Composite binder, electrolyte membrane, preparation method and battery

Abstract

The invention relates to a composite binder, an electrolyte membrane, a preparation method and a battery. The composite binder comprises a binder main material and cross-linked molecules, the binder main material has a first functional group; the cross-linked molecule comprises a main chain and second functional groups, the main chain comprises a dynamic cross-linked structure sensitive to heat, the dynamic cross-linked structure comprises at least one of reversible chemical bonds and heat-sensitive functional groups, and the two ends of the main chain are provided with the second functional groups which are combined with the first functional groups in a reaction mode. The problem of poor mechanical property of the binder in the related art can be solved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a composite binder, an electrolyte membrane, a preparation method and a battery. Background Art

[0002] The development of all-solid-state batteries is a key technological path to further increase the energy density and improve battery safety of lithium-ion batteries. Among existing all-solid-state battery approaches, sulfide electrolytes, with their advantages such as high ionic conductivity and low elastic modulus, are considered the primary technology for next-generation solid-state battery development. Sulfide electrolyte membranes, a key component for the proper operation of solid-state batteries, are prepared using either wet or dry methods. Wet-process electrolyte membrane preparation requires a solvent as a medium for electrolyte dispersion and slurry preparation. However, due to the chemical instability of sulfide electrolytes, side reactions with solvents often occur during the wet process, resulting in a decrease in ionic conductivity after membrane formation, adversely affecting battery rate performance. Furthermore, the use, evaporation, and recovery of solvents increase electrolyte membrane manufacturing costs and environmental risks. In contrast, the solvent-free dry process for preparing sulfide electrolyte membranes avoids these side reactions, improving membrane ionic conductivity while reducing manufacturing costs and environmental risks.

[0003] Selecting the right binder is key to achieving dry-process membrane formation of sulfide electrolytes. Currently, the mainstream binder for dry-process electrolyte membrane formation is polytetrafluoroethylene (PTFE). Its linear structure and low surface energy properties enable crystal planes to slip under shear force, forming a fiber structure with a high aspect ratio. The fibers entangle and bond with each other, forming a bonded network. Therefore, an electrolyte membrane with certain mechanical properties can be formed under solvent-free conditions. However, PTFE still has the following disadvantages: 1. Poor anti-reduction performance. The CF structure in PTFE is easily reduced. Since the electrolyte membrane is in direct contact with the negative electrode, the strong reducing environment at the electrolyte membrane / negative electrode interface during charge and discharge can cause the PTFE binder remaining in the electrolyte membrane to be reduced to carbon and lithium fluoride, the active lithium is consumed, and the fibrous structure of the binder is destroyed, resulting in a decrease in the strength of the electrolyte membrane.

[0004] 2. Inadequate mechanical properties. PTFE is composed entirely of (CF2-CF2) chain structures, resulting in weak interaction and poor adhesion with sulfide electrolytes. This results in insufficient mechanical properties after membrane formation, making the electrolyte membrane susceptible to breakage and tearing during transfer or assembly. Furthermore, poor mechanical strength makes it difficult to further thin the electrolyte membrane (>60μm), resulting in a decrease in battery energy density. Summary of the Invention

[0005] The embodiments of the present application provide a composite adhesive, an electrolyte membrane, a preparation method, and a battery to solve the problem of poor mechanical properties of adhesives in related technologies.

[0006] In a first aspect, a composite adhesive is provided, comprising an adhesive main material and cross-linking molecules; The main binder material has a first functional group; The cross-linking molecule includes a main chain and a second functional group, the main chain contains a dynamic cross-linking structure that is sensitive to heat, the dynamic cross-linking structure includes at least one of a reversible chemical bond and a heat-sensitive functional group, and the second functional group that reacts and combines with the first functional group is provided at both ends of the main chain.

[0007] In some embodiments, the first functional group includes one of a carbon-carbon double bond, an epoxy group, a cyano group, and a halogenated hydrocarbon; The second functional group includes one of a halogenated hydrocarbon, a mercapto group, an isocyanate group, and an olefin group.

[0008] In some embodiments, the main material of the adhesive includes one or more of styrene-butadiene rubber, isoprene rubber, butyl rubber, chloroprene rubber, styrene-butadiene-styrene block copolymer and polybutadiene.

[0009] In some embodiments, the molecular weight of the main binder material is 50,000 to 1,000,000.

[0010] In some embodiments, the reversible chemical bond comprises one of an imine bond, a metal coordination bond, a borate bond, a disulfide bond, and a silicon-oxygen bond; The heat-sensitive functional group includes one of maleic anhydride and meta-vinylamine ester.

[0011] In some embodiments, the cross-linking molecule further includes a third functional group, and the main chain is provided with a third functional group for reacting and bonding with the third functional group of another cross-linking molecule.

[0012] In some embodiments, the third functional group is a functional group that undergoes a cross-linking reaction under electron beam or ultraviolet irradiation.

[0013] In some embodiments, the third functional group includes one of acrylate, allyl, alkynyl, and epoxy bond.

[0014] In some embodiments, the third functional group is disposed in the main chain, or the cross-linking molecule further includes a side chain, the side chain is connected to the main chain, and the third functional group is disposed on the side chain.

[0015] In some embodiments, the main chain further comprises a carbon chain; When the third functional group is disposed in the main chain, the reversible chemical bond, the second functional group and the third functional group are connected through the carbon chain to form the cross-linked molecule; When the third functional group is disposed on the side chain, the reversible chemical bond is connected to the second functional group via the carbon chain, and the carbon chain is also connected to the side chain.

[0016] In some embodiments, the molecular weight of the cross-linking molecule is ≥200.

[0017] In some embodiments, the molar ratio of the main binder material to the cross-linking molecules is 1:(1-100).

[0018] In a second aspect, a method for preparing the composite adhesive as described above is provided, comprising: Under protective gas, the main material of the adhesive and the cross-linking molecules are added to the solvent, and then the initiator is added. After the reaction is completed, a composite adhesive is obtained.

[0019] In some embodiments, the amount of the initiator added is 0.1% to 5% of the molar weight of the cross-linking molecules.

