Secondary battery, electric equipment and preparation method of secondary battery

Abstract

The invention discloses a secondary battery, electric equipment and a preparation method of the secondary battery. The secondary battery comprises a shell, an electrode assembly and a supporting layer, the shell is a metal shell and comprises a first shell body and a second shell body, the first shell body comprises a bottom wall and a side wall connected with the periphery of the bottom wall, the second shell body covers a pit formed by the side wall and the bottom wall, part of the second shell body is connected with the side wall, and the electrode assembly is arranged in the pit. At least part of the supporting layer is arranged between the second shell and the electrode piece on the outermost side of the electrode assembly, and the supporting layer and at least part of the edge of the electrode piece on the outermost side are overlapped when observed in the first direction. The material of the supporting layer comprises at least one of polycarbonate, polyamide, polyformaldehyde and polybutylene terephthalate; or the supporting layer is insulating gummed paper. When the secondary battery is subjected to a hot-pressing formation process, the supporting layer can play a certain role in supporting the second shell so as to weaken the extrusion of the middle part of the second shell on the electrode assembly, so that the outward protruding degree of the bottom wall can be reduced.

Description

Technical Field

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

[0002] With the development of various electronic devices, secondary batteries have become an indispensable part of daily life. For example, mobile phones, tablets, laptops and digital cameras all require secondary batteries to provide power for normal operation. Steel-shell batteries are a type of secondary batteries. The outer shell of a steel-shell battery generally includes a shell body and a shell cover. The electrode assembly is arranged in the pit of the shell body, and the shell cover seals the pit of the shell body. However, the existing steel-shell batteries have the problem of the bottom wall of the shell body bulging outward when leaving the factory, resulting in the steel-shell battery being too thick. Summary of the invention

[0003] For the steel shell battery in the prior art, the inventors found that the reason why the bottom wall of the shell body bulges outward is that when the steel shell battery is subjected to the hot pressing process, the edges of the shell cover are supported by the side walls of the shell body, resulting in the deformation degree of the middle part of the shell cover being greater than the deformation degree of the edges. As a result, the middle part of the shell cover squeezes the electrode assembly, and the squeezed electrode assembly further squeezes the bottom wall of the shell body, causing the bottom wall of the shell body to bulge outward, thereby causing the steel shell battery to be relatively thick.

[0004] In view of the above situation, it is necessary to provide a secondary battery that can improve the problem of uneven thickness.

[0005] The first aspect of the present application provides a secondary battery, comprising a shell, an electrode assembly and a support layer. The shell is a metal shell, and the shell includes a first shell and a second shell arranged opposite to each other along a first direction, the first shell includes a bottom wall and a side wall, the side wall is connected to the periphery of the bottom wall and forms a pit with the bottom wall, the second shell covers the pit, and part of the second shell is connected to the side wall. The first direction is the thickness direction of the shell. The electrode assembly is arranged in the pit, and the electrode assembly includes an outermost pole piece. At least part of the support layer is arranged between the second shell and the outermost pole piece, and when viewed along the first direction, the support layer overlaps at least part of the edge of the outermost pole piece. The material of the support layer includes at least one of polycarbonate, polyamide, polyoxymethylene and polybutylene terephthalate; or, the support layer is insulating adhesive tape.

[0006] By making the support layer include the above-mentioned materials or insulating adhesive tape, the support layer can have a certain compressive strength. At least part of the support layer is arranged between the second shell and the outermost pole piece, and the support layer overlaps at least part of the edge of the outermost pole piece. When the secondary battery is subjected to a hot pressing process, the support layer can play a certain supporting role on the second shell to reduce the extrusion of the electrode assembly by the middle part of the second shell, thereby facilitating the reduction of the extrusion of the electrode assembly on the bottom wall and reducing the degree of outward protrusion of the bottom wall, thereby improving the problem of the secondary battery being too thick.

[0007] In one or more of the above embodiments, the support layer does not exceed the edge of the outermost pole piece when viewed along the first direction. On the premise of ensuring that the support layer can support the second shell, it is beneficial to save the material of the support layer and reduce the overall weight of the secondary battery.

[0008] In one or more of the above embodiments, the secondary battery includes a pole lug connected to the electrode assembly, and when viewed along the first direction, the edge of the outermost pole piece includes a pole lug extending edge and a non-pole lug extending edge, and the support layer at least overlaps with the non-pole lug extending edge. In this case, during the hot pressing process of the secondary battery, since the deformation degree of the second shell at the non-pole lug extending edge is greater than the deformation degree of the second shell at the pole lug extending edge, by making the support layer at least overlap with the non-pole lug extending edge, the support layer can at least support the main deformed part of the second shell, which is beneficial to reduce the overall deformation degree of the second shell and improve the problem of the secondary battery being too thick while saving the material of the support layer and reducing the overall weight of the secondary battery.

[0009] In one or more of the above embodiments, the support layer overlaps all edges of the outermost pole piece when viewed along the first direction. In this case, during the hot pressing process of the secondary battery, the support layer can better support the second shell, which is conducive to better reducing the overall deformation of the second shell and further improving the problem of the secondary battery being too thick.

