Secondary battery and electric device

Abstract

The application discloses a secondary battery and a power utilization device. The secondary battery comprises an electrode assembly, the electrode assembly comprises a first pole piece, a second pole piece and a first diaphragm, the first pole piece comprises a first lug, the first lug is arranged on one side of the first pole piece in the width direction; the first diaphragm comprises a first adhesive layer and a base film arranged in a stack; the first adhesive layer comprises a first part and a second part arranged in sequence along the winding direction, the first part is farther away from the winding center than the second part; the first part comprises a first region and a second region, the second part comprises a third region and a fourth region arranged in sequence along the width direction of the first diaphragm, the first region and the third region are located on the same side of the first lug in the width direction of the first diaphragm; the bonding strength between the first region and the first pole piece is F1, the bonding strength between the fourth region and the first pole piece is F4, and F1 / F4 is greater than or equal to 1.1. The end of the first diaphragm on the side of the first lug is not easy to be folded due to falling.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage, in particular to a secondary battery and a power utilization device. BACKGROUND

[0002] After the electrode assembly of the secondary battery is packaged in the shell, there is a certain space between the head of the electrode assembly (the side close to the tab) and the shell, which causes the electrolyte to accumulate at the head of the electrode assembly. When the secondary battery falls, the end of the separator of the electrode assembly is impacted by the electrolyte, which easily causes the end of the separator to fold, and further causes the short circuit between the electrode plates of different polarities to fail. SUMMARY

[0003] Therefore, it is necessary to provide a secondary battery which can improve the problem of the end of the separator at the head of the electrode assembly folding, and reduce the risk of the secondary battery falling.

[0004] A first aspect of the embodiments of the present application provides a secondary battery, which comprises an electrode assembly, the electrode assembly comprising a first electrode plate, a second electrode plate and a first separator, the first electrode plate comprising a first tab, the first tab being arranged on one side of the first electrode plate in the width direction; the first electrode plate, the first separator and the second electrode plate are sequentially stacked and form a winding structure; the first separator comprises a first adhesive layer and a base film which are sequentially arranged in the thickness direction of the first separator, the first adhesive layer facing the first electrode plate; the first adhesive layer comprises a first part and a second part which are connected in the winding direction of the winding structure, the first part being farther away from the winding center of the winding structure compared with the second part; the first part comprises a first region and a second region which are sequentially arranged in the width direction of the first separator, the first region and the first tab being on the same side of the first separator in the width direction; the second part comprises a third region and a fourth region which are sequentially arranged in the width direction of the first separator, the third region and the first tab being on the same side of the first separator in the width direction; the adhesive strength between the first region and the first electrode plate is F1, the adhesive strength between the fourth region and the first electrode plate is F4, and F1 / F4≥1.1.

[0005] In the above electrode assembly, when the secondary battery falls, the first part corresponding to the first separator is farther away from the winding center of the winding structure than the second part corresponding to the second separator, that is, the first part corresponding to the first separator is located at a more outer circle of the winding structure, so the first part corresponding to the first separator is subjected to a smaller binding force of the winding structure. Furthermore, the impact force of the electrolyte on the first part corresponding to the first separator on the side of the first tab (i.e., the head of the electrode assembly) is greater than that on the second part corresponding to the second separator, and the first part corresponding to the first separator in the first region is located at the position of the electrode assembly head where the electrolyte accumulates, so the first region corresponding to the first separator is subjected to a greater impact force of the electrolyte. By setting the bonding strength F1 between the first region close to the first tab side in the first part and the first tab to be relatively large, the firmness of the bonding between the first region and the first tab is improved, so that when the electrolyte impacts the first region corresponding to the first separator, the first region corresponding to the first separator is not easy to separate from the first tab, thereby making the first separator at the end of the electrode assembly head not easy to fold due to falling, reducing the risk of short circuit of the secondary battery caused by direct contact between the first tab and the second tab. At the same time, since the fourth region corresponding to the winding structure is closer to the winding center than the first part corresponding to the winding structure, the winding binding force of the inner circle of the winding is greater, and the position of the fourth region corresponding to the winding structure is more prone to poor electrolyte infiltration problem, therefore the bonding strength F4 between the fourth region and the first tab should not be too large, so as to avoid aggravating the poor electrolyte infiltration problem at the winding center of the winding structure. By setting F1 / F4≥1.1, the first region has a relatively high bonding strength compared to the fourth region, so as to achieve the above technical effects.

[0006] In one or more of the above embodiments, 1.5≤F1 / F4≤3.5.

[0007] In the above embodiments, the bonding strength F1 between the first region and the first tab and the bonding strength F4 between the fourth region and the first tab should not be too large. If the bonding strength F1 between the first region and the first tab is too large, the probability of the first region corresponding to the first separator having a folding problem increases. By setting 1.2≤F1 / F4≤3.5, both the probability of the first region corresponding to the first separator having a folding problem and the probability of the first region corresponding to the first separator having a poor electrolyte infiltration problem can be reduced.

[0008] In one or more of the above embodiments, 1.8≤F1 / F4≤2.5.

[0009] In the above embodiments, in order to reduce both the probability of the first region corresponding to the first separator having a folding problem and the probability of the first region corresponding to the first separator having a poor electrolyte infiltration problem, it is further preferred that 1.8≤F1 / F4≤2.5.

[0010] In one or more of the above embodiments, 10 N / m ≤ F1 ≤ 20 N / m; 6 N / m ≤ F4 ≤ 8 N / m.

[0011] In the above embodiments, F1 is in the range of 10 N / m to 20 N / m, which can take into account both the probability of reducing the probability of the first diaphragm corresponding to the first region being folded and the probability of reducing the problem of electrolyte infiltration in the position corresponding to the first region; F4 is in the range of 6 N / m to 8 N / m, which can take into account both the adhesion between the first diaphragm corresponding to the fourth region and the first or second tab and the probability of reducing the problem of electrolyte infiltration in the winding structure corresponding to the fourth region.

[0012] In one or more of the above embodiments, the electrode assembly includes a plurality of folded tab regions, each folded tab region corresponding to a folded first diaphragm, and the first part is a first adhesive layer of N folded first diaphragms corresponding to N folded tab regions located at the end of the electrode assembly, wherein 1 ≤ N ≤ 3.

[0013] In the above embodiments, the first diaphragm located at the end of the electrode assembly from 1 fold to 3 fold is more likely to be folded due to the lack of restraint of the inner coil tab and diaphragm in the winding structure, and is more likely to be impacted by electrolyte when the electrode assembly falls, which increases the probability of the first diaphragm at this position being folded. Therefore, the adhesion of the part of the first adhesive layer located at the end of the electrode assembly from 1 fold to 3 fold is increased, which reduces the probability of the first diaphragm at the end being folded due to falling. In addition, the more folds of the end of the electrode assembly occupied by the first part, the closer the position of the increased adhesion in the first diaphragm to the winding inner coil of the winding structure, thereby easily leading to the problem of poor electrolyte infiltration in the winding inner coil.

[0014] In one or more of the above embodiments, part of the first tab is located at the outermost coil of the winding structure, the first tab includes a first surface facing the winding center of the winding structure and a second surface away from the winding center of the winding structure, and the first diaphragm is in contact with the first surface.

[0015] In the above embodiments, the diaphragm in contact with the outermost coil tab of the winding structure is more likely to be folded at the end of the electrode assembly due to the lack of restraint of the inner coil tab and diaphragm, so the adhesion of the part of the diaphragm in contact with the outermost coil tab of the winding structure is increased, which is beneficial to reduce the probability of the diaphragm in the corresponding region being folded.

[0016] In one or more of the above embodiments, the width of the first diaphragm is H, the width of the first region is H1, and 5% ≤ H1 / H ≤ 50%.

