Secondary battery and electric device

Abstract

A secondary battery and an electric device, the secondary battery comprising an electrode assembly, the electrode assembly comprising a first electrode sheet, a second electrode sheet and a first separator which are stacked and form a winding structure; along a winding direction of the first separator, the first separator comprises a first part and a second part which are sequentially arranged, the first part is closer to a winding start end of the winding structure compared with the second part; the first part comprises a first ceramic layer, and the second part comprises a second ceramic layer; the first electrode sheet comprises a first tab; the first ceramic layer comprises a first region and a second region, and part of the first tab and part of the first region overlap when viewed along a thickness direction of the first separator; a thickness of the first region is H1, a thickness of the second region is H2, a thickness of the second ceramic layer is H3, 2um<=H2<=10um, 0<=H1 / H2<=1, and 1.2<=H2 / H3<=10. The first ceramic layer is arranged to improve the structural strength of the first part and reduce the possibility of short circuit of the electrode assembly.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to a secondary battery and an electrical device. Background Art

[0002] In secondary batteries, the closer the electrode assembly is to the starting point of winding, the greater the winding pressure. Li-Co particles, carbon powder, and other particles can easily fall onto the inner diaphragm, squeezing it and causing it to puncture. This can lead to direct contact and short-circuiting of electrodes of different polarities, significantly deteriorating Hi-pot test (High Potential) test results and the K value (the battery's voltage drop per unit time, a measure of the lithium battery's self-discharge rate). Summary of the Invention

[0003] In view of this, it is necessary to provide a secondary battery that can improve the puncture resistance of the diaphragm and reduce the possibility of short circuit of the electrode assembly.

[0004] The embodiment of the first aspect of the present application provides a secondary battery, the secondary battery including an electrode assembly, the electrode assembly including a first electrode sheet, a second electrode sheet and a first diaphragm, the first electrode sheet, the first diaphragm and the second electrode sheet are sequentially stacked to form a winding structure; along the winding direction of the first diaphragm, the first diaphragm includes a first part and a second part arranged in sequence, compared with the second part, the first part is closer to the winding starting end of the winding structure; along the thickness direction of the first diaphragm, the first part includes a first ceramic layer and a first base film stacked, and the second part includes a second ceramic layer stacked layer and a second base film; the first pole piece includes a first current collector and a first pole ear, the first pole ear is connected to the first current collector and extends from one side in the width direction of the first current collector; the first ceramic layer includes a first region and a second region sequentially arranged along the width direction of the first diaphragm; when observed along the thickness direction of the first diaphragm, part of the first pole ear overlaps with part of the first region; the thickness of the first region is H1, the thickness of the second region is H2, the thickness of the second ceramic layer is H3, 2μm≤H2≤10μm, 0≤H1 / H2≤1, and 1.2≤H2 / H3≤10.

[0005] In the aforementioned secondary battery, the thickness H2 of the second region of the first ceramic layer near the winding starting end of the winding structure is set to 2μm≤H2≤10μm, which is beneficial for improving the structural strength of the first portion of the first diaphragm near the winding starting end, making the first portion less susceptible to puncture, thereby reducing the possibility of a short circuit caused by direct contact between the first and second pole pieces. In addition, the ceramic material in the first ceramic layer has pores, which is beneficial for storing electrolyte. By providing a thicker first ceramic layer in the first portion, the electrolyte can easily penetrate into the winding center, reducing the situation of insufficient electrolyte near the winding center. By ensuring that 1.2≤H2 / H3≤10, that is, the thickness H2 of the second region near the winding starting end of the wound structure is greater than the thickness H3 of the second ceramic layer away from the winding starting end, the first ceramic layer can be given a certain thickness to provide sufficient puncture resistance to the first portion, while also improving the problem of insufficient electrolyte in the winding center and reducing the loss of secondary battery volume energy density caused by thickening the ceramic layer on the entire first separator. At the same time, the thickness difference between the first portion and the second portion can be kept from being too large, thereby reducing the impact on the secondary battery volume energy density and the flatness of the electrode assembly. Because the first electrode sheet includes a first tab, the provision of the first tab will increase the thickness at that location. Therefore, setting the thickness of the first region overlapping with the first tab to be less than the thickness of the second region can reduce the loss of secondary battery volume energy density caused by the overlapping thickness of the first tab.

[0006] In one or more of the above embodiments, 1.5≤H2 / H3≤5.

[0007] In the above embodiment, when H2 / H3 is within the above range, the puncture resistance of the first portion can be further improved and the electrolyte shortage problem in the winding center can be improved, while taking into account the volume energy density of the secondary battery and the flatness of the electrode assembly.

[0008] In one or more of the above embodiments, 0.2≤H1 / H2≤0.5.

[0009] In the above embodiment, H1 / H2 is within the above range, so that a ceramic layer of a certain thickness is also provided on the first region to improve the electrolyte infiltration near the first electrode tab, and H1 / H2≤0.5, so that there is a certain thickness difference between the first region and the second region, reducing the excessive thickness at the position of the first electrode tab caused by the superposition of the thickness of the first electrode tab and the ceramic layer, thereby reducing the loss of volume energy density of the secondary battery.

[0010] In the above embodiment, by setting H1 = H3, the manufacturing process of the first diaphragm can be simplified.

[0011] In one or more of the above embodiments, 0.3 μm≤H3≤1.5 μm.

[0012] In the above embodiment, when the above range is met, the structural strength of the second portion can be improved while the thickness of the second portion does not increase too much, thereby reducing the impact on the volume energy density of the secondary battery.

[0013] In one or more of the above embodiments, 2 μm≤H2≤3 μm.

[0014] In the above embodiment, when H2 satisfies the above range, it can enhance the puncture resistance of the first part while reducing the influence of the thickness of the first ceramic layer and the thickness of the electrode assembly after winding, thereby reducing the loss of volume energy density of the secondary battery.

[0015] In one or more of the above embodiments, the first membrane includes a multi-fold membrane segment, and the first portion includes N-fold membrane segments located at the starting end of the winding, where 1≤N≤15.

[0016] In the above embodiment, the winding structure is subject to greater winding pressure near the starting point. By thickening the first ceramic layer in the first portion near the starting point, the puncture resistance of the first separator in this portion can be improved. This also improves the electrolyte wetting of the electrode assembly near the center of the winding, making it less susceptible to lithium deposition near the center of the winding and improving the cycling performance of the secondary battery. If N is too small, the first portion will not be sufficient to increase the overall strength of the first separator, resulting in minimal improvement in the puncture resistance of the first separator and difficulty for the electrolyte to penetrate the center of the electrode assembly. If N is too large, the first portion will significantly affect the overall thickness of the electrode assembly, resulting in a significant loss in the volumetric energy density of the secondary battery.

[0017] In one or more of the above embodiments, 2≤N≤7.

[0018] In the above embodiment, the overall thickness of the electrode assembly can be further reduced while increasing the puncture resistance of the first separator near the winding starting end, improving the electrolyte infiltration effect on the electrode assembly, and reducing the risk of lithium plating.

[0019] In one or more of the above embodiments, along the width direction of the first pole piece, the width of the first region is W1, and 10 mm ≤ W1 ≤ 30 mm.

[0020] In the above embodiment, when the width of the first region is too large, the width of the second region will become narrower, and the thickened portion will become narrower. This will reduce the thickened area of ​​the first portion, which is not conducive to reducing the risk of the first portion being punctured. If the width of the first region is too small, the first tab will easily overlap with the second region, resulting in an increase in the thickness of the wound electrode assembly and a loss in the volumetric energy density of the secondary battery. When 10mm≤W1≤30mm is met, the second region can be maximized without increasing the thickness of the electrode assembly, thereby reducing the risk of the first portion being punctured and improving the safety performance of the secondary battery.