[0010] In one or more of the above embodiments, the support layer has a ring structure. In this case, during the hot pressing process of the secondary battery, the support layer can be more evenly stressed when supporting the second shell, which is conducive to making the overall deformation of the second shell more uniform and better improving the problem of the secondary battery being too thick.

[0011] In one or more of the above embodiments, the secondary battery includes a pole ear connected to the electrode assembly, and the size of the outermost pole piece along the extension direction of the pole ear is L. The annular structure includes an inner wall and an outer wall, and the distance between the inner wall and the outer wall is W, 0.05≤W / L≤0.2. By setting 0.05≤W / L, the width of the support layer (the distance W between the inner wall and the outer wall) will not be too small, so that the position where the support layer plays a supporting role can be closer to the effective pressure area during the hot pressing process, and the support effect of the support layer on the second shell will not be too weak, which is conducive to reducing the degree of outward protrusion of the bottom wall. By setting W / L≤0.2, the width of the support layer will not be too large, and the support layer can better improve the problem of the secondary battery being too thick while making the volume of the support layer smaller, which is conducive to reducing the overall weight of the secondary battery.

[0012] In one or more of the above embodiments, along the first direction, the maximum distance between the second shell and the outermost pole piece is D, and the thickness of the portion of the support layer provided between the second shell and the outermost pole piece is H, 0.2≤H / D≤0.7. By setting 0.2≤H / D, the thickness of the support layer will not be too small, so that the supporting effect of the support layer on the second shell will not be too weak, which is beneficial to reduce the degree of outward protrusion of the bottom wall. By setting H / D≤0.7, the thickness of the support layer will not be too large, so that the supporting effect of the support layer on the second shell will not be too strong, which is beneficial to ensure the effect of hot pressing of the secondary battery and reduce the risk of subsequent lithium deposition in the secondary battery.

[0013] In one or more of the above embodiments, 0.3≤H / D≤0.6. By setting 0.3≤H / D, it is helpful to further reduce the degree of outward protrusion of the bottom wall. By setting H / D≤0.6, it is helpful to further ensure the effect of hot pressing of the secondary battery.

[0014] In one or more of the above embodiments, the support layer is an insulating tape, and the insulating tape includes polyimide tape and / or polyester tape. Polyimide tape has good high temperature resistance and electrical insulation performance, which is beneficial to reduce the possibility of melting failure of the support layer during the hot pressing process of the secondary battery, and is beneficial to reduce the risk of short circuit in the secondary battery. Polyester tape has good compressive strength and electrical insulation performance, which is beneficial to improve the supporting effect of the support layer on the second shell, and is beneficial to reduce the risk of short circuit in the secondary battery.

[0015] In one or more of the above embodiments, the outer shell is a steel shell.

[0016] In one or more of the above embodiments, the thickness of the second shell is 0.75 mm to 1.5 mm.

[0017] The second aspect of the present application provides an electrical device, comprising the secondary battery of the first aspect of the present application. The bottom wall of the secondary battery protrudes slightly outward, so the volume occupied by the secondary battery is small, which is conducive to improving the space utilization rate of the electrical device.

[0018] The third aspect of the present application provides a method for preparing a secondary battery, which is used to prepare the secondary battery as described in the first aspect of the present application, and the preparation method includes the following steps: placing a support layer on the outermost pole piece of the electrode assembly, so that the support layer overlaps at least part of the edge of the outermost pole piece along the first direction; connecting the positive electrode and the negative electrode of the electrode assembly to the positive electrode lead-out terminal and the negative electrode lead-out terminal of the first shell respectively; placing the electrode assembly and the support layer in the pit of the first shell, so that the support layer is farther away from the bottom wall of the first shell than the electrode assembly; sealing the second shell and the first shell, and performing hot pressing to obtain a secondary battery. It is conducive to preparing a secondary battery with a lesser degree of outward protrusion of the bottom wall. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A front view of a secondary battery provided in accordance with an embodiment of the present application.

[0020] Figure 2 A top view of a secondary battery provided in accordance with an embodiment of the present application.

[0021] Figure 3 For along Figure 1 Cross-section along the midline AA.

[0022] Figure 4 For along Figure 2 Cross-section along section line BB.

[0023] Figure 5 For along Figure 2 Cross-section along the center line CC.

[0024] Figure 6 This is a schematic diagram of the structure in which the support layer provided in the first embodiment of the present application is arranged on the outermost pole piece.

[0025] Figure 7 A schematic diagram of the structure in which the support layer provided in the second embodiment of the present application is arranged on the outermost pole piece.

[0026] Figure 8 A schematic diagram of the structure in which the support layer provided in the third embodiment of the present application is arranged on the outermost pole piece.

[0027] Fig. 9 An overall schematic diagram of an electrical device provided in one embodiment of the present application.

[0028] Main component symbols 1000, electrical equipment; 100, secondary battery; 10, outer shell; 101, pit; 11, first shell; 111, bottom wall; 112, side wall; 12, second shell; 20, electrode assembly; 201, outermost pole piece; 2011, pole ear extending edge; 2012, non-pole ear extending edge; 21, negative pole piece; 22, positive pole piece; 23, diaphragm; 30, supporting layer; 40, pole ear; 41, negative pole ear; 42, positive pole ear; 50, pole column; 60, insulating member; X, first direction. DETAILED DESCRIPTION

[0029] 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.

