Cell, secondary battery, and electronic device

Abstract

The invention discloses a battery cell, a secondary battery and an electronic device, the battery cell comprises an electrode assembly, and the thickness direction of the electrode assembly is a first direction. The electrode assembly comprises a first pole piece, a diaphragm and a second pole piece which are stacked and wound. The electrode assembly comprises a first straight section, a first bent section, a second straight section and a second bent section which are connected in sequence. The first straight section and the second straight section are oppositely arranged in the first direction, and the first bent section and the second bent section are oppositely arranged in the second direction. The first pole piece comprises a first current collector, a first active material layer and a first solid electrolyte layer. The first active material layer is arranged on at least one side surface of the first current collector along the thickness direction of the first current collector. And in at least part of the first pole piece located at the first bending section and / or the second bending section, a first solid electrolyte layer is arranged in at least part of the area, far away from the surface of the first current collector, of the first active material layer. The battery cell is favorable for improving the cycle performance.

Description

Technical Field

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

[0002] In existing wound cells, the corners have a large tension, which results in a small gap between the corner pole pieces. During the cell cycle, the corners are prone to lithium deposition or electrolyte infiltration and bridge breakage due to insufficient electrolyte, which reduces the cell cycle performance. Summary of the invention

[0003] In view of the above situation, the present application provides a battery cell, which is beneficial to improving the cycle performance of the battery cell.

[0004] An embodiment of the present application provides a battery cell, which includes an electrode assembly, and the thickness direction of the electrode assembly is a first direction. The electrode assembly includes a first pole piece, a diaphragm, and a second pole piece stacked and wound. The electrode assembly includes a first straight section, a first bent section, a second straight section, and a second bent section connected in sequence. Observed along a third direction, the first straight section and the second straight section are arranged relative to each other along the first direction, and the first bent section and the second bent section are arranged relative to each other along the second direction. The first direction, the second direction, and the third direction are perpendicular to each other. The first pole piece includes a first current collector, a first active material layer, and a first solid electrolyte layer. Along the thickness direction of the first current collector, the first active material layer is arranged on at least one side surface of the first current collector. In at least a portion of the first pole piece located in the first bent section and / or the second bent section, a first solid electrolyte layer is provided in at least a portion of the surface of the first active material layer away from the first current collector.

[0005] In the above-mentioned battery cell, the first solid electrolyte layer can provide physical support for the first bending section and / or the second bending section, thereby improving the structural stability of the corners of the battery cell. The first solid electrolyte layer can also promote the desolvation of lithium ions through dielectric action, thereby providing ion channels at the corners of the battery cell, reducing the risk of interface problems such as lithium deposition or electrolyte infiltration and bridge breakage at the corners of the battery cell due to insufficient electrolyte, thereby improving the cycle performance of the battery cell. At the same time, since the lithium deposition problem at the corner position is solved, the expansion rate of the battery cell is reduced.

[0006] In some embodiments of the present application, along the third direction, the ratio of the length of the first solid electrolyte layer to the length of the first active material layer where the first solid electrolyte layer is located is A 1 , 60%≤A 1 ≤100%, so as to reduce the risk of interface problems such as lithium deposition or electrolyte infiltration and bridge breaking due to insufficient electrolyte at the corners of the battery cell, improve the cycle performance of the battery cell, and help reduce the space waste caused by the first solid electrolyte layer protruding from the first active material layer, thereby improving the energy density of the battery cell.

[0007] In some embodiments of the present application, in at least a portion of the first electrode sheet located in the first bending section or the second bending section, along the winding direction of the first electrode sheet, the ratio of the width of the first solid electrolyte layer to the width of the first active material layer where the first solid electrolyte layer is located is B 1 , 50%≤B 1 ≤100%, so as to reduce the risk of interface problems such as lithium deposition or electrolyte infiltration and bridge breaking due to insufficient electrolyte at the corners of the battery cell, improve the cycle performance of the battery cell, and help reduce the space waste caused by the first solid electrolyte layer protruding from the first active material layer, thereby improving the energy density of the battery cell.

[0008] In some embodiments of the present application, the coating weight per unit area of ​​the first solid electrolyte layer is W 1 , 0.5mg / cm 2 ≤W 1 ≤5mg / cm 2 , when W 1 If W is too small, the lithium ion transmission efficiency will be reduced. 1 If W is too large, the thickness of the solid electrolyte layer will be too thick, affecting the volume energy density of the battery cell, and increasing the transmission path of lithium ions, as well as increasing production costs and material costs. 1 Set to 0.5mg / cm 2 ≤W 1 ≤5mg / cm 2 , in order to improve the lithium ion transmission efficiency and the energy density of the battery cell, and to shorten the lithium ion transmission path and reduce material and production costs.

[0009] In some embodiments of the present application, 1 mg / cm 2 ≤W 1 ≤3mg / cm 2 , in order to further improve the lithium ion transmission efficiency and the energy density of the battery cell, and further help shorten the lithium ion transmission path and reduce material costs and production costs.

[0010] In some embodiments of the present application, the first solid electrolyte layer includes a first solid electrolyte, and the material of the first solid electrolyte includes at least one of an organic solid electrolyte and an inorganic solid electrolyte; wherein the organic solid electrolyte includes a block copolymer, the block copolymer includes a conductive polymer and a lithium-conducting polymer, the conductive polymer includes at least one of pyrrole, aniline, thiophene, polyacetylene, p-phenylene terephthalamide or 3,4-ethylenedioxythiophene, and the lithium-conducting polymer includes at least one of polyethylene oxide, polyethylene glycol, polypropylene oxide, poly(ethylene glycol) acrylate or poly(ethylene glycol) methacrylate; the inorganic solid electrolyte includes at least one of an oxide solid electrolyte and a sulfide solid electrolyte, the oxide solid electrolyte includes at least one of lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide or lithium lanthanum titanate, and the sulfide solid electrolyte includes at least one of lithium sulfur silver germanium and lithium sulfur phosphorus.

[0011] In some embodiments of the present application, the first solid electrolyte layer also includes a first binder and a first conductor, the material of the first binder includes at least one of polyvinylidene fluoride, polyacrylic acid and carboxymethyl cellulose, and the material of the first conductor includes at least one of carbon nanotubes, carbon black, conductive graphite and graphene.

[0012] In some embodiments of the present application, the ratio of the mass of the first binder to the mass of the first solid electrolyte layer is W 2 , 1% ≤ W 2 ≤10% to increase the peel strength between the first solid electrolyte layer and the first active material layer and improve the cycle performance of the battery. 1 If W is too small, the solid electrolyte layer is prone to powdering and falling off, affecting the stability and life of the battery cell. 1 If it is too large, it may increase the mechanical stress between the solid electrolyte layer and the active material layer, causing the battery cell to deform easily.

[0013] In some embodiments of the present application, the first pole piece includes a second solid electrolyte layer and a third solid electrolyte layer. In the first pole piece located in the first straight section, a second solid electrolyte layer is provided in a partial area of ​​the surface of the first active material layer away from the first current collector. In the first pole piece located in the second straight section, a third solid electrolyte layer is provided in a partial area of ​​the surface of the first active material layer away from the first current collector. The second solid electrolyte layer and the third solid electrolyte layer can promote the desolvation of lithium ions through dielectricization, thereby cooperating with the first solid electrolyte layer to expand the range of the ion channel, further reducing the risk of interface problems such as lithium precipitation or electrolyte infiltration and broken bridges at the corners of the battery cell due to insufficient electrolyte, thereby improving the cycle performance of the battery cell.

[0014] In some embodiments of the present application, the first bending section includes N 1The first pole piece is located at 1 / 3N inside the first bending section. 1 In the first electrode sheet of the layer, along the winding direction of the first electrode sheet, the two ends of the first solid electrolyte layer are respectively connected to the second solid electrolyte layer and the third solid electrolyte layer, so as to specifically expand the range of the ion channel inside the first bending section, reduce the risk of interface problems such as lithium deposition or electrolyte infiltration and bridge breaking due to insufficient electrolyte inside the first bending section, and thus improve the cycle performance of the battery cell.

[0015] In some embodiments of the present application, the second bending section includes N 2 The first pole piece is located at 1 / 3N inside the second bending section. 2 In the first electrode sheet of the layer, along the winding direction of the first electrode sheet, the two ends of the first solid electrolyte layer are respectively connected to the second solid electrolyte layer and the third solid electrolyte layer, so as to specifically expand the range of the ion channel inside the second bending section, reduce the risk of interface problems such as lithium deposition or electrolyte infiltration and bridge breaking due to insufficient electrolyte in the first electrode sheet inside the second bending section, thereby improving the cycle performance of the battery cell.

[0016] In some embodiments of the present application, along the second direction, the length of the second solid electrolyte layer is L 1 , 0.5mm≤L 1 ≤2mm, which is beneficial to improving the cycle performance and energy density of the battery. And / or along the second direction, the length of the third solid electrolyte layer is L 2 , 0.5mm≤L 2 ≤2mm, which is beneficial to improving the cycle performance and energy density of the battery.

[0017] In some embodiments of the present application, 1 mm ≤ L 1 ≤1.5mm; and / or, 1mm≤L 2 ≤1.5mm.

[0018] In some embodiments of the present application, the first pole piece is a negative pole piece, and the second pole piece is a positive pole piece.

[0019] In some embodiments of the present application, the second pole piece includes a second current collector, a second active material layer and a fourth solid electrolyte layer. Along the thickness direction of the second current collector, the second active material layer is arranged on at least one side surface of the second current collector. In at least a portion of the second pole piece located in the first bending section and / or the second bending section, a fourth solid electrolyte layer is provided in at least a portion of the surface of the second active material layer away from the second current collector.

[0020] In some embodiments of the present application, in the second electrode sheet of the same layer located in the first bending section, on the side facing the winding center of the electrode assembly, the ratio of the area of ​​the fourth solid electrolyte layer to the area of ​​the second active material layer where the fourth solid electrolyte layer is located is C1 On the side away from the winding center of the electrode assembly, the ratio of the area of ​​the fourth solid electrolyte layer to the area of ​​the second active material layer where the fourth solid electrolyte layer is located is C 2 ; C 1 >C 2 , so that the first solid electrolyte layer provides the first pole sheet with sufficient ion channels for receiving lithium ions on the side facing the winding center of the electrode assembly, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell.