[0021] In one or more of the above embodiments, the materials of the first ceramic layer and the second ceramic layer each independently include at least one of aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, barium titanate, and boehmite.

[0022] In the above embodiments, alumina, silica, titanium dioxide, zirconium oxide, barium titanate and boehmite have good mechanical strength, high hardness and compressive resistance, which is beneficial to making the first diaphragm less likely to be punctured by impurities such as particles and powder, thereby improving the safety of the secondary battery.

[0023] An embodiment of the second aspect of the present application provides a secondary battery, which includes an electrode assembly, the electrode assembly includes a first electrode sheet, a second electrode sheet and a first diaphragm, the first electrode sheet, the first diaphragm and the second electrode sheet are stacked in sequence to form a winding structure; the first electrode sheet includes a first current collector and a first electrode tab, the first electrode tab is connected to the first current collector and extends from one side in the width direction of the first current collector; along the width direction of the first diaphragm, the first diaphragm includes a third part and a fourth part arranged in sequence; observed along the thickness direction of the first diaphragm, part of the first electrode tab overlaps with part of the third part; the third part includes a third base film, and the fourth part includes a fourth ceramic layer and a fourth base film stacked along the thickness direction of the first diaphragm; the thickness of the third part is H4, the thickness of the fourth part is H5, H4<H5; the thickness of the fourth ceramic layer is H7, 2μm≤H7≤10μm.

[0024] In the aforementioned secondary battery, a fourth ceramic layer is provided in the fourth portion, and its thickness ranges from 2μm to 10μm. This layer has good mechanical strength, which helps reduce the possibility of puncturing the first separator and the risk of short circuiting due to direct contact between the first and second electrode sheets. Furthermore, the thickness H4 of the third portion, which overlaps the first tab, is less than the thickness H5 of the fourth portion, which reduces the thickness of the wound electrode assembly and helps minimize the loss of volumetric energy density in the secondary battery.

[0025] In one or more of the above embodiments, along the width direction of the first pole piece, the width of the third portion is W2, 10 mm ≤ W2 ≤ 30 mm.

[0026] In the above embodiment, when the width W2 of the third portion is too large, the width of the fourth portion will become narrower, that is, the thickened portion will become narrower, which will reduce the area where the strength of the first diaphragm is increased, which is not conducive to reducing the risk of the first diaphragm being punctured. If the width of the third portion is too small, the first tab will easily overlap with the fourth ceramic layer of the fourth portion, thereby increasing the thickness of the wound electrode assembly and causing a loss in the volume energy density of the secondary battery. When 10mm≤W2≤30mm is met, the fourth portion can be maximized without increasing the thickness of the electrode assembly, thereby reducing the risk of the first portion being punctured and improving the safety performance of the secondary battery.

[0027] In one or more of the above embodiments, the third part also includes a third ceramic layer. The third ceramic layer and the third base membrane are stacked along the thickness direction of the first diaphragm. The thickness of the third ceramic layer is H6, and the thickness of the fourth ceramic layer is H7. 0.2≤H6 / H7≤0.5.

[0028] In the above embodiment, the provision of the third ceramic layer is beneficial to improving the electrolyte infiltration near the first electrode tab, and when H6 / H7≤0.5 is satisfied, it can reduce the thickness superposition of the first electrode tab and the third ceramic layer, and reduce the increase in thickness of the electrode assembly after winding, which is beneficial to reducing the volume energy density loss of the secondary battery.

[0029] In one or more of the above embodiments, 0.3 μm ≤ H6 ≤ 1.5 μm.

[0030] In the above embodiment, when the above range is met, the structural strength of the fourth portion can be improved while the thickness of the fourth portion is not easily increased too much, thereby reducing the impact on the volume energy density of the secondary battery.

[0031] In one or more of the above embodiments, 2 μm ≤ H7 ≤ 3 μm.

[0032] In the above embodiment, when 2μm≤H7≤3μm is satisfied, the thickness of the fourth ceramic layer can be made greater than that of the third ceramic layer, while the thickness of the fourth ceramic layer is not easily made too large, thereby reducing the impact on the overall thickness of the electrode assembly.

[0033] An embodiment of the third aspect of the present application provides an electrical device, comprising the secondary battery in any of the above embodiments.

[0034] In the above-mentioned electrical device, by thickening the thickness of a part of the first diaphragm, the first diaphragm is not easily punctured, so that the first electrode is not easily short-circuited with the second electrode, thereby improving the safety of the secondary battery and further improving the safety of the electrical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1is a perspective view of a secondary battery in one embodiment of the present application.

[0036] Figure 2 yes Figure 1 Cross-sectional view along the II-II direction.

[0037] Figure 3 yes Figure 2 Enlarged view of part III.

[0038] Figure 4 yes Figure 2 Schematic diagram of the structure of the diaphragm.

[0039] Figure 5 This is a partial cross-sectional view of the first diaphragm after expansion in one embodiment of the present application.

[0040] Figure 6 This is a partial top view of the first diaphragm after expansion in one embodiment of the present application.

[0041] Figure 7 This is a partial cross-sectional view of the first diaphragm after expansion in one embodiment of the present application.

[0042] Figure 8 is a partial cross-sectional view of an electrode assembly in one embodiment of the present application.

[0043] Figure 9 This is a partial top view of the first diaphragm after expansion in one embodiment of the present application.

[0044] Figure 10 This is a partial cross-sectional view of the first diaphragm after expansion in one embodiment of the present application.

[0045] Figure 11 This is a partial cross-sectional view of the first diaphragm after expansion in one embodiment of the present application.

[0046] Figure 12 It is a structural diagram of an electrical device in an embodiment of the present application.

[0047] Description of main component symbols

[0048] 1000. Electric device; 100. Secondary battery; 10. Electrode assembly;

[0049] 11. First pole piece; 111. First current collector; 112. First active material layer; 113. First pole tab;

[0050] 12. Second pole piece; 121. Second current collector; 122. Second active material layer; 123. Second pole tab;

[0051] 13. Diaphragm; 13a. First diaphragm; 131. First portion; 1311. First basement membrane;

[0052] 1312, first ceramic layer; 1312a, first region; 1312b, second region; 132, second portion;

[0053] 1321, second base film; 1322, second ceramic layer; 133, first adhesive layer; 134, third portion;

[0054] 1341, third base film; 1342, third ceramic layer; 135, fourth portion; 1351, fourth base film;

[0055] 1352, fourth ceramic layer; 13b, second diaphragm; 13c, diaphragm segment; 10a, starting end;

[0056] 10b, tail end; 101, main body area; 1011, straight section; 102, corner area;

[0057] 1021. Bending section; 20. Shell; 200. Device body.

[0058] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0059] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0061] In the description of the embodiments of the present application, technical terms such as "first" and "second" 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.

[0062] It should be noted that the thickness, length, width and other dimensions of various components in the embodiments of the present application shown in the drawings are for illustrative purposes only and should not constitute any limitation to the present application.

[0063] In secondary batteries, the closer the electrode assembly is to the center of the winding, the greater the winding pressure. Li-Co particles, carbon powder, and other particles are easily dropped onto the separator in the inner ring of the winding structure, squeezing the separator and causing it to be punctured. This can lead to direct contact and short circuits between electrodes of different polarities, significantly worsening Hi-pot test results and K values.