[0030] 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.

[0031] Unless otherwise specified, the term "plurality" as used herein means two or more than two.

[0032] The terms "first", "second", etc. are only used to distinguish different objects and shall not be understood as indicating or implying relative importance or implying the quantity, specific order or primary and secondary relationship of the indicated technical features.

[0033] 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 of the related listed items.

[0034] It should be understood that, considering the actual processing tolerance factors, in the technical solution of the present application, when the two elements are arranged parallel / vertically and in the same direction, there may be a certain angle between the two elements, and a tolerance of 0-±10% is allowed between the two elements. A tolerance of 0-±10% is allowed between the two elements greater than, equal to or less than.

[0035] An embodiment of the present application provides a secondary battery, including a shell, an electrode assembly and a support layer. The shell is a metal shell, and the shell includes a first shell and a second shell arranged opposite to each other along a first direction. The first shell includes a bottom wall and a side wall, and the side wall is connected to the periphery of the bottom wall and forms a pit with the bottom wall. The second shell covers the pit, and part of the second shell is connected to the side wall. The first direction is the thickness direction of the shell. The electrode assembly is arranged in the pit, and the electrode assembly includes an outermost pole piece. At least part of the support layer is arranged between the second shell and the outermost pole piece, and when viewed along the first direction, the support layer overlaps at least part of the edge of the outermost pole piece. The material of the support layer includes at least one of polycarbonate, polyamide, polyoxymethylene and polybutylene terephthalate; or, the support layer is insulating tape.

[0036] In the secondary battery of the present application, by making the support layer include the above-mentioned material or insulating adhesive tape, the support layer can have a certain compressive strength. At least part of the support layer is arranged between the second shell and the outermost pole piece, and the support layer overlaps at least part of the edge of the outermost pole piece. When the secondary battery is subjected to a hot pressing process, the support layer can play a certain supporting role on the second shell to reduce the extrusion of the electrode assembly by the middle part of the second shell, thereby facilitating the reduction of the extrusion of the electrode assembly on the bottom wall and reducing the degree of outward protrusion of the bottom wall, thereby improving the problem of the secondary battery being too thick.

[0037] Some embodiments of the present application will be described below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0038] See also Figures 1 to 3 An embodiment of the present application provides a secondary battery 100 including a housing 10 , an electrode assembly 20 and a support layer 30 .

[0039] The housing 10 includes a first housing 11 and a second housing 12, and the first housing 11 and the second housing 12 are arranged opposite to each other along a first direction X, and the first direction X is the thickness direction of the housing 10. The first housing 11 may be the body of the secondary battery 100, and the second housing 12 may be the cover of the secondary battery 100. The first housing 11 includes a bottom wall 111 and a side wall 112, and the side wall 112 is connected to the periphery of the bottom wall 111 and forms a pit 101 with the bottom wall 111. The second housing 12 covers the pit 101 and is recessed toward the bottom wall 111. Part of the second housing 12 is connected to the side wall 112, and the connection method between the second housing 12 and the side wall 112 includes but is not limited to adhesive connection or welding connection. In some embodiments, the housing 10 is a metal housing, for example, the housing 10 is a steel shell, and the materials of the first housing 11 and the second housing 12 both include steel, and the second housing 12 is welded to the side wall 112.

[0040] In some embodiments, the wall thickness of the first shell 11 is 0.75 mm to 1.5 mm. For example, the wall thickness of the first shell 11 is 0.75 mm, 1 mm, 1.25 mm, 1.5 mm, or any value between the listed endpoints.

[0041] In some embodiments, the thickness of the second housing 12 is 0.75 mm to 1.5 mm. For example, the thickness of the second housing 12 is 0.75 mm, 1 mm, 1.25 mm, 1.5 mm, or any value between the listed endpoints.

[0042] The pit 101 is filled with an electrolyte, and the electrolyte includes an electrolyte salt. In some embodiments, the electrolyte salt includes at least one of an organic lithium salt or an inorganic lithium salt. The electrolyte salt includes but is not limited to lithium hexafluorophosphate (LiPF 6), bis(trifluoromethanesulfonyl)imide lithium LiN (CF 3 SO 2 ) 2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO 2 F) 2 )(LiFSI), lithium hexafluorocesium oxide (LiCsF 6 ), lithium perchlorate (LiClO 4 ) or lithium trifluoromethanesulfonate (LiCF 3 SO 3 ) at least one of.

[0043] The electrode assembly 20 is disposed in the recess 101. Figure 3 The electrode assembly 20 includes a negative electrode sheet 21, a positive electrode sheet 22 and a separator 23, wherein the separator 23 separates the negative electrode sheet 21 from the positive electrode sheet 22. In some embodiments, the electrode assembly 20 is a stacked structure, wherein a plurality of negative electrode sheets 21 and a plurality of positive electrode sheets 22 are alternately stacked, and the separator 23 is disposed between any adjacent negative electrode sheets 21 and positive electrode sheets 22. In some embodiments, the electrode assembly 20 is a winding structure, wherein a single negative electrode sheet 21 and a single positive electrode sheet 22 are stacked and then wound, and the separator 23 is disposed between the negative electrode sheet 21 and the positive electrode sheet 22.