[0020] In some embodiments, the initiator comprises one or more of di-tert-butyl peroxide, dicumyl peroxide, benzoyl peroxide, azoisobutyronitrile and boron trifluoride etherate; and / or, the solvent comprises one or more of toluene, xylene, chlorobenzene, isobutyl isobutyrate, nonyl acetate, tetrahydrofuran cyclohexane, decahydronaphthalene, carbon tetrachloride, hexane, heptane, octane, nonane, decane, undecane and dodecane; And / or, the protective gas includes one or more of nitrogen and argon.

[0021] In some embodiments, the reaction temperature is set at 25-100° C., and the reaction time is 1-4 hours.

[0022] In a third aspect, an electrolyte membrane is provided, which includes a sulfide electrolyte, a lithium salt, and any composite binder as described above.

[0023] In some embodiments, the mass ratio of the sulfide electrolyte to the composite binder is (100-x):x, where x ranges from 0.5 to 1.5, and the mass ratio of the composite binder to the lithium salt is 1:(1-2).

[0024] In some embodiments, the sulfide electrolyte includes one or more of yLi2S-(100-y)P2S5, Li-aPS, and Li6PS5b, wherein y ranges from 25 to 75, a is Si, Ge, Sn, Al, or Y, and b is Cl, Br, or I.

[0025] In some embodiments, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium bis(oxalatoborate), and lithium hexafluorophosphate.

[0026] In a fourth aspect, a method for preparing an electrolyte membrane as described above is provided, comprising: uniformly mixing a sulfide electrolyte, a composite binder and a lithium salt under heating conditions, and preparing the electrolyte membrane by rolling.

[0027] In a fifth aspect, a battery is provided, comprising the electrolyte membrane as described above.

[0028] The beneficial effects of the technical solution provided by this application include: The composite adhesive provided by the present application is obtained by modifying the main material of the adhesive using cross-linking molecules, wherein the ends of the cross-linking molecules are provided with a second functional group, and the cross-linking molecules use the second functional groups at both ends to react with the first functional groups of the main material of the adhesive, respectively, to achieve permanent bonding between the cross-linking molecules and the main material of the adhesive, and more cross-linking molecules will react with more main materials of the adhesive, thereby forming a primary cross-linking network. Compared with PTFE, which is entirely composed of CF2-CF2 chain structures, the composite adhesive with a primary cross-linking network of the present application has a stronger interaction force with the sulfide electrolyte, higher adhesion, and enhanced mechanical properties of the electrolyte after film formation. The electrolyte membrane is not easily damaged or torn during transfer or assembly. At the same time, stronger mechanical strength is conducive to further thinning of the electrolyte membrane, and has a higher battery energy density at the same thickness.

[0029] The main chain of the cross-linked molecule contains a dynamic cross-linked structure that is sensitive to heat. Under heating conditions, the dynamic cross-linked structure will undergo a reversible reaction, and then continuously break and reorganize, so that the composite adhesive exhibits good viscous flow properties from a macroscopic perspective. On the one hand, this viscous flow property is conducive to the uniform mixing of the composite adhesive and the electrolyte to form an electrolyte membrane with uniform components; on the other hand, this reversible reaction is conducive to the composite adhesive maintaining the adhesion performance of the composite adhesive through reversible cross-linking reaction under different external force states, thereby realizing the self-repair function of the composite adhesive or the electrolyte membrane. When the electrolyte membrane is subjected to external force to produce cracks during the preparation of the electrolyte membrane, the dynamic cross-linked bonds can be broken and reconstructed under heating conditions. The broken dynamic cross-linked structure can be reformed under this stimulation, restoring the primary cross-linked network to achieve the purpose of repair. Therefore, the composite adhesive provided in this application is conducive to the self-repair of the electrolyte membrane after structural damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0031] Figure 1 Schematic diagram of the structures of different cross-linking molecules provided in the examples of this application; Figure 2 Schematic diagram of the reaction process between the cross-linking molecules and the main binder material provided in the embodiment of the present application; Figure 3 This is a schematic diagram of the cross-linked molecular structure used in some embodiments of the present application; Figure 4 This is an SEM image of the dry-process electrolyte membrane prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0032] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0033] See also Figure 1 and Figure 2 As shown, an embodiment of the present application provides a composite adhesive, which includes an adhesive main material and a cross-linking molecule; the adhesive main material has a first functional group; the cross-linking molecule includes a main chain and a second functional group, the main chain contains a dynamic cross-linking structure that is sensitive to heat, the dynamic cross-linking structure includes at least one of a reversible chemical bond and a heat-sensitive functional group, and the two ends of the main chain are provided with the second functional group that reacts and combines with the first functional group, and the dynamic cross-linking structure is located between the second functional groups at the two ends, so that after the dynamic cross-linking structure is broken, the two second functional groups are respectively located on the two halves of the main chain.

[0034] The composite adhesive provided by the present application is obtained by modifying the main material of the adhesive using cross-linking molecules, wherein the ends of the cross-linking molecules are provided with a second functional group, and the cross-linking molecules use the second functional groups at both ends to react with the first functional groups of the main material of the adhesive, respectively, to achieve permanent bonding between the cross-linking molecules and the main material of the adhesive, and more cross-linking molecules will react with more main materials of the adhesive, thereby forming a primary cross-linking network. Compared with PTFE, which is entirely composed of CF2-CF2 chain structures, the composite adhesive with a primary cross-linking network of the present application has a stronger interaction force with the sulfide electrolyte, higher adhesion, and enhanced mechanical properties of the electrolyte after film formation. The electrolyte membrane is not easily damaged or torn during transfer or assembly. At the same time, stronger mechanical strength is conducive to further thinning of the electrolyte membrane, and has a higher battery energy density at the same thickness.