[0017] In the above embodiments, if the width of the first region is too small, the bonding force between the end of the first diaphragm near the head of the electrode assembly and the first pole piece is difficult to meet the requirements, and the improvement of the folding of the first diaphragm corresponding to the first region is small; if the width of the first part is too large, it will affect the infiltration effect of the electrolyte at the position corresponding to the first part. When 5%≤H1 / H≤50%, the bonding force requirement of the first region can be met, so that the end of the first diaphragm near the head of the electrode assembly is not easy to fold, and the infiltration effect of the electrolyte is not easy to be affected.

[0018] In one or more of the above embodiments, 8%≤H1 / H≤30%.

[0019] In the above embodiments, in order to reduce the probability of folding of the end of the first diaphragm near the head of the electrode assembly and reduce the influence on the infiltration effect of the electrolyte, it is further preferred that 8%≤H1 / H≤30%.

[0020] In one or more of the above embodiments, 10%≤H1 / H≤20%.

[0021] In the above embodiments, in order to reduce the probability of folding of the end of the first diaphragm near the head of the electrode assembly and reduce the influence on the infiltration effect of the electrolyte, it is further preferred that 10%≤H1 / H≤20%.

[0022] In one or more of the above embodiments, the width of the third region is H3, 0.95≤H3 / H1≤1.05, and the bonding strength between the third region and the first pole piece is F3, 0.95≤F3 / F1≤1.05.

[0023] In the above embodiments, the third region is a region with a width comparable to that of the first region, and the bonding force of the third region is set to be comparable to that of the first region. In the process of preparing the first diaphragm, the third region and the first region can be prepared in one step along the length direction of the first diaphragm, simplifying the preparation process of the first diaphragm, and only increasing the bonding force at the third region, which has less influence on the electrolyte infiltration at the position corresponding to the fourth region, and accordingly has less influence on the electrolyte infiltration of the inner coil of the winding structure.

[0024] In one or more of the above embodiments, the bonding strength between the second region and the first pole piece is F2, 0.95≤F2 / F1≤1.05.

[0025] In the above embodiments, the adhesion of the second region is set to be equivalent to that of the first region, that is, the adhesion of the first part is set to be substantially uniform, so that in the process of preparing the first separator, the first region and the second region can be prepared in one step along the width direction of the first separator, simplifying the preparation process of the first separator, and increasing the adhesion of the first part, which is beneficial to reducing the increase in the spacing between the first and second electrode tabs at the end of the electrode assembly due to poor adhesion of the first separator at the later stage of the electrode assembly cycle, electrolyte bridge breaking, and further triggering the purple stain and lithium precipitation problems at the end of the electrode assembly. In addition, only increasing the adhesion at the first part has less effect on electrolyte infiltration at the corresponding position of the second part, and accordingly has less effect on electrolyte infiltration at the inner coil of the winding structure.

[0026] In one or more of the above embodiments, the first part further includes a fifth region, the fifth region is located on the opposite side of the first tab in the width direction of the first separator, and the first region, the second region, and the fifth region are sequentially arranged along the width direction of the first separator; the width of the fifth region is H5, and 5%≤H5 / H≤50%; the adhesion strength between the fifth region and the first tab is F5, and 0.95≤F5 / F1≤1.05.

[0027] In the above embodiments, in the width direction of the first separator, electrolyte is prone to accumulate on the side of the first tab (i.e., the side of the head of the electrode assembly in the present application) and the side opposite to the first tab (defined as the side of the tail of the electrode assembly in the present application), so the first separator located on the side of the head of the electrode assembly and the side of the tail of the electrode assembly has a higher probability of being folded due to electrolyte impact. On the basis of increasing the adhesion of the first region located on the side of the head of the electrode assembly, further increasing the adhesion of the fifth region located on the side of the tail of the electrode assembly to be equivalent to that of the first region can further reduce the probability of the first separator corresponding to the fifth region on the side of the tail of the electrode assembly being folded.

[0028] In one or more of the above embodiments, the second part further includes a sixth region, the sixth region is located on the opposite side of the first tab in the width direction of the first separator, and the third region, the fourth region, and the sixth region are sequentially arranged along the width direction of the first separator; the width of the sixth region is H6, and 5%≤H6 / H≤50%; the adhesion strength between the sixth region and the first tab is F6, and 0.95≤F6 / F1≤1.05.

[0029] In the above embodiments, on the basis of increasing the adhesion of the third region located on the side of the head of the electrode assembly, further increasing the adhesion of the sixth region located on the side of the tail of the electrode assembly to be equivalent to that of the first region can further reduce the probability of the first separator corresponding to the sixth region on the side of the tail of the electrode assembly being folded.

[0030] In one or more of the above embodiments, the first adhesive layer includes a first adhesive, and a unit area coating weight of the first adhesive in the first region is greater than a unit area coating weight of the first adhesive in the fourth region.

[0031] In the above embodiments, the greater the unit area coating weight of the first adhesive, the greater the coating thickness and the greater the adhesive force. The adhesive force of the first region is increased by increasing the coating thickness of the first adhesive in the first region. Compared with the case where the coating thickness of the first adhesive in the entire first adhesive layer is increased, this scheme can increase the adhesive force between the first region and the first tab while reducing the overall thickness of the electrode assembly, thereby reducing the loss of the volume energy density of the secondary battery and reducing the probability of poor electrolyte infiltration at the position corresponding to the fourth region due to excessive adhesive force of the fourth region.

[0032] In one or more of the above embodiments, the material of the first adhesive includes polyvinylidene fluoride; or the material of the first adhesive includes polymethyl methacrylate.

[0033] In the above embodiments, the polyvinylidene fluoride material has a large interfacial gap, which is beneficial for storing electrolyte and can reduce the influence on the electrolyte infiltration effect while increasing the adhesive strength between the first region and the first tab. Compared with polyvinylidene fluoride, the particles of polymethyl methacrylate material are smaller, and the thickness of the polymethyl methacrylate coating is thinner under the same adhesive force, which is beneficial for reducing the thickness of the electrode assembly and reducing the loss of the volume energy density.

[0034] In one or more of the above embodiments, the particle size of the polyvinylidene fluoride is 15 um to 30 um; or the particle size of the polymethyl methacrylate is 0.1 um to 15 um.

[0035] In one or more of the above embodiments, the unit area coating weight of the polyvinylidene fluoride in the first region is G1, and the unit area coating weight of the polyvinylidene fluoride in the fourth region is G2, 4 mg / 5000 mm 2 ≤ G1 ≤ 10 mg / 5000 mm 2 , 0.5 mg / 5000 mm 2 ≤ G2 < 4 mg / 5000 mm 2 ; or the unit area coating weight of the polymethyl methacrylate in the first region is G3, and the unit area coating weight of the polymethyl methacrylate in the fourth region is G4, 0.7 mg / 5000 mm 2 ≤ G3 ≤ 10 mg / 5000 mm 2 , 0.1 mg / 5000 mm 2 ≤ G4 < 0.7 mg / 5000 mm 2In the above embodiment, the first region is less likely to separate from the first tab by increasing the adhesion of the first region through thickening the polyvinylidene fluoride coating of the first region, thereby reducing the risk of drop failure of the electrode assembly. Alternatively, the first region is less likely to separate from the first tab by increasing the adhesion of the first region through thickening the polymethyl methacrylate coating of the first region, thereby reducing the risk of drop failure of the electrode assembly.

[0036] In one or more of the above embodiments, the first region includes a first adhesive, and the fourth region includes a second adhesive; the material of the first adhesive includes polymethyl methacrylate, and the material of the second adhesive includes polyvinylidene fluoride.

[0037] In the above embodiment, compared with the polyvinylidene fluoride material, the polymethyl methacrylate material has smaller particles and better adhesion. By using a material with greater adhesion in the first region to increase the adhesion of the first region, and under the premise of the same thickness, the polymethyl methacrylate coating has greater adhesion, thereby not easily increasing the thickness of the first region, which is beneficial to reducing the loss of volumetric energy density.