[0044] In some embodiments, the negative electrode plate 21 includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer is arranged on two opposite sides of the negative electrode current collector along the thickness direction. The positive electrode plate 22 includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer is arranged on two opposite sides of the positive electrode current collector along the thickness direction. The negative electrode current collector includes but is not limited to copper foil, copper alloy foil, nickel foil, titanium foil, nickel foam or copper foam, and the positive electrode current collector includes but is not limited to aluminum foil and aluminum alloy foil. In some embodiments, the negative electrode current collector is copper foil, and the positive electrode current collector is aluminum foil. The material of the negative electrode active material layer includes but is not limited to graphite, hard carbon, soft carbon, silicon, silicon oxygen material and silicon carbon material. The material of the positive electrode active material layer includes but is not limited to lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate and lithium manganese oxide.

[0045] In some embodiments, the diaphragm 23 is an insulating film material such as a polyethylene film, a polypropylene film, a polyester film, or a polyimide film.

[0046] See also Figures 3 to 5The electrode assembly 20 includes an outermost pole piece 201, and the outermost pole piece 201 is closest to the second shell 12 along the first direction X. When the electrode assembly 20 is a stacked structure, the outermost pole piece 201 is the pole piece closest to the second shell 12 among the pole pieces of the electrode assembly 20 along the thickness direction of the electrode assembly 20; when the electrode assembly 20 is a wound structure, the outermost pole piece 201 is the flat area of ​​the pole piece located at the outermost layer of the winding that is closest to the second shell 12.

[0047] In some embodiments, see Figure 5 and Figure 6 The secondary battery 100 includes a tab 40 connected to the electrode assembly 20, and the tab 40 includes a negative tab 41 and a positive tab 42. The negative tab 41 is electrically connected to the negative current collector, and the positive tab 42 is electrically connected to the positive current collector. The connection method between the negative tab 41 and the negative current collector and the positive tab 42 and the positive current collector includes but is not limited to integral cutting and welding. The negative tab 41 and the positive tab 42 may extend out of the electrode assembly 20 in the same or different directions. In some embodiments, refer to Figures 6 to 8 , observed along the first direction X, depending on whether there is a pole ear 40 extending, the edge of the outermost pole piece 201 includes a pole ear extending edge 2011 and a non-pole ear extending edge 2012, and the distance between the pole ear extending edge 2011 and the side wall 112 is greater than the distance between the non-pole ear extending edge 2012 and the side wall 112.

[0048] In some embodiments, the number of negative electrode tabs 41 and positive electrode tabs 42 are both multiple, and the multiple negative electrode tabs 41 are stacked in sequence along the first direction X, and then welded together to form a negative electrode tab bundle, and the negative electrode tab bundle is welded to the housing 10 (see Figure 4 ). A plurality of positive electrode tabs 42 are stacked in sequence along the first direction X, and are welded together to form a positive electrode tab bundle. The positive electrode tab bundle is welded to the pole 50, and the pole 50 is insulated and arranged in the housing 10 (see Figure 5 ). In some embodiments, the positive electrode tab bundle is electrically connected to the pole 50 through an adapter, and the material of the adapter includes but is not limited to conductive materials such as copper, aluminum, nickel, and nickel alloy. In some embodiments, see Figure 5 The pole 50 is insulated and arranged on the housing 10 through an insulating member 60, and the insulating member 60 includes but is not limited to an insulating gasket and an insulating sleeve, the insulating gasket is arranged between the contact surface of the pole 50 and the housing 10, and the insulating sleeve is wrapped around the outer periphery of the pole 50. The material of the insulating member 60 includes but is not limited to plastic and rubber.

[0049] See also Figure 3, at least part of the support layer 30 is disposed between the second shell 12 and the outermost pole piece 201, and when viewed along the first direction X, the support layer 30 overlaps at least part of the edge of the outermost pole piece 201. For example, the support layer 30 overlaps with the pole ear protruding edge 2011, or the support layer 30 overlaps with the non-pole ear protruding edge 2012, or the support layer 30 overlaps with part of the pole ear protruding edge 2011 and part of the non-pole ear protruding edge 2012. Alternatively, the support layer 30 overlaps with both the pole ear protruding edge 2011 and the non-pole ear protruding edge 2012. The material of the support layer 30 includes at least one of polycarbonate, polyamide, polyoxymethylene and polybutylene terephthalate. Alternatively, the support layer 30 is insulating adhesive tape.

[0050] By making the support layer 30 include the above-mentioned materials or insulating adhesive tape, the support layer 30 can have a certain compressive strength. At least part of the support layer 30 is arranged between the second shell 12 and the outermost pole piece 201, and the support layer 30 overlaps at least part of the edge of the outermost pole piece 201. When the secondary battery 100 is subjected to the hot pressing process, the support layer 30 can play a certain supporting role on the second shell 12 to reduce the extrusion of the middle part of the second shell 12 on the electrode assembly 20, thereby facilitating the reduction of the extrusion of the electrode assembly 20 on the bottom wall 111, reducing the degree of outward protrusion of the bottom wall 111, thereby improving the problem of the secondary battery 100 being too thick.