[0035] The main chain of the cross-linked molecule contains a dynamic cross-linked structure that is sensitive to heat. Under heating conditions, the dynamic cross-linked structure will undergo a reversible reaction, and then continuously break and reorganize, so that the composite adhesive exhibits good viscous flow properties from a macroscopic perspective. On the one hand, this viscous flow property is conducive to the uniform mixing of the composite adhesive and the electrolyte to form an electrolyte membrane with uniform components; on the other hand, this reversible reaction is conducive to the composite adhesive maintaining the adhesion performance of the composite adhesive through reversible cross-linking reaction under different external force states, thereby realizing the self-repair function of the composite adhesive or the electrolyte membrane. When the electrolyte membrane is subjected to external force to produce cracks during the preparation of the electrolyte membrane, the dynamic cross-linked bonds can be broken and reconstructed under heating conditions. The broken dynamic cross-linked structure can be reformed under this stimulation, restoring the primary cross-linked network to achieve the purpose of repair. Therefore, the composite adhesive provided in this application is conducive to the self-repair of the electrolyte membrane after structural damage.

[0036] In order to achieve permanent bonding between the main binder material and the cross-linking molecules, in some preferred embodiments, the first functional group includes one of a carbon-carbon double bond, an epoxy group, a cyano group, and a halogenated hydrocarbon; the second functional group includes one of a halogenated hydrocarbon, a thiol group, an isocyanate, and an olefin.

[0037] For example, a carbon-carbon double bond can react with a halogenated hydrocarbon, a thiol, an isocyanate, or an olefin; for example, an epoxy group can react with a thiol group; for example, a halogenated hydrocarbon can react with a thiol group; for example, a cyano group can react with a halogenated hydrocarbon.

[0038] The cross-linking molecules use the halogenated hydrocarbons, thiol groups, isocyanates or olefins at both ends to react with the carbon-carbon double bonds, epoxy groups, cyano groups or halogenated hydrocarbons in the main binder material to achieve reaction with the main binder material. Once the reaction forms a bond, the bond will not break due to increasing the temperature and is not reversible.

[0039] It should be noted that the first functional group may be located in the main chain of the main binder material or in the side chain of the main binder material.

[0040] It should be noted that the second functional group may exist as an end group of the cross-linked molecule, that is, as an end group of the main chain of the cross-linked molecule, or on a side chain of the cross-linked molecule.

[0041] The second functional groups at both ends of the cross-linking molecule may be the same or different, as long as they can react and combine with the main material of the binder.

[0042] As an example, in the present application, the main material of the adhesive includes one or more of styrene-butadiene rubber, isoprene rubber, butyl rubber, chloroprene rubber, styrene-butadiene-styrene block copolymer and polybutadiene.

[0043] The aforementioned binder material has a low glass transition temperature, exhibiting excellent flexibility and tensile strength. This type of binder material softens and transforms into a viscous fluid state at a certain temperature, facilitating uniform mixing with the sulfide electrolyte in a solvent-free environment, forming a well-formed bonding network and providing excellent compatibility with dry electrolyte film formation processes. Furthermore, the binder material, primarily composed of hydrocarbons, has low polarity and resists side reactions with the sulfide electrolyte, thus maintaining the high ionic conductivity of the electrolyte membrane.

[0044] In addition, among the above-mentioned adhesives, styrene-butadiene rubber, isoprene rubber, butyl rubber, chloroprene rubber, styrene-butadiene-styrene block copolymer and polybutadiene have strong anti-reduction ability, so the obtained composite adhesive can be prevented from being reduced.

[0045] As an example, in this application, the molecular weight of the main binder material is 50,000 to 1,000,000.

[0046] Among them, the larger the molecular weight of the above-mentioned binder main material, the higher the degree of molecular chain entanglement, and the higher the bonding force that can be obtained; as the molecular weight of the binder main material increases, the temperature at which it is converted into a viscous flow state becomes higher, which is not conducive to uniform mixing of the electrolyte and the binder. Therefore, it is necessary to select a binder main material with a suitable molecular weight, such as 50,000, 100,000, 120,000, 200,000, 300,000, 370,000, 460,000, 520,000, 660,000, 780,000, 840,000, 920,000 or 980,000, etc.

[0047] In order to achieve the above-mentioned reversible reaction, as an example, in the present application, the reversible chemical bond includes one of an imine bond, a metal coordination bond, a borate bond, a disulfide bond and a silicon-oxygen bond; the thermosensitive functional group includes one of maleic anhydride and m-vinylamine ester.

[0048] The above chemical bonds or functional groups have the function of dynamic cross-linking under heating conditions. Specifically, after reaching a certain temperature, the above chemical bonds or functional groups are continuously broken and reconstructed, which is reversible. From a macroscopic perspective, they show good viscosity flow characteristics, which is conducive to uniform mixing with the electrolyte.

[0049] In order to further improve the mechanical strength of the electrolyte membrane, see Figure 1 and Figure 2 As shown, the cross-linking molecule also includes a third functional group, and the main chain is provided with a third functional group for reacting and combining with the third functional group of another cross-linking molecule. That is to say, the third functional groups can react with each other, and once a bond is formed, the bond will not be broken due to increasing the temperature, and is not reversible.

[0050] When the cross-linking molecules react with the main material of the binder to form a composite binder, the first functional group and the second functional group will react, usually by heating, and the third functional group will also react with each other. In order to enable the two reactions to proceed normally, to avoid mutual interference as much as possible, and to reduce the difficulty of preparation, in this application, the third functional group is a functional group that undergoes a cross-linking reaction under electron beam or ultraviolet irradiation. In other words, this application can first allow the cross-linking molecules and the main material of the binder to react through the first functional group and the second functional group under heating conditions to form a primary cross-linking network. After that, after being pressed into an electrolyte membrane, it can be subjected to electron beam or ultraviolet irradiation to allow the third functional groups of the cross-linking molecules to react again to form a permanent cross-linking structure. The permanent cross-linking structure is superimposed on the primary cross-linking network to finally form a composite binder with a secondary cross-linking network. Since the composite binder now contains both a dynamic cross-linking structure that can achieve a reversible reaction and an irreversible permanent cross-linking structure, the mechanical strength of the electrolyte membrane is further improved.

[0051] As an example, in the present application, the third functional group includes one of acrylate, allyl, alkynyl, and epoxy bond.

