CN117285699A

CN117285699A - Solid electrolyte prepolymerization liquid, solid electrolyte and electrochemical device

Info

Publication number: CN117285699A
Application number: CN202311225018.7A
Authority: CN
Inventors: 徐耿标; 李俊焕; 杨成林; 李子坤; 黄友元
Original assignee: Shenzhen Beiteri New Energy Technology Research Institute Co ltd
Current assignee: Shenzhen Beiteri New Energy Technology Research Institute Co ltd
Priority date: 2023-09-21
Filing date: 2023-09-21
Publication date: 2023-12-26

Abstract

The invention discloses a solid electrolyte prepolymerization solution, a solid electrolyte and an electrochemical device, wherein the solid electrolyte prepolymerization solution comprises a first monomer, an initiator and a plasticizer solution; the first monomer includes at least one of an alicyclic epoxy monomer containing an ester group, an epoxy monomer containing an ester group and a heterocyclic group, and the first monomer contains at least three epoxy groups. According to the solid electrolyte prepolymerization solution, the solid electrolyte and the electrochemical device, the alicyclic epoxy monomer containing the ester group and/or the epoxy monomer containing the ester group and the heterocyclic group with at least three epoxy groups are used as polymer monomers, and the epoxy groups in the monomers can form a strong crosslinking structure in the curing process, so that the solid electrolyte with small curing shrinkage and excellent mechanical performance is obtained, and the phenomenon of solid-liquid separation after curing can be reduced.

Description

Solid electrolyte prepolymerization liquid, solid electrolyte and electrochemical device

Technical Field

The invention relates to the technical field of electrochemistry, in particular to solid electrolyte prepolymerization liquid, solid electrolyte and an electrochemistry device.

Background

Lithium ion secondary batteries have been widely recognized as a revolutionary technology in the field of electric energy storage in recent decades of technological progress. The advantages are a high energy density, a long cycle life and no so-called "memory effect". This means that such a battery can store more energy while maintaining a longer service life and without losing its energy storage capacity due to repeated charging and discharging. Because of these outstanding advantages, lithium ion secondary batteries have been dominant in many applications, such as portable electronic devices, electric vehicles, and renewable energy storage.

Although lithium ion secondary batteries have such many advantages, the use of liquid electrolytes in which large amounts of flammable small molecule solvents are present creates a series of safety concerns. These include short circuits that may occur inside the battery, leakage of electrolyte, and even combustion or explosion that may occur under certain extreme conditions. These safety concerns limit the use of lithium ion batteries in certain high risk applications, such as aerospace and large power storage systems.

To overcome these drawbacks of liquid lithium ion batteries, researchers have begun exploring the use of solid state electrolytes as alternatives. Solid electrolytes fall into two broad categories, inorganic solid electrolytes and polymeric solid electrolytes. Among them, polymer solid electrolytes are receiving attention because of their excellent processability and high adaptability to the shape of a battery. In addition, the polymer solid electrolyte can be produced in a large scale by a coating process, a lamination process and the like, and the production cost is expected to be reduced.

However, while polymer solid state electrolytes show great potential, they also present challenges in the manufacturing process. One major problem is that existing solid state electrolytes have significant shrinkage during curing, which can cause the interface between the electrolyte and the electrode to become undesirable. In addition, the solidified electrolyte may undergo a solid-liquid separation phenomenon, thereby causing further deterioration in interface performance between the electrolyte and the electrode. These problems increase the internal resistance of the battery, thereby reducing the overall performance and efficiency of the battery.

Accordingly, there is a need to provide a new solid electrolyte pre-polymer solution, solid electrolyte and electrochemical device, which solve the problems of the prior art.

Disclosure of Invention

The invention aims to provide a solid electrolyte pre-polymerization liquid, a solid electrolyte and an electrochemical device, wherein the solid electrolyte pre-polymerization liquid has the characteristics of small curing shrinkage and excellent mechanical property, and can reduce the phenomenon of solid-liquid separation after curing.

In order to achieve the above purpose, the technical scheme provided by the invention is as follows:

in a first aspect, the present invention provides a solid electrolyte pre-polymerization solution comprising a first monomer, an initiator, and a plasticizer solution; the first monomer includes at least one of an alicyclic epoxy monomer containing an ester group, an epoxy monomer containing an ester group and a heterocyclic group, and the first monomer contains at least three epoxy groups.

In one or more embodiments of the invention, the first monomer is selected from compounds of formula I-A or formula I-B:

wherein R is ₁ Is a multi-ring containing epoxy groups, n is a positive integer; r is R ₂ Is a multi-membered ring or an alkane chain, x, y and z are all positive integers, and x is more than or equal to 1, y is more than or equal to 1, x+y is more than or equal to 3, and z is more than or equal to 1.

In one or more embodiments of the invention, the initiator is lithium tetrafluoroborate.

In one or more embodiments of the invention, the plasticizer solution includes a solvent, an additive, and a lithium salt; the mass fraction of the solvent in the plasticizer solution is 50-70%, the mass fraction of the additive in the plasticizer solution is 5-15%, and the mass fraction of the lithium salt in the plasticizer solution is 20-40%.

In one or more embodiments of the present invention, the solvent includes at least one of ethyl propionate, diethyl carbonate, fluoroethylene carbonate, ethylene carbonate; and/or the additive comprises at least one of 1, 3-propane sultone, adiponitrile, ethylene glycol bis (propionitrile) ether, 1,3, 6-hexane trinitrile; and/or the lithium salt comprises at least one of lithium hexafluorophosphate and lithium bis-fluorosulfonyl imide.