[0051] In some embodiments, the support layer 30 is an insulating tape, and the insulating tape includes polyimide tape and / or polyester tape. The polyimide tape has good high temperature resistance and electrical insulation performance, which is conducive to reducing the possibility of melting failure of the support layer 30 during the hot pressing process of the secondary battery 100, and is conducive to reducing the risk of short circuit of the secondary battery 100. The polyester tape has good compressive strength and electrical insulation performance, which is conducive to improving the supporting effect of the support layer 30 on the second shell 12, and is conducive to reducing the risk of short circuit of the secondary battery 100.

[0052] In some embodiments, see Figure 3, along the first direction X, the maximum distance between the second shell 12 and the outermost pole piece 201 is D, and the thickness of the portion of the support layer 30 disposed between the second shell 12 and the outermost pole piece 201 is H, 0.2≤H / D≤0.7. For example, the value of H / D is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or any value between the listed endpoint values. By setting 0.2≤H / D, the thickness of the support layer 30 will not be too small, so that the supporting effect of the support layer 30 on the second shell 12 will not be too weak, thereby helping to reduce the degree of outward protrusion of the bottom wall 111. By setting H / D≤0.7, the thickness of the support layer 30 will not be too large, so that the supporting effect of the support layer 30 on the second shell 12 will not be too strong, which is conducive to ensuring the effect of hot pressing of the secondary battery 100 and reducing the risk of subsequent lithium deposition of the secondary battery 100.

[0053] In some embodiments, 0.3≤H / D≤0.6. By setting 0.3≤H / D, the degree of outward protrusion of the bottom wall 111 is further reduced. By setting H / D≤0.6, the effect of thermocompression formation of the secondary battery 100 is further ensured.

[0054] In some embodiments, 34 um≤H≤119 um. For example, H is 34 um, 50 um, 70 um, 95 um, 119 um, or any value between the listed endpoints.

[0055] In some embodiments, the support layer 30 does not extend beyond the edge of the outermost pole piece 201 when viewed along the first direction X. That is, along the thickness direction of the electrode assembly 20, the orthographic projection of the support layer 30 is located within the orthographic projection of the outermost pole piece 201. On the premise of ensuring that the support layer 30 can support the second shell 12, it is beneficial to save the material of the support layer 30 and to reduce the overall weight of the secondary battery 100.

[0056] In some embodiments, see Figure 6 , viewed along the first direction X, the support layer 30 at least overlaps with the non-tab extension edge 2012. Figure 6As shown, the outermost pole piece 201 includes a pole tab extending edge 2011 and three non-pole tab extending edges 2012, and the secondary battery 100 includes three long strips of support layers 30, and the three support layers 30 overlap with the three non-pole tab extending edges 2012. In this case, during the hot pressing process of the secondary battery 100, since the deformation degree of the second shell 12 at the non-pole tab extending edge 2012 is greater than the deformation degree of the second shell 12 at the pole tab extending edge 2011, by making the support layer 30 overlap with the non-pole tab extending edge 2012 at least, the support layer 30 can at least support the main deformed part of the second shell 12, which is beneficial to reduce the overall deformation degree of the second shell 12 and improve the problem of the secondary battery 100 being too thick, while saving the material of the support layer 30 and reducing the overall weight of the secondary battery 100.

[0057] In some embodiments, see Figure 7 , viewed along the first direction X, the support layer 30 overlaps all edges of the outermost pole piece 201. Figure 7 As shown, the outermost pole piece 201 includes a pole tab extending edge 2011 and three non-pole tab extending edges 2012, and the secondary battery 100 includes four long strips of support layers 30, and the four support layers 30 overlap with the pole tab extending edge 2011 and the three non-pole tab extending edges 2012. In this case, during the hot pressing process of the secondary battery 100, the support layer 30 can better support the second shell 12, which is conducive to better reducing the overall deformation of the second shell 12, and further improving the problem of the secondary battery 100 being too thick.

[0058] In some embodiments, see Figure 8 , the support layer 30 has a ring structure. Figure 8 As shown, the outermost pole piece 201 includes a pole tab extending edge 2011 and three non-pole tab extending edges 2012, and the secondary battery 100 includes a support layer 30 with an annular structure, and a single support layer 30 overlaps with a pole tab extending edge 2011 and three non-pole tab extending edges 2012. In this case, during the hot pressing process of the secondary battery 100, the support layer 30 can be more evenly stressed when supporting the second shell 12, which is conducive to making the overall deformation degree of the second shell 12 more uniform, and better improving the problem of the secondary battery 100 being too thick.

[0059] In some embodiments, the outermost pole piece 201 includes two pole ear extending edges 2011 and two non-pole ear extending edges 2012. The two pole ear extending edges 2011 are arranged oppositely along the length direction of the outermost pole piece 201, and the two non-pole ear extending edges 2012 are arranged oppositely along the width direction of the outermost pole piece 201. Alternatively, the two pole ear extending edges 2011 are arranged oppositely along the width direction of the outermost pole piece 201, and the two non-pole ear extending edges 2012 are arranged oppositely along the length direction of the outermost pole piece 201. It should be understood that the number of pole ear extending edges 2011 and non-pole ear extending edges 2012 included in the outermost pole piece 201 is not limited.