[0038] In one or more of the above embodiments, the unit area coating weight of the polymethyl methacrylate in the first region is G5, and the unit area coating weight of the polyvinylidene fluoride in the fourth region is G6, 0.7 mg / 5000 mm 2 ≤G5≤10 mg / 5000 mm 2 , 0.5 mg / 5000 mm 2 ≤G6≤4 mg / 5000 mm 2 .

[0039] In one or more of the above embodiments, the first tab is a cathode tab.

[0040] In the above secondary battery, by increasing the adhesion of the first region, the end of the first separator is less likely to be folded due to dropping, reducing the risk of contact between the first tab and the second tab, and improving the use safety of the secondary battery.

[0041] The second aspect of the present application provides a power device including the secondary battery in the above embodiment.

[0042] In the above power device, by improving the adhesion of the first separator in the secondary battery, the drop performance and use safety of the secondary battery are improved, thereby improving the use safety of the power device. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is a perspective view of a secondary battery in an embodiment of the present application.

[0044] Figure 2 isFigure 1 Cross-sectional view of the secondary battery in FIG. 1 along the II-II direction.

[0045] Figure 3 Figure 2 Enlarged view of the III portion in FIG. 1.

[0046] Figure 4 Partial cross-sectional view of the electrode assembly in one embodiment of the present application.

[0047] Figure 5 Plan view of the first adhesive layer in one embodiment of the present application.

[0048] Figure 6 Plan view of the first adhesive layer in one embodiment of the present application.

[0049] Figure 7 Schematic view of the separator in one embodiment of the present application.

[0050] Figure 8 Partial cross-sectional view of the electrode assembly in one embodiment of the present application.

[0051] Figure 9 Schematic view of the electric device in one embodiment of the present application.

[0052] Explanation of main element symbols

[0053] 1000, electric device; 100, secondary battery; 10, electrode assembly; 11, first electrode sheet;

[0054] 111, first current collector; 112, first active material layer; 113, first tab; 11a, end portion;

[0055] 11b, first surface; 11c, second surface; 12, second electrode sheet; 121, second current collector;

[0056] 122, second active material layer; 123, second tab; 13, separator; 13a, first separator;

[0057] 131, base film; 132, first adhesive layer; 1321, first portion; 1321a, first region;

[0058] 1321b, second region; 1321c, fifth region; 1322, second portion; 1322a, third region;

[0059] 1322b, fourth region; 1322c, sixth region; 10a, electrode sheet region; 10b, main body region;

[0060] 10c, corner region; 101, straight section; 102, curved section; 133, ceramic layer;​

[0061] 134, second adhesive layer; 13b, second separator; 20, housing; 200, device body

[0062] X, first direction; Y, second direction; R, winding direction.

[0063] The following detailed description will further describe the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0064] The technical solutions in the embodiments of the present application will be described in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments.

[0065] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0066] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly specified.

[0067] After the electrode assembly of the secondary battery is packaged in the housing, there is a certain space between the head of the electrode assembly (close to the tab side) and the housing, which causes the electrolyte to accumulate at the head of the electrode assembly. When the secondary battery falls, the end of the separator of the electrode assembly is impacted by the electrolyte, which easily causes the end of the separator to be folded, and then causes the different polarity of the electrode plate to contact and short circuit failure.

[0068] Embodiments of the present application provide a secondary battery, comprising an electrode assembly, the electrode assembly comprising a first electrode sheet, a second electrode sheet and a first separator, the first electrode sheet comprising a first tab, the first tab being disposed on one side of the first electrode sheet in a width direction of the first electrode sheet; the first electrode sheet, the first separator and the second electrode sheet are sequentially stacked and form a winding structure; the first separator comprises a first adhesive layer and a base film which are sequentially stacked in a thickness direction of the first separator, the first adhesive layer facing the first electrode sheet; the first adhesive layer comprises a first portion and a second portion which are connected along a winding direction of the winding structure, the first portion being farther away from a winding center of the winding structure than the second portion; the first portion comprises a first region and a second region which are sequentially disposed in the width direction of the first separator, the first region and the first tab being located on the same side of the first separator in the width direction; the second portion comprises a third region and a fourth region which are sequentially disposed in the width direction of the first separator, the third region and the first tab being located on the same side of the first separator in the width direction; an adhesive strength between the first region and the first electrode sheet is F1, an adhesive strength between the fourth region and the first electrode sheet is F4, and F1 / F4≥1.1.

[0069] In the above electrode assembly, when the secondary battery falls, the first separator corresponding to the first portion is farther away from the winding center of the winding structure than the second separator corresponding to the second portion, i.e., the first separator corresponding to the first portion is located in the outermost circle of the winding structure, so the first separator corresponding to the first portion is subjected to a smaller binding force of the winding structure. Furthermore, the impact force of the electrolyte on the first separator corresponding to the first portion on the side of the first tab (i.e., the head of the electrode assembly) is greater than the impact force of the electrolyte on the first separator corresponding to the second portion, and the first separator corresponding to the first region in the first portion is located at the position of the head of the electrode assembly where the electrolyte accumulates, so the first separator corresponding to the first region is subjected to a greater impact force of the electrolyte at the position. By setting the adhesive strength F1 between the first region close to the side of the first tab in the first portion and the first electrode sheet to be relatively large, the firmness of the adhesion between the first region and the first electrode sheet is improved, so that when the electrolyte impacts the first separator corresponding to the first region, the first separator corresponding to the first region is less likely to separate from the first electrode sheet, thereby making the first separator at the end of the head of the electrode assembly less likely to be folded due to falling, reducing the risk of short circuit of the secondary battery caused by direct contact between the first electrode sheet and the second electrode sheet. Since the winding structure corresponding to the fourth region is closer to the winding center than the winding structure corresponding to the first portion, the winding binding force of the inner circle of the winding structure is greater, and the position of the winding structure corresponding to the fourth region is more likely to have a problem of poor electrolyte wetting, so the adhesive strength F4 between the fourth region and the first electrode sheet should not be too large, so as not to exacerbate the problem of poor electrolyte wetting at the winding center of the winding structure. By setting F1 / F4≥1.1, the first region has a relatively high adhesive strength compared to the fourth region, so as to achieve the above technical effects.

[0070] Embodiments of the present application will be further described below with reference to the accompanying drawings.

[0071] As Figure 1 With Figure 2 As shown in FIG. 1, an embodiment of the present application provides a secondary battery 100, which includes an electrode assembly 10 and a case 20, the electrode assembly 10 being accommodated in the case 20. The electrode assembly 10 includes a first electrode tab 11, a second electrode tab 12, and a separator 13, the separator 13 being disposed between the first electrode tab 11 and the second electrode tab 12, the separator 13 being configured to separate the first electrode tab 11 and the second electrode tab 12.

[0072] In some embodiments, the case 20 is a flexible packaging bag, such as an aluminum-plastic film. In other embodiments, the case 20 is a hard shell, such as a plastic shell, or a metal shell including at least one of a steel alloy, an aluminum alloy, and a copper alloy.

[0073] In some embodiments, the case 20 is filled with an electrolyte (not shown in the figure), the electrolyte including a solvent, an electrolyte salt, and an additive.

[0074] In some embodiments, the electrolyte salt includes at least one of an organic lithium salt or an inorganic lithium salt.

[0075] In some embodiments, the electrolyte salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis-trifluoromethanesulfonimide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium hexafluorocerate (LiCsF6), lithium perchlorate (LiClO4), or lithium trifluoromethanesulfonate (LiCF3SO3).

[0076] In some embodiments, the first electrode tab 11 and the second electrode tab 12 are of different polarities. For example, the first electrode tab 11 is a cathode electrode tab, and the second electrode tab 12 is an anode electrode tab. For another example, the first electrode tab 11 is an anode electrode tab, and the second electrode tab 12 is a cathode electrode tab.

