Compound adhesive, battery cell and preparation method thereof and battery

Abstract

The application belongs to the field of batteries, and particularly relates to a compounded binder, a battery cell and a battery, wherein the compounded binder comprises the following components in percentage by weight: a high molecular matrix resin: 40-70%, the high molecular matrix resin being selected from one or more of fluoroelastomer and / or silane modified polyether resin; a functional modified filler: 1-30%, the functional modified filler being selected from one or more of high-thermal-conductivity inorganic filler and flexible nanofiber; and a solvent: the balance. The binder in the application can homogenize current, disperse stress and lead out heat from the root source, and can also construct an internal heat conduction network by using high-thermal-conductivity filler, and can directively coat the edge gap to guide the heat, so as to eradicate the whole chain internal cause of the angle position current gathering heat generation-internal heat accumulation-bonding failure-insulation breakdown-thermal runaway short circuit, and can guarantee the long-term operation stability of the battery cell.

Description

Technical Field

[0001] This invention belongs to the field of batteries, and particularly relates to a compound binder, a battery cell, a method for preparing the same, and a battery. Background Technology

[0002] Currently, solid-state batteries, especially sulfide solid electrolyte batteries, generally employ a hot-pressing process to bond single-layer or multi-layer solid electrolyte membranes with electrode sheets (positive / negative electrodes) during cell fabrication. During cell assembly, the four corners of a rectangular cell become stress concentration areas. Existing processes typically use single-component binders or simple physical mixtures to fix the interface between the electrolyte membrane and electrode sheets. During hot pressing, the pressure and temperature at the corners of the rectangular cell are significantly higher than at the center, easily leading to the following interface defects: The binder's fluidity changes abruptly with localized high pressure, causing a large amount to be squeezed out of the interface, resulting in uneven binder distribution and the formation of voids; the combined effect of corner friction and heat transfer causes localized overheating, leading to thermal decomposition of the binder and the generation of gas, resulting in bubble stratification at the interface; after high-temperature softening, the binder's shear strength becomes insufficient, causing interlayer slippage, microcracks in the brittle sulfide electrolyte, increased interfacial impedance, and even internal short circuits within the cell, severely restricting the yield of solid-state battery molding and electrochemical cycle performance.

[0003] Meanwhile, due to the high mechanical compressive stress at the corners, it is difficult to balance the thermal conductivity and mechanical properties of a single binder system, resulting in high contact resistance at the cell corner interface. During charging and discharging, due to the current edge effect, the current density in the corner area is large, and the high impedance continuously generates Joule heat and accumulates, forming local high-temperature hot spots and triggering thermal runaway. At the same time, the binder layer at the corners is prone to microcracks due to stress tension, which can lead to contact failure between the solid electrolyte and the electrode sheet, or form micro-conductive pathways, causing potential micro-short circuits or even battery failure.

[0004] To alleviate the aforementioned corner interface failure problem, current production processes require strict control of hot pressing temperature and pressure, employing a conservative hot pressing process with low temperature, low pressure, and long holding time. However, while this conservative process avoids corner defects, it also leads to insufficient bonding at the interface in the central area of ​​the cell, resulting in poor batch consistency and keeping the mass production yield at a low level for a long time.

[0005] To improve the above problems, the patent document with publication number CN224036355U adds an independent external insulating coating to the surface of the corner of the battery cell. However, this insulating coating is a passive physical protection on the surface, which can only achieve surface burr isolation and shallow current regulation. It cannot penetrate into the electrode sheet to solve the problems of heat accumulation and intrinsic failure. Moreover, the coating has poor adhesion and limited protective effect.

[0006] The patent document with publication number CN218769610U improves the electrode and cell with lithium plating at corners by applying adhesive / conventional glue to the corners of the electrode to form an insulating buffer layer. The aim is to solve the problems of corner lithium plating, local hot spots and stress cracking. However, the use of ordinary adhesive materials for application / applying glue, without targeted stress relief and heat conduction design, can only alleviate the surface lithium plating and does not improve the corner interface problem.

[0007] Patent document CN223728783U discloses an electrode, a battery cell, and a battery. It prevents corner warping, interface peeling, and cyclic expansion of the electrode by coating the edges and corners with a conventional PVDF (polyvinylidene fluoride) adhesive layer. However, the PVDF adhesive used lacks sufficient chemical stability in a sulfide environment, is prone to side reactions, has low ionic conductivity, and exhibits decreased mechanical properties at high temperatures (>120°C), failing to meet the combined requirements of corner deformation resistance and thermal conductivity.

[0008] Patent document CN120674430A discloses a thermally safe edge-sealed electrode, its preparation method and battery. It uses ordinary flame-retardant sealant layer to coat the corners and edges of the electrode. However, this method only relies on flame-retardant components for passive protection and lacks an active heat conduction path. It cannot suppress the initial heat accumulation, and the interfacial bonding force between the flame-retardant sealant layer and the sulfide electrolyte is weak, and it is easy to peel off and fail after long-term cycling.

[0009] In summary, existing technologies have failed to address the issues of corner stress concentration, heat accumulation, interfacial slip, and chemical stability simultaneously, based on the intrinsic properties of adhesives. Therefore, there is an urgent need for a composite adhesive system that combines high cohesion, high temperature resistance, high ionic conductivity, and chemical coupling capabilities. Summary of the Invention

[0010] To address the shortcomings of existing technologies, this invention provides a compound binder, a battery cell, a method for preparing the same, and a battery. The compound binder can suppress initial heat accumulation at the corners of the battery cell.

[0011] In a first aspect, the present invention provides a compound adhesive, wherein the compound adhesive comprises the following components by weight percentage: Polymer matrix resin: 40%-70%, wherein the polymer matrix resin is selected from fluororubber and silane-modified polyether resin; Functional modified filler: 1.0%-30%, wherein the functional modified filler is selected from one or more of high thermal conductivity inorganic fillers and flexible nanofibers; Solvent: Balance.