[0060] In some embodiments, see Figure 8 , along the extension direction of the pole ear 40, the size of the outermost pole piece 201 is L. The annular structure includes an inner wall 301 and an outer wall 302, and the distance between the inner wall 301 and the outer wall 302 is W, 0.05≤W / L≤0.2. For example, the value of W / L is 0.05, 0.1, 0.15, 0.2 or any value between the listed endpoint values. By setting 0.05≤W / L, the width of the support layer 30 will not be too small, so that the position where the support layer 30 plays a supporting role can be closer to the effective pressure area during the hot pressing process, and the support role of the support layer 30 on the second shell 12 can be not too weak, which is conducive to reducing the degree of outward protrusion of the bottom wall 111. By setting W / L≤0.2, the width of the support layer 30 will not be too large, which can better improve the problem of the secondary battery 100 being too thick and make the volume of the support layer 30 smaller, which is conducive to reducing the overall weight of the secondary battery 100. It should be understood that when the support layer 30 has an annular structure, the width of the support layer 30 refers to the distance W between the inner wall 301 and the outer wall 302 .

[0061] In some embodiments, the inner wall 301 is perpendicular to the outermost pole piece 201. In some embodiments, the outer wall 302 is perpendicular to the outermost pole piece 201.

[0062] In some embodiments, 1320um≤W≤5280um. For example, W is 1320um, 2000um, 3000um, 4000um, 5280um, or any value between the listed endpoints.

[0063] It should be understood that when the thickness H of the support layer 30 takes a larger value in the thickness range, the width of the support layer 30 should take a smaller value in the width range.

[0064] See also Fig. 9One embodiment of the present application provides an electric device 1000, comprising the secondary battery 100 as described above. The bottom wall 111 of the secondary battery 100 protrudes slightly outward, so that the volume occupied by the secondary battery 100 is small, which is conducive to improving the space utilization of the electric device 1000. The electric device 1000 includes, but is not limited to, electronic devices such as electronic book players, mobile phones, fax machines, copiers, printers, headphones, video recorders, LCD TVs, recorders, radios, cameras, tablet computers, and laptop computers.

[0065] An embodiment of the present application provides a method for preparing a secondary battery 100, comprising the following steps: Step 1: disposing the support layer 30 on the outermost pole piece 201 of the electrode assembly 20 , so that along the first direction X, the support layer 30 overlaps at least a portion of the edge of the outermost pole piece 201 .

[0066] Step 2: Connect the positive electrode and the negative electrode of the electrode assembly 20 to the positive electrode lead-out terminal and the negative electrode lead-out terminal of the first shell 11 respectively.

[0067] Step 3: Place the electrode assembly 20 and the support layer 30 in the recess 101 of the first shell 11 , so that the support layer 30 is farther away from the bottom wall 111 of the first shell 11 than the electrode assembly 20 .

[0068] Step 4: The second shell 12 and the first shell 11 are sealed and connected, and hot pressing is performed to obtain the secondary battery 100. The preparation method of the present application is conducive to preparing a secondary battery 100 with a bottom wall 111 that protrudes outwards to a lesser extent.

[0069] In some embodiments, in step one, the support layer 30 is welded or bonded to the outermost pole piece 201 of the electrode assembly 20, so that the support layer 30 can remain fixed relative to the outermost pole piece 201, which helps to reduce the possibility of the support layer 30 being offset and thus affecting the support effect.

[0070] In some embodiments, in step two, the pole 50 is insulated and disposed on the side wall 112 of the first shell 11, the positive lead-in end of the first shell 11 is the pole 50, and the negative lead-in end of the first shell 11 is the side wall 112, so that the positive pole tab 42 of the electrode assembly 20 is welded to the positive pole lead-in end of the first shell 11, and the negative pole tab 41 of the electrode assembly 20 is welded to the negative pole lead-in end of the first shell 11.

[0071] In some embodiments, in step three, the electrode assembly 20 and the support layer 30 are placed into the recess 101 of the first shell 11 with the end of the electrode assembly 20 without the support layer 30 facing the bottom wall 111 of the first shell 11 .

[0072] In some embodiments, in step four, the second shell 12 is covered on the recess 101 of the first shell 11 along the thickness direction of the electrode assembly 20, and the second shell 12 and the side wall 112 of the first shell 11 are sealed and connected by gluing or welding.

[0073] In order to verify the effect of the solution provided in the present application on the secondary battery 100 , the inventors of the present application conducted the following experiment. The experiment included 1 group of comparative examples and 16 groups of embodiments. Each group of comparative examples and embodiments included 20 secondary batteries 100 .

[0074] The preparation process of the secondary battery 100 in Example 1 includes the following steps: Preparation of positive electrode sheet 22: The positive electrode active material lithium cobalt oxide, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride (PVDF) are dissolved in N-methylpyrrolidone (NMP) solution at a weight ratio of 97.5:1:1.5 to form a positive electrode slurry. Aluminum foil is used as a positive electrode current collector, and the positive electrode slurry is coated on the positive electrode current collector. After drying, cold pressing, and slitting, the positive electrode sheet 22 is obtained.

[0075] Preparation of the negative electrode sheet 21: Mix the negative electrode active material artificial graphite, the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) in a weight ratio of 96:1.5:2.5, add deionized water, and stir evenly under the action of a vacuum mixer to obtain a negative electrode slurry; use copper foil as the negative electrode current collector, and evenly coat the negative electrode slurry on the negative electrode current collector; dry, and then cold press, cut, and slit to obtain the negative electrode sheet 21.

