In-situ curing method of a polymer electrolyte and solid-state lithium-ion battery

Abstract

This invention discloses an in-situ solidification method for polymer electrolytes and a solid-state lithium-ion battery, relating to a method for preparing lithium-ion battery electrolytes. A negative electrode sheet is prepared by physically embedding an initiator into a polar binder network of a negative electrode slurry; a polymer electrolyte precursor solution without initiator is injected into the assembled battery cell; after injection, the solution is allowed to stand for a specific time to allow the initiator to dissolve in the liquid phase in a controlled manner, followed by heating to trigger in-situ polymerization. This invention spatially decouples the permeation kinetics of the precursor from the polymerization reaction activity, solving the problems of premature monomer gelation and blockage of the injection channels. Simultaneously, the controlled directional polymerization reverses the volume shrinkage vector to point inwards towards the interior of the negative electrode, forming an interface anchoring structure with extremely high peel strength; and a crosslinking density gradient decreasing from the negative electrode to the positive electrode is spontaneously constructed within the electrolyte, breaking the technical bias of mutual exclusion between mechanical strength and ionic conductivity, and improving the interface stability and overall performance of the solid-state battery.

Description

Technical Field

[0001] This invention relates to a method for preparing a lithium-ion battery electrolyte, and more particularly to an in-situ solidification method for a polymer electrolyte and a solid-state lithium-ion battery. Background Technology

[0002] With the rapid development of electric vehicles and energy storage, high energy density and high safety have become the core goals of lithium-ion battery research and development. Traditional liquid lithium-ion batteries use organic liquid electrolytes, which are prone to thermal runaway under extreme conditions such as overcharging, compression, or high temperature, posing serious safety hazards such as fire and explosion. Therefore, using non-flammable or flame-retardant polymer solid electrolytes to replace traditional liquid electrolytes is considered by the industry to be one of the ultimate solutions to battery safety problems.

[0003] Among the many polymer solid electrolyte preparation processes, in-situ thermally initiated polymerization technology has shown great industrialization potential due to its ability to maintain good physical contact between the electrode and the electrolyte. This technology typically involves pre-mixing polymer monomers, inorganic lithium salts, organic solvents, and thermal initiators to prepare a homogeneous liquid precursor solution, which is then injected into the dry cell. Heating causes the monomers to undergo cross-linking polymerization under the action of the initiator, thereby generating a three-dimensional polymer network in situ inside the cell.

[0004] However, with the deepening research on polymer reaction kinetics and electrochemical interface mechanisms, existing homogeneous in-situ polymerization technology has revealed two fundamental contradictions that are difficult to reconcile in practical applications: First, there is a contradiction between the permeation kinetics and reactivity of the precursor solution. In order to ensure that the precursor solution can fully wet the micropores of the high-density electrode, the solution must maintain an extremely low initial viscosity. However, in the existing technology, the thermal initiator and polymer monomers coexist in the same liquid phase system. Under normal temperature conditions during storage, turnover and injection, the precursor is prone to premature polymerization of monomers due to thermodynamic fluctuations, mainly manifested as local gelation or explosive polymerization. This not only leads to an abnormal increase in solution viscosity and deterioration of the wetting effect, but may even cause blockage of the injection pipeline, which seriously restricts the yield and process reliability of large-scale continuous production.

[0005] Secondly, there is the contradiction between isotropic volume shrinkage and interfacial mechanical instability caused by homogeneous polymerization. During the cross-linking phase transition, polymer monomers inevitably experience a 5%-15% volume shrinkage. Since the initiators in the existing technology are uniformly distributed in the liquid phase, the polymerization reaction inside the cell is a bulk homogeneous nucleation. This disordered polymerization leads to isotropic distribution of shrinkage stress, which manifests macroscopically as follows: under the pull of shrinkage stress, the generated polymer network tends to be extracted from the micron / nanoscale pores on the electrode surface, thereby generating a large number of microscopic gaps between the solid electrolyte and the electrode active material. These physical gaps not only significantly increase the interfacial charge transfer impedance of the battery, but also destroy the uniformity of ion transport, making it very easy to induce the nucleation and growth of lithium dendrites at the edge of the micropores, ultimately leading to a sharp drop in battery cycle life or even short-circuit failure.

[0006] Therefore, the industry urgently needs to develop a novel in-situ solidification mechanism that can spatially decouple the injection stability from the polymerization reaction activity, and reconstruct the direction of the polymerization shrinkage vector from the physical and mechanical level, thereby completely eliminating the interfacial shrinkage gap and meeting the commercialization requirements of high-energy-density solid-state lithium-ion batteries. Summary of the Invention

[0007] This invention overcomes the shortcomings of the prior art and provides an in-situ curing method for polymer electrolytes and a solid-state lithium-ion battery.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is: an in-situ curing method for polymer electrolytes, comprising the following steps:

[0009] S1. The initiator is mixed with the negative electrode active material and the binder to form a negative electrode slurry, which is then coated onto the current collector and dried under conditions below the initial decomposition temperature of the initiator to obtain a negative electrode sheet.

