage capacity of the electrolyte. On the contrary, if S1 or S2 is too small, the recessed structure 40 will be too close to the edges of both sides of the positive electrode sheet 10. When processing the recessed structure 40, the second active material layer 22 is prone to fall off, that is, powder loss, which affects the service life of the battery.

[0159] In one possible implementation, S1 may be, for example, 0.5 mm, 1 mm, 2 mm, 2.5 mm, 0.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, or 6 mm.

[0160] In one possible implementation, S2 may be, for example, 0.5 mm, 1 mm, 2 mm, 2.5 mm, 0.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, or 6 mm.

[0161] In one possible implementation, reference Figure 8 and Fig.10 As shown, along the length direction of the negative electrode sheet 20 , the distance S3 between the recessed structure 40 and the empty foil area 23 satisfies 1 mm≤S3≤10 mm.

[0162] In one possible implementation, S3 may be, for example, 1 mm, 1.5 mm, 2 mm, 3 mm, 3.5 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, or 10 mm.

[0163] In one possible implementation, reference Fig. 9 As shown, along the length direction of the negative electrode sheet 20 , the distance S4 between the recessed structure 40 and the double-sided coating area 25 satisfies 0.5 mm≤S4≤5 mm.

[0164] In one possible implementation, S4 may be, for example, 0.5 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, or 5 mm.

[0165] In a possible implementation, the first current collector 11 includes aluminum foil, and the tensile strength cf of the first current collector 11 satisfies: 200Mpa≤Cf. In this embodiment, the first current collector 11 uses high tensile strength aluminum foil, and the tensile strength Cf of the first current collector 11 can be, for example, 200Mpa, 220Mpa, 230Mpa, 240Mpa or 250Mpa.

[0166] The first active material layer 12 includes lithium iron phosphate, lithium iron manganese phosphate, lithium manganese phosphate or a ternary material. Since the gram capacity of lithium iron phosphate, lithium iron manganese phosphate, lithium manganese phosphate or a ternary material is relatively low and the surface density of the positive electrode sheet 10 is large, the present application uses a high-strength aluminum foil through the first current collector 11. The high-strength aluminum foil has a large tensile strength, which prevents the positive electrode sheet 10 from breaking during the rolling process of the positive electrode sheet 10. When the positive electrode sheet 10 is wound to prepare a battery cell, if the winding stress in the arc area of ​​the positive electrode sheet 10 is too large, the problem of damage and breakage of the arc area of ​​the positive electrode sheet 10 can be reduced.

[0167] In one possible implementation, reference Figure 2 As shown, the thickness Hc of the first active material layer 12 and the thickness Ha of the second active material layer 22 satisfy: Hc>Ha.

[0168] In one possible implementation, reference Figure 1 and Fig.13 As shown, in the innermost circle of the battery cell, the negative electrode single-sided area 24 has a first bending section 241, and along the length direction of the positive electrode sheet 10, the head end of the positive electrode sheet 10 in the innermost circle of the battery cell does not exceed the first bending section 241. That is, a paste withdrawal length Q1 is formed at the head of the positive electrode sheet 10, and the head of the positive electrode sheet 10, that is, the positive electrode sheet 10 is located at the end of the innermost circle of the battery cell.

[0169] With such a structure, when the thickness Hc of the first active material layer 12 and the thickness Ha of the second active material layer 22 satisfy: Hc>Ha, the thickness difference of the head of the positive electrode sheet 10 located in the innermost circle of the battery cell can be effectively compensated, the flatness of the battery cell can be improved, the battery interface after formation can be uniform, the pressure on the battery cell can be consistent, the electrolyte distribution inside the battery cell can be uniform, the problem of black spots and lithium precipitation caused by excessive accumulation of electrolyte during the cycle process can be reduced, the cycle life of the battery can be improved, and the problem of ridges on the sides of the battery can be solved.

[0170] In a possible implementation, the active material in the second active material layer 22 in the negative electrode sheet 20 may include at least one of natural graphite, artificial graphite, mesophase microcarbon beads (MCMB for short), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, silicon-carbon composites, and silicon-oxygen composites. In some embodiments, the second active material layer 22 may also include a conductive agent and a binder, which may be selected according to actual needs.

[0171] Exemplarily, the conductive agent includes but is not limited to one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers; the binder may be but is not limited to one or more of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin and carboxymethyl cellulose (CMC).

