Battery cell and secondary battery

Abstract

The invention relates to the technical field of batteries, and discloses a battery cell and a secondary battery. The battery cell comprises a first electrode, a diaphragm and a plurality of second electrodes, the diaphragm comprises sub-diaphragms located on the two opposite sides of the first electrode, each sub-diaphragm comprises an extension part exceeding the first electrode in the width direction of the first electrode, and the extension parts are bonded with one another; the first electrode and the diaphragm form a composite diaphragm pole piece, the composite diaphragm pole piece is provided with a plurality of straight areas and arc areas, the arc areas are connected with the adjacent straight areas, and the arc areas are provided with inner arc top ends; the multiple second electrodes and the straight areas are stacked in a crossed mode, and the ends of the second electrodes and the arc areas are oppositely arranged in the width direction. The second electrode is provided with a first side face facing the arc area, and the distance A between the first side face and the top end of the inner arc is larger than or equal to 0.1 mm. The distance prevents edge transverse burrs of the second electrode from piercing the diaphragm in the arc area to be conducted with the first electrode to form short circuit, thermal runaway caused by battery short circuit is avoided, and the safety performance of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to battery cells and secondary batteries. Background Art

[0002] Lithium-ion batteries have become the main power source for consumer electronics and electric vehicles due to their many advantages. With people's growing demand, lithium-ion batteries are gradually developing towards fast charging, long life, high energy density and high safety.

[0003] With the widespread application of lithium-ion batteries, higher requirements have been placed on their performance, which has gradually promoted the development of lithium-ion batteries towards high energy density and high rate. Laminated cells are widely used in the field of fast charging and high energy density batteries due to their advantages such as low internal resistance, high energy density and long cycle life.

[0004] When the thickness of the battery cell is constant, the thinner the foil is, the higher the corresponding active material content can be. Therefore, the use of high-strength thin foil can effectively improve the energy density of the battery cell, but when cutting the pole piece, the active material at the edge of the pole piece is easy to fall off when stacking. If the active material falls on the diaphragm, it will cause the diaphragm to break after hot pressing, causing the positive and negative poles of the battery cell to directly contact, forming an internal short circuit, and then increasing the voltage attenuation, and finally causing the K value of the battery cell to increase and become defective. Summary of the invention

[0005] In view of this, the present invention provides a battery cell and a secondary battery to solve the problem that when cutting the pole pieces, the active material at the edge of the pole piece is easily dropped onto the diaphragm during the stacking process, causing damage to the diaphragm and short circuit of the positive and negative electrodes.

[0006] In a first aspect, the present invention provides a battery cell, comprising: a first electrode, a diaphragm and a plurality of second electrodes, wherein the diaphragm comprises a sub-diaphragm located on opposite sides of the first electrode, the sub-diaphragm comprises an extension portion extending beyond the first electrode along the width direction of the first electrode, and the extension portions are bonded to each other; the first electrode and the diaphragm form a composite diaphragm pole piece, the composite diaphragm pole piece has a plurality of straight areas and arc areas, the arc areas connect adjacent straight areas, and the arc areas have an inner arc top; the plurality of second electrodes are cross-stacked with the straight areas, and along the width direction, the ends of the second electrodes and the arc areas are arranged opposite to each other; the second electrode has a first side facing the arc area, and the distance between the first side and the inner arc top is A, A≥0.1mm.

[0007] Beneficial effect: By limiting the distance between the first side surface of the second electrode and the top of the inner arc of the arc area to be greater than or equal to 0.1 mm, this distance can prevent the lateral burrs on the edge of the second electrode from piercing the diaphragm in the arc area and conducting with the first electrode to form a short circuit, thereby avoiding thermal runaway caused by battery short circuit and improving the safety performance of the battery.

[0008] In an optional implementation, a first insulating layer is provided between the first electrode in the arc region and the inner sub-diaphragm.

[0009] Beneficial effect: By providing the first insulating layer on the inner side of the first electrode in the arc region, the insulation performance of the arc region can be effectively improved, and the second electrode can be prevented from piercing the diaphragm and causing a short circuit with the first electrode.

[0010] In an optional embodiment, the surface resistance of the first insulating layer is greater than the surface resistance of the separator.

[0011] Beneficial effect: The larger the surface resistance of the first insulating layer, the stronger the ability to prevent leakage, thereby improving the overall insulation effect.

[0012] In an optional implementation, a second insulating layer is provided on the first side, and the second insulating layer covers the current collector of the second electrode.