[0064] An embodiment of the present application provides a secondary battery, which includes an electrode assembly, the electrode assembly including a first electrode sheet, a second electrode sheet and a first diaphragm, the first electrode sheet, the first diaphragm and the second electrode sheet are stacked in sequence to form a winding structure; along the winding direction of the first diaphragm, the first diaphragm includes a first part and a second part arranged in sequence, and compared with the second part, the first part is closer to the winding starting end of the winding structure; along the thickness direction of the first diaphragm, the first part includes a first ceramic layer and a first base film arranged in a stacked manner, and the second part includes a second ceramic layer and a second base film arranged in a stacked manner; the first electrode sheet includes a first electrode tab, the first electrode tab is connected to the first current collector and extends from one side in the width direction of the first electrode sheet; the first ceramic layer includes a first region and a second region arranged in sequence along the width direction of the first electrode sheet; along the thickness direction of the first diaphragm, part of the first electrode tab overlaps part of the first region; the thickness of the first region is H1, the thickness of the second region is H2, and the thickness of the second ceramic layer is H3, 0≤H1 / H2≤1, and 1.2≤H2 / H3≤10.

[0065] In the above-mentioned secondary battery, the thickness H2 of the second region in the first ceramic layer near the winding starting end of the winding structure is set to be greater than the thickness H3 of the second ceramic layer away from the winding starting end, which is beneficial to improving the structural strength of the first part of the first diaphragm near the winding starting end, making the first part less likely to be punctured, thereby reducing the possibility of short circuit caused by direct contact between the first electrode plate and the second electrode plate. In addition, the ceramic material in the first ceramic layer has pores, which is beneficial for storing electrolyte. By providing a thicker first ceramic layer in the first part, the electrolyte can easily penetrate into the winding center, reducing the situation of insufficient electrolyte near the winding center. By setting 1.2≤H2 / H3≤10, the first ceramic layer can have a certain thickness to provide sufficient puncture resistance to the first part, while improving the problem of insufficient electrolyte in the winding center. At the same time, the thickness difference between the first part and the second part can be not too large, thereby reducing the impact on the volume energy density of the secondary battery and the flatness of the electrode assembly. Because the first electrode sheet includes the first electrode tab, the setting of the first electrode tab will cause the thickness at the location to increase. Therefore, the thickness of the first area overlapping with the first electrode tab is set to be smaller than the thickness of the second area, which can reduce the loss of volume energy density of the secondary battery caused by the superposition of the thickness at the first electrode tab position.

[0066] The embodiments of the present application are further described below with reference to the accompanying drawings.

[0067] like Figure 1 and Figure 2As shown, an embodiment of the present application provides a secondary battery 100, which includes an electrode assembly 10 and a housing 20. The electrode assembly 10 is accommodated in the housing 20. The electrode assembly 10 includes a first electrode sheet 11, a second electrode sheet 12, and a diaphragm 13. The diaphragm 13 is disposed between the first electrode sheet 11 and the second electrode sheet 12, and is used to separate the first electrode sheet 11 and the second electrode sheet 12.

[0068] In some embodiments, the housing 20 is a flexible packaging bag, such as an aluminum-plastic film. In other embodiments, the housing 20 is a hard shell, such as a plastic shell, or a metal shell including at least one of steel alloy, aluminum alloy, and copper alloy.

[0069] In some embodiments, an electrolyte (not shown) is injected into the housing 20 , and the electrolyte components include a solvent, an electrolyte salt, and an additive.

[0070] In some embodiments, the electrolyte salt includes at least one of an organic lithium salt or an inorganic lithium salt.

[0071] In some embodiments, the electrolyte salt includes but is not limited to at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium hexafluorocesium oxide (LiCsF6), lithium perchlorate (LiClO4) or lithium trifluoromethanesulfonate (LiCF3SO3).

[0072] In some embodiments, the first electrode 11 and the second electrode 12 have different polarities. For example, the first electrode 11 is an anode electrode and the second electrode 12 is a cathode electrode. For another example, the first electrode 11 is a cathode electrode and the second electrode 12 is an anode electrode.

[0073] See also Figure 2 and Figure 3 In some embodiments, the first electrode 11 includes a first current collector 111 and a first active material layer 112. The first active material layer 112 is arranged on at least one surface of the first current collector 111 along the thickness direction of the first electrode 11, and the diaphragm 13 is arranged between the first active material layer 112 and the second electrode 12.

[0074] See also Figure 2 and Figure 3 In some embodiments, the first current collector 111 has two opposite surfaces along the thickness direction of the first electrode sheet 11. A first active material layer 112 is provided on at least one surface of the first current collector 111, for example, the first active material layer 112 is provided on both surfaces of the first current collector 111.

[0075] See also Figure 2 and Figure 3 In some embodiments, the second electrode sheet 12 includes a second current collector 121 and a second active material layer 122. Along the thickness direction of the second electrode sheet 12, the second current collector 121 has two opposing surfaces, and the second active material layer 122 is disposed on at least one surface of the second current collector 121. For example, the second active material layer 122 is disposed on both surfaces of the second current collector 121.

[0076] See also Figure 1 and Figure 2 In some embodiments, for the wound electrode assembly 10 , the first electrode sheet 11 further includes a first electrode tab 113 . The first electrode tab 113 is disposed on one side of the first current collector 111 in the width direction, and the first electrode tab 113 is welded to the first current collector 111 .

[0077] In some embodiments, the second electrode sheet 12 further includes a second electrode tab 123 . The second electrode tab 123 is disposed on one side of the second current collector 121 in the width direction. The second electrode tab 123 is welded to the second current collector 121 .

[0078] In some embodiments, the first electrode tab 113 and the second electrode tab 123 are disposed on the same side of the electrode assembly 10 .

[0079] Taking the first electrode piece 11 as an anode electrode piece and the second electrode piece 12 as a cathode electrode piece as an example, the first current collector 111 and the second current collector 121 can be metal layers. The material of the first current collector 111 can be at least one of copper, nickel, tantalum, titanium, etc., such as copper foil. The material of the second current collector 121 can be at least one of aluminum, nickel, tantalum, titanium, etc., such as aluminum foil.

[0080] Taking the first electrode 11 as an anode electrode and the second electrode 12 as a cathode electrode as an example, the first active material layer 112 includes an anode active material, which may include at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen material, silicon-carbon material, etc. The second active material layer 122 includes a cathode active material, which may include at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganese oxide, etc.

[0081] Taking the first electrode piece 11 as an anode electrode piece and the second electrode piece 12 as a cathode electrode piece as an example, the first electrode tab 113 is the anode electrode piece and the second electrode tab 123 is the cathode electrode piece. The material of the first electrode tab 113 includes at least one of copper, nickel, copper-nickel alloy, nickel-chromium alloy, copper-nickel-plated, nickel-plated copper, silver-plated copper, stainless steel (e.g., 304 stainless steel), etc.; the material of the second electrode tab 123 includes at least one of aluminum, aluminum alloy, nickel, nickel-plated aluminum, silver-plated aluminum, etc.

[0082] See also Figure 2 and Figure 3In some embodiments, the first pole piece 11, the diaphragm 13 and the second pole piece 12 are stacked and wound to form a wound structure.

[0083] For example, the diaphragm 13 includes a first diaphragm 13a, and the first electrode piece 11, the first diaphragm 13a, and the second electrode piece 12 are sequentially stacked to form a wound structure. For another example, the diaphragm 13 also includes a second diaphragm 13b, and the first electrode piece 11, the first diaphragm 13a, the second electrode piece 12, and the second diaphragm 13b are sequentially stacked and wound to form a wound structure.

[0084] In some embodiments, the structure and material of the second diaphragm 13b are the same as those of the first diaphragm 13a.

[0085] In the related art, a portion of the first active material layer 112 on the first electrode sheet 11 is removed to expose a portion of the first current collector 111 to form a hollow foil area, and the first electrode tab 113 is welded to the hollow foil area.

[0086] Hipot test (High Potential test) refers to an insulation resistance test that tests the resistance between the anode tab and the cathode tab. It is used to detect whether there is a short circuit inside the battery cell and to identify defective products with folded separators 13 and particles piercing the separator 13, avoiding the occurrence of defective products with zero voltage and K value.