In one or more embodiments of the present invention, the solid electrolyte pre-polymerization solution further includes a second monomer including at least one of a heterocyclic compound, a vinyl ether compound, and a polyvinyl alcohol nitrile compound.

In one or more embodiments of the present invention, the heterocyclic compound includes at least one of an epoxy compound, an oxetane compound, an isopentane compound, a furan ring compound, and a pyridine compound; and/or the vinyl ether compound comprises at least one of vinyl methyl ether, vinyl ethyl ether and vinyl phenyl ether; and/or the polyvinyl alcohol nitrile compound comprises at least one of polyvinyl alcohol acetonitrile, polyvinyl alcohol malononitrile, polyvinyl alcohol acrylonitrile, polyvinyl alcohol isovaleronitrile and polyvinyl alcohol cyclopentyl propionitrile.

In one or more embodiments of the present invention, in the solid electrolyte pre-polymerization solution, the mass fraction of the first monomer is 5 to 15%, and the molar ratio of the first monomer to the second monomer is 1 (0.2 to 3).

In a second aspect, the present invention provides a solid electrolyte formed by curing a solid electrolyte pre-polymer liquid as described above by means of cationic polymerization.

In one or more embodiments of the invention, the solid state electrolyte includes a polymer molecular chain of the structure shown in formula iii:

wherein n is a positive integer, n ₁ And R is a chain group containing an epoxy functional group and is a positive integer greater than or equal to 2.

In a third aspect, the present invention provides an electrochemical device comprising a solid electrolyte as described above.

Compared with the prior art, the solid electrolyte pre-polymerization liquid, the solid electrolyte and the electrochemical device provided by the invention have the advantages that the alicyclic epoxy monomer containing the ester group and/or the epoxy monomer containing the ester group and the heterocyclic group with at least three epoxy groups are used as polymer monomers, and the epoxy groups in the monomers can form a strong cross-linking structure in the curing process, so that the solid electrolyte with small curing shrinkage and excellent mechanical property is obtained, and the solid-liquid separation phenomenon after curing can be reduced.

Drawings

FIG. 1 is a comparative graph after curing of the solid electrolyte pre-polymer solutions of example 1 and comparative example 1 of the present invention;

FIG. 2 is an elastic modulus test chart of the solid electrolytes in example 1 and comparative example 1 of the present invention;

FIG. 3 is a graph showing DSC test results of a solid electrolyte and a corresponding liquid plasticizer in example 1 of the present invention;

FIG. 4 is an infrared spectrum of the solid electrolyte pre-polymer solution before and after curing in example 1 of the present invention;

FIG. 5 is a graph showing the gram capacity distribution of the parallel sample battery in example 1 of the present invention

FIG. 6 is a graph of 0.5C/0.5C cycling at 0deg.C for the finished cell of example 1 of the present invention;

fig. 7 is a rate graph of the finished battery in example 1 of the present invention.

Detailed Description

The following describes specific embodiments of the present invention in detail with reference to examples, but it should be understood that the scope of the present invention is not limited by the specific embodiments.

In the following description, "%" and "parts" indicating amounts are weight basis unless otherwise specified. All numbers expressing quantities of features and physical characteristics used in the specification and claims are to be understood as being modified in all instances by the term "about" unless otherwise indicated. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can be varied appropriately by those skilled in the art utilizing the desired properties sought to be obtained by the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers subsumed within that range and any range within that range, e.g., 1 to 5 includes 1, 1.2, 1.4, 1.55, 2, 2.75, 3, 3.80, 4, 5, and the like.

It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus; the term "preferred" refers to a preferred option, but is not limited to the option selected.

With the rapid development of modern technology, lithium ion secondary batteries are widely used due to their high energy density, long cycle life and no memory effect. Polymer solid electrolytes are receiving considerable attention for their excellent processability and high adaptability to the shape of the battery. However, the current polymer solid electrolyte has problems of curing shrinkage during the preparation process and solid-liquid separation phenomenon after curing, which may cause degradation of battery performance.

Therefore, the inventor provides a brand new technical realization idea: a novel solid electrolyte prepolymer is prepared by specific chemical components. Through intensive studies, the inventors have found that an alicyclic epoxy monomer having an ester group and/or an epoxy monomer having an ester group and a heterocyclic group having a plurality of (at least three) epoxy groups is a preferable polymer monomer, and epoxy groups in these monomers can form a strong crosslinked structure during curing, thereby obtaining a solid electrolyte having a small curing shrinkage and excellent mechanical properties.

In an exemplary embodiment, the first monomer is selected from compounds of formula I-A or formula I-B:

The ester group (-COO-) in the first monomer is a polar functional group with a high dipole moment. From a molecular dynamics point of view, the main role played by the ester groups in the polymer is to increase intermolecular interactions, in particular hydrogen bonding and dipole-dipole interactions. This enhanced intermolecular interaction contributes to the formation of a stable, uniform solid electrolyte structure. From an electrochemical point of view, the polar nature of the ester groups may enhance the transport properties of lithium ions. The ester group can provide a better dissolution and migration environment for lithium ions, thereby being beneficial to improving the lithium ion conductivity of the solid electrolyte. In addition, the ester group can also interact with other components (such as a plasticizer, a solvent and the like), so that the compatibility of the whole system is improved, and the phenomena of solidification shrinkage and solid-liquid separation in the solidification process are reduced.

The cycloaliphatic group in the first monomer is non-polar and provides hydrophobicity and rigidity to the polymer. The rigidity of the alicyclic structure may enhance the mechanical strength of the polymer, thereby avoiding electrolyte rupture due to mechanical stress during battery operation. Meanwhile, the hydrophobicity can reduce the content of water molecules in the electrolyte, thereby improving the chemical stability of the battery.