[0010] S2. Assemble the negative electrode, separator, and positive electrode into a battery cell, and inject a polymer electrolyte precursor solution into the battery cell; the precursor solution includes a polymer monomer, an inorganic lithium salt, and an organic solvent, and no initiator is added to the precursor solution before it is injected into the battery cell; the polymer monomer includes at least one multifunctional crosslinking agent.

[0011] S3. After the electrolyte-filled cell is left to stand at 15-35℃ for 12-36 hours, the temperature is then raised to 40-80℃ to carry out an in-situ polymerization reaction, thereby obtaining the solid-state lithium-ion battery.

[0012] In a preferred embodiment of the present invention, the binder is a polymer containing at least one polar functional group selected from carboxyl, hydroxyl, or amide groups; the initiator is an azo compound or an organic peroxide containing polar groups.

[0013] In a preferred embodiment of the present invention, the polymer monomer includes at least one selected from methyl methacrylate, butyl acrylate, vinylene carbonate, or propylene carbonate;

[0014] The multifunctional crosslinking agent includes at least one of ethylene glycol dimethacrylate, polyethylene glycol diacrylate, or trimethylolpropane triacrylate.

[0015] In a preferred embodiment of the present invention, the initiator includes at least one of benzoyl peroxide, azobisisobutyronitrile, or azobisisoheptanenitrile;

[0016] The initiator accounts for 0.05%-1.5% of the total solid mass in the negative electrode slurry.

[0017] In a preferred embodiment of the present invention, the inorganic lithium salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalate-borate), lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, or lithium di(oxalate-borate).

[0018] The organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene sulfite, and fluoroethylene carbonate.

[0019] In a preferred embodiment of the present invention, in step S3, the heating time of the in-situ polymerization reaction is 3-8 hours.

[0020] In a preferred embodiment of the present invention, the mass ratio of the initiator to the binder in the negative electrode slurry is 1:2 to 1:20; the binder forms a network structure, and the initiator is embedded in the network structure.

[0021] In a preferred embodiment of the present invention, in step S3, the solid electrolyte permeates into the micropores of the negative electrode active material and polymerizes to form an interface anchoring structure, wherein the depth of the interface anchoring structure is 0.5 μm-5 μm.

[0022] In a preferred embodiment of the present invention, the negative electrode active material includes at least one of graphite, silicon-based materials, or lithium titanate.

[0023] A solid-state lithium-ion battery, prepared by any of the methods described above, the battery comprising a positive electrode, a negative electrode, and a solid electrolyte located between the positive and negative electrodes;

[0024] The polymer molecular chain end groups of the solid electrolyte contain characteristic groups generated by the decomposition of an initiator pre-placed in the negative electrode; inside the solid electrolyte, the concentration of the characteristic groups at the contact interface between the solid electrolyte and the negative electrode is higher than that at the contact interface between the solid electrolyte and the positive electrode, and the solid electrolyte exhibits a heterogeneous distribution in the thickness direction, with the concentration gradually decreasing or stepwise decreasing from the negative electrode side to the positive electrode side.

[0025] The solid electrolyte and the negative electrode have an interface anchoring structure, and the crosslinking density of the solid electrolyte at the contact interface between the solid electrolyte and the negative electrode is higher than its crosslinking density at the contact interface between the solid electrolyte and the positive electrode.

[0026] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0027] This invention, by pre-placing the initiator in the negative electrode slurry and strictly limiting the precursor solution to an initiator-free state before liquid injection, completely decouples the permeation kinetics and polymerization reactivity of the polymer monomer in a spatial dimension, eliminating the potential thermodynamic spontaneous reaction hazards caused by the coexistence of monomer and initiator in the liquid phase system. This spatial isolation mechanism ensures that the precursor solution maintains an extremely low initial viscosity throughout the storage and liquid injection process, guaranteeing perfect wetting of the micropores of the high-density electrode. Compared with the traditional homogeneous in-situ polymerization scheme of premixing initiator and monomer, this invention fundamentally eliminates the problems of premature gelation and blockage of liquid injection channels caused by environmental temperature fluctuations, significantly improving the yield and absolute reliability of large-scale continuous production of solid-state batteries.

[0028] By leveraging the directional distribution and in-situ triggering of the initiator at the negative electrode interface, this invention successfully induces the polymerization reaction to spread in a controlled manner from the inside of the negative electrode micropores towards the electrolyte bulk. It cleverly reverses the volume shrinkage vector during the polymer phase transition process from the traditional centripetal shrinkage to pointing towards the inside of the negative electrode, thereby generating a strong self-tightening effect at the interface. Accompanying this controlled growth process, the newly formed polymer chains and the negative electrode active material undergo deep molecular-level physical entanglement and topological pinning, forming an interface anchoring structure with extremely high peel strength. This completely overcomes the fatal drawback of existing homogeneous polymerization technology, which causes the polymer to be extracted from the pores and generate nanoscale interfacial gaps due to isotropic shrinkage. This provides an indestructible mechanical support for suppressing lithium dendrite nucleation and buffering the charge and discharge volume expansion of silicon-based and other negative electrodes from a physical level.