[0087] The K value refers to the voltage drop of the secondary battery 100 per unit time, and is used to reflect the internal short circuit condition of the secondary battery 100 .

[0088] See also Figure 2 、 Figure 4 、 Figure 5 and Figure 6 ,in Figure 5 is a cross-sectional view of the first diaphragm 13a when viewed along the width direction of the first diaphragm 13a after the first diaphragm 13a is unfolded. Figure 6 is a top view of the first diaphragm 13a when viewed along the thickness direction of the first diaphragm 13a after the first diaphragm 13a is unfolded. Figure 5 As shown, along the winding direction R of the first diaphragm 13a, the first diaphragm 13a includes a first portion 131 and a second portion 132, which are arranged in sequence. Compared to the second portion 132, the first portion 131 is closer to the winding starting end 10a of the winding structure. The first portion 131 includes a first ceramic layer 1312 and a first base film 1311, which are stacked along the thickness direction of the first diaphragm 13a. The second portion 132 includes a second base film 1321 and a second ceramic layer 1322. Figure 5 L1 is used to indicate the boundary between the first portion 131 and the second portion 132. Figure 6The first electrode sheet 11 includes a first current collector 111 and a first electrode tab 113. The first electrode tab 113 is disposed on one side of the first current collector 111 in the width direction. The first ceramic layer 1312 includes a first region 1312a and a second region 1312b arranged sequentially along the width direction of the first separator 13a. When viewed along the thickness direction of the first separator 13a, a portion of the first electrode tab 113 overlaps with a portion of the first region 1312a. The thickness of the first region 1312a is H1, the thickness of the second region 1312b is H2, and the thickness of the second ceramic layer 1322 is H3.

[0089] In some embodiments, the materials of the first base film 1311 and the second base film 1321 independently include at least one of polyethylene, polypropylene, polyimide, polyamide, polysulfone, polyacrylonitrile, polyester, cellulose, polyphenylene sulfide, polyacrylate, polyethylene terephthalate, polyphenylene amide, polyarylethersulfoneketone, aramid or aromatic sulfone.

[0090] In some embodiments, the materials of the first ceramic layer 1312 and the second ceramic layer 1322 each independently include at least one of aluminum oxide (Al2O3), silicon dioxide (SiO2), titanium dioxide (TiO2), zirconium oxide (ZrO2), barium titanate (BaTiO3), and boehmite (AlOOH).

[0091] The placement of the first tab 113 increases the thickness of the layer at that location. To reduce the overlap between the thickness of the first tab 113 and the first ceramic layer 1312, the first ceramic layer 1312 is divided into two regions, a first region 1312a and a second region 1312b, arranged sequentially along the width of the first diaphragm 13a. When viewed along the thickness of the first diaphragm 13a, a portion of the first tab 113 overlaps with a portion of the first region 1312a, and the thickness H1 of the first region 1312a does not exceed the thickness H2 of the second region 1312b.

[0092] In some embodiments, the thickness H1 of the first region 1312a is 0, that is, no ceramic layer is provided in the first diaphragm 13a corresponding to the first region 1312a. At this time, H1 / H2=0, thereby further reducing the thickness at the position of the first electrode tab 113 after winding.

[0093] In some embodiments, 0

[0094] ​In some embodiments, H1=H2. It can be understood that when the thickness H1 of the first region 1312a is equal to the thickness H2 of the second region 1312b, when coating the first ceramic layer 1312, it is easy to coat and form the first region 1312a and the second region 1312b at the same time.

[0095] In some embodiments, 0.2≤H1 / H2≤0.5. When H1 / H2≥0.2, the ceramic layer material provided in the first region 1312a has a certain thickness, which can enhance the strength of the first diaphragm 13a near the first electrode tab 113 and improve the electrolyte infiltration near the first electrode tab 113. When H1 / H2≤0.5, there is a certain thickness difference between the first region 1312a and the second region 1312b, which reduces the excessive thickness at the location of the first electrode tab 113 caused by the superposition of the thickness of the first electrode tab 113 and the ceramic layer, thereby reducing the loss of volume energy density of the secondary battery 100.

[0096] The ceramic layer material has good mechanical strength, high hardness, and compressive resistance, which helps prevent the first separator 13a from being punctured by impurities such as particles and powder, thereby improving the safety of the secondary battery 100. The provision of the first ceramic layer 1312 helps to improve the mechanical strength of the first portion 131 near the winding center of the winding structure, making the first portion 131 less susceptible to puncture, thereby reducing the possibility of short circuits caused by direct contact between the first and second pole pieces 11, 12, and improving Hipot test results and K value.

[0097] In addition, the ceramic material in the first ceramic layer 1312 has pores, which is conducive to storing electrolyte and guiding the flow of electrolyte. The closer to the winding center of the electrode assembly 10, the greater the winding pressure, the less likely it is for the electrolyte to penetrate, and the electrolyte near the winding center is easily squeezed out during the pressure process of the electrode assembly 10, resulting in insufficient electrolyte near the winding center. By providing the first ceramic layer 1312 on the first part 131, the electrolyte is easily penetrated into the winding center, reducing the situation of poor electrolyte infiltration or swelling near the winding center, thereby reducing the situation of lithium deposition between the first pole piece 11 and the second pole piece 12.

[0098] In some embodiments, the first base film 1311 and the second base film 1321 are made of the same material and have the same thickness, which is beneficial to the production and preparation of the first diaphragm 13 a.

[0099] See Figure 7 , Figure 7 yes Figure 6 The thickness of the first region 1312a is H1, and the thickness of the second region 1312b is H2. Figure 7In the illustrated embodiment, H1 < H2, which is beneficial to reducing the loss of the volumetric energy density of the secondary battery 100 caused by the thickness superposition of the first tab 113 and the first region 1312a.

[0100] In some embodiments, the ratio range of the thickness H3 of the second ceramic layer 1322 to the thickness H2 of the second region 1312b is 1.2 ≤ H2 / H3 ≤ 10. By making H2 / H3 within the above range, the first ceramic layer 1312 can have a certain thickness to provide sufficient puncture resistance to the first part 131, while improving the problem of insufficient electrolyte in the winding center, and the thickness difference between the first part 131 and the second part 132 will not be too large, so as to reduce the impact on the volumetric energy density of the secondary battery 100 and the flatness of the electrode assembly 10.

[0101] In some embodiments, the ratio range of the thickness H3 of the second ceramic layer 1322 to the thickness H2 of the second region 1312b is preferably 1.5 ≤ H2 / H3 ≤ 5. When H2 / H3 is within the above range, the puncture resistance of the first part 131 can be further improved and the problem of insufficient electrolyte in the winding center can be improved, while taking into account the volumetric energy density of the secondary battery 100 and the flatness of the electrode assembly 10.

[0102] In some embodiments, H1 = H3. By setting it like this, the manufacturing process of the first separator 13a can be simplified.

[0103] Refer to Figure 6 And Figure 7 , in some embodiments, along the width direction of the first electrode tab 11, the width of the first region 1312a is W1, and 10 mm ≤ W1 ≤ 30 mm. For example, W1 can be 10 mm, 12 mm, 15 mm, 18 mm, 20 mm, 22 mm, 25 mm, 28 mm or 30 mm. For example, the width of the first separator 13a is 80 mm, the width of the first ceramic layer 1312 is equal to the width of the first separator 13a, the width W1 of the first region 1312a is 20 mm, and the width of the second region 1312b is 60 mm.