[0076] Preparation of the diaphragm 23: The base material layer of the diaphragm 23 is polyethylene (PE), and an alumina ceramic layer is coated on both sides of the base material layer of the diaphragm 23. Finally, a binder polyvinylidene fluoride (PVDF) is coated on both sides of the ceramic layer and dried.

[0077] Preparation of electrolyte: In a dry argon atmosphere glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of 3:5:2, and lithium salt LiPF was added. 6 , and then mixed evenly to obtain an electrolyte solution, in which LiPF 6 The mass concentration is 12.5%.

[0078] Preparation of secondary battery 100: After stacking positive electrode sheet 22, separator 23 and negative electrode sheet 21, electrode assembly 20 is obtained. CCD positioning is used to set support layer 30 on the outermost electrode sheet 201 of electrode assembly 20 by using robot, wherein support layer 30 is polyimide tape; positive electrode tab 42 and negative electrode tab 41 are respectively welded to the positive electrode lead-in terminal and negative electrode lead-in terminal on first shell 11, wherein the dimension L of the outermost electrode sheet 201 of electrode assembly 20 along the extension direction of tab is 26.4mm; the stacked electrode assembly 20 is placed in the first In a shell 11, ensure that the electrode assembly 20 and the first shell 11 are well matched, wherein the first shell 11 and the second shell 12 are made of steel, the wall thickness of the first shell 11 is 1.25 mm, the thickness of the second shell 12 is 1.25 mm, and along the thickness direction of the first shell 11, the distance between the assembly surface of the first shell 11 and the second shell 12 and the outermost pole piece 201 of the electrode assembly 20 is 0.17 mm; the second shell 12 and the first shell 11 are assembled, sealed by laser welding, and hot pressed to obtain a secondary battery 100.

[0079] The preparation process of the secondary battery 100 in Comparative Example 1 is substantially the same as that in Example 1, except that the secondary battery 100 in Comparative Example 1 does not have a support layer 30 disposed between the second housing 12 and the outermost pole piece 201 .

[0080] The preparation process of the secondary battery 100 in Examples 2 to 6 is basically the same as that in Example 1, except that the material of the support layer 30 in Examples 2 to 6 is different from that in Example 1. The material of the support layer 30 in Example 2 is polycarbonate, the material of the support layer 30 in Example 3 is polyamide, the material of the support layer 30 in Example 4 is polyoxymethylene, the material of the support layer 30 in Example 5 is polybutylene terephthalate, and the support layer 30 in Example 6 is polyester tape.

[0081] The preparation process of the secondary battery 100 in Embodiments 7 to 12 is substantially the same as that in Embodiment 1, except that the thickness of the support layer 30 in Embodiments 7 to 12 is different from that in Embodiment 1.

[0082] The preparation process of the secondary battery 100 in Examples 13 to 16 is substantially the same as that in Example 1, except that the width of the support layer 30 in Examples 13 to 16 is different from that in Example 1.

[0083] After the secondary batteries 100 in the comparative example and the embodiment were prepared, the protrusion of the bottom wall 111 was measured. In addition, all the secondary batteries 100 in each group were subjected to a lithium deposition test to observe the lithium deposition of the secondary batteries 100. After the test, the experimental results were recorded in Table 1.

[0084] The specific process of measuring the protrusion of the bottom wall 111 is as follows: use a laser thickness gauge to emit a beam of highly collimated, monochromatic laser focused on the bottom wall 111 and receive the laser reflected back from the bottom wall 111, and obtain multiple time values ​​required for the laser to focus on different positions of the bottom wall 111 and reflect back in a scanning mode; calculate the time difference between the minimum and maximum values ​​of the multiple time values, and the result output by the laser thickness gauge based on the time difference is the protrusion of the bottom wall 111.

[0085] The specific process of lithium extraction test is as follows: (1) Maintain the test temperature at 25°C; (2) The secondary battery 100 was left to stand for 30 min; (3) 1.3C constant current charging to 4.1V, then constant voltage charging to 1C; (4) 1C constant current charging to 4.2V, then constant voltage charging to 0.7C; (5) 0.7C constant current charging to 4.3V, then constant voltage charging to 0.025C; (6) Let stand for 5 minutes; (7) 0.7C constant current discharge to 3V; (8) Let stand for 5 minutes; (9) Steps 3 to 8 are repeated 800 times; (10) Disassemble the secondary batteries 100 and observe whether lithium deposition occurs on the negative electrode plates 21. Count the number of secondary batteries 100 with lithium deposition on the negative electrode plates 21 in each group. Count the number of secondary batteries 100 with lithium deposition on the negative electrode plates 21 in this group of experiments as N. Then, the lithium deposition incidence rate of the secondary batteries 100 in this group of experiments is N / 20.

[0086] Table 1 In Table 1, the protrusion of the bottom wall 111 in Examples 1 to 16 is less than the protrusion of the bottom wall 111 in Comparative Example 1. That is, the present application provides a support layer 30 between the second housing 12 and the outermost pole piece 201, and the support layer 30 is a polyimide tape or a polyester tape, or the material of the support layer 30 includes at least one of polycarbonate, polyamide, polyoxymethylene and polybutylene terephthalate, which is conducive to reducing the degree of outward protrusion of the bottom wall 111, thereby improving the problem of the secondary battery 100 being too thick.