[0172] The second current collector 21 in the negative electrode sheet 20 includes, but is not limited to, a foil or a porous plate made of metal such as copper, nickel, titanium or iron, or alloys thereof.

[0173] The present invention also provides a battery, comprising a housing and the above-mentioned battery cell, wherein a receiving cavity is formed inside the housing, and the battery cell is arranged in the receiving cavity. An electrolyte is injected into the receiving cavity so that the battery cell is immersed in the electrolyte.

[0174] In the battery provided by the embodiment of the present invention, the number of battery cells can be 1, 2, 3 or more, which is not specifically limited here.

[0175] A battery provided by the present invention may be a soft-pack battery or an aluminum shell battery.

[0176] In order to verify that the present application has the beneficial technical effect of increasing the liquid retention capacity of the battery, improving the rate performance and cycle life, a comparative test is performed on the battery provided in the present application and the existing conventional batteries.

[0177] Preparation of positive electrode sheet 10: lithium iron phosphate LFP, a mixture of conductive carbon black and carbon nanotubes, and PVDF are uniformly stirred in a mass ratio of 96.50:2:1.5 to prepare positive electrode slurry; an aluminum foil with a thickness of 13 μm is selected as the first current collector 11, and the positive electrode slurry is coated on the front and back sides of the first current collector 11 by a coating machine, and is dried and rolled to compact to 2.65 in sequence. The surface density of the positive electrode slurry coating is 0.01817 g / cm2, and the coating thickness is 142 μm, which is the thickness obtained by disassembly measurement when the fresh battery is 2.5V; a first pole ear groove 14 with a fixed size is provided on the positive electrode sheet, and a first pole ear 50 is welded in the first pole ear groove 14 by laser or ultrasonic welding, and the thickness of the first pole ear 50 is 100 μm; the height of the welding point of the first pole ear 50 is 21 μm; the thickness of the aluminum foil is 13 μm; the thickness of the pole ear glue 15 is 16 μm.

[0178] Preparation of negative electrode sheet 20: Graphite, conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose are placed in deionized water at a mass ratio of 97.2:0.5:1.3:1, and the above slurry is stirred evenly to obtain negative electrode slurry; copper foil with a thickness of 4 μm is selected as the second current collector 21, and the negative electrode slurry is evenly coated on the second current collector 21 by a coating machine, and the coating surface density is 0.00823 g / cm2; after drying, rolling and compacting to 1.65 and slitting, the coating thickness of the second active material layer 22 is 108 μm, which is the thickness obtained by disassembly measurement when the fresh battery is 2.5V;

[0179] The cut negative electrode sheet 20 is laser etched to form grooves 221 for electrolyte infiltration and ion rapid transmission. The grooves 221 are set on the entire surface of the negative electrode sheet 20. The grooves 221 here are matrix grooves. The spacing between adjacent grooves 221 is set to 1280μm, the depth of the grooves 221 is 18μm, and the width of the grooves 221 is 80μm.

[0180] The concave structure 40 is processed in the negative electrode single-sided area 24 of the negative electrode sheet 20, and the circumscribed circle diameter R of the protrusion 41 is 500μm; the depth Sd of the inner concave cavity 42 is 16μm; the distance W between the centers of two adjacent protrusions 41 is 1450μm; the distances S1 and S2 between the concave structure 40 and the two side edges of the negative electrode sheet 20 are the same and are both 1.7mm; along the length direction of the negative electrode sheet 20: the distance S3 between the concave structure 40 and the empty foil area 23 is 3.5mm; along the length direction of the negative electrode sheet 20: the distance S4 between the concave structure 40 and the double-sided coating area 25 is 1.5mm. Then the negative electrode sheet 20 is laser etched to process the groove 221, and the concave structure 40 is embossed, and then the negative electrode sheet is obtained after cleaning and sheeting.

