Battery cell and secondary battery

Abstract

The utility model 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 application relates to the technical field of battery, in particular to a battery cell and a secondary battery. BACKGROUND

[0002] Lithium ion battery has become the main power source for consumer electronics and electric vehicles due to its many advantages. With the increasing demand of people, lithium ion battery gradually develops towards fast charging, long life, high energy density and high safety.

[0003] With the wide application of lithium ion battery, higher requirements are put forward for its performance, which has gradually promoted the development of lithium ion battery towards high energy density and high rate. The laminated battery cell is widely used in the field of fast charging and high energy density battery due to its small internal resistance, high energy density and long cycle life.

[0004] When the thickness of the battery cell is constant, the thinner the thickness of the foil, the more the active material content can be increased. Therefore, using high-strength thin foil can effectively improve the energy density of the battery cell, but the active material at the edge of the pole piece is easy to fall off during the cutting of the pole piece. If the active material falls on the separator and is hot pressed, it will cause the separator to be damaged, causing the positive and negative electrodes to be directly connected, forming an internal short circuit, which will further increase the voltage decay, and ultimately lead to an increase in the K value of the battery cell and poor performance. SUMMARY

[0005] Therefore, the present application provides a battery cell and a secondary battery to solve the problem of active material falling off during the cutting of the pole piece and causing the separator to be damaged and the positive and negative electrodes to be short-circuited.

[0006] In a first aspect, the present application provides a battery cell, comprising: a first electrode, a separator and a plurality of second electrodes, wherein the separator comprises a sub-separator located on the opposite sides of the first electrode, the sub-separator comprises an extension part extending beyond the first electrode along the width direction of the first electrode, and the extension parts are bonded to each other; the first electrode and the separator form a composite separator pole piece, the composite separator pole piece has a plurality of flat areas and arc areas, the arc areas connect adjacent flat areas, and the arc areas have inner arc top ends; the plurality of second electrodes are stacked in cross with the flat areas, and the end of the second electrode and the arc area are oppositely arranged along the width direction; the second electrode has a first side surface facing the arc area, and the distance between the first side surface and the inner arc top end is A, A is greater than or equal to 0.1mm.

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

[0008] In an optional embodiment, the first electrode at the circular-arc region and the inner side of the sub-separator are provided with a first insulating layer.

[0009] Beneficial effects: The first insulating layer provided on the inner side of the first electrode at the circular-arc region can effectively improve the insulation performance of the circular-arc region and prevent the second electrode from piercing the separator and the first electrode to cause short circuit.

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

[0011] Beneficial effects: The greater the surface resistance of the first insulating layer, the stronger the ability to prevent electric leakage, and the overall insulation effect is improved.

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

[0013] Beneficial effects: 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 edge of the current collector of the second electrode from piercing the separator to cause short circuit.

[0014] In an optional embodiment, the second electrode has two opposite surfaces, and the second insulating layer covers the part of the two surfaces close to the circular-arc region and the first side.

[0015] Beneficial effects: The second insulating layer is U-shaped, and the second insulating layer covers the first side of the second electrode and the edge part of the two surfaces. The edge of the second electrode has better insulation performance, effectively avoiding the burr of the edge of the second electrode from piercing the separator of the first electrode, and improving the safety and reliability of the battery.

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

[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 second electrode burr from piercing the diaphragm to cause short circuit, and the width C of the second insulating layer is greater than the edge powder width of the pole piece, which can effectively prevent the edge powder from causing battery voltage test failure after hot pressing and the dust from falling into the battery to cause battery K value failure. The distance D ensures that the first insulating layer does not enter the opposite area of the first electrode and the second electrode, ensures the consistency of the battery thickness, and can reduce the battery internal resistance. The thickness E of the first insulating layer is greater than the height of the longitudinal burr of the pole piece, and the width of the first insulating layer can effectively cover the circular arc area, effectively prevent the second electrode burr from piercing the diaphragm to cause short circuit, and ensure the insulation performance of the battery.

[0018] In an optional embodiment, the thickness E of the first insulating layer is 5-20 μm, the first electrode includes a current collector and an active material layer located on both sides of the current collector, at least part of the inner side of the active material layer at the circular arc area is a thinning area, the thickness G of the thinning area is 10-100 μm, and the thickness H of the active material layer at the flat area is satisfied: E+G≤H.

[0019] Beneficial effects: this structure reduces the thickness of the circular arc area, ensures that both sides are not too thick, prevents the diaphragm and the pole piece from being compounded to produce bubbles during compounding, and reduces the risk of lithium precipitation in the circular 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 part of the inner side of the active material layer at the circular arc area has a thinning area, and the width F of the first insulating layer along the development direction of the battery and the width K of the thinning area along the development direction of the battery satisfy: 30%≤F / K<100%.