The heterocyclic groups in the first monomer, especially nitrogen, oxygen or sulfur containing heterocycles, have a certain polarity. Like the ester groups, these heterocyclic groups can enhance intermolecular interactions and provide better lithium ion transport channels. This feature helps to increase the conductivity of the solid state electrolyte. Heterocyclic groups may also provide additional functional groups, such as amino, hydroxyl or thiol groups, which may further enhance intermolecular interactions, especially in crosslinked polymers.

The epoxy group in the first monomer is a highly reactive three-membered ring structure. In the preparation of solid electrolytes, epoxy groups may react with initiators or other functional groups (e.g., hydroxyl groups, amine groups, etc.) to form crosslinked structures. The crosslinked structure can greatly enhance the mechanical strength and thermal stability of the polymer. The highly crosslinked structure makes the polymer more uniform and stable, thereby reducing cure shrinkage and solid-liquid separation during curing. The crosslinked structure may also limit the movement of the polymer chains, thereby reducing the migration obstruction of lithium ions in the polymer, which means that the crosslinked structure helps to increase the lithium ion conductivity of the solid state electrolyte. Meanwhile, due to the high reactivity of the epoxy group, the epoxy group can also react with other functional groups to form various crosslinking points, so that the crosslinking density and stability of the polymer are further improved.

Further, the inclusion of multiple (at least three) epoxy groups in the first monomer means that the solid electrolyte can form multi-site crosslinks during curing, resulting in a more uniform and stable three-dimensional network structure. The network structure is beneficial to reducing shrinkage in the curing process, ensuring close contact between the solid electrolyte and the electrode, and reducing the internal impedance of the battery.

In addition, the inventor finds that the alicyclic epoxy monomer containing the ester group and the heterocyclic group have lower HOMO energy level, and the polymer formed by polymerization of the alicyclic epoxy monomer has excellent electrochemical stability and voltage resistance, does not generate free carbonyl at high voltage (more than 4.6V), can be matched with a high-voltage positive electrode, and is beneficial to improving the energy density of a battery. The first monomer has a lower HOMO level because it contains polar groups such as ester groups. These polar groups can form coordination bonds or solvation with lithium ions by dipole-dipole interactions or hydrogen bonding, etc. This results in a complex or solution system between the lithium ions and the first monomer in which the lithium ions absorb some of the electrons from the first monomer, thereby lowering the HOMO level of the first monomer. This phenomenon is known as the charge transfer effect, and affects the electronic structure and energy level distribution of molecules.

Note that HOMO (Highest Occupied Molecular Orbital) is an occupied molecular orbital having the highest energy in a molecule. The HOMO level is a major factor determining the electron loss capability of a species upon oxidation. A lower HOMO means that the molecule requires more energy to remove an electron when oxidized. Molecules in the electrolyte are more easily oxidized when the battery is operated at high voltage. If the HOMO energy level of a molecule is low, it requires more energy to oxidize. This means that molecules with low HOMO levels are more difficult to oxidize than molecules with higher HOMO levels at the same voltage.

The electrochemical stability of an electrolyte means that the electrolyte does not react poorly with the electrodes over the voltage range in which the battery operates. Molecules with low HOMO levels are less likely to react chemically with the positive electrode because they are more difficult to oxidize, thereby improving electrochemical stability. Many organic molecules, particularly those containing oxygen functionality, are susceptible to decomposition at high voltages, yielding free carbonyl groups. The free carbonyl group is a highly reactive functional group that readily reacts with the electrode or other electrolyte molecule, resulting in reduced cell performance. Since the HOMO levels of the alicyclic epoxy monomer containing an ester group and the epoxy monomer containing an ester group and a heterocyclic group are lower, it is more difficult to oxidize at high voltages, which reduces the possibility of decomposition to produce free carbonyl groups.

The initiator is an important component of the solid electrolyte pre-polymerization solution, which can promote the ring-opening polymerization reaction between the first monomers, thereby realizing rapid and uniform curing. The type and amount of initiator may be selected as appropriate to control the rate and extent of the curing reaction. Generally, initiators can be divided into thermal initiators and photoinitiators. Thermal initiators refer to compounds capable of generating active species such as radicals or cations under heating conditions, such as persulfates, azo compounds, peroxides, and the like. Photoinitiators refer to compounds capable of generating active species such as free radicals or cations under light conditions, e.g., benzophenone, thiol, aromatic amine, and the like.

Preferably, the initiator is lithium tetrafluoroborate (LiBF ₄ ). In the solid electrolyte prepolymer liquid, lithium tetrafluoroborate can be co-initiated with trace water to generate Lewis acid active centers, and the first monomer is induced to undergo ring-opening polymerization reaction, wherein the principle of the polymerization reaction is cationic polymerization. At the moment, lithium tetrafluoroborate is used as a carrier and an initiator, so that the problem that the battery is negatively influenced by the residual initiator in the traditional gel electrolyte system, such as gas generation of the initiator, is avoided. In addition, lithium tetrafluoroborate can precede lithium hexafluorophosphate (LiPF ₆ ) And a polymerization active center is formed, so that side reactions caused by further decomposition of lithium hexafluorophosphate are avoided. In addition, compared with the conventional method which uses lithium hexafluorophosphate as an initiator, the method which uses lithium tetrafluoroborate as the initiator for the polymerization of the first monomer is beneficial to reducing the curing temperature (the curing can be initiated at about 45 ℃), and avoids the influence of high temperature on the battery performance.