[0181] Prepare the battery:

[0182] The structure of the diaphragm 30 in the present application is bonding layer 32-ceramic layer 312-substrate layer 311-bonding layer 32, the thickness of the substrate layer 311 is 5μm, the thickness of the ceramic layer 312 is 2μm, and the thickness of the single-sided bonding layer 32 is 0.75μm; the electrolyte includes lithium salt LiPF6 and a solvent, and the solvent includes ethylene carbonate EC, diethyl carbonate DEC and methyl ethyl carbonate EMC, wherein the molar ratio of the three is DEC:EC:EMC=1:1:1. After the above-mentioned cut positive electrode sheet 10, separator 30, and negative electrode sheet 20 are stacked in sequence, the ceramic layer 312 of the separator 30 faces the positive electrode sheet 10, and is wound into a wound structure battery cell, wherein the paste withdrawal length of the end of the positive electrode sheet 10 located at the innermost circle of the battery cell is 5 mm, and the paste folding length of the negative single-sided area 24 of the negative electrode sheet 20 is 4 mm. After the battery cell is packaged, injected, formed, and second-sealed, a lithium-ion battery is obtained.

[0183] In Examples 1 to 6 and Comparative Examples 1 to 3, the thickness Hc of the first active material layer 12 is 142 μm, the thickness Ha of the second active material layer 22 is 108 μm, the tensile strength cf of the first current collector 11 is 250 MPa, the thickness Hp of the first pole tab 50 is 100 μm, and the thickness Ht of the pole tab glue 15 is 16 μm; the thickness Hs of the welding trace formed by the welding position of the first pole tab 50 and the first current collector 11 is 21 μm; the depth Dc of the avoidance groove 13 is 0, and the length Q1 of the paste withdrawal at the end of the positive electrode sheet 10 is 5 mm in the innermost circle of the battery cell. The negative single-sided area 24 of the negative electrode sheet 20 is in the innermost circle of the battery cell, that is, the head position of the negative electrode sheet 20, and the paste folding lengths Q2 and Q3 on the front and back sides of the negative electrode sheet 20 are both 4 mm.

[0184] The A surface and the C surface of the negative electrode sheet head are two opposite surfaces of the negative electrode sheet 20 , that is, the front and back surfaces of the negative electrode sheet 20 .

[0185] The specific parameters are shown in Table 1:

[0186] Table 1

[0187]

[0188]

[0189] In Examples 1 to 6 and Comparative Examples 1 to 3, the parameters and performance test results of the lithium-ion batteries are shown in Table 2:

[0190] Table 2

[0191]

[0192]

[0193] From Table 2, it can be seen from Examples 1 to 5 and Comparative Examples 1 to 3 that if either the depth D of the groove 221 or the width L of the groove 221 is reduced, the liquid retention of the battery will be reduced, resulting in a decrease in the cycle retention rate. If the depth D of the groove 221 and the width L of the groove 221 are too large, Hc / D×L is likely to exceed the specified range, the liquid retention is increased, but the negative electrode weight loss rate is too high, resulting in a decrease in the ratio of positive and negative electrode active materials, an increase in the problem of negative electrode cycle lithium precipitation, and a decrease in the cycle retention rate; if the depth D of the groove 221 and the width L of the groove 221 are too small, Hc / D×L is lower than the specified range, the improvement in the battery liquid retention is not obvious, and the improvement in the rate discharge performance is not significant.

[0194] Increasing the liquid retention capacity can help the battery have a suitable amount of electrolyte to improve the battery's cycle performance.

[0195] It can be seen from Example 1, Example 6, and Comparative Examples 1 to 2 that the greater the air permeability f of the diaphragm 30 and the smaller the porosity e, the lower the absorption capacity of the diaphragm 30 for the electrolyte, and at the same time affects the rate at which lithium ions penetrate the diaphragm 30, resulting in a decrease in the cycle retention rate and rate discharge capacity retention rate of the battery.

[0196] It can be seen from Example 1 and Comparative Example 3 that the negative electrode single-sided area 24 is provided with a recessed structure 40, which plays a supporting role, increases the gap between the inner layers of the battery cell, improves the electrolyte storage capacity, and can improve the cycle performance.

[0197] According to the different paste folding conditions of the negative electrode single-sided area 24, the depth of the avoidance groove 13, the thickness of the pole ear glue 15, and the thickness of the first pole ear 50 relative to the first embodiment, the seventh to tenth embodiments are listed, the differences between the seventh to tenth embodiments and the first embodiment, and the parameters and performance test results of the lithium ion battery are shown in the following Table 3:

[0198] Table 3

[0199]

[0200] Referring to Table 3, it can be seen from Example 1, Example 7 and Comparative Example 4 that since the thickness of the positive electrode sheet is greater than that of the negative electrode sheet, Figure 1 and Fig.13 As shown in the figure, the positive electrode sheet has a paste withdrawal length Q1 at the head position of the innermost circle of the winding core, which makes the winding core thinner at the 1# position. The paste folding length Q2 on the A side of the negative electrode head and the paste folding length Q3 on the C side can make up for the thickness difference between the winding core at the 1# position and the 2# position, improve the overall flatness of the battery, reduce the problems of black spot lithium precipitation on the interface and ridge formation on the side of the battery, and reduce the battery cycle expansion rate.

