In-situ grain boundary modified solid-state electrolyte, preparation method and application thereof

Abstract

This invention belongs to the field of solid-state battery technology, specifically disclosing an in-situ grain boundary modified solid electrolyte, its preparation method, and its application. The solid electrolyte of this invention is composed of Li3InCl6 and functional additives. Functional additives are used to construct a functionalized interface layer at the electrolyte particles and grain boundaries, achieving in-situ F / P / S / N-rich soft grain boundary modification. By constructing a uniform, continuous, and low-residue functionalized interface layer, the solid electrolyte of this invention enables the composite solid electrolyte to have more stable interfacial contact, a lower tendency for interfacial side reactions, and higher short-circuit resistance on the lithium metal anode side. This solves the problems of electron leakage, interfacial side reactions, and defect-induced lithium penetration at the lithium metal anode / halide solid electrolyte interface, thereby improving the overall performance of all-solid-state batteries. This invention also provides a solid electrolyte layer prepared using this solid electrolyte and an all-solid-state lithium battery.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, and in particular to an in-situ grain boundary modified solid electrolyte, its preparation method, and its application. Background Technology

[0002] All-solid-state lithium metal batteries possess the potential to combine high energy density with high safety, making them an important development direction for next-generation energy storage systems. The most commonly used negative electrode in all-solid-state lithium batteries is the lithium metal anode. While it boasts extremely high theoretical capacity and low potential, direct contact with the solid electrolyte can easily lead to interfacial instability, inducing side reactions, localized current concentration, and lithium permeation, ultimately resulting in capacity decay or even short-circuit failure. Therefore, constructing a stable, uniform, and sustainably functioning anode / electrolyte interface is crucial for the practical application of all-solid-state lithium metal batteries.

[0003] Currently, halide solid electrolytes have attracted widespread attention due to their high ionic conductivity, good cathode compatibility, and relatively mild processing conditions. Among them, Li3InCl6 material has been used in composite cathode and solid-state battery research due to its good room-temperature ion transport capability and high-voltage cathode adaptability. However, Li3InCl6 also suffers from anode / electrolyte interface problems. To address the insufficient interface stability of the Li3InCl6 anode side, existing research has employed strategies such as surface coating, intermediate layer introduction, anode alloying, composite electrolytes, and in-situ interface modulation to reduce interface impedance and improve cycle stability. However, existing interface modification methods still suffer from uneven coverage, complex processes, weak interlayer bonding, and insufficient long-term stability, making it difficult to simultaneously achieve high ion transport, low electron leakage, chemical passivation, and mechanical compatibility. Especially in powder electrolytes, grain boundaries, pores, and defects easily become side reactions and lithium permeation channels.

[0004] Therefore, there is an urgent need for an interface stabilization method that can be constructed in situ at the grain boundaries of Li3InCl6, is uniformly distributed, and has self-limiting characteristics, in order to achieve synergistic suppression of electron leakage, interface side reactions, and defect-induced short circuits, thereby obtaining all-solid-state lithium batteries with better electrochemical performance and greater practicality. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention provides an in-situ F / P / S / N-rich soft grain boundary modified composite Li3InCl6 solid electrolyte. Addressing the problems of electron leakage, continuous interfacial side reactions, and lithium dendrite penetration induced by grain boundary defects in halide solid electrolytes at the lithium metal anode side, this invention constructs a uniform and continuous functionalized interfacial layer in-situ on the surface of Li3InCl6 particles and in the grain boundary region using functional additives, achieving synergistic regulation of the grain boundary chemical environment and local transport behavior. Specifically, the F / P / S / N-rich component can induce the formation of an electronically insulating and ion-conducting self-limiting passivation layer in the early stages of lithium contact, effectively reducing interfacial electron transport and side reaction activity; simultaneously, the flexible grain boundary network formed by in-situ polymerization can enhance interparticle interfacial bonding, buffer local stress concentration, and uniformly distribute Li... + Flux distribution is improved, thereby suppressing abnormal nucleation and penetrating growth of lithium at grain boundaries, pores, and microcracks. Based on the above synergistic mechanism, the composite solid electrolyte of the present invention can significantly improve the interface stability, short-circuit resistance, and cycle durability of lithium metal anode, thus obtaining an all-solid-state lithium battery that combines high safety and long cycle stability.

[0006] This invention also provides a method for preparing and applying a composite Li3InCl6 solid electrolyte.

[0007] The present invention also provides a composite Li3InCl6 solid electrolyte layer and an all-solid-state lithium battery.

[0008] In a first aspect, the present invention provides an in-situ grain boundary modified composite Li3InCl6 solid electrolyte, wherein the raw material components of the solid electrolyte include: Li3InCl6 powder and functional additives.

[0009] The functional additives include lithium (fluorosulfonyl) (difluorophosphono)imide (LiN(SO2F)(POF2, molecular formula LiF3NO3PS) and tetrakis(4-vinylpyridine)lithium hexafluorophosphate ([Li(C7H7N)4]PF6, molecular formula C 28 H 28 F6LiN4P).