[0021] In some embodiments of the present application, in the second electrode sheet of the same layer located in the second bending section, on the side facing the winding center of the electrode assembly, the ratio of the area of ​​the fourth solid electrolyte layer to the area of ​​the second active material layer where the fourth solid electrolyte layer is located is C 1 '; On the side away from the winding center of the electrode assembly, the ratio of the area of ​​the fourth solid electrolyte layer to the area of ​​the second active material layer where the fourth solid electrolyte layer is located is C 2 ′; C 1 ′>C 2 ', so that the fourth solid electrolyte layer can provide the first electrode sheet with an ion channel sufficient to receive lithium ions on the side facing the winding center of the electrode assembly, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell.

[0022] In some embodiments of the present application, in the second electrode sheet of the same layer located in the first bending section, on the side facing the winding center of the electrode assembly, the coating weight per unit area of ​​the fourth solid electrolyte layer is W 3 On the side away from the winding center of the electrode assembly, the coating weight per unit area of ​​the fourth solid electrolyte layer is W 4 ; W 3 >W 4 , so that the fourth solid electrolyte layer can provide the first electrode sheet with an ion channel sufficient to receive lithium ions on the side facing the winding center of the electrode assembly, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell.

[0023] In some embodiments of the present application, in the second electrode sheet of the same layer located in the second bending section, on the side facing the winding center of the electrode assembly, the coating weight per unit area of ​​the fourth solid electrolyte layer is W 3 '; On the side away from the winding center of the electrode assembly, the coating weight per unit area of ​​the fourth solid electrolyte layer is W 4 ′;W 3 ′>W 4 ', so that the first solid electrolyte layer can provide the first pole sheet with an ion channel sufficient to receive lithium ions on the side facing the winding center of the electrode assembly, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell.

[0024] In some embodiments of the present application, in the first electrode sheet of the same layer located in the first bending section, on the side facing the winding center of the electrode assembly, the ratio of the area of ​​the first solid electrolyte layer to the area of ​​the first active material layer where the first solid electrolyte layer is located is C 3 On the side away from the winding center of the electrode assembly, the ratio of the area of ​​the first solid electrolyte layer to the area of ​​the first active material layer where the first solid electrolyte layer is located is C 4 ; C 4 >C 3 , so that the first solid electrolyte layer can provide the first pole sheet with sufficient ion channels for receiving lithium ions on the side away from the winding center of the electrode assembly, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell.

[0025] In some embodiments of the present application, in the first electrode sheet of the same layer located in the second bending section, on the side facing the winding center of the electrode assembly, the ratio of the area of ​​the first solid electrolyte layer to the area of ​​the first active material layer where the first solid electrolyte layer is located is C 3 '; On the side away from the winding center of the electrode assembly, the ratio of the area of ​​the first solid electrolyte layer to the area of ​​the first active material layer where the fourth solid electrolyte layer is located is C 4 ′; C 4 ′>C 3 ', so that the first solid electrolyte layer can provide the first pole sheet with an ion channel sufficient to receive lithium ions on the side away from the winding center of the electrode assembly, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell.

[0026] In some embodiments of the present application, in the first electrode sheet of the same layer located in the first bending section, on the side facing the winding center of the electrode assembly, the coating weight per unit area of ​​the first solid electrolyte layer is W 5 On the side away from the winding center of the electrode assembly, the coating weight per unit area of ​​the first solid electrolyte layer is W 6 ; W 6 >W 5 , so that the first solid electrolyte layer can provide the first pole sheet with sufficient ion channels for receiving lithium ions on the side away from the winding center of the electrode assembly, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell.

[0027] In some embodiments of the present application, in the first electrode sheet of the same layer located in the second bending section, on the side facing the winding center of the electrode assembly, the coating weight per unit area of ​​the first solid electrolyte layer is W 5 '; On the side away from the winding center of the electrode assembly, the coating weight per unit area of ​​the first solid electrolyte layer is W 6 ′;W 6 ′>W5 ', so that the first solid electrolyte layer can provide the first pole sheet with an ion channel sufficient to receive lithium ions on the side away from the winding center of the electrode assembly, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell.

[0028] An embodiment of the present application further provides a secondary battery, which includes any one of the battery cells in the above embodiments.

[0029] An embodiment of the present application further provides an electronic device, which includes the secondary battery in the above embodiment.

[0030] In the above-mentioned battery cell, secondary battery and electronic device, the first solid electrolyte layer can provide physical support for the first bending section and / or the second bending section, thereby improving the structural stability of the corner of the battery cell. The first solid electrolyte layer can also promote the desolvation of lithium ions through dielectric action, thereby providing ion channels at the corners of the battery cell, reducing the risk of interface problems such as lithium precipitation or electrolyte infiltration and bridge breaking due to insufficient electrolyte at the corners of the battery cell, thereby improving the cycle performance of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic structural diagram of a battery cell observed along a third direction in an embodiment of the present application.

[0032] Figure 2 It is a schematic structural diagram of a first pole piece having a first solid electrolyte layer in a battery cell in an embodiment of the present application.

[0033] Figure 3 It is a schematic diagram of the structure of the second solid electrolyte layer and the third solid electrolyte layer of the battery cell in one embodiment of the present application.

[0034] Figure 4 It is a schematic structural diagram of the fourth solid electrolyte layer of a battery cell in one embodiment of the present application.

[0035] Figure 5 It is a schematic diagram of the structure in which a secondary battery is assembled in an electronic device in one embodiment of the present application.

[0036] Main component symbols

[0037] Battery Cell 100

[0038] Secondary battery 200

[0039] Electronic device 300

[0040] Electrode assembly 10

[0041] The first straight section 10A

[0042] The first bending section 10B

[0043] The second straight section 10C

[0044] The second bending section 10D

[0045] The first pole piece 11

[0046] First current collector 111

[0047] First active material layer 112

[0048] First Area 1121

[0049] Second area 1122

[0050] Third Area 1123

[0051] First solid electrolyte layer 113

[0052] Second solid electrolyte layer 114

[0053] The third solid electrolyte layer 115

[0054] Diaphragm 12

[0055] The second pole piece 13

[0056] Second current collector 131

[0057] Second active material layer 132

[0058] Fourth solid electrolyte layer 133

[0059] First tab 20

[0060] Second pole ear 30

[0061] First direction X

[0062] Second direction Y

[0063] The third direction Z

[0064] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0065] 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 of the embodiments.

[0066] It should be noted that when an element is considered to be "connected" to another element, it may be directly connected to the other element or there may be a centrally disposed element at the same time. When an element is considered to be "disposed" on another element, it may be directly disposed on the other element or there may be a centrally disposed element at the same time.

[0067] When a value is considered to be "equal" to another value, it means that the two are equal within a set deviation, and the set deviation range is within 5%. In other words, when at least one of the two values ​​fluctuates within the set deviation range, even if their values ​​are not equal, they are still judged to be approximately equal. When a value is considered to be in a ratio of "1:1" to another value, it means that the two are equal within a set deviation, and the set deviation range is within 5%. In other words, when at least one of the two values ​​fluctuates within the set deviation range, even if their values ​​are not equal, they are still judged to be equal in ratio.

[0068] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more related listed items. The term "overlap" used herein refers to the overlap of the projections of two parts or the overlap of the projections of two parts.

[0069] An embodiment of the present application provides a battery cell, which includes an electrode assembly, and the thickness direction of the electrode assembly is a first direction. The electrode assembly includes a first pole piece, a diaphragm, and a second pole piece stacked and wound. The electrode assembly includes a first straight section, a first bent section, a second straight section, and a second bent section connected in sequence. Observed along a third direction, the first straight section and the second straight section are arranged relative to each other along the first direction, and the first bent section and the second bent section are arranged relative to each other along the second direction. The first direction, the second direction, and the third direction are perpendicular to each other. The first pole piece includes a first current collector, a first active material layer, and a first solid electrolyte layer. Along the thickness direction of the first current collector, the first active material layer is arranged on at least one side surface of the first current collector. In at least a portion of the first pole piece located in the first bent section and / or the second bent section, a first solid electrolyte layer is provided in at least a portion of the surface of the first active material layer away from the first current collector.

[0070] In the above-mentioned battery cell, the first solid electrolyte layer can provide physical support for the first bending section and / or the second bending section, thereby improving the structural stability of the corners of the battery cell. The first solid electrolyte layer can also promote the desolvation of lithium ions through dielectric action, thereby providing ion channels at the corners of the battery cell, reducing the risk of interface problems such as lithium deposition or electrolyte infiltration and bridge breaking due to insufficient electrolyte at the corners of the battery cell, thereby improving the cycle performance of the battery cell.

[0071] The embodiments of the present application are further described below in conjunction with the accompanying drawings.

[0072] See also Figure 1 , an embodiment of the present application provides a battery cell 100. The battery cell 100 includes an electrode assembly 10, a first pole tab 20, and a second pole tab 30. The electrode assembly 10 is used to convert chemical energy into electrical energy. The polarity of the first pole tab 20 is opposite to the polarity of the second pole tab 30. One end of the first pole tab 20 is connected to the electrode assembly 10, and the other end of the first pole tab 20 is configured to be electrically connected to an external circuit. One end of the second pole tab 30 is connected to the electrode assembly 10, and the other end of the second pole tab 30 is configured to be electrically connected to an external circuit.

[0073] The thickness direction of the electrode assembly 10 is the first direction X, the width direction of the electrode assembly 10 is the second direction Y, and the length direction of the electrode assembly 10 is the third direction Z. The first direction X, the second direction Y and the third direction Z are perpendicular to each other.

[0074] The electrode assembly 10 includes a first electrode sheet 11 , a separator 12 , and a second electrode sheet 13 which are stacked and wound. The first electrode tab 20 is connected to the first electrode sheet 11 , and the second electrode tab 30 is connected to the second electrode sheet 13 .

[0075] The electrode assembly 10 includes a first straight section 10A, a first bent section 10B, a second straight section 10C, and a second bent section 10D connected in sequence. When viewed along the third direction Z, the first straight section 10A and the second straight section 10C are arranged opposite to each other along the first direction X. The first bent section 10B and the second bent section 10D are arranged opposite to each other along the second direction Y. The first bent section 10B and the second bent section 10D are located at the corners of the battery cell 100.