[0201] It can be seen from Examples 8 to 10 and Comparative Example 4 that avoidance grooves 13 are provided on both sides of the first pole tab groove 14, and the depth Dc of the avoidance groove 13 is ≥ the thickness Ht of the pole tab glue 15, which can compensate for the thickness of the pole tab glue 15 and improve the volume energy density ED of the battery cell; at the same time, the thickness of the positive pole tab and the pole tab glue 15 of the positive pole tab is controlled so that along the thickness direction of the positive electrode sheet 10: the thickness Hp of the first pole tab 50, the thickness Hs of the welding mark formed at the welding position of the first pole tab 50 and the first current collector 11, the thickness Ht of the pole tab glue 15, and the thickness Hc of the first active material layer 12 satisfy: Hp+Hs+2×Ht≤2×Hc, which can improve the volume energy density ED and flatness of the battery.

[0202] Parameter test method:

[0203] A groove 221 is etched on the negative electrode sheet 20 by laser, and the size of the groove 221 is measured by: testing the width L of the groove 221: using an element analysis microscope to take a photo of the groove 221 on the surface of the negative electrode sheet 20 at a magnification of 100 times, and testing the width L of the groove 221; the closest distance between two adjacent grooves 221 is tested using an element analysis microscope, and the distance S between the grooves 221 is tested at a magnification of 50 times; the depth of the groove 221 is tested using an element analysis microscope, and the depth D of the groove 221 is tested at a magnification of 200 times.

[0204] Porosity of the substrate layer 311: Use a micrometer to measure the thickness of the substrate layer 311, and use a cutter to cut a sample of a certain area of ​​the substrate layer 311 to obtain the apparent volume of the sample, and the apparent volume of the sample = the thickness of the sample × the area of ​​the sample; put the sample into a Microdensitometer for testing to obtain the true volume of the sample, and the porosity of the sample = the apparent volume of the sample - the true volume of the sample / the apparent volume of the sample × 100%.

[0205] Air permeability test of diaphragm 30: Use an air permeability meter, take a diaphragm sample with a length ≥38mm and a width ≥38mm, place the diaphragm sample to be tested flatly into the test area, test pressure 0.05MPa, test for 8s, and the final displayed value is the air permeability value of the diaphragm sample.

[0206] Thickness of the diaphragm 30: Under the protection of liquid nitrogen, use an ion grinder to cut the cross section of the diaphragm sample, use a scanning electron microscope energy spectrometer, select the magnification of the pole piece at 500x~1kx, and the magnification of the diaphragm 30 at 5kx~10kx, find the cross-sectional positions of the current collector, active material layer, substrate layer 311, ceramic layer 312 and bonding layer 32 respectively, and take the average value of the thickness of the test sample at 5 different positions.

[0207] The first current collector 11 is made of aluminum foil, and the tensile strength σ and elongation at break δ of the aluminum foil are tested: an aluminum foil is cut into strips with a length of 60 to 70 cm and a width of 1.5 cm. The aluminum foil is stretched at a stretching rate of 10 cm / min in a tensile testing machine, and the maximum strength displayed is regarded as the tensile strength of the aluminum foil, which is recorded as σc.

[0208] Liquid retention test: The liquid retention is the amount of electrolyte that is ultimately retained in the lithium-ion battery. To ensure the consumption of electrolyte during the formation of the lithium-ion battery, a certain amount of electrolyte is usually injected, and then the excess electrolyte is extracted after formation. It is measured by weighing, the injection volume n1, the electrolyte extraction volume n2; liquid retention = n1-n2.