[0104] If the width of the first region 1312a is too large, the width of the second region 1312b will become narrower, and the thickened portion will become narrower. This will reduce the thickened area of ​​the first portion 131, which is not conducive to reducing the risk of puncture of the first portion 131. If the width of the first region 1312a is too small, the first electrode tab 113 will easily overlap with the second region 1312b, resulting in an increase in the thickness of the wound electrode assembly 10 and a loss in the volumetric energy density of the secondary battery 100. When 10mm≤W1≤30mm is met, the second region 1312b can be maximized without increasing the thickness of the electrode assembly 10, thereby reducing the risk of puncture of the first portion 131 and improving the safety performance of the secondary battery 100.

[0105] In some embodiments, 2 μm ≤ H2 ≤ 10 μm; 0.3 μm ≤ H3 ≤ 1.5 μm. When H2 and H3 meet the above ranges, the structural strength of the first portion 131 and the second portion 132 can be improved while the thickness of the first portion 131 and the second portion 132 is not increased excessively, thereby reducing the impact on the volume energy density of the secondary battery 100.

[0106] In some embodiments, 2 μm ≤ H2 ≤ 3 μm. Within this range, the influence of the thickness of the first ceramic layer 1312 and the thickness of the electrode assembly 10 after winding can be reduced, thereby reducing the volume energy density loss of the secondary battery 100.

[0107] See Figure 2 and Figure 4 In some embodiments, the first membrane 13a includes a multi-fold membrane segment 13c, and the first portion 131 includes N-fold membrane segments 13c located at the winding starting end 10a of the winding structure, where 1≤N≤15.

[0108] The winding structure is subject to greater winding pressure near the center of the winding. By increasing the thickness of the first ceramic layer 1312 in the first portion 131 near the center of the winding, the puncture resistance and electrolyte penetration of the first separator 13a near the center of the winding of the electrode assembly 10 are improved. This makes the first separator 13a near the center of the winding of the electrode assembly 10 less susceptible to puncture and reduces the risk of lithium deposition in the center of the winding, thereby improving the cycling performance of the secondary battery 100. If N is too small, the first portion 131 will not be sufficient to increase the overall strength of the first separator 13a, and the improvement in the puncture resistance of the first separator 13a will be minimal. Moreover, it will be difficult for the electrolyte to penetrate the center of the electrode assembly 10. If N is too large, the first portion 131 will significantly affect the overall thickness of the electrode assembly 10, resulting in a significant loss in the volumetric energy density of the secondary battery 100.

[0109] See Figure 2 and Figure 4In some embodiments, the electrode assembly 10 includes a main body region 101 and two corner regions 102, wherein the main body region 101 is located between the two corner regions 102. The boundary line P1 between the main body region 101 and the corner region 102 is as shown in FIG. Figure 2 As shown, the electrode assembly 10 includes a straight section 1011 and a curved section 1021, which are connected in sequence. The area where the straight section 1011 is located is the main region 101, and the area where the curved section 1021 is located is the corner region 102. The dividing line P2 between two adjacent folded membrane segments 13c is located at the middle position of the curved segment 1021 along the winding direction R. It can be understood that the folded membrane segment 13c located at the winding end 10b of the winding structure is the portion between the winding end 10b and the dividing line P2.

[0110] In some embodiments, 2≤N≤7. Within this range, the overall thickness of the electrode assembly 10 can be further reduced while improving the wetting effect of the electrolyte on the electrode assembly 10 and reducing the risk of lithium plating.

[0111] In some embodiments, the first diaphragm 13a further includes a first adhesive layer 133, which is disposed on a side of the first ceramic layer 1312 away from the first base film 1311, and / or, the first adhesive layer 133 is disposed on a side of the second ceramic layer 1322 away from the second base film 1321, and / or, the first adhesive layer 133 is disposed on a side of the first base film 1311 away from the first ceramic layer 1312, and / or, the first adhesive layer 133 is disposed on a side of the second base film 1321 away from the second ceramic layer 1322. Figure 8 The first adhesive layer 133 is disposed on a side of the first ceramic layer 1312 away from the first base film 1311 and on a side of the first base film 1311 away from the first ceramic layer 1312. After the electrode assembly 10 is wound to form a wound structure, the first adhesive layer 133 can enhance the bond strength between the first separator 13a and the first and second electrode sheets 11, 12, making the first separator 13a less likely to fold, reducing the risk of contact between the first and second electrode sheets 11, 12, and improving battery safety.

[0112] In some embodiments, the first adhesive layer 133 includes a binder, and the material of the binder includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyvinyl alcohol, sodium carboxymethyl cellulose, and acrylate.

[0113] See Figure 9 and Figure 10 , Figure 10 yes Figure 9Cross-sectional view along the thickness direction of the first diaphragm 13a. In some embodiments, along the width direction of the first diaphragm 13a, the first diaphragm 13a includes a third portion 134 and a fourth portion 135 arranged in sequence. When viewed along the thickness direction of the first diaphragm 13a, part of the first tab 113 overlaps part of the third portion 134. L2 is the dividing line between the third portion 134 and the fourth portion 135.

[0114] The third portion 134 includes a third base film 1341, and the fourth portion 135 includes a fourth ceramic layer 1352 and a fourth base film 1351 stacked along the thickness direction of the first diaphragm 13a. The thickness of the third portion 134 is H4, and the thickness of the fourth portion 135 is H5, where H4<H5.

[0115] After the fourth ceramic layer 1352 is provided on the fourth portion 135, the thickness of the fourth portion 135 is increased compared to the third portion 134. Furthermore, the fourth ceramic layer 1352 has good mechanical strength, which helps reduce the possibility of puncturing the first separator 13a and the risk of a short circuit caused by direct contact between the first and second electrode sheets 11, 12. Furthermore, by limiting H4 to H5, the thickness overlap at the first electrode tab 113 is reduced, thereby reducing the thickness of the electrode assembly 10 after winding, which helps minimize the loss of volumetric energy density of the secondary battery 100.

[0116] In some embodiments, the material of the third base film 1341 and the fourth base film 1351 each independently includes at least one of polyethylene, polypropylene, polyimide, polyamide, polysulfone, polyacrylonitrile, polyester, cellulose, polyphenylene sulfide, polyacrylate, polyethylene terephthalate, poly(p-phenylene amide), poly(arylether sulfone ketone), aramid, or aramid. In some embodiments, the third base film 1341 and the fourth base film 1351 are made of the same material and have the same thickness, which facilitates the production of the first diaphragm 13a.

[0117] In some embodiments, the width of the third portion 134 along the width direction of the first pole piece 11 is W2, 10 mm ≤ W2 ≤ 30 mm. For example, W2 can be 10 mm, 12 mm, 15 mm, 18 mm, 20 mm, 22 mm, 25 mm, 28 mm, or 30 mm.

[0118] When the width W2 of the third portion 134 is too large, the width of the fourth portion 135 will become narrower, that is, the thickened portion will become narrower, which will reduce the area where the strength of the first diaphragm 13a is increased, which is not conducive to reducing the risk of the first diaphragm 13a being punctured. If the width of the third portion 134 is too small, the first electrode tab 113 will easily overlap with the fourth ceramic layer 1352 of the fourth portion 135, thereby increasing the thickness of the wound electrode assembly 10 and causing a loss in the volume energy density of the secondary battery 100. When 10mm≤W2≤30mm is satisfied, the fourth portion 135 can be increased as much as possible without increasing the thickness of the electrode assembly 10, thereby reducing the risk of the first portion 131 being punctured and improving the safety performance of the secondary battery 100.

[0119] See Figure 11 In some embodiments, the third portion 134 further includes a third ceramic layer 1342. The third ceramic layer 1342 and the third base film 1341 are stacked along the thickness direction of the first diaphragm 13a. The thickness of the third ceramic layer 1342 is H6, and the thickness of the fourth ceramic layer 1352 is H7. 0.2≤H6 / H7≤0.5.