[0013] Beneficial effect: The second insulating layer covers the edge of the current collector of the second electrode, which can effectively improve the insulation performance of the edge of the second electrode and prevent the burrs of the current collector at the edge of the second electrode from piercing the diaphragm and causing a short circuit.

[0014] In an optional implementation, the second electrode has two opposite surfaces, and the second insulating layer covers portions of the two surfaces close to the arc region and the first side surface.

[0015] Beneficial effect: The second insulating layer is U-shaped, and covers the first side surface and the edge portions of the two surfaces of the second electrode. The edge of the second electrode has better insulation performance, which effectively prevents the burrs on the edge of the second electrode from piercing the diaphragm of the first electrode, thereby improving the safety and reliability of the battery.

[0016] In an optional embodiment, the thickness B of the second insulating layer is 4μm-20μm; and / or, along the extension direction of the straight area, the width C of the second insulating layer is 10μm-20μm; and / or, after the battery cell is unfolded, the distance D between the first side surface and the side of the first insulating layer close to the first side surface is 0.2mm-10mm; the thickness E of the first insulating layer is 5μm-20μm; and / or, the width F of the first insulating layer along the unfolding direction of the battery cell is 1mm-10mm.

[0017] Beneficial effects: The thickness B of the second insulating layer is greater than the height of the longitudinal burr of the pole piece, which can effectively prevent the burr of the second electrode from piercing the diaphragm and causing a short circuit. The width C of the second insulating layer is greater than the edge powder loss width of the pole piece, which can effectively prevent the edge powder loss from causing poor battery withstand voltage test after hot pressing and dust from falling into the battery, causing poor battery K value. The distance D ensures that the first insulating layer does not enter the area where the first electrode and the second electrode are opposite, ensures the consistency of battery thickness, and can reduce the internal resistance of the battery. The thickness E of the first insulating layer is greater than the height of the longitudinal burr of the pole piece. The width of the first insulating layer can effectively cover the arc area, effectively preventing the burr of the second electrode from piercing the diaphragm and causing a short circuit, and ensuring the insulation performance of the battery.

[0018] In an optional embodiment, the thickness E of the first insulating layer is 5μm-20μm, the first electrode includes a current collector and an active material layer located on both sides of the current collector, at least a portion of the active material layer on the inner side of the arc area is a thinned area, the thickness G of the thinned area is 10μ-100μm, and the thickness of the active material layer in the straight area is H, wherein E+G≤H.

[0019] Beneficial effect: This structure reduces the thickness of the arc area, ensures that the two sides are not too thick, prevents bubbles from being generated when the diaphragm and the electrode are compounded, and reduces the risk of lithium deposition in the arc area of ​​the battery.

[0020] In an optional embodiment, the first electrode includes a current collector and an active material layer located on both sides of the current collector, at least a portion of the active material layer on the inner side of the arc area has a thinning zone, and the width F of the first insulating layer along the expansion direction of the battery cell and the width K of the thinning zone along the expansion direction of the battery cell satisfy: 30%≤F / K<100%.

[0021] Beneficial effect: This structure reduces the thickness of the arc area, ensures that the two sides are not too thick, prevents bubbles from being generated when the diaphragm and the electrode are compounded, and reduces the risk of lithium deposition in the arc area of ​​the battery.

[0022] In an optional embodiment, the first electrode is a positive electrode, the second electrode is a negative electrode, the first electrode in the straight area includes a current collector and an active material layer arranged on the current collector, the second electrode also has a second side surface arranged opposite to the first side surface, the active material layer has a third side surface and a fourth side surface arranged at intervals along the winding direction of the battery cell, the third side surface is arranged close to the first side surface, and the fourth side surface is arranged close to the second side surface, and the distance J between the first side surface and the third side surface and the distance J between the second side surface and the fourth side surface are 0.1mm-3mm.

[0023] Beneficial effect: This distance not only reduces the loss of battery energy density, but also ensures that the negative electrode covers the positive electrode, reducing the risk of battery lithium plating.

[0024] In a second aspect, the present invention further provides a secondary battery, comprising: the above-mentioned battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 is a schematic structural diagram of a first type of battery cell according to an embodiment of the present invention;

[0027] Figure 2 for Figure 1 The schematic diagram of the partial structure of the battery cell after it is unfolded is shown;

[0028] Figure 3 is a schematic structural diagram of a second battery cell according to an embodiment of the present invention;

[0029] Figure 4 is a schematic structural diagram of a third battery cell according to an embodiment of the present invention;

[0030] Figure 5 for Figure 4 A is a partial enlarged schematic diagram;

[0031] Figure 6 is a schematic diagram of a partial structure of a fourth battery cell after expansion according to an embodiment of the present invention;

[0032] Figure 7 is a schematic diagram of a partial structure of a fifth battery cell after expansion according to an embodiment of the present invention;

[0033] Figure 8 It is a schematic diagram of the partial structure of the sixth battery cell after expansion according to an embodiment of the present invention.