[0077] As Figure 2 With Figure 3 In some embodiments, the first electrode tab 11 includes a first current collector 111 and a first active material layer 112, the first active material layer 112 being disposed on at least one surface of the first current collector 111 along a first current collector 111 thickness direction, the separator 13 being disposed between the first active material layer 112 and the second electrode tab 12. The first current collector 111 thickness direction is the first direction X.

[0078] In some embodiments, the first current collector 111 has two opposite surfaces along the thickness direction of the first tab 11. The thickness direction of the first tab 11 is consistent with the thickness direction of the first current collector 111, and the thickness direction of the first tab 11 is the first direction X. The first active material layer 112 is arranged on at least one surface of the first current collector 111, for example, the first active material layer 112 is arranged on both opposite surfaces of the first current collector 111.

[0079] Referring to Figure 2 and Figure 3 In some embodiments, the second tab 12 includes a second current collector 121 and a second active material layer 122. The second current collector 121 has two opposite surfaces along the thickness direction of the second tab 12, and the thickness direction of the second tab 12 is consistent with the thickness direction of the second current collector 121. The second active material layer 122 is arranged on at least one surface of the second current collector 121, for example, the second active material layer 122 is arranged on both opposite surfaces of the second current collector 121.

[0080] Referring to Figure 2 In some embodiments, for the electrode assembly 10 of the winding structure, the first tab 11 further includes a first tab lug 113, the first tab lug 113 is welded to the first current collector 111, and the first tab lug 113 is arranged on one side of the first tab 11 in the width direction of the first tab 11, and the width direction of the first tab 11 is the second direction Y.

[0081] In some embodiments, the second tab 12 further includes a second tab lug 123, the second tab lug 123 is welded to the second current collector 121, and the second tab lug 123 is arranged on one side of the second tab 12 in the width direction of the second tab 12, and the width direction of the second tab 12 is the second direction Y.

[0082] In some embodiments, the first tab lug 113 and the second tab lug 123 are arranged on the same side of the electrode assembly 10.

[0083] Taking the first tab 11 as the cathode tab and the second tab 12 as the anode tab as an example, the first current collector 111 and the second current collector 121 can be metal layers. The first current collector 111 can be a metal layer including at least one of aluminum, nickel, tantalum, titanium, etc., for example, an aluminum foil. The second current collector 121 can be a metal layer including at least one of copper, nickel, tantalum, titanium, etc., for example, a copper foil.

[0084] Taking the first tab 11 as the cathode tab and the second tab 12 as the anode tab as an example, the polarity of the first active material layer 112 is cathode, and the first active material layer 112 includes a cathode active material, which can include at least one of lithium cobaltate, lithium nickel cobalt manganese acid, lithium nickel cobalt aluminum acid, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganese acid. The polarity of the second active material layer 122 is anode, and the second active material layer 122 includes an anode active material, which can include at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen material, silicon-carbon material, etc.

[0085] Please refer to Figure 3 With Figure 4 In some embodiments, the separator 13 includes a first separator 13a and a second separator 13b. The first tab 11, the first separator 13a, the second tab 12, and the second separator 13b are sequentially stacked and form a winding structure, and the first tab 11 is located at the outermost turn of the winding structure along the winding direction R. The first separator 13a includes a first adhesive layer 132 and a base film 131 stacked along the thickness direction of the first separator 13a, and the first adhesive layer 132 faces the first tab 11. The thickness direction of the first separator 13a is the first direction X.

[0086] The first adhesive layer 132 can bond the first separator 13a to the first tab 11, so that the first separator 13a is not prone to folding or wrinkling relative to the first tab 11.

[0087] In the related secondary battery 100, after the winding electrode assembly 10 is packaged, there is a certain space between the head of the electrode assembly 10 and the shell 20, and the head of the electrode assembly 10 refers to the side of the electrode assembly 10 provided with the tab. This makes it easy for electrolyte to accumulate at the head of the electrode assembly 10. When the secondary battery 100 falls, the electrolyte accumulated at the head of the electrode assembly 10 is easy to impact the head of the electrode assembly 10, so that the separator 13 at the head of the electrode assembly 10 and close to the end of the electrode assembly 10 is easy to separate from the tab under the impact of the electrolyte, and then the separator 13 at the end of the electrode assembly 10 is wrinkled or folded, thereby causing the two tabs with opposite polarities to directly contact and short circuit, resulting in failure of the secondary battery 100.

[0088] Please refer to Figure 2 With Figure 5 In some embodiments, the first adhesive layer 132 includes a first portion 1321 and a second portion 1322 sequentially arranged along the winding direction R of the winding structure, and the first portion 1321 is farther away from the winding center of the winding structure than the second portion 1322. The first portion 1321 includes a first region 1321a and a second region 1321b sequentially arranged along the width direction of the first separator 13a, and the first region 1321a and the first tab 113 are located on the same side of the width direction of the first separator 13a.

[0089] The second part 1322 includes a third region 1322a and a fourth region 1322b arranged in sequence along the width direction of the first diaphragm 13a, and the third region 1322a is located on the same side of the first lug 113 in the width direction of the first diaphragm 13a. The bonding strength between the first region 1321a and the first tab 11 is F1, and the bonding strength between the fourth region 1322b and the first tab 11 is F4, and F1 / F4≥1.1.

[0090] When the secondary battery 100 falls, the first diaphragm 13a corresponding to the first part 1321 is farther away from the winding center of the winding structure than the second diaphragm 13b corresponding to the second part 1322, that is, the first diaphragm 13a corresponding to the first part 1321 is located in the outermost circle of the winding structure, so the first diaphragm 13a corresponding to the first part 1321 is subjected to a smaller binding force of the winding structure. Furthermore, the impact force of the electrolyte on the first diaphragm 13a corresponding to the first part 1321 on the side of the first lug 113 (i.e. the head of the electrode assembly 10) is greater than that on the first diaphragm 13a corresponding to the second part 1322, and the first diaphragm 13a corresponding to the first region 1321a in the first part 1321 is located in the position of the electrode assembly 10 head where the electrolyte accumulates, so the first diaphragm 13a corresponding to the first region 1321a is subjected to a greater impact force of the electrolyte.

[0091] By setting the bonding strength F1 between the first region 1321a close to the side of the first lug 113 in the first part 1321 and the first tab 11 to be relatively large, the firmness of the bonding between the first region 1321a and the first tab 11 is improved, so that when the electrolyte impacts the first diaphragm 13a corresponding to the first region 1321a, the first diaphragm 13a corresponding to the first region 1321a is not easy to separate from the first tab 11, thereby making the first diaphragm 13a at the end of the electrode assembly 10 head not easy to fold due to falling, and reducing the risk of short circuit of the secondary battery 100 caused by direct contact between the first tab 11 and the second tab 12. At the same time, since the winding structure corresponding to the fourth region 1322b is closer to the winding center than the winding structure corresponding to the first part 1321, the winding binding force of the inner winding circle is greater, and the position of the winding structure corresponding to the fourth region 1322b is more prone to poor electrolyte infiltration, therefore the bonding strength F4 between the fourth region 1322b and the first tab 11 should not be too large, so as not to exacerbate the problem of poor electrolyte infiltration at the winding center of the winding structure. By setting F1 / F4≥1.1, the first region 1321a has a relatively high bonding strength compared to the fourth region 1322b, so as to achieve the above technical effects.

[0092] In some embodiments, 1.5≤F1 / F4≤3.5. The adhesion strength F1 between the first region 1321a and the first tab 11 and the adhesion strength F4 between the fourth region 1322b and the first tab 11 should not be too different. If the adhesion strength F1 between the first region 1321a and the first tab 11 is too large, the probability of the first region 1321a corresponding position being prone to poor electrolyte infiltration increases. By setting 1.5≤F1 / F4≤3.5, the probability of the first region 1321a corresponding first diaphragm 13a being prone to folding and the probability of the first region 1321a corresponding position being prone to poor electrolyte infiltration can be reduced.