[0120] The provision of the third ceramic layer 1342 helps enhance the structural strength of the first separator 13a, making the third portion 134 less susceptible to puncture and improving electrolyte wetting near the first electrode tab 113. Furthermore, when H6 / H7 ≤ 0.5 is satisfied, the combined thickness of the first electrode tab 113 and the third ceramic layer 1342 can be reduced, minimizing the increase in thickness of the electrode assembly 10 after winding, thereby reducing the volumetric energy density loss of the secondary battery 100.

[0121] In some embodiments, 2 μm ≤ H7 ≤ 10 μm; 0.3 μm ≤ H6 ≤ μ1.5 μm. When the above ranges are met, the structural strength of the third portion 134 and the fourth portion 135 can be improved while the thickness of the third portion 134 and the fourth portion 135 is not easily increased excessively, thereby reducing the impact on the volume energy density of the secondary battery 100.

[0122] In some embodiments, 2 μm ≤ H7 ≤ 3 μm. When 2 μm ≤ H7 ≤ 3 μm is satisfied, the thickness of the fourth ceramic layer 1352 can be greater than that of the third ceramic layer 1342 , while not being too thick, thereby reducing the impact on the overall thickness of the electrode assembly 10 .

[0123] See also Figure 12 , an embodiment of the present application further provides an electric device 1000 , which includes the secondary battery 100 in any of the above embodiments.

[0124] By increasing the thickness of a portion of the first diaphragm 13a, the first diaphragm 13a is less likely to be punctured, thereby preventing the first electrode 11 from short-circuiting with the second electrode 12, thereby improving the safety of the secondary battery 100 and further improving the safety of the electrical device 1000.

[0125] In some embodiments, the electrical device 1000 may be a mobile phone, a laptop computer, a tablet computer, a drone, an electric tool, an electric toy, a game console, a video recorder, a portable recorder, a radio, or a smart watch, etc., which are not listed here one by one.

[0126] In some embodiments, the power-consuming device 1000 further includes a device body 200, and the secondary battery 100 is installed in the device body 200. Since the power-consuming 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.

[0127] To verify the effects of different configurations of the first separator 13a on the performance of the secondary battery 100, the inventors conducted the following experiments:

[0128] 1.Hipot test:

[0129] The first electrode sheet 11, the first diaphragm 13a, and the second electrode sheet 12 are stacked in sequence and wound to produce the electrode assembly 10. The leakage current generated by the electrode assembly 10 under the test high voltage output by the high-voltage machine is compared with the set judgment current. If the detected leakage current value is greater than or equal to the preset value, the tested product is judged to have passed the test (OK); if the detected leakage current value is less than the preset value, the test voltage is instantly cut off and the tested product is judged to have failed the test (NG). In this experiment, the preset value of the judgment current is 5mΩ. When the leakage current value is less than 5mΩ, it means that the device can conduct electricity but the resistance is too small, indicating a short circuit point, and the device is judged to be NG; when the leakage current value is greater than or equal to 5mΩ, the device is judged to be OK. 1,000 electrode assemblies 10 are tested in each comparative example and each example group, and the pass rate of the Hipot test is recorded for each group. The Hipot test pass rate is the ratio of the number of electrode assemblies 10 that passed the test in the same group to the total number of electrode assemblies 10 tested in the same group. For example, the number of electrode assemblies 10 in the same group that pass the test is X1, and 1000 electrode assemblies 10 are tested in each group, so the Hipot test pass rate is recorded as "X1 / 1000".

[0130] 2. K value test (voltage drop per unit time test):

[0131] The electrode assembly 10 is assembled into a secondary battery 100. When the secondary battery 100 stores 60% of the power, its voltage is measured at 25±5°C and recorded as the first voltage. After standing for 48 hours, its voltage is measured again and recorded as the second voltage. The voltage drop per unit time is recorded as K, where K = (first voltage - second voltage) / standing time. 1000 secondary batteries 100 are tested for each comparative example and each example. A K value of less than 0.006mV / h is determined to have passed the K value test (OK), and a K value greater than or equal to 0.006mV / h is determined to have failed the K value test (NG). 1000 secondary batteries 100 are tested for each comparative example and each example, and the K value test pass rate of each group is recorded. The K value test pass rate is the ratio of the number of secondary batteries 100 that passed the test in the same group to the total number of secondary batteries 100 in the group. For example, the number of secondary batteries 100 in the same group that pass the test is X2, and each group tests 1000 secondary batteries 100. The K value test pass rate is recorded as "X2 / 1000".

[0132] 3. Test on the probability of lithium deposition:

[0133] Twenty secondary batteries 100 were taken for testing in each group of comparative examples and each group of examples.

[0134] The secondary battery 100 is placed in a test environment at a temperature of 25°C and left to stand for 30 minutes. The battery is then charged to 4.5V according to the following charging steps:

[0135] ①5C constant current charging to 4.23V, constant voltage charging to 4C;

[0136] ②4C constant current charging to 4.3V, constant voltage charging to 3C;

[0137] ③3C constant current charging to 4.5V, constant voltage charging to 2C;

[0138] ④2C constant current charging to 4.5V, constant voltage charging cut-off current to 0.05C;

[0139] After standing for 10 minutes, discharge according to the following steps:

[0140] 0.2C constant current discharge to 3V.

[0141] The above charge and discharge process is one cycle. After repeating 1200 cycles, when the secondary battery 100 is in a fully charged state (the designed maximum voltage of the secondary battery 100 is 4.5V), the secondary battery 100 is disassembled to obtain the anode electrode. The surface of the anode electrode opposite to the first area 1312a, the second area 1312b, the third part 134 or the fourth part 135 is observed. The non-lithium-deposited area is black and the lithium-deposited area is grayish white. If the lithium deposition area on the surface of the anode electrode is greater than or equal to 1mm 2, it is determined to be lithium deposition and the test fails. Otherwise, the test passes. The probability of lithium deposition in each group is recorded. The probability of lithium deposition is the ratio of the number of secondary batteries 100 in the same group that have lithium deposition to the total number of secondary batteries 100 in the group. For example, if the number of secondary batteries 100 in the same group that have lithium deposition is X3, and each group tests 20 secondary batteries 100, the probability of lithium deposition is recorded as "X3 / 20".

[0142] 4. Volume energy density test:

[0143] The volume energy density of the secondary battery 100 was calculated as follows: volume energy density = first discharge cycle capacity / (secondary battery length × secondary battery width × thickness). The volume energy densities of the 20 secondary batteries 1000 in the same group were averaged and recorded in Tables 1 and 2.

[0144] 5. Measurement of H1, H2, H3, H4 and H5:

[0145] The first diaphragm 13a was separated from the electrode, and the first diaphragm 13a in the first region 1312a was cut into 2 cm x 2 cm diaphragm samples. These samples were affixed to conductive adhesive and placed on a SEM (Scanning Electron Microscope) sample stage for testing. H1 was obtained by observing the cross-section of the diaphragm sample using the SEM and measuring the thickness of the ceramic layer. The same testing method was used to measure the first diaphragm 13a in the second region 1312b, the first diaphragm 13a in the second portion 132, the first diaphragm 13a in the third portion 134, and the first diaphragm 13a in the fourth portion 135, respectively, to obtain H2, H3, H4, and H5.

[0146] 6. Measurement of W1 and W2:

[0147] Use a micrometer to measure W1 and W2.