[0052] As an example, in the cross-linked molecules, first, each end group on both sides contains a functional group, which can realize the addition reaction of the carbon-carbon double bond with the main material of the binder, with the purpose of forming a primary cross-linked network between the molecular chains; secondly, there is a dynamic cross-linked structure, the purpose of which is to achieve uniform compounding during the mixing stage of the electrolyte and the composite binder. At the same time, for problems such as cracks and breakage generated during the electrolyte film formation process, self-repair can be achieved through multiple heating and rolling. Finally, there is a third functional group in the cross-linked molecule. As the number of the third functional group increases, the more permanent cross-linked structures there are, the greater the density of the secondary cross-linked network formed, and better mechanical properties of the electrolyte membrane can be achieved. Therefore, the dynamic cross-linked structure and the number of the third functional group in the cross-linked molecules of this application are set according to actual needs, such as see Figure 1In scheme (a), the cross-linking molecule has a dynamic cross-linking structure and a third functional group, and both the dynamic cross-linking structure and the third functional group are between the two second functional groups; in scheme (b), the cross-linking molecule has a dynamic cross-linking structure and two third functional groups, and both the dynamic cross-linking structure and the third functional group are between the two second functional groups, and both third functional groups are arranged on the same side of the dynamic cross-linking structure; in scheme (c), the cross-linking molecule has a dynamic cross-linking structure and two third functional groups, and both the dynamic cross-linking structure and the third functional group are between the two second functional groups, and the two third functional groups are arranged on both sides of the dynamic cross-linking structure. The permanent cross-linking structure in the secondary cross-linking network does not break at high temperatures, thereby preventing the problem of weakening the mechanical strength of the membrane due to the breakage of cross-linking bonds at high temperatures.

[0053] It should be noted that, in the present application, the third functional group can be set in the main chain, or the cross-linking molecule further includes a side chain, the side chain is connected to the main chain, and the third functional group can be set on the side chain.

[0054] In fact, the cross-linking molecules provided in this application are long-chain molecules with good flexibility, which is conducive to the formation of cross-links between the binder chain segments and improves the mechanical properties of the electrolyte membrane.

[0055] Wherein, the main chain of the cross-linked molecule also includes a carbon chain.

[0056] When the third functional group is disposed in the main chain, the reversible chemical bond, the second functional group and the third functional group are connected through the carbon chain to form the cross-linked molecule; When the third functional group is disposed on the side chain, the reversible chemical bond is connected to the second functional group via the carbon chain, and the carbon chain is also connected to the side chain.

[0057] As an example, in the present application, the molecular weight of the cross-linking molecule is ≥200.

[0058] When the binder main material / cross-linking molecule molar ratio is low, the number of cross-linking molecules is small, and the mechanical properties are not significantly improved. However, when the binder main material / cross-linking molecule ratio is too high, the polar functional groups in the binder chain increase, and the side reaction with the sulfide electrolyte becomes more obvious, resulting in a decrease in ionic conductivity. Based on this, as an example, in this application, the molar ratio of the binder main material to the cross-linking molecule is 1: (1-100). For example, it can be 1:1, 1:10, 1:18, 1:26, 1:45, 1:62, 1:76, 1:88, or 1:100.

[0059] It is understandable that the cross-linked molecular structure can contain three functional group structures, of which the two end groups are second functional groups that can undergo addition reactions with the carbon-carbon double bonds in the main binder material. Their function is to graft the cross-linked molecular structure onto the main binder material chain segment through chemical reactions during the preparation stage of the composite binder; the second is a heat-sensitive dynamic cross-linked structure, whose function is to dynamically break and form bonds under heating conditions during the heating and mixing process of the sulfide electrolyte, the composite binder and the lithium salt, which is conducive to the softening of the composite binder and the formation of a viscous flow state, thereby achieving uniform compounding with the sulfide electrolyte. If the composite binder does not have the dynamic breaking and forming function under heating, then during the mixing stage of the sulfide electrolyte and the composite binder, the composite binder cannot be completely transformed into a viscous flow state because the cross-linked network cannot be disconnected, which seriously affects the uniform mixing of the electrolyte and the composite binder. At the same time, after the electrolyte membrane is formed, the dynamic cross-linking structure restores the cross-linking function at room temperature to form a dynamic primary cross-linking network, which is beneficial to improving the mechanical strength of the electrolyte membrane; thirdly, the cross-linking molecular structure contains a third functional group with permanent cross-linking properties, that is, after initiating cross-linking, it will no longer break and rebuild with temperature changes. The function of the third functional group of the cross-linking molecule is to initiate cross-linking after the electrolyte membrane is formed to form a permanent cross-linking structure. The third functional group does not undergo cross-linking in the early stage of mixing the sulfide electrolyte and the composite binder to avoid a decrease in the viscosity of the composite binder, resulting in uneven mixing. In the cross-linking molecule, the end group, the dynamic cross-linking structure and the third functional group are connected by a carbon chain (CH2) n Make connections, where 1≤n≤5.

[0060] The dynamic cross-linking structure in the above-mentioned cross-linking molecules can break and reconstruct the cross-linking bonds under heating conditions, and the third functional group contained therein triggers cross-linking through ultraviolet light or electron beam, thereby avoiding the problem of decreased binder fluidity caused by premature cross-linking during the mixing stage of the electrolyte, composite binder and lithium salt.

[0061] Furthermore, the present application also provides a method for preparing a composite adhesive, by adding an initiator to realize an addition reaction between the main material of the adhesive and the cross-linking molecules under certain reaction conditions, thereby preparing a composite adhesive having a cross-linked network structure.

[0062] The reaction must be carried out in a glass bottle protected by an inert atmosphere to avoid oxidation of the reactants or products.

[0063] Specifically, the preparation method includes: adding the main material of the adhesive and the cross-linking molecules to a solvent under protective gas, then adding an initiator, setting the reaction temperature at 25-100°C, the reaction time at 1-4 hours, and washing with water and ethanol after the reaction to obtain a composite adhesive.

[0064] It should be noted that if only a composite adhesive having a primary cross-linked network is required to be formed, the composite adhesive having a primary cross-linked network can be obtained after washing with water and ethanol.

[0065] If a composite adhesive having a secondary cross-linked network is to be formed, a third functional group needs to be provided in the above cross-linked molecules. At the same time, after the above is washed with water and ethanol, an electron beam or ultraviolet irradiation is performed to obtain a composite adhesive having a secondary cross-linked network.

