A curved pole core, a curved battery and a preparation method thereof

Abstract

In order to overcome the problem that the shape of existing curved batteries cannot remain stable for a long time, and wrinkles are easily formed on the diaphragm and the pole piece at the bending part of the pole core, resulting in lithium deposition in the battery, the present invention provides a curved battery, including a battery cell and a splint located on both sides of the battery cell, the battery cell including a curved portion formed at the bending part and a straight portion formed at the non-bending part, the splint has the same curved shape as the battery cell to be attached to the surface of the battery cell, the battery cell includes stacked pole pieces and diaphragms, and an active material layer is arranged on the surface of the pole piece, and the surface density of the active material layer of the pole piece at the curved part is lower than that at the straight part; the present invention facilitates the bending of the bare battery cell by setting the surface density of the battery cell pole piece coated at the curved part to be lower than the surface density coated at the straight part; at the same time, the splints with a curved shape are fixed on both sides of the battery cell, and the splints can effectively prevent the curvature of the battery from changing during use, thereby avoiding the morphological change of the battery and damaging the battery performance.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible batteries, and in particular to a curved pole core, a curved battery and a preparation method thereof. Background Art

[0002] Curved batteries play an important role in specific fields such as wearable devices such as VR headsets, AR headsets, and telescopes. They can increase the energy density per unit volume of batteries, thereby improving the battery life of wearable devices. In the past, the process of making curved soft-package lithium-ion batteries was generally to obtain conventional batteries through packaging, liquid injection, and formation, and then the batteries were rolled or molded to obtain curved soft-package lithium-ion batteries; however, this method may cause damage to the battery, and some soft-package lithium-ion batteries have large-area wrinkles and damage on the appearance.

[0003] The patent number CN106159119B-A soft-package lithium-ion battery and its manufacturing method further improves the manufacturing method. It pre-hot-presses the pole core that matches the arched shell through a hot-pressing mold, and prepares the arched shell through a shell punching mold; then the pole core is heat-sealed and packaged in the arched shell. In this way, the pole core and the shell are made into an arch in the initial stage of battery manufacturing, so that the shape of the arch can remain stable to a certain extent during use. It can improve the phenomenon of large-area wrinkling and damage on the appearance of the battery to a certain extent. However, in the early stage, the pole core was only hot-pressed once, and the curved shape could not remain stable for a long time. At the same time, the shape of the curved battery that can be produced is single, which cannot meet the shape requirements of multiple types of curved batteries. In addition, wrinkles are prone to appear at the diaphragm and the pole piece at the bending part of the pole core, which leads to lithium deposition in the battery, seriously damaging the battery cycle and safety performance; therefore, how to overcome the above-mentioned technical problems and defects has become a key problem that needs to be solved. Summary of the invention

[0004] In view of the problem that the shape of existing curved batteries cannot remain stable for a long time, and wrinkles are easily formed on the diaphragm and pole piece at the curved part of the pole core, resulting in lithium deposition in the battery, the present invention provides a curved pole core, a curved battery and a preparation method thereof.

[0005] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0006] In one aspect, the present invention provides a curved pole core, comprising a battery core and clamps located on both sides of the battery core, wherein the battery core comprises a curved portion formed at a curved position and a straight portion formed at a non-curved position, wherein the clamps have the same curved shape as the battery core so as to be attached to the surface of the battery core, wherein the battery core comprises a stacked pole piece and a diaphragm, wherein an active material layer is disposed on the surface of the pole piece, and the surface density of the active material layer of the pole piece at the curved portion is lower than that at the straight portion;

[0007] The surface density of the active material layer of the pole piece coated on one side of the curved part = coefficient * surface density of the active material layer of the pole piece coated on one side of the straight part; the value range of the coefficient is 0.1-0.9; the surface density of the active material layer of the pole piece coated on one side of the straight part is 1-30 mg / cm 2 ; Wherein, the coefficient refers to the ratio of the spacing between microcracks in the coating material at the bending protrusion of the pole piece to the upper limit standard value of the spacing between microcracks at the corresponding bending curvature; the upper limit standard value of the spacing at the microcrack protrusion is 8-15mm.

[0008] Optionally, the curvature of the curved portion and the coefficient satisfy the following relationship:

[0009] When 0<bending rate≤1μm -1 When , the coefficient ranges from 0.7 to 0.9;

[0010] When 1μm -1 <Bending rate≤10μm -1 When , the coefficient ranges from 0.5 to 0.7;

[0011] When 10μm -1 <Bending rate≤100μm -1 When , the coefficient ranges from 0.3 to 0.5;

[0012] When 100 μm -1 < curvature, the coefficient ranges from 0.1 to 0.3.

[0013] Optionally, the N / P value of the battery cell at the bent portion is in the range of 1.1-1.3.

[0014] Optionally, the electrode sheet includes a positive electrode sheet and a negative electrode sheet, the positive electrode sheet and the negative electrode sheet are respectively located on both sides of the diaphragm, and the positive electrode sheet, the diaphragm and the negative electrode sheet are stacked to form the battery cell.

[0015] Optionally, the projection of the positive electrode sheet on the clamping plate falls within the coverage of the clamping plate, and the projection of the clamping plate on the diaphragm falls within the coverage of the diaphragm; the length of the positive electrode sheet is L1mm, the width of the positive electrode sheet is M1mm, the length of the clamping plate is L2mm, the width of the clamping plate is M2mm, the length of the diaphragm is L3mm, the width of the diaphragm is M3mm, and the relationship is satisfied: L1 <L2<L3,M1<M2<M3。

[0016] Optionally, L1 and L2 satisfy the relationship: 2≤L2-L1≤4; M1 and M2 satisfy the relationship: 2≤M2-M1≤4; L3 and L2 satisfy the relationship: 2≤L3-L2≤4; M3 and M2 satisfy the relationship: 2≤M3-M2≤4.

[0017] Optionally, a bonding layer is provided on one side of the two clamping plates facing the battery core.

[0018] Optionally, adhesive tape is further included, and the clamping plate is fixed to the four corners of the battery cell by the adhesive tape, and the clamping plate is fixed to the bent portion of the battery cell by the adhesive tape.

[0019] Another aspect of the present invention provides a curved battery, comprising the curved pole core and a battery shell as described above, wherein the battery shell has the same curved shape as the curved pole core, and the curved pole core is arranged inside the battery shell.

[0020] Another aspect of the present invention provides a method for preparing a curved battery, comprising the following steps:

[0021] The positive electrode sheet, the negative electrode sheet and the separator are stacked to form a battery cell;

[0022] The curved clamping plate is attached and assembled to two larger surfaces of the battery cell to form a curved pole core;

[0023] The curved pole core is placed in a battery casing having the same curved shape and packaged to form a battery.

[0024] Optionally, the curved portion and the straight portion of the battery cell both extend in a linear direction, the cross-sections of the battery cell perpendicular to the linear direction are the same, and the active material layer on the pole piece is coated perpendicular to the linear direction.