[0029] By utilizing the heterogeneous distribution formed by the controlled diffusion of the initiator from the negative electrode to the electrolyte during the static stage, this invention spontaneously constructs a characteristic group concentration gradient and crosslinking density gradient that decrease from the negative electrode interface to the positive electrode interface within the solid electrolyte. This ingenious microscopic asymmetric structure enables the interface region near the negative electrode to possess extremely high shear modulus to block dendrite penetration, while the appropriate amount of initiator diffused to the positive electrode side ensures complete solidification of the liquid phase of the entire battery while endowing the bulk and positive electrode interface regions with high free volume and ion mobility. This mechanism breaks the industry's technical prejudice that mechanical strength and ionic conductivity are mutually restrictive in traditional solid electrolytes, achieving a deep decoupling and synergistic win-win situation between extremely low interfacial charge transfer impedance and excellent rate performance.

[0030] By precisely defining the mass ratio of initiator to polar binder and physically embedding it in the microstructure formed by the binder, this invention introduces a kinetic buffering mechanism for the initiator dissolution process, effectively regulating the rate and flux of initiator release into the liquid precursor. This microstructure ensures a high degree of temporal and spatial synchronization between the physical wetting front and the chemical initiation front of the precursor solution, avoiding premature blockage of local interfaces due to excessively rapid initiator dissolution. Compared to conventional solidification methods where initiators are randomly distributed, this restricted release mechanism greatly enhances the integrity and uniformity of the interpenetrating structure between the electrolyte network and the electrode skeleton, endowing solid-state lithium-ion batteries with excellent long cycle life and resistance to thermal runaway. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a flowchart of an in-situ curing method for a polymer electrolyte according to the present invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0035] The present invention provides an in-situ solidification method for polymer electrolytes and a solid-state lithium-ion battery thereof, which is particularly suitable for high-energy-density energy storage systems that require extremely high interfacial mechanical stability and ion transport efficiency, such as lithium-ion batteries using high-density graphite anodes, high-volume-expansion-rate silicon-based anodes, or high-nickel ternary cathodes.

[0036] It should be specifically stated that the solid-state lithium-ion battery and solid-state electrolyte described in this invention refer to a battery system that exhibits non-flowing solid-state characteristics in its macroscopic physical morphology. Because the precursor solution of this invention contains organic solvents, such as carbonate solvents, these organic solvents are firmly bound within the generated three-dimensional polymer cross-linked network after the in-situ polymerization reaction, resulting in no macroscopic leakage of free liquid electrolyte. Therefore, the term "solid-state" in this invention encompasses gel polymer electrolytes or quasi-solid / semi-solid-state battery systems known in the art, and their macroscopic solid-state properties should not be questioned due to the presence of solvent molecules at the internal microscopic level.

[0037] Furthermore, the characteristic group described in this invention refers to the chemical residues that are stably bound to the ends of the polymer molecular chains by covalent bonds after the initiator, which is pre-placed in the negative electrode, decomposes upon heating to generate free radicals and initiates a chain polymerization reaction of the polymer monomers. The chemical structure of this characteristic group is uniquely determined by the type of initiator used. For example, when azobisisobutyronitrile is used as the initiator, the isobutyronitrile free radicals generated upon heating initiate the polymerization of the monomers, and the isobutyronitrile group (-C(CH3)2CN) remaining at the ends of the polymer chains is the characteristic group described in this invention. The concentration distribution of this characteristic group inside the solid electrolyte objectively reflects the diffusion and consumption trajectory of the initiator at the polymerization front.

[0038] The core concept of this invention lies in breaking the technical bias of homogeneous mixing of initiators and monomers in traditional in-situ polymerization technology, and proposing a physicochemical mechanism of interface-constrained polymerization and topological pinning synergy.

[0039] Specifically, this invention physically embeds the initiator in the polar binder network structure of the negative electrode slurry beforehand, while the precursor solution injected into the battery cell remains in an absolutely initiator-free state. During the settling stage after injection, the precursor solution rapidly wets the micropores of the electrode sheet due to its extremely low initial viscosity; simultaneously, driven by the concentration gradient, the pre-placed initiator slowly and controllably dissolves from the binder network into the liquid-phase precursor; this controlled dissolution mechanism allows the initiator to spontaneously form a heterogeneous distribution within the battery cell before curing, with extremely high concentration on the negative electrode side and extremely low concentration on the positive electrode side.

[0040] When the polymerization is triggered by heating, the high concentration of initiator induces the reaction to start first from inside the micropores of the negative electrode and spread towards the electrolyte and the positive electrode. This controlled directional growth process cleverly reverses the volume shrinkage vector generated by the polymer phase transition from the traditional centripetal shrinkage to pointing towards the inside of the negative electrode. Under the action of shrinkage stress, the newly formed polymer chain segments become deeply physically entangled with the active material particles of the negative electrode, forming an interface anchoring structure similar to an expansion bolt, i.e., topological pinning, which fundamentally eliminates the micro gaps at the interface.

[0041] Meanwhile, due to the spatial difference in initiator concentration, the resulting solid electrolyte exhibits a gradient distribution of crosslinking density that decreases from the negative electrode to the positive electrode in the thickness direction. This asymmetric structure enables the interface near the negative electrode to have extremely high shear modulus to suppress lithium dendrites, while the bulk and positive electrode sides maintain high free volume to ensure excellent ionic conductivity. Ultimately, this achieves a deep decoupling and synergistic win-win between the battery's mechanical strength and electrochemical performance.