[0034] Description of reference numerals:

[0035] 1. first electrode; 1011. current collector; 1012. active material layer; 10121. thinning area; 10122. third side surface; 10123. fourth side surface; 102. diaphragm; 103. straight area; 104. arc area;

[0036] 2. second electrode; 201. first side surface; 202. second side surface;

[0037] 3. first insulating layer; 301. middle portion; 302. overlapping portion;

[0038] 4. Second insulation layer. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0040] Combine the following Figures 1 to 8 , describing an embodiment of the present invention.

[0041] According to an embodiment of the present invention, on the one hand, a battery cell is provided, comprising: a first electrode 1, a diaphragm 102 and a plurality of second electrodes 2, wherein the diaphragm 102 comprises a sub-diaphragm located on opposite sides of the first electrode 1, the sub-diaphragm comprises an extension portion extending beyond the first electrode 1 along the width direction of the first electrode 1, and the extension portions are bonded to each other; the first electrode 1 and the diaphragm 102 form a composite diaphragm pole piece, the composite diaphragm pole piece has a plurality of straight regions 103 and arc regions 104, the arc regions 104 connect adjacent straight regions 103, and the arc regions 104 have an inner arc top; the plurality of second electrodes 2 are cross-stacked with the straight regions 103, and along the width direction, the ends of the second electrodes 2 and the arc regions 104 are arranged opposite to each other; the second electrode 2 has a first side surface 201 facing the arc region 104, and the distance between the first side surface 201 and the inner arc top is A, wherein A≥0.1mm.

[0042] When manufacturing the battery cell using the present embodiment, the first electrode 1 and the diaphragm 102 are compounded together to form a composite diaphragm pole piece, and then the continuous composite diaphragm pole piece is stacked with multiple second electrodes 2. There are no burrs on the edge of the continuous first electrode 1, and there are inevitably burrs on the edge of the discontinuous second electrode 2 when cutting. The burrs of the second electrode 2 are facing the arc region 104 of the continuous electrode, which can easily pierce the diaphragm 102 and contact the continuous first electrode 1, thereby causing a short circuit. In order to avoid the short circuit, the distance between the first side surface 201 of the second electrode 2 and the inner arc top of the arc region 104 is limited to be greater than or equal to 0.1 mm. This distance can prevent the lateral burrs on the edge of the second electrode 2 from piercing the diaphragm 102 in the arc region 104 and conducting with the first electrode 1 to form a short circuit, thereby avoiding thermal runaway caused by battery short circuit and improving the safety performance of the battery.

[0043] It should be noted that the first electrode 1 is a continuous electrode strip, and the second electrode 2 is a cut single electrode.

[0044] In one embodiment, Figure 1 and Figure 3As shown, a first insulating layer 3 is provided between the first electrode 1 at the arc region 104 and the inner sub-diaphragm. Providing the first insulating layer 3 on the inner side of the first electrode 1 at the arc region 104 can effectively improve the insulation performance of the arc region and prevent the second electrode 2 from piercing the diaphragm 102 and causing a short circuit with the first electrode 1.

[0045] Furthermore, the surface resistance of the first insulating layer 3 is greater than the surface resistance of the diaphragm 102. The greater the surface resistance of the first insulating layer 3, the stronger the ability to prevent leakage, thereby improving the overall insulation effect. The first insulating layer 3 is made of insulating material, and the surface resistance of the insulating material is ≥100Ω / cm 2 .

[0046] Specifically, the first insulating layer 3 includes at least one of an inert substance coating, an organic polymer insulating coating and an insulating adhesive tape. The inert substance coating has the advantages of high temperature resistance, good electrical insulation performance, high mechanical strength, etc. The organic polymer insulating coating has the advantages of good flexibility and ductility, easy processing, light weight, etc. The insulating adhesive tape has the advantages of strong ready-to-use and easy removal, etc.

[0047] Further, the material of the inert substance coating includes a binder and an inert substance, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylate, polyimide, polyamide, polyamideimide, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polyacrylonitrile, polyacrylate, polyacrylic acid, sodium polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate or polyhexafluoropropylene; the inert substance includes at least one of silicon dioxide, aluminum fluoride, aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate.