[0021] Beneficial effects: this structure reduces the thickness of the circular arc area, ensures that both sides are not too thick, prevents the diaphragm and the pole piece from being compounded to produce bubbles during compounding, and reduces the risk of lithium precipitation in the circular 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 at the flat area includes a current collector and an active material layer arranged on the current collector, the second electrode further 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, 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. 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 0.1-3 mm.

[0023] Beneficial effects: this distance reduces the loss of battery energy density, ensures that the negative electrode covers the positive electrode, and reduces the risk of lithium precipitation in the battery.

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

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the specific embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

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

[0027] Figure 2 FIG. 2 is a structural schematic diagram of a second battery cell according to an embodiment of the present application; Figure 1

[0028] Figure 3 FIG. 3 is a structural schematic diagram of a third battery cell according to an embodiment of the present application;

[0029] Figure 4 FIG. 4 is a structural schematic diagram of a fourth battery cell according to an embodiment of the present application;

[0030] Figure 5 FIG. 5 is a structural schematic diagram of a fifth battery cell according to an embodiment of the present application; Figure 4

[0031] Figure 6 FIG. 6 is a structural schematic diagram of a sixth battery cell according to an embodiment of the present application.

[0032] Figure 7 FIG. 7 is a structural schematic diagram of a seventh battery cell according to an embodiment of the present application.

[0033] Figure 8 FIG. 8 is a structural schematic diagram of an eighth battery cell according to an embodiment of the present application.

[0034] BRIEF DESCRIPTION OF DRAWINGS

[0035] 1, first electrode; 1011, current collector; 1012, active material layer; 10121, thinning area; 10122, third side; 10123, fourth side; 102, separator; 103, flat area; 104, circular arc area;

[0036] 2, second electrode; 201, first side; 202, second side;

[0037] 3, first insulating layer; 301, middle part; 302, lap joint part;

[0038] 4, second insulating layer. ​​DETAILED DESCRIPTION

[0039] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of the present application.

[0040] The embodiments of the present application are described below with reference to the accompanying drawings. Figures 1 to 8

[0041] According to the embodiments of the present application, in one aspect, an electric core is provided, comprising: a first electrode 1, a diaphragm 102 and a plurality of second electrodes 2, wherein the diaphragm 102 comprises sub-diaphragms located on opposite sides of the first electrode 1, the sub-diaphragms comprise extension parts beyond the first electrode 1 along the width direction of the first electrode 1, and the extension parts are bonded to each other; the first electrode 1 and the diaphragm 102 form a composite diaphragm electrode sheet, the composite diaphragm electrode sheet has a plurality of flat areas 103 and circular arc areas 104, the circular arc areas 104 are connected to adjacent flat areas 103, and the circular arc areas 104 have inner arc top ends; the plurality of second electrodes 2 are cross-stacked with the flat areas 103, and the end parts of the second electrodes 2 and the circular arc areas 104 are oppositely arranged along the width direction; the second electrode 2 has a first side surface 201 facing the circular arc area 104, and the distance between the first side surface 201 and the inner arc top end is A, wherein A≥0.1mm.

[0042] When the electric core of the present embodiment is manufactured, the first electrode 1 and the diaphragm 102 are compounded together to form a composite diaphragm electrode sheet, and then the continuous composite diaphragm electrode sheet is Z-stacked with the plurality of second electrodes 2. The edge of the continuous first electrode 1 does not have burrs, and the edge of the discontinuous second electrode 2 inevitably has burrs when cut. The burr of the second electrode 2 directly faces the circular arc area 104 of the continuous electrode, which is easy to pierce the diaphragm 102 and contact the continuous first electrode 1, thereby causing short circuit. In order to avoid short circuit, the distance between the first side surface 201 of the second electrode 2 and the inner arc top end of the circular arc area 104 is greater than or equal to 0.1mm. This distance can prevent the edge transverse burr of the second electrode 2 from piercing the diaphragm 102 of the circular arc area 104 and the first electrode 1 to form 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 sheet strip, and the second electrode 2 is a single electrode sheet after cutting.

[0044] In one embodiment, as Figure 1 and Figure 3 ​As shown, the first electrode 1 at the circular arc region 104 and the inner side of the sub-septum are provided with a first insulating layer 3. The inner side of the first electrode 1 at the circular arc region 104 is provided with the first insulating layer 3, which can effectively improve the insulation performance of the circular arc region and prevent the second electrode 2 from piercing the septum 102 and the first electrode 1 to cause short circuit.