[0042] Traceability of experimental materials and preparation of self-made materials:

[0043] Azobisisobutyronitrile (AIBN): Product No. A104255, purity ≥98%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0044] Methyl methacrylate (MMA): Product No. M890210, purity 99.0%, contains stabilizer, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0045] Polyethylene glycol diacrylate (PEGDA): Product number P109708, average molecular weight of PEG ~400, contains MEHQ stabilizer, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0046] Lithium hexafluorophosphate (LiPF6): Product number L822100, purity 99.5%, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0047] Ethylene carbonate (EC): Product number E105728, purity ≥99.9%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0048] Diethyl carbonate (DEC): Product No. D707989, purity ≥99.9%, battery grade, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0049] Anhydrous ethyl acetate (EA): Product No. 10009418, analytical grade, purity ≥99.5%, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0050] Sodium carboxymethyl cellulose (CMC-Na): Product No. C104984, viscosity: 300-800 mPa.s, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0051] Styrene-butadiene rubber (SBR): Product number HXJ3679, purchased from Shenzhen Ruijite Biotechnology Co., Ltd.;

[0052] Graphite: Model G434785, purity ≥99.9%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0053] Conductive carbon black (Super-P): Product code Super P Li, purity ≥99% (battery grade), purchased from the Science Compass platform.

[0054] In addition to the materials purchased above, the conventional auxiliary reagents such as deionized water used in the embodiments of the present invention are all commercially available analytical grade; the positive electrode sheet (such as lithium iron phosphate positive electrode sheet or ternary positive electrode sheet) and polyethylene (PE) separator are all commercially available battery materials commonly used in the field.

[0055] like Figure 1 As shown, an in-situ curing method for a polymer electrolyte includes the following steps:

[0056] S1. The initiator is mixed with the negative electrode active material and the binder to form a negative electrode slurry, which is then coated onto the current collector and dried under conditions below the initial decomposition temperature of the initiator to obtain a negative electrode sheet.

[0057] S2. Assemble the negative electrode, separator, and positive electrode into a battery cell, and inject a polymer electrolyte precursor solution into the battery cell; the precursor solution includes a polymer monomer, an inorganic lithium salt, and an organic solvent, and no initiator is added to the precursor solution before it is injected into the battery cell; the polymer monomer includes at least one multifunctional crosslinking agent.

[0058] S3. After the electrolyte-filled cell is left to stand at 15-35℃ for 12-36 hours, the temperature is then raised to 40-80℃ to carry out an in-situ polymerization reaction, thereby obtaining the solid-state lithium-ion battery.

[0059] Each step will be explained in detail below:

[0060] The core of step S1 is to pre-embed the initiator in the microstructure of the negative electrode while ensuring that it does not undergo thermal deactivation during the entire electrode preparation process.

[0061] Preferably, when preparing the negative electrode slurry, a high molecular polymer containing polar functional groups is selected as a binder. This type of binder can form a dense three-dimensional network structure after the solvent evaporates.

[0062] Preferably, an azo compound or organic peroxide containing polar groups is uniformly dispersed in the slurry as an initiator. During the drying process after coating, the initiator molecules are firmly embedded in the gaps between the binder network and the negative electrode active material particles.

[0063] Furthermore, to completely remove the solvent from the slurry without damaging the chemical activity of the initiator, this invention strictly limits the drying temperature to be lower than the initial decomposition temperature of the selected initiator. In actual industrial operation, to balance drying efficiency and low-temperature requirements, a low-boiling-point organic solvent is preferably used as the dispersion medium for the slurry, combined with a high-vacuum drying process. This synergistic effect of low temperature and high vacuum enables the solvent to be rapidly vaporized and removed at a temperature far below its atmospheric boiling point, thereby producing a negative electrode sheet with high electrochemical activity and a sufficient amount of pre-placed active initiator.

[0064] Step S2 aims to completely decouple the permeation kinetics of polymer monomers from their polymerization reactivity in a spatial dimension.

[0065] Preferably, the precursor solution is prepared by mixing polymer monomers, inorganic lithium salts and organic solvents in a predetermined ratio; wherein, the polymer monomers must contain at least one multifunctional crosslinking agent, which is the material basis for subsequently constructing a three-dimensional crosslinking network and forming a crosslinking density gradient inside the electrolyte.

[0066] Crucially, the precursor solution must be substantially free of initiators before being injected into the battery cell. This means that the mass fraction of initiators in the solution must not exceed 0.001% through strict control of the formulation process. This spatial isolation mechanism allows the precursor solution to maintain an extremely low initial viscosity throughout the entire process of storage, handling, and injection, fundamentally eliminating problems such as premature monomer gelation and blockage of injection channels caused by environmental temperature fluctuations. This ensures perfect wetting of the micropores of the high-density electrode by the solution.

[0067] Step S3 is key to achieving the interface anchoring structure and heterogeneous cross-linking density distribution.

[0068] Preferably, the battery cell after liquid injection needs to be left to stand at room temperature (15-35℃) for 12-36 hours.