[0048] Furthermore, the organic polymer insulating coating includes at least one of polyimide, silicone resin, epoxy resin, polyurethane, acrylic resin, silicone mud, polytetrafluoroethylene, polystyrene, polyethylene, and polypropylene.

[0049] Furthermore, the insulating tape includes one of polyimide, polyester tape (PET), highland barley paper, aramid paper, glass fiber tape, and polypropylene tape.

[0050] In one embodiment, Figure 4 and Figure 5As shown, the first side 201 is provided with a second insulating layer 4, and the second insulating layer 4 covers the current collector 1011 of the second electrode 2. The second insulating layer 4 covers the edge of the current collector 1011 of the second electrode 2, which can effectively improve the insulation performance of the edge of the second electrode 2 and prevent the burrs of the current collector 1011 at the edge of the second electrode 2 from piercing the diaphragm 102 and causing a short circuit.

[0051] Furthermore, the surface resistance of the second insulating layer 4 is greater than that of the diaphragm 102. The greater the surface resistance of the second insulating layer 4, the stronger the ability to prevent leakage, thereby improving the overall insulation effect. The second insulating layer 4 is made of insulating material, and the surface resistance of the insulating material is ≥100Ω / cm2.

[0052] Specifically, the second insulating layer 4 includes at least one of an inert material coating, an organic polymer insulating coating and an insulating adhesive tape. The first insulating layer 3 and the second insulating layer 4 are made of the same material, which will not be described in detail herein.

[0053] In one embodiment, Figure 4 and Figure 5 As shown, the second electrode 2 has two opposite surfaces, and the second insulating layer 4 covers the portions of the two surfaces close to the arc region 104 and the first side surface 201. The second insulating layer 4 is U-shaped, and the second insulating layer 4 covers the first side surface 201 and the edge portions of the two surfaces of the second electrode 2. The edge of the second electrode 2 has better insulation performance, which effectively prevents the burrs of the edge of the second electrode 2 from piercing the diaphragm 102 of the first electrode 1, thereby improving the safety and reliability of the battery.

[0054] In one embodiment, the thickness B of the second insulating layer 4 is 4 μm-20 μm, and the width C of the second insulating layer 4 is 10 μm-20 μm along the extension direction of the straight region 103. The thickness B of the second insulating layer 4 is greater than the height of the longitudinal burr of the first electrode 1, which can effectively prevent the burr of the second electrode 2 from piercing the diaphragm 102 and causing a short circuit. The width C of the second insulating layer 4 is greater than the edge powder falling width of the first electrode 1, which can effectively prevent the edge powder from causing a poor battery withstand voltage test after hot pressing and dust falling into the battery to cause a poor battery K value.

[0055] It should be noted that the longitudinal direction of the first electrode 1 refers to the direction perpendicular to the surface of the first electrode 1 , that is, the Z-stack direction of the battery cell, and the K value refers to the voltage drop of the battery per unit time.

[0056] In one embodiment, Figure 2 As shown, after the battery cell is unfolded, the distance D between the first side surface 201 and the side of the first insulating layer 3 close to the first side surface 201 is 0.2 mm-10 mm. This distance D ensures that the first insulating layer 3 does not enter the area opposite to the first electrode 1 and the second electrode 2, ensures the consistency of the battery thickness, and can reduce the internal resistance of the battery.

[0057] In one embodiment, Figure 6 and Figure 7 As shown, the thickness E of the first insulating layer 3 is 5μm-20μm, and the width F of the first insulating layer 3 along the unfolding direction of the battery cell is 1mm-10mm. The thickness E of the first insulating layer 3 is greater than the height of the longitudinal burr of the first electrode 1, and the width of the first insulating layer 3 can effectively cover the arc area 104, effectively preventing the burr of the second electrode 2 from piercing the diaphragm 102 to cause a short circuit, thereby ensuring the insulation performance of the battery.

[0058] In one embodiment, the thickness E of the first insulating layer 3 is 5 μm-20 μm, the first electrode 1 includes a current collector 1011 and an active material layer 1012 located on both sides of the current collector 1011, at least part of the active material layer 1012 on the inner side of the arc region 104 has a thinning area 10121, the thickness G of the thinning area 10121 is 10 μm-100 μm, and the thickness of the active material layer 1012 in the straight region 103 is H, where E+G≤H. This structure reduces the thickness of the arc region 104, ensures that the two sides are not too thick, prevents the diaphragm 102 and the first electrode 1 from compounding to generate bubbles, and reduces the risk of lithium deposition in the arc region of the battery.

