Composite electrolyte, method of preparation and lithium ion battery

Abstract

The application provides a composite electrolyte, a preparation method and a lithium ion battery, and belongs to the technical field of lithium batteries.The composite electrolyte comprises a polymer matrix, the polymer matrix is formed by in-situ polymerization of a composition comprising a cyclic ether compound; and surface-modified inorganic nanoparticles uniformly dispersed in the polymer matrix, the surface-modified inorganic nanoparticles are obtained by modifying the surface of the inorganic nanoparticles with a silane coupling agent, and the surface-modified inorganic nanoparticles are grafted with organic functional groups and lithium salt on the surface.The composite electrolyte has excellent ionic conductivity, good mechanical strength and thermal stability, can effectively reduce the agglomeration of the inorganic nanoparticles, and improves the safety and cycle performance of the battery.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a composite electrolyte, its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are widely used in consumer electronics, electric vehicles, and energy storage systems due to their advantages such as high energy density, high operating voltage, long cycle life, and low self-discharge rate. The electrolyte, as the core functional material in the battery that connects the positive and negative electrodes and promotes lithium-ion migration, directly affects the battery's safety, rate performance, and cycle life.

[0003] While current mainstream organic liquid electrolytes have high ionic conductivity, they also have inherent defects such as flammability, volatility, and poor thermal stability. They are prone to thermal runaway under high temperature or overcharge conditions, making it difficult to meet the stringent safety requirements of high energy density batteries.

[0004] To overcome the aforementioned problems, polymer electrolytes and polymer-inorganic composite electrolytes have gradually become a research focus. By introducing inorganic ceramic particles into a polymer matrix, the mechanical strength, thermal stability, and ion conduction behavior of the material can be improved. However, existing polymer / inorganic composite electrolytes still fall short of practical application requirements in terms of ionic conductivity, mechanical strength, and safety. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this application provides a composite electrolyte, a preparation method, and a lithium-ion battery, which can solve the problem that existing composite electrolytes are difficult to meet practical requirements in terms of ionic conductivity, mechanical strength, and safety.

[0006] To address the aforementioned problems, the first aspect of this application provides a composite electrolyte, comprising:

[0007] The polymer matrix is ​​formed by in-situ polymerization of a composition containing cyclic ether compounds;

[0008] Surface-modified inorganic nanoparticles are uniformly dispersed in a polymer matrix. These nanoparticles are obtained by modifying their surface with a silane coupling agent. Furthermore, organic functional groups and lithium salts are grafted onto the surface of the surface-modified inorganic nanoparticles.

[0009] In one embodiment of the first aspect of this application, the composition comprising a cyclic ether compound further comprises a plasticizer, wherein the plasticizer comprises at least one selected from 1,2-dimethoxyethane, succinate, and ethylene carbonate.

[0010] In one embodiment of the first aspect of this application, the volume ratio of the cyclic ether compound to the plasticizer in the composition comprising the cyclic ether compound is 3:7 to 7:3.

[0011] In one embodiment of the first aspect of this application, the cyclic ether compound is selected from at least one of 1,3-dioxolane, tetrahydrofuran, substituted dioxolane, oxetane and 1,3,5-trioxacyclohexane; or, the cyclic ether compound is 1,3-dioxolane or a derivative thereof substituted with alkyl, alkoxy or haloalkyl groups.

[0012] In one embodiment of the first aspect of this application, the silane coupling agent is a silane containing one or more hydrolyzable groups and an organic functional group; wherein the organic functional group is one of amino, epoxy, or (meth)acryloyloxy; and / or, the silane coupling agent is at least one of γ-aminopropyltriethoxysilane, 3-epoxypropyltrimethoxysilane, and 3-(methacryloyloxy)propyltrimethoxysilane.

[0013] In one embodiment of the first aspect of this application, the inorganic nanoparticles include at least one of silicon nitride, titanium dioxide, and aluminum oxide.

[0014] In one embodiment of the first aspect of this application, the amount of surface-modified inorganic nanoparticles used is 1-5 wt% of the total mass of the raw materials forming the composite electrolyte.

[0015] In one embodiment of the first aspect of this application, the in-situ polymerization is initiated by a polymerization initiator, which is at least one of lithium hexafluorophosphate or lithium difluorooxalate borate.

[0016] In one embodiment of the first aspect of this application, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

[0017] Secondly, this application provides a method for preparing the composite electrolyte as explained in the first aspect embodiment, comprising:

[0018] Inorganic nanoparticles were surface modified using silane coupling agents to graft organic functional groups onto their surfaces.

[0019] The obtained surface-modified inorganic nanoparticles, lithium salt, and polymerization initiator capable of initiating ring-opening polymerization of cyclic ether compounds are dispersed in an organic solvent containing cyclic ether compounds to obtain a uniformly dispersed composite electrolyte precursor.

[0020] The composite electrolyte precursor was solidified in situ to obtain the composite electrolyte.

[0021] As an embodiment of the second aspect, the inorganic nanoparticles are surface-modified using a silane coupling agent to graft organic functional groups onto their surface, including:

[0022] The silane coupling agent is dissolved in a mixed solvent of water and alcohol, the pH is adjusted to acidic, and hydrolysis is carried out to obtain a hydrolyzed silane solution.

[0023] Inorganic nanoparticles were added to a hydrolyzed silane solution and stirred under heating conditions to allow the silane coupling agent to be covalently grafted onto the surface of the nanoparticles. After the reaction was completed, the nanoparticles were washed and dried to obtain surface-modified inorganic nanoparticles.

[0024] Thirdly, this application also provides a lithium-ion battery, including the composite electrolyte explained in the first aspect embodiment, or the composite electrolyte prepared by the preparation method explained in the second aspect embodiment.

[0025] Due to the above technical solution, this application has at least the following beneficial effects:

[0026] The composite electrolyte according to the embodiments of this application improves interfacial compatibility and reduces agglomeration by surface-modified inorganic nanoparticles and in-situ polymerized polymer matrix, thereby improving ionic conductivity and mechanical strength. It has excellent ionic conductivity, good mechanical strength and thermal stability, and can effectively reduce the agglomeration of inorganic nanoparticles, thereby improving the safety and cycle performance of the battery. Attached Figure Description

[0027] Figure 1 This is a flowchart illustrating the preparation method of the composite electrolyte according to an embodiment of this application;

[0028] Figure 2 The flowchart illustrates the preparation method of the composite electrolyte according to an embodiment of this application.