[0076] It should be noted that the test reference standard used for the specific position of the boundary between the straight section and the bent section is: ISO15708:2002 "Non-destructive testing-Radiation methods-Computed tomography". The specific test method is: place the battery cell on the stage of an X-ray computed tomography scanner after discharging, and measure the angle of the outer contour of the electrode assembly every 1 mm near the junction of the straight section and the bent section of the battery cell, along the direction from the straight section to the bent section, using an X-ray computed tomography scanner. When the angle deviation between the outer contour of the electrode assembly and the width direction of the electrode assembly is equal to 1°, it is defined as the boundary between the straight section and the bent section; the extension line passing through the boundary between the straight section and the bent section and extending along the length direction of the electrode assembly is defined as the boundary between the straight section and the bent section.

[0077] Please continue reading Figure 1 , the first pole piece 11 includes a first current collector 111, a first active material layer 112 and a first solid electrolyte layer 113. Along the thickness direction of the first current collector 111, the first active material layer 112 is disposed on at least one side surface of the first current collector 111. In at least a portion of the first pole piece 11 located in the first bending section 10B and / or the second bending section 10D, at least a portion of the surface of the first active material layer 112 away from the first current collector 111 is provided with the first solid electrolyte layer 113.

[0078] The first solid electrolyte layer 113 can provide physical support for the first bending segment 10B and / or the second bending segment 10D, thereby improving the structural stability of the corners of the battery cell 100. The first solid electrolyte layer 113 can also promote the desolvation of lithium ions through dielectric action, thereby providing ion channels at the corners of the battery cell 100, reducing the risk of interface problems such as lithium deposition or electrolyte infiltration and bridge breakage at the corners of the battery cell 100 due to insufficient electrolyte, thereby improving the cycle performance of the battery cell 100.

[0079] Please also read Figure 1 and Figure 2 In some embodiments, along the third direction Z, the ratio of the length of the first solid electrolyte layer 113 to the length of the first active material layer 112 where the first solid electrolyte layer 113 is located is A 1 , 60%≤A 1 ≤100%. When A 1 When the value is too small (less than 60%), it is easy for other regions of the first active material layer 112 to produce lithium deposition or electrolyte infiltration and bridge breakage due to insufficient electrolyte, resulting in reduced cycle performance of the battery cell 100. 1When the value is too large (less than 100%), the first solid electrolyte layer 113 may easily protrude from the first active material layer 112, resulting in space waste, which may reduce the energy density of the battery cell 100. 1 ≤100%, so as to reduce the risk of interface problems such as lithium deposition or electrolyte infiltration and bridge breaking due to insufficient electrolyte at the corners of the battery cell 100, improve the cycle performance of the battery cell 100, and help reduce the space waste caused by the first solid electrolyte layer 113 protruding from the first active material layer 112, thereby improving the energy density of the battery cell 100.

[0080] Optionally, A 1 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100% and 60%≤A 1 Any other value within the range of ≤100%.

[0081] The length of the first solid electrolyte layer 113 and the length of the first active material layer 112 are obtained by disassembling the electrode assembly 10, taking out the first pole piece 11, flattening the first pole piece 11, and then measuring with a ruler.

[0082] Please continue reading Figure 2 In some embodiments, when 60%≤A 1 When the ratio of the active material layer to the active material layer is less than 100%, the first active material layer 112 includes a first region 1121, a second region 1122, and a third region 1123 sequentially arranged along the third direction Z, wherein the first solid electrolyte layer 113 covers the second region 1122, and the first region 1121 and the third region 1123 are not provided with the first solid electrolyte layer 113. Along the third direction Z, the length of the first region 1121 is D 1 , the length of the third region 1123 is D 2 , D 1 and D 2 Adjust according to the diffusion difficulty of the electrolyte.

[0083] Specifically, along the third direction Z, when the infiltration difficulty of the electrolyte at the top of the corner of the battery cell 100 is higher than the infiltration difficulty of the electrolyte at the bottom of the corner of the battery cell 100 (such as when the top of the battery cell 100 faces upward and the bottom of the battery cell 100 faces downward), D 1 <D 2 , so as to reduce the risk of interface problems such as lithium deposition or electrolyte infiltration and bridge breakage due to insufficient electrolyte at the top of the corner of the battery cell 100, and improve the cycle performance of the battery cell 100. Along the third direction Z, when the infiltration difficulty of the electrolyte at the bottom of the corner of the battery cell 100 is higher than the infiltration difficulty of the electrolyte at the top of the corner of the battery cell 100 (such as when the bottom of the battery cell 100 faces upward and the top of the battery cell 100 faces downward), D 1 >D2 , so as to reduce the risk of interface problems such as lithium deposition or electrolyte infiltration and bridge breakage due to insufficient electrolyte at the bottom of the corner of the battery cell 100, and improve the cycle performance of the battery cell 100. Along the third direction Z, when the infiltration difficulty of the electrolyte at the top of the corner of the battery cell 100 is not significantly different from that at the bottom of the corner of the battery cell 100, D 1 =D 2 .

[0084] Please continue reading Figure 1 and Figure 2 In some embodiments, in at least a portion of the first electrode sheet 11 located in the first bending section 10B or the second bending section 10D, along the winding direction of the first electrode sheet 11, the ratio of the width of the first solid electrolyte layer 113 to the width of the first active material layer 112 where the first solid electrolyte layer 113 is located is B 1 , 50%≤B 1 ≤100%. When B 1 When B is too small (less than 60%), other regions of the first active material layer 112 may easily produce lithium deposition or electrolyte infiltration and bridge breakage due to insufficient electrolyte, resulting in reduced cycle performance of the battery cell 100. 1 When the value is too large (greater than 100%), the first solid electrolyte layer 113 may easily protrude from the first active material layer 112, resulting in space waste, which may reduce the energy density of the battery cell 100. 1 ≤100%, so as to reduce the risk of interface problems such as lithium deposition or electrolyte infiltration and bridge breaking due to insufficient electrolyte at the corners of the battery cell 100, improve the cycle performance of the battery cell 100, and help reduce the space waste caused by the first solid electrolyte layer 113 protruding from the first active material layer 112, thereby improving the energy density of the battery cell 100.

[0085] Optionally, B 1 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100% and 50% ≤ B 1 Any other value within the range of ≤100%.

[0086] The width of the first solid electrolyte layer 113 is obtained by disassembling the electrode assembly 10, taking out the first pole piece 11, flattening the first pole piece 11, and then measuring with a ruler. The width of the first active material layer 112 is the width of the first pole piece 11 located in the first bending section 10B or the second bending section 10D. After defining the range of the first bending section 10B and the second bending section 10D using the method mentioned above, the electrode assembly 10 is disassembled, the first pole piece 11 is taken out and flattened, and the width of each layer of the first pole piece 11 located in the first bending section 10B or the second bending section 10D is measured with a ruler to obtain the width of each layer of the first active material layer 112 located in the first bending section 10B or the second bending section 10D.

[0087] Please continue reading Figure 1 In some embodiments, the first solid electrolyte layer 113 is coated on the surface of the first active material layer 112 by extrusion spraying. The coating weight per unit area of ​​the first solid electrolyte layer 113 is W 1 , 0.5mg / cm 2 ≤W 1 ≤5mg / cm 2 When W 1 Too small (less than 0.5mg / cm 2 ), it is easy to make the first solid electrolyte layer 113 too thin and reduce the lithium ion transmission efficiency. 1 When it is too large (greater than 5mg / cm 2 ), it is easy to make the first solid electrolyte layer 113 too thick, resulting in reduced energy density, and also prolonging the lithium ion transmission path, increasing material costs and production costs. 2 ≤W 1 ≤5mg / cm 2 , so as to improve the lithium ion transmission efficiency and the energy density of the battery cell 100, and is conducive to shortening the transmission path of lithium ions and reducing material costs and production costs.

[0088] Optionally, W 1 0.5mg / cm 2 , 1mg / cm 2 , 1.5mg / cm 2 , 2mg / cm 2 , 2.5mg / cm 2 、3mg / cm 2 、3.5mg / cm 2 , 4mg / cm 2 , 4.5mg / cm 2 , 5mg / cm 2 and 0.5mg / cm 2 ≤W 1 ≤5mg / cm2 Any other value in the range.

[0089] The coating weight per unit area of ​​the first solid electrolyte layer 113 is W 1 The measurement can be performed in the following manner: 1) at a test temperature of 25°C, the secondary battery 200 is discharged to 0 SOC%, the first pole piece 11 is disassembled, and the first pole piece 11 is cleaned with dimethyl carbonate (DMC) and then dried; 2) a punching area S is cut from the first pole piece 11 of the first bending section 10B. 2 The first electrode sheet 11 of the embodiment is used as a sample of the first bending section 10B, wherein the area of ​​the first current collector 111, the area of ​​the first active material layer 112 and the area of ​​the first solid electrolyte layer 113 in the sample are all S 2 , weigh it using a balance, and record the weight as W 总 , the cross section of the sample of the first bending section 10B is observed under a scanning electron microscope, and a clear boundary line between the first active material layer 112 and the first solid electrolyte layer 113 can be observed. The thickness d of the first active material layer 112 is obtained by measuring the cross section of the sample using a scanning electron microscope. 1 ; 3) Use a scraper to scrape off the first solid electrolyte layer 113 and part of the first active material layer 112 located on the surface of the first active material layer 112. The scraping position needs to exceed the boundary between the first active material layer 112 and the first solid electrolyte layer 113 to ensure that the first solid electrolyte layer 113 is completely scraped off. Weigh the remaining first active material layer 112 and the first current collector 111, and record the weight as W'. Observe and measure the thickness d of the remaining first active material layer 112 under a scanning electron microscope. 2 , and then use solvent N-methylpyrrolidone (NMP) to wash away the remaining first active material layer 112, dry it, and weigh the weight of the first current collector 111, which is recorded as W 0 , calculate the compaction density ρ of the first active material layer 112 at the first bending section 10B 1 =(W′-W 0 ) / (d 2 ×S 2 ); 4) Calculate the coating weight per unit area of ​​the first solid electrolyte layer 113 by the following formula: W=[(W 总 -W 0 )-ρ 1 ×S 2 ×d 1 ] / S 2 .

[0090] Furthermore, 1 mg / cm 2 ≤W 1 ≤3mg / cm 2, so as to further improve the lithium ion transmission efficiency and the energy density of the battery cell 100, and further help to shorten the lithium ion transmission path and reduce material costs and production costs.