[0087] In Table 1, according to Example 1, Example 7 to Example 12, the protrusion of the bottom wall 111 in Example 1, Example 8 to Example 12 is significantly less than the protrusion of the bottom wall 111 in Example 7, the protrusion of the bottom wall 111 in Example 1, Example 9 to Example 12 is significantly less than the protrusion of the bottom wall 111 in Example 8, the lithium deposition rate of the secondary battery 100 in Example 1, Example 7 to Example 11 is significantly less than the lithium deposition rate of the secondary battery 100 in Example 12, and the lithium deposition rate of the secondary battery 100 in Example 1, Example 7 to Example 10 is significantly less than the lithium deposition rate of the secondary battery 100 in Example 11. That is, by setting 0.2≤H / D≤0.7, the present application can reduce the degree of outward protrusion of the bottom wall 111 while ensuring the effect of hot pressing and reducing the risk of subsequent lithium deposition in the secondary battery 100. By setting 0.3≤H / D≤0.6, the outward protrusion of the bottom wall 111 can be further reduced while the effect of hot pressing can be further ensured, thereby further reducing the risk of subsequent lithium deposition in the secondary battery 100.

[0088] In Table 1, according to Examples 13 to 16, the protrusion of the bottom wall 111 in Examples 14 to 16 is significantly less than that in Example 13, and the protrusion of the bottom wall 111 in Example 15 is equivalent to that in Example 16, but the width of the support layer 30 in Example 15 is less than that in Example 16. That is, by setting 0.05≤W / L≤0.2, the present application can reduce the outward protrusion of the bottom wall 111 while making the volume of the support layer 30 smaller, which is beneficial to reducing the overall weight of the secondary battery 100.

[0089] In addition, those skilled in the art should recognize that the above embodiments are only used to illustrate the present application, and are not intended to limit the present application. As long as they are within the essential scope of the present application, appropriate changes and modifications to the above embodiments are within the scope disclosed in the present application.

Claims

1. A secondary battery, characterized in that: include: The shell is a metal shell, comprising a first shell and a second shell arranged opposite to each other along a first direction, the first shell comprising a bottom wall and a side wall, the side wall being connected to the periphery of the bottom wall and forming a pit with the bottom wall, the second shell covering the pit, and a part of the second shell being connected to the side wall; the first direction is the thickness direction of the shell; An electrode assembly is disposed in the recess; the electrode assembly comprises an outermost electrode sheet; A support layer, at least part of which is disposed between the second shell and the outermost pole piece, and when observed along the first direction, the support layer overlaps with at least part of the edge of the outermost pole piece; the material of the support layer includes at least one of polycarbonate, polyamide, polyoxymethylene and polybutylene terephthalate; or, the support layer is insulating tape.

2. The secondary battery according to claim 1, characterized in that: When viewed along the first direction, the support layer does not extend beyond the edge of the outermost pole piece.

3. The secondary battery according to claim 1, characterized in that: The secondary battery includes a tab connected to the electrode assembly. When viewed along the first direction, the edge of the outermost pole piece includes a tab extending edge and a non-tab extending edge. The support layer at least overlaps the non-tab extending edge.

4. The secondary battery according to claim 3, characterized in that: When viewed along the first direction, the support layer overlaps all edges of the outermost pole piece.

5. The secondary battery according to any one of claims 1 to 4, characterized in that: The supporting layer has a ring-shaped structure.

6. The secondary battery according to claim 5, characterized in that: The secondary battery includes a pole lug connected to the electrode assembly, and along the extension direction of the pole lug, the size of the outermost pole piece is L; the support layer includes an inner wall and an outer wall, the distance between the inner wall and the outer wall is W, 0.05≤W / L≤0.

2.

7. The secondary battery according to claim 1, characterized in that: Along the first direction, the maximum distance between the second shell and the outermost pole piece is D, the thickness of the portion of the support layer disposed between the second shell and the outermost pole piece is H, and 0.2≤H / D≤0.

7.

8. The secondary battery according to claim 7, characterized in that: 0.3≤H / D≤0.

6.

9. The secondary battery according to claim 1, characterized in that: The supporting layer is insulating tape, and the insulating tape includes polyimide tape and / or polyester tape.

10. The secondary battery according to claim 1, characterized in that: The shell is a steel shell.

11. The secondary battery according to claim 10, characterized in that: The thickness of the second shell is 0.75 mm to 1.5 mm.

12. An electrical equipment, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 11.

13. A method for preparing a secondary battery according to any one of claims 1 to 11, characterized in that: The following steps are involved: The support layer is arranged on the outermost electrode piece of the electrode assembly, so that the support layer overlaps at least a portion of the edge of the outermost electrode piece along the first direction; Connecting the positive electrode and the negative electrode of the electrode assembly to the positive electrode lead-out terminal and the negative electrode lead-out terminal of the first shell, respectively; Placing the electrode assembly and the support layer in the recess of the first shell so that the support layer is farther away from the bottom wall of the first shell than the electrode assembly; The second shell and the first shell are sealed and connected, and then hot pressed to obtain the secondary battery.

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