[0029] Figure 3 This is a schematic diagram of the reaction mechanism of inorganic nanoparticle surface modification in an embodiment of this application;

[0030] Figure 4 This is a schematic diagram illustrating the chemical principle of in-situ ring-opening polymerization of the composite electrolyte precursor in an embodiment of this application. Detailed Implementation

[0031] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present application.

[0032] As described in the background above, traditional lithium-ion battery electrolytes are mostly organic liquid electrolytes, which pose safety hazards such as flammability, high volatility, and susceptibility to thermal runaway. Although polymer and inorganic composite electrolytes have shown some improvement, they generally face problems such as poor compatibility between inorganic nanoparticles and organic matrices, easy aggregation, discontinuous ion channels, low room temperature ionic conductivity, and unstable electrode or electrolyte-matrix interfaces, making it difficult to meet the development requirements of high energy density and high safety lithium-ion batteries.

[0033] For example, the interfacial compatibility between inorganic nanoparticles and organic polymer matrices is generally poor, leading to severe agglomeration of nanoparticles during dispersion. This results in localized stress concentration regions and discontinuous ion transport channels, thereby weakening overall ionic conductivity and cycle stability. Simultaneously, the solvent and lithium salt system of traditional organic electrolytes are poorly matched with solid or quasi-solid polymer matrices, easily forming an unstable interfacial layer at the electrode-electrolyte interface, accelerating battery performance degradation. More critically, existing inorganic fillers are mostly untreated ceramic particles, dispersed in the organic phase solely through physical mixing. This results in weak interfacial bonding, making it difficult to achieve chemically compatible and stable interfacial structures at the microscale, further restricting the improvement of the overall performance of composite electrolytes. These problems collectively prevent existing composite electrolytes from meeting practical requirements in terms of ionic conductivity, mechanical strength, and safety.

[0034] To address the aforementioned technical issues, this application provides a composite electrolyte. By using a silane coupling agent to modify the surface of inorganic nanoparticles and combining them with cyclic ether compounds, plasticizers, and a specific lithium salt system, the inorganic nanoparticles are stably and uniformly dispersed in an organic system. This results in the construction of a composite electrolyte with high ionic conductivity, excellent mechanical properties, and high safety, and its application in lithium-ion batteries.

[0035] The composite electrolyte of this application embodiment will be described below with reference to specific embodiments.

[0036] The composite electrolyte of this application embodiment includes: a polymer matrix, which is formed by in-situ polymerization of a composition containing cyclic ether compounds; and surface-modified inorganic nanoparticles uniformly dispersed in the polymer matrix. The surface-modified inorganic nanoparticles are obtained by modifying their surface with a silane coupling agent, and the surface of the surface-modified inorganic nanoparticles is grafted with organic functional groups and lithium salts.

[0037] Cyclic ether compounds are used as polymerization monomers, such as tetrahydrofuran, 1,3-dioxolane, or oxetane. These cyclic ether compounds can be used alone or in mixtures of two or more. The polymerization process can take place after the electrolyte precursor is infused into the battery, for example, by heating, light irradiation, or the addition of a general polymerization initiator, thereby directly forming a polymer network inside the battery. This in-situ polymerization method helps to achieve close contact between the electrolyte and the electrode, reducing interfacial resistance.

[0038] The uniform dispersion of inorganic nanoparticles in the polymer matrix of this application can be achieved through various physical methods, such as high-speed shear stirring, ultrasonic dispersion, or ball milling, to disperse the inorganic nanoparticles in the composition of cyclic ether compounds to form a stable suspension. This uniform dispersion can avoid local stress concentration and interruption of ion transport pathways caused by particle agglomeration.

[0039] Surface-modified inorganic nanoparticles are obtained by modifying their surfaces with silane coupling agents. Silane coupling agents typically possess one or more groups capable of reacting with the hydroxyl groups on the surface of inorganic particles, and an organic group capable of compatibility or reaction with organic polymers. For example, compounds containing alkoxysilane groups can be selected as silane coupling agents and grafted onto the surface of inorganic nanoparticles via hydrolysis-condensation reactions. This modification process aims to improve the interfacial compatibility between inorganic particles and the organic polymer matrix.

[0040] Furthermore, organic functional groups and lithium salts are grafted onto the surface of surface-modified inorganic nanoparticles. The introduction of organic functional groups can enhance the interaction between the inorganic particles and the polymer matrix, for example, through van der Waals forces, hydrogen bonds, or covalent bonds. For instance, organic groups such as amino, epoxy, or (meth)acryloyloxy groups can be introduced into the silane coupling agent, allowing them to remain on the nanoparticle surface after grafting. Simultaneously, lithium salts are also grafted onto the surface of the inorganic nanoparticles, for example, by pre-mixing the lithium salt with the silane coupling agent, or by surface loading the lithium salt after grafting with the silane coupling agent. This surface-grafted lithium salt can directly participate in lithium-ion transport and form a microenvironment favorable for lithium-ion migration on the surface of the inorganic particles.

[0041] The composite electrolyte of this application embodiment forms a polymer matrix through in-situ polymerization, ensuring good interfacial contact between the electrolyte and the electrode. Simultaneously, inorganic nanoparticles, surface-modified with a silane coupling agent and grafted with organic functional groups and lithium salts, are uniformly dispersed within the matrix, significantly improving the compatibility of the organic-inorganic interface and effectively suppressing nanoparticle aggregation. Therefore, this composite electrolyte exhibits excellent ionic conductivity, mechanical strength, and thermal stability, thereby enhancing the overall safety and cycle life of lithium-ion batteries.