[0148] Comparative Examples and Examples

[0149] Preparation of Secondary Battery 100:

[0150] (1) Preparation of cathode electrode:

[0151] The cathode active material is lithium cobalt oxide, the cathode conductive agent is acetylene black, and the cathode binder is polyvinylidene fluoride (PVDF, with a weight average molecular weight of 5×10 5) are mixed in a mass ratio of 94:3:3, N-methylpyrrolidone (NMP) is added as a solvent, and stirred under the action of a vacuum mixer to a cathode slurry with a solid content of 75wt% and a uniform system. An aluminum foil with a thickness of 8μm is selected as the cathode current collector, and a foam glue is pasted at a preset position on one surface of the cathode current collector aluminum foil along its thickness direction. The cathode slurry is evenly coated on one surface of the cathode current collector aluminum foil along its thickness direction, and dried at 110°C to obtain a cathode pole piece with a cathode active material layer (thickness 80μm) coated on one side. Thereafter, the above steps are repeated on the other surface of the aluminum foil along its thickness direction to obtain a cathode pole piece with a cathode active material layer coated on both sides. The previously pasted foam glue is then torn off to create an empty aluminum foil area for welding the cathode tab.

[0152] (2) Preparation of anode electrode

[0153] The anode active material graphite powder, silicon powder, conductive agent conductive carbon black (Sμper P), and binder styrene-butadiene rubber (SBR) are mixed in a weight ratio of 67.5:30:1:1.5, and then deionized water is added as a solvent to prepare an anode slurry with a solid content of 50wt%, and stirred evenly. A copper foil with a thickness of 5μm is selected as the anode current collector. The anode slurry is evenly coated on one surface of the anode current collector copper foil along its thickness direction, and dried at 90°C to obtain a single-sided anode pole piece. After the above steps are completed, the single-sided coating of the anode pole piece is completed. Thereafter, the above steps are repeated on the other surface of the anode pole piece along its thickness direction to obtain an anode pole piece with a double-sided coating of the anode active material layer.

[0154] (3) Preparation of diaphragm 13

[0155] ① Preparation of the first diaphragm 13a: When preparing the first diaphragm 13a of the comparative example and the embodiment shown in Table 1, a first base film 1311 and a second base film 1321 with a thickness of 4.5 μm and a width of 80 mm are taken, and a first ceramic layer 1312 is coated on the first base film 1311 by gravure coating, and a second ceramic layer 1322 is coated on the second base film 1321 to form a first part 131 and a second part 132 distributed along the length direction of the first diaphragm 13a. The various parameters of the first part 131 and the second part 132 are shown in Table 1 below.

[0156] When preparing the first diaphragm 13a of the comparative example and the embodiment shown in Table 2, the third ceramic layer 1342 is coated on the third base film 1341 by gravure coating, and the fourth ceramic layer 1352 is coated on the fourth base film 1351 to form a third part 134 and a fourth part 135 distributed in sequence along the width direction of the first diaphragm 13a. The various parameters of the third part 134 and the fourth part 135 are shown in Table 2 below.

[0157] ② The preparation method of the second diaphragm 13b is the same as the preparation method of the first diaphragm 13a.

[0158] (4) Preparation of electrolyte

[0159] In a dry argon atmosphere, ethylene carbonate, ethyl methyl carbonate and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solution, and then lithium hexafluorophosphate was added to the organic solvent to dissolve and mix uniformly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0160] (5) Assembly of the Secondary Battery 100

[0161] Ultrasonic welding is used to weld aluminum tabs to the empty aluminum foil area preset for welding cathode tabs to obtain cathode tabs welded to cathode tabs; ultrasonic welding is used to weld nickel tabs to the empty copper foil area preset for welding anode tabs to obtain anode tabs welded to anode tabs. The first diaphragm 13a, the cathode tabs welded to cathode tabs, the second diaphragm 13b, and the anode tabs welded to anode tabs prepared above are stacked in order and wound to obtain an electrode assembly 10. In Table 1, the cathode tabs and the anode tabs are located on the side where the first area 1312a of the electrode assembly 10 is located. In Table 2, the cathode tabs and the anode tabs are located on the side where the third part 134 of the electrode assembly 10 is located. The wound electrode assembly 10 includes 15 layers, with a total of 30 folds.

[0162] The electrode assembly 10 is placed in an aluminum-plastic film packaging bag, with the cathode tab and anode tab extending from the top seal of the packaging bag. After dehydration at 80° C., the electrolyte is injected and the bag is packaged.

[0163] The parameter control and test results of various embodiments and comparative examples are shown in Tables 1 and 2.

[0164] Table 1

[0165]

[0166]

[0167]

[0168]

[0169] From the comparison of the experimental data of Comparative Example 1-1 and Comparative Example 1-2 to Comparative Example 1-6 and Example 1-1 to Example 1-33 in Table 1, it can be seen that the provision of the first ceramic layer 1312 and the second ceramic layer 1322 in the electrode assembly 10 can significantly improve the Hipot test pass rate and the K value test pass rate, and reduce the probability of lithium deposition in the first region 1312a and the second region 1312b. This is because the provision of the ceramic layer improves the mechanical strength of the first diaphragm 13a, making the first diaphragm 13a less likely to be punctured by falling particles or carbon powder, and the ceramic layer has a certain porosity, which is conducive to improving the infiltration and storage of the electrolyte, and is conducive to reducing the probability of lithium deposition in the first region 1312a and the second region 1312b. From the experimental data of Comparative Examples 1-2, 1-3, and Examples 1-1 to 1-7, it can be seen that when the thickness H2 of the second region 1312b is less than 2μm, the Hipot test pass rate and the K value test pass rate are still not ideal, and the probability of lithium deposition in the first region 1312a and the second region 1312b is still high; and when H2>10μm, the loss of volume energy density of the secondary battery 100 is more serious. Therefore, when 2μm≤H2≤10μm, a higher Hipot test pass rate and K value test pass rate can be obtained, the probability of lithium deposition in the first region 1312a and the second region 1312b is low, and a higher volume energy density can be taken into account. Further, 2μm≤H2≤3μm is preferred. Comparison of the experimental data from Comparative Example 1-4 and Examples 1-1 and 1-8 to 1-14 shows that when H1 / H2>1, the volumetric energy density of the secondary battery 100 is compromised. To ensure a higher volumetric energy density for the secondary battery 100, the thickness H1 of the first region 1312a overlapping the first tab 113 is limited to be less than or equal to the thickness H2 of the second region 1312b, i.e., 0≤H1 / H2≤1. When H1 / H2=0, the first region 1312a is not provided with the first ceramic layer 1312. While the volumetric energy density of the secondary battery 100 is higher, the probability of lithium deposition in the first region 1312a is increased. This is because the absence of the ceramic layer in the first region 1312a results in poor electrolyte wetting in the first region 1312a. To balance electrolyte wetting in the first region 1312a and the volumetric energy density of the secondary battery 100, 0.2≤H1 / H2≤0.5 is preferred.Comparison of the experimental data from Comparative Examples 1-5 and 1-6 with Examples 1-1 and 1-15 to 1-21 shows that when H2 / H3 = 1, i.e., H2 = H3, the thickness of the second portion 132 is equal to the thickness of the second region 1312b, resulting in a significant loss in the volumetric energy density of the secondary battery 100. When H2 / H3 > 10, the difference between the thickness of the second portion 132 and the thickness of the second region 1312b is significant, resulting in a smaller thickness of the second portion 132, leading to lower Hipot and K-value test pass rates. To achieve both a higher volumetric energy density and a higher Hipot and K-value test pass rate, the limit is 1.2 ≤ H2 / H3 ≤ 10; further, 1.5 ≤ H2 / H3 ≤ 5 is preferred. Comparison of the experimental data from Example 1-1 and Examples 1-22 to 1-25 shows that when the width W1 of the first region 1312a is less than 10 mm, the first tab 113 is at risk of overlapping with the second region 1312b, causing the first tab 113 to overlap with the thickness of the thicker second region 1312b, resulting in a loss in the volumetric energy density of the secondary battery 100. When W1 is greater than 30 mm, the width of the thicker second region 1312b is smaller, resulting in lower Hipot test pass rates and K-value test pass rates. To balance higher volumetric energy density with higher Hipot test pass rates and K-value test pass rates, the limit is 10 mm ≤ W1 ≤ 30 mm. Comparing the experimental data of Example 1-1 and Examples 1-26 to 1-33 shows that when the number of folds N of the first portion 131 is greater than 15, the volumetric energy density of the secondary battery 100 is low due to the large number of thickened areas of the ceramic layer. When the number of folds N of the first portion 131 is too small, the Hipot test pass rate and the K-value test pass rate are low. To achieve both high volumetric energy density and high Hipot test pass rates and K-value test pass rates, the limit is 1 ≤ N ≤ 15; further, 2 ≤ N ≤ 7 is preferred.