Lithium tetrafluoroborate is a commonly used lithium salt for lithium ion batteries, which has high solubility and low viscosity and can provide high lithium ion conductivity. The lithium tetrafluoroborate also has higher thermal stability and chemical stability, can be kept stable at high temperature and high voltage, and is not easy to decompose or react. In the solid electrolyte prepolymer liquid, lithium tetrafluoroborate is used as a carrier and an initiator, and can be co-initiated with trace water to generate Lewis acid active centers to induce a first monomer to perform ring-opening polymerization reaction.

The principle of co-initiating lithium tetrafluoroborate with trace water to generate Lewis acid active centers is as follows: when lithium tetrafluoroborate is dissolved in a plasticizer solution containing trace amounts of water, the following hydrolysis reaction occurs:

LiBF ₄ +H ₂ O→LiOH+HBF ₄

in this reaction, lithium tetrafluoroborate undergoes nucleophilic substitution reaction with water molecules to produce lithium hydroxide and tetrafluoroboric acid. Among them, tetrafluoroboric acid is a strong Lewis acid that coordinates with the epoxy groups in the epoxy monomer, thereby opening the epoxy ring and creating a cationic active center. These cationic active centers are capable of ring-opening polymerization with other epoxy monomers to form a crosslinked network structure. The type of such polymerization is cationic polymerization.

The lithium tetrafluoroborate is used as the initiator, so that the problem that the battery is negatively influenced by the residual initiator in the traditional gel electrolyte system is avoided. Initiators commonly used in conventional gel electrolyte systems, such as persulfates, azo compounds, peroxides, etc., generate certain amounts of free radicals or small molecule products during the curing process, which can have some negative effects on the cell, such as gassing, swelling, aging, etc. While lithium tetrafluoroborate is used as an initiator, no free radical or small molecular product is generated in the curing process, and no harmless LiOH and HBF are generated ₄ These products can form a complex or solution system with other components without any effect on the battery.

Meanwhile, side reactions caused by further decomposition of lithium hexafluorophosphate are avoided. Lithium hexafluorophosphate is another commonly used lithium salt for lithium ion batteries, which has higher solubility and higher lithium ion conductivity. However, lithium hexafluorophosphate also has low thermal and chemical stability, and it is susceptible to decomposition or reaction at high temperatures and high voltages, producing some deleterious products such as PF ₅ 、PF ₃ 、POF ₃ HF, etc. These products can have some negative impact on the cell, such as corrosion, oxidation, reduced conductivity, etc. And lithium tetrafluoroborate is used as an initiator, and the lithium tetrafluoroborate and trace water react at a high speed, so that a polymerization active center can be formed before lithium hexafluorophosphate, further decomposition of the lithium hexafluorophosphate is inhibited, and the safety and performance of the battery are protected.

And, lithium tetrafluoroborate can lower the curing temperature because it has higher reactivity and lower activation energy, and can initiate the ring-opening polymerization reaction of the first monomer at a lower temperature. Reactivity refers to the ability of a molecule to react, and is affected by factors such as the structure and electronic state of the molecule. Activation energy refers to the minimum energy required for a molecule to react and reflects the ease and rate of reaction. Generally, the higher the reactivity, the lower the activation energy, the more readily the reaction occurs, and the faster the reaction rate.

Lithium tetrafluoroborate has high reactivity because it contains fluorine atoms with strong electronegativity and boron atoms with weak electronegativity, which makes it have a large dipole moment and polarization ability. Dipole moment refers to the product of the distance and magnitude between positive and negative charges in a molecule, and reflects the degree of non-uniformity of the charge distribution in the molecule. Polarizability refers to the attractive interaction between positive and negative charges in a molecule, which reflects the degree of stability of the charge distribution in the molecule. In general, the larger the dipole moment, the more polarizable the molecule will be and the more susceptible the molecule will interact and react with other molecules. The lithium tetrafluoroborate has larger dipole moment and polarization capacity due to the fluorine atoms with strong electronegativity and the boron atoms with weak electronegativity, so that the lithium tetrafluoroborate has higher reactivity.

Lithium tetrafluoroborate has a low activation energy because it co-initiates with trace amounts of water to form Lewis acid active centers that can coordinate with the epoxy groups in the epoxy monomer, thereby opening the epoxy ring and forming cationic active centers. These cationic active centers are capable of ring-opening polymerization with other epoxy monomers to form a crosslinked network structure.

The main functions of the plasticizer solution are to increase the flexibility of the polymer, to improve its compatibility with lithium salts and electrode materials, and to improve the ion transport properties of the electrolyte. The plasticizer solution can improve the solubility and compatibility between the first monomer and the initiator, thereby improving the flowability and uniformity of the prepolymer solution. The plasticizer solution can also adjust the viscosity and surface tension of the prepolymer solution, thereby facilitating the coating or injection of the prepolymer solution on the electrode. The plasticizer solution can also increase the solubility of lithium salts and lithium ion conductivity in the prepolymer solution, thereby improving the electrochemical performance of the electrolyte. The plasticizer solution may include one or more organic solvents and one or more lithium salts and one or more additives.

Specifically, the plasticizer solution includes a solvent, an additive, and a lithium salt. Wherein, the mass fraction of the solvent in the plasticizer solution can be 50-70%; for example, 50%, 58.3%, 60%, 65%, 68%, 70%, etc.; of course, other values between 50 and 70% are also possible, without limitation. The mass fraction of the additive in the plasticizer solution can be 5-15%; for example, 5%, 5.2%, 6%, 8%, 13%, 15%, etc. may be mentioned; of course, other values between 5 and 15% are also possible, without limitation. The mass fraction of the lithium salt in the plasticizer solution can be 20-40%; for example, 20%, 23.5%, 28%, 30%, 36%, 40%, etc.; of course, other values between 20 and 40% are also possible, without limitation.