[0042] In one embodiment of this application, the composition comprising cyclic ether compounds further comprises a plasticizer. A plasticizer is a substance that can increase the plasticity or flowability of a material, lower its glass transition temperature and melting point, thereby improving the material's flexibility and processing properties. In polymer electrolyte systems, plasticizers typically reduce the interaction forces between polymer chains, increase chain segment mobility, and thus reduce the crystallinity of the polymer, providing more free volume and channels for ion transport.

[0043] In some embodiments, the plasticizer may include at least one of 1,2-dimethoxyethane, succinate, and ethylene carbonate. These specific plasticizers are selected for combination with cyclic ether compounds to optimize the performance of the composite electrolyte. 1,2-Dimethoxyethane is a commonly used linear ether solvent with low viscosity and high dielectric constant, effectively dissolving lithium salts and promoting lithium-ion transport. Its molecular structure allows it to form weak interactions with polymer segments, thereby increasing the polymer's flexibility. Succinate is a polar aprotic solvent with a high dielectric constant, facilitating the dissociation of lithium salts. Simultaneously, the cyano group in its molecular structure has strong coordinating ability, forming weak coordination with lithium ions, thereby promoting lithium-ion transport. Ethyl carbonate is a cyclic carbonate solvent with a very high dielectric constant, a commonly used solvent component in lithium-ion battery electrolytes, and can greatly promote the dissociation of lithium salts. Its high dielectric constant is crucial for improving the ionic conductivity of the electrolyte. In practical applications, a single plasticizer can be selected based on the required electrolyte properties, such as ionic conductivity, mechanical strength, and electrochemical window, as well as cost considerations. Alternatively, two or more of the aforementioned plasticizers can be combined to achieve synergistic effects. For example, a mixture of 1,2-dimethoxyethane and ethylene carbonate can be used to balance the advantages of low viscosity and high dielectric constant.

[0044] In the embodiments of this application, by introducing a plasticizer into the composition containing cyclic ether compounds, the problem of cyclic ether compounds easily forming highly crystalline structures during in-situ polymerization, leading to insufficient room-temperature ionic conductivity and affecting battery rate performance, is effectively solved. Specifically, the addition of plasticizer can significantly reduce the crystallinity of the polymer matrix, increase the free volume and mobility of polymer chain segments, thereby providing more and smoother channels for lithium-ion transport. At the same time, the introduction of plasticizer also improves the flexibility of the polymer matrix and its contact performance with the electrode interface. When the plasticizer in this application is specifically at least one of 1,2-dimethoxyethane, butadiene nitrile, and ethylene carbonate, these specific plasticizers have good compatibility with cyclic ether compounds and have high dielectric constants, which can effectively promote the dissociation of lithium salts, increase carrier concentration, and further improve the effective transport number of lithium ions and overall ionic conductivity. This technical solution, combined with the introduction of the aforementioned surface-modified inorganic nanoparticles, can not only construct a polymer matrix with both high mechanical strength and thermal stability, but also form a more uniform and continuous ion transport network at the microscopic level, thereby significantly improving the room temperature ionic conductivity and cycle stability of the composite electrolyte and meeting the requirements of high-rate charge and discharge.

[0045] In some embodiments, in the compositions comprising cyclic ether compounds, the volume ratio of the cyclic ether compounds to the plasticizers of the present application is 3:7 to 7:3.

[0046] In this application, the cyclic ether compounds are key monomers for forming the polymer matrix. During in-situ polymerization, they open rings to form polymer chains, thereby constructing the framework structure of the composite electrolyte and endowing the electrolyte with the necessary mechanical strength and structural stability.

[0047] The main function of plasticizers is to increase the flexibility of the polymer matrix, lower its glass transition temperature, and provide more free volume and solvation environment for lithium-ion transport, thereby effectively improving the ionic conductivity of the electrolyte. The volume ratio settings in the embodiments of this application can precisely balance the functions of these two components. For example, when the volume ratio is close to 3:7, the proportion of plasticizer is relatively high, which helps to form a more flexible electrolyte system with stronger ionic conductivity, suitable for scenarios requiring higher ion migration rates. When the volume ratio is close to 7:3, the proportion of cyclic ether compounds is relatively high, and the polymer matrix formed after polymerization will have higher crosslinking density and mechanical strength, thus providing better structural stability and resistance to deformation. Furthermore, the volume ratio can also be set to an intermediate value, such as 5:5, to achieve a good trade-off between ionic conductivity and mechanical strength.

[0048] By precisely controlling the volume ratio of cyclic ether compounds to plasticizers within the range of 3:7 to 7:3 using the above technical solution, phase separation problems in the electrolyte system caused by ratio imbalance can be effectively avoided, ensuring the uniform mixing and stable existence of each component at the microscale. This precise ratio control allows the polymer matrix to maintain sufficient mechanical strength while fully leveraging the plasticizer's role in improving ionic conductivity, thereby significantly improving lithium-ion transport efficiency without sacrificing structural stability. Furthermore, this optimized ratio also helps improve the compatibility of the electrolyte and electrode interface, reducing interfacial impedance, and thus enhancing the overall performance stability and safety of the composite electrolyte, providing a solid foundation for the application of high-energy-density and high-safety lithium-ion batteries.

[0049] In some embodiments of this application, the cyclic ether compounds are selected from at least one of 1,3-dioxolane, tetrahydrofuran, substituted dioxolane, oxetane, and 1,3,5-trioxacyclohexane; or, the cyclic ether compounds of this application are 1,3-dioxolane or its alkyl, alkoxy, or haloalkyl-substituted derivatives.

[0050] Cyclic ether compounds, as monomer precursors for polymer matrices, directly influence the efficiency of in-situ polymerization, the flexibility, crystallinity, and lithium-ion transport capacity of the resulting polymers. Selecting cyclic ether compounds with specific cyclic structures and suitable ring strains ensures efficient ring-opening polymerization under mild conditions, forming polymer networks with good mechanical properties and ion transport channels.

[0051] By introducing substituents such as alkyl, alkoxy, or haloalkyl groups onto cyclic ether compounds, the physicochemical properties of the polymer matrix can be finely controlled. For example, alkyl substitution can increase the flexibility of the polymer chain and reduce crystallinity, thereby improving the room-temperature ionic conductivity; alkoxy substitution can introduce additional polar sites, enhancing the solubility of lithium salts and the solvation of lithium ions; haloalkyl substitution can adjust the dielectric constant and flame retardancy of the polymer, further improving the overall performance of the electrolyte. The introduction of these substituents aims to optimize the interaction between the polymer and lithium salts, as well as the interfacial compatibility between the polymer and inorganic nanoparticles.