[0093] In some embodiments, 1.8≤F1 / F4≤2.5. In order to reduce the probability of the first region 1321a corresponding first diaphragm 13a being prone to folding and the probability of the first region 1321a corresponding position being prone to poor electrolyte infiltration, it is further preferred that 1.8≤F1 / F4≤2.5.

[0094] In some embodiments, 10N / m≤F1≤20N / m. F1 is in the range of 10N / m to 20N / m, the probability of the first region 1321a corresponding first diaphragm 13a being prone to folding and the probability of the first region 1321a corresponding position being prone to poor electrolyte infiltration can be reduced.

[0095] In some embodiments, 6N / m≤F4≤8N / m. F4 is in the range of 6N / m to 8N / m, the adhesion between the fourth region 1322b corresponding first diaphragm 13a and the first tab 11 or the second tab 12 and the probability of the fourth region 1322b corresponding winding structure being prone to poor electrolyte infiltration can be reduced.

[0096] Please refer to Figure 5 In some embodiments, the width of the first diaphragm 13a is H, the width of the first region 1321a is H1, and 5%≤H1 / H≤50%. If the width of the first region 1321a is too small, the adhesion between the first diaphragm 13a tail end near the head of the electrode assembly 10 and the first tab 11 is difficult to meet the requirements, and the improvement of the first region 1321a corresponding first diaphragm 13a prone to folding is small. If the width of the first region 1321a is too large, it will affect the electrolyte infiltration effect at the position corresponding to the first region 1321a.

[0097] When 5%≤H1 / H≤50%, the adhesion requirement of the first region 1321a can be met, so that the first diaphragm 13a tail end near the head of the electrode assembly 10 is not prone to folding, and the electrolyte infiltration effect is not prone to being affected.

[0098] In some embodiments, 8%≤H1 / H≤30%. In order to reduce the probability of the first separator 13a being folded at the end of the head of the electrode assembly 10 and to reduce the influence on the effect of electrolyte infiltration, it is further preferred that 8%≤H1 / H≤30%.

[0099] In some embodiments, it is further preferred that 10%≤H1 / H≤20%.

[0100] Referring to Figure 5 In some embodiments, the width of the third region 1322a is H3, 0.95≤H3 / H1≤1.05, and the bonding strength between the third region 1322a and the first tab 11 is F3, 0.95≤F3 / F1≤1.05. The third region 1322a is a region with a width comparable to that of the first region 1321a. By setting the bonding strength of the third region 1322a to be comparable to that of the first region 1321a, the third region 1322a and the first region 1321a can be prepared in one step along the length direction of the first separator 13a in the process of preparing the first separator 13a, which simplifies the preparation process of the first separator 13a and only increases the bonding strength at the third region 1322a, which has little influence on the electrolyte infiltration at the corresponding position of the fourth region 1322b and accordingly has little influence on the electrolyte infiltration of the inner winding of the winding structure.

[0101] In some embodiments, the bonding strength between the second region 1321b and the first tab 11 is F2, 0.95≤F2 / F1≤1.05. By setting the bonding strength of the second region 1321b to be comparable to that of the first region 1321a, i.e., setting the bonding strength of the first part 1321 to be substantially uniform, the first region 1321a and the second region 1321b can be prepared in one step along the width direction of the first separator 13a in the process of preparing the first separator 13a, which simplifies the preparation process of the first separator 13a and increases the bonding strength of the first part 1321, which is beneficial to reducing the increase in the spacing between the first tab 11 and the second tab 12 at the end 11a of the electrode assembly 10 due to poor bonding strength of the first separator 13a at the later stage of the cycle of the electrode assembly 10, electrolyte bridge breaking, and further triggering the purple stain and lithium precipitation problems at the end 11a of the electrode assembly 10. In addition, only increasing the bonding strength at the first part 1321 has little influence on the electrolyte infiltration at the corresponding position of the second part 1322 and accordingly has little influence on the electrolyte infiltration of the inner winding of the winding structure.

[0102] Referring to Figure 6In some embodiments, the first portion 1321 further comprises a fifth region 1321c, the fifth region 1321c is located at the opposite side of the first tab 113 in the width direction of the first separator 13a, and the first region 1321a, the second region 1321b and the fifth region 1321c are sequentially arranged in the width direction of the first separator 13a. The width of the fifth region 1321c is H5, and 5%≤H5 / H≤50%. The bonding strength between the fifth region 1321c and the first tab 11 is F5, and 0.95≤F5 / F1≤1.05.

[0103] In the width direction of the first separator 13a, the electrolyte is prone to accumulate on the side of the first tab 113 (the head side of the electrode assembly 10) and the side opposite to the first tab 113 (defined as the tail side of the electrode assembly 10 in the present application), and thus the first separator 13a on the head side of the electrode assembly 10 and the tail side of the electrode assembly 10 is more likely to be folded due to the impact of the electrolyte. On the basis of increasing the bonding force of the first region 1321a on the head side of the electrode assembly 10, further increasing the bonding force of the fifth region 1321c on the tail side of the electrode assembly 10 to be equivalent to the bonding force of the first region 1321a can further reduce the probability of folding of the first separator 13a corresponding to the fifth region 1321c on the tail side of the electrode assembly 10.

[0104] Please refer to Figure 6 In some embodiments, the second portion 1322 further comprises a sixth region 1322c, the sixth region 1322c is located at the opposite side of the first tab 113 in the width direction of the first separator 13a, the third region 1322a, the fourth region 1322b and the sixth region 1322c are sequentially arranged in the width direction of the first separator 13a; the width of the sixth region 1322c is H6, and 5%≤H6 / H≤50%; the bonding strength between the sixth region 1322c and the first tab 11 is F6, and 0.95≤F6 / F1≤1.05.

[0105] On the basis of increasing the bonding force of the third region 1322a on the head side of the electrode assembly 10, further increasing the bonding force of the sixth region 1322c on the tail side of the electrode assembly 10 to be equivalent to the bonding force of the first region 1321a can further reduce the probability of folding of the first separator 13a corresponding to the sixth region 1322c on the tail side of the electrode assembly 10.

[0106] Please refer to Figure 5 Or Figure 6 In some embodiments, the first adhesive layer 132 comprises a first adhesive, and the unit area coating weight of the first adhesive in the first region 1321a is greater than the unit area coating weight of the first adhesive in the fourth region 1322b.

[0107] The greater the unit area coating weight of the first adhesive is, the greater the coating thickness is, and the greater the bonding force is. The bonding force of the first region 1321a is improved by increasing the first adhesive coating thickness of the first region 1321a. Compared with the case where the first adhesive coating thickness of the entire first adhesive layer 132 is increased, this scheme can improve the bonding force between the first region 1321a and the first tab 11 while reducing the overall thickness of the electrode assembly 10, which is conducive to reducing the loss of the volumetric energy density of the secondary battery 100 and reducing the probability of the problem of poor electrolyte infiltration at the position corresponding to the fourth region 1322b due to excessive bonding force of the fourth region 1322b.

[0108] In some embodiments, the material of the first adhesive includes polyvinylidene fluoride. The polyvinylidene fluoride material has a large interfacial gap, which is conducive to storing electrolyte and can reduce the influence on the electrolyte infiltration effect while improving the bonding strength between the first region 1321a and the first tab 11.

[0109] In some embodiments, the particle size of the polyvinylidene fluoride is 15 um to 30 um.

[0110] In some embodiments, the material of the first adhesive includes polymethyl methacrylate. Compared with polyvinylidene fluoride, the particles of polymethyl methacrylate material are smaller, and the thickness of the polymethyl methacrylate coating is thinner under the same bonding force, which is conducive to reducing the thickness of the electrode assembly 10 and reducing the loss of the volumetric energy density of the secondary battery 100.

[0111] In some embodiments, the particle size of the polymethyl methacrylate is 0.1 um to 15 um.