[0045] Further, the surface resistance of the first insulating layer 3 is greater than the surface resistance of the septum 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 an 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 high polymer insulating coating, and an insulating adhesive paper. The inert substance coating has the advantages of high temperature resistance, good electrical insulation performance, and high mechanical strength. The organic high polymer insulating coating has the advantages of good flexibility and ductility, easy processing, light weight, and the like. The insulating adhesive paper has the advantages of strong usability and easy removal.

[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, polyamide-imide, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polyacrylonitrile, polyacrylate, polyacrylic acid, sodium polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, or polyhexafluoropropylene; and the inert substance includes at least one of silicon dioxide, aluminum fluoride, aluminum oxide, silicon monoxide, 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] Further, the organic high polymer insulating coating includes at least one of polyimide, silicone resin, epoxy resin, polyurethane, acrylic resin, silicone mastic, polytetrafluoroethylene, polystyrene, polyethylene, and polypropylene.

[0049] Further, the insulating adhesive paper includes one of polyimide, polyethylene terephthalate (PET) adhesive paper, barley paper, aramid paper, glass fiber adhesive tape, and polypropylene adhesive paper.

[0050] In one embodiment, as Figure 4 and Figure 5As shown, the first side surface 201 is provided with the 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 edge of the current collector 1011 of the second electrode 2 from piercing the diaphragm 102 to cause short circuit.

[0051] Further, the surface resistance of the second insulating layer 4 is greater than the surface resistance 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 an 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 substance coating, an organic polymer insulating coating, and an insulating adhesive paper. The materials of the first insulating layer 3 and the second insulating layer 4 are the same, and will not be described in detail here.

[0053] In one embodiment, as shown in Figure 4 and Figure 5 The second electrode 2 has two opposite surfaces, and the second insulating layer 4 covers the portions of the two surfaces close to the circular arc region 104 and the first side surface 201. The second insulating layer 4 is in a U shape, and the second insulating layer 4 covers the first side surface 201 of the second electrode 2 and the edge portions of the two surfaces. The edge of the second electrode 2 has better insulation performance, which effectively prevents 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 4μm-20μm, and the width C of the second insulating layer 4 along the extension direction of the flat region 103 is 10μm-20μm. 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 to cause short circuit. The width C of the second insulating layer 4 is greater than the edge powder width of the first electrode 1, which can effectively prevent the edge powder from causing the battery to fail the pressure test after hot pressing and the dust from falling into the battery to cause the battery to fail the 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, i.e., the Z stacking direction of the battery cell. The K value refers to the voltage drop of the battery per unit time.

[0056] In one embodiment, as shown in Figure 2 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 0.2mm-10mm. The distance D ensures that the first insulating layer 3 does not enter the opposite region of the first electrode 1 and the second electrode 2, thereby ensuring the consistency of the battery thickness and reducing the battery internal resistance.

[0057] In one embodiment, such as 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 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 separator 102 and causing a short circuit, thus 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, and the first electrode 1 includes a current collector 1011 and active material layers 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 thinning region 10121, the thickness G of the thinning region 10121 is 10 μm-100 μm, and the thickness H of the active material layer 1012 in the straight region 103, wherein E+G≤H. This structure reduces the thickness of the arc region 104, ensuring that the two sides are not excessively thick, preventing the formation of bubbles when the separator 102 and the first electrode 1 are combined, and reducing the risk of lithium plating in the arc region of the battery.

[0059] Furthermore, the two ends of the arc region 104 are thinning areas 10121, or the entire arc region 104 is a thinning area 10121.

[0060] Specifically, the middle portion of the inner side of the current collector 1011 in the arc region 104 is not coated with the active material layer 1012, while the two ends of the inner side of the current collector 1011 in the arc region 104 are coated with the active material layer 1012. The first insulating layer 3 has a middle portion 301 disposed on the current collector 1011 without the active material layer 1012 and an overlapping portion 302 overlapping the active material layer 1012. The current collector 1011 without the active material layer 1012 can also be referred to as the empty foil region.

[0061] It should be noted that, Figure 6 and Figure 7 The rectangular dashed box in the figure refers to the active material layer 1012 that was removed.

[0062] In one embodiment, such as Figure 6 and Figure 7As shown, the first electrode 1 includes a current collector 1011 and active material layers 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 thinning region 10121. The width F of the first insulating layer 3 along the unfolding direction of the cell and the width K of the thinning region 10121 along the unfolding direction of the cell satisfy: 30% ≤ F / K < 100%. This structure reduces the thickness of the arc region 104, ensuring that the two sides are not excessively thick, preventing the formation of bubbles when the separator 102 and the first electrode 1 are combined, and reducing the risk of lithium plating 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 for the thickness H of the active material layer 1012 in the flat region 103, the width F of the first insulating layer 3, and the width K of the thinning region 10121 are all mm.