[0010] According to a specific embodiment of the present invention, lithium (fluorosulfonyl) (difluorophosphono)imide and tetrakis(4-vinylpyridine)lithium hexafluorophosphate are used to achieve in-situ functionalization modification of Li3InCl6 grain boundaries through a synergistic mechanism of "chemical passivation-structural solidification". Specifically, the former can undergo an interfacial reaction in the early stages of lithium metal contact and form a LiF / Li-rich mixture. x PO y F zThe F / P / S / N-rich inorganic passivation layer of / Li2S / Li3N suppresses electron leakage and interfacial side reactions; the latter, through UV-induced in-situ polymerization, constructs a flexible continuous network at the grain boundaries, enhancing particle bonding and homogenizing Li. + Flux distribution. The two work together to construct a soft grain boundary interface that combines high ion transport, electronic insulation, and mechanical buffering capabilities, thereby effectively suppressing lithium dendrite penetration and improving interface stability.

[0011] This invention utilizes two in-situ grain boundary modification functional additives to construct a uniform, continuous, and low-residue functionalized interface layer at the particles and grain boundaries of traditional Li3InCl6 electrolytes. This transforms the initial interfacial reaction of lithium metal contact from a random, continuous, and deeply expanding side reaction into a localized, thin-layered, and confined interface reconstruction process, thereby reducing continuous interface consumption and impedance growth. The functionalized grain boundary layer of this composite Li3InCl6 solid electrolyte can construct a continuous electron blocking network between electrolyte particles, weakening the local electron flux at grain boundaries, pores, and microcracks, reducing the probability of abnormal nucleation of lithium metal at defect sites inside the electrolyte, and inhibiting lithium penetration along defect channels and inducing short circuits from the source.

[0012] According to some embodiments of the present invention, the mass of the functional additive is 0.002% to 4% of the mass of the Li3InCl6 powder; preferably, the mass of the functional additive is 0.02% to 2% of the mass of the Li3InCl6 powder.

[0013] According to some embodiments of the present invention, in the functional additive, the molar ratio of lithium (fluorosulfonyl) (difluorophosphono)imide and tetrakis(4-vinylpyridine)lithium hexafluorophosphate is (1~10):(1~10); preferably, the molar ratio is (1~3):(1~3).

[0014] A second aspect of the present invention provides a method for preparing a composite Li3InCl6 solid electrolyte as described in the first aspect of the present invention, characterized by comprising the following steps:

[0015] S1. Disperse and dissolve the functional additive in an organic solvent, and filter to obtain a functional additive wetting solution; under an inert atmosphere, add the functional additive wetting solution dropwise to anhydrous Li3InCl6 powder to obtain a wetted powder.

[0016] S2. The moist powder is sealed and left to stand under an inert atmosphere, then placed under an inert atmosphere at room temperature for pre-evaporation treatment, and then the pre-evaporated powder is subjected to ultraviolet light irradiation treatment to obtain in-situ polymerized and fixed electrolyte powder.

[0017] S3. The electrolyte powder that has been fixed by in-situ polymerization is subjected to vacuum annealing at 60~80 ℃ and then cooled to obtain the in-situ grain boundary modified composite Li3InCl6 solid electrolyte.

[0018] According to some embodiments of the present invention, the anhydrous Li3InCl6 powder is obtained by dehydrating Li3InCl6 powder prepared by wet method under an inert atmosphere at 60~120 °C for 6~24 h.

[0019] According to some embodiments of the present invention, in step S1, the concentration of the functional additive impregnation solution is 0.005~0.2 mol / L, and the amount added is 20~300 μL / g based on the mass of Li3InCl6 powder.

[0020] According to some preferred embodiments of the present invention, the concentration of the functional additive impregnation solution is 0.05~0.1mol / L, and the amount added is 30~200 μL / g based on the mass of Li3InCl6 powder.

[0021] This invention has revealed that only suitable dosages and concentrations of the functional additives mentioned above can achieve good in-situ modification. Excessive amounts of functional additives may lead to an excessively thick and uneven modification interface, thereby increasing the Li... + Cross-interface migration impedance exacerbates interfacial polarization and may lead to local agglomeration of polymer components, disrupting the continuity of grain boundary ion transport and reducing effective interparticle contact, thereby affecting its electrochemical performance.

[0022] According to some embodiments of the present invention, the organic solvent includes a mixed solvent containing acetonitrile and tetrahydrofuran, wherein the volume ratio of acetonitrile to tetrahydrofuran in the mixed solvent is (1~9):(1~9).

[0023] According to some embodiments of the present invention, the method of adding dropwise is as follows: after each addition of the functional additive wetting liquid, the powder is mixed for 1 to 5 minutes before the next addition is made, until all the wetting liquid is added to form a wet powder without free liquid.

[0024] According to some embodiments of the present invention, in step S2, the settling time is 0.5 to 6 hours; the pre-evaporation treatment time is 0.5 to 4 hours.

[0025] According to some embodiments of the present invention, in step S2, the power density of the ultraviolet irradiation treatment is 5~50 mW / cm². 2 The irradiation time is 5 to 120 minutes. During the irradiation process, the powder is turned or vibrated every 5 to 20 minutes to ensure that the powder is evenly exposed to light.