[0025] According to the curved battery provided by the present invention, the surface density of the battery cell electrode sheets coated on the curved portion is set lower than the surface density of the electrode sheets coated on the straight portion, thereby facilitating the bending of the bare battery cell. At the same time, the curved splints are fixed on both sides of the battery cell. The splints can effectively prevent the curvature of the battery from changing during use, thereby avoiding changes in the battery's morphology and damaging the battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1This is a schematic diagram of the assembly of the "S"-shaped bent battery cell and the clamp.

[0028] Figure 2 This is a schematic diagram of the structure of a "C" type battery with two pole ears on the same side of the pole piece.

[0029] Figure 3 This is a schematic diagram of the structure of a "C" type battery with double pole ears on both sides of the pole piece.

[0030] Figure 4 Schematic diagram of the electrode coating method for an "S" type battery.

[0031] Figure 5 It is a left view schematic diagram of a "C" type splint.

[0032] Figure 6 Schematic diagram of the top view of the "C" type splint.

[0033] The reference numerals in the drawings of the specification are as follows:

[0034] 1-battery cell; 11-positive electrode sheet; 12-diaphragm; 13-negative electrode sheet; 14-positive electrode ear; 15-negative electrode ear; 16-bent portion; 17-straight portion; 2-splitting plate; 21-first curved surface; 22-second curved surface; 23-side surface; 3-tape. DETAILED DESCRIPTION

[0035] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0036] In the description of the present invention, it should be understood that the terms "longitudinal", "radial", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0037] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0038] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0039] like Figure 1 As shown, in one embodiment, the present invention provides a curved pole core, including a battery cell 1 and a clamping plate 2 located on both sides of the battery cell 1, wherein the battery cell 1 includes a curved portion 16 formed at the curved portion and a straight portion 17 formed at the non-curved portion, and the clamping plate 2 has the same curved shape as the battery cell 1 to be attached to the surface of the battery cell 1, and the battery cell 1 includes a stacked pole piece and a diaphragm 12, and an active material layer is arranged on the surface of the pole piece, and the surface density of the pole piece of the battery cell 1 at the curved portion 16 is lower than that at the straight portion 17; the surface density of the active material layer of the pole piece coated on one side of the curved portion = coefficient * the surface density of the active material layer of the pole piece coated on one side of the straight portion; the value range of the coefficient is 0.1-0.9; the surface density of the active material layer of the pole piece coated on one side of the straight portion is 1-30 mg / cm 2 ; Wherein, the coefficient refers to the ratio of the spacing between microcracks in the coating material at the bending protrusion of the pole piece to the upper limit standard value of the spacing between microcracks at the corresponding bending curvature; the upper limit standard value of the spacing at the microcrack protrusion is 8-15mm.

[0040] Specifically, the surface density of the active material layer of the electrode sheet in the curved portion 16 is lower than that in the straight portion 17 , thereby facilitating the bending of the bare cell 1 .

[0041] Furthermore, the shape of the curved pole core may be S-shaped, C-shaped or other curved shapes.

[0042] The splint 2 has the same curved shape as the battery cell 1 to meet the application requirements. The splint 2 can effectively prevent the curvature of the battery from changing during use, avoid changes in the battery's shape, and damage the battery's performance. The material of the splint 2 includes but is not limited to polypropylene sheet (PP), polyethylene sheet (PE), polybutylene terephthalate resin sheet (PBT), polyimide sheet (PI), polyvinylidene fluoride sheet (PVDF), and polytetrafluoroethylene sheet (PTFE).

[0043] In some embodiments, the thickness of the single-piece curved splint 2 is between 0.5 and 5.0 mm. In some preferred embodiments, the thickness of the single-piece curved splint 2 is 1.0 mm.

[0044] The material of the clamping plate 2 should have the following properties: it is a polymer compound with a molecular weight of ≥ 1 million, a melting starting temperature of ≥ 150°C, between -50-150°C, good shape stability and certain mechanical toughness, good chemical inertness, resistance to strong acids and alkalis, water and various organic solvents, and an aging life of at least 10 years, thereby accompanying the full life cycle of the bending pole core;

[0045] The material of the splint 2 is non-toxic and has good adhesion. Polar functional groups such as hydroxyl (-OH) and carboxyl (-COOH) can be grafted onto the organic molecular chain of the raw material, thereby improving the adhesion of the splint 2.

[0046] In some embodiments, the surface density of the active material layer of the pole piece coated on one side of the curved portion varies with the curvature of the bending, and the surface density of the active material layer of the pole piece coated on one side of the curved portion = coefficient * surface density of the active material layer of the pole piece coated on one side of the straight portion, wherein the coefficient refers to the ratio of the spacing between microcracks in the coating material at the curved protrusion of the pole piece to the upper limit standard value of the spacing between microcracks under the corresponding bending curvature.

[0047] In some embodiments, the upper limit standard value of the spacing between microcrack protrusions is 8-15 mm. In some preferred embodiments, the upper limit standard value of the spacing between microcrack protrusions is 10 mm.

[0048] like Figure 1 As shown, in one embodiment, the curvature of the curved portion and the coefficient satisfy the following relationship:

[0049] When 0<bending rate≤1μm -1 When , the coefficient ranges from 0.7 to 0.9;

[0050] When 1μm -1 <Bending rate≤10μm -1 When , the coefficient ranges from 0.5 to 0.7;

[0051] When 10μm -1 <Bending rate≤100μm -1 When , the coefficient ranges from 0.3 to 0.5;

[0052] When 100 μm -1 < curvature, the coefficient ranges from 0.1 to 0.3.

[0053] In some preferred embodiments, when 0<curvature≤1 μm -1When , the value range of the coefficient is 0.8.

[0054] In some preferred embodiments, when 1 μm -1 <Bending rate≤10μm -1 When , the value range of the coefficient is 0.6.

[0055] In some preferred embodiments, when 10 μm -1 <Bending rate≤100μm -1 When , the value range of the coefficient is 0.4.

[0056] In some preferred embodiments, when 100 μm -1 < curvature, the value range of the coefficient is 0.2.

[0057] Specifically, the surface density of the active material layer of the pole piece coated on the curved portion 16 is set lower than the surface density of the active material layer of the pole piece coated on the straight portion 17 , thereby facilitating the bending of the bare cell 1 .

[0058] In a preferred embodiment, the surface density of the active material layer of the electrode on the straight portion is 1-16 mg / cm 2 Specifically, the surface density of the active material layer of the pole piece coated on one side of the straight portion is 1 mg / cm 2 , 2mg / cm 2 、3mg / cm 2 , 4mg / cm 2 , 5mg / cm 2 , 6mg / cm 2 , 7mg / cm 2 , 8mg / cm 2 , 9mg / cm 2 、10mg / cm 2 、11mg / cm 2 , 12mg / cm 2 、13mg / cm 2 、14mg / cm 2 、15mg / cm 2 、16mg / cm 2 、17mg / cm 2 、18mg / cm 2 、19mg / cm 2 , 20mg / cm 2 , 21mg / cm 2 , 22mg / cm 2 , 23mg / cm 2 , 24mg / cm 2 , 25mg / cm 2 , 26mg / cm2 , 27mg / cm 2 、28mg / cm 2 , 29mg / cm 2 or 30mg / cm 2 Any point value or a range of values ​​consisting of any two point values ​​in .