It should be noted that the solvent is the main component of the plasticizer solution, and is mainly used to dissolve other components, such as additives and lithium salts, to form a uniform liquid system. It provides a medium for the other components so that they can be dispersed and uniformly present at the microscopic level, thereby forming a uniform prepolymer solution. The solvent can also adjust the viscosity and surface tension of the prepolymer solution, thereby affecting the mobility and wettability of the prepolymer solution on the electrode. In the present invention, the mass fraction of the solvent in the plasticizer solution is 50 to 70%, because if the mass fraction of the solvent is too low, the first monomer and the initiator may not be sufficiently dissolved and mixed, and are too viscous, thereby affecting the uniformity of the prepolymer; if the mass fraction of the solvent is too high, it may cause the viscosity of the prepolymer to be too low, thereby affecting the stability of the prepolymer on the electrode and possibly reducing the ionic conductivity of the electrolyte.

The solvent in the plasticizer solution may be at least one of ethyl propionate, diethyl carbonate, fluoroethylene carbonate, and ethylene carbonate. These solvents have both a higher solubility and a lower viscosity, enabling the first monomer and initiator to be fully dissolved and mixed. These solvents also have a high polarity and polarizability and are capable of forming a charge transfer effect with the first monomer and the initiator. These solvents also have high thermal and chemical stability and are stable at high temperatures and high voltages. Ethyl propionate, diethyl carbonate, fluoroethylene carbonate, ethylene carbonate have viscosities of 0.43, 0.45, 0.46, 0.47 mPa-s, respectively, at 25 ℃ that are much lower than commonly used polymer solid electrolyte solvents such as glycerin (1.41 mPa-s) and ethylene glycol (16.06 mPa-s); the relative dielectric constants at 25℃are 6.02, 3.06, 2.63, 2.75, respectively, which are much higher than common polymer solid electrolyte solvents such as glycerol (42.5) and ethylene glycol (37.7); the decomposition temperatures at 200℃are >250 ℃, >300 ℃, respectively, much higher than the commonly used polymer solid electrolyte solvents such as glycerol (182 ℃) and ethylene glycol (197 ℃).

Further, ethyl propionate, diethyl carbonate, fluoroethylene carbonate, ethylene carbonate can form polar interactions, such as dipole-dipole interactions or hydrogen bonding, with ester groups and heterocyclic groups in the first monomer, so that the solubility and dispersibility of the first monomer are enhanced, and the uniformity of the prepolymer liquid is improved; the epoxy resin can form a charge transfer effect with epoxy groups in the first monomer, so that the HOMO energy level of the first monomer is reduced, the electrochemical stability of the first monomer is improved, the energy difference between the first monomer and the anode is increased, and the possibility of oxidization is reduced; can form pi-pi stacking action with alicyclic groups in the first monomer, thereby increasing the steric hindrance and rigidity of the first monomer and improving the Tg and lithium ion conductivity of the first monomer.

The additives may be used to adjust and optimize the properties of the plasticizer solution, such as to increase the lithium ion transport properties or to improve the stability of the electrolyte, to improve the compatibility between the first monomer and the initiator, and thereby avoid phase separation or precipitation phenomena. The additive also increases the reactivity between the first monomer and the initiator, thereby accelerating the curing reaction. In the present invention, the mass fraction of the additive in the plasticizer solution is 5 to 15%, because if the mass fraction of the additive is too low, insufficient compatibility between the first monomer and the initiator may be caused, thereby affecting the stability of the prepolymer; if the mass fraction of the additive is too high, it may result in too fast a reaction between the first monomer and the initiator, thereby affecting the controllability of the prepolymer solution.

The additive in the plasticizer solution may be at least one of 1, 3-propane sultone, adiponitrile, ethylene glycol bis (propionitrile) ether, 1,3, 6-hexane tri-nitrile. These additives all have good compatibility and can form a uniform mixture with the first monomer and the initiator. These additives are also highly reactive and are capable of forming a synergistic effect with the first monomer and the initiator. These additives are also less toxic and corrosive and can protect the safety and life of the battery. These additives are capable of forming polar interactions, such as dipole-dipole interactions or hydrogen bonding, with the ester groups and heterocyclic groups in the first monomer, thereby enhancing the compatibility between the first monomer and the solvent, avoiding phase separation or precipitation phenomena; can form a synergistic effect with the epoxy group in the first monomer, thereby increasing the reactivity between the first monomer and the initiator, accelerating the curing reaction and shortening the curing time.

Lithium salts are sources that provide lithium ions, which are the primary carriers in lithium ion batteries, to achieve the conductivity function of the electrolyte. During the charge and discharge of the battery, lithium ions migrate between the positive electrode and the negative electrode. The lithium salt can also form a charge transfer effect with the first monomer and the initiator, thereby affecting the HOMO level and electrochemical stability of the first monomer. In the present invention, the mass fraction of the lithium salt in the plasticizer solution is 20 to 40% because if the mass fraction of the lithium salt is too low, the concentration of lithium ions in the prepolymer solution is insufficient, thereby affecting the conductivity of the electrolyte; if the mass fraction of lithium salt is too high, supersaturation of lithium ions in the prepolymer solution may be caused, thereby affecting the uniformity of the electrolyte.

The lithium salt in the plasticizer solution may be at least one of lithium hexafluorophosphate and lithium bis-fluorosulfonyl imide. These lithium salts have high solubility and high lithium ion conductivity and can provide sufficient lithium ions. These lithium salts also have high thermal and chemical stability and are stable at high temperatures and high voltages. These lithium salts also have low water sensitivity and air sensitivity, and can be stored and used at normal temperature and pressure. These lithium salts are capable of forming coordination bonds or solvation with the ester groups and heterocyclic groups in the first monomer, thereby increasing the solubility and lithium ion conductivity of the lithium salts in the prepolymer solution and enhancing the conductivity function of the electrolyte.