[0066] The amount of initiator added is 0.1% to 5% of the molar weight of the crosslinking molecules, and can be 0.1%, 0.5%, 1%, 3%, or 5%. Insufficient initiator content will reduce the grafting rate between the crosslinking molecules and the main binder material, affecting the crosslinking effect; excessive initiator content may cause oxidation and cleavage of double bonds in the main binder material, resulting in a decrease in molecular weight.

[0067] The initiator includes one or more of di-tert-butyl peroxide, dicumyl peroxide, benzoyl peroxide, azoisobutyronitrile and boron trifluoride ether complex.

[0068] The solvent includes one or more of toluene, xylene, chlorobenzene, isobutyl isobutyrate, nonyl acetate, tetrahydrofuran, cyclohexane, decahydronaphthalene, carbon tetrachloride, hexane, heptane, octane, nonane, decane, undecane and dodecane.

[0069] The protective gas includes one or more of nitrogen and argon.

[0070] Furthermore, the present application also provides an electrolyte membrane, which includes a sulfide electrolyte, a lithium salt and the composite binder as described above.

[0071] The mass ratio of the sulfide electrolyte to the composite binder is (100-x):x, where x ranges from 0.5 to 1.5, and the mass ratio of the composite binder to the lithium salt is 1:(1-2).

[0072] The sulfide electrolyte includes one or more of yLi2S-(100-y)P2S5, Li-aPS, and Li6PS5b, wherein y is in the range of 25 to 75, a is Si, Ge, Sn, Al or Y, and b is Cl, Br or I.

[0073] The particle size D of the sulfide electrolyte used 50 Between 1 and 5 μm, the maximum particle size D max <9μm.

[0074] The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium bis(oxalatoborate), and lithium hexafluorophosphate.

[0075] The dry electrolyte membrane obtained in this application comprises a sulfide electrolyte, a lithium salt and a composite binder. Among them, the sulfide electrolyte is the main carrier of lithium ion transmission and is the core material for the electrolyte membrane to realize the lithium ion transmission function. The composite binder is used to bond the electrolyte particles to form a dense and continuous electrolyte phase and provide mechanical support. The composite binder has good mechanical properties, and its viscous flow characteristics at high temperatures help to uniformly compound with the sulfide electrolyte to form an electrolyte membrane with uniform composition. Since the mechanism of lithium ion transmission in the electrolyte membrane is solid-phase transmission, there is a binder between the electrolyte powders, thereby blocking the ion transmission path. By adding lithium salts, the polar functional groups in the binder can be dissociated to form an ion transmission path, thereby improving the ion transmission capacity of the binder. The lithium salt lithiates the binder and provides lithium ions, which cooperates with the composite binder to realize the transmission of lithium ions in the bonding network, improve the ionic conductivity of the electrolyte membrane, and improve the decline in ionic conductivity caused by the addition of the binder.

[0076] Furthermore, the proportion of polar functional groups in the composite binder is relatively low, generally no more than 10% by weight, and no more than 0.15% by weight of the total electrolyte membrane. Therefore, the side reactions of the composite binder with the sulfide electrolyte caused by the grafting of polar groups are limited, and do not cause a decrease in the ionic conductivity of the electrolyte membrane.

[0077] In the present application, the method for preparing the above electrolyte membrane comprises the following steps: The sulfide electrolyte, composite binder, and lithium salt are mixed uniformly under heating conditions and rolled to form an electrolyte membrane. The electrolyte membrane is then composited with the electrode sheet by rolling or transfer printing. The membrane is then irradiated with electron beams or ultraviolet light to induce cross-linking of the third functional group, forming an electrolyte membrane with excellent mechanical strength. The third functional group requires electron beam or ultraviolet light to initiate cross-linking, avoiding premature cross-linking in the previous preparation process, which can cause processing difficulties.

[0078] The electrolyte membrane is prepared by roller-pressing a mixture of sulfide electrolyte, composite binder, and lithium salt. Cracking caused by uneven stress on the electrolyte membrane during the roller-pressing process or insufficient mechanical strength during the thinning process can be repaired by a secondary heating roller-pressing process. The principle is that the dynamic cross-linked structure breaks under heating conditions and then re-forms new bonds in the damaged areas after returning to room temperature, thus achieving repair.

[0079] Furthermore, in the process of forming a secondary cross-linked network of the composite electrolyte membrane / electrode sheet, the cross-linking molecules can also form a cross-linked network at the electrode / electrolyte membrane interface, thereby enhancing the adhesion between the electrolyte membrane and the electrode, improving the contact and peeling strength between the electrolyte membrane and the electrode interface, and helping to reduce the interface impedance.

[0080] As an optional solution, the sulfide electrolyte, composite binder and lithium salt are uniformly mixed in the above proportions under solvent-free conditions, the heating temperature is set to 100-150°C, the mixing time is 0.5-2 hours, and the environmental conditions are a low humidity room (dew point <45°C) or an inert atmosphere glove box.

[0081] Alternatively, the mixed material can be rolled in a roller press to form a membrane. The roller press temperature is set at 130-150°C in a low-humidity room or an inert atmosphere glove box.

[0082] As an optional solution, the prepared sulfide electrolyte membrane has a thickness of 30 to 100 μm.

[0083] As an optional solution, the membrane can be laminated to an electrode or substrate through a secondary roll-pressing process. The electrodes can include lithium iron phosphate cathodes, ternary material cathodes, graphite anodes, silicon anodes, or metallic lithium anodes. The substrates can include copper foil, aluminum foil, titanium foil, or stainless steel foil. Alternatively, the membrane can be formed as a self-supporting membrane without lamination to any substrate.

[0084] Through ultraviolet or electron beam irradiation, the third functional group in the electrolyte membrane is stimulated to cross-link, forming a secondary cross-linking network, thereby improving the mechanical properties of the electrolyte membrane.

[0085] Furthermore, the present application also provides a battery, which includes a positive electrode, a negative electrode and the electrolyte membrane.