[0059] like Figure 1 As shown, in one embodiment, the N / P value of the battery cell 1 at the bent portion is in the range of 1.1-1.3.

[0060] In some preferred embodiments, the N / P value ranges from 1.15 to 1.2. Specifically, N / P=(negative electrode single surface surface density*negative electrode active material discharge specific capacity*negative electrode active material addition ratio) / (positive electrode single surface surface density*positive electrode active material charge specific capacity*positive electrode active material addition ratio).

[0061] When the N / P value is between 1.1 and 1.3, the negative electrode has sufficient lithium insertion sites to accommodate the lithium released from the positive electrode, which will not cause lithium deposition at the negative electrode, and the battery cell can be reversibly charged and discharged in a cycle.

[0062] like Figure 2 and Figure 3 As shown, in one embodiment, the electrode sheets include a positive electrode sheet 11 and a negative electrode sheet 13, the positive electrode sheet 11 and the negative electrode sheet 13 are respectively located on both sides of the diaphragm 12, and the positive electrode sheet 11, the diaphragm 12 and the negative electrode sheet 13 are stacked to form the battery cell 1.

[0063] In some embodiments, the positive electrode sheet 11 includes a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder.

[0064] In some embodiments, the positive electrode active material is not limited to ternary materials (LiNi x Co y Mn 1-x-y or LiNi x Co y Al 1-x-y etc.), LiCoO2, LiMn2O4, LiFePO4, NaxMO2 (M is a transition metal atom, 0<x≤1), NaxM1[M2(CN)6] (M is a transition metal atom, 0<x≤2), Na x M y (X a O b ) z Z w (M is a transition metal ion, X is P, S, W, etc., and Z is F, OH, etc.)

[0065] In some embodiments, the conductive agent includes, but is not limited to, one or more of conductive carbon black SP, conductive graphite KS-6, carbon nanofiber VGCF, single-walled carbon nanotubes SWCNTs, and multi-walled carbon nanotubes MWCNTs.

[0066] In some embodiments, in some embodiments, the positive electrode binder includes but is not limited to one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylic resin.

[0067] In some embodiments, the mass percentage of each component in the positive electrode active material layer is: 85-98% of positive electrode active material, 0.5-2.5wt% of conductive agent, and 1.0-2.0wt% of binder.

[0068] The mass ratio of the positive electrode active material in the positive electrode active material layer is within the above range, so that the secondary battery has a higher capacity.

[0069] In some embodiments, the positive electrode current collector is selected from a metal material that can conduct electrons. Preferably, the positive electrode current collector includes one or more of copper, nickel, tin, copper, and stainless steel. In a more preferred embodiment, the positive electrode current collector is selected from aluminum foil.

[0070] In some embodiments, the positive electrode sheet can be prepared according to conventional methods in the art. For example, the positive electrode active material layer is usually prepared by coating a positive electrode slurry made of a positive electrode active material, a positive electrode conductive agent, a positive electrode binder and any other components on a positive electrode current collector, and then drying and cold pressing. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0071] In some embodiments, the solid content of the positive electrode slurry is between 45% and 75%. Preferably, the solid content of the positive electrode slurry is between 50% and 65%.

[0072] In some embodiments, the negative electrode sheet 13 includes a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder.

[0073] In some embodiments, the negative electrode active material includes, but is not limited to, one or more of natural graphite, artificial graphite, micron silicon, nano silicon, silicon carbon, silicon oxygen (silicon oxide), hard carbon (resin carbon, carbon black, etc.) and soft carbon (coke, graphitized mesophase carbon microbeads, carbon fibers, etc.).

[0074] In some embodiments, the conductive agent includes, but is not limited to, one or more of conductive carbon black SP, conductive graphite KS-6, single-walled carbon nanotubes SWCNTs, multi-walled carbon nanotubes MWCNTs, and graphene.

[0075] In some embodiments, the binder includes, but is not limited to, one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA).

[0076] In some embodiments, the mass percentage of each component in the negative electrode active material layer is: 85-96% of negative electrode active material, 0.5-2.5wt% of conductive agent, and 1.0-3.5wt% of binder.

[0077] In some embodiments, the negative electrode current collector is selected from a metal material that can conduct electrons. Preferably, the negative electrode current collector includes one or more of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0078] In some embodiments, the negative electrode sheet can be prepared according to conventional methods in the art. For example, the negative electrode active material layer is usually prepared by coating a negative electrode slurry made of a negative electrode active material, a negative electrode conductive agent, a negative electrode binder and any other components on a negative electrode current collector, and then drying and cold pressing. The solvent can be an aqueous solvent, but is not limited thereto.

[0079] In some embodiments, the solid content of the negative electrode slurry is between 40-65%. In some preferred embodiments, the solid content of the negative electrode slurry is between 45-55%.

[0080] In some embodiments, the diaphragm 12 plays a role in conducting lithium ion transmission, blocking electron transmission, and isolating the positive and negative electrodes 13 to prevent short circuits in the curved battery. The diaphragm 12 includes but is not limited to a polypropylene PP diaphragm 12, a polyethylene PE diaphragm 12, a PP / PE composite diaphragm 12, and a polyimide PI diaphragm 12. Preferably, a ceramic coating composed of PVDF and Al2O3 is sprayed or coated on both sides or one side of the base film, which can improve the high temperature resistance, liquid absorption and liquid retention of the diaphragm 12, reduce the mechanical micro-short circuit during the cycle, and effectively improve the cycle life. At the same time, it can neutralize the free HF in the electrolyte, increase the micropore tortuosity, reduce self-discharge, and finally improve the fit between the electrode and the diaphragm 12, shorten the transmission distance of lithium ions, and avoid the problem of lithium precipitation in the curved battery during charging and discharging. Preferably, the porosity of the diaphragm 12 is between 35-55%, and preferably, the porosity of the diaphragm 12 is between 40-50%.

[0081] like Figure 2 and Figure 3As shown, in some embodiments, the positive electrode sheet 11, the separator 12, and the negative electrode sheet 13 are stacked in a "Z" shape on a stacking machine, and the bare battery cell 1 after the stacking process is completed uses adhesive tape 3 to fix the separator 12. Then, the positive and negative electrode sheet 13 tab foils are pre-welded, cut, and the positive and negative tabs 15 are welded.

[0082] like Figure 2 and Figure 3 As shown, in some embodiments, the positive electrode tab 14 and the negative electrode tab 15 can be welded at the same end or different ends of the battery cell 1 .