[0026] This invention reveals that in-situ polymerization under ultraviolet (UV) irradiation requires appropriate UV irradiation intensity. Excessively high UV power density may lead to overly rapid polymerization and localized over-crosslinking of tetra(4-vinylpyridine) groups, resulting in uneven polymer enrichment regions and reduced grain boundary ion transport continuity. It may also cause local decomposition of functional components and damage to the grain boundary structure, leading to interfacial stress concentration and intensified local polarization, making it difficult to form a stable and uniform soft grain boundary interface layer, thereby affecting the performance of the subsequently prepared battery.

[0027] According to some embodiments of the present invention, in step S3, the annealing time is 6~24 h, and the vacuum degree is ≤100 Pa; the cooling is natural cooling to room temperature in a vacuum or inert atmosphere.

[0028] A third aspect of the present invention provides a composite solid electrolyte layer, which is obtained by pressing the composite Li3InCl6 solid electrolyte described in the first aspect of the present invention into a film.

[0029] According to some embodiments of the present invention, the pressing pressure is 100~400 MPa.

[0030] According to some embodiments of the present invention, the method of pressing the film is as follows: the composite Li3InCl6 solid electrolyte is added into an insulating mold and cold-pressed for 1 to 5 minutes under a pressure of 100 to 400 MPa to obtain a solid electrolyte layer with a thickness of 300 to 1000 μm.

[0031] A fourth aspect of the present invention provides the application of the composite Li3InCl6 solid electrolyte as described in the first aspect of the present invention in the preparation of all-solid-state lithium batteries.

[0032] A fifth aspect of the present invention provides an all-solid-state lithium battery, comprising a positive electrode, a negative electrode, and a composite solid-state electrolyte layer as described in the third aspect of the present invention; the composite solid-state electrolyte layer is located between the positive electrode and the negative electrode.

[0033] The positive electrode sheet includes a positive current collector and a positive active layer disposed on the positive current collector. The positive active layer includes a positive active material, a conductive agent, and the composite Li3InCl6 solid electrolyte described in the first aspect of the present invention.

[0034] According to some embodiments of the present invention, in the positive electrode active layer, the mass ratio of the positive electrode active material, the conductive agent and the composite Li3InCl6 solid electrolyte is (60~80):(1~5):(15~35); the positive electrode active material includes NCM712.

[0035] The beneficial effects of this invention are:

[0036] 1) In the composite Li3InCl6 solid electrolyte provided by the present invention, uncontrollable interfacial side reactions are transformed into a self-limiting passivation process: by introducing F / P / S / N-rich film-forming precursors in advance into the grain boundaries and particle contact areas of Li3InCl6, the interfacial reaction in the initial stage of lithium metal contact is transformed from random, continuous, and deeply extended side reactions into a local, thin-layer, and limited interfacial reconstruction process, thereby reducing continuous interfacial consumption and impedance growth.

[0037] 2) This invention forms a functionalized grain boundary layer through functional additives, which synergistically inhibits electron leakage and defect-induced lithium penetration: The functionalized grain boundary layer formed in situ can construct a continuous electron blocking network between electrolyte particles, weaken the local electron flux at grain boundaries, pores and microcracks, reduce the probability of abnormal nucleation of metallic lithium at defect sites inside the electrolyte, and inhibit lithium penetration along defect channels and induce short circuits from the source.

[0038] 3) The all-solid-state lithium battery prepared using the composite Li3InCl6 solid electrolyte of the present invention has good capacity performance and coulombic efficiency, excellent long-cycle stability and interface durability; and the preparation process of the composite solid electrolyte is simple, suitable for industrial production, and has good application prospects.

[0039] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Detailed Implementation

[0040] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0041] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0042] Example 1

[0043] This embodiment provides an in-situ grain boundary modification method for Li3InCl6 solid electrolyte, and prepares a composite Li3InCl6 solid electrolyte suitable for all-solid-state lithium metal batteries.

[0044] The specific steps of the method in this embodiment are as follows:

[0045] 1) Pretreatment of anhydrous Li3InCl6 powder:

[0046] The Li3InCl6 powder prepared by wet method was placed in an argon atmosphere glove box, where the H2O and O2 contents were both below 0.1 ppm. Low-temperature dehydration was carried out under dynamic vacuum conditions at a temperature of 90 ℃ for 15 h. After the treatment, it was cooled to room temperature, and the entire process was kept in anhydrous and oxygen-free conditions to obtain fully dehydrated anhydrous Li3InCl6 powder.

[0047] 2) Preparation of functional additive impregnation solution:

[0048] In an argon-atmospheric glove box, weigh lithium (fluorosulfonyl) (difluorophosphono)imide (LiN(SO2F)(POF2, molecular formula LiF3NO3PS) and tetrakis(4-vinylpyridine)lithium hexafluorophosphate ([Li(C7H7N)4]PF6, molecular formula C 28 H 28 F6LiN4P) was added to anhydrous acetonitrile / anhydrous tetrahydrofuran mixed solvent and stirred until completely dispersed or dissolved to obtain a low-concentration anhydrous functional additive wetting solution; after preparation, the wetting solution was filtered through a 0.22 μm anhydrous organic solvent resistant filter membrane and sealed for later use;

[0049] The molar ratio of lithium (fluorosulfonyl) (difluorophosphono)imide to tetra(4-vinylpyridine)lithium hexafluorophosphate is 1:1; the volume ratio of anhydrous acetonitrile to anhydrous tetrahydrofuran is controlled at 1:1; and the total concentration of functional additives is controlled at 0.05 mol / L.