[0209] Measurement of the size of the recessed structure 40: tested using an elemental analysis microscope, taking photos at a magnification of 200 times, and testing the circumscribed circle diameter R of a single protrusion 41 and the depth Sd of the inner cavity 42, in μm; the spacing W between the centers of the circumscribed circles of two adjacent protrusions 41, in mm; tested the spacing S1 and S2 between the recessed structure 40 and the two side edges of the negative electrode sheet 20 at a magnification of 50 times, along the length direction of the negative electrode sheet 20: the distance S3 between the recessed structure 40 and the empty foil area 23, and the distance S4 between the recessed structure 40 and the double-sided coating area 25.

[0210] 25℃ cycle test: In a 25℃ environment, the lithium-ion battery is charged at 2C constant current to the full charge voltage. The maximum voltage of the battery design is 3.65V, and then constant voltage charging is performed at the maximum voltage until the current is 0.002C, and then constant current discharge is performed at a discharge current of 0.05C until the final voltage is 2.5V, and the discharge capacity of the first cycle is recorded. After that, the above steps are repeated for charging and discharging cycles, and the capacity retention rate and cell thickness expansion rate when the cycle reaches 1000T are recorded; during the cycle, the appearance of the cell is recorded to see if there is any side edge ridges.

[0211] Cycle capacity retention rate = (discharge capacity times of the 1000th cycle / discharge capacity of the first cycle) × 100%.

[0212] Fully charge the battery before the cycle and test the battery thickness B1 before the cycle. After 1000 cycles, fully charge the battery and test the battery thickness B2. Battery thickness expansion rate = (B2-B1) / B1×100%;

[0213] Volume energy density: The volume energy density of lithium-ion batteries is ED = E / V, where E is the discharge energy of the battery. The test method is to charge the lithium-ion battery to the upper voltage limit at a current of 0.2C, then charge it at a constant voltage until the current drops to 0.02C, and then discharge it at a current of 0.2C to 2.5V. The discharged energy is E. V is the volume of the lithium-ion battery. The volume of the lithium-ion battery is obtained by measuring the thickness, width and length of the lithium-ion battery and calculating the product of the three. E / V is the volume energy density obtained by the test.

[0214] 2C rate discharge capacity retention rate: Charge the lithium-ion battery to the upper limit voltage at a current of 0.5C, then charge at a constant voltage until the current drops to 0.05C, let it stand for 5 minutes, then discharge at a current of 0.2C until the current drops to 2.5V, and the capacity is C0. After standing for 5 minutes, charge the lithium-ion battery to the upper limit voltage at a current of 0.2C, then charge at a constant voltage until the current drops to 0.02C, let it stand for 5 minutes, then discharge at a current of 2C until the current drops to 2.5V, and the capacity is C1. C1 / C0 is the capacity retention rate.

[0215] In order to verify that the present invention can effectively improve the flatness of the battery at the head position of the positive electrode sheet, the two cases where the A side and C side of the negative electrode sheet have a paste folding length of 4mm and the A side and C side of the negative electrode sheet have no paste folding, that is, the paste folding length of the A side and C side of the negative electrode sheet is 0 are compared, and each is tested. Figure 1 The thickness of the cells shown are at positions 1#, 2#, 3#, 4#, 5#, 6#, 7#, 8#, and 9#. Fig.14 and Fig.15 As shown, Fig.14 and Fig.15 It is known that when the battery cell is folded on the A / C surface of the negative electrode sheet, the thickness at position 1# is closer to the thickness at positions 2# to 9#. Therefore, the present application can effectively improve the flatness of the battery cell thickness corresponding to the head position of the positive electrode sheet 10 of the battery cell.

[0216] It should be noted here that the numerical values ​​and numerical ranges involved in this application are approximate values. Due to the influence of the manufacturing process, there may be a certain range of errors, which can be considered negligible by those skilled in the art.

[0217] In the description of the present invention, it is necessary to understand that the terms used such as “center”, “length”, “width”, “thickness”, “top”, “bottom”, “up”, “down”, “left”, “right”, “front”, “back”, “vertical”, “horizontal”, “inside”, “outside”, “axial”, “circumferential”, etc. to indicate directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred position or component must have a specific direction, a specific structure and operation, and therefore cannot be understood as limiting the present invention.