The plasticizer solution determines the solubility of lithium salt, the existence state of cationic polymerization active center and the like, and the LiPF in the organic solid electrolyte of the cationic initiation system ₆ The side reactions of decomposition are more pronounced. The formula of the invention designs different types of plasticizers, and the content of the plasticizers comprises main solvents, additives, lithium salt proportions and the like in the plasticizers. The side reaction of further decomposition of lithium salt is inhibited, a plasticizer system with moderate DN value (quantitative description of Lewis acid) is obtained, and the pH value of electrolyte after solidification is kept balanced. The design is favorable for improving the acid-base stability of the organic solid electrolyte and the pole piece, and the corresponding semi-solid battery can obtain better performance. In addition, the invention performs design experiments related to the compatibility of the components of the plasticizer with the polymer material, for example, solvents which are easy to cause gas generation, such as hexanediol Diether (DEC) and the like, are avoided in the system.

In the solvent of the plasticizer, the ester solvent can generate similar compatibility with-COO-and-O-chain segments in the main chain of the solid electrolyte polymer, so that the interaction between the polymer chain and the plasticizer is improved, and the absorption capacity of the polymer to the plasticizer is further enhanced. The characteristics are beneficial to improving the compatibility of the polymer and the plasticizer solution, and avoid the problems of solid-liquid separation and the like.

In an exemplary embodiment, the main composition of the plasticizer system is as follows: 10-15% Ethyl Propionate (EP), 25-40% diethyl carbonate (DEC), 2-10% fluoroethylene carbonate (FEC), 1-15% Ethylene Carbonate (EC), 1-5% 1, 3-propane sultone (1, 3-PS), 1-5% Adiponitrile (AND), 1-5% ethylene glycol bis (propionitrile) ether (DENE), 1-5% 1,3, 6-Hexanetrinitrile (HTCN), 10-40% lithium hexafluorophosphate (LiPF) ₆ ) And 10 to 40% lithium bis (fluorosulfonyl) imide (LiFSI).

In an exemplary embodiment, the solid electrolyte pre-polymerization solution provided by the present invention further includes a second monomer for copolymerizing with the first monomer. The simple first monomer may have steric hindrance problems during polymerization, and may result in lower polymerization degree to affect electrolyte performance. This example modifies the first monomer polymer system by copolymerization with the second monomer to further improve the performance of the solid state electrolyte. The second monomer may be at least one of a heterocyclic compound, a vinyl ether compound, and a polyvinyl alcohol nitrile compound. Most of the compounds are ether compounds with flexible chains, have strong solvation capability, are more favorable for transmitting lithium ions and improve the conductivity of the organic solid electrolyte. The mechanism of participation of the ether flexible chain in polymerization is more beneficial to improving the flexibility of the molecular chain, the reactivity of the monomer, the toughening effect and the like.

The first monomer mainly includes an alicyclic epoxy monomer having an ester group or an epoxy monomer having an ester group and a heterocyclic group. The complex structure of the first monomer may lead to steric hindrance at the time of polymerization, which may affect the degree and speed of polymerization. Steric hindrance is caused by the complexity and bulk size of the molecular structure. When certain large and/or structurally complex monomers participate in the reaction, their steric structure may prevent access to the reaction center and the reaction. Such obstruction can reduce the rate of polymerization reactions, potentially leading to incomplete polymerization and low degrees of polymerization.

The second monomer such as heterocyclic compounds, vinyl ether compounds, and polyvinyl alcohol nitriles compounds generally have a relatively simple structure. Such structures do not readily cause steric hindrance and thus can participate more readily in the reaction. The ether chains contained in the vinyl ether compounds and the polyvinyl alcohol nitrile compounds are flexible, the flexible chains have higher mobility and plasticity, and the flexible chains can improve the flexibility and flowability of the polymer chains, and can provide a certain space among molecules, so that the reaction center is easier to access, and the steric hindrance is reduced. The second monomer participates in copolymerization to break the regularity and symmetry of the polymer chain of the first monomer, thereby increasing the randomness and asymmetry of the polymer chain and reducing the steric hindrance of the first monomer.

The coexistence of the first monomer and the second monomer may lead to a synergistic effect during the polymerization. The second monomer may act as a seed to help the first monomer polymerize more efficiently or form a synergistic segment with the first monomer, thereby reducing overall steric hindrance.

Specifically, the heterocyclic compound may be at least one of an epoxy compound, an oxetane compound, an isopentane compound, a furan ring compound, and a pyridine compound. The vinyl ether compound may be at least one of vinyl methyl ether, vinyl ethyl ether, and vinyl phenyl ether. The polyvinyl alcohol nitrile compound may be at least one of polyvinyl alcohol acetonitrile, polyvinyl alcohol malononitrile, polyvinyl alcohol acrylonitrile, polyvinyl alcohol isovaleronitrile, polyvinyl alcohol cyclopentylpropionitrile, and the like.

In an exemplary embodiment, in the solid electrolyte pre-polymerization solution, the mass fraction of the first monomer is 5-15%, and the molar ratio of the first monomer to the second monomer is 1: (0.2-3).

In one embodiment, the invention also provides a solid electrolyte which is formed by solidifying a solid electrolyte prepolymer containing the monomer shown in the formula I-A through cationic polymerization. The solid electrolyte comprises a polymer molecular chain with a structure shown in a formula III:

Wherein the multi-membered ring can be a four-membered ring, a five-membered ring, a six-membered ring and the like, R can be a chain group containing an epoxy functional group or a branched chain containing both an ester group and an epoxy group, n is a positive integer, n ₁ Is a positive integer of 2 or more.