[0170] Table 2

[0171]

[0172]

[0173] From the comparison of the experimental data of Comparative Example 2-1, Comparative Example 2-2 and Example 1-1 in Table 2, it can be seen that compared with the case of H4<H5, when H4>H5 or H4=H5, the volume energy density of the secondary battery 100 is lower. This is because when the thickness of the third portion 134 overlapping with the first electrode tab 113 is larger, the thickness of the first electrode tab 113 is superimposed on the thickness of the third portion 134, resulting in an increase in the thickness of the secondary battery 100, thereby making the volume energy density of the secondary battery 100 lower. From the comparison of the experimental data of Comparative Example 2-3, Comparative Example 2-4 and Example 2-1 to Example 2-7, it can be seen that when the thickness H7 of the fourth ceramic layer 1352 is less than 2μm, the Hipot test pass rate and the K value test pass rate are low, and the probability of lithium deposition in the fourth part 135 is relatively high. This is because when the thickness of the fourth ceramic layer 1352 is small, the puncture resistance of the first diaphragm 13a is low, and particles or carbon powder can easily cause the first diaphragm 13a to be punctured, resulting in a micro-short circuit, which leads to a low Hipot test pass rate and a K value test pass rate, and because the ceramic layer is thin, the fourth part 135 is prone to poor electrolyte infiltration, which leads to a high probability of lithium deposition in the fourth part 135; when the thickness H7 of the fourth ceramic layer 1352 is greater than 10μm, the increase in the thickness of the ceramic layer leads to an increase in the thickness of the secondary battery 100, resulting in a lower volume energy density of the secondary battery 100. Therefore, in order to balance the high Hipot test pass rate and the K-value test pass rate, the low probability of lithium deposition in the fourth portion 135 and the high volumetric energy density, the thickness of 2μm≤H7≤10μm is limited; further, 2μm≤H7≤3μm is preferred. Comparing the experimental data of Examples 2-8 to 2-12, it can be seen that when the ratio H6 of the thickness of the third ceramic layer 1342 to the thickness H7 of the fourth ceramic layer 1352 (H6 / H7) is less than 0.2, the thickness of the third ceramic layer 1342 is low and the probability of lithium deposition in the third portion 134 is high; when H6 / H7>0.5, the volumetric energy density of the secondary battery 100 is reduced. Therefore, in order to balance the low probability of lithium deposition in the third portion 134 and the high volumetric energy density of the secondary battery 100, the thickness of 0.2≤H6 / H7≤0.5 is limited. Comparing the experimental data of Examples 2-10 and 2-13 to 2-16 shows that when the width W2 of the third portion 134 is less than 10 mm, there is a risk that the first tab 113 overlaps with the fourth portion 135, causing the thickness of the first tab 113 to overlap with the thickness of the thicker fourth portion 135, resulting in a loss in the volumetric energy density of the secondary battery 100. When W2 is greater than 30 mm, the width of the thicker fourth portion 135 is smaller, resulting in lower Hipot test pass rates and K-value test pass rates. To achieve both higher volumetric energy density and higher Hipot test pass rates and K-value test pass rates, the limit is 10 mm ≤ W2 ≤ 30 mm.

[0174] Those skilled in the art should recognize that the above embodiments are merely intended to illustrate the present application and are not intended to limit the present application. Any appropriate changes and modifications to the above embodiments fall within the scope of the present application as long as they are within the spirit of the present application.

Claims

1. A secondary battery, characterized in that: The secondary battery includes an electrode assembly, the electrode assembly including a first electrode sheet, a second electrode sheet, and a first separator, wherein the first electrode sheet, the first separator, and the second electrode sheet are sequentially stacked to form a wound structure; along a winding direction of the first separator, the first separator includes a first portion and a second portion sequentially arranged, and the first portion is closer to a winding starting end of the wound structure than the second portion; Along the thickness direction of the first diaphragm, the first portion includes a first ceramic layer and a first base film that are stacked, and the second portion includes a second ceramic layer and a second base film that are stacked; The first electrode sheet includes a first current collector and a first electrode tab, wherein the first electrode tab is connected to the first current collector and extends from one side in the width direction of the first current collector; the first ceramic layer includes a first region and a second region sequentially arranged along the width direction of the first separator; along the width direction of the first separator, a portion of the first electrode tab overlaps with at least a portion of the first region; The thickness of the first region is H1, the thickness of the second region is H2, the thickness of the second ceramic layer is H3, 2 μm≤H2≤10 μm, 0.2≤H1 / H2≤1, and 1.2≤H2 / H3≤10; Along the width direction of the first pole piece, the width of the first region is W1, 10 mm ≤ W1 ≤ 30 mm.

2. The secondary battery according to claim 1, wherein 1.5≤H2 / H3≤5.

3. The secondary battery according to claim 1 or 2, wherein: 0.2≤H1 / H2≤0.

5.

4. The secondary battery according to claim 1, wherein 0.3μm≤H3≤1.5μm.

5. The secondary battery according to claim 4, wherein 2μm≤H2≤3μm.

6. The secondary battery according to claim 1, wherein The first diaphragm includes a multi-fold diaphragm segment, and the first part includes N folds of the diaphragm segment located at the starting end of the winding, 2≤N≤15.

7. The secondary battery according to claim 6, wherein 2≤N≤7。 8. The secondary battery according to claim 1, wherein The materials of the first ceramic layer and the second ceramic layer each independently include at least one of aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, barium titanate, and boehmite.

9. The secondary battery according to claim 1, wherein The secondary battery includes an electrode assembly, the electrode assembly including a first electrode sheet, a second electrode sheet, and a first separator, wherein the first electrode sheet, the first separator, and the second electrode sheet are sequentially stacked to form a wound structure; the first electrode sheet includes a first current collector and a first electrode tab, the first electrode tab being connected to the first current collector and extending from one side in a width direction of the first current collector; the first separator includes a third portion and a fourth portion sequentially arranged along the width direction of the first separator; and when viewed along the thickness direction of the first separator, a portion of the first electrode tab overlaps a portion of the third portion; The third part includes a third base membrane, and the fourth part includes a fourth ceramic layer and a fourth base membrane stacked along the thickness direction of the first diaphragm; the thickness of the third part is H4, the thickness of the fourth part is H5, H4<H5; the thickness of the fourth ceramic layer is H7, 2μm≤H7≤10μm.

10. The secondary battery according to claim 9, wherein Along the width direction of the first pole piece, the width of the third portion is W2, 10mm≤W2≤30mm.

11. The secondary battery according to claim 9 or 10, wherein: The third part further includes a third ceramic layer. The third ceramic layer and the third base film are stacked along the thickness direction of the first diaphragm. The thickness of the third ceramic layer is H6, and 0.2 μm≤H6 / H7≤0.5 μm.

12. The secondary battery according to claim 11, wherein 0.3μm≤H6≤1.5μm.

13. The secondary battery according to claim 12, wherein 2μm≤H7≤3μm.

14. An electrical device, characterized in that: The secondary battery according to any one of claims 1 to 13 is included.

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