[0218] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0219] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, they can be fixedly connected, detachably connected, or integrated; they can be mechanically connected, electrically connected, or can communicate with each other; they can be directly connected, or indirectly connected through an intermediate medium, so that the internal communication of two elements or the interaction relationship between two elements can be achieved. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0220] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0221] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery cell, characterized in that: include: A positive electrode sheet (10), a negative electrode sheet (20), and a separator (30) arranged between the positive electrode sheet (10) and the negative electrode sheet (20), wherein the positive electrode sheet (10), the negative electrode sheet (20), and the separator (30) are stacked and then wound; The positive electrode sheet (10) comprises a first current collector (11) and a first active material layer (12) arranged on the surface of the first current collector (11), wherein the first active material layer (12) comprises lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate or a ternary material; The negative electrode sheet (20) comprises a second current collector (21) and a second active material layer (22) arranged on two opposite surfaces of the second current collector (21), and the surface of the negative electrode sheet (20) has a groove (221); The thickness of the first active material layer (12) is Hc, the thickness of the second active material layer (22) is Ha, and 1<Hc / Ha≤1.5 is satisfied; Along the length direction of the negative electrode sheet (20), the winding start end of the second current collector (21) has a negative electrode single-sided area (24), in which the first side surface of the second current collector (21) is provided with the second active material layer (22) and the second side surface of the second current collector (21) is not provided with the second active material layer (22), and the negative electrode single-sided area (24) is provided with a recessed structure (40), and the recessed structure (40) includes a plurality of recessed portions (43).

2. The battery cell according to claim 1, characterized in that: A plurality of the grooves (221) are arranged at intervals on the surface of the second active material layer (22); and / or, The depth D of the groove (221) satisfies 3 μm≤D≤50 μm; and / or, The width L of the groove (221) satisfies 30 μm≤L≤180 μm; and / or, The distance S between two adjacent grooves (221) satisfies 500 μm ≤ S ≤ 2500 μm; and / or, The recessed structure (40) is formed by being recessed from the second side surface of the second current collector (21) toward the first side surface of the second current collector (21).

3. The battery cell according to claim 1, characterized in that: Along the winding direction of the battery cell, the negative electrode single-sided area (24) comprises a first bent section (241), a first straight section (242), a second bent section (243) and a second straight section (244); the recessed structure (40) located in the first straight section (242) and the recessed structure (40) located in the second straight section (244) are arranged opposite to each other.

4. The battery cell according to claim 1, characterized in that: The recessed portion (43) comprises an indented portion (431) located at the center of the recessed portion (43) and an outdented portion (432) located at the outer edge of the indented portion (431).

5. The battery cell according to claim 3, characterized in that: The negative electrode single-sided region (24) further comprises an extension segment (245), the extension segment (245) being connected to an end of the first bent segment (241) away from the first straight segment (242), and the second active material layer (22) of the extension segment (245) and the second active material layer (22) of the first straight segment (242) partially overlapping; Along the length direction of the positive electrode sheet (10), the winding start end of the positive electrode sheet (10) at the innermost circle of the battery cell does not exceed the extension section (245).

6. The battery cell according to claim 4, characterized in that: The height distance between the bottom wall of the recessed portion (431) and the second side surface of the second current collector (21) is H1, wherein 5 μm≤H1≤30 μm; and / or, The height distance between the top of the outer protrusion (432) and the second side surface of the second current collector (21) is H2, wherein 5 μm≤H2≤30 μm.

7. The battery cell according to claim 1, characterized in that: The negative electrode sheet (20) comprises a negative electrode double-sided region, in which the second active material layer (22) is provided on both opposite side surfaces of the second current collector (21), and the groove (221) is provided on the second active material layer (22) of the negative electrode double-sided region and / or the negative electrode single-sided region (24).

8. The battery cell according to claim 1, characterized in that: In the thickness direction of the negative electrode sheet (20), the projection of the groove (221) located in the negative electrode single-sided area (24) does not overlap with the projection of the recess (43).

9. The battery cell according to claim 2, characterized in that: The thickness Hc of the first active material layer (12), the depth D of the groove (221), and the width L of the groove (221) satisfy: 0.05≤Hc / D×L≤0.

26.

10. The battery cell according to claim 3, characterized in that: The thickness Hc of the first active material layer (12), the depth D of the groove (221), and the width L of the groove (221) satisfy: 0.08≤Hc / D×L≤0.

15.

11. The battery cell according to any one of claims 1 to 4, characterized in that: The first active material layer (12) is disposed on two opposite surfaces of the first current collector (11), a first electrode tab groove (14) is provided in the first active material layer (12), and the first current collector (11) is exposed from the first electrode tab groove (14); A first pole lug (50) is disposed in the first pole lug groove (14), and the first pole lug (50) is connected to the first current collector (11).