[0083] like Figure 2 and Figure 3 As shown, in one embodiment, the projection of the positive electrode sheet 11 on the negative electrode sheet 13 falls within the coverage of the clamping plate 2, and the projection of the clamping plate 2 on the diaphragm 12 falls within the coverage of the diaphragm 12; the length of the positive electrode sheet 11 is L1mm, the width of the positive electrode sheet 11 is M1mm, the length of the clamping plate 2 is L2mm, the width of the clamping plate 2 is M2mm, the length of the diaphragm 12 is L3mm, the width of the diaphragm 12 is M3mm, and the relationship is satisfied: L1 <L2<L3,M1<M2<M3。

[0084] Specifically, the area of ​​the positive electrode sheet 11 is smaller than that of the negative electrode sheet 13, and the area of ​​the negative electrode sheet 13 is smaller than that of the diaphragm 12; thereby ensuring that the battery will not have lithium deposition at the negative electrode or short circuit between the positive and negative electrodes during the charge and discharge process.

[0085] Furthermore, the size of the clamping plate 2 is consistent with the size of the negative electrode sheet 13. The clamping plates 2 are fixed on both sides of the battery cell 1, and the size of the clamping plates 2 is consistent with the size of the negative electrode sheet 13, so that the battery cell 1 is fixed between the two clamping plates 2, and the battery cell 1 is prevented from moving between the two clamping plates 2, resulting in the battery cell 1 being not firmly fixed, the battery cell 1 being deformed, and being unable to maintain stability for a long time.

[0086] like Figure 2 and Figure 3 As shown, in one embodiment, L1 and L2 satisfy the relationship: 2≤L2-L1≤4; M1 and M2 satisfy the relationship: 2≤M2-M1≤4; L3 and L2 satisfy the relationship: 2≤L3-L2≤4; M3 and M2 satisfy the relationship: 2≤M3-M2≤4.

[0087] In a preferred embodiment, L1 and L2 satisfy the relationship: 3=L2-L1; M1 and M2 satisfy the relationship: 3=M2-M1; L3 and L2 satisfy the relationship: 3=L3-L2; M3 and M2 satisfy the relationship: 3=M3-M2.

[0088] When L1 and L2 satisfy the relationship: 2≤L2-L1≤4; M1 and M2 satisfy the relationship: 2≤M2-M1≤4; L3 and L2 satisfy the relationship: 2≤L3-L2≤4; M3 and M2 satisfy the relationship: 2≤M3-M2≤4, it can not only ensure that the battery will not have problems such as negative electrode lithium deposition and positive and negative electrode short circuit during the charging and discharging process; but also avoid the problem that the negative electrode sheet 13 and the diaphragm 12 are too large in size, resulting in a large battery volume and low battery volume energy density.

[0089] like Figure 1 and Figure 2 As shown, in one embodiment, a bonding layer is provided on one side of the two clamping plates 2 facing the battery core 1 .

[0090] Specifically, the adhesive layer includes one or more of PVDF glue, SBR, PP, EVA hot melt adhesive, PO hot melt adhesive, PUR hot melt adhesive, TPR material, TPU hot melt adhesive, polyamide PA, polyester PES, polyethylene and polyester amide PEA.

[0091] The side of the clamping plate 2 facing the bare battery cell 1 is sprayed with an adhesive layer glue to improve the fit between the clamping plate 2 and the battery cell 1 so that the battery cell 1 and the clamping plate 2 are tightly fixed.

[0092] like Figure 5 and Figure 6 As shown, in one embodiment, the side of the clamping plate 2 away from the battery cell 1 is a first curved surface 21, and the side of the clamping plate 2 close to the battery cell 1 is a second curved surface 22. The first curved surface 21 and the second curved surface 22 are connected at both ends by two side surfaces 23. The side surfaces 23 are arranged in the thickness direction of the clamping plate 2. The angle formed between the first curved surface 21 and the side surfaces 23 is an R1 angle. The R1 angle is a rounded angle. The arc length of the R1 angle is C1. The thickness of the clamping plate 2 is H. C1 and H satisfy the relationship: C1≥H / 2, in units of mm.

[0093] The angle formed between the second curved surface 22 and the side surface 23 is R2, which is a rounded angle. The arc length of R2 is C2, the thickness of the clamping plate 2 is H, and C2 and H satisfy the relationship: C2 ≥ H / 10, in mm;

[0094] The four inner angles of the first curved surface 21 are all R3 angles, the R3 angle is a rounded angle, the arc length of the R3 angle is C3, the thickness of the clamping plate 2 is H, and C3 and H satisfy the relationship: C3 ≥ H / 2, the unit is mm;

[0095] The rounded corners of the R1 angle, the R2 angle and the R3 angle are set to prevent the junction between the clamping plate 2 and the aluminum-plastic film shell from being too sharp and damaging the aluminum-plastic film.

[0096] like Figure 1 and Figure 2As shown, in one embodiment, adhesive tape 3 is further included, and the clamping plate 2 is fixed to the four corners of the battery cell 1 by the adhesive tape 3 , and the clamping plate 2 is fixed to the bent portion 16 of the battery cell 1 by the adhesive tape 13 .

[0097] Then, the curved splint 2 is bonded to the two larger surfaces of the battery cell 1. When bonding, the side of the splint 2 with the adhesive layer is facing the outer surface of the battery cell 1. After the splint 2 is bonded to the battery cell 1, the four corners of the splint 2 and the battery cell 1 are fixed by adhesive tape 3, and the splint 2 and the curved portion 16 of the battery cell 1 are also fixed by adhesive tape 3.

[0098] Preferably, the adhesive tape 3 base material is made of corrosion-resistant and high-temperature-resistant polyethylene terephthalate (PET) or polyimide (PI), and preferably, the adhesive tape 3 base material is made of polyimide (PI). Preferably, the adhesive layer of the adhesive tape 3 is made of polymethyl methacrylate (PMMA).

[0099] Another aspect of the present invention provides a curved battery, comprising the curved pole core and a battery shell as described above, wherein the battery shell has the same curved shape as the curved pole core, and the curved pole core is arranged inside the battery shell.

[0100] Another aspect of the present invention provides a method for preparing a curved battery, comprising the following steps:

[0101] The positive electrode sheet 11, the negative electrode sheet 13 and the separator 12 are stacked to form a battery cell 1;

[0102] The curved clamping plate 2 is attached and assembled to the two larger surfaces of the battery core 1 to form a curved pole core;

[0103] The curved pole core is placed in a battery casing having the same curved shape and packaged to form a battery.

[0104] The specific steps include:

[0105] The positive electrode sheet 11, the separator 12 and the negative electrode sheet 13 are stacked alternately to form a battery cell 1;

[0106] In one embodiment, the thickness of the battery cell 1 is 1.0-5.0 mm.

[0107] In a preferred embodiment, the thickness of the battery cell 1 is 1.0-4.0 mm. Specifically, the thickness of the battery cell 1 is 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, 2.6 mm, 2.7 mm, 2.8 mm, 2.9 mm, 3.0 mm, 3.1 mm, 3.2 mm, 3.3 mm, 3.4 mm, 3.5 mm, 3.6 mm, 3.7 mm, 3.8 mm, 3.9 mm, 4.0 mm, 4.1 mm, 4.2 mm, 4.3 mm, 4.4 mm, 4.3. mm, 4.6 mm, 4.7 mm, 4.8 mm, 4.9 mm or 5.0 mm, any one of the values ​​or a range consisting of any two values.