[0012] According to an embodiment of the present invention, the compounded adhesive further comprises 5%-10% plasticizer by weight percentage.

[0013] According to an embodiment of the present invention, the fluororubber is selected from vinylidene fluoride-hexafluoropropylene binary copolymer; the silane-modified polyether resin is selected from one or more of epoxy silane-modified polyether resin, mercaptosilane-modified polyether resin, trimethoxysilane-modified polyether resin, ethoxysilane-modified polyether resin, and isocyanate-based silane-modified polyether resin.

[0014] According to an embodiment of the present invention, the compounded binder comprises, by weight percentage, 1.0%-30% of highly thermally conductive inorganic filler and 1.0%-10% of flexible nanofibers.

[0015] Secondly, the present invention provides a battery cell, the battery cell comprising an electrode sheet and an electrolyte membrane, wherein a reinforcing adhesive layer is disposed between the electrolyte membrane and at least one electrode sheet, the reinforcing adhesive layer being formed by the aforementioned compound adhesive, the reinforcing adhesive layer being disposed in a corner reinforcement region, the corner reinforcement region being a region defined by recessing inward from the four corner edges of the electrolyte membrane by 0.5 mm to 2 mm.

[0016] According to an embodiment of the present invention, the length of the corner reinforcement region is 10%-18% of the length of the sulfide solid electrolyte membrane or electrode sheet, the width is 10%-18% of the width of the sulfide solid electrolyte membrane or electrode sheet, and the thickness of the reinforcing adhesive layer is 5-15 μm; preferably, the length of the corner reinforcement region is 12%-18% of the length of the sulfide solid electrolyte membrane or electrode sheet, and the width is 12%-18% of the width of the sulfide solid electrolyte membrane or electrode sheet.

[0017] Secondly, the present invention provides a method for forming a reinforced adhesive layer at the corner of a battery cell, the method comprising the following steps: 1) Mix, disperse, and filter the components of the above-mentioned compound binder to form a slurry; 2) Coating a slurry onto the electrolyte membrane or electrode sheet, wherein the coating method is selected from any of the following methods: a) coating the slurry onto the corner reinforcement region on the side of the electrolyte membrane-electrode sheet away from the electrode sheet to form a reinforced bonding layer; b) coating the slurry onto the corner reinforcement region on the surface of the electrode sheet to form a reinforced bonding layer with a local high concentration of bonding in the corner reinforcement region. 3) Dry the reinforced adhesive layer after applying the slurry; 4) After drying, the electrode sheet or electrode sheet-electrolyte membrane is combined with at least one of the electrode sheet and electrolyte membrane and then pressed to obtain the battery cell.

[0018] According to an embodiment of the present invention, the corner reinforcement region refers to the region at the four corners corresponding to the corners of the battery cell, which is recessed inward by 0.5-2mm along the corner edge. The length of the corner reinforcement region is 10%-18% of the length of the sulfide solid electrolyte membrane or electrode sheet, and the width is 10%-18% of the width of the sulfide solid electrolyte membrane or electrode sheet. The thickness of the reinforcing adhesive layer is 5-15μm.

[0019] According to an embodiment of the present invention, step 3) of drying the reinforced adhesive layer after coating the slurry includes the following steps: placing the electrode or electrode-electrolyte membrane with the reinforced adhesive layer at a constant temperature of 60-80°C until the final solid content is ≥85%. Retaining a trace amount of residual solvent can improve the micro-flowability of the compounded adhesive during the subsequent hot pressing process, help fill the interface pores, and at the same time avoid cracking and curling defects of the reinforced adhesive layer caused by high temperature and rapid drying.

[0020] According to an embodiment of the present invention, the pressing in step 4) includes the following steps: first, pre-baking at a temperature of 40-80℃ and normal pressure for 5-20 minutes for molding; then, heating to 80-140℃ and pressurizing to 100-300MPa; maintaining constant temperature and pressure for 5-30 minutes for shaping; finally, slowly depressurizing at 2-5MPa / min; and after depressurization, cooling to room temperature at a gradient of 5℃ / min.

[0021] Thirdly, the present invention provides a battery cell, which is prepared by the above method.

[0022] Fourthly, the present invention provides a battery comprising the aforementioned battery cell.

[0023] Beneficial effects 1) This invention provides a reinforced bonding layer at the corner between the electrode sheet and the electrolyte membrane inside the battery cell. The reinforced bonding layer is obtained by compounding an adhesive, which contains a fluororubber + silane-modified polyether biphase composite adhesive. It is compatible with sulfide systems and has advantages such as temperature resistance, insulation, lithium conduction, and covalent bonding. At the same time, the compounding adhesive also includes strongly coupled high thermal conductivity inorganic fillers and flexible nanofibers. The high thermal conductivity inorganic fillers are used to improve the in-plane thermal conductivity and can construct a three-dimensional continuous thermally conductive network in the reinforced bonding layer to quickly dissipate the Joule heat accumulated during charging and discharging and eliminate local hot spots. The flexible nanofibers can form an interwoven mesh skeleton in the reinforced bonding layer, which can significantly improve the tensile strength and tear resistance of the reinforced bonding layer. It can flexibly stretch with the corner deformation and completely suppress the generation of microcracks. The synergistic combination of the two gives the corner area the dual characteristics of "fast heat dissipation + deformation resistance", which solves the contradiction of "poor thermal conductivity leading to heat accumulation" and "insufficient toughness leading to cracking" of the adhesive at the corner.