[0050] 3) Capillary threshold wetting treatment:

[0051] The anhydrous Li3InCl6 powder obtained in step 1) was placed in a mixing container under an argon atmosphere. Under continuous slight stirring, the functional additive wetting solution obtained in step 2) was added to the powder dropwise. The wetting solution entered the particle contact area and grain boundary area by means of capillary action between powder particles.

[0052] The amount of wetting liquid added is 100 μL / g based on the powder mass. The addition method is as follows: after each addition, mix for 2 minutes before adding the next addition, until all the wetting liquid is added to form a uniformly wetted powder without free liquid.

[0053] 4) Homogenization and settling with solvent pre-evaporation:

[0054] The wet powder obtained in step 3) was placed in an argon atmosphere and sealed for 3 h to allow the functional additives to be further evenly distributed between the Li3InCl6 powder particles. After standing, a semi-open container was used to perform room temperature pre-evaporation treatment in an argon atmosphere for 2 h to reduce the free solvent content in the powder. During the pre-evaporation process, the powder was kept in a loose state and contact with external water and oxygen was avoided.

[0055] 5) UV in-situ polymerization fixation:

[0056] The pre-volatile powder obtained in step 4) is evenly spread in a tray, and the powder layer thickness is controlled to be 2 mm. In a sealed container or glove box under argon atmosphere, the powder is irradiated with ultraviolet light with a wavelength of 365 nm, and the tetra(4-vinylpyridine) groups are in-situ polymerized and fixed in the grain boundary and particle contact area of ​​Li3InCl6.

[0057] The ultraviolet light irradiation power density is 20 mW / cm². 2 The irradiation time is 60 minutes; during the irradiation process, the powder is slightly turned or vibrated every 10 minutes to ensure that the powder is evenly exposed to light.

[0058] 6) Low-temperature dynamic vacuum annealing:

[0059] The powder treated with ultraviolet light in step 5) was transferred to a vacuum drying container and annealed at low temperature under dynamic vacuum conditions of 70 °C for 12 h with a vacuum degree not exceeding 100 Pa. After annealing, it was naturally cooled to room temperature to obtain F / P / S / N-rich soft grain boundary modified Li3InCl6 composite solid electrolyte powder.

[0060] Finally, the prepared composite Li3InCl6 solid electrolyte powder was sealed and stored in an argon atmosphere glove box for subsequent pressing, battery assembly and performance testing.

[0061] Example 2

[0062] This embodiment provides an in-situ grain boundary modification method for Li3InCl6 solid electrolyte, and prepares a composite Li3InCl6 solid electrolyte suitable for all-solid-state lithium metal batteries.

[0063] The specific steps of the method in this embodiment are as follows:

[0064] 1) Pretreatment of anhydrous Li3InCl6 powder: The method is the same as in Example 1;

[0065] 2) Preparation of functional additive impregnation solution:

[0066] In a nitrogen-atmospheric glove box, weigh lithium (fluorosulfonyl) (difluorophosphono)imide (LiN(SO2F)(POF2, molecular formula LiF3NO3PS) and tetrakis(4-vinylpyridine)lithium hexafluorophosphate ([Li(C7H7N)4]PF6, molecular formula C 28 H 28F6LiN4P) was added to anhydrous acetonitrile / anhydrous tetrahydrofuran mixed solvent and stirred until completely dispersed or dissolved to obtain a low-concentration anhydrous functional additive wetting solution; after preparation, the wetting solution was filtered through a 0.22 μm anhydrous organic solvent resistant filter membrane and sealed for later use;

[0067] The molar ratio of lithium (fluorosulfonyl) (difluorophosphono)imide to tetra(4-vinylpyridine)lithium hexafluorophosphate is 3:1; the volume ratio of anhydrous acetonitrile to anhydrous tetrahydrofuran is controlled at 2:1; and the total concentration of functional additives is controlled at 0.01 mol / L.

[0068] 3) Capillary threshold wetting treatment:

[0069] The anhydrous Li3InCl6 powder obtained in step 1) was placed in a mixing container under a nitrogen atmosphere. Under continuous slight stirring, the functional additive wetting liquid obtained in step 2) was added to the powder dropwise. The wetting liquid entered the particle contact area and grain boundary area by capillary action between the powder particles.

[0070] The amount of wetting liquid added is 30 μL / g based on the powder mass. The addition method is as follows: after each addition, mix for 4 minutes before adding the next addition, until all the wetting liquid is added to form a uniformly wetted powder without free liquid.