[0108] When the thickness of the bent battery cell 1 is less than or equal to 5 mm, the purpose of making the bent battery cell 1 bendable can be achieved, and the situation that the bent battery cell 1 is too thick and difficult to bend can be avoided.

[0109] When the thickness of the bent battery cell 1 is greater than or equal to 1.0 mm, the energy density of the bent battery cell 1 can be guaranteed, the battery life of the wearable device can be maintained, and the problem of too low energy density of the soft-pack battery due to the small thickness of the bent battery cell 1 can be avoided.

[0110] Then, the curved splint 2 is bonded to the two larger surfaces of the battery cell 1. When bonding, the side of the splint 2 with the adhesive layer is facing the outer surface of the battery cell 1. After the splint 2 is bonded to the battery cell 1, the four corners of the splint 2 and the battery cell 1 are fixed by adhesive tape 3, and the splint 2 and the curved portion 16 of the battery cell 1 are also fixed by adhesive tape 3.

[0111] Afterwards, the highly flexible aluminum-plastic film is punched out into a shell having the same curved shape as the splint 2 using a customized die on a shell punching machine.

[0112] like Figure 1 As shown, the bare battery cell 1 with the bent splint 2 after molding is loaded into the aluminum-plastic film shell and top-sealed and side-sealed on the heat sealer. Among them, the copper seal head of the heat sealer needs to be customized according to the shape and size of the bent battery so that the sealing thickness of the aluminum-plastic film bag is uniform. Preferably, the packaging temperature is between 180 and 200°C, and preferably, the packaging temperature is 185°C. Preferably, the packaging time is between 3 and 10s, and preferably, the packaging time is 6s. Preferably, the packaging pressure is between 0.3 and 0.6Mpa, and preferably, the packaging pressure is between 0.4Mpa.

[0113] The packaged battery cell 1 is placed in a vacuum drying oven for baking. Preferably, the vacuum degree is between -80 and -100 Pa, and more preferably, the vacuum degree is -95 Pa.

[0114] Preferably, the baking temperature is between 80-110°C, more preferably, the baking temperature is 90°C.

[0115] Preferably, the baking time is 24-72 hours, more preferably, the baking time is 48 hours.

[0116] Preferably, the moisture content of the positive electrode sheet 11 after baking needs to be less than 150 ppm, more preferably, the moisture content of the positive electrode sheet 11 after baking needs to be less than 100 ppm.

[0117] Preferably, the moisture content of the negative electrode sheet 13 after baking needs to be less than 250 ppm, more preferably, the moisture content of the negative electrode sheet 13 after baking needs to be less than 150 ppm.

[0118] Preferably, the moisture content of the mixed sample of the positive electrode sheet 11, the negative electrode sheet 13 and the separator 12 after baking needs to be less than 400 ppm. More preferably, the moisture content of the mixed sample of the positive electrode sheet 11, the negative electrode sheet 13 and the separator 12 after baking needs to be less than 300 ppm.

[0119] After baking, if the moisture content meets the requirements, take it out and inject liquid; otherwise, bake it for a longer time until the moisture content meets the requirements.

[0120] Before filling, the physical and chemical indicators of the electrolyte need to be tested. Preferably, the moisture content needs to be less than 20ppm and the free acid (HF) content needs to be less than 50ppm. When the ambient dew point is ≤-30%RH, use a vacuum filling machine to fill the battery cell 1, vacuum evacuate, and seal the edges. The copper sealing head of the vacuum filling machine needs to be customized according to the shape and size of the curved battery, so that the sealing thickness of the aluminum-plastic film bag is uniform everywhere.

[0121] Preferably, the thickness of the double PP layer of the aluminum-plastic film after melting accounts for 60-85% of the thickness of the double PP layer before melting. More preferably, the thickness of the double PP layer of the aluminum-plastic film after melting accounts for 75% of the thickness of the double PP layer before melting.

[0122] The battery after injection is placed in an incubator for a certain period of time. During this process, the electrolyte can fully infiltrate the positive electrode sheet 11, the negative electrode sheet 13 and the diaphragm 12. Preferably, the incubator temperature is between 25-50°C and the standing time is 24-72h. Preferably, the incubator temperature is 45°C and the standing time is 48h.

[0123] After the battery is left to stand, it is pre-formed. The pressure clamp 2 of the formation cabinet needs to be customized according to the shape and size of the curved battery, so that the force is evenly applied to all parts of the battery and the solid electrolyte interface membrane SEI membrane grows evenly. Preferably, the pressure of the pressure clamp 2 is between 3-8kg / cm 2 Preferably, the pressure of the pressure clamp 2 is 6kg / cm 2 .

[0124] Perform step-rate constant current charging at a certain temperature, and step-charge to a certain cut-off voltage. During this process, the lithium ions migrated from the positive electrode material are partially reacted at the interface between the negative electrode material and the electrolyte to form a SEI film. Preferably, the pre-forming temperature is between 20-45°C, and preferably, the pre-forming temperature is 40°C. Preferably, the step rate is between 0.01C-0.5C, and preferably, the rate is between 0.05C-0.2C. Preferably, the step rate charging cut-off voltage is between 3.2-3.6V, and preferably, the step rate charging cut-off voltage is between 3.3-3.5V.

[0125] The pre-formed battery is subjected to secondary sealing and degassing, and the aluminum-plastic film airbag is punctured by a vacuum sealer, and vacuum air is extracted to perform vacuum sealing. The copper seal head of the vacuum sealer needs to be customized according to the shape and size of the curved battery, so that the sealing thickness of the aluminum-plastic film bag is uniform at all locations. Preferably, the thickness of the aluminum-plastic film double-layer PP layer after melting accounts for 60-85% of the thickness of the double-layer PP layer before melting, and preferably, the thickness of the aluminum-plastic film double-layer PP layer after melting accounts for 75% of the thickness of the double-layer PP layer before melting.

[0126] The batteries after secondary sealing and degassing are divided into different capacities, and the same forming cabinet as the pre-forming one is used. The pressure clamp 2 of the forming cabinet can be customized according to the shape and size of the curved battery, so that the force is evenly applied to all parts of the battery. Preferably, the pressure of the pressure clamp 2 is between 1-5kg / cm 2 Preferably, the pressure of the pressure clamp 2 is 3kg / cm 2 Preferably, the separation temperature is between 20-30°C, more preferably, the separation temperature is 25°C.

[0127] First, the battery cell 1 is charged at a constant current and constant voltage at a certain rate, and then the battery cell 1 is discharged at a constant current to a lower cut-off voltage at a certain rate. Preferably, the charging rate is between 0.1C and 0.5C, and more preferably, the charging rate is 0.2C. Preferably, the discharge rate is between 0.1C and 0.5C, and more preferably, the discharge rate is 0.2C.