[0069] Specifically, during this kinetic settling period, the precursor solution fully wets the micropores of the electrode sheet; at the same time, the initiator pre-placed in the negative electrode binder network structure begins to slowly and controllably dissolve into the liquid-phase precursor under the drive of the concentration gradient.

[0070] It must be noted that, due to the physical barrier effect of the binder network, the dissolution rate of the initiator is effectively regulated, avoiding a large-scale release in an instant; after a set set set time, the initiator spontaneously forms a concentration gradient distribution that decreases from the negative electrode to the positive electrode inside the cell.

[0071] It should be noted that although the concentration of the very small amount of initiator diffused to the positive electrode side is much lower than that to the negative electrode side, it has reached the critical concentration for initiating the gelation or solidification of the monomer.

[0072] Furthermore, after the settling period, the battery cell is heated to 40-80℃ to trigger an in-situ polymerization reaction.

[0073] Because the initiator concentration is highest at the negative electrode interface, the polymerization reaction is initiated first from inside the micropores of the negative electrode and spreads towards the electrolyte bulk and the positive electrode; this controlled directional growth process reverses the volume shrinkage vector generated by the polymer phase transition from the traditional centripetal shrinkage to pointing towards the inside of the negative electrode.

[0074] Furthermore, under the action of contractile stress, the newly formed polymer chains become deeply physically entangled with the negative electrode active material, forming an interfacial anchoring structure with extremely high peel strength, completely eliminating interfacial micro-gaps. At the same time, due to the spatial difference in initiator concentration, the final solid electrolyte exhibits a gradient distribution of crosslinking density that decreases from the negative electrode to the positive electrode in the thickness direction, achieving a deep decoupling and synergistic improvement of battery mechanical strength and ionic conductivity.

[0075] Example 1:

[0076] S1. Taking the preparation of 100g of negative electrode solid powder as an example. Weigh 4.0g of sodium carboxymethyl cellulose powder, add it to 100g of deionized water, and stir at 500rpm for 2h to form a uniform and transparent colloid.

[0077] Subsequently, 89.2g of graphite powder and 2.0g of conductive carbon black were added to the adhesive solution, and homogenized at a high shear speed of 2000rpm for 2h. Then, 8.0g of 50% (w / w) styrene-butadiene rubber aqueous emulsion was added, the speed was reduced to 500rpm, and stirring was continued for 0.5h to obtain an aqueous base slurry.

[0078] Weigh 0.8 g of azobisisobutyronitrile and completely dissolve it in 10.0 g of anhydrous ethyl acetate to prepare an initiator solution. Under high-speed shear at 1500 rpm, add the initiator solution dropwise to the above-mentioned aqueous substrate slurry at a constant flow rate of 1.0 mL / min and stir in a sealed container for 1 h.

[0079] After precise ingredient preparation as described above, the final total solid mass of the negative electrode slurry is 100g; of which, the mass of the initiator accounts for 0.8% of the total solid mass; the mass ratio of the initiator to the binder is 1:10.

[0080] The above-mentioned negative electrode slurry was uniformly coated onto a 9μm thick copper foil current collector using a coating machine, with the coating surface density controlled at 10mg / cm². 2The electrode was then continuously dried at 45°C and -0.098 MPa for 24 hours to completely remove water and ethyl acetate, and to ensure that the drying temperature was much lower than the initial decomposition temperature of AIBN. The dried electrode was then rolled and punched to obtain a negative electrode with a pre-added atomizing agent.

[0081] S2. Under a high-purity argon atmosphere where the water and oxygen content are both less than 0.1 ppm, ethylene carbonate and diethyl carbonate are mixed at a mass ratio of 1:1 as the base solvent; lithium hexafluorophosphate is added to the mixture until the concentration is 1.0 mol / L, and the mixture is stirred evenly to obtain the base electrolyte.

[0082] Subsequently, 5% methyl methacrylate and 2% polyethylene glycol diacrylate by mass were added to the basic electrolyte, and the mixture was stirred thoroughly to obtain a polymer electrolyte precursor solution. Gas chromatography analysis showed that the background content of the initiator in this precursor solution was 0 (below the detection limit of 0.001 wt%).

[0083] The negative electrode, separator and positive electrode prepared above are stacked in sequence, and the bare cell is formed by electrode tab welding and aluminum-plastic film encapsulation; the above precursor solution is injected into the bare cell with an injection coefficient of 3.0 g / Ah, and the cell is sealed after being vacuum-stressed at -0.09 MPa for 5 minutes.

[0084] S3. After the battery cell is filled and sealed, it is left to stand at 25°C for 24 hours. During this kinetic standing period, the precursor solution fully wets the micropores of the electrode sheet, while the initiator embedded in the negative electrode binder network is controlled to dissolve into the liquid phase.

[0085] After standing, the temperature was raised to 60°C and kept constant for 5 hours to trigger the in-situ polymerization reaction. After the reaction was completed, the temperature was lowered to room temperature to obtain a solid-state lithium-ion battery.