[0052] More preferably, the cyclic ether compound of this application is at least one of 1,3-dioxolane, 4-methyl-1,3-dioxolane, 2-methoxy-1,3-dioxolane, or 4-trifluoromethyl-1,3-dioxolane.

[0053] This application optimizes the formation process and final properties of the polymer matrix from the source through precise selection and structural control of cyclic ether compounds. Specifically, the selected cyclic ether compounds possess suitable ring strain, ensuring efficient and complete ring-opening polymerization during in-situ polymerization, thereby avoiding the problems of inefficient polymerization leading to inhomogeneous or poor-performing polymer matrices. Simultaneously, these cyclic ether compounds and their alkyl, alkoxy, or haloalkyl-substituted derivatives can form polymer chains with good flexibility and low crystallinity after polymerization, providing ample free volume and effective transport channels for rapid lithium-ion transport, significantly improving the ion conductivity of the composite electrolyte, especially at room temperature.

[0054] Furthermore, by introducing specific substituents, the polarity and hydrophobicity of the polymer matrix can be effectively adjusted, resulting in superior interfacial compatibility with the organic functional groups on the surface of the surface-modified inorganic nanoparticles and the lithium salt. This constructs a stable and continuous organic-inorganic interface, effectively suppressing the aggregation of inorganic nanoparticles and ensuring uniform lithium-ion transport throughout the composite electrolyte. This optimized polymer matrix, in synergy with the aforementioned plasticizer and surface-modified inorganic nanoparticles, jointly constructs a composite electrolyte possessing high ionic conductivity, excellent mechanical properties, and high safety, providing a high-performance electrolyte solution for lithium-ion batteries.

[0055] In some embodiments, the silane coupling agent of this application is a silane containing one or more hydrolyzable groups and an organic functional group; wherein the organic functional group of this application is one of amino, epoxy, or (meth)acryloyloxy.

[0056] The structural design of the silane coupling agent enables it to effectively connect to both the surface of inorganic nanoparticles and organic polymer matrices or lithium salt systems. The silane contains one or more hydrolyzable groups, typically alkoxy groups such as methoxy, ethoxy, or chloro groups, which hydrolyze in the presence of water to generate silanol groups (-Si-OH). These silanol groups can undergo condensation reactions with the hydroxyl groups (-OH) on the surface of the inorganic nanoparticles to form stable covalent bonds (-Si-O-inorganic), thereby firmly grafting the silane coupling agent onto the surface of the inorganic nanoparticles.

[0057] Silane coupling agents also contain an organic functional group designed to form a strong interaction with lithium salts in the organic polymer matrix or electrolyte. The organic functional group is limited to one of amino, epoxy, or (meth)acryloyloxy groups. Amino groups possess a certain degree of basicity, enabling them to react with acidic groups in the polymer matrix or interact with polymer segments through hydrogen bonding, while also facilitating the dissociation of lithium salts. Epoxy groups have a strained ring structure, readily undergoing ring-opening reactions, and can form covalent bonds with the polymer matrix, thereby significantly enhancing interfacial bonding. (Methacryloxy groups), on the other hand, possess polymerizable double bonds, enabling them to participate in in-situ polymerization processes, covalently bonding inorganic particles to the polymer network, achieving a tight organic-inorganic phase bond.

[0058] Furthermore, this application specifically defines the type of silane coupling agent, including at least one of γ-aminopropyltriethoxysilane, 3-epoxypropyltrimethoxysilane, and 3-(methacryloyloxy)propyltrimethoxysilane.

[0059] Among them, the amino terminus of γ-aminopropyltriethoxysilane (APS) can interact with organic polymer matrices or lithium salts, while its triethoxysilane terminus can hydrolyze and form covalent bonds with the surface of inorganic nanoparticles. The epoxy group of 3-epoxypropyltrimethoxysilane (GPTMS) can undergo ring-opening reactions with active hydrogen atoms (such as hydroxyl and amino groups) in the polymer matrix to form stable covalent bonds, while its trimethoxysilane terminus is coupled to the inorganic surface. The (meth)acryloyloxy group of 3-(methacryloyloxy)propyltrimethoxysilane (MPS) can participate in the in-situ polymerization reaction of the polymer matrix, covalently bonding inorganic nanoparticles to the polymer network, while its trimethoxysilane terminus is coupled to the inorganic surface. These specific silane coupling agents have been verified to exhibit excellent grafting ability and stability in the field of composite electrolytes, ensuring the reliability and consistency of the modification process.

[0060] In the embodiments of this application, by precisely selecting the structure and type of the silane coupling agent, it is ensured that the hydrolyzable groups it contains can form stable covalent bonds with the surface of inorganic nanoparticles, while its organic functional groups (such as amino, epoxy, or (meth)acryloyloxy) can form strong interactions with the polymer matrix or lithium salt system formed by in-situ polymerization of cyclic ether compounds, including hydrogen bonding, covalent crosslinking, or participation in copolymerization. This dual-action mechanism fundamentally solves the problem of poor interfacial compatibility and easy aggregation between inorganic nanoparticles and organic matrices.

[0061] In some embodiments, the inorganic nanoparticles include at least one of silicon nitride, titanium dioxide, and aluminum oxide.

[0062] Introducing specific types of inorganic nanoparticles, namely at least one of silicon nitride, titanium dioxide, or aluminum oxide, into composite electrolytes can significantly improve their overall performance. These materials possess high dielectric constants, effectively promoting lithium salt dissociation and increasing the number of freely moving lithium ions, thereby enhancing the ionic conductivity of the composite electrolyte. Simultaneously, these inorganic nanoparticles also exhibit excellent mechanical strength and thermal stability, enhancing the overall mechanical properties and heat resistance of the composite electrolyte. Combined with the surface modification treatment of the inorganic nanoparticles described in this application, these specific types of nanoparticles can form good interfacial compatibility with the polymer matrix, effectively avoiding the problem of inorganic particle agglomeration in traditional technologies and ensuring uniform dispersion of nanoparticles in the polymer matrix. This uniform dispersion not only optimizes the ion transport path and reduces local stress concentration but also further strengthens the stability of the organic-inorganic interface, enabling the composite electrolyte to maintain high ionic conductivity while also possessing excellent mechanical strength, thermal stability, and long cycle life.