[0086] As an optional solution, the positive electrode of the battery can be a ternary positive electrode, a lithium iron phosphate positive electrode, or a lithium-rich manganese-based positive electrode material; the negative electrode of the battery can be graphite, pure silicon, silicon carbon, silicon oxygen, or metallic lithium material.

[0087] The battery provided in this application can be in the form of a molded battery, a soft-pack battery, a square battery, etc. The battery has all the characteristics and advantages of the electrolyte membrane described above, which will not be repeated here. In general, the battery has good electrochemical performance.

[0088] In summary, this application relates to an innovative composite binder and preparation method for dry-process electrolyte membranes suitable for all-solid-state lithium batteries. Specifically, it describes a functional binder network based on a dual-crosslinking structure (dynamic crosslinking + permanent crosslinking) for improving the mechanical properties, electrochemical stability, and interfacial compatibility of sulfide electrolyte membranes with electrode materials. This application also proposes a dry-process electrolyte membrane preparation process compatible with this composite binder, aiming to address core issues in existing dry-process binders, such as weak mechanical properties, significant side reactions, and low ionic conductivity.

[0089] The composite binder provided in this application comprises a two-stage crosslinking structure. The dynamic crosslinking structure enables the electrolyte membrane to self-repair upon mechanical damage, while also enhancing its strength. The permanent crosslinking structure further enhances the membrane's mechanical strength and adhesion to electrodes. The resulting electrolyte membrane exhibits high ionic conductivity, and the composite binder contains a low proportion of polar functional groups in the total binder. This results in no significant side effects on electrodes, significantly improving electrochemical performance.

[0090] This application utilizes the dynamic cross-linking properties of the dynamic cross-linking structure to achieve a viscous flow state through a heating and mixing process, enabling uniform mixing with the sulfide electrolyte and lithium salt and roll-forming the membrane. Secondly, the permanent cross-linking properties of the permanent cross-linking structure further strengthen the internal cross-linking network of the electrolyte membrane, enhancing the mechanical strength of the electrolyte membrane and its adhesion to the substrate.

[0091] The main materials and cross-linked molecular structures of the adhesives used in the preparation of this application are conventional rubber products and functional groups. The preparation method is mature and suitable for large-scale production and use.

[0092] The present application is described below through specific examples. It should be noted that the following specific examples are only for illustrative purposes and do not limit the scope of the present application in any way. In addition, unless otherwise specified, methods without specific conditions or steps are conventional methods, and the reagents and materials used can be obtained from commercial channels.

[0093] Example 1 Composite adhesive preparation: A certain amount of styrene-butadiene-styrene block polymer, crosslinking molecules and initiator are added to xylene solvent. Figure 3 As shown in (a), the crosslinking molecule used has an olefin end group, an imine bond as the dynamic crosslinking structure, and an acrylate tertiary functional group. The molar ratio of the adhesive's main material to the crosslinking molecule is 1:10, and benzoyl peroxide is used as the initiator, at 0.1% of the molar weight of the crosslinking molecules. The mixture is stirred at 80°C for 2 hours, and the reaction product is washed with water to obtain a composite adhesive. Dry electrolyte membrane preparation: (1) A certain amount of Li6PS5Cl electrolyte, composite binder, and lithium salt were mixed in a mass ratio of 99:1:1 at a mixing temperature of 130°C. The uniformly mixed electrolyte membrane precursor was roll-pressed at a rolling temperature of 130°C to prepare an electrolyte membrane. The electrolyte membrane was then composited with a silicon-carbon negative electrode by roll-pressing at room temperature to prepare a composite electrode sheet.

[0094] (2) The prepared composite electrode is irradiated under electron beam for 0.2 hours to obtain an electrolyte membrane with a secondary cross-linked network, such as Figure 4 shown.

[0095] Solid-state battery preparation The composite electrode was assembled with the ternary positive electrode and molded under a pressure of 400 MPa to prepare a solid-state battery.

[0096] Example 2 Different from Example 1, the main material of the adhesive in this embodiment is styrene-butadiene rubber.

[0097] Example 3 Different from Example 1, the main material of the binder in this embodiment is polybutadiene.

[0098] Example 4 Different from Example 1, the main material of the adhesive in this embodiment is isoprene rubber.

[0099] Example 5 The difference from Example 1 is that, see Figure 3 As shown in (b), in this embodiment, the end group (second functional group) of the cross-linking molecule is a thiol group, and the initiator is azoisobutyronitrile.

[0100] Example 6 The difference from Example 1 is that, see Figure 3 As shown in (c), in this embodiment, the end group (second functional group) of the cross-linking molecule is a brominated alkane.

[0101] Example 7 The difference from Example 1 is that, see Figure 3 As shown in (d), in this embodiment, the cross-linking molecular end group (second functional group) is isocyanate, and the initiator is boron trifluoride etherate complex.

[0102] Example 8 The difference from Example 1 is that, see Figure 3 As shown in (e), the dynamic cross-linking structure of the cross-linking molecules in this embodiment is a borate ester bond.

[0103] Example 9 Different from Example 1, the dynamic cross-linking structure of the cross-linking molecules in this embodiment is a silicon-oxygen bond.

[0104] Example 10 The difference from Example 1 is that, see Figure 3 As shown in (f), the dynamic cross-linking structure of the cross-linking molecules in this embodiment is a disulfide bond.

[0105] Example 11 Different from Example 1, the dynamic cross-linking structure of the cross-linking molecules in this embodiment is m-vinylamine ester.

[0106] Example 12 Different from Example 1, the third functional group of the cross-linking molecule in this embodiment is an allyl group.

[0107] Example 13 Different from Example 1, the third functional group of the cross-linking molecule in this embodiment is an epoxy bond.

[0108] Example 14 Different from Example 1, the molar ratio of the main binder material to the cross-linking molecules in this embodiment is 1:50.

[0109] Example 15 Different from Example 1, the lithium salt used in this example is lithium perchlorate.

[0110] Example 16 Different from Example 1, the lithium salt used in this example is lithium bis(fluorosulfonyl)imide.

[0111] Example 17 Different from Example 1, the mass ratio of the sulfide electrolyte to the binder and the lithium salt in this example is 98.5:0.5:1.