[0071] 4) Homogenization and settling with solvent pre-evaporation:

[0072] The wet powder obtained in step 3) was placed in a nitrogen atmosphere and sealed for 2 h to allow the functional additives to be further evenly distributed between the Li3InCl6 powder particles. After standing, a semi-open container was used to perform room temperature pre-evaporation treatment in a nitrogen atmosphere for 1 h to reduce the free solvent content in the powder. During the pre-evaporation process, the powder was kept in a loose state and contact with external water and oxygen was avoided.

[0073] 5) UV in-situ polymerization fixation:

[0074] The pre-volatile powder obtained in step 4) is evenly spread in a tray, and the powder layer thickness is controlled to be 2 mm. In a nitrogen atmosphere sealed container or glove box, the powder is irradiated with ultraviolet light with a wavelength of 365 nm, and the tetra(4-vinylpyridine) groups are in-situ polymerized and fixed in the grain boundary and particle contact area of ​​Li3InCl6.

[0075] The ultraviolet light irradiation power density is 8 mW / cm². 2 The irradiation time is 100 min; during the irradiation process, the powder is slightly turned or vibrated every 15 min to ensure that the powder is evenly exposed to light.

[0076] 6) Low-temperature dynamic vacuum annealing:

[0077] The powder treated with ultraviolet light in step 5) was transferred to a vacuum drying container and annealed at low temperature under dynamic vacuum conditions of 65 °C for 8 h with a vacuum degree not exceeding 100 Pa. After annealing, it was naturally cooled to room temperature to obtain F / P / S / N-rich soft grain boundary modified Li3InCl6 composite solid electrolyte powder.

[0078] Finally, the prepared composite Li3InCl6 solid electrolyte powder was sealed and stored in a nitrogen atmosphere glove box for subsequent pressing, battery assembly and performance testing.

[0079] Example 3

[0080] This embodiment provides an in-situ grain boundary modification method for Li3InCl6 solid electrolyte, and prepares a composite Li3InCl6 solid electrolyte suitable for all-solid-state lithium metal batteries.

[0081] The specific steps of the method in this embodiment are as follows:

[0082] 1) Pretreatment of anhydrous Li3InCl6 powder: The method is the same as in Example 1;

[0083] 2) Preparation of functional additive impregnation solution:

[0084] In an inert atmosphere glove box, weigh lithium (fluorosulfonyl) (difluorophosphono)imide (LiN(SO2F)(POF2, molecular formula LiF3NO3PS) and tetrakis(4-vinylpyridine)lithium hexafluorophosphate ([Li(C7H7N)4]PF6, molecular formula C 28 H 28 F6LiN4P) was added to anhydrous acetonitrile / anhydrous tetrahydrofuran mixed solvent and stirred until completely dispersed or dissolved to obtain a low-concentration anhydrous functional additive wetting solution; after preparation, the wetting solution was filtered through a 0.22 μm anhydrous organic solvent resistant filter membrane and sealed for later use;

[0085] The molar ratio of lithium (fluorosulfonyl) (difluorophosphono)imide to tetra(4-vinylpyridine)lithium hexafluorophosphate is 1:3; the volume ratio of anhydrous acetonitrile to anhydrous tetrahydrofuran is controlled at 1:3; and the total concentration of functional additives is controlled at 0.1 mol / L.

[0086] 3) Capillary threshold wetting treatment:

[0087] The anhydrous Li3InCl6 powder obtained in step 1) was placed in a mixing container under an argon atmosphere. Under continuous slight stirring, the functional additive wetting solution obtained in step 2) was added to the powder dropwise. The wetting solution entered the particle contact area and grain boundary area by means of capillary action between powder particles.

[0088] The amount of wetting liquid added is 200 μL / g based on the powder mass. The addition method is as follows: after each addition, mix for 4 minutes before adding the next addition, until all the wetting liquid is added to form a uniformly wetted powder without free liquid.

[0089] 4) Homogenization and settling with solvent pre-evaporation:

[0090] The wet powder obtained in step 3) was placed in an argon atmosphere and sealed for 5 h to allow the functional additives to be further evenly distributed among the Li3InCl6 powder particles. After standing, a semi-open container was used to perform room temperature pre-evaporation treatment in an argon atmosphere for 4 h to reduce the free solvent content in the powder. During the pre-evaporation process, the powder was kept in a loose state and contact with external water and oxygen was avoided.

[0091] 5) UV in-situ polymerization fixation:

[0092] The pre-volatile powder obtained in step 4) is evenly spread in a tray, and the powder layer thickness is controlled to be 2 mm. In a sealed container or glove box under argon atmosphere, the powder is irradiated with ultraviolet light with a wavelength of 365 nm, and the tetra(4-vinylpyridine) groups are in-situ polymerized and fixed in the grain boundary and particle contact area of ​​Li3InCl6.

[0093] The ultraviolet light irradiation power density is 40 mW / cm². 2 The irradiation time is 30 minutes; during the irradiation process, the powder is slightly turned or vibrated every 8 minutes to ensure that the powder is evenly exposed to light.