[0091] In some embodiments, the first solid electrolyte layer 113 includes a first binder, and the ratio of the mass of the first binder to the mass of the first solid electrolyte layer 113 is W. 2 , 1% ≤ W 2 ≤10%. When W 2 When W is too small (less than 1%), the peel strength between the first solid electrolyte layer 113 and the first active material layer 112 is likely to be weak. 2 When the ratio is too large (greater than 10%), the excessive adhesive may block the pores on the surface of the first active material layer 112, causing lithium deposition, thereby reducing the cycle performance of the battery cell 100. 2 ≤10%, so as to increase the peel strength between the first solid electrolyte layer 113 and the first active material layer 112 and improve the cycle performance of the battery cell 100 .

[0092] Optionally, W 2 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% and 1% ≤ W 2 Any other value within the range of ≤10%.

[0093] In some embodiments, the material of the first binder includes at least one of PVDF (polyvinylidene fluoride), PAA (polyacrylic acid), and CMC (carboxymethyl cellulose).

[0094] In some embodiments, the first solid electrolyte layer 113 includes a first conductive agent, and the material of the first conductive agent includes at least one of carbon nanotubes, carbon black, conductive graphite, and graphene.

[0095] In some embodiments, the ratio of the mass of the first conductive agent to the mass of the first solid electrolyte layer 113 is 0.1% to 3%.

[0096] It should be noted that, in the preparation process of the battery cell 100, the slurry of the first solid electrolyte layer 113 is first prepared, and then the slurry of the first solid electrolyte layer 113 is applied to the surface of the first active material layer 112 by extrusion spraying. The slurry of the first solid electrolyte layer 113 includes a first solid electrolyte, a solvent, a first binder and a first conductive agent. The material of the first solid electrolyte includes at least one of an organic solid electrolyte and an inorganic solid electrolyte; wherein the organic solid electrolyte includes a block copolymer, the block copolymer includes a conductive polymer and a lithium conductive polymer, the conductive polymer includes at least one of pyrrole, aniline, thiophene, polyacetylene, p-phenylene terephthalamide or 3,4-ethylenedioxythiophene, and the lithium conductive polymer includes at least one of polyethylene oxide, polyethylene glycol, polypropylene oxide, poly(ethylene glycol) acrylate or poly(ethylene glycol) methacrylate; the inorganic solid electrolyte includes at least one of an oxide solid electrolyte and a sulfide solid electrolyte, and the oxide solid electrolyte includes lithium aluminum titanium phosphate (LATP[Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 ]), lithium aluminum germanium phosphate (LAGP[Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 ]), lithium lanthanum zirconium oxide (Li 7 La 3 Zr 2 O 12 ), lithium lanthanum zirconium tantalum oxide, lithium zinc germanium oxide (LZGO [Li 14 ZnGeO 4 ]) or lithium lanthanum titanate, the sulfide solid electrolyte includes lithium silver germanium sulfur (LGPS, Li 10 G 2 S 12 ), lithium phosphorus sulfate (LPS, Li 2 SP 2 S 5 ) at least one of the following. The solvent includes N-methylpyrrolidone. The slurry of the first solid electrolyte layer 113 is cured to form the first solid electrolyte layer 113. Wherein, W 2 is the ratio of the mass of the first binder in the cured first solid electrolyte layer 113 to the mass of the first solid electrolyte layer 113. 2 The measurement method is as follows: a portion of the first solid electrolyte layer 113 is scraped off with a scraper on the first electrode 11 and the scraped first solid electrolyte layer 113 is collected, and the mass m of the scraped first solid electrolyte layer 113 is weighed with an electronic balance. 1; Then the scraped first solid electrolyte layer 113 is dissolved in N-methylpyrrolidone to prepare a solid electrolyte solution with a mass concentration of 0.5%, and the absorbance of the solid electrolyte solution is measured by infrared spectrometer, and compared with the absorbance of the standard solution, the mass m of the first binder in the solution is calculated. 2 ; The mass percentage content W of the first binder in the first solid electrolyte layer 113 2 =m 2 / m 1 ×100%.

[0097] Please continue reading Figure 1 and Figure 2 In some embodiments, the peel strength between the first solid electrolyte layer 113 and the first active material layer 112 is S 1 , 0.2N / m≤S 1 ≤5N / m. When S 1 When S is too small (less than 0.2 N / m), the first solid electrolyte layer 113 is likely to fall off, resulting in reduced cycle performance of the battery cell 100. 1 When the load is too large (greater than 5 N / m), the mechanical stress between the first solid electrolyte layer 113 and the first active material layer 112 is likely to increase, causing deformation of the electrode assembly 10. 1 ≤5N / m, so as to improve the cycle performance of the battery cell 100 and help improve the structural stability of the electrode assembly 10.

[0098] Optionally, S 1 0.2N / m, 0.5N / m, 1N / m, 1.5N / m, 2N / m, 2.5N / m, 3N / m, 3.5N / m, 4N / m, 4.5N / m, 5N / m and 0.2N / m≤S 1 Any other value within the range of ≤5N / m.

[0099] Furthermore, 1N / m≤S 1 ≤3N / m, so as to further improve the cycle performance of the battery cell 100 and further help to improve the structural stability of the electrode assembly 10.

[0100] See also Figure 3In some embodiments, the first pole piece 11 includes a second solid electrolyte layer 114 and a third solid electrolyte layer 115. In the first pole piece 11 located in the first straight section 10A, the second solid electrolyte layer 114 is provided in a partial area of ​​the surface of the first active material layer 112 away from the first current collector 111. In the first pole piece 11 located in the second straight section 10C, the third solid electrolyte layer 115 is provided in a partial area of ​​the surface of the first active material layer 112 away from the first current collector 111. The second solid electrolyte layer 114 and the third solid electrolyte layer 115 can promote the desolvation of lithium ions through dielectricization, thereby cooperating with the first solid electrolyte layer 113 to expand the range of the ion channel, further reducing the risk of interface problems such as lithium precipitation or electrolyte infiltration and broken bridges at the corners of the battery cell 100 due to insufficient electrolyte, thereby improving the cycle performance of the battery cell 100.

[0101] In some embodiments, the first bending segment 10B includes N 1 The first pole piece 11 is located at 1 / 3N of the inner side of the first bending section 10B. 1 In the first electrode sheet 11 of the first layer, along the winding direction of the first electrode sheet 11, the two ends of the first solid electrolyte layer 113 are connected to the second solid electrolyte layer 114 and the third solid electrolyte layer 115 respectively. Specifically, during the cycle of the battery cell 100, the electrolyte infiltration effect of the inner ring electrode sheet of the battery cell 100 is poorer than that of the outer ring electrode sheet, that is, the first electrode sheet 11 located on the inner side of the first bending section 10B is more likely to have the problem of insufficient electrolyte than the first electrode sheet 11 located on the outer side of the first bending section 10B. By 1 In the first electrode piece 11 of the layer, the two ends of the first solid electrolyte layer 113 are respectively connected to the second solid electrolyte layer 114 and the third solid electrolyte layer 115, so as to specifically expand the range of the ion channel inside the first bending segment 10B, reduce the risk of interface problems such as lithium deposition or electrolyte infiltration and bridge breaking due to insufficient electrolyte inside the first bending segment 10B, and thus improve the cycle performance of the battery cell 100.

[0102] Optionally, N 1=3, 6, 9, 12, 15, etc. It should be noted that when 1 / 3N 1 If it is a non-integer, it is smaller than and closest to 1 / 3N. 1 An integer is used as a reference, for example, N 1 =4, then in a first electrode sheet 11 located inside the first bending section 10B, the two ends of the first solid electrolyte layer 113 are connected to the second solid electrolyte layer 114 and the third solid electrolyte layer 115 respectively.

[0103] Please continue reading Figure 3 In some embodiments, the second bending segment 10D includes N 2The first pole piece 11 is located at 1 / 3N inside the second bending section 10D. 2 In the first electrode sheet 11 of the layer, along the winding direction of the first electrode sheet 11, the two ends of the first solid electrolyte layer 113 are connected to the second solid electrolyte layer 114 and the third solid electrolyte layer 115 respectively. Specifically, during the cycle of the battery cell 100, the electrolyte infiltration effect of the inner ring electrode sheet of the battery cell 100 is poorer than that of the outer ring electrode sheet, that is, the first electrode sheet 11 located on the inner side of the second bending section 10D is more likely to have the problem of insufficient electrolyte than the first electrode sheet 11 located on the outer side of the second bending section 10D. By 2 In the first electrode piece 11 of the layer, the two ends of the first solid electrolyte layer 113 are respectively connected to the second solid electrolyte layer 114 and the third solid electrolyte layer 115, so as to specifically expand the range of the ion channel inside the second bending segment 10D, reduce the risk of interface problems such as lithium deposition or electrolyte infiltration and bridge breaking due to insufficient electrolyte in the first electrode piece 11 inside the second bending segment 10D, and thus improve the cycle performance of the battery cell 100.

[0104] Optionally, N 2 =3, 6, 9, 12, 15, etc. What needs to be explained is that when 1 / 3N 2 When it is a non-integer, the integer less than and closest to 1 / 3N 1 is used as a reference, for example, N 2 =7, then in the two layers of the first electrode sheet 11 located inside the second bending section 10D, the two ends of the first solid electrolyte layer 113 are connected to the second solid electrolyte layer 114 and the third solid electrolyte layer 115 respectively.

[0105] Please continue reading Figure 3 In some embodiments, along the second direction Y, the length of the second solid electrolyte layer 114 is L 1 , 0.5mm≤L 1 ≤2mm. When L 1 If the diameter is too small (less than 0.5 mm), the range of the ion channel provided by the second solid electrolyte layer 114 is too narrow, resulting in reduced cycle performance of the battery cell 100. In addition, since the winding radius of the inner circle is relatively small, the 1 / 3N diameter of the inner circle is too small. 1 Layer or 1 / 3N 2 The first solid electrolyte layer 113 of the first bending section 10B or the second bending section 10D of the layer is prone to fall off. The provision of the second solid electrolyte layer 114 is conducive to increasing the overlapping area of ​​the solid electrolyte layer and the active material layer, reducing the risk of the solid electrolyte layer falling off. When the length L of the second solid electrolyte layer 114 is 1If the L is too small (less than 0.5 mm), the risk of the solid electrolyte layer falling off increases. The falling particles may pierce the diaphragm and cause a short circuit. 1 When the distance L is too large (greater than 2 mm), the second solid electrolyte layer 114 may occupy a large space in the first direction X, resulting in space waste, and thus reducing the energy density of the battery cell 100. 1 ≤2mm, which is beneficial to improving the cycle performance and energy density of the battery cell 100.