[0024] 2) The reinforced adhesive layer in this invention relies on the high temperature resistance and high insulation of fluororubber, the polyether homogenizes the corner current and reduces the heat source, and the silane bonds the interface and internal thermal conductivity to actively eliminate the endogenous heat source and defects, homogenize the current, disperse the stress and remove the heat from the source. At the same time, the compounded high thermal conductivity filler constructs an internal thermal conductive network, and the directional coating seals the gaps and conducts away the accumulated heat, thereby effectively blocking the whole chain of internal causes of corner current accumulation and heat generation - internal heat accumulation - adhesive failure - insulation breakdown - thermal runaway short circuit, which can ensure the long-term operational stability of the battery cell.

[0025] 3) The silane groups of this invention form Si-O / Si-S covalent bonds with sulfides / electrode fillers / electrodes, resulting in reliable interfacial bonding, integrated curing at the edges and corners, and strong adhesion to the substrate, preventing detachment during cycling.

[0026] 4) This invention strengthens the bonding layer by directly constructing a gradient-differentiated bonding interface structure in the corner reinforcement area, achieving precise matching of the performance of different areas of the battery cell to the operating conditions. Without reducing the energy density of the battery cell, it maximizes the safety and stability of weak areas, balancing performance, cost, and mass production. It suppresses thermal runaway and blocks short-circuit paths from the inside of the corners, which is an intrinsic active modification of the internal materials, resulting in a stronger interface bond and more thorough protection. It breaks through the mindset of uniform coating across the entire area in traditional processes. At the same time, it proposes a directional coating + gradient temperature isostatic pressing process in the corner area of ​​the battery cell, forming a reinforced bonding layer only in the stress concentration area of ​​the corner of the battery cell. This achieves precise supply of functions and significantly reduces material consumption (saving more than 70% of adhesive compared to full-area coating). It achieves a balance between process integration, high performance, and low cost, without reducing the energy density of the battery cell. Attached Figure Description

[0027] Figure 1 This is a flowchart of the battery cell preparation process in Embodiment 2 of the present invention.

[0028] Figure 2 This is a schematic diagram of the formation of a reinforced adhesive layer on the surface of the electrolyte membrane in Embodiment 1 of the present invention.

[0029] Figure 3 for Figure 2 Top view.

[0030] Figure 4 This is a schematic diagram of the formation of a reinforced adhesive layer on the surface of the negative electrode in Embodiment 2 of the present invention.

[0031] Figure 5 This is a schematic diagram of the active material layer with corner site adhesive layer in Example 2.

[0032] In the figure, 1-reinforced adhesive layer, 2-electrolyte membrane, 3-active material layer, 4-current collector. Detailed Implementation

[0033] The following detailed description, in conjunction with specific embodiments, provides a more comprehensive account of the compound binder, battery cell, preparation method, and battery of the present invention. It should be understood that the following embodiments are merely illustrative and explanatory of the invention and should not be construed as limiting the scope of protection of the invention. All technologies implemented based on the above description of the present invention are covered within the scope of protection intended by the present invention.

[0034] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0035] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0036] In the description of this application, "same chemical composition" should be interpreted broadly, that is, the main components of the two have the same chemical composition, or the two have substantially the same chemical composition, but may have errors or impurities within the acceptable range that can be understood by those skilled in the art.

[0037] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0038] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0039] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0040] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0041] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0042]

Compound adhesive

[0043] Functional modified filler: 1%-30% of the functional modified filler is selected from one or more of high thermal conductivity inorganic fillers and flexible nanofibers.

[0044] Plasticizer: 5%-10%.

[0045] Solvent: Balance.

[0046] According to an embodiment of the present invention, the fluororubber is selected from vinylidene fluoride-hexafluoropropylene (VDF-HFP) binary copolymer, and the performance of the vinylidene fluoride-hexafluoropropylene binary copolymer (PVDF-HFP) can be optimized by adjusting the content of HFP monomer. The silane-modified polyether resin is selected from one or more of epoxy-silane-modified polyether resin, mercaptosilane-modified polyether resin, trimethoxysilane-modified polyether resin, ethoxysilane-modified polyether resin, and isocyanate-based silane-modified polyether resin, with a molecular weight of 1000~10000 g / mol and a viscosity of 5000-50000 mPa·s.

[0047] According to an embodiment of the present invention, the compound binder includes 1%-30% of high thermal conductivity inorganic filler. The high thermal conductivity inorganic filler is selected from one or more of inorganic sulfide electrolytes, oxide electrolytes, boron nitride (BN), aluminum nitride, silicon nitride, graphene, carbon nanotubes, and carbon nanofibers. The particle size of the high thermal conductivity inorganic filler is 500nm-2μm. The high thermal conductivity inorganic filler is used to improve the in-plane thermal conductivity, which can construct a three-dimensional continuous thermally conductive network in the binder layer, quickly dissipate the accumulated Joule heat of charging and discharging, and eliminate local hot spots.

[0048] According to an embodiment of the present invention, the compound adhesive comprises 1%-10% flexible nanofibers, wherein the flexible nanofibers are selected from one or more of aramid nanofibers, polyimide nanofibers, polyetherketone nanofibers, polybenzimidazole nanofibers, and cellulose nanofibers. The flexible nanofibers have a diameter of 5-50 nm and a length of 0.5-10 μm. The flexible nanofibers are used to enhance the tensile strength and toughness of the corner region. The aspect ratio of the flexible nanofibers is 10-2000. At the current aspect ratio, the flexible nanofibers can form an interwoven mesh skeleton in the adhesive layer, which greatly improves the tensile strength and tear resistance of the adhesive layer. It can flexibly stretch with the corner deformation and completely suppress the generation of microcracks.

[0049] According to an embodiment of the present invention, the plasticizer is selected from dibutyl phthalate (DBP) or triphenyl phosphate (TPP). The plasticizer is used to reduce the glass transition temperature (Tg) of the binder, improve the flexibility of the binder, and at the same time, improve the flexibility and flowability of the binder at room temperature and low temperature, ensuring that the binder can fully penetrate and fill the micropores of the electrolyte and electrode sheet in the initial stage of hot pressing, reduce the interfacial impedance, and improve the low temperature cycling stability of the battery cell.