12. The battery cell according to claim 11, characterized in that: The first active material layer (12) is provided with an avoidance groove (13), a step is formed between the avoidance groove (13) and the edge of the corresponding first pole lug groove (14), and pole lug glue (15) is provided in each of the avoidance grooves (13), and the pole lug glue (15) covers the connection position between the first pole lug (50) and the first current collector (11).

13. The battery cell according to claim 12, characterized in that: The depth Dc of the avoidance groove (13) and the thickness Ht of the tab glue (15) satisfy: Dc≥Ht; and / or, The first electrode tab (50) is welded to the first current collector (11), and along the thickness direction of the positive electrode sheet (10), the thickness of the welding trace formed by the welding position of the first electrode tab (50) and the first current collector (11) is Hs, which satisfies: Hs≤40 μm; and / or, Along the thickness direction of the positive electrode sheet (10): the thickness Hp of the first electrode tab (50), the thickness Hs of the welding mark formed by the welding position of the first electrode tab (50) and the first current collector (11), the thickness Ht of the electrode tab glue (15), and the thickness Hc of the first active material layer (12) satisfy: Hp+Hs+2×Ht≤2×Hc.

14. The battery cell according to claim 1, characterized in that: The diaphragm (30) comprises a substrate layer (311), an adhesive layer (32) arranged on one side surface of the substrate layer (311), and a ceramic layer (312) arranged on the other side surface of the substrate layer (311), wherein the ceramic layer (312) is arranged on the side of the substrate layer (311) facing the positive electrode sheet (10); and the adhesive layer (32) is arranged on the side of the substrate layer (311) facing the negative electrode sheet (20).

15. The battery cell according to claim 14, characterized in that: The ceramic layer (312) comprises an aluminum oxide material; and / or, The porosity e of the substrate layer (311) satisfies 35%≤e≤80%; and / or, The porosity of the ceramic layer (312) is greater than the porosity of the bonding layer (32); and / or, The air permeability f of the diaphragm (30) satisfies: 40 sec / 100 cc≤f≤200 sec / 100 cc; and / or, The adhesive layer (32) comprises at least one of water-based PVDF and water-based PMMA, polyacrylic acid, polytetrafluoroethylene, epoxy resin, chloroprene rubber, and methyl methacrylate.

16. The battery cell according to claim 1, characterized in that: The second active material layer (22) located in the negative electrode single-sided area (24) comprises a plurality of protrusions (41), and the protrusions (41) are arranged corresponding to the recesses (43).

17. The battery cell according to claim 16, characterized in that: The circumscribed circle diameter R of the protrusion (41) satisfies 300 μm≤R≤2000 μm; and / or, The depth Sd of the concave portion (43) satisfies: 3 μm ≤ Sd ≤ 30 μm; and / or, The distance W between the centers of the circumscribed circles of two adjacent protrusions (41) satisfies: 1000 μm≤W≤5000 μm.

18. The battery cell according to claim 9, characterized in that: Along the width direction of the negative electrode sheet (20): the spacing between the recessed structure (40) and the two side edges of the negative electrode sheet (20) are S1 and S2 respectively, wherein 0.5 mm ≤ S1 ≤ 6 mm, and / or 0.5 mm ≤ S2 ≤ 6 mm.

19. The battery cell according to claim 9, characterized in that: The negative electrode sheet (20) further comprises a hollow foil area (23) and a double-sided coating area (25); along the length direction of the negative electrode sheet (20), the negative electrode single-sided area (24) is connected between the hollow foil area (23) and the double-sided coating area (25); along the length direction of the negative electrode sheet (20): The distance S3 between the recessed structure (40) and the empty foil area (23) satisfies 1mm≤S3≤10mm; and / or, The distance S4 between the recessed structure (40) and the double-sided coating area (25) satisfies 0.5 mm ≤ S4 ≤ 5 mm.

20. The battery cell according to any one of claims 1 to 4, characterized in that: The first current collector (11) comprises aluminum foil, and the tensile strength cf of the first current collector (11) satisfies: 200Mpa≤Cf.

21. A battery, characterized in that: It comprises a shell and the battery cell according to any one of claims 1 to 20, wherein a receiving cavity is formed inside the shell, and the battery cell is arranged in the receiving cavity.

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