[0086] To verify the criticality of the core parameters, based on Example 1, the proportion of initiator, the mass ratio of initiator to binder, and the standing time were adjusted as individual variables. The specific parameters are as follows:

[0087] Example 2:

[0088] The amount of azobisisobutyronitrile (AIB) in S1 was adjusted to 0.05 g, and the amount of graphite powder was adjusted to 89.95 g. At this point, the initiator accounted for 0.05% of the total solid mass, and the mass ratio of initiator to binder was adjusted to 1:160. The remaining steps were the same as in Example 1.

[0089] Example 3:

[0090] The amount of azobisisobutyronitrile (AIB) in S1 was adjusted to 1.5 g, and the amount of graphite powder was adjusted to 88.5 g. At this point, the initiator accounted for 1.5% of the total solid mass, and the mass ratio of initiator to binder was adjusted to 1:5.33. The remaining steps were the same as in Example 1.

[0091] Example 4:

[0092] Keep the azobisisobutyronitrile (AIBN) feed amount constant at 0.8g. Adjust the sodium carboxymethyl cellulose in S1 to 0.8g, the styrene-butadiene rubber aqueous emulsion to 1.6g (equivalent to 0.8g solids), and simultaneously adjust the graphite powder feed amount to 95.6g. At this point, the mass ratio of initiator to binder is 1:2 (initiator percentage remains at 0.8%). The remaining steps are the same as in Example 1.

[0093] Example 5:

[0094] The azobisisobutyronitrile (AIBN) feed amount remains unchanged at 0.8g. The sodium carboxymethyl cellulose in S1 is adjusted to 8.0g, and the styrene-butadiene rubber aqueous emulsion to 16.0g (equivalent to 8.0g solids). Simultaneously, the graphite powder feed amount is adjusted to 81.2g. At this point, the initiator to binder mass ratio is 1:20 (initiator percentage remains at 0.8%). The remaining steps are the same as in Example 1.

[0095] Example 6:

[0096] Adjust the settling time in S3 to 12 hours, and the remaining steps are the same as in Example 1.

[0097] Example 7:

[0098] Adjust the settling time in S3 to 36 hours, and the remaining steps are the same as in Example 1.

[0099] To highlight the necessity of the parameter range of this invention and the generational advantage of the overall technical solution, the following comparative examples were designed:

[0100] Comparative Example 1:

[0101] Adjust the amount of azobisisobutyronitrile (AIBN) in S1 to 0.03 g. At this point, the initiator accounts for 0.03% of the total solid mass. The remaining steps are the same as in Example 1.

[0102] Comparative Example 2:

[0103] Adjust the amount of azobisisobutyronitrile (AIBN) in S1 to 1.7g, at which point the initiator accounts for 1.7% of the total solid mass. The remaining steps are the same as in Example 1.

[0104] Comparative Example 3:

[0105] Keeping the azobisisobutyronitrile (AIB) content constant at 0.8 g, adjust the total solid binder content to 0.8 g. At this point, the mass ratio of initiator to binder is 1:1. The remaining steps are the same as in Example 1.

[0106] Comparative Example 4:

[0107] Keeping the azobisisobutyronitrile (AIB) content constant at 0.8 g, adjust the total solid binder content to 20.0 g. At this point, the mass ratio of initiator to binder is 1:25. The remaining steps are the same as in Example 1.

[0108] Comparative Example 5:

[0109] Adjust the settling time in S3 to 10 hours, and follow the same steps as in Example 1.

[0110] Comparative Example 6:

[0111] Adjust the settling time in S3 to 40 hours, and the remaining steps are the same as in Example 1.

[0112] Comparative Example 7:

[0113] No initiator is added to the negative electrode slurry (it contains only graphite, conductive agent, and binder). When preparing the precursor solution in S2, 0.8% (by mass) of azobisisobutyronitrile (AIBN) is directly dissolved in the precursor solution. After injection and sealing, the solution is not allowed to stand; it is directly heated to 60°C for 5 hours.

[0114] To objectively evaluate the microstructure characteristics and macroscopic electrochemical performance of the solid-state batteries in each embodiment and comparative example, the following specific test methods were used for characterization.

[0115] Precursor solution viscosity stability test:

[0116] Take 10 mL of the prepared precursor solution and test its initial viscosity at 25 °C. After standing at 25°C for 24 hours, its viscosity was tested again. Calculate the viscosity change rate. This indicator is used to visually reflect the anti-gelling ability of the precursor solution during the injection process window.

[0117] Interface peel strength test:

[0118] The fully cured battery cell was disassembled, and a 20mm×100mm negative electrode and solid electrolyte laminate strip was cut. The negative electrode side was fixed on a flat substrate, and a lead tape was attached to one end of the solid electrolyte. The solid electrolyte layer was peeled off at a peel angle of 180° and a tensile speed of 50mm / min. The average load during the stable peeling stage was recorded, and the interfacial peel strength was calculated in N / mm.

[0119] Asymmetric gelation rate difference test:

[0120] After disassembling the solidified battery cell, a 10μm thick layer of solid electrolyte adhering to the negative electrode surface was taken as sample A, and a 10μm thick layer of solid electrolyte adhering to the positive electrode surface was taken as sample B; the initial mass of each sample was weighed. Using dimethyl carbonate as solvent, the sample was refluxed at 60°C for 24 h to thoroughly wash away uncrosslinked monomers and free solvent. It was then dried under vacuum at 80°C to constant weight, and the mass of the remaining polymer network was measured. Calculate the unilateral gelation rate. ; Calculate the difference in asymmetric gelation rate If the difference is significantly greater than 0, it directly proves from the perspective of polymer physics that there is a crosslinking density gradient that decreases from the negative electrode to the positive electrode inside the electrolyte.