[0050] According to an embodiment of the present invention, the solvent is selected from one or more of alkanes or ester solvents. The alkanes are selected from one or more of n-heptane, n-hexane, n-octane, and n-decane. The ester solvents are selected from ethyl acetate, butyl butyrate, and esters with a main chain C greater than or equal to 4 that are compatible with solid electrolytes. The solvent is used to adjust the viscosity of the slurry. The solvents selected and used in the present invention are suitable for the spot coating process requirements of screen printing and inkjet printing, are residue-free, volatile, and do not affect the electrochemical performance of the battery cell.

[0051] [Battery Cell] A battery cell includes an electrode sheet and an electrolyte membrane. A reinforcing adhesive layer is disposed between the electrolyte membrane and at least one electrode sheet. The reinforcing adhesive layer is formed by the aforementioned compound adhesive. The reinforcing adhesive layer is disposed in a corner reinforcement region, which is a region defined by indentation of 0.5 mm to 2 mm from the four corner edges of the electrolyte membrane.

[0052] According to an embodiment of the present invention, the length of the corner reinforcement region is 10%-18% of the length of the sulfide solid electrolyte membrane or electrode sheet, the width is 10%-18% of the length of the sulfide solid electrolyte membrane or electrode sheet, and the thickness of the reinforcing adhesive layer is 5-15 μm.

[0053] According to an embodiment of the present invention, the electrode sheet includes a negative electrode sheet and a positive electrode sheet.

[0054] According to an embodiment of the present invention, the battery cell includes a negative electrode, an electrolyte membrane, and a positive electrode that are sequentially laminated together.

[0055] According to an embodiment of the present invention, the reinforcing adhesive layer is located between the electrode sheet and the electrolyte membrane, and the reinforcing adhesive layer is covered by an adhesive between the electrode sheet and the electrolyte membrane, forming an integral structure with the adhesive layer.

[0056] According to an embodiment of the present invention, the reinforcing adhesive layer is disposed on the electrolyte membrane or the electrode sheet.

[0057] According to an embodiment of the present invention, when the reinforcing adhesive layer is disposed on the electrode sheet, it is disposed on the side surface of the electrode sheet that contacts the electrolyte membrane.

[0058] According to an embodiment of the present invention, the maximum temperature difference at each cell corner is less than or equal to 1.5℃, and the interface contact resistance is less than or equal to 8.5mΩ·cm. 2 After 100 cycles at a 0.5C rate, the capacity retention rate is greater than or equal to 90%.

[0059] [Battery Cell Manufacturing Methods] A method for forming a reinforcing adhesive layer at the corner of a battery cell includes the following steps: 1) Refining pretreatment of slurry: Mix, disperse and filter the components of the above-mentioned compound binder to form a uniform slurry.

[0060] 2) Coating the electrolyte membrane with a slurry, the coating method being selected from any of the following methods: a) coating the slurry on the corner reinforcement area of ​​the electrolyte membrane surface in the electrolyte membrane-electrode sheet to form a reinforced bonding layer; b) coating the slurry on the corner reinforcement area of ​​the electrode sheet surface to form a reinforced bonding layer with a local high concentration of bonding area in the corner reinforcement area.

[0061] 3) Dry the reinforced adhesive layer after applying the slurry.

[0062] 4) After drying, the electrolyte membrane or electrode sheet is combined with at least one of the positive electrode sheet, negative electrode sheet, and electrolyte membrane and then pressed to obtain the battery cell.

[0063] According to an embodiment of the present invention, the positive electrode and the negative electrode respectively include a corresponding current collector and an active material layer on the surface of the current collector.

[0064] According to an embodiment of the present invention, the electrolyte membrane is a sulfide electrolyte membrane.

[0065] According to an embodiment of the present invention, the corner reinforcement region refers to the region at the four corners corresponding to the corners of the battery cell, which is recessed inward by 0.5-2mm along the corner edge. The length of this region is 10%-18% of the length of the sulfide solid electrolyte membrane or electrode sheet, and the width is 10%-18% of the width of the sulfide solid electrolyte membrane or electrode sheet. Preferably, the corner reinforcement region is rectangular with dimensions of 5mm x 5mm to 12mm x 12mm.

[0066] According to an embodiment of the present invention, the corner reinforcement area corresponding to the edge corner has a rounded corner structure, and the rounded corner R is 0.5~1.5mm.

[0067] According to an embodiment of the present invention, the thickness of the reinforced adhesive layer is 5-15 μm.

[0068] According to an embodiment of the present invention, method a) specifically includes the following steps: after the solid electrolyte membrane and the electrode sheet are composited, a compound adhesive slurry is coated on the four corner reinforcement areas of the surface of the electrolyte membrane away from the electrode sheet using a precision coating device. The corner reinforcement areas are recessed by 0.5-2mm along the four corner edges of the electrolyte membrane-electrode sheet. The corner reinforcement areas are rectangular with dimensions of 5mm x 5mm to 12mm x 12mm. The corners of the corner reinforcement areas and the corresponding corners of the electrolyte membrane-electrode sheet adopt a rounded corner structure with a rounded corner radius of 0.5-1.5mm. The thickness of the reinforcement adhesive layer is 5-15μm.

[0069] According to an embodiment of the present invention, method b) specifically includes the following steps: spraying a compound adhesive slurry onto the corner reinforcement area of ​​the electrode sheet surface using one of screen printing, inkjet printing, and dispensing spraying technologies to form a local high-concentration adhesive area and obtain a reinforced adhesive layer.