[0128] The batteries after capacity separation are triple-sealed and heat-sealed using the same heat sealer as the packaging. The copper seal head of the heat sealer needs to be customized according to the shape and size of the curved battery so that the thickness of the seal at each location of the aluminum-plastic film bag is uniform. Preferably, the packaging temperature is between 180 and 200°C, and preferably, the packaging temperature is 185°C. Preferably, the packaging time is between 3 and 10s, and preferably, the packaging time is 6s. Preferably, the packaging pressure is between 0.3 and 0.6Mpa, and preferably, the packaging pressure is between 0.4Mpa.

[0129] After the three seals, the battery is cut, folded and ironed. The battery cutting, folding and ironing machine is used to cut, fold and iron the battery side seal edges. The finished battery looks like Figure 6 shown.

[0130] like Figure 1 As shown, in one embodiment, the curved portion 16 and the straight portion 17 of the battery cell 1 both extend in a linear direction, the cross-section of the battery cell 1 perpendicular to the linear direction is the same, and the active material layer on the pole piece is coated perpendicular to the linear direction.

[0131] The coating direction of the positive electrode sheet 11 and the negative electrode sheet 13 is carried out in a direction perpendicular to the linear direction. This is because the microcracks at the coating protrusions of the bent portion 16 of the bent battery cell 1 will increase with the increase of the bending degree. By reducing the coating surface density of the electrode sheet at the bent portion 16 with the increase of the bending degree, the microcracks and the degree of material falling at the coating protrusions can be reduced.

[0132] like Figure 4 As shown, in order to make an "S"-shaped curved battery, there are two curved parts in the lateral direction of the positive and negative electrode coating, so the present invention adopts a step-by-step coating process, and the coating is carried out in sequence from top to bottom and from left to right.

[0133] The present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0134] Example 1: This example manufactures a "C"-shaped curved battery.

[0135] Preparation of splint:

[0136] The customized curvature is 0.1 μm -1 , thickness is 1.0mm, shape is "C", R1 angle of the splint is 0.5mm, R2 angle of the splint is 0.1mm, R3 angle of the splint is 0.5mm, and the inner surface of the polypropylene plate (PP) with a length and width of 82mm×52mm is coated with PVDF glue.

[0137] Preparation of positive electrode:

[0138] The positive electrode active material lithium cobalt oxide, the conductive agent conductive carbon black (SP), and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95:1.5:3.5, and then N-methylpyrrolidone (NMP) is added as a solvent to prepare a positive electrode slurry, which is then stirred evenly.

[0139] The slurry was coated on the surface of the aluminum foil. The coating density of the slurry on the flat surface was 15.5 mg / cm 2 The coating density of the slurry on the curved part is 12.4 mg / cm2 , compacted density is 3.8g / cm 3 ; The calculated coefficient of the surface density of the positive electrode sheet is 0.8; the positive electrode sheet is cut into a size of 80mm×50mm for standby use.

[0140] Preparation of negative electrode:

[0141] The negative electrode active material SiC, the conductive agent single-walled carbon nanotubes (SWCNTs), and the binder polyacrylic acid (PAA) are mixed in a mass ratio of 93:2.5:4.5, and then deionized water is added as a solvent to prepare a negative electrode slurry, which is then stirred evenly.

[0142] The slurry is evenly coated on the surface of the copper foil. The coating density of the slurry on the flat surface is 1.9 mg / cm 2 The coating density of the slurry on the curved part is 1.52 mg / cm 2 , compacted density is 0.9g / cm 3 The negative electrode sheet has a surface density calculation coefficient of 0.8, and the negative electrode sheet is cut into a size of 82 mm × 52 mm for later use.

[0143] Preparation of diaphragm:

[0144] A double-sided ceramic glue-coated 12+2+2 diaphragm is used as the diaphragm.

[0145] Preparation of battery cells:

[0146] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, so that the separator is located between the positive electrode sheet and the negative electrode sheet to play an isolating role, the number of positive electrode sheets and negative electrode sheets are 11 and 12 respectively, and the thickness of the battery cell is 2.0 mm; the positive electrode ear is welded at the end of the positive electrode sheet, and the negative electrode ear is welded at the end of the negative electrode sheet to obtain a battery cell;

[0147] The side of the splint coated with PVDF glue is facing the outer surface of the battery core. After the splint and the battery core are attached to each other, the splint and the battery core are fixed at four corners by adhesive tape to obtain a curved pole core.

[0148] Preparation of lithium-ion batteries:

[0149] The battery shell is punched out into a "C"-shaped shell on a shell punching machine.

[0150] The curved pole core is loaded into a shell and placed in a package, and is manufactured into a curved battery through processes such as liquid injection, formation, secondary sealing and degassing, capacity division, cutting, folding and ironing.

[0151] Example 2

[0152] Example 2 is used to illustrate a curved pole core, a curved battery and a preparation method thereof disclosed in the present invention, and includes most of the operation steps in Example 1, except that:

[0153] In this embodiment, an "S"-shaped curved battery is manufactured.

[0154] Example 3

[0155] Example 3 is used to illustrate a curved pole core, a curved battery and a preparation method thereof disclosed in the present invention, and includes most of the operation steps in Example 1, except that:

[0156] Preparation of splint:

[0157] The customized curvature is 101μm -1 , thickness is 1.0mm, shape is "C", R1 angle of the splint is 0.5mm, R2 angle of the splint is 0.1mm, R3 angle of the splint is 0.5mm, and the inner surface of the polypropylene plate (PP) with a length and width of 82mm×52mm is coated with PVDF glue.

[0158] Preparation of positive electrode:

[0159] The slurry was coated on the surface of the aluminum foil. The coating density of the slurry on the flat surface was 15.5 mg / cm 2 The coating density of the slurry on the curved part is 1.55 mg / cm 2 , compacted density is 3.8g / cm 3 ; The calculation coefficient of the surface density of the positive electrode sheet is 0.1; cut the positive electrode sheet into a size of 80mm×50mm for standby use.

[0160] Preparation of negative electrode:

[0161] The slurry is evenly coated on the surface of the copper foil. The coating density of the slurry on the flat surface is 1.9 mg / cm 2 The coating density of the slurry on the curved part is 0.19 mg / cm 2 , compacted density is 0.9g / cm 3 The negative electrode sheet surface density calculation coefficient is 0.1, and the negative electrode sheet is cut into a size of 82 mm × 52 mm for later use.

[0162] Example 4

[0163] Example 4 is used to illustrate a curved pole core, a curved battery and a preparation method thereof disclosed in the present invention, and includes most of the operation steps in Example 1, except that:

[0164] Preparation of positive electrode:

[0165] The slurry was coated on the surface of the aluminum foil. The coating density of the slurry on the flat surface was 15.5 mg / cm 2 The coating density of the slurry on the curved part is 13.95 mg / cm 2, compacted density is 3.8g / cm 3 ; The calculated coefficient of the surface density of the positive electrode sheet is 0.9; the positive electrode sheet is cut into a size of 80mm×50mm for standby use.