[0065] In one embodiment, such as Figure 8 As shown, the first electrode 1 is the positive electrode, and the second electrode 2 is the negative electrode. The first electrode 1 in 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, and the fourth side 10123 is disposed close to the second side 202. 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 reduces the energy density loss of the battery and ensures that the negative electrode covers the positive electrode, reducing the risk of lithium plating in the battery.

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

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

[0068] According to an embodiment of the present invention, in another aspect, a secondary battery is also provided, comprising: the aforementioned battery cell.

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

[0070] During cell manufacturing, the first electrode 1 with multiple tabs is thermally bonded to the separator 102 to form a continuous composite separator electrode sheet. Then, it is Z-stacked with several second electrodes 2. This effectively prevents the active material on the first electrode 1 from falling onto the separator 102 during cutting, which would affect the cell's K-value. This also prevents damage to the separator 102 from causing micro-short circuits inside the cell, effectively reducing the cell's K-value. At the same time, in the width direction, one electrode sheet of the cell is always covered by the arc area 104 of another electrode sheet, leaving no allowance. This simplifies the process and significantly improves process efficiency. It can reduce the short circuit rate of the continuous electrode arc area of ​​the thermally bonded Z-stacked battery, with a battery insulation resistance ≥0.1 megohms; reduce micro-short circuits in the thermally bonded Z-stacked battery, with a K-value less than 0.1 mV / h; and ensure the thickness consistency of the thermally bonded Z-stacked battery, with a battery flatness ≤0.1 mm.

[0071] In one embodiment, the secondary battery further includes a casing, the casing having a receiving cavity, and the battery cell being disposed within the receiving cavity of the casing. The casing protects the battery cell from physical damage and chemical corrosion. Secondary batteries offer advantages such as high energy density, long cycle life, no memory effect, and low self-discharge rate.

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

Claims

1. A battery cell, characterized in that, include: A first electrode (1), a diaphragm (102), and a plurality of second electrodes (2), wherein the diaphragm (102) includes sub-diaphragms located on opposite sides of the first electrode (1), the sub-diaphragms including extensions extending beyond the first electrode (1) along the width direction of the first electrode (1), the extensions being bonded to each other. The first electrode (1) and the diaphragm (102) form a composite diaphragm electrode sheet, the composite diaphragm electrode sheet having multiple flat regions (103) and arc regions (104), the arc regions (104) connecting adjacent flat regions (103), and the arc regions (104) having an inner arc top; Multiple second electrodes (2) are stacked intersectingly with the flat region (103), and the ends of the second electrodes (2) and the arc region (104) are arranged opposite each other along the width direction; 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 ≥ 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 sheet resistance of the first insulating layer (3) is greater than the sheet resistance of the diaphragm (102).

4. The battery cell according to claim 2, characterized in that, The first side (201) is provided with a second insulating layer (4), which 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 opposing surfaces, and the second insulating layer (4) covers the portions of the two surfaces near the arcuate 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 4μm-20μm; And / or, along the extension direction of the straight region (103), the width C of the second insulating layer (4) is 10μm-20μm; And / or, after the battery cell is unfolded, the distance D between the first side surface (201) and the side of the first insulating layer (3) closest to the first side surface (201) is 0.2mm-10mm; And / or, the thickness E of the first insulating layer (3) is 5μm-20μm; And / or, the width F of the first insulating layer (3) along the unfolding direction of the battery cell is 1mm-10mm.

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 5μm-20μm. The first electrode (1) includes a current collector (1011) and active material layers (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) is a thinning region (10121). The thickness G of the thinning region (10121) is 10μm-100μm. The thickness H of the active material layer (1012) in the straight region (103) is 10μm-100μm. Wherein, E+G≤H.

8. The battery cell according to any one of claims 2 to 6, characterized in that, The first electrode (1) includes a current collector (1011) and active material layers (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 thinning region (10121). The width F of the first insulating layer (3) along the unfolding direction of the cell and the width K of the thinning region (10121) along the unfolding direction of the 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) in 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 surface (202) disposed opposite to the first side surface (201). The active material layer (1012) has a third side surface (10122) and a fourth side surface (10123) disposed at intervals along the winding direction of the battery cell. The third side surface (10122) is disposed close to the first side surface (201), and the fourth side surface (10123) is disposed 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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