In an exemplary embodiment, the solid electrolyte is formed from a solid electrolyte pre-polymer solution comprising the aforementioned first monomer (formula I-A) and a second monomer by cationic polymerization. The solid electrolyte comprises a polymer molecular chain with a structure shown in a formula IV:

wherein the multi-membered ring can be a four-membered ring, a five-membered ring, a six-membered ring and the like, R can be a chain group containing an epoxy functional group or a branched chain containing both an ester group and an epoxy group, n is a positive integer, n ₁ 、n ₂ Is a positive integer, and is not less than 20 and not more than n ₁ ≤30，n ₁ And n ₂ The ratio of (2) to (3) is 1. Although the degree of crosslinking formed by the simple in-situ solidification of the first monomer is larger, the formed organic solid electrolyte is favorable for improving the safety performance, the polymerization of the material has larger steric hindrance, and the conductivity of the formed organic solid electrolyte is smaller. After the second monomer is compounded to serve as a comonomer, the conductivity of the organic solid electrolyte is improved, the comprehensive performance of the material is further improved, but excessive second monomers can cause the heat resistance of the material to be reduced, and the safety performance is not facilitated. And n is to ₁ And n ₂ The ratio of (2) is limited to 1 (0.2-3), which is favorable for obtaining the material with both safety performance and electrochemical performance.

In one embodiment of the present invention, there is also provided an electrochemical device comprising a solid electrolyte as described above.

The invention also provides a battery preparation method, which specifically comprises the following steps:

s101: and uniformly mixing the monomer, the initiator and the plasticizer solution to obtain the solid electrolyte prepolymer.

The monomers in step S101 include at least the aforementioned first monomer including at least one of an alicyclic epoxy monomer containing an ester group, an epoxy monomer containing an ester group and a heterocyclic group, and the first monomer contains at least three epoxy groups.

S102: and injecting the solid electrolyte prepolymer into the soft package battery to complete the battery assembly.

In step S102, the solid electrolyte pre-polymerization solution is injected into the soft package battery, and the solid electrolyte pre-polymerization solution is in a liquid state, so that the wettability of the solid electrolyte pre-polymerization solution to the positive and negative electrodes of the battery cell is excellent, and then the solid state battery in contact with the positive and negative electrodes at molecular level is obtained by performing cationic polymerization and thermal curing, so that the interface performance is greatly improved. The positive electrode of the battery is high-nickel ternary, the negative electrode of the battery is graphite or silicon-based, and the diaphragm is a porous framework material such as polypropylene, polyethylene or a cellulose film.

S103: and (3) standing the assembled battery for a period of time, and heating to enable the solid electrolyte prepolymer to undergo cationic polymerization reaction so as to solidify and form the solid electrolyte.

The heating temperature in step S103 is 40 to 80℃and may be, for example, 40℃45℃50℃55℃60℃65℃70℃75℃80℃or the like, but may be any other value within 40 to 80℃and is not limited thereto. The cationic polymerization reaction time is 5 to 24 hours, and may be, for example, 5 hours, 6 hours, 8 hours, 10 hours, 12 hours, 15 hours, 17 hours, 20 hours, 21 hours, 22 hours, 23 hours, or 24 hours, or other values within the above range, and the present invention is not limited thereto.

S104: and performing processes such as formation, aging, packaging, capacity division and the like on the battery after the solidification, and thus, the preparation of a finished battery is completed.

The invention will be further illustrated with reference to specific examples.

Example 1

5 parts by mass of a first monomer (structural formula shown as formula I-A1), 1 part by mass of an initiator (lithium tetrafluoroborate) and 94 parts by mass of a plasticizer solution (comprising 14wt% of ethyl propionate, 40wt% of diethyl carbonate, 3wt% of fluoroethylene carbonate, 13wt% of ethylene carbonate, 5.7wt% of 1, 3-propane sultone, 1.3wt% of adiponitrile, 2wt% of ethylene glycol bis (propionitrile) ether, 1wt% of 1,3, 6-hexanetrinitrile, 10wt% of lithium hexafluorophosphate and 10wt% of lithium difluorosulfonimide) were uniformly mixed to obtain a solid electrolyte prepolymer.

And (3) injecting the solid electrolyte prepolymer into the soft package battery in a drying room (the relative humidity is lower than 2 percent and the dew point is lower than-40 ℃), and completing battery assembly.

And standing the assembled battery for 24-72 h at room temperature, transferring the assembled battery into a hot oven, slowly heating to 60 ℃ for reaction for 6h, and enabling the solid electrolyte prepolymer to undergo cationic polymerization reaction so as to be solidified into the solid electrolyte.

The battery after curing is subjected to the procedures of formation, aging, packaging, capacity division and the like, and a finished battery (the negative electrode of the battery is natural graphite, the positive electrode is NCM523, and the nominal capacity is 1.7 Ah) is prepared.

Example 2

The first monomer in example 1 was replaced with a monomer having the structural formula of I-B1, and the other preparation conditions were the same as in example 1 to prepare a finished battery.

Example 3

The first monomer in example 1 was replaced with a monomer having the structural formula of i-B2 (where i=m=n=2), and the other preparation conditions were the same as in example 1, to prepare a finished battery.

Example 4

The first monomer in example 1 was replaced with a monomer having the structural formula of i-B3 (where i=m=n=o=2), and the other preparation conditions were the same as in example 1, to prepare a finished battery.