[0070] According to an embodiment of the present invention, step 1) includes the following steps: the polymer matrix resin, functional modified filler, plasticizer and solvent are put into a high-speed dispersion device and stirred and dispersed at 3000 rpm for 30 min. The filler and fiber agglomerates are broken by high shear force to achieve extremely uniform dispersion of each component molecule; then, a 300-mesh high-precision filter is used to filter out large particulate impurities and undispersed agglomerates to ensure the uniformity and stability of the slurry and avoid local defects after coating.

[0071] According to an embodiment of the present invention, step 3) of drying the reinforced adhesive layer after coating the slurry includes the following steps: placing the electrode or electrode-electrolyte layer with the reinforced adhesive layer at a constant temperature of 60-80°C until the final solid content is ≥85%. Retaining a trace amount of residual solvent can improve the micro-flowability of the adhesive during subsequent hot pressing, help fill the interface pores, and at the same time avoid cracking and curling defects of the adhesive layer caused by high temperature and rapid drying.

[0072] According to an embodiment of the present invention, the pressing in step 4) is isostatic pressing.

[0073] According to an embodiment of the present invention, the isostatic pressing includes the following steps: first, pre-baking at a temperature of 40-80℃ and normal pressure for 5-20 minutes for molding; then, heating to 80-140℃ and pressurizing to 100-300MPa; maintaining constant temperature and pressure for 5-30 minutes for shaping; finally, slowly depressurizing at 2-5MPa / min; and after depressurization, cooling to room temperature at a gradient of 5℃ / min.

[0074]

Battery

[0075] This invention abandons the traditional molding method of single-sided / double-sided rigid hot pressing and pressure attenuation at the corners, and instead adopts a three-stage warm isostatic pressing (WIP) process of low-temperature preforming + medium-temperature isostatic pressing for pressure holding and densification + gradient pressure relief and constant temperature shaping. Relying on the isotropic and uniform pressure characteristics of fluids, it completely solves the industry pain points of uneven pressure between the battery cell plane and corners and inconsistent interface bonding, and accurately matches the dynamic molding law of compound binder melting and flow, micropore filling and interface stress relief.

[0076] The temperature during the preforming stage is 40-80℃, and the pre-baking is carried out at normal pressure for 5-20 minutes. Under low temperature conditions, the corner compound adhesive is initially softened and slightly wetted at the interface between the electrode sheet and the electrolyte, thus eliminating large pores and poor connection defects at the interface in advance and avoiding local extrusion and coating displacement problems caused by direct high-pressure molding.

[0077] In the isothermal and isostatic pressing main molding stage, the temperature is raised to 80-140℃ and the pressure is increased to 100-300MPa. The constant temperature and pressure are maintained for 5-30 minutes. Utilizing the uniform pressure characteristics of isothermal and isostatic fluid throughout the entire area without dead corners, the pressure in the cell plane, right-angle corners, and rounded corners is completely consistent, which completely solves the problems of pressure attenuation and loose bonding at the corners of traditional rigid hot pressing. The high-temperature adapted adhesive melts and flows, and the three-dimensional thermally conductive network and fiber toughening skeleton are evenly spread, achieving atomic-level dense bonding at the solid-solid interface and simultaneously eliminating high-resistance areas at the corner interfaces.

[0078] During the gradient decompression and shaping stage, a constant temperature is maintained, and pressure is slowly released in stages at 2-5 MPa / min. After decompression, the temperature is gradually reduced to room temperature at a rate of 5℃ / min. This logic of decompressing first and then cooling can completely release residual stress at the interface, avoid material shrinkage deformation and interface delamination caused by rapid pressure and temperature drops, lock in a uniform and dense interface structure throughout, and prevent corner cracking, overheating, and micro-short circuit failure in the later stages of the process.

[0079] The battery cell prepared by this invention differs from the traditional homogeneous bonding structure. A dedicated reinforced bonding layer is formed at the four corner interfaces of the battery cell. The reinforced bonding layer adopts a three-dimensional thermally conductive network and a fiber toughening skeleton. Compared with the traditional bonding interface, the thermal conductivity is increased by more than 50%, the tensile strength is increased by more than 30%, and the interface density, flexibility, and thermal conductivity are comprehensively optimized. The planar area of ​​the battery cell maintains the original structure without sacrificing the overall energy density of the battery cell, achieving the optimal structural design of "strengthening weak areas and maintaining efficiency in conventional areas".

[0080] [Examples and Comparative Examples] In the following embodiments, the positive electrode, negative electrode, and electrolyte layer are prepared according to the following steps.

[0081] Preparation steps of the positive electrode: The positive electrode active material (LiNi) is prepared... 0.8 Co 0.1 Mn 0.1 O2), electrolyte Li6PS5Cl, conductive agent (C45), and binder NBR are dispersed in butyl butyrate solvent at a mass ratio of 80:14.5:1.5:4, with a solid content of 57%. The mixture is stirred at 2000 rpm for 30 min in a planetary mixer to prepare a positive electrode slurry. The slurry is uniformly coated onto the surface of an aluminum current collector, with a thickness controlled at 700 μm. It is then dried at room temperature for 2 h, followed by vacuum drying at 80 °C for 5 h to remove the butyl butyrate solvent, yielding the positive electrode sheet.

[0082] Preparation steps of the negative electrode sheet: The negative electrode active material (silicon-carbon composite negative electrode material), electrolyte Li6PS5Cl, conductive agent (C45), and binder SBR are dispersed in butyl butyrate solvent at a mass ratio of 60:30:2:8, with a solid content of 53%. The mixture is stirred at 2000 rpm for 30 min in a planetary mixer to prepare a negative electrode slurry. The slurry is uniformly coated on the surface of a copper current collector with a thickness controlled at 300 μm. It is first dried at room temperature for 2 h, then vacuum dried at 80℃ for 5 h to remove the butyl butyrate solvent, thus obtaining the negative electrode sheet.