[0112] Please refer to Figure 5 or Figure 6 In some embodiments, the unit area coating weight of the polyvinylidene fluoride in the first region 1321a is G1, and the unit area coating weight of the polyvinylidene fluoride in the fourth region 1322b is G2, 4 mg / 5000 mm 2 ≤G1≤10 mg / 5000 mm 2 , 0.5 mg / 5000 mm 2 ≤G2<4 mg / 5000 mm 2 .

[0113] By thickening the polyvinylidene fluoride coating of the first region 1321a, the bonding force of the first part 1321 is improved, so that the first region 1321a is not easy to separate from the first tab 11, thereby reducing the risk of drop failure of the electrode assembly 10.

[0114] In some embodiments, the unit area coating weight of the polymethyl methacrylate in the first region 1321a is G3, the unit area coating weight of the polymethyl methacrylate in the fourth region 1322b is G4, 0.7 mg / 5000 mm 2 ≤G3≤10 mg / 5000 mm 2 , 0.1 mg / 5000 mm 2 ≤G4<0.7 mg / 5000 mm 2 .

[0115] By thickening the polymethyl methacrylate coating of the first region 1321a, the adhesion of the first region 1321a is improved, so that the first region 1321a is not easy to separate from the first pole piece 11, thereby reducing the risk of drop failure of the electrode assembly 10.

[0116] Referring to Figure 5 or Figure 6 In some embodiments, the first region 1321a includes a first adhesive, and the fourth region 1322b includes a second adhesive. The material of the first adhesive includes polymethyl methacrylate, and the material of the second adhesive includes polyvinylidene fluoride.

[0117] Compared with polyvinylidene fluoride material, the particle of polymethyl methacrylate material is smaller, and the adhesion effect is better. By using a material with greater adhesion in the first region 1321a to improve the adhesion of the first region 1321a, and under the premise of the same thickness, the adhesion of the polymethyl methacrylate coating is greater, thereby not easy to increase the thickness of the first region 1321a, which is beneficial to reduce the loss of the volume energy density of the secondary battery 100.

[0118] In some embodiments, the unit area coating weight of the polymethyl methacrylate in the first region 1321a is G5, the unit area coating weight of the polyvinylidene fluoride in the fourth region 1322b is G6, 0.7 mg / 5000 mm 2 ≤G5≤10 mg / 5000 mm 2 , 0.5 mg / 5000 mm 2 ≤G6≤4 mg / 5000 mm 2 .

[0119] Understandably, when the unit area coating weight of the polymethyl methacrylate material is greater than the unit area coating weight of the polyvinylidene fluoride, the adhesion of the first region 1321a is better than that of the fourth region 1322b, thereby being beneficial to improve the folding problem of the first separator 13a.

[0120] Referring to Figure 2 and Figure 7In some embodiments, the electrode assembly 10 comprises a plurality of folded tab regions 10a, each of which corresponds to a first separator 13a, and the first portion 1321 is a first adhesive layer 132 of the N-th first separator 13a corresponding to the N-th folded tab region 10a at the end 11a of the electrode assembly 10, wherein 1≤N≤3.

[0121] The first separators 13a at the 1st to 3rd positions from the end 11a of the electrode assembly 10 are more likely to be folded due to the lack of restraint from the innermost coil of the wound structure, and are more likely to be impacted by electrolyte when the electrode assembly 10 falls, which increases the probability of the first separators 13a at these positions being folded. Therefore, the adhesion of the first separators 13a at the 1st to 3rd positions from the end 11a of the electrode assembly 10 is increased, which reduces the probability of the first separators 13a at the end being folded due to falling. In addition, the more positions occupied by the first portion 1321 at the end 11a of the electrode assembly 10, the closer the positions with increased adhesion of the first separators 13a to the innermost coil of the wound structure, which is more likely to cause poor electrolyte impregnation of the innermost coil.

[0122] Referring to Figure 2 and Figure 3 In some embodiments, the first tab 11 comprises a first surface 11b facing the center of the wound structure and a second surface 11c away from the center of the wound structure, and the first separator 13a is in contact with the first surface 11b.

[0123] The separators 13 in contact with the outermost coil of the wound structure are more likely to be folded at the end 11a of the electrode assembly 10 due to the lack of restraint from the innermost coil of the wound structure, and therefore the adhesion of the separators 13 in contact with the outermost coil of the wound structure is increased, which reduces the probability of the separators 13 at these positions being folded.

[0124] Referring to Figure 2 and Figure 7 In some embodiments, the electrode assembly 10 comprises a main body region 10b and two corner regions 10c, and a flat region is located between the two corner regions 10c. The boundary P1 between the main body region 10b and the corner region 10c is as shown in Figure 2 The electrode assembly 10 comprises a flat section 101 and a curved section 102, which are connected in sequence, the flat section 101 is located in the main body region 10b, and the curved section 102 is located in the corner region 10c. The boundary P2 between two adjacent folded tab regions 10a is located at the middle of the curved section 102 in the winding direction R. It can be understood that the first folded tab region 10a at the end 11a of the electrode assembly 10 is located between the end 11a of the electrode assembly 10 and the boundary P2.

[0125] In some embodiments, the base film 131 is an insulating film material such as a polyethylene film, a polypropylene film, a polyester film, or a polyimide film.

[0126] Please see Figure 8 In some embodiments, the first separator 13a further includes a ceramic layer 133 disposed between the first adhesive layer 132 and the base film 131. The ceramic layer 133 facilitates the storage of more electrolyte in the first separator 13a for lithium ion transport, thereby reducing lithium plating at the first electrode 11 and the second electrode 12.

[0127] Please see Figure 8 In some embodiments, the first diaphragm 13a includes a second adhesive layer 134, which is disposed on the side of the base membrane 131 facing away from the first adhesive layer 132, and faces the second electrode 12 and is bonded to the second electrode 12.

[0128] Please see Figure 9 The embodiments of this application also provide an electrical device 1000, which includes the secondary battery 100 in any of the above embodiments.

[0129] By improving the adhesion of the first separator 13a in the secondary battery 100, the drop performance and safety of the secondary battery 100 are improved, thereby improving the safety of the electrical device 1000.

[0130] In some embodiments, the electrical device 1000 may be a mobile phone, laptop computer, tablet computer, drone, power tool, electric toy, game console, video recorder, portable recorder, radio, or smartwatch, etc., which will not be listed here.

[0131] In some embodiments, the electrical device 1000 further includes a device body 200, and a secondary battery 100 is installed in the device body 200. Since the electrical device 1000 adopts the technical solution of the secondary battery 100 in any of the above embodiments, it has at least the beneficial effects brought about by the technical solution of any of the above embodiments of the secondary battery 100, which will not be described in detail here.

[0132] To verify the effect of different settings of the separator 13 on the performance of the secondary battery 100, the inventors conducted the following experiment:

[0133] 1. Peel strength test of the first diaphragm 13a.

[0134] The peel strength of the separator 13 was tested according to GB / T 2792-2014 "Test method of adhesive tape peel strength" using a high-iron tensile testing machine for the examples and comparative examples of the present application. The peel strength was used to characterize the adhesive strength of the first portion 1321 and the adhesive strength of the second portion 1322 in Tables 1 and 2, and the test procedure was as follows:

[0135] The secondary battery 100 was discharged to 3.0 V, and then disassembled, and the first separator 13a was taken out as a whole, and the surface was wiped with a dust-free paper to remove the electrolyte.

[0136] The first portion 1321 of the first separator 13a was cut into a strip-shaped sample. The green adhesive 12 mm wide at one end was pasted on paper, and then the strip-shaped sample of the first separator 13a was compounded, rolled 4 times, and the width was cut to 12 mm. A 180° peel was used, the first separator 13a of the strip-shaped sample was in the upper clamp, the green adhesive was in the lower clamp, the speed was 20 mm / min, the tensile data of the position of 10-40 mm was taken, the average value was calculated, and the adhesive strength of the first portion 1321 of the first separator 13a in one secondary battery 100 was obtained, with the unit of N / m.