[0112] Example 18 Different from Example 2, the mass ratio of the sulfide electrolyte to the binder and the lithium salt in this example is 98.5:0.5:1.

[0113] Example 19 Different from Example 5, the molar ratio of the main binder material to the cross-linking molecules in this embodiment is 1:20.

[0114] Example 20 Different from Example 1, the sulfide electrolyte in this example is 25Li2S-75P2S5.

[0115] Example 21 Different from Example 1, the sulfide electrolyte in this embodiment is Li 10 GeP2S 12 .

[0116] Example 22 Different from Example 1, the irradiation time of the electrolyte membrane in this example is 0.5 hours.

[0117] Example 23 Different from Example 1, the electrolyte membrane in this embodiment does not contain the third functional group.

[0118] Example 24 Different from Example 2, the electrolyte membrane in this example does not contain the third functional group.

[0119] Example 25 Different from Example 8, the electrolyte membrane in this example does not contain the third functional group.

[0120] Comparative Example 1 The LPSC electrolyte and the PTFE binder were mixed in a high-speed mixer at a mass ratio of 99:1 to obtain a sulfide electrolyte / PTFE mixture.

[0121] The sulfide / binder composite is placed in a roller press, and the heating temperature of the roller press is 100° C. After the mixture is roller-pressed, an electrolyte membrane is obtained.

[0122] Comparative Example 2 Different from Example 1, no cross-linking molecules are added in this example.

[0123] Comparative Example 3 Different from Example 1, no lithium salt is added in this example.

[0124] Comparative Example 4 Different from Example 1, the electrolyte membrane in this example is not irradiated with electron beams.

[0125] The following describes the performance test process and results of the composite binder and sulfide electrolyte membrane: (1) Tensile strength of composite adhesive At room temperature, a tensile test was performed using a universal tensile testing machine at a speed of 60 mm / min to test the tensile strength of the composite adhesives prepared in the above examples and comparative examples, with the unit being MPa.

[0126] (2) Electrolyte membrane tensile strength and peeling force The tensile strength of the electrolyte membrane was tested at room temperature and inert gas conditions using a universal tensile testing machine at a speed of 60 mm / min to test the tensile strength of the composite adhesives prepared in the above examples and comparative examples, in MPa.

[0127] The peel strength of the electrolyte membrane was tested at room temperature under inert gas conditions using a universal tensile testing machine at a speed of 60 mm / min and a peel angle of 180°. The tensile strength of the adhesives prepared in the above examples and comparative examples was tested in N / cm.

[0128] (3) Ionic conductivity and capacity retention At room temperature, the sulfide solid electrolyte membranes prepared in the above examples and comparative examples were punched out to prepare samples with a diameter of 10 mm. The samples were placed in a test mold with aluminum foil used as blocking cells at both ends. The ionic conductivity was tested using electrochemical impedance spectroscopy.

[0129] In an inert gas atmosphere, the electrolyte membrane and positive electrode sheets, which are composited onto the negative electrode, were sequentially placed into a molded battery and pressed into shape at 375 MPa. At room temperature, the battery was cycled at a 0.5C / 0.5C charge / discharge rate within the 2.5-4.2 V range, and the cycle performance data was recorded.

[0130] Table 1 Tensile strength of composite adhesives

[0131] Table 2 Tensile strength and peeling force of electrolyte membrane

[0132] Table 3 Ionic conductivity of electrolyte membrane and capacity retention after 50 cycles

[0133] Examples 1-4 in Table 1 show that after cross-linking, the tensile strength of the PTFE binder used in the current dry electrolyte membrane based on different binder main materials has been greatly improved compared to Comparative Example 1, proving that the composite binder provided in this application has been significantly improved in terms of mechanical properties. Example 1, Comparative Example 2 and Comparative Example 4 compare the mechanical properties of the binder main material without cross-linking molecules and after grafting with cross-linking molecules but without electron beam irradiation, proving that after cross-linking molecule modification and electron beam modification, the tensile strength of the composite binder is significantly improved, proving the effectiveness of the cross-linking molecular structure design and the secondary cross-linking network. Examples 5-13 show that different end groups, dynamic cross-linking structures and permanent cross-linking structures can all obtain excellent tensile strength and peeling force, proving that the cross-linking molecular functional groups provided in this application are effective.

[0134] Examples 1-4 in Table 2 show that the tensile strength and peeling force of the electrolyte membrane provided by the present application are significantly better than the technical solutions adopted in Comparative Examples 1 and 2. The comparison between Examples 1-4 and Comparative Example 4 proves that the peeling force and tensile strength of the electrolyte membrane are significantly improved after permanent cross-linking is induced by electron beam irradiation. Examples 14 and 19 illustrate that increasing the proportion of cross-linked molecules can further improve the mechanical properties and peeling force of the electrolyte membrane, but the mechanical performance benefits brought by further increasing the dosage are decreasing. Example 22 illustrates that extending the electron beam irradiation time can promote the improvement of the cross-linking degree of the binder, thereby obtaining higher tensile strength and peeling force. Examples 1-2 and Examples 17-18 demonstrate the effect of different binder addition amounts on the mechanical properties of the electrolyte membrane. The results show that when the binder addition amount is reduced from 1% to 0.5%, the tensile strength and peeling force of the electrolyte membrane are significantly reduced. This result illustrates the positive correlation between the binder content and the mechanical properties of the electrolyte membrane.

[0135] Furthermore, in Table 2, when comparing Example 1 with Examples 23-25, the effects of the lithium salt on the electrolyte membrane are essentially the same, even though both contain lithium salts. However, the inclusion of the third functional group in Example 1 allows for the formation of a permanent crosslinked structure, resulting in greater tensile strength and peel strength. When comparing Example 1 with Comparative Example 3, while Comparative Example 3 does not contain a lithium salt but does contain a third functional group, Example 1 contains both a lithium salt and a third functional group. The addition of the lithium salt to the electrolyte membrane plasticizes the binder, reducing tensile strength and peel strength. However, the actual tensile strength and peel strength of Example 1 and Comparative Example 3 are similar, indicating that the permanent crosslinked structure formed by the third functional group can alleviate the reduction in tensile strength and peel strength caused by the addition of the lithium salt.