[0121] Asymmetric interface impedance testing:

[0122] The assembled full cell was subjected to AC impedance spectroscopy testing, with the test frequency range set from 100 kHz to 0.01 Hz and the amplitude set at 5 mV. The charge transfer impedance at the negative electrode-electrolyte interface in the high-frequency region was extracted using equivalent circuit fitting. And the charge transfer impedance at the positive electrode and electrolyte interface in the mid-frequency region. .

[0123] The samples prepared in Examples 1-7 and Comparative Examples 1-7 were tested according to the above test methods, and the results are summarized in Table 1.

[0124] Table 1. Microstructure and electrochemical performance test results of each embodiment and comparative example.

[0125] Example 1 1.2 1.85 92.5 78.4 14.1 15.2 18.5 Example 2 1.1 1.52 85.1 71.2 13.9 12.4 16.1 Example 3 1.3 2.1 96.8 82.5 14.3 22.8 20.4 Example 4 1.2 1.68 90.2 81.1 9.1 18.5 19.2 Example 5 1.1 1.6 94.1 72.5 21.6 14.1 24.5 Example 6 1.2 1.55 95.2 68.4 26.8 13.8 28.6 Example 7 1.3 1.75 88.4 85.2 3.2 19.5 17.8 Comparative Example 1 1.1 0.65 65.2 42.1 23.1 35.4 55.2 Comparative Example 2 1.4 2.45 98.5 88.6 9.9 68.5 45.2 Comparative Example 3 1.2 0.85 82.1 80.5 1.6 28.4 26.5 Comparative Example 4 1.1 0.52 95.6 35.4 60.2 12.5 85.4 Comparative Example 5 1.2 0.95 96.5 25.8 70.7 11.8 125.6 Comparative Example 6 1.4 1.15 84.5 83.8 0.7 25.6 24.8 Comparative Example 7 358.5 0.45 85.6 85.2 0.4 32.5 31.8

[0126] This invention fundamentally eliminates the thermodynamic instability caused by the coexistence of monomers and initiators in the liquid phase by pre-placing the initiator in the negative electrode slurry and keeping the precursor solution in an initiator-free state. As shown in Table 1, comparing Example 1 with Comparative Example 7, the viscosity of the traditional internal mixing method surged by 358.5% within 24 hours, which could easily lead to blockage of the injection pipeline; while the viscosity change rate of Example 1 of this invention was only 1.2%, demonstrating excellent fluid stability and completely solving the problem of injection consistency in the large-scale continuous production of solid-state batteries.

[0127] By utilizing the directional distribution and controlled dissolution of the initiator at the negative electrode interface, this invention induces a controlled growth of the polymerization reaction from the interior of the negative electrode micropores towards the electrolyte bulk. Comparing the high peel strength of 1.85 N / mm in Example 1 with the relatively low peel strength of only 0.45 N / mm in Comparative Example 7, this controlled directional growth cleverly directs the volume shrinkage vector during polymerization towards the interior of the negative electrode, promoting deep physical entanglement between the generated polymer chains and the active material of the negative electrode. This results in a topologically pinned structure with extremely high peel strength, overcoming the drawback of polymer extraction from pores caused by isotropic shrinkage in existing homogeneous polymerization techniques.

[0128] Furthermore, this invention achieves perfect control over the dissolution kinetics of the initiator by precisely limiting the mass ratio of the initiator to the binder and the standing time, thereby constructing an asymmetric crosslinking density gradient. Data from Example 1 shows that the gelation rate on the negative electrode side reaches 92.5%, significantly higher than the 78.4% on the positive electrode side, with a difference of 14.1%. This ingenious microscopic asymmetric structure allows the interface region near the negative electrode to have a high crosslinking density to prevent dendrite penetration, while the appropriate amount of initiator diffused to the positive electrode side ensures complete solidification of the liquid phase while giving the positive electrode interface region a high free volume. This mechanism breaks the technical bias of the traditional solid electrolyte where mechanical strength and ionic conductivity are mutually restrictive.

[0129] Conversely, the synergistic effect is disrupted when the critical parameter range defined by this invention is deviated from. When the ratio of initiator to binder is lower than the lower limit of 1:1 as shown in Comparative Example 3, the initiator dissolves instantly due to the lack of sufficient network embedding buffer, resulting in a sharp drop in the gel rate difference to 1.6%, the disappearance of the gradient structure, and a significant decrease in peel strength. When the standing time is lower than the lower limit of 10 hours as shown in Comparative Example 5, the initiator fails to diffuse effectively to the positive electrode side, resulting in a gel rate of only 25.8% on the positive electrode side and a distorted increase in the positive electrode interface impedance to 125.6Ω.