[0083] Preparation steps of the electrolyte membrane: The sulfide electrolyte powder (Li6PS5Cl) and the adhesive solution are mixed at a mass ratio of 95:3 and dispersed at high speed for 20 min to prepare an electrolyte slurry. The slurry is uniformly coated on the surface of the negative electrode or aluminum current collector, with the dry thickness controlled at 100 μm. It is first dried at room temperature for 2 h, then vacuum dried at 80℃ for 5 h to remove the solvent and obtain a solid electrolyte membrane.

[0084] Example 1 This embodiment provides a compound adhesive, which, by weight, comprises 60 wt% polymer resin, 15 wt% functional modified filler, 5 wt% DBP plasticizer, and 20 wt% butyl butyrate. The polymer resin is a vinylidene fluoride-hexafluoropropylene binary copolymer and an epoxy-silane-terminated polyether, the epoxy-silane-terminated polyether having a molecular weight of 5000 g / mol. The functional modified filler comprises 10 wt% boron nitride thermally conductive filler and 5 wt% aramid nanofibers.

[0085] First, epoxy silane-terminated polyether and PVDF-HFP were added to a high-speed mixer at a ratio of 10wt%:90wt%. Then, 20wt% of butyl butyrate was added and stirred until completely transparent. Finally, 10wt% of boron nitride thermally conductive filler, 5wt% of aramid nanofibers and 5wt% of plasticizer DBP were added in sequence. The mixture was dispersed at 3000rpm for 30min, filtered through a 300-mesh filter, and stirred until a homogeneous sulfide electrolyte slurry was formed.

[0086] See Figure 2 and Figure 3 As shown, the negative electrode sheet is cut into a size of 60mm x 80mm, and the sulfide electrolyte slurry is coated on the negative electrode sheet to form a sulfide solid electrolyte film with a thickness of 100μm. In the four corner reinforcement areas of the sulfide solid electrolyte film, the slurry is coated at fixed points using a screen printing process, and the thickness of the slurry coating is precisely controlled to be 10μm. The coating layer forms a rectangle with two sides of 8mm each. The corner reinforcement area is 8mm x 8mm with a rounded corner R1.5mm, and the rectangle is recessed 1mm along the edge of the electrode sheet to form a reinforcement layer.

[0087] The sulfide electrolyte membrane-negative electrode sheet with a reinforcing layer is pre-dried at 60℃ for 40 minutes to increase the solid content of the slurry to 88%. The positive electrode sheet and the electrolyte membrane-negative electrode sheet are assembled according to conventional processes. Thermostatic pressing (i.e., coating the side of the sulfide electrolyte membrane opposite to the negative electrode sheet with conventional adhesive and combining it with the positive electrode sheet to form a negative electrode-sulfide electrolyte membrane-positive electrode structure) is then performed: pre-baking at 75℃ for 20 minutes to allow the compounded adhesive to initially flow and fill the pores at the corners; then the temperature is increased to 90℃ and the pressure is increased to 100MPa and held at isothermal isostatic pressure for 20 minutes, followed by isothermal gradient depressurization and cooling at 5℃ / min to room temperature for shaping to obtain the battery cell.

[0088] Example 2 This embodiment provides a compound adhesive comprising 60 wt% polymer resin, 15 wt% functional modified filler, 5 wt% DBP plasticizer and 20 wt% butyl butyrate, wherein the functional modified filler comprises 10 wt% boron nitride thermally conductive filler and 5 wt% aramid nanofibers.

[0089] The polymer resin is a vinylidene fluoride-hexafluoropropylene binary copolymer and an epoxy silane-terminated polyether, wherein the molecular weight of the epoxy silane-terminated polyether is 5000 g / mol. The epoxy silane-terminated polyether and PVDF-HFP are added to a high-speed mixer at a ratio of 10wt%:90wt%, and 20wt% butyl butyrate is added. The mixture is stirred until completely transparent. Then, 10wt% boron nitride thermally conductive filler, 5wt% aramid nanofibers and 5wt% DBP plasticizer are added sequentially. The mixture is dispersed at 3000 rpm for 30 min, filtered through a 300-mesh filter, and stirred until a homogeneous functional slurry is formed.

[0090] See Figure 4 and Figure 5 As shown, in the four corner areas of a 150μm thick negative electrode sheet, a paste was applied to the four corners of a 62mm x 82mm negative electrode using screen printing, precisely controlling the coating thickness to 10μm, 8mm on each side, with a corner reinforcement area of ​​8mm x 8mm, a corner radius of 1.5mm, and a 1mm inward reduction along the electrode edge (i.e., the corner reinforcement area size is 8mm x 8mm, 1mm inward reduction along the electrode edge, corner radius of 1.5mm, coating thickness 10μm). Pre-drying at 60℃ for 40 minutes increased the paste solid content to 88%. Additionally, a sulfide electrolyte was coated onto a 50μm thick PET film. The coating is 100μm thick and cut into 65mm x 85mm sizes. After drying, a sulfide electrolyte membrane is obtained. The sulfide electrolyte membrane is then transferred onto the negative electrode sheet. The transfer is carried out by a flat hot pressing process at 60℃ for 10 minutes. The positive electrode, sulfide electrolyte membrane, and negative electrode stack are assembled according to conventional processes. The thermostatic pressing is then performed: pre-baking at 75℃ for 20 minutes to allow the compounded binder to initially flow and fill the pores at the corners; then the temperature is raised to 90℃ and the pressure is increased to 100MPa and held at thermostatic pressure for 20 minutes. Then, the pressure is released at a constant temperature gradient and the temperature is lowered to room temperature at 5℃ / min for shaping.

[0091] Example 3 The compound binder provided in this embodiment includes 60 wt% polymer resin, 15 wt% functional modified filler, 5 wt% DBP plasticizer and 20 wt% butyl butyrate. The 15 wt% functional modified filler includes 5 wt% boron nitride thermally conductive filler, 5 wt% sulfide electrolyte ion-conducting material and 5 wt% aramid nanofibers. The polymer resin is vinylidene fluoride-hexafluoropropylene binary copolymer and epoxy silane-terminated polyether.