[0059] Furthermore, both ends of the arc region 104 are thinned areas 10121 , or the entire arc region 104 is the thinned area 10121 .

[0060] Specifically, the middle part of the inner side of the current collector 1011 at the arc region 104 is not coated with the active material layer 1012, and both ends of the inner side of the current collector 1011 at the arc region 104 are coated with the active material layer 1012, and the first insulating layer 3 has a middle part 301 arranged on the current collector 1011 not coated with the active material layer 1012 and an overlapping part 302 overlapped on the active material layer 1012. Among them, the current collector 1011 not coated with the active material layer 1012 can also be called an empty foil area.

[0061] It should be noted that Figure 6 and Figure 7 The rectangular dotted frame in FIG. 1 represents the active material layer 1012 that has been scraped off.

[0062] In one embodiment, Figure 6 and Figure 7As shown, the first electrode 1 includes a current collector 1011 and an active material layer 1012 located on both sides of the current collector 1011, at least part of the active material layer 1012 on the inner side of the arc region 104 has a thinning area 10121, and the width F of the first insulating layer 3 along the expansion direction of the battery cell and the width K of the thinning area 10121 along the expansion direction of the battery cell satisfy: 30%≤F / K<100%. This structure reduces the thickness of the arc region 104, ensures that the two sides are not too thick, prevents the diaphragm 102 and the first electrode 1 from compounding to generate bubbles, and reduces the risk of lithium deposition in the arc region of the battery.

[0063] Furthermore, F is 1mm-15mm, and K is 1mm-30mm.

[0064] It should be noted that the units of the thickness H of the active material layer 1012 in the straight region 103 , the width F of the first insulating layer 3 , and the width K of the thinned region 10121 are all mm.

[0065] In one embodiment, Figure 8 As shown, the first electrode 1 is a positive electrode, the second electrode 2 is a negative electrode, the first electrode 1 of the flat region 103 includes a current collector 1011 and an active material layer 1012 disposed on the current collector 1011, the second electrode 2 also has a second side 202 disposed opposite to the first side 201, the active material layer 1012 has a third side 10122 and a fourth side 10123 disposed at intervals along the winding direction of the battery cell, the third side 10122 is disposed close to the first side 201, the fourth side 10123 is disposed close to the second side 202, and the distance J between the first side 201 and the third side 10122 and the distance J between the second side 202 and the fourth side 10123 are 0.1mm-3mm. This distance not only reduces the energy density loss of the battery, but also ensures that the negative electrode covers the positive electrode, reducing the risk of lithium deposition in the battery.

[0066] It can be understood that, in another embodiment, the first electrode 1 is a negative electrode, and the second electrode 2 is a positive electrode.

[0067] It should be noted that Figures 1 to 5 The black area in the middle refers to the active material layer of the second electrode 2. Figure 8 The black area in ref. 1 is the active material layer of the first electrode 1 .

[0068] According to an embodiment of the present invention, on the other hand, a secondary battery is provided, including: the above-mentioned battery cell.

[0069] Furthermore, the first electrode 1 and the diaphragm 102 are composited into a continuous composite diaphragm pole piece, the first insulating layer 3 is provided in the arc region 104 of the first electrode 1, the first insulating layer 3 is provided in the thinned area 10121 or the empty foil area at the arc region 104 of the continuous first electrode 1, and the second insulating layer 4 is provided at the edge of the discontinuous second electrode 2.

[0070] When manufacturing the battery cell, the first electrode 1 containing multiple poles is first thermally composited with the diaphragm 102 to form a continuous composite diaphragm electrode piece, and then Z-stacked with a plurality of second electrodes 2. This can effectively prevent the active material on the first electrode 1 from falling onto the diaphragm 102 during cutting to affect the K value of the battery cell, thereby preventing the diaphragm 102 from being damaged and causing a micro short circuit inside the battery cell, which can effectively reduce the K value of the battery cell; at the same time, in the width direction, one electrode piece of the battery cell is always covered by the arc area 104 of the other electrode piece, and no margin is left, the process is simpler, and the process efficiency can be significantly improved. The short-circuit rate of the continuous electrode arc area of ​​the thermal composite Z-stack battery can be reduced, and the battery insulation resistance can be ≥0.1 megohms; the micro short circuit of the thermal composite Z-stack battery is reduced, and the K value is less than 0.1mV / h; the thickness consistency of the thermal composite Z-stack battery is ensured, and the battery flatness is ≤0.1mm.