[0094] 6) Low-temperature dynamic vacuum annealing:

[0095] The powder treated with ultraviolet light in step 5) was transferred to a vacuum drying container and annealed at low temperature under dynamic vacuum conditions of 75 °C for 20 h with a vacuum degree not exceeding 100 Pa. After annealing, it was naturally cooled to room temperature to obtain F / P / S / N-rich soft grain boundary modified Li3InCl6 composite solid electrolyte powder.

[0096] Finally, the prepared composite Li3InCl6 solid electrolyte powder was sealed and stored in an argon atmosphere glove box for subsequent pressing, battery assembly and performance testing.

[0097] Comparative Example 1

[0098] This comparative example provides an in-situ grain boundary modification method for Li3InCl6 solid electrolyte. This comparative example is basically the same as Example 1, except that in step 2) of this comparative example, the total concentration of functional additives in the functional additive impregnation solution is 0.3 mol / L. Other steps and processes are consistent with Example 1; finally, composite Li3InCl6 solid electrolyte powder is prepared.

[0099] Comparative Example 2

[0100] This comparative example provides an in-situ grain boundary modification method for Li3InCl6 solid electrolyte. This comparative example is basically the same as Example 1, except that in step 2) of this comparative example, only lithium (fluorosulfonyl) (difluorophosphono)imide is used as the functional additive, the total amount of functional additive is the same as in Example 1, and the other steps and processes are the same as in Example 1; finally, composite Li3InCl6 solid electrolyte powder is prepared.

[0101] Comparative Example 3

[0102] This comparative example provides an in-situ grain boundary modification method for Li3InCl6 solid electrolyte. This comparative example is basically the same as Example 1, except that in step 2) of this comparative example, only tetrakis(4-vinylpyridine)lithium hexafluorophosphate is used as the functional additive. The total amount of functional additive is the same as in Example 1, and the other steps and processes are the same as in Example 1. Finally, composite Li3InCl6 solid electrolyte powder is prepared.

[0103] Comparative Example 4

[0104] This comparative example provides an in-situ grain boundary modification method for Li3InCl6 solid electrolyte. This comparative example is basically the same as Example 1, except that in step 3) of this comparative example, the amount of wetting liquid added is 10 μL / g based on the powder mass. Other steps and processes are consistent with Example 1; finally, composite Li3InCl6 solid electrolyte powder is prepared.

[0105] Comparative Example 5

[0106] This comparative example provides an in-situ grain boundary modification method for Li3InCl6 solid electrolyte. This comparative example is essentially the same as Example 1, except that in step 5) of this comparative example, the ultraviolet light irradiation power density is 70 mW / cm². 2 The other steps and processes are the same as in Example 1; finally, composite Li3InCl6 solid electrolyte powder is prepared.

[0107] Comparative Example 6

[0108] This comparative example provides an in-situ grain boundary modification method for Li3InCl6 solid electrolyte. This comparative example is essentially the same as Example 1, except that in step 6), the low-temperature dynamic vacuum annealing conditions are: low-temperature annealing is performed under dynamic vacuum conditions at 90 °C for 12 h, with a vacuum degree not exceeding 100 Pa; other steps and processes are consistent with Example 1; finally, composite Li3InCl6 solid electrolyte powder is prepared.

[0109] The key process parameters for the above embodiments and comparative examples are shown in Table 1 below:

[0110] Preparation example:

[0111] 1) Fabrication of positive and negative electrodes and electrolyte layer in all-solid-state lithium metal batteries:

[0112] The pretreatment of all-solid-state batteries for assembly was carried out in an argon atmosphere glove box with H2O and O2 contents both below 0.1 ppm.

[0113] The NCM712 cathode material was vacuum dried at 110 °C for 8 h. The NCM712, the F / P / S / N-rich soft grain boundary modified Li3InCl6 composite solid electrolyte powder prepared in each example and comparative example, and the conductive agent were mixed at a mass ratio of 70:25:3. The conductive agent was conductive carbon black (acetylene black or vapor-grown carbon fiber could be selected). The mixture was ball-milled for 40 min to obtain a uniform cathode composite powder.

[0114] Another F / P / S / N-rich soft grain boundary modified Li3InCl6 composite solid electrolyte powder was added into an insulating mold and cold-pressed at 250 MPa for 3 min to obtain a solid electrolyte isolation layer with a thickness of 600 μm.

[0115] The positive electrode composite powder was uniformly spread on one side of the electrolyte layer, and the NCM712 areal loading was controlled at 5 mg / cm³. 2 Then, it is pressed again at 250 MPa for 3 minutes to make the positive electrode composite layer and the electrolyte isolation layer form a tight contact.

[0116] The lithium metal anode is cut into lithium sheets with a thickness of 250 μm inside the glove box to match the size of the electrolyte layer. The surface oxide layer is scraped off before assembly to expose the fresh lithium metal surface.