[0106] Optionally, L 1 0.5mm, 1mm, 1.5mm, 2mm and 0.5mm≤L 1 Any other value within the range of ≤2mm.

[0107] Furthermore, 1mm≤L 1 ≤1.5mm, which is beneficial to further improve the cycle performance and energy density of the battery cell 100.

[0108] Please continue reading Figure 3 In some embodiments, along the second direction Y, the length of the third solid electrolyte layer 115 is L 2 , 0.5mm≤L 2 ≤2mm. When L 2 If the diameter is too small (less than 0.5 mm), the range of the ion channel provided by the third solid electrolyte layer 115 is too narrow, resulting in reduced cycle performance of the battery cell 100. In addition, since the winding radius of the inner circle is relatively small, the 1 / 3N diameter of the inner circle is too small. 1 Layer or 1 / 3N 2 The first solid electrolyte layer 113 of the first bending section 10B or the second bending section 10D of the layer is prone to fall off. The provision of the third solid electrolyte layer 115 is conducive to increasing the overlapping area of ​​the solid electrolyte layer and the active material layer, reducing the risk of the solid electrolyte layer falling off. When the length L of the third solid electrolyte layer 115 is 1 If the L is too small (less than 0.5 mm), the risk of the solid electrolyte layer falling off increases. The falling particles may pierce the diaphragm and cause a short circuit. 2 When the distance L is too large (greater than 2 mm), the third solid electrolyte layer 115 may occupy a large space in the first direction X, resulting in space waste, and thus reducing the energy density of the battery cell 100. 2 ≤2mm, which is beneficial to improving the cycle performance and energy density of the battery cell 100.

[0109] Optionally, L 2 0.5mm, 1mm, 1.5mm, 2mm and 0.5mm≤L 2Any other value within the range of ≤2mm.

[0110] Furthermore, 1mm≤L 2 ≤1.5mm, which is beneficial to further improve the cycle performance and energy density of the battery cell 100.

[0111] Among them, the above L 1 and L 2 The testing method is to disassemble the electrode assembly 10, take out the first electrode piece 11, flatten the electrode piece, and use a ruler to measure the second solid electrolyte layer 114 located on the first straight section 10A to obtain L 1 , use a ruler to measure the length of the third solid electrolyte layer 115 located on the second straight section 10C to obtain L 2 .

[0112] Please continue reading Figure 1 In some embodiments, the first electrode 11 is a negative electrode, and the second electrode 13 is a positive electrode. The first solid electrolyte layer 113 is disposed on the first electrode 11 to better improve the corner interface, thereby achieving better improvement of corner expansion and improving the cycle life of the battery cell.

[0113] In some embodiments, the second pole piece 13 includes a second current collector 131, a second active material layer 132 and a fourth solid electrolyte layer 133. Along the thickness direction of the second current collector 131, the second active material layer 132 is disposed on at least one side surface of the second current collector 131. In at least part of the second pole piece 13 located in the first bending section 10B and / or the second bending section 10D, the fourth solid electrolyte layer 133 is provided in at least part of the surface of the second active material layer 132 away from the second current collector 131. The fourth solid electrolyte layer 133 can provide physical support for the first bending section 10B and / or the second bending section 10D, thereby improving the structural stability of the corners of the battery 100. The fourth solid electrolyte layer 133 can also promote the desolvation of lithium ions through dielectricization, thereby providing ion channels at the corners of the battery 100, reducing the risk of interface problems such as lithium precipitation or electrolyte infiltration and broken bridges at the corners of the battery 100 due to insufficient electrolyte, thereby improving the cycle performance of the battery 100.

[0114] In some embodiments, in the second electrode sheet 13 of the same layer located in the first bending section 10B, on the side facing the winding center of the electrode assembly 10, the ratio of the area of ​​the fourth solid electrolyte layer 133 to the area of ​​the second active material layer 132 where the fourth solid electrolyte layer 133 is located is C 1 On the side away from the winding center of the electrode assembly 10, the ratio of the area of ​​the fourth solid electrolyte layer 133 to the area of ​​the second active material layer 132 where the fourth solid electrolyte layer 133 is located is C 2 ; C1 >C 2 Specifically, at the corner of the battery cell 100, the second pole piece 13 covers the first pole piece 11. On the side of the second pole piece 13 facing the winding center, the winding radius of the second pole piece 13 is larger than the winding radius of the first pole piece 11. The corresponding CB value (the ratio of the negative electrode lithium insertion capacity of the battery cell to the positive electrode lithium removal capacity) of the first pole piece 11 and the second pole piece 13 is insufficient, and the risk of interface problems such as lithium deposition is relatively high. By limiting C 1 >C 2 , so that the fourth solid electrolyte layer 133 provides the first pole piece 11 with an ion channel sufficient to receive lithium ions on the side facing the winding center of the electrode assembly 10, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell 100.

[0115] In some embodiments, in the second electrode sheet 13 of the same layer located in the second bending section 10D, on the side facing the winding center of the electrode assembly 10, the ratio of the area of ​​the fourth solid electrolyte layer 133 to the area of ​​the second active material layer 132 where the fourth solid electrolyte layer 133 is located is C 1 '; On the side away from the winding center of the electrode assembly 10, the ratio of the area of ​​the fourth solid electrolyte layer 133 to the area of ​​the second active material layer 132 where the fourth solid electrolyte layer 133 is located is C 2 ′; C 1 ′>C 2 Specifically, at the corner of the battery cell 100, the second pole piece 13 covers the first pole piece 11. On the side of the second pole piece 13 facing the winding center, the winding radius of the second pole piece 13 is larger than the winding radius of the first pole piece 11. The corresponding CB value (the ratio of the negative electrode lithium insertion capacity of the battery cell to the positive electrode lithium removal capacity) of the first pole piece 11 and the second pole piece 13 is insufficient, and the risk of interface problems such as lithium deposition is relatively high. By limiting C 1 ′>C 2 ', so that the first solid electrolyte layer 113 provides the second pole piece 13 with an ion channel sufficient to receive lithium ions on the side facing the winding center of the electrode assembly 10, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell 100.

[0116] In the above embodiment, C 1 , C 2 , C 1 ′ and C 2The measurement method of ' is as follows: disassemble the electrode assembly 10, take out the second pole piece 13 and flatten it, use a ruler to measure the length and width of the fourth solid electrolyte layer 133 on the side facing the winding center and calculate the product to obtain the area of ​​the fourth solid electrolyte layer 133, use a ruler to measure the length and width of the corresponding second pole piece 13 in the first bending section 10B or the second bending section 10D and calculate the product to obtain the area of ​​the corresponding second pole piece 13 in the first bending section 10B or the second bending section 10D. Because there is no area in the second pole piece 13 in the first bending section 10B and the second bending section 10D that is not coated with the second active material layer 132, the area of ​​the corresponding second pole piece 13 in the first bending section 10B or the second bending section 10D used here is equivalent to the area of ​​the second active material layer 132 in the first bending section 10B or the second bending section 10D. Calculate the area of ​​the fourth solid electrolyte layer 133 and divide it by the area of ​​the second active material layer 132 to obtain C 1 or C 1 ′. C 2 or C 2 The measurement and calculation method of C 1 or C 1 The measurement and calculation methods of ′ are similar.

[0117] In some embodiments, in the second electrode sheet 13 of the same layer located in the first bending section 10B, on the side facing the winding center of the electrode assembly 10, the coating weight per unit area of ​​the fourth solid electrolyte layer 133 is W 3 On the side away from the winding center of the electrode assembly 10, the coating weight per unit area of ​​the fourth solid electrolyte layer 133 is W 4 ; W 3 >W 4 Specifically, at the corner of the battery cell 100, the second pole piece 13 covers the first pole piece 11. On the side of the second pole piece 13 facing the winding center, the winding radius of the second pole piece 13 is larger than the winding radius of the first pole piece 11. The corresponding CB value (the ratio of the negative electrode lithium insertion capacity of the battery cell to the positive electrode lithium removal capacity) of the first pole piece 11 and the second pole piece 13 is insufficient, and the risk of interface problems such as lithium deposition is relatively high. By limiting W 3 >W 4 , so that the fourth solid electrolyte layer 133 provides the first pole piece 11 with an ion channel sufficient to receive lithium ions on the side facing the winding center of the electrode assembly 10, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell 100.

[0118] In some embodiments, in the second electrode sheet 13 of the same layer located in the second bending section 10D, on the side facing the winding center of the electrode assembly 10, the coating weight per unit area of ​​the fourth solid electrolyte layer 133 is W 3'; On the side away from the winding center of the electrode assembly 10, the coating weight per unit area of ​​the fourth solid electrolyte layer 133 is W 4 ′;W 3 ′>W 4 '. Specifically, at the corner of the battery cell 100, the second pole piece 13 covers the first pole piece 11. On the side of the second pole piece 13 facing the winding center, the winding radius of the second pole piece 13 is larger than the winding radius of the first pole piece 11. The corresponding CB value (the ratio of the negative electrode lithium insertion capacity of the battery cell to the positive electrode lithium removal capacity) of the first pole piece 11 and the second pole piece 13 is insufficient, and the risk of interface problems such as lithium deposition is relatively high. By limiting W 3 ′>W 4 ', so that the fourth solid electrolyte layer 133 provides the first pole piece 11 with an ion channel sufficient to receive lithium ions on the side facing the winding center of the electrode assembly 10, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell 100.

[0119] The above W 3 , W 4 , W 3 ′ and W 4 The measurement method of ′ refers to W in the previous article. 1 measurement method.