[0092] Epoxy silane-terminated polyether and PVDF-HFP were added to a high-speed mixer at a ratio of 10wt%:90wt%, along with 20wt% butyl butyrate. The mixture was stirred until completely transparent. Then, 5wt% boron nitride thermally conductive filler, 5wt% sulfide electrolyte ion-conducting material, 5wt% aramid nanofibers, and 5wt% DBP plasticizer were added sequentially. The mixture was dispersed at 3000rpm for 30min, filtered through a 300-mesh filter, and stirred until a homogeneous functional slurry was formed.

[0093] The negative electrode sheet-sulfide electrolyte membrane is cut to a size of 60mm x 80mm, and the thickness of the sulfide electrolyte membrane is 100μm. In the four corner areas of the sulfide solid electrolyte membrane, the paste is applied at fixed points using screen printing process, and the coating thickness is precisely controlled to 10μm, 8mm on each side, and the corner reinforcement area is 8mm x 8mm with a corner radius of R1.5mm. It is recessed 1mm along the edge of the electrode sheet to obtain a reinforced bonding layer.

[0094] The negative electrode sheet with a reinforced adhesive layer and the sulfide electrolyte membrane are first pre-dried at 60℃ for 40 minutes to increase the solid content of the slurry to 88%. Then, the positive electrode sheet and the electrolyte membrane-negative electrode sheet are assembled according to conventional processes. The assembled structure is then subjected to isothermal isostatic pressing: pre-baking at 75℃ for 20 minutes allows the compounded binder to initially flow and fill the pores at the corners. Subsequently, the temperature is raised to 90℃ and the pressure is increased to 100MPa and held at isothermal isostatic pressure for 20 minutes. Then, the pressure is released at a constant temperature gradient and the temperature is lowered to room temperature at 5℃ / min for shaping to obtain the battery cell.

[0095] Example 4 The compound binder provided in this embodiment comprises 60 wt% polymer resin, 15 wt% functional modified filler, 5 wt% DBP plasticizer, and 20 wt% butyl butyrate. The 15 wt% functional modified filler includes 10 wt% modified graphene thermally conductive filler and 5 wt% aramid nanofibers, and the polymer resin is a vinylidene fluoride-hexafluoropropylene binary copolymer and an epoxy-silane modified polyether resin.

[0096] Epoxy silane modified polyether resin and PVDF-HFP were added to a high-speed mixer at a ratio of 10wt%:90wt%, and 20wt% butyl butyrate was added. The mixture was stirred until completely transparent. Then, 10wt% modified graphene thermally conductive filler, 5wt% aramid nanofibers and 5wt% DBP plasticizer were added in sequence. The mixture was dispersed at 3000rpm for 30min, filtered through a 300-mesh filter, and stirred until a homogeneous functional slurry was formed.

[0097] In the four corner areas of a 150μm thick negative electrode sheet, a paste was applied using screen printing to precisely coat the four corners of a 62mm x 82mm negative electrode, with a coating thickness of 10μm, 8mm on each side, and a corner reinforcement area of ​​8mm x 8mm. The corner radius was 1.5mm, and the coating was recessed 1mm along the edge of the electrode sheet. The paste was pre-dried at 60℃ for 40 minutes to increase its solid content to 88%. In addition, a sulfide electrolyte is coated on a 50μm PET film to form a 100μm thick sulfide electrolyte film, which is then cut into 65mm x 85mm sizes. The sulfide electrolyte film is then transferred onto the negative electrode to obtain a negative electrode-sulfide electrolyte film. The transfer process is carried out by a flat plate hot pressing process at a constant temperature of 60℃ for 10 minutes. The positive and negative electrode-sulfide electrolyte film are assembled according to conventional processes. Thermostatic pressing is then performed: pre-baking at 75℃ for 20 minutes allows the compounded binder to initially flow and fill the pores at the corners. Subsequently, the temperature is increased to 90℃ and the pressure is increased to 100MPa and held at isothermal isostatic pressure for 20 minutes. Then, the pressure is released at a constant temperature gradient and the temperature is reduced to room temperature at 5℃ / min for shaping to obtain the battery cell.

[0098] Example 5 The difference between this embodiment and Example 1 is that the ratio of epoxy silane-terminated polyether to PVDF-HFP is 2wt%:98wt%.

[0099] Example 6 The difference between this embodiment and Example 1 is that the ratio of epoxy silane-terminated polyether to PVDF-HFP is 50wt%:50wt%.

[0100] Example 7 The difference between this embodiment and Example 1 is that the functional modified filler is 15 wt% boron nitride + 5 wt% polyimide nanofibers, and the butyl butyrate content is 15 wt%.

[0101] Example 8 The difference between this embodiment and Example 1 is that the plasticizer is 7 wt% triphenyl phosphate and the butyl butyrate is 18 wt%.

[0102] Example 9 The difference between this embodiment and Example 1 is that the plasticizer is 10 wt% triphenyl phosphate and the butyrate is 15 wt%.

[0103] Example 10 The difference between this embodiment and Example 1 is that the functional modified filler consists of 8 wt% carbon nanotubes and 7 wt% polyetherketone nanofibers.

[0104] Table 1. Ingredients of the compounded adhesives in Examples 1-10 Comparative Example 1 PVDF-HFP was used as the single binder (without adding silane-modified polyether or functional fillers), and butyl butyrate solvent (20 wt%) and DBP plasticizer (5 wt%) were added in the same proportion as in Example 1, with the balance being PVDF-HFP. A uniform coating method was used, with a coating thickness of 10 μm. Other hot-pressing parameters (temperature, pressure, time, depressurization method, etc.) and cell assembly structure remained consistent with Example 1, resulting in the battery cell.