[0117] 2) Assembly of all-solid-state lithium metal batteries:

[0118] The prepared positive electrode composite layer / composite Li3InCl6 solid electrolyte layer structure is placed in a mold battery (Swagelok type battery or coin cell pressure battery can also be selected), with one side of the positive electrode composite layer connected to the positive electrode current collector, which is made of aluminum foil (or stainless steel sheet or carbon-coated aluminum foil can also be selected); then a fresh lithium metal sheet is attached to the other side of the solid electrolyte layer and lightly pressed at 60 MPa for 2 min to make the lithium metal anode and the solid electrolyte layer form a sufficient solid-solid contact, with the current collector on the anode side made of copper foil (or stainless steel sheet or nickel sheet can also be selected); finally, the NCM712 positive electrode composite layer / composite Li3InCl6 solid electrolyte layer / lithium metal anode structure is formed, and the battery is encapsulated by applying a constant stacking pressure of 30 MPa.

[0119] Battery performance test:

[0120] The assembled all-solid-state batteries were connected to a multi-channel battery charge-discharge test system and placed in a constant-temperature test chamber for testing; the batteries were maintained at a constant stacking pressure of 25 MPa. Before testing, the batteries were left to stand at 40 °C for 8 hours, the open-circuit voltage was recorded, and it was confirmed that there were no short circuits or abnormal voltage fluctuations.

[0121] Constant current charge-discharge tests were then conducted, with the voltage window set at 2.5–4.3 V. Rate was calculated based on the mass of the NCM712 active material, with 1 C corresponding to 190 mA / g. The battery was first activated and cycled for 3 cycles at 0.075 C, followed by a long-term cycle test of 1000 cycles at 0.6 C. During charging, the battery was charged at a constant current to the upper voltage limit, and if necessary, maintained at a constant voltage until the cutoff current reached 0.03 C. During discharging, the battery was discharged at a constant current to the lower voltage limit. During the tests, the specific capacity, coulombic efficiency, energy efficiency, voltage polarization, and capacity retention were recorded for each charge-discharge cycle to evaluate the battery's cycle stability and interface durability.

[0122] The test results are shown in Table 2 below:

[0123] The test results above show that the all-solid-state battery prepared by the technical solution of this invention has better overall performance. Its initial discharge specific capacity, initial coulombic efficiency, and cycle capacity retention are significantly better than the comparative example, exhibiting excellent cycle stability and interface durability. This is mainly attributed to the fact that the F / P / S / N-rich soft grain boundary functionalized interface constructed in this invention can simultaneously achieve synergistic regulation of interface chemical stabilization and grain boundary transport homogenization. On one hand, this invention, by pre-introducing F / P / S / N-rich components into Li3InCl6 particles and grain boundaries, transforms the initial interface reaction of lithium metal contact from a continuously expanding uncontrollable side reaction into a localized, self-limiting interface passivation process, forming in-situ LiF- and Li-rich components. x PO y F z The presence of stable interface layers such as Li₂S and Li₃N, which are electronically insulating and ionically conductive, effectively reduces the continuous consumption of active lithium and electrolyte caused by interfacial side reactions, slows down the growth of interfacial impedance, and improves the initial coulombic efficiency and capacity retention. On the other hand, the flexible grain boundary network formed by in-situ polymerization can construct continuous electron blocking and stress buffer structures between electrolyte particles, reducing local electron leakage and current concentration at grain boundaries, pores, and microcracks, inhibiting abnormal lithium nucleation at defect sites and penetration growth along grain boundaries, thereby effectively improving the battery's short-circuit withstand capability and long-cycle stability. Simultaneously, this soft grain boundary structure contributes to the uniformity of Li₂S and Li₃N. +Flux distribution and maintaining stable solid-solid contact reduce interfacial polarization and mechanical mismatch during cycling, ultimately achieving high initial discharge specific capacity, excellent coulombic efficiency, and long-term cycling stability.

[0124] In Comparative Example 1, the excessively high concentration of functional additives (0.3 mol / L) led to an over-enrichment of functional components in the Li3InCl6 grain boundary region, resulting in an excessively thick and uneven interface layer. On one hand, the excessive LiF / Li... x PO y F z The phase will significantly increase Li + Cross-interfacial migration impedance exacerbates interfacial polarization; on the other hand, local aggregation of polymeric components disrupts the continuity of ion transport at grain boundaries, reducing effective interparticle contact. These factors together lead to a continuous increase in interfacial impedance and a deterioration in local current distribution, ultimately resulting in a significant decrease in initial coulombic efficiency and cycling stability.

[0125] In Comparative Examples 2 and 3, only lithium (fluorosulfonyl) (difluorophosphono)imide and tetrakis(4-vinylpyridine)lithium hexafluorophosphate were used as functional additives, respectively. The lack of synergistic effect between the two resulted in the inability to simultaneously achieve interfacial chemical passivation and grain boundary structure stabilization. While a single lithium salt additive could form a certain inorganic passivation layer, it lacked a continuous flexible grain boundary network, making it difficult to effectively buffer interfacial stress and uniform Li... + Flux efficiency is affected; while single polymeric additives can improve particle contact, their electron blocking and interfacial chemical stabilization capabilities are insufficient, making them prone to persistent side reactions and localized electron leakage. Therefore, neither can effectively suppress lithium dendrite growth along defect channels, ultimately leading to a significant decrease in initial coulombic efficiency and cycle stability.