[0063] In some embodiments, the amount of surface-modified inorganic nanoparticles used is 1-5 wt% of the total mass of the raw materials forming the composite electrolyte of this application.

[0064] The amount of surface-modified inorganic nanoparticles used refers to the percentage of the mass of the surface-modified inorganic nanoparticles added during the preparation of the composite electrolyte, relative to the total mass of all raw materials used to form the composite electrolyte (including cyclic ether compounds, plasticizers, lithium salts, polymerization initiators, and the surface-modified inorganic nanoparticles of this application). Precisely controlling the amount of surface-modified inorganic nanoparticles within the range of 1-5 wt% can effectively solve a series of problems caused by improper dosage. When the amount of surface-modified inorganic nanoparticles used in this application is too low, its mechanical strengthening effect on the polymer matrix is ​​not significant, and its promoting effect on lithium salt dissociation and ion transport is limited, making it difficult to fully realize its potential to improve the overall performance of the composite electrolyte. Conversely, if the amount is too high, although surface modification has improved dispersibility, excessive nanoparticles may still lead to local agglomeration, increasing the viscosity of the composite electrolyte precursor, thereby affecting the subsequent in-situ polymerization process and the uniformity of the final composite electrolyte. More importantly, excessive nanoparticle content can increase the tortuosity of ion transport paths and even block some ion channels, thereby reducing ion conductivity.

[0065] In the embodiments of this application, by limiting the amount of surface-modified inorganic nanoparticles to an optimized range of 1-5 wt%, the synergistic enhancement effect on the mechanical strength, thermal stability, and ionic conductivity of the composite electrolyte can be maximized while ensuring uniform dispersion of the nanoparticles. This not only avoids local stress concentration and ion channel discontinuity caused by particle agglomeration, but also effectively improves the overall performance of the composite electrolyte without significantly increasing the viscosity of the system, enabling it to exhibit superior cycle stability and rate performance in lithium-ion batteries.

[0066] In some embodiments, in-situ polymerization is initiated by a polymerization initiator, and the polymerization initiator in this application is at least one of lithium hexafluorophosphate or lithium difluorooxalate borate.

[0067] In some embodiments, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide. At the same concentration, LiTFSI can release more free lithium ions than other lithium salts (such as LiPF6 and LiClO4), directly contributing to the improvement of ionic conductivity.

[0068] Preferably, the concentration of the lithium salt is 0.5-2 M. When the concentration is below 0.5 M, the absolute number of free lithium ions in the system is insufficient to form a continuous ion transport network, resulting in low ionic conductivity (typically below 10). -4 The concentration of lithium salt (S / cm) is insufficient to meet the high-rate charge-discharge requirements of batteries. Excessive concentration can also lead to excessively high viscosity of the precursor solution, affecting its wetting effect on the electrodes and separator, and potentially causing the final polymer film to become brittle and its mechanical properties to deteriorate. Therefore, in this application, the lithium salt concentration is kept within this range, achieving an ionic conductivity of 4.5-5.0 × 10⁻⁶ for the composite electrolyte. -4 The high S / cm level enables the battery to maintain stable cycling at 0.5C or even 1C rates.

[0069] This application also discloses a method for preparing a composite electrolyte, referring to... Figure 1 and Figure 2 , Figure 1 A flowchart illustrating the preparation method of the composite electrolyte according to an embodiment of this application is shown; Figure 2 Another flowchart of the preparation method of the composite electrolyte according to an embodiment of this application is shown.

[0070] like Figure 1 As shown, the method includes S110-S130.

[0071] S110, using a silane coupling agent to modify the surface of the inorganic nanoparticles of this application, thereby grafting organic functional groups onto their surface. Corresponding to... Figure 2 S1.

[0072] For example, firstly, the silane coupling agent is dissolved in a mixed solvent of water and alcohol, the pH is adjusted to acidic, and hydrolysis is carried out to obtain a hydrolyzed silane solution. Adjusting the pH to acidic catalyzes the hydrolysis of the alkoxy groups in the silane coupling agent to silanol groups, thereby improving the hydrolysis efficiency and the stability of the hydrolysis products, and preventing self-condensation of the silane coupling agent during hydrolysis. The pH of the solution can be adjusted to the range of 3-6 by adding a small amount of inorganic acid, such as hydrochloric acid, nitric acid, or sulfuric acid. Alternatively, organic acids, such as acetic acid or citric acid, can be used to adjust the pH to 4-5 to provide a mild acidic environment that promotes the hydrolysis reaction.

[0073] Next, the inorganic nanoparticles are added to the hydrolyzed silane solution of this application, and the reaction is stirred under heating conditions, for example, for 0.5-2 hours, so that the silane coupling agent is grafted onto the surface of the nanoparticles through covalent bonds. After the reaction is completed, the nanoparticles are washed and dried to obtain the surface-modified inorganic nanoparticles of this application.

[0074] like Figure 3 As shown, the reaction mechanism of surface modification is as follows: First, consider the reaction pathway of γ-aminopropyltriethoxysilane (KH550) on the left. Hydrolysis occurs, converting the ethoxy group into silanol groups (-Si-OH). Then, these silanol groups undergo a condensation reaction with the hydroxyl groups (-OH) on the surface of the inorganic nanoparticles (represented by gray spheres in the figure), forming stable covalent bonds (Si-O- particles). After the reaction, the KH550 molecules are "anchored" to the nanoparticle surface through chemical bonds, while the amino group (-NH2) at the other end is exposed, becoming a new functional group on the particle surface.