[0136] Table 3 Examples 1-4 use different binder main materials, and Examples 5-13 use different cross-linking molecules. Compared with Comparative Example 1, higher ionic conductivity is obtained, indicating that the polar groups in the binder do not cause side reactions to the sulfide electrolyte and have good compatibility. At the same time, compared with Comparative Example 3, it can be seen that the addition of lithium salts can improve the ionic conductivity of the electrolyte membrane, indicating that the polar functions in the binder assume part of the ion transport function and improve the overall ionic conductivity of the electrolyte membrane. Examples 1-4 and Examples 5-13 show good cycle capacity retention rates, which are significantly improved compared to Comparative Example 1, indicating that the embodiments disclosed in this application have high compatibility with the electrode, stable chemical properties, and overcome the problem of negative electrode side reactions caused by the current use of PTFE binders. Comparison of Example 1 with Comparative Example 4 shows that the binder forms a permanent cross-linked structure after irradiation cross-linking, and the cycle performance is improved, indicating that the contact between the electrode / electrolyte membrane interface is closer after cross-linking, which is conducive to reducing the interface impedance and improving the cycle performance.

[0137] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A composite adhesive, characterized in that: It includes a binder main material and cross-linking molecules; The main binder material has a first functional group; The cross-linking molecule includes a main chain and a second functional group, the main chain contains a dynamic cross-linking structure that is sensitive to heat, the dynamic cross-linking structure includes at least one of a reversible chemical bond and a heat-sensitive functional group, and the second functional group that reacts and combines with the first functional group is provided at both ends of the main chain.

2. The composite adhesive according to claim 1, wherein: The first functional group includes one of a carbon-carbon double bond, an epoxy group, a cyano group and a halogenated hydrocarbon; The second functional group includes one of a halogenated hydrocarbon, a mercapto group, an isocyanate group, and an olefin group.

3. The composite adhesive according to claim 2, wherein: The main material of the adhesive includes one or more of styrene-butadiene rubber, isoprene rubber, butyl rubber, chloroprene rubber, styrene-butadiene-styrene block copolymer and polybutadiene.

4. The composite adhesive according to claim 1, wherein: The molecular weight of the main binder material is 50,000 to 1,000,000.

5. The composite adhesive according to claim 1, wherein: The reversible chemical bond comprises one of an imine bond, a metal coordination bond, a borate ester bond, a disulfide bond and a silicon-oxygen bond; The heat-sensitive functional group includes one of maleic anhydride and meta-vinylamine ester.

6. The composite adhesive according to claim 1, wherein: The cross-linking molecule further includes a third functional group, and the main chain is provided with a third functional group for reacting and bonding with the third functional group of another cross-linking molecule.

7. The composite adhesive according to claim 6, wherein: The third functional group is a functional group that undergoes a cross-linking reaction under electron beam or ultraviolet irradiation.

8. The composite adhesive according to claim 7, wherein: The third functional group includes one of acrylate, allyl, alkynyl, and epoxy bond.

9. The composite adhesive according to claim 1, wherein: The third functional group is arranged in the main chain, or the cross-linking molecule further includes a side chain, the side chain is connected to the main chain, and the third functional group is arranged on the side chain.

10. The composite adhesive according to claim 9, wherein: The main chain also includes a carbon chain; When the third functional group is disposed in the main chain, the reversible chemical bond, the second functional group and the third functional group are connected through the carbon chain to form the cross-linked molecule; When the third functional group is disposed on the side chain, the reversible chemical bond is connected to the second functional group via the carbon chain, and the carbon chain is also connected to the side chain.

11. The composite adhesive according to claim 1, wherein: The molecular weight of the cross-linking molecule is ≥200.

12. The composite adhesive according to claim 1, wherein: The molar ratio of the main binder material to the cross-linking molecules is 1: (1-100).

13. A method for preparing the composite adhesive according to any one of claims 1 to 12, characterized in that: It includes: Under protective gas, the main material of the adhesive and the cross-linking molecules are added to the solvent, and then the initiator is added. After the reaction is completed, a composite adhesive is obtained.

14. The method for preparing the composite adhesive according to claim 13, wherein: The amount of the initiator added is 0.1% to 5% of the molar weight of the cross-linking molecules.

15. The method for preparing the composite adhesive according to claim 13, wherein: The initiator comprises one or more of di-tert-butyl peroxide, dicumyl peroxide, benzoyl peroxide, azoisobutyronitrile and boron trifluoride ether complex; and / or, the solvent comprises one or more of toluene, xylene, chlorobenzene, isobutyl isobutyrate, nonyl acetate, tetrahydrofuran cyclohexane, decahydronaphthalene, carbon tetrachloride, hexane, heptane, octane, nonane, decane, undecane and dodecane; And / or, the protective gas includes one or more of nitrogen and argon.

16. The method for preparing the composite adhesive according to claim 13, wherein: The reaction temperature is set at 25-100°C and the reaction time is 1-4 hours.

17. An electrolyte membrane, characterized in that The composite binder comprises a sulfide electrolyte, a lithium salt and the composite binder according to any one of claims 1 to 12.

18. The electrolyte membrane according to claim 17, wherein: The mass ratio of the sulfide electrolyte to the composite binder is (100-x):x, where x ranges from 0.5 to 1.

5. The mass ratio of the composite binder to the lithium salt is 1:(1-2).

19. The electrolyte membrane according to claim 17, wherein: The sulfide electrolyte includes one or more of yLi2S-(100-y)P2S5, Li-aPS, and Li6PS5b, wherein y is in the range of 25 to 75, a is Si, Ge, Sn, Al or Y, and b is Cl, Br or I.

20. The electrolyte membrane according to claim 17, wherein: The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium bis(oxalatoborate), and lithium hexafluorophosphate.

21. A method for preparing an electrolyte membrane according to any one of claims 17 to 20, characterized in that: It includes: The sulfide electrolyte, composite binder and lithium salt are uniformly mixed under heating conditions, and the electrolyte membrane is prepared by roller pressing.

22. A battery, characterized in that: It comprises the electrolyte membrane according to any one of claims 17 to 20.

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