[0126] In Comparative Example 4, the amount of functional additive wetting solution was too small (10 μL / g), which resulted in the wetting solution not being able to completely wet the Li3InCl6 powder. This caused insufficient modification of the Li3InCl6 grain boundaries, resulting in the failure to form a continuous functionalized interface layer in some grain boundaries and particle contact areas. It was difficult to effectively construct an electron blocking network and a stable ion transport channel. Electron leakage, interface side reactions, and abnormal lithium deposition were still likely to occur at local defects, which in turn induced lithium dendrites to penetrate and grow along the grain boundaries, ultimately leading to a decrease in battery cycle stability and interface durability.

[0127] In Comparative Example 5, during the UV in-situ polymerization fixation treatment, the UV irradiation power density was too high (70 mW / cm²). 2This leads to the rapid polymerization and localized over-crosslinking of tetra(4-vinylpyridine) groups, forming uneven polymer enrichment regions and reducing the continuity of grain boundary ion transport. At the same time, excessive ultraviolet irradiation may also cause local decomposition of functional components and damage to the Li3InCl6 grain boundary structure, resulting in interface stress concentration and intensified local polarization, making it difficult to form a stable and uniform soft grain boundary interface layer, ultimately reducing the battery cycle stability and interface durability.

[0128] In Comparative Example 6, the excessively high vacuum annealing temperature (90 °C) caused structural instability and component migration in the functionalized interface layer during annealing, which easily led to the shrinkage of the polymer network, embrittlement of the grain boundary interface, and decomposition of some active components. At the same time, the high temperature may also induce the deterioration of the Li3InCl6 grain boundary structure and the expansion of local defects, destroying the original uniform and continuous soft grain boundary interface layer, weakening the electron blocking and stress buffering capacity, thereby aggravating the interface side reactions and the penetration and growth of lithium dendrites along the defect channels, ultimately leading to a significant decrease in battery cycle performance.

[0129] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A solid electrolyte with in-situ grain boundary modification, characterized in that, The raw material components of the solid electrolyte include: Li3InCl6 powder and functional additives; The functional additives include lithium (fluorosulfonyl) (difluorophosphono)imide and tetra(4-vinylpyridine)lithium hexafluorophosphate.

2. The solid electrolyte according to claim 1, characterized in that, The mass of the functional additive is 0.002% to 4% of the mass of the Li3InCl6 powder.

3. The solid electrolyte according to claim 1, characterized in that, In the functional additive, the molar ratio of lithium (fluorosulfonyl) (difluorophosphono)imide and tetrakis(4-vinylpyridine)lithium hexafluorophosphate is (1~10):(1~10).

4. The method for preparing a solid electrolyte according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Disperse and dissolve the functional additive in an organic solvent, and filter to obtain a functional additive wetting solution; under an inert atmosphere, add the functional additive wetting solution dropwise to anhydrous Li3InCl6 powder to obtain a wetted powder. S2. The moist powder is sealed and left to stand under an inert atmosphere, and then placed under an inert atmosphere at room temperature for pre-evaporation treatment. The pre-evaporated powder is then subjected to ultraviolet light irradiation treatment to obtain electrolyte powder that is fixed by in-situ polymerization. S3. The electrolyte powder that has been fixed by in-situ polymerization is subjected to vacuum annealing at 60~80 ℃ and then cooled to obtain the in-situ grain boundary modified composite Li3InCl6 solid electrolyte.

5. The preparation method according to claim 4, characterized in that, In step S1, the concentration of the functional additive wetting solution is 0.005~0.2 mol / L, and the amount added is 20~300 μL / g based on the mass of Li3InCl6 powder. The dropwise addition method is as follows: after each drop of the functional additive wetting solution, mix the powder for 1~5 min, and then add the next dropwise addition until all the wetting solution is added to form a wet powder without free liquid.

6. The preparation method according to claim 4, characterized in that, In step S2, the settling time is 0.5~6 hours; the pre-evaporation treatment time is 0.5~4 hours; and the power density of the ultraviolet irradiation treatment is 5~50 mW / cm³. 2 The irradiation time is 5 to 120 minutes. During the irradiation process, the powder is turned or vibrated every 5 to 20 minutes to ensure that the powder is evenly exposed to light.

7. The preparation method according to claim 4, characterized in that, In step S3, the annealing time is 6~24 h, and the vacuum degree is ≤100 Pa; the cooling is natural cooling to room temperature in a vacuum or inert atmosphere.

8. A composite solid electrolyte layer, characterized in that, It is prepared by pressing the solid electrolyte according to any one of claims 1 to 3 into a membrane.

9. The application of the solid electrolyte as described in any one of claims 1 to 3 in the preparation of all-solid-state lithium batteries.

10. A fully solid-state lithium battery, characterized in that, It includes a positive electrode, a negative electrode, and the composite solid electrolyte layer as described in claim 8; the composite solid electrolyte layer is located between the positive electrode and the negative electrode. The positive electrode sheet includes a positive current collector and a positive active layer disposed on the positive current collector, wherein the positive active layer includes a positive active material, a conductive agent, and a solid electrolyte as described in any one of claims 1 to 3.

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