[0075] The reaction pathway on the right: Using 3-epoxypropyltrimethoxysilane (KH560), similar to the left, the methoxy group of KH560 hydrolyzes to a silanol group, which then condenses with the hydroxyl groups on the surface of the inorganic nanoparticles to form a covalent bond. After the reaction, the KH560 molecule is grafted onto the particle surface, and its terminal epoxy group becomes a new functional group on the particle surface. Figure 3 The structure on the surface of the particle on the lower right side represents the grafting of organic chains with epoxy groups.

[0076] S120 involves dispersing the obtained surface-modified inorganic nanoparticles, lithium salt, and a polymerization initiator capable of initiating ring-opening polymerization of cyclic ether compounds in an organic solvent containing the cyclic ether compound, thereby obtaining a uniformly dispersed composite electrolyte precursor. Figure 2 S2.

[0077] Combination Figure 4 The diagram shown illustrates the chemical principle of in-situ ring-opening polymerization of the composite electrolyte precursor in the embodiments of this application.

[0078] like Figure 4 As shown, Figure 4 The five-membered ring structure on the left is the chemical structural formula of 1,3-dioxolane (DOL). It is a cyclic ether compound containing two oxygen atoms and three carbon atoms.

[0079] At room temperature, DOL is a low-viscosity liquid. When DOL is mixed with plasticizers, lithium salts, and modified nanoparticles, the resulting composite electrolyte precursor is a highly fluid liquid. The intermediate reaction conditions are achieved using an initiator, such as lithium hexafluorophosphate (LiPF6) or lithium difluorooxalate borate (LiDFOB). After these lithium salts dissociate in the system, their cations (Li... + ) or anion (PF6) - DFOB - The DOL monomers can interact with the oxygen atoms on the DOL ring, making the ring structure unstable and thus opening the DOL ring, initiating the polymerization reaction. After polymerization, multiple DOL monomers link together to form a long-chain polymer, and the system changes from a liquid state to a quasi-solid or solid state. This liquid state is very beneficial for filling into the battery, as it can fully wet the electrodes and separator, forming good interfacial contact, which is usually difficult to achieve with solid electrolytes.

[0080] S130, the composite electrolyte precursor of this application is cured in situ to obtain the composite electrolyte of this application.

[0081] The embodiments of this application effectively solve the core problem of uneven dispersion of inorganic nanoparticles in organic systems, thereby ensuring the uniformity and performance improvement of the composite electrolyte. The composite electrolyte prepared by this method, when combined with specific components such as the aforementioned cyclic ether compounds, plasticizers, silane coupling agents, inorganic nanoparticles, lithium salts, and polymerization initiators, can achieve high room temperature and medium-high temperature ionic conductivity, and exhibits excellent capacity retention and interfacial stability under long-cycle and high-rate charge-discharge conditions, providing a high-performance electrolyte solution for various applications such as high-safety power batteries and energy storage batteries.

[0082] This application provides a lithium-ion battery comprising the composite electrolyte described in the above embodiments. Because the composite electrolyte possesses high ionic conductivity, mechanical strength, and other properties, the battery containing this composite electrolyte also exhibits these effects and has high safety. Further details are omitted here.

[0083] The composite electrolyte and its preparation method according to the present application will be described in detail below with reference to specific embodiments.

[0084] Example 1

[0085] 1) Surface modification of inorganic nanoparticles:

[0086] Anhydrous ethanol and deionized water were mixed at a volume ratio of 3:1 to obtain a mixed solvent. γ-aminopropyltriethoxysilane (KH550) was added to this mixed solvent to a mass fraction of 3 wt%. The pH of the system was adjusted to 4-5 with dilute hydrochloric acid, and the mixture was stirred and hydrolyzed at room temperature (approximately 25°C) for 12 hours to obtain a hydrolyzed silane solution. Titanium dioxide (TiO2) nanoparticles with an average particle size of approximately 50 nm were weighed and added to the above hydrolyzed silane solution, with a TiO2 mass fraction of 5 wt%. The reaction was stirred at 70°C for 6 hours. After the reaction was completed, the product was centrifuged, washed three times alternately with ethanol and deionized water, and then vacuum dried at 70°C for 12 hours to obtain surface-modified TiO2 nanoparticles.

[0087] 2) Preparation of composite electrolyte precursor:

[0088] Under dry argon protection, 1,3-dioxolane and 1,2-dimethoxyethane were mixed at a volume ratio of 5:5 to obtain a mixed organic solvent. Lithium hexafluorophosphate (LiPF6) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were added to this mixed solvent, controlling the LiPF6 concentration at 1.5 M and the LiTFSI concentration at 1.0 M. The mixture was stirred at 60 °C until the lithium salt was completely dissolved. Then, the surface-modified TiO2 nanoparticles prepared in step S1 were slowly added under continuous stirring, ensuring a mass fraction of 3 wt% in the system. The mixture was stirred at 60 °C for 4 hours, supplemented with ultrasonic dispersion, to obtain a uniformly dispersed composite electrolyte precursor solution.

[0089] 3) Preparation of composite electrolyte membrane and battery:

[0090] The aforementioned composite electrolyte precursor solution was uniformly cast onto the surface of a polypropylene (PP) separator in an inert atmosphere glove box, with the coating amount controlled. Subsequently, the mixture was kept at 60°C for 12 hours to allow the 1,3-dioxolane to undergo ring-opening polymerization initiated by LiPF6, forming the composite electrolyte membrane. Lithium iron phosphate (LiFePO4) positive electrode and graphite negative electrode were selected, and the composite electrolyte membrane was placed between the positive and negative electrodes in a glove box to assemble a CR2032 coin cell. The ionic conductivity of the prepared composite electrolyte at 25°C was measured to be approximately 4.5 × 10⁻⁶. -4 S / cm, the assembled battery retains more than 96% of its capacity after 200 cycles at 0.5C rate.

[0091] Example 2

[0092] This embodiment is basically the same as Embodiment 1, except that:

[0093] In step 1), 3-epoxypropyltrimethoxysilane (KH560) was used as a silane coupling agent with a mass fraction of 4 wt%, a hydrolysis pH of 4, and a hydrolysis time of 16 hours. Alumina (Al2O3) nanoparticles with an average particle size of about 100 nm were used to modify the surface by reacting at 80°C for 6 hours.