[0105] Performance analysis was performed on the battery cells of Examples 1-10 and Comparative Example 1. The cells were tested under conditions of 55°C and 100 cycles at a 0.5C rate. Infrared thermal imagers were used to measure the temperatures at the four corners and the center of the cell surface after it had been fully charged and left to stand for 5 minutes, and the maximum temperature difference at the corners was calculated. A four-probe contact impedance test was used to measure the actual contact resistance at the interface, and the differences between the corners and the center were compared.

[0106] As shown in Table 2, the battery cell prepared in Example 1 underwent corner strengthening, with a maximum temperature difference of 1.0℃ at the cell corners and an interface contact resistance of 8.2 mΩ·cm. 2 The capacity retention rate after 100 cycles at 0.5C was 93.8%; the maximum temperature difference at the corner of the cell prepared in Comparative Example 1 was 4.2℃, and the interface contact resistance was 19.5mΩ·cm. 2 After 100 cycles at 0.5C, significant localized heating occurred at the cell corners, resulting in a surge in internal resistance. The capacity retention rate after 100 cycles at 0.5C was 82.7%. Furthermore, after treating the cell corners using the method of this invention, the maximum temperature difference at the cell corners was less than or equal to 2.0℃, and the interface contact resistance was less than or equal to 10mΩ·cm. 2 The capacity retention rate after 100 cycles at 0.5C is greater than or equal to 90%. At the same time, no obvious local heating or internal resistance surge was observed at the corner. This indicates that the method of the present invention for treating the corner can effectively block the entire chain of internal causes of corner current accumulation-internal heat accumulation-bonding failure-insulation breakdown-thermal runaway short circuit, thus ensuring the long-term operational stability of the cell.

[0107] Table 2 Performance test results of the battery cells prepared in Examples 1-10 and Comparative Example 1 The parts of this invention not described in detail are techniques known to those skilled in the art.

[0108] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0109] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A compound adhesive, characterized in that, By weight percentage, it contains the following components: Polymer matrix resin: 40%-70%, wherein the polymer matrix resin is selected from fluororubber and silane-modified polyether resin; Functional modified filler: 1%-30%, wherein the functional modified filler is selected from one or more of high thermal conductivity inorganic fillers and flexible nanofibers; Solvent: Balance.

2. The compound adhesive according to claim 1, characterized in that, The compounded adhesive also includes 5%-10% plasticizer by weight percentage.

3. The compound adhesive according to claim 1, characterized in that, The fluororubber is selected from vinylidene fluoride-hexafluoropropylene binary copolymer; the silane-modified polyether resin is selected from one or more of epoxy silane-modified polyether resin, mercaptosilane-modified polyether resin, trimethoxysilane-modified polyether resin, ethoxysilane-modified polyether resin, and isocyanate-based silane-modified polyether resin.

4. The compound adhesive according to any one of claims 1-3, characterized in that, The compound binder comprises 1.0%-30% of highly thermally conductive inorganic fillers and 1.0%-10% of flexible nanofibers by weight percentage.

5. A battery cell, characterized in that, The battery cell includes an electrode sheet and an electrolyte membrane. A reinforcing adhesive layer is disposed between the electrolyte membrane and at least one electrode sheet. The reinforcing adhesive layer is formed by the compound adhesive according to any one of claims 1-4. The reinforcing adhesive layer is disposed in a corner reinforcement region. The corner reinforcement region refers to the area defined by indentation of 0.5 mm to 2 mm from the four corner edges of the electrolyte membrane.

6. The battery cell according to claim 5, characterized in that, The length of the corner reinforcement region is 10%-18% of the length of the electrolyte membrane or electrode sheet, the width is 10%-18% of the length of the electrolyte membrane or electrode sheet, and the thickness of the reinforcement adhesive layer is 5-15 μm.

7. A method for forming a reinforcing adhesive layer at the corner of a battery cell, characterized in that, The method includes the following steps: 1) The compound binder according to any one of claims 1-4 is mixed, dispersed, and filtered to form a slurry; 2) Coating a slurry onto the electrolyte membrane or electrode sheet, wherein the coating method is selected from any of the following methods: a) coating the slurry onto the corner reinforcement region on the side of the electrolyte membrane-electrode sheet away from the electrode sheet to form a reinforced bonding layer; b) coating the slurry onto the corner reinforcement region on the surface of the electrode sheet to form a reinforced bonding layer with a local high concentration of bonding in the corner reinforcement region. 3) Dry the reinforced adhesive layer after applying the slurry; 4) After drying, the electrode sheet or electrode sheet-electrolyte membrane is combined with at least one of the electrode sheet and electrolyte membrane and then pressed to obtain the battery cell.

8. The method for forming a reinforced adhesive layer at the corner of a battery cell according to claim 7, characterized in that, Step 3) Drying the reinforced adhesive layer after coating with slurry includes the following steps: placing the electrode or electrode-electrolyte membrane with the reinforced adhesive layer at a constant temperature of 60-80℃ until the final solid content is ≥85%. Retaining a trace amount of residual solvent can improve the micro-flowability of the adhesive during subsequent hot pressing, help fill the interface pores, and at the same time avoid cracking and curling defects of the adhesive layer caused by high temperature and rapid drying.

9. The method for forming a reinforced adhesive layer at the corner of a battery cell according to claim 7 or 8, characterized in that, The pressing in step 4) includes the following steps: first, pre-baking at 40-80℃ and normal pressure for 5-20 minutes for molding; then, heating to 80-140℃ and pressurizing to 100-300MPa; maintaining constant temperature and pressure for 5-30 minutes for shaping; finally, slowly releasing pressure at 2-5MPa / min in stages; and after releasing pressure, cooling to room temperature at a gradient of 5℃ / min.

10. A battery, characterized in that, The battery includes the cell described in claim 5 or 6.

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