[0137] The second portion 1322 of the first separator 13a was cut into a strip-shaped sample. The green adhesive 12 mm wide at one end was pasted on paper, and then the strip-shaped sample of the first separator 13a was compounded, rolled 4 times, and the width was cut to 12 mm. A 180° peel was used, the first separator 13a of the strip-shaped sample was in the upper clamp, the green adhesive was in the lower clamp, the speed was 20 mm / min, the tensile data of the position of 10-40 mm was taken, the average value was calculated, and the adhesive strength of the second portion 1322 of the first separator 13a in one secondary battery 100 was obtained, with the unit of N / m.

[0138] The peel strength test was performed on 20 secondary batteries 100 for each example and comparative example, and the average value was obtained to obtain the adhesive strength of the first portion 1321 of each example and comparative example.

[0139] 2. Drop test.

[0140] The secondary battery 100 was pretreated at 25°C, and after standing for 60 min in a normal temperature environment, the voltage of the lithium ion battery before the drop test was tested; the secondary battery 100 was loaded into a clamp, and the drop equipment was used to freely drop from a position 1.5 m away from the ground in the following order: head-tail-head right corner-tail right corner-head left corner-tail left corner (angle: 45±15°), repeated for 6 rounds. After the drop, the lithium ion battery was placed at room temperature for 24 h, and the voltage of the secondary battery 100 was measured and recorded. The appearance of the lithium ion battery was checked before and after the test and photographed. The pass criteria for the drop test were: no smoke, no leakage, and voltage drop <50 mV. 20 secondary batteries 100 were tested, and the number of batteries that passed the test was A, and the test pass rate was A / 20.

[0141] 3. Lithium precipitation rate test.

[0142] 20 secondary batteries 100 were tested for each group of comparative examples and each group of examples.

[0143] The secondary battery 100 was placed in an environment with a test temperature of 25°C for 30 min, and was subjected to step charging to 4.5V according to the following charging steps:

[0144] ① 5C constant current charging to 4.23V, constant voltage charging to 4C;

[0145] ② 4C constant current charging to 4.3V, constant voltage charging to 3C;

[0146] ③ 3C constant current charging to 4.4V, constant voltage charging to 2C;

[0147] ④ 2C constant current charging to 4.5V, constant voltage charging to 0.05C;

[0148] After standing for 10 min, the following steps were performed for discharging:

[0149] 0.2C constant current discharging to 3V.

[0150] The above charging and discharging process was one cycle, and after 1200 cycles, when the secondary battery 100 was in a fully charged state (the maximum voltage of the battery design was 4.5V), the secondary battery 100 was disassembled to obtain a negative electrode sheet. The surface of the negative electrode sheet was black in the area where lithium was not precipitated, and was grayish white in the area where lithium was precipitated. If the lithium deposition area on the surface of the negative electrode sheet was greater than or equal to 1mm 2 , it was determined that lithium precipitation occurred, the test was failed, otherwise the test was passed. 20 were tested for each group, the number of failures was B, and the lithium precipitation rate was B / 20.

[0151] Comparative examples and examples

[0152] Preparation of the secondary battery 100:

[0153] (1) Preparation of the cathode sheet:

[0154] The cathode active material lithium cobaltate, the cathode conductive agent acetylene black, and the cathode binder polyvinylidene fluoride (PVDF, weight average molecular weight 5×10 5The cathode slurry was prepared by mixing the cathode active material, conductive agent, binder and solvent in a mass ratio of 94:3:3, using N-methyl pyrrolidone (NMP) as the solvent, and stirring in a vacuum blender until the solid content was 75 wt% and the system was uniform. An aluminum foil with a thickness of 8 μm was selected as the cathode current collector, and a piece of foam tape was attached to a predetermined position on one surface of the aluminum foil along its thickness direction. The cathode slurry was uniformly coated on one surface of the cathode current collector aluminum foil along its thickness direction, and then dried at 110°C to obtain a cathode electrode sheet with a single-side coated cathode active material layer (thickness: 80 μm). Then, the above steps were repeated on the other surface of the aluminum foil along its thickness direction to obtain a cathode electrode sheet with a double-side coated cathode active material layer. Finally, the piece of foam tape was removed to create an empty aluminum foil area for welding the cathode tab.

[0155] (2) Preparation of the anode electrode sheet:

[0156] The anode active material graphite powder, silicon powder, conductive agent conductive carbon black (Super P), and binder styrene-butadiene rubber (SBR) were mixed in a weight ratio of 67.5:30:1:1.5, and then deionized water was added as a solvent to prepare an anode slurry with a solid content of 50 wt% and uniform stirring. A copper foil with a thickness of 5 μm was selected as the anode current collector. The anode slurry was uniformly coated on one surface of the anode current collector copper foil along its thickness direction, and then dried at 90°C to obtain a single-side anode electrode sheet. After the above steps were completed, the single-side coating of the anode electrode sheet was completed. Then, the above steps were repeated on the other surface of the anode electrode sheet along its thickness direction to obtain an anode electrode sheet with a double-side coated anode active material layer.

[0157] (3) Preparation of the separator 13:

[0158] ① Preparation of the first separator 13a: In the preparation of the first separator 13a of the comparative examples and examples shown in Table 1, the first adhesive layer 132 was coated on the base film 131 in a gravure coating manner to form the first part 1321 and the second part 1322 distributed along the width direction of the first separator 13a, and the parameters of the first part 1321 and the second part 1322 are shown in Table 1.

[0159] ② Preparation of the second separator 13b: The comparative examples and examples in Table 1 and Table 2 used a polyethylene (PE) porous film with a thickness of 8 μm as the second separator 13b.

[0160] (4) Preparation of the electrolyte:

[0161] In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solution, and then lithium salt lithium hexafluorophosphate was dissolved and mixed uniformly in the organic solvent to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0162] (5) assembling the secondary battery 100;

[0163] The aluminum tab is welded on the preset empty aluminum foil area for welding the cathode tab using ultrasonic welding, to obtain a cathode tab piece welded with the cathode tab. The nickel tab is welded on the preset empty copper foil area for welding the anode tab using ultrasonic welding, to obtain an anode tab piece welded with the anode tab. The above-prepared separator 13, the cathode tab piece welded with the cathode tab, the separator 13, and the anode tab piece welded with the anode tab are stacked in sequence, with the cathode tab on the same side of the electrode assembly 10 as the first part 1321, to obtain the electrode assembly 10 by winding. The electrode assembly 10 is placed in an aluminum plastic film packaging bag, and the above-mentioned cathode tab and anode tab both extend from the top sealing edge of the packaging bag. After moisture is removed at 80°C, electrolyte is injected and packaged.

[0164] The parameter control and test results of each example and comparative example are shown in Table 1.

[0165] Table 1

[0166]

[0167] In Table 1, by comparing the experimental data of Comparative Example 1-1 and Example 1-23, it can be seen that by setting F1 / F4≥1.1, the pass rate of the secondary battery in the drop test can be improved. By comparing the experimental data of Example 1-1 to Example 1-10, it can be seen that by increasing the ratio of F1 / F4, the pass rate of the secondary battery in the drop test can be improved, because as F1 increases, the adhesion between the first region and the first tab is more firm, and the first tab and the second tab are less likely to be short-circuited due to the folding of the first separator corresponding to the first region. By setting, it is also seen that as F1 increases, the lithium precipitation rate of the winding structure corresponding to the first part also increases, because as the adhesion between the first region and the first tab increases, the difficulty of electrolyte infiltration into the first part increases, causing the tab position corresponding to the first part to be prone to lithium precipitation due to lack of electrolyte. When F1 / F4>3.5, the pass rate of the drop test does not further increase, but the lithium precipitation rate of the winding structure at the first part position further deteriorates due to the further increase of F1. In order to obtain a higher pass rate of the secondary battery in the drop test, while taking into account reducing the probability of lithium precipitation of the winding structure corresponding to the first part, it is preferred that 1.5≤F1 / F4≤3.5; on this basis, it is further preferred that 1.8≤F1 / F4≤2.5.