[0094] In step 2), 1,3-dioxolane and succinic anionyl (SN) were mixed at a volume ratio of 3:7. Lithium difluorooxalate borate (LiDFOB) (concentration 2.0 M) was used as the polymerization initiator, and the LiTFSI concentration was 0.8 M. The mass fraction of the surface-modified Al2O3 nanoparticles was 2 wt%.

[0095] The obtained composite electrolyte precursor was assembled into a battery with a LiFePO4 positive electrode and a lithium metal anode. The ionic conductivity at 25℃ was measured to be approximately 5.0 × 10⁻⁶. -4 With a capacity of S / cm, the capacity retention is approximately 97% after 300 cycles at a 0.5C rate. After 200 cycles at a 1C rate, the capacity retention is still greater than 94%.

[0096] Example 3

[0097] This embodiment uses different plasticizer systems to investigate the effect of different plasticizers on ionic conductivity.

[0098] Using the methods and conditions described in Example 1, TiO2 nanoparticles were surface-modified with 3-(methacryloyloxy)propyltrimethoxysilane (KH570). The hydrolysis conditions of KH570 were the same as in Example 1, except that the silane coupling agent was replaced with KH570 at a mass fraction of 3 wt%. Hydrolysis was carried out at pH 4.5 and room temperature for 12 hours, followed by reaction with TiO2 at 70°C for 4 hours to obtain surface-modified TiO2 nanoparticles.

[0099] A mixed organic solvent was obtained by mixing 1,3-dioxolane and a mixed plasticizer consisting of succinate (SN) and ethylene carbonate (EC) at a volume ratio of 7:3 (SN:EC volume ratio 1:1). LiPF6 and LiTFSI were added to the mixed solvent to achieve a LiPF6 concentration of 2.5 M and a LiTFSI concentration of 1.0 M. The mixture was stirred and dissolved at 60 °C. Subsequently, surface-modified TiO2 nanoparticles with a particle content of 4 wt% were added. The mixture was stirred at 60 °C for 6 hours to obtain the composite electrolyte precursor.

[0100] The composite electrolyte precursor of this embodiment was cast onto the surface of a separator and heated at 60°C for 12 hours to form a composite electrolyte membrane. This membrane was then assembled with a LiNi0.6Co0.2Mn0.2O2 (NCM622) positive electrode and a graphite negative electrode to form a coin cell. At -20°C, the battery's 0.5C discharge capacity still reached approximately 82% of its room temperature 0.5C capacity, and after 100 cycles at -10°C, the capacity retention rate was higher than 92%. This demonstrates excellent low-temperature performance and interface stability.

[0101] Comparative Example 1

[0102] Comparative Example 1 uses unmodified inorganic nanoparticles to examine the necessity of surface modification in this application.

[0103] Unmodified TiO2 nanoparticles (average particle size of about 50 nm) were used directly without surface treatment with methacryloyloxypropylcyclotetrasiloxane.

[0104] Using the same solvent system (1,3-dioxolane / DME volume ratio 5:5), lithium salt system (LiPF6 concentration 1.5 M, LiTFSI concentration 1.0 M), and TiO2 addition amount (3 wt%) as in Example 1, the mixture was stirred and mixed at 60°C for 4 hours in the same manner.

[0105] Results showed that significant TiO2 agglomeration and sedimentation were observed in the system, indicating poor precursor stability. After standing for 24 hours, particle accumulation appeared in the lower layer, while the upper solution was relatively clear. The above precursor was used to prepare composite dielectric materials and assemble LiFePO4 graphite batteries. Test results showed that Comparative Example 1 had an ionic conductivity of approximately 2.6 × 10⁻⁶ at 25 °C. -4 S / cm, significantly lower than in Example 1 (approximately 4.8 × 10⁻⁶). -4 The capacity retention rate was only about 87% after 200 cycles at 0.5C, and the interfacial impedance in the AC impedance spectrum increased significantly with cycling. The electrolyte membrane of Comparative Example 1 also had a rough and non-uniform appearance. The above results indicate that without surface modification by the specific small molecule crosslinking agent of this application, the inorganic nanoparticles have poor compatibility and dispersion with the organic system, which seriously affects the ion conduction and cycling stability of the composite dielectric material, verifying the necessity and effectiveness of the surface modification step of this application.

[0106] Comparative Example 2

[0107] The role of inorganic high-dielectric fillers was verified by using a system without inorganic nanoparticles containing high dielectric constant.

[0108] Using the 1,3-dioxolane / DME solvent system with LiPF6 and LiTFSI concentration conditions in Example 1, but without adding any inorganic nanoparticles, only a pure organic polymer electrolyte precursor was prepared.

[0109] Similar to Example 1, the precursor was cast onto a separator and cured at 60°C to form a pure polymer electrolyte membrane, which was then assembled into a battery with a LiFePO4 graphite electrode. At 25°C, the ionic conductivity of the pure polymer electrolyte membrane in Comparative Example 2 was approximately 2.2 × 10⁻⁶. -4 The S / cm ratio was significantly lower than that of Example 1 containing modified TiO2; the capacity retention after 200 cycles at 1C was approximately 89%, also lower than that of Example 1. Due to the lack of high-dielectric-constant inorganic nanoparticles, the lithium salt in Comparative Example 2 exhibited insufficient dissociation, resulting in limited ion conductivity. This further demonstrates that the technical solution employing modified high-dielectric-constant ceramic nanoparticles in this application has significant advantages in improving conductivity and cycling performance.

[0110] Comparative Example 3

[0111] The volume ratio of 1,3-dioxolane to plasticizer, which is outside the preferred range of this application, is used to illustrate the importance of this ratio range.

[0112] Under the same conditions as in Example 1, only the volume ratio of 1,3-dioxolane to DME was adjusted to 9:1 (outside the preferred range of 3:7 to 7:3 of this application), while keeping other conditions unchanged, and using the same modified TiO2 nanoparticles as in Example 1.