[0166] Preparation of negative electrode:

[0167] The negative electrode active material graphite, the conductive agent SP, the conductive agent multi-walled carbon nanotubes (MWCNTs), the binder sodium carboxymethyl cellulose CMC, and the polystyrene butadiene copolymer emulsion are mixed in a mass ratio of 94.0:1.5:1.0:2.0:1.5, and then deionized water is added as a solvent to prepare a negative electrode slurry, which is stirred evenly.

[0168] The slurry is evenly coated on the surface of the copper foil. The coating density of the slurry on the flat surface is 9.9 mg / cm 2 The coating density of the slurry on the curved part is 8.91 mg / cm 2 , compacted density is 1.75g / cm 3 The calculated coefficient of the surface density of the negative electrode sheet is 0.9, and the negative electrode sheet is cut into a size of 82 mm × 52 mm for later use.

[0169] Preparation of battery cells:

[0170] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role. The number of positive electrode sheets and negative electrode sheets are 9 and 10 respectively, and the thickness of the battery cell is 2.7 mm. The positive electrode ear is welded at the end of the positive electrode sheet, and the negative electrode ear is welded at the end of the negative electrode sheet to obtain a battery cell.

[0171] Example 5

[0172] Example 5 is used to illustrate a curved pole core, a curved battery and a method for preparing the same disclosed in the present invention, and includes most of the operation steps in Example 1, except that:

[0173] Preparation of battery cells:

[0174] The positive electrode sheet, separator and negative electrode sheet prepared above are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role. The number of positive electrode sheets and negative electrode sheets are 5 and 6 respectively, and the thickness of the battery cell is 1.0 mm.

[0175] Example 6

[0176] Example 6 is used to illustrate a curved pole core, a curved battery and a preparation method thereof disclosed in the present invention, and includes most of the operation steps in Example 1, except that: this example manufactures an "S"-shaped curved battery.

[0177] Preparation of battery cells:

[0178] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an isolating role. The number of positive electrode sheets and negative electrode sheets are 28 and 29 respectively, and the thickness of the battery cell is 5.0 mm.

[0179] Comparative Example 1:

[0180] Comparative Example 1 is used to illustrate a curved pole core, a curved battery and a preparation method thereof disclosed in the present invention, and includes most of the operation steps in Example 1, except that:

[0181] After lamination, the two sides of the battery cell are not fixed with clamps, and a "C" shaped arc hot press is used for hot pressing and shaping. The hot pressing conditions are temperature of 45°C, pressure of 0.4Mpa, and time of 10s.

[0182] Comparative Example 2

[0183] Comparative Example 2 is used to illustrate a curved pole core, a curved battery and a preparation method thereof disclosed in the present invention, and includes most of the operation steps in Example 1, except that:

[0184] Preparation of positive electrode:

[0185] The slurry was coated on the surface of the aluminum foil. The coating density of the slurry on the flat surface was 15.5 mg / cm 2 The coating density of the slurry on the curved part is 15.5 mg / cm 2 , compacted density is 3.8 g / cm 3 ; The calculation coefficient of the surface density of the positive electrode sheet is 1.0; the positive electrode sheet is cut into a specification of 80mm×50mm and set aside.

[0186] Preparation of negative electrode:

[0187] The slurry is evenly coated on the surface of the copper foil. The coating density of the slurry on the flat surface is 1.9 mg / cm 2 The coating density of the slurry on the curved part is 1.9 mg / cm 2 , compacted density is 0.9g / cm 3 The negative electrode sheet surface density calculation coefficient is 1.0, and the negative electrode sheet is cut into a size of 82 mm × 52 mm for later use.

[0188] Comparative Example 3:

[0189] Comparative Example 3 is used to illustrate a curved pole core, a curved battery and a preparation method thereof disclosed in the present invention, and includes most of the operation steps in Example 1, except that:

[0190] Preparation of positive electrode:

[0191] The slurry was coated on the surface of the aluminum foil. The coating density of the slurry on the flat surface was 15.5 mg / cm 2 The coating density of the slurry on the curved part is 1.24 mg / cm 2 , compacted density is 3.8g / cm 3 ; The calculated coefficient of the surface density of the positive electrode sheet is 0.08; the positive electrode sheet is cut into a size of 80mm×50mm for standby use.

[0192] Preparation of negative electrode:

[0193] The slurry is evenly coated on the surface of the copper foil. The coating density of the slurry on the flat surface is 1.9 mg / cm 2 The coating density of the slurry on the curved part is 0.152 mg / cm 2 , compacted density is 0.9g / cm 3 The calculated coefficient of the surface density of the negative electrode sheet is 0.08, and the negative electrode sheet is cut into a size of 82 mm × 52 mm for later use.

[0194] Comparative Example 4:

[0195] Comparative Example 4 is used to illustrate a curved pole core, a curved battery and a preparation method thereof disclosed in the present invention, and includes most of the operation steps in Example 1, except that:

[0196] Preparation of battery cells:

[0197] The positive electrode sheet, separator and negative electrode sheet prepared above are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role. The number of positive electrode sheets and negative electrode sheets are 2 and 3 respectively, and the thickness of the battery cell is 0.5 mm.

[0198] Comparative Example 5:

[0199] Comparative Example 5 is used to illustrate a curved pole core, a curved battery and a preparation method thereof disclosed in the present invention, and includes most of the operation steps in Example 1, except that:

[0200] In this embodiment, an "S"-shaped curved battery is manufactured.

[0201] Preparation of battery cells:

[0202] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an isolating role. The number of positive electrode sheets and negative electrode sheets are 34 and 35 respectively, and the thickness of the battery cell is 6.0 mm.

[0203] Performance Testing:

[0204] Battery full charge thickness test:

[0205] Test method: Place the curved batteries prepared in Examples 1-6 and Comparative Examples 1-5 in a charger, use a standardized charging mode, and measure the instant thickness after full charging.

[0206] Battery capacity test

[0207] Test method: Place the curved batteries prepared in Examples 1-6 and Comparative Examples 1-5 in a charger, use a standardized charging mode, and measure the instant thickness after full charging.

[0208] (1) Standard charging

[0209] At 25±2℃, charge at a constant current of 0.2C to the upper limit voltage, and then charge at a constant voltage. Charging is completed when the charging current is less than 0.02C or the charging time is greater than 7h.

[0210] (2) Thickness test

[0211] Use a battery thickness tester to test the thickness of a fully charged battery cell.

[0212] Battery capacity test:

[0213] Test method: The curved batteries prepared in Examples 1-6 and Comparative Examples 1-5 were subjected to standard charge and discharge, and then the cell capacity was measured.

[0214] (1) Standard charging

[0215] At 25±2℃, charge at a constant current of 0.2C to the upper limit voltage, and then charge at a constant voltage. Charging is completed when the charging current is less than 0.02C or the charging time is greater than 7h.

[0216] (2) Standard discharge

[0217] At 25±2℃, place for 30 min, discharge with 0.2C constant current to the lower limit voltage, and measure the 0.2C discharge capacity of the battery cell.