[0120] Please continue reading Figure 4 In some embodiments, in the first electrode sheet 11 of the same layer located in the first bending section 10B, on the side facing the winding center of the electrode assembly 10, the ratio of the area of ​​the first solid electrolyte layer 113 to the area of ​​the first active material layer 112 where the first solid electrolyte layer 113 is located is C 3 On the side away from the winding center of the electrode assembly 10, the ratio of the area of ​​the first solid electrolyte layer 113 to the area of ​​the first active material layer 112 where the first solid electrolyte layer 113 is located is C 4 ; C 4 >C 3 Specifically, at the corner of the battery cell 100, the first pole piece 11 covers the second pole piece 13. On the side of the first pole piece 11 facing the winding center, the winding radius of the first pole piece 11 is larger than the winding radius of the second pole piece 13. The corresponding CB value (the ratio of the negative electrode lithium insertion capacity of the battery cell to the positive electrode lithium removal capacity) of the first pole piece 11 and the second pole piece 13 is larger, and the risk of interface problems such as lithium deposition is smaller. By limiting C 4 >C 3 , so that the first solid electrolyte layer 113 provides the first pole piece 11 with an ion channel sufficient to receive lithium ions on the side away from the winding center of the electrode assembly 10, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell 100.

[0121] In some embodiments, in the first electrode sheet 11 of the same layer located in the second bending section 10D, on the side facing the winding center of the electrode assembly 10, the ratio of the area of ​​the first solid electrolyte layer 113 to the area of ​​the first active material layer 112 where the first solid electrolyte layer 113 is located is C 3 '; On the side away from the winding center of the electrode assembly 10, the ratio of the area of ​​the first solid electrolyte layer 113 to the area of ​​the first active material layer 112 where the first solid electrolyte layer 113 is located is C 4 ′; C 4 ′>C 3 Specifically, at the corner of the battery cell 100, the first pole piece 11 covers the second pole piece 13. On the side of the first pole piece 11 facing the winding center, the winding radius of the first pole piece 11 is larger than the winding radius of the second pole piece 13. The corresponding CB value (the ratio of the negative electrode lithium insertion capacity of the battery cell to the positive electrode lithium removal capacity) of the first pole piece 11 and the second pole piece 13 is larger, and the risk of interface problems such as lithium deposition is smaller. By limiting C 4 ′>C 3 ', so that the first solid electrolyte layer 113 can provide the first pole piece 11 with an ion channel sufficient to receive lithium ions on the side away from the winding center of the electrode assembly 10, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell 100.

[0122] C 3 , C 4 , C 3 ′ and C 4 The measurement and calculation method of ′ refer to C 1 , C 2 , C 1 ′ and C 2 The measurement and calculation method of ′.

[0123] In some embodiments, in the first electrode sheet 11 of the same layer located in the first bending section 10B, on the side facing the winding center of the electrode assembly 10, the coating weight per unit area of ​​the first solid electrolyte layer 113 is W 5 On the side away from the winding center of the electrode assembly 10, the coating weight per unit area of ​​the first solid electrolyte layer 113 is W 6 ; W 6 >W 5 Specifically, at the corner of the battery cell 100, the first pole piece 11 covers the second pole piece 13. On the side of the first pole piece 11 facing the winding center, the winding radius of the first pole piece 11 is larger than the winding radius of the second pole piece 13. The corresponding CB value (the ratio of the negative electrode lithium insertion capacity of the battery cell to the positive electrode lithium removal capacity) of the first pole piece 11 and the second pole piece 13 is larger, and the risk of interface problems such as lithium deposition is smaller. By limiting W 6 >W5 , so that the first solid electrolyte layer 113 provides the first pole piece 11 with an ion channel sufficient to receive lithium ions on the side away from the winding center of the electrode assembly 10, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell 100.

[0124] In some embodiments, in the first electrode sheet 11 of the same layer located in the second bending section 10D, on the side facing the winding center of the electrode assembly 10, the coating weight per unit area of ​​the first solid electrolyte layer 113 is W 5 '; On the side away from the winding center of the electrode assembly 10, the coating weight per unit area of ​​the first solid electrolyte layer 113 is W 6 ′;W 6 ′>W 5 '. Specifically, at the corner of the battery cell 100, the first pole piece 11 covers the second pole piece 13. On the side of the first pole piece 11 facing the winding center, the winding radius of the first pole piece 11 is larger than the winding radius of the second pole piece 13. The corresponding CB value (the ratio of the negative electrode lithium insertion capacity of the battery cell to the positive electrode lithium removal capacity) of the first pole piece 11 and the second pole piece 13 is larger, and the risk of interface problems such as lithium deposition is smaller. By limiting W 6 ′>W 5 ', so that the first solid electrolyte layer 113 can provide the first pole piece 11 with an ion channel sufficient to receive lithium ions on the side away from the winding center of the electrode assembly 10, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell 100.

[0125] Where W 5 , W 6 , W 5 ′ and W 6 The measurement method of ′ refers to W in the previous article. 1 measurement method.

[0126] See also Figure 5 One embodiment of the present application further provides a secondary battery 200, and the secondary battery 200 includes the battery cell 100 in any of the above embodiments. After the secondary battery 200 is discharged, the active material can be activated by charging and the secondary battery 200 can be used continuously.

[0127] Please continue reading Figure 5 One embodiment of the present application further provides an electronic device 300, which includes the secondary battery 200 in any of the above embodiments. Optionally, the electronic device 300 can be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, etc.

[0128] The specific implementation of the battery cell 100 in the embodiment and the comparative example is described below.

[0129] Battery cycle test:

[0130] At a test temperature of 25°C, the secondary battery 200 was left standing for 30 minutes, and step-charged according to the following charging steps: (a) 2.0C constant current charging to 4.23V, constant voltage charging to 1.8C; (b) 1.8C constant current charging to 4.3V, constant voltage charging to 1.4C; (c) 1.4C constant current charging to 4.4V, constant voltage charging to 1.0C; (d) 1.0C constant current charging to 4.5V, constant voltage charging to 0.05C; After standing for 10 minutes, discharge according to the following steps: 1C DC discharge to 3V. The above charging and discharging process is one cycle, which is repeated 1000 cycles. 20 cells were tested in each group of comparative examples and embodiments.

[0131] (1) Using a PPG thickness tester, the initial cell thickness and the cell thickness after 1000 cycles of each cell were tested and the thickness expansion rate was calculated;

[0132] Thickness expansion rate of each battery cell = [(battery cell thickness after 1000 cycles - initial battery cell thickness) / initial battery cell thickness] × 100%;

[0133] The thickness expansion rate in each group of comparative examples or embodiments is the average thickness expansion rate of 20 battery cells in each group.

[0134] (2) Calculate the capacity retention rate of the battery cell;

[0135] The capacity retention rate of each battery cell = discharge capacity after 1000 cycles / initial discharge capacity × 100%.

[0136] The capacity retention rate in each group of comparative examples or embodiments is the average value of the capacity retention rates of 20 cells in each group.

[0137] (3) Disassemble the battery cell and observe whether there is grayish white lithium deposition on the electrode piece at the corner of the battery cell. Record the number of lithium deposition on the corner of the negative electrode piece in each group of 20 battery cells of the comparative example or the embodiment as X. 1 , then the lithium deposition rate of the negative electrode corner in each comparative example or embodiment = X 1 / 20.

[0138] (4) Calculate the volume energy density of the battery cell = platform voltage × first cycle discharge capacity / (initial length of the battery cell × initial width of the battery cell × initial thickness of the battery cell).

[0139] (5) Perform a high voltage insulation test (Hipot test) on the battery cell and calculate the test pass rate. The Hipot test (High Potential test) refers to an insulation resistance test. The test method is to detect the leakage current generated by the electrode assembly 10 under the test voltage output by the high voltage machine, and then calculate the resistance value = test voltage / leakage current. The calculated resistance value is compared with the set judgment resistance. If the detected resistance value is greater than or equal to the preset value, the product under test is judged to have passed the test (OK); if the detected resistance value is less than the preset value, the test voltage is instantly cut off and the product under test is judged to have failed the test (NG). The preset value of the judgment resistance in this test is 5mΩ. When the resistance value is lower than 5mΩ, it means that it can be turned on but the resistance value is too small, there is a short circuit point, and it is judged to be NG; when the resistance value is greater than or equal to 5mΩ, it is judged to be OK. 20 battery cells are taken for testing in each group of embodiments, and the number of battery cells that pass the test is X. 2 The test pass rate is X 2 / 100.

[0140] Embodiment 1:

[0141] A battery cell 100, 50% SOC, initial thickness 1.4mm, length 110mm, width 50mm, assembly process is as follows:

[0142] (1) Preparation of negative electrode sheet (corresponding to the first electrode sheet): provide a copper foil with a thickness of 6 μm as a negative electrode current collector; mix the negative electrode active materials artificial graphite, conductive carbon black (Super P), and styrene-butadiene rubber (SBR) in a weight ratio of 96:1.5:2.5, add deionized water as a solvent, prepare a slurry with a weight percentage of 50 wt%, and stir evenly; dissolve the solid electrolyte material lithium titanium aluminum phosphate, the first binder polyvinylidene fluoride, and the first conductive agent carbon nanotube in a solvent N-methylpyrrolidone in a weight percentage ratio of 94%:5%:1% to prepare a solid electrolyte slurry, and stir evenly; use two nozzles to simultaneously apply the above two slurries on one surface of the copper foil by extrusion spraying, and then dry at 110°C to obtain a negative electrode sheet with a negative electrode active material layer coated on one side. When preparing a double-sided coated negative electrode sheet, repeat the above steps on the other surface of the negative electrode sheet to obtain a negative electrode sheet with a negative electrode active material layer coated on both sides. The coated electrode sheet is then subjected to a cold pressing process. The thickness of the single-sided negative electrode active material layer of the straight section after cold pressing is 105 μm. A portion of the negative electrode active material layer is etched away by laser to expose the negative electrode current collector below the negative electrode active material layer. The negative electrode tab is welded on the exposed negative electrode current collector. The negative electrode tab is made of copper. (2) Preparation of the positive electrode sheet (corresponding to the second electrode sheet): Provide an aluminum foil with a thickness of 8 μm as the positive electrode current collector; paste foam glue at the position where the positive electrode tab needs to be welded on the positive electrode current collector;2 ), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%, and stirred evenly. The slurry is evenly coated on one surface of the aluminum foil, and then dried at 90°C to obtain a positive electrode sheet coated with a positive electrode active material on one side. When preparing a double-sided coated positive electrode sheet, repeat the above coating steps on the other surface of the aluminum foil. The coated electrode sheet is then subjected to a cold pressing process. The thickness of the single-sided positive electrode active material layer after cold pressing is 95μm. The foam glue is heated to fall off to reveal the positive electrode collector covered with the foam glue, and the positive electrode ear is welded on the exposed positive electrode collector. The material of the positive electrode ear is aluminum.