[0113] Test results show that the ionic conductivity of this system at 25℃ is approximately 3.1 × 10⁻⁶. -4 The S / cm ratio was significantly lower than in Example 1; simultaneously, the electrolyte membrane was relatively hard and brittle, prone to microcracks, and exhibited poor interfacial contact. After 200 cycles at 0.5C, the capacity retention was approximately 81%. Comparative Example 3 shows that if the 1,3-dioxolane ratio is too high, although the mechanical strength of the membrane increases after polymerization, insufficient plasticizer in the system restricts chain segment movement. Furthermore, the methacryloyloxy groups grafted onto the particle surface fail to form an effective copolymer with the sufficient DOL polymer network, preventing the inorganic particles from fully anchoring and thus reducing ion conduction and cycling performance. This verifies the rationality and necessity of the volume ratio range defined in this application.

[0114] Comparative Example 4

[0115] Comparative Example 4 uses a conventional silane coupling agent (KH570) instead of the methacryloyloxypropylcyclotetrasiloxane of this application to compare the effects of different modifiers.

[0116] The method of Example 1 was followed, but the modifier in step S1 was replaced with 3-(methacryloyloxy)propyltrimethoxysilane (KH570), and a conventional hydrolysis process was adopted: KH570 was dissolved in a mixed solvent of water and ethanol (water:ethanol = 1:3), the pH was adjusted to 4-5, and after hydrolysis at room temperature for 12 hours, TiO2 nanoparticles were added, and the reaction was carried out at 70°C for 6 hours. After washing and drying, KH570 modified TiO2 nanoparticles were obtained.

[0117] Step S2 is exactly the same as in Example 1, using a 5:5 DOL / DME mixed solvent, 1.5 M LiPF6 and 1.0 M LiTFSI, and adding the above-mentioned KH570 modified TiO2 nanoparticles to prepare a composite electrolyte precursor and assemble the battery.

[0118] The test results show that the ionic conductivity of Comparative Example 4 at 25℃ is approximately 3.8 × 10⁻⁶. -4 The S / cm was slightly lower than in Example 1; after 200 cycles at 0.5C, the capacity retention was approximately 92%. Although KH570 can also improve particle dispersion to some extent, its long-chain flexible structure can only provide physical entanglement and cannot form a rigid interfacial layer and a strong chemical bond network like the small molecule crosslinking agent of this application. During long-term cycling, the interfacial impedance of Comparative Example 4 increased faster than that of Example 1, indicating that its interfacial stability is still insufficient. This comparison fully demonstrates that the methacryloyloxypropylcyclotetrasiloxane used in this application has unique structural advantages and unexpected technical effects.

[0119] As can be seen from Examples 1-3 and Comparative Examples 1-4, the embodiments of this application have achieved comprehensive optimization of the composite dielectric material in terms of ionic conductivity, mechanical properties and electrochemical stability, verifying the effectiveness and superiority of the technical solution of this application.

[0120] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A composite electrolyte, characterized in that, include: A polymer matrix formed by in-situ polymerization of a composition comprising cyclic ether compounds; Surface-modified inorganic nanoparticles are uniformly dispersed in the polymer matrix. The surface-modified inorganic nanoparticles are obtained by modifying their surface with a silane coupling agent, and the surface of the surface-modified inorganic nanoparticles is grafted with organic functional groups and lithium salts.

2. The composite electrolyte according to claim 1, characterized in that, The composition comprising cyclic ether compounds further comprises a plasticizer, wherein the plasticizer comprises at least one selected from 1,2-dimethoxyethane, succinate, and ethylene carbonate.

3. The composite electrolyte according to claim 2, characterized in that, In the composition comprising cyclic ether compounds, the volume ratio of the cyclic ether compounds to the plasticizer is 3:7 to 7:

3.

4. The composite electrolyte according to any one of claims 1-3, characterized in that, The cyclic ether compound is selected from at least one of 1,3-dioxolane, tetrahydrofuran, substituted dioxolane, oxetane, and 1,3,5-trioxetane; or, The cyclic ether compounds are 1,3-dioxolane or derivatives thereof substituted with alkyl, alkoxy, or haloalkyl groups.

5. The composite electrolyte according to any one of claims 1-3, characterized in that, The silane coupling agent is a silane containing one or more hydrolyzable groups and an organic functional group; wherein the organic functional group is one of amino, epoxy, or (meth)acryloyloxy; and / or, The silane coupling agent is at least one of γ-aminopropyltriethoxysilane, 3-epoxypropyltrimethoxysilane, and 3-(methacryloyloxy)propyltrimethoxysilane.

6. The composite electrolyte according to any one of claims 1-3, characterized in that, The inorganic nanoparticles include at least one of silicon nitride, titanium dioxide, and aluminum oxide.

7. The composite electrolyte according to any one of claims 1-3, characterized in that, The amount of the surface-modified inorganic nanoparticles used is 1-5 wt% of the total mass of the raw materials used to form the composite electrolyte.

8. A method for preparing a composite electrolyte as described in any one of claims 1-7, characterized in that, include: The inorganic nanoparticles were surface modified using a silane coupling agent to graft organic functional groups onto their surface. The obtained surface-modified inorganic nanoparticles, lithium salt, and polymerization initiator capable of initiating ring-opening polymerization of cyclic ether compounds are dispersed in an organic solvent containing a composition of cyclic ether compounds to obtain a uniformly dispersed composite electrolyte precursor. The composite electrolyte precursor is solidified in situ to obtain the composite electrolyte.

9. The preparation method according to claim 8, characterized in that, The inorganic nanoparticles are surface-modified using a silane coupling agent to graft organic functional groups onto their surface, including: The silane coupling agent is dissolved in a mixed solvent of water and alcohol, the pH is adjusted to acidic, and hydrolysis is carried out to obtain a hydrolyzed silane solution. Inorganic nanoparticles were added to the hydrolyzed silane solution and stirred under heating conditions to allow the silane coupling agent to be covalently grafted onto the surface of the nanoparticles. After the reaction was completed, the nanoparticles were washed and dried to obtain the surface-modified inorganic nanoparticles.

10. A lithium-ion battery, characterized in that, The composite electrolyte includes any one of claims 1-7, or a composite electrolyte prepared by the preparation method described in claim 8 or 9.

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