[0071] In one embodiment, the secondary battery further includes a housing, etc. The housing has a receiving cavity, the battery cell is arranged in the receiving cavity of the housing, and the housing protects the battery cell to prevent physical damage and chemical corrosion. The secondary battery has the advantages of high energy density, long cycle life, no memory effect, low self-discharge rate, etc.

[0072] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A battery cell, characterized in that: include: A first electrode (1), a diaphragm (102), and a plurality of second electrodes (2), wherein the diaphragm (102) comprises sub-diaphragms located on two opposite sides of the first electrode (1), the sub-diaphragms comprise extensions extending beyond the first electrode (1) along a width direction of the first electrode (1), and the extensions are bonded to each other; The first electrode (1) and the diaphragm (102) form a composite diaphragm pole piece, the composite diaphragm pole piece having a plurality of straight regions (103) and arc regions (104), the arc regions (104) connecting adjacent straight regions (103), and the arc regions (104) having an inner arc top end; A plurality of the second electrodes (2) are cross-stacked with the straight region (103), and along the width direction, the end of the second electrode (2) and the arc region (104) are arranged opposite to each other; The second electrode (2) has a first side surface (201) facing the arc region (104), and the distance between the first side surface (201) and the top of the inner arc is A, where A is ≥ 0.1 mm.

2. The battery cell according to claim 1, characterized in that: A first insulating layer (3) is provided between the first electrode (1) at the arc region (104) and the inner sub-diaphragm.

3. The battery cell according to claim 2, characterized in that: The surface resistance of the first insulating layer (3) is greater than the surface resistance of the diaphragm (102).

4. The battery cell according to claim 2, characterized in that: The first side surface (201) is provided with a second insulating layer (4), and the second insulating layer (4) covers the current collector of the second electrode (2).

5. The battery cell according to claim 4, characterized in that: The second electrode (2) has two opposite surfaces, and the second insulating layer (4) covers portions of the two surfaces close to the arc region (104) and the first side surface (201).

6. The battery cell according to claim 4, characterized in that: The thickness B of the second insulating layer (4) is 4 μm-20 μm; and / or, along the extension direction of the straight region (103), the width C of the second insulating layer (4) is 10 μm-20 μm; And / or, after the battery cell is unfolded, a distance D between the first side surface (201) and a side of the first insulating layer (3) close to the first side surface (201) is 0.2 mm-10 mm; And / or, the thickness E of the first insulating layer (3) is 5 μm-20 μm; And / or, the width F of the first insulating layer (3) along the unfolding direction of the battery core is 1 mm-10 mm.

7. The battery cell according to any one of claims 2 to 6, characterized in that: The thickness E of the first insulating layer (3) is 5 μm-20 μm, the first electrode (1) comprises a current collector (1011) and an active material layer (1012) located on both sides of the current collector (1011), at least part of the active material layer (1012) on the inner side of the arc region (104) is a thinned region (10121), the thickness G of the thinned region (10121) is 10 μm-100 μm, and the thickness of the active material layer (1012) in the straight region (103) is H, wherein E+G≤H.

8. The battery cell according to any one of claims 2 to 6, characterized in that: The first electrode (1) comprises a current collector (1011) and an active material layer (1012) located on both sides of the current collector (1011), at least a portion of the active material layer (1012) on the inner side of the arc region (104) has a thinned area (10121), and a width F of the first insulating layer (3) along the expansion direction of the battery cell and a width K of the thinned area (10121) along the expansion direction of the battery cell satisfy: 30%≤F / K<100%.

9. The battery cell according to any one of claims 1 to 6, characterized in that: The first electrode (1) is a positive electrode, and the second electrode (2) is a negative electrode. The first electrode (1) of the straight region (103) comprises a current collector (1011) and an active material layer (1012) arranged on the current collector (1011). The second electrode (2) further comprises a second side surface (202) arranged opposite to the first side surface (201). The active material layer (1012) comprises a third side surface (10122) and a fourth side surface (10123) arranged at intervals along the winding direction of the battery cell. The third side surface (10122) is arranged close to the first side surface (201), and the fourth side surface (10123) is arranged close to the second side surface (202). The distance J between the first side surface (201) and the third side surface (10122) and the distance J between the second side surface (202) and the fourth side surface (10123) are 0.1 mm to 3 mm.

10. A secondary battery, characterized in that: include: The battery cell according to any one of claims 1 to 9.

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