[0143] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed at a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF4) was added to the basic organic solvent. 6 ) are dissolved and mixed evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0144] (4) Preparation of isolation membrane: A 7 μm thick polyethylene porous polymer film was used as the isolation membrane.

[0145] (5) Preparation of electrode assembly: The positive electrode sheet, the separator and the negative electrode sheet are wound and arranged. After the winding, the positive electrode sheet and the negative electrode sheet in the electrode assembly are 24 layers each, of which the positive electrode sheet and the negative electrode sheet located in the first bending section and the second bending section are 12 layers each. The first solid electrolyte layer is arranged on the surface of the negative electrode active material layer located in the first bending section away from the negative electrode current collector and the number of layers of the negative electrode sheet covered by the first solid electrolyte layer is 1.

[0146] (6) Electrode assembly: Place the aluminum-plastic film with holes punched and formed in an assembly fixture, with the holes facing upward, place the electrode assembly in the holes, and apply external force to press it. Then, cover the electrode assembly with another aluminum-plastic film with holes punched and formed, with the holes facing downward, and heat-seal the four sides of the two aluminum-plastic films by hot pressing to obtain an assembled electrode assembly.

[0147] (7) Liquid injection packaging: The assembled electrode assembly is injected with electrolyte, and the battery cell is obtained through processes such as vacuum packaging, static standing, hot pressing, and shaping.

[0148] Comparative Example 1: The pole piece at the corner of the battery cell is not provided with a solid electrolyte layer. It should be noted that the parameters of Comparative Example 1 are the same as those of Example 1 except that the solid electrolyte layer is not provided.

[0149] Examples 2 to 20: Except for the parameters mentioned in Table 1, all other parameters are the same as those in Example 1, wherein the coating method of the fourth solid electrolyte layer in the second electrode piece is similar to the coating method of the first solid electrolyte layer in the first electrode piece.

[0150] Examples 21 to 32: Except for the parameters mentioned in Table 2, all other parameters are the same as those in Example 20.

[0151] Example 33 to Example 50: Except for the parameters involved in Table 3, all other parameters are the same as those in Example 20.

[0152] Examples 51 to 70: Except for the parameters mentioned in Table 4, all other parameters are the same as those in Example 20.

[0153] Table 1

[0154]

[0155]

[0156] It can be seen from Comparative Example 1 and Examples 1 to 10 that, in at least a portion of the first pole piece located in the first bending section and / or the second bending section, a first solid electrolyte layer is provided in at least a portion of the surface of the first active material layer away from the first current collector, which can improve the cycle performance of the battery cell, and as the number of layers of the first solid electrolyte layer increases, the improvement effect becomes better.

[0157] It can be seen from Comparative Example 1 and Examples 11 to 15 that in at least part of the second pole piece located in the first bending section and / or the second bending section, at least part of the surface of the second active material layer away from the second current collector is provided with a fourth solid electrolyte layer, which can further improve the cycle performance of the battery cell, and as the number of layers of the fourth solid electrolyte layer increases, the improvement effect is better. It can be seen from Examples 1 to 5 and Examples 11 to 15 that the improvement effect of directly setting the first solid electrolyte layer on the negative pole piece is better than the improvement effect of setting the first solid electrolyte layer on the positive pole piece.

[0158] It can be seen from Examples 16 to 20 that the improvement effect is better when solid electrolyte layers are provided on both the positive electrode sheet and the negative electrode sheet, and the improvement effect is better as the number of solid electrolyte layers increases.

[0159] Table 2

[0160]

[0161] It can be seen from Examples 20 to 23 that by limiting 60%≤A 1≤100%, can improve the cycle performance of the battery. It should be noted that when A 1 When the A is greater than 100%, the first solid electrolyte layer is likely to protrude from the first active material layer, resulting in space waste and a reduction in the energy density of the battery cell. Therefore, A is not provided. 1 >100% embodiment.

[0162] It can be seen from Examples 20, 24 to 26 that by limiting 50%≤B 1 ≤100%, can improve the cycle performance of the battery. It should be noted that when B 1 When the ratio is greater than 100%, the first solid electrolyte layer is likely to protrude from the first active material layer, resulting in space waste and a decrease in the energy density of the battery cell. Therefore, B is not provided. 1 >100% embodiment.

[0163] It can be seen from Examples 20, 27 to 32 that by limiting the concentration of 0.5 mg / cm 2 ≤W 1 ≤5mg / cm 2 , can improve the cycle performance of the battery. 1 Less than 0.5mg / cm 2 When W 1 More than 5mg / cm 2 When the coating weight of the first solid electrolyte layer is large and the thickness of the first solid electrolyte layer is large, the volume energy density loss of the battery cell is large. At the same time, the transmission distance of lithium ions is increased due to the large thickness of the first solid electrolyte layer, which increases the lithium deposition rate at the corner of the negative electrode. Therefore, in order to take into account the improvement of the cycle performance of the battery cell, reduce the loss of the volume energy density of the battery cell and reduce the lithium deposition rate at the corner of the negative electrode, W 1 Set to 0.5mg / cm 2 ≤W 1 ≤5mg / cm 2 On this basis, 1 mg / cm 2 ≤W 1 ≤3mg / cm 2 .

[0164] Table 3

[0165]

[0166] It can be seen from Example 20 and Example 33 to Example 38 that when L 1When L is less than 0.5 mm, the effect on the cycle capacity retention rate is small, and because the winding radius of the inner circle is small, the first solid electrolyte layer located in the inner circle is easier to fall off. 1 When L is too small, the probability of internal short circuit of the electrode assembly increases due to the powder loss of the first solid electrolyte layer, and the pass rate of the high-voltage insulation test is low. 1 When L is greater than 2 mm, the cycle capacity retention rate and high-voltage insulation test pass rate are higher; however, the thickness of the overlapping area between the second solid electrolyte layer and the first active material layer will increase. 1 When the L is larger, the volume energy density of the battery cell will decrease. Therefore, in order to take into account a higher cycle capacity retention rate, a high voltage insulation test pass rate and a higher volume energy density, the limit is 0.5mm≤L 1 ≤2mm, further, preferably 1mm≤L 1 ≤1.5mm. It can be seen from Examples 20 and 39 to 44 that when L 2 When L is less than 0.5 mm, the effect on the cycle capacity retention rate is small, and because the winding radius of the inner circle is small, the first solid electrolyte layer located in the inner circle is easier to fall off. 2 When L is too small, the probability of internal short circuit of the electrode assembly increases due to the powder loss of the first solid electrolyte layer, and the pass rate of the high-voltage insulation test is low. 2 When L is greater than 2 mm, the cycle capacity retention rate and the high-voltage insulation test pass rate are higher; however, the thickness of the overlapping area between the third solid electrolyte layer and the first active material layer will increase. 2 When the L is larger, the volume energy density of the battery cell will decrease. Therefore, in order to take into account a higher cycle capacity retention rate, a high voltage insulation test pass rate and a higher volume energy density, the limit is 0.5mm≤L 2 ≤2mm, further, preferably 1mm≤L 2 ≤1.5mm. It can be seen from Examples 45 to 50 that when L 1 and L 2 When the diameters of L and L are both within the range of 0.5 mm to 2 mm, a higher cycle capacity retention rate, a high voltage insulation test pass rate and a higher volume energy density can be obtained. 1 and L 2 Between 1mm and 1.5mm.

[0167] Table 4

[0168]

[0169]

[0170]

[0171] It can be seen from Example 20 and Example 51 to Example 55 that in the same layer of positive electrode sheets located in the first bending section, when C 1 >C 2 Compared with C 1 =C 2 and C 1 <C 2 In the case of C, the improvement of cycle capacity retention is more significant; in the same layer of positive electrode sheet located in the second bending section, when C 1 ′>C 2 ′, compared with C 1 ′=C 2 ′ and C 1 ′<C 2 ', the improvement in cycle capacity retention is more significant. This is because at the corner of the battery cell, the positive electrode sheet covers the negative electrode sheet. On the side of the positive electrode sheet facing the winding center, the winding radius of the positive electrode sheet is larger than that of the negative electrode sheet. The corresponding CB value (the ratio of the negative electrode capacity of the battery cell to the positive electrode capacity) of the negative electrode sheet and the positive electrode sheet is insufficient, resulting in a greater risk of interface problems such as lithium deposition. By limiting C 1 >C 2 and / or C 1 ′>C 2 ', so that the fourth solid electrolyte layer can provide the negative electrode plate with sufficient ion channels for receiving lithium ions on the side facing the winding center of the electrode assembly, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell.

[0172] It can be seen from Example 20 and Example 56 to Example 60 that in the same layer of positive electrode sheets located in the first bending section, when W 3 >W 4 Compared with W 3 =W 4 and W 3 <W 4 In the case of W, the improvement of cycle capacity retention is more significant; in the same layer of positive electrode sheet located in the second bending section, when W 3 ′>W 4 ′, compared with W 3 ′=W 4 ′ and W 3 ′<W 4 ', the improvement in cycle capacity retention is more significant. This is because at the corner of the battery cell, the positive electrode sheet covers the negative electrode sheet. On the side of the positive electrode sheet facing the winding center, the winding radius of the positive electrode sheet is larger than that of the negative electrode sheet. The corresponding CB value (the ratio of the negative electrode capacity of the battery cell to the positive electrode capacity) of the negative electrode sheet and the positive electrode sheet is insufficient, resulting in a greater risk of interface problems such as lithium deposition. By limiting W 3 >W4 and / or W 3 ′>W 4 ', so that the fourth solid electrolyte layer can provide the negative electrode plate with sufficient ion channels for receiving lithium ions on the side facing the winding center of the electrode assembly, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell.

[0173] It can be seen from Example 20 and Example 61 to Example 65 that in the same layer of negative electrode sheets located in the first bending section, when C 4 >C 3 Compared with C 3 =C 4 and C 4 <C 3 In the case of C, the improvement of cycle capacity retention is more significant; in the same layer of negative electrode sheet located in the second bending section, when C 4 ′>C 3 ′, compared with C 3 ′=C 4 ′ and C 4 ′<C 3 ', the improvement in cycle capacity retention is more significant. This is because at the corner of the battery cell, the negative electrode sheet covers the positive electrode sheet, and on the side of the negative electrode sheet facing the winding center, the winding radius of the positive electrode sheet is larger than that of the negative electrode sheet. The corresponding CB value (the ratio of the negative electrode lithium insertion capacity of the battery cell to the positive electrode lithium removal capacity) of the negative electrode sheet and the positive electrode sheet is insufficient, resulting in a greater risk of interface problems such as lithium deposition. By limiting C 4 >C 3 and / or C 4 ′>C 3 ', so that the fourth solid electrolyte layer can provide the negative electrode plate with sufficient ion channels for receiving lithium ions on the side facing the winding center of the electrode assembly, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell.