[0218] Fully charged internal resistance test before cycling:

[0219] Test method: The curved batteries prepared in Examples 1-6 and Comparative Examples 1-5 were subjected to standard charging to test the internal resistance in the fully charged state.

[0220] (1) Standard charging

[0221] At 25±2℃, charge at a constant current of 0.2C to the upper limit voltage, and then charge at a constant voltage. Charging is completed when the charging current is less than 0.02C or the charging time is greater than 7h.

[0222] (2) Internal resistance test

[0223] Use a battery internal resistance tester to test the voltage and internal resistance of a fully charged battery cell.

[0224] Normal temperature cycle test:

[0225] Test method: The curved batteries prepared in Examples 1-6 and Comparative Examples 1-5 were charged and discharged at 1C / 1C at room temperature to measure the cycle life.

[0226] 25±2℃, charge to the upper limit voltage with 1.0C constant current, then charge to the lower limit voltage with constant voltage until the charging current is less than 0.1C, leave for 30 min, discharge to the lower limit voltage with 1.0C constant current, leave for 30 min;

[0227] One cycle is defined as one charge and one discharge. When the discharge capacity of the Nth cycle is ≥ 80% of the initial capacity and the discharge capacity of the N+1th cycle is < 80% of the initial capacity, then N is the cycle life of the battery cell.

[0228] Fully charged internal resistance test after cycle:

[0229] Test method: The curved batteries prepared in Examples 1-6 and Comparative Examples 1-5 were subjected to standard charging to test the internal resistance in the fully charged state.

[0230] (1) Standard charging

[0231] At 25±2℃, charge at a constant current of 0.2C to the upper limit voltage, and then charge at a constant voltage. Charging is completed when the charging current is less than 0.02C or the charging time is greater than 7h.

[0232] (2) Internal resistance test

[0233] Use a battery internal resistance tester to test the voltage and internal resistance of a fully charged battery cell.

[0234] The test results are shown in Table 1:

[0235] Table 1 Test results of Examples 1-6 of the present invention and Comparative Examples 1-5

[0236]

[0237] The results of Examples 1-4 and Comparative Example 1 show that by providing a splint on the outer wall of the bare battery cell, the curved shape of the battery during the charge and discharge cycle can be maintained for a long time, and wrinkles are not easy to appear on the diaphragm and the pole piece at the bending of the pole core, which significantly improves the cycle life of the curved battery. The results of Example 1, Example 5 and Example 6 and Comparative Examples 4-5 show that when the thickness of the battery is between 1.0-5.0 mm, it can not only ensure the energy density of the curved battery cell and maintain the endurance of the wearable device, but also prevent large cracks from appearing at the bending when the pole piece is bent, thereby damaging the battery performance. The results of Example 3 and Comparative Examples 2 and 3 show that by selecting a suitable coating surface density conversion coefficient at the bending according to the degree of bending of the battery cell, it can not only ensure the energy density of the curved battery cell, but also prevent large cracks from appearing at the bending when the pole piece is bent, thereby improving the telecommunications cycle performance.

[0238] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A curved pole core, characterized in that: The battery cell comprises a battery cell and clamps located on both sides of the battery cell, wherein the battery cell comprises a curved portion formed at a curved position and a straight portion formed at a non-curved position, the clamps have the same curved shape as the battery cell so as to be attached to the surface of the battery cell, the battery cell comprises a stacked pole piece and a diaphragm, an active material layer is arranged on the surface of the pole piece, and the surface density of the active material layer of the pole piece at the curved portion is lower than that at the straight portion; The surface density of the active material layer of the pole piece coated on one side of the curved part = coefficient * surface density of the active material layer of the pole piece coated on one side of the straight part; the value range of the coefficient is 0.1-0.9; the surface density of the active material layer of the pole piece coated on one side of the straight part is 1-30 mg / cm 2 ; Wherein, the coefficient refers to the ratio of the spacing between microcracks in the coating material at the bending protrusion of the pole piece to the upper limit standard value of the spacing between microcracks at the corresponding bending curvature; the upper limit standard value of the spacing at the microcrack protrusion is 8-15mm.

2. The curved pole core according to claim 1, characterized in that: The curvature of the curved portion and the coefficient satisfy the following relationship: When 0<bending rate≤1μm -1 When , the coefficient ranges from 0.7 to 0.9; When 1μm -1 <Bending rate≤10μm -1 When , the coefficient ranges from 0.5 to 0.7; When 10μm -1 <Bending rate≤100μm -1 When , the coefficient ranges from 0.3 to 0.5; When 100 μm -1 < curvature, the coefficient ranges from 0.1 to 0.

3.

3. The curved pole core according to claim 1, characterized in that: The N / P value of the battery cell at the bent portion is in the range of 1.1-1.

3.

4. The curved pole core according to claim 1, characterized in that: The electrode sheets include a positive electrode sheet and a negative electrode sheet, the positive electrode sheet and the negative electrode sheet are respectively located on both sides of the diaphragm, and the positive electrode sheet, the diaphragm and the negative electrode sheet are stacked to form the battery cell.

5. The curved pole core according to claim 4, characterized in that: The projection of the positive electrode sheet on the clamping plate falls within the coverage of the clamping plate, and the projection of the clamping plate on the diaphragm falls within the coverage of the diaphragm; the length of the positive electrode sheet is L1mm, the width of the positive electrode sheet is M1mm, the length of the clamping plate is L2mm, the width of the clamping plate is M2mm, the length of the diaphragm is L3mm, the width of the diaphragm is M3mm, and the relationship is satisfied: L1 <L2<L3,M1<M2<M3。 6. The curved pole core according to claim 5, characterized in that: The L1 and L2 satisfy the relationship: 2≤L2-L1≤4; the M1 and M2 satisfy the relationship: 2≤M2-M1≤4; the L3 and L2 satisfy the relationship: 2≤L3-L2≤4; the M3 and M2 satisfy the relationship: 2≤M3-M2≤4.

7. The curved pole core according to claim 1, characterized in that: A bonding layer is provided on one side of the two clamping plates facing the battery core.

8. The curved pole core according to claim 1, characterized in that: It also includes adhesive tape; the clamping plate and the four corners of the battery core are fixed by the adhesive tape, and the clamping plate and the bent part of the battery core are fixed by the adhesive tape.

9. A curved battery, characterized in that: It comprises a curved pole core and a battery shell as described in any one of claims 1 to 8, wherein the battery shell has the same curved shape as the curved pole core, and the curved pole core is arranged inside the battery shell.

10. A method for preparing a curved battery as claimed in claim 9, characterized in that: The following steps are involved: The positive electrode sheet, the negative electrode sheet and the separator are stacked to form a battery cell; The curved clamping plate is attached and assembled to two larger surfaces of the battery cell to form a curved pole core; The curved pole core is placed in a battery casing having the same curved shape and packaged to form a battery.

11. The method for preparing a curved battery according to claim 10, characterized in that: The curved portion and the straight portion of the battery cell both extend in a linear direction, the cross-sections of the battery cell perpendicular to the linear direction are the same, and the active material layer on the pole piece is coated perpendicular to the linear direction.

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