[0168] As can be seen from the experimental data of Comparative Example 1-1 and Examples 1-11 to 1-13, the first part is the first adhesive layer of the N-fold first separator corresponding to the N-fold electrode sheet region at the end of the electrode assembly. As N increases, the number of folds of the first part in the electrode assembly increases, and the area of the first region with increased adhesion also increases, which makes the pass rate of the drop test of the secondary battery increase with the increase of N. However, it is also found that the lithium precipitation rate of the winding structure at the position corresponding to the first part increases with the increase of N. This is because the inner winding of the winding structure is more prone to poor electrolyte infiltration than the outer winding of the winding structure, which leads to lithium precipitation. As N increases, the first part is closer to the inner winding of the winding structure, and the adhesion between the first region in the first part and the first electrode sheet is increased, which exacerbates the risk of lack of electrolyte in the winding structure corresponding to the first part, and makes the lithium precipitation rate of the winding structure corresponding to the first part increase. Therefore, in order to improve the pass rate of the drop test of the secondary battery and reduce the probability of lithium precipitation in the winding structure corresponding to the first part, the value of N is 1 to 3.

[0169] As can be seen from the experimental data of Comparative Example 1-1, Example 1-1 and Examples 1-14 to 1-23, when H1 / H < 5%, compared with Comparative Example 1-1, the pass rate of the drop test of the secondary battery is improved but not significantly, and as H1 / H increases, the lithium precipitation rate of the winding structure corresponding to the first part increases. This is because as the width of the first region with increased adhesion increases, the difficulty of electrolyte infiltration into the first part also increases, which easily leads to lithium precipitation in the winding structure corresponding to the first part due to poor electrolyte infiltration. In order to improve the pass rate of the drop test of the secondary battery and reduce the probability of lithium precipitation in the winding structure corresponding to the first part, 5%≤H1 / H≤50% is set. Preferably, 8%≤H1 / H≤30%. Further preferably, 10%≤H1 / H≤20%.

[0170] Those skilled in the art should understand that the above embodiments are only used to illustrate the present application, and are not used as a limitation to the present application. Any appropriate changes and modifications made to the above embodiments within the spirit and principles of the present application fall within the scope of the present application.

Claims

1. A secondary battery, comprising an electrode assembly, characterized in that, The electrode assembly includes a first electrode, a second electrode, and a first diaphragm. The first electrode includes a first tab, which is disposed on one side of the width direction of the first electrode. The first electrode, the first diaphragm, and the second electrode are stacked sequentially to form a wound structure. The first diaphragm includes a first adhesive layer and a base film stacked along the thickness direction of the first diaphragm, with the first adhesive layer facing the first electrode. The first adhesive layer includes a first portion and a second portion connected along the winding direction of the winding structure, wherein the first portion is farther away from the winding center of the winding structure than the second portion; The first part includes a first region and a second region arranged sequentially along the width direction of the first diaphragm, the first region and the first electrode tab being located on the same side of the width direction of the first diaphragm; the second part includes a third region and a fourth region arranged sequentially along the width direction of the first diaphragm, the third region and the first electrode tab being located on the same side of the width direction of the first diaphragm; the bonding strength between the first region and the first electrode is F1, the bonding strength between the fourth region and the first electrode is F4, and F1 / F4≥1.

1.

2. The secondary battery as described in claim 1, characterized in that, 1.5≤F1 / F4≤3.

5.

3. The secondary battery as described in claim 2, characterized in that, 1.8≤F1 / F4≤2.

5.

4. The secondary battery as described in claim 1, characterized in that, 10N / m≤F1≤20N / m; 6N / m≤F4≤8N / m.

5. The secondary battery as described in claim 1, characterized in that, The electrode assembly includes a multi-fold electrode region, each fold of the electrode region corresponding to a fold of the first separator. The first part is the first adhesive layer of the N-fold first separator corresponding to the N-fold electrode region located at the end of the electrode assembly, wherein 1≤N≤3.

6. The secondary battery as described in claim 5, characterized in that, The first electrode portion is located at the outermost ring of the winding structure. The first electrode includes a first surface facing the winding center of the winding structure and a second surface away from the winding center of the winding structure. The first diaphragm is in contact with the first surface.

7. The secondary battery as described in claim 1, characterized in that, The width of the first diaphragm is H, the width of the first region is H1, and 5% ≤ H1 / H ≤ 50%.

8. The secondary battery as described in claim 7, characterized in that, 8%≤H1 / H≤30%.

9. The secondary battery as described in claim 8, characterized in that, 10%≤H1 / H≤20%.

10. The secondary battery as described in claim 7, characterized in that, The width of the third region is H3, 0.95≤H3 / H1≤1.05, and the bonding strength between the third region and the first electrode is F3, 0.95≤F3 / F1≤1.

05.

11. The secondary battery as described in claim 7, characterized in that, The bonding strength between the second region and the first electrode is F2, 0.95≤F2 / F1≤1.

05.

12. The secondary battery as described in claim 7, characterized in that, The first part further includes a fifth region, which is located on the opposite side of the first electrode tab in the width direction of the first diaphragm. The first region, the second region, and the fifth region are arranged sequentially along the width direction of the first diaphragm. The width of the fifth region is H5, and 5%≤H5 / H≤50%. The bonding strength between the fifth region and the first electrode is F5, and 0.95≤F5 / F1≤1.

05.

13. The secondary battery as described in claim 9, characterized in that, The second part further includes a sixth region, which is located on the opposite side of the first electrode tab in the width direction of the first diaphragm. The third region, the fourth region, and the sixth region are arranged sequentially along the width direction of the first diaphragm. The width of the sixth region is H6, and 5%≤H6 / H≤50%. The bonding strength between the sixth region and the first electrode is F6, and 0.95≤F6 / F1≤1.

05.

14. The secondary battery as described in claim 1, characterized in that, The first adhesive layer includes a first adhesive, wherein the coating weight per unit area of ​​the first adhesive in the first region is greater than the coating weight per unit area of ​​the first adhesive in the fourth region.

15. The secondary battery as described in claim 14, characterized in that, The material of the first adhesive includes polyvinylidene fluoride; or, the material of the first adhesive includes polymethyl methacrylate.

16. The secondary battery as described in claim 15, characterized in that, The polyvinylidene fluoride has a particle size of 15 μm to 30 μm; or the polymethyl methacrylate has a particle size of 0.1 μm to 15 μm.

17. The secondary battery as described in claim 15, characterized in that, The coating weight of polyvinylidene fluoride per unit area in the first region is G1, and the coating weight of polyvinylidene fluoride per unit area in the fourth region is G2, 4 mg / 5000 mm². 2 ≤G1≤10mg / 5000mm 2 0.5mg / 5000mm 2 ≤G2<4mg / 5000mm 2 ;or, The coating weight of polymethyl methacrylate per unit area in the first region is G3, and the coating weight of polymethyl methacrylate per unit area in the fourth region is G4, 0.7 mg / 5000 mm. 2 ≤G3≤10mg / 5000mm 2 0.1mg / 5000mm 2 ≤G4<0.7mg / 5000mm 2 .

18. The secondary battery as described in claim 1, characterized in that, The first region includes a first adhesive, and the fourth region includes a second adhesive; The first adhesive is made of polymethyl methacrylate, and the second adhesive is made of polyvinylidene fluoride.

19. The secondary battery as described in claim 18, characterized in that, The coating weight per unit area of ​​polymethyl methacrylate in the first region is G5, and the coating weight per unit area of ​​polyvinylidene fluoride in the fourth region is G6, 0.7 mg / 5000 mm. 2 ≤G5≤10mg / 5000mm 2 0.5mg / 5000mm 2 ≤G6≤4mg / 5000mm 2 .

20. The secondary battery as described in claim 1, characterized in that, The first electrode is a cathode electrode.

21. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 20.

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