[0130] The above data objectively demonstrate that the initiator ratio of 0.05% to 1.5%, the embedding ratio of 1:2 to 1:20, and the settling window of 12h to 36h, as defined in this invention, constitute the critical process boundary for achieving interface-constrained polymerization and topological pinning mechanisms. Once outside this multidimensional parameter range, the dissolution kinetics of the initiator and the polymerization thermodynamics of the monomer will lose their balance, leading to a precipitous deterioration in interfacial mechanical strength or ion transport performance. This confirms the profound nonlinear synergistic effect among the above characteristics.

[0131] In summary, this invention breaks through the inherent paradigm of homogeneous mixing of initiators and monomers in traditional in-situ polymerization technology. By physically embedding the initiator within the negative electrode polar binder network and employing a specific injection and settling process, the permeation kinetics of the precursor solution and the polymerization reactivity are completely decoupled spatially. This restricted release mechanism not only fundamentally eliminates the risk of premature gelation during injection but also induces the polymerization reaction to spread in a controlled manner from the micropores of the negative electrode to the electrolyte bulk, reversing the volume shrinkage vector into an interfacial anchoring force. This eliminates nanoscale interfacial gaps while spontaneously constructing an asymmetric crosslinking density gradient. This invention, with its extremely simplified process reconstruction, perfectly resolves the fundamental contradiction between interfacial mechanical stability and ion transport efficiency in solid-state batteries, providing a promising new in-situ curing solution for the large-scale industrialization of high-energy-density, high-safety solid-state lithium-ion batteries.

[0132] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for in-situ curing of a polymer electrolyte, characterized in that, Includes the following steps: S1. The initiator is mixed with the negative electrode active material and binder to form a negative electrode slurry, which is then coated onto the current collector and dried under conditions below the initial decomposition temperature of the initiator to obtain a negative electrode sheet. S2. Assemble the negative electrode, separator, and positive electrode into a battery cell, and inject a polymer electrolyte precursor solution into the battery cell; the precursor solution includes a polymer monomer, an inorganic lithium salt, and an organic solvent, and no initiator is added to the precursor solution before it is injected into the battery cell; the polymer monomer includes at least one multifunctional crosslinking agent. S3. After the electrolyte-filled cell is left to stand at 15-35℃ for 12-36 hours, the temperature is then raised to 40-80℃ to carry out an in-situ polymerization reaction, thereby obtaining the solid-state lithium-ion battery.

2. The in-situ curing method for a polymer electrolyte according to claim 1, characterized in that, The binder is a polymer containing at least one polar functional group selected from carboxyl, hydroxyl, or amide groups; the initiator is an azo compound or organic peroxide containing polar groups.

3. The in-situ curing method for a polymer electrolyte according to claim 1, characterized in that, The polymer monomer includes at least one of methyl methacrylate, butyl acrylate, vinylene carbonate, or propylene carbonate. The multifunctional crosslinking agent includes at least one of ethylene glycol dimethacrylate, polyethylene glycol diacrylate, or trimethylolpropane triacrylate.

4. The in-situ curing method for a polymer electrolyte according to claim 1, characterized in that, The initiator includes at least one of benzoyl peroxide, azobisisobutyronitrile, or azobisisoheptanenitrile; The initiator accounts for 0.05%-1.5% of the total solid mass in the negative electrode slurry.

5. The in-situ curing method for a polymer electrolyte according to claim 1, characterized in that, The inorganic lithium salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, or lithium difluorooxalateborate. The organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene sulfite, and fluoroethylene carbonate.

6. The in-situ curing method for a polymer electrolyte according to claim 1, characterized in that, In step S3, the heating time for the in-situ polymerization reaction is 3-8 hours.

7. The in-situ curing method for a polymer electrolyte according to claim 1, characterized in that, The mass ratio of the initiator to the binder in the negative electrode slurry is 1:2 to 1:20; the binder forms a network structure, and the initiator is embedded in the network structure.

8. The in-situ curing method for a polymer electrolyte according to claim 1, characterized in that, In step S3, the solid electrolyte permeates into the micropores of the negative electrode active material and polymerizes to form an interface anchoring structure with a depth of 0.5 μm-5 μm.

9. The in-situ curing method for a polymer electrolyte according to claim 1, characterized in that, The negative electrode active material includes at least one of graphite, silicon-based materials, or lithium titanate.

10. A solid-state lithium-ion battery, prepared by the method according to any one of claims 1-9, characterized in that, The battery includes a positive electrode, a negative electrode, and a solid electrolyte located between the positive and negative electrodes; The polymer molecular chain end groups of the solid electrolyte contain characteristic groups generated by the decomposition of an initiator pre-placed in the negative electrode; inside the solid electrolyte, the concentration of the characteristic groups at the contact interface between the solid electrolyte and the negative electrode is higher than that at the contact interface between the solid electrolyte and the positive electrode, and the solid electrolyte exhibits a heterogeneous distribution in the thickness direction, with the concentration gradually decreasing or stepwise decreasing from the negative electrode side to the positive electrode side. The solid electrolyte and the negative electrode have an interface anchoring structure, and the crosslinking density of the solid electrolyte at the contact interface between the solid electrolyte and the negative electrode is higher than its crosslinking density at the contact interface between the solid electrolyte and the positive electrode.

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