[0174] It can be seen from Example 20 and Example 66 to Example 70 that in the same layer of negative electrode sheets located in the first bending section, when W 6 >W 5 Compared with W 5 =W 6 and W 6 <W 5 In the case of W, the improvement of cycle capacity retention is more significant; in the same layer of negative electrode sheet located in the second bending section, when W 6 ′>W 5 ′, compared with W 5 ′=W 6 ′ and W 6 ′<W 5', the improvement in cycle capacity retention is more significant. This is because at the corner of the battery cell, the negative electrode sheet covers the positive electrode sheet, and on the side of the positive electrode sheet facing the winding center, the winding radius of the positive electrode sheet is larger than that of the negative electrode sheet. The corresponding CB value (the ratio of the negative electrode lithium embedding capacity of the battery cell to the positive electrode lithium de-embeddable capacity) of the negative electrode sheet and the positive electrode sheet is insufficient, resulting in a greater risk of interface problems such as lithium deposition. By limiting W 6 >W 5 and / or W 6 ′>W 5 ', so that the fourth solid electrolyte layer can provide the negative electrode plate with sufficient ion channels for receiving lithium ions on the side facing the winding center of the electrode assembly, thereby reducing the risk of interface problems such as lithium plating and improving the cycle performance of the battery cell.

[0175] In addition, those skilled in the art may also make other changes within the spirit of the present application. Of course, these changes made according to the spirit of the present application should be included in the scope disclosed in the present application.

Claims

1. A battery cell, characterized in that: The battery cell includes an electrode assembly, wherein the thickness direction of the electrode assembly is a first direction, the electrode assembly includes a first electrode sheet, a diaphragm, and a second electrode sheet that are stacked and wound, and the electrode assembly includes a first straight section, a first bent section, a second straight section, and a second bent section that are sequentially connected, and when viewed along a third direction, the first straight section and the second straight section are arranged opposite to each other along the first direction, the first bent section and the second bent section are arranged opposite to each other along the second direction, and the first direction, the second direction, and the third direction are perpendicular to each other; The first pole piece includes a first current collector, a first active material layer and a first solid electrolyte layer. Along the thickness direction of the first current collector, the first active material layer is arranged on at least one side surface of the first current collector. In at least a portion of the first pole piece located in the first bending section and / or the second bending section, the first solid electrolyte layer is provided in at least a portion of the surface of the first active material layer away from the first current collector.

2. The battery cell according to claim 1, characterized in that: Along the third direction, a ratio of a length of the first solid electrolyte layer to a length of the first active material layer where the first solid electrolyte layer is located is A1, 60%≤A1≤100%; and / or, In at least part of the first pole piece located in the first bending section or the second bending section, along the winding direction of the first pole piece, the ratio of the width of the first solid electrolyte layer to the width of the first active material layer where the first solid electrolyte layer is located is B1, 50%≤B1≤100%.

3. The battery cell according to claim 1, characterized in that: The coating weight per unit area of ​​the first solid electrolyte layer is W1, 0.5 mg / cm 2 ≤W1≤5mg / cm 2 .

4. The battery cell according to claim 3, characterized in that: 1mg / cm 2 ≤W1≤3mg / cm 2 。 5. The battery cell according to claim 1, characterized in that: The first solid electrolyte layer includes a first solid electrolyte, and the material of the first solid electrolyte includes at least one of an organic solid electrolyte and an inorganic solid electrolyte; wherein the organic solid electrolyte includes a block copolymer, the block copolymer includes a conductive polymer and a lithium-conducting polymer, the conductive polymer includes at least one of pyrrole, aniline, thiophene, polyacetylene, p-phenylene terephthalamide or 3,4-ethylenedioxythiophene, and the lithium-conducting polymer includes at least one of polyethylene oxide, polyethylene glycol, polypropylene oxide, poly(ethylene glycol) acrylate or poly(ethylene glycol) methacrylate; the inorganic solid electrolyte includes at least one of an oxide solid electrolyte and a sulfide solid electrolyte, the oxide solid electrolyte includes at least one of lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide or lithium lanthanum titanate, and the sulfide solid electrolyte includes at least one of lithium silver germanium sulfur and lithium phosphorus sulfur.

6. The battery cell according to claim 5, characterized in that: The first solid electrolyte layer also includes a first binder and a first conductor, the material of the first binder includes at least one of polyvinylidene fluoride, polyacrylic acid and carboxymethyl cellulose, and the material of the first conductor includes at least one of carbon nanotubes, carbon black, conductive graphite and graphene.

7. The battery cell according to claim 6, characterized in that: The ratio of the mass of the first binder to the mass of the first solid electrolyte layer is W2, and 1%≤W2≤10%.

8. The battery cell according to claim 1, characterized in that: The first pole piece includes a second solid electrolyte layer and a third solid electrolyte layer. In the first pole piece located in the first straight section, a partial area of ​​the surface of the first active material layer away from the first current collector is provided with the second solid electrolyte layer. In the first pole piece located in the second straight section, a partial area of ​​the surface of the first active material layer away from the first current collector is provided with the third solid electrolyte layer. The first bending section includes the first pole piece of the N1 layer, and in the first pole piece of the 1 / 3N1 layer located inside the first bending section, along the winding direction of the first pole piece, two ends of the first solid electrolyte layer are respectively connected to the second solid electrolyte layer and the third solid electrolyte layer; and / or, The second bending section includes the first pole piece of the N2 layer. In the first pole piece of the 1 / 3N2 layer located on the inner side of the second bending section, along the winding direction of the first pole piece, the two ends of the first solid electrolyte layer are respectively connected to the second solid electrolyte layer and the third solid electrolyte layer.

9. The battery cell according to claim 8, characterized in that: Along the second direction, the length of the second solid electrolyte layer is L1, 0.5 mm ≤ L1 ≤ 2 mm; and / or, Along the second direction, the length of the third solid electrolyte layer is L2, 0.5 mm≤L2≤2 mm.

10. The battery cell according to claim 9, characterized in that: 1mm≤L1≤1.5mm; and / or, 1mm≤L2≤1.5mm.

11. The battery cell according to any one of claims 1 to 10, characterized in that: The first pole piece is a negative pole piece, and the second pole piece is a positive pole piece.

12. The battery cell according to claim 11, characterized in that: The second pole piece includes a second current collector, a second active material layer and a fourth solid electrolyte layer. Along the thickness direction of the second current collector, the second active material layer is arranged on at least one side surface of the second current collector. In at least a portion of the second pole piece located in the first bending section and / or the second bending section, the fourth solid electrolyte layer is provided in at least a portion of the surface of the second active material layer away from the second current collector.

13. The battery cell according to claim 12, characterized in that: In the second pole piece of the same layer located in the first bending section, on the side facing the winding center of the electrode assembly, the ratio of the area of ​​the fourth solid electrolyte layer to the area of ​​the second active material layer where the fourth solid electrolyte layer is located is C1; on the side away from the winding center of the electrode assembly, the ratio of the area of ​​the fourth solid electrolyte layer to the area of ​​the second active material layer where the fourth solid electrolyte layer is located is C2; C1>C2; and / or, In the second pole piece of the same layer located in the second bending section, on the side facing the winding center of the electrode assembly, the ratio of the area of ​​the fourth solid electrolyte layer to the area of ​​the second active material layer where the fourth solid electrolyte layer is located is C1′; on the side away from the winding center of the electrode assembly, the ratio of the area of ​​the fourth solid electrolyte layer to the area of ​​the second active material layer where the fourth solid electrolyte layer is located is C2′; C1′>C2′.

14. The battery cell according to claim 12, characterized in that: In the second pole piece in the same layer of the first bending section, on the side facing the winding center of the electrode assembly, the coating weight per unit area of ​​the fourth solid electrolyte layer is W3; on the side away from the winding center of the electrode assembly, the coating weight per unit area of ​​the fourth solid electrolyte layer is W4; W3>W4; and / or, In the second pole piece of the same layer located in the second bending section, on the side facing the winding center of the electrode assembly, the unit area coating weight of the fourth solid electrolyte layer is W3′; on the side away from the winding center of the electrode assembly, the unit area coating weight of the fourth solid electrolyte layer is W4′; W3′>W4′.

15. The battery cell according to claim 11, characterized in that: In the first pole piece of the same layer located in the first bending section, on the side facing the winding center of the electrode assembly, the ratio of the area of ​​the first solid electrolyte layer to the area of ​​the first active material layer where the first solid electrolyte layer is located is C3; on the side away from the winding center of the electrode assembly, the ratio of the area of ​​the first solid electrolyte layer to the area of ​​the first active material layer where the first solid electrolyte layer is located is C4; C4>C3; and / or, In the first pole piece of the same layer located in the second bending section, on the side facing the winding center of the electrode assembly, the ratio of the area of ​​the first solid electrolyte layer to the area of ​​the first active material layer where the first solid electrolyte layer is located is C3′; on the side away from the winding center of the electrode assembly, the ratio of the area of ​​the first solid electrolyte layer to the area of ​​the first active material layer where the first solid electrolyte layer is located is C4′; C4′>C3′.

16. The battery cell according to claim 11, characterized in that: In the first pole piece of the same layer located in the first bending section, on the side facing the winding center of the electrode assembly, the coating weight per unit area of ​​the first solid electrolyte layer is W5; on the side away from the winding center of the electrode assembly, the coating weight per unit area of ​​the first solid electrolyte layer is W6; W6>W5; and / or, In the first pole piece of the same layer located in the second bending section, on the side facing the winding center of the electrode assembly, the unit area coating weight of the first solid electrolyte layer is W5′; on the side away from the winding center of the electrode assembly, the unit area coating weight of the first solid electrolyte layer is W6′; W6′>W5′.

17. A secondary battery, characterized in that: The secondary battery comprises the battery cell according to any one of claims 1 to 16.

18. An electronic device, characterized in that: The electronic device includes the secondary battery as claimed in claim 17.

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