Example 5

The first monomer in example 1 was replaced with a monomer having the structural formula of I-B4, and the other preparation conditions were the same as in example 1 to prepare a finished battery.

Example 6

The first monomer in example 1 was replaced with a mixture of 2.91 parts by mass of the first monomer (structural formula shown as formula I-A1) and 2.09 parts by mass of the second monomer (structural formula shown as formula II-1), the molar ratio of the first monomer to the second monomer was 1:1, and the other production conditions were the same as in example 1, to produce a finished battery.

Example 7

The second monomer in example 6 was replaced with a monomer having a structural formula shown in formula II-2, wherein the mass of the first monomer was 4.03 parts by mass, the mass of the second monomer was 0.97 parts by mass, the molar ratio of the first monomer to the second monomer was 1:1, and the other preparation conditions were the same as in example 6, to prepare a finished battery.

Example 8

The second monomer in example 6 was replaced with a monomer having a structural formula of formula II-3, wherein the mass of the first monomer was 4.01 parts by mass, the mass of the second monomer was 0.99 parts by mass, the molar ratio of the first monomer to the second monomer was 1:1, and the other preparation conditions were the same as in example 6, to prepare a finished battery.

Example 9

The second monomer in example 6 was replaced with a monomer having the structural formula of formula ii-4 (where m=20, n=5), wherein the mass of the first monomer was 1.45 parts by mass, the mass of the second monomer was 3.55 parts by mass, the molar ratio of the first monomer to the second monomer was about 1:1, and the remaining production conditions were the same as in example 6, to produce a finished battery.

Example 10

The second monomer in example 6 was replaced with a monomer having a structural formula shown in formula II-5, wherein the mass of the first monomer was 3.27 parts by mass, the mass of the second monomer was 1.73 parts by mass, the molar ratio of the first monomer to the second monomer was 1:1, and the other preparation conditions were the same as in example 6, to prepare a finished battery.

Example 11

The second monomer in example 6 was replaced with a monomer having a structural formula of formula ii-6 (where n=25), wherein the mass of the first monomer was 0.44 parts by mass, the mass of the second monomer was 4.56 parts by mass, the molar ratio of the first monomer to the second monomer was about 1:1, and the other production conditions were the same as in example 6, to prepare a finished battery.

Example 12

The mass of the first monomer in example 6 was replaced with 2.05 parts by mass and the mass of the second monomer was replaced with 2.95 parts by mass, so that the molar ratio of the first monomer to the second monomer was 1:2, and the other production conditions were the same as in example 6, to prepare a finished battery.

Example 13

The mass of the first monomer in example 6 was replaced with 1.58 parts by mass and the mass of the second monomer was replaced with 3.42 parts by mass, so that the molar ratio of the first monomer to the second monomer was 1:3, and the other production conditions were the same as in example 6, to prepare a finished battery.

Example 14

The mass of the first monomer in example 6 was replaced with 3.68 parts by mass and the mass of the second monomer was replaced with 1.32 parts by mass, so that the molar ratio of the first monomer to the second monomer was 2:1, and the other production conditions were the same as in example 6, to prepare a finished battery.

Example 15

The mass of the first monomer was replaced with 4.03 parts by mass and the mass of the second monomer was replaced with 0.97 parts by mass in example 6 so that the molar ratio of the first monomer to the second monomer was 3:1, and the other production conditions were the same as in example 6, to prepare a finished battery.

Comparative example 1

The first monomer in example 1 was replaced with a monomer having a structural formula shown in formula iv (containing two epoxy groups), and the remaining preparation conditions were the same as those in example 1, to prepare a finished battery.

Comparative example 2

The first monomer in example 1 was replaced with a second monomer having a structural formula of II-1, and the other preparation conditions were the same as in example 1 to prepare a finished battery.

Performance testing

(1) Thermal stability test

The German relaxation-resistant STA 449F 5 series thermogravimetric differential thermal analyzer is adopted, a high-pressure crucible is equipped for testing, a liquid sample to be tested is added into the stainless steel gold-plated high-pressure crucible, a crucible cover is covered, the volatilization loss of a sample caused by heating is avoided, the heat change caused by the self decomposition of the sample in the heating process is analyzed, and the thermal stability of the sample is judged.

(2) Infrared spectroscopic analysis

The infrared spectrograms of the solid electrolyte pre-polymer solution before and after curing were analyzed by using a Nicolet iS50 Fourier transform infrared spectrum analyzer manufactured by Thermo-Fisher company of America. The test range is 3000-600cm ^-1 。

(3) Capacity of 0.5 g

The solid electrolyte prepolymer is injected into an assembled battery core, short-term performance testing is completed through the steps of pre-sealing, standing, solidifying, forming, aging, secondary sealing and capacity division according to the process of a soft package battery, and in the capacity division step, the clamp pressure is 3.5N, 0.5C/0.5C charge and discharge is carried out once (2.75V-4.2V), so that the discharge capacity is obtained, and the gram capacity is calculated according to the amount of active substances.

(4) Low temperature cycle performance

Charging at 0℃at 0.5C/0.5C, CC+CV/CC: constant current (4.2V) +constant voltage (0.025C) discharge: constant current (2.75V).

(5) Rate capability

Multiplying power charging: (1) discharge to 2.75V at a given current of 0.2C, rest for 10min. (2) Charging to cut-off voltage of 4.2V with constant current of 0.2C, charging to cut-off current of 0.025C with constant voltage of 4.2V, and standing for 10min. (3) Charging to a termination voltage of 2.75V at a given current of 0.2C, and standing for 10min after discharging is finished; recorded as initial cell capacity. (4) Then charging to 4.2V with given current, stopping at 0.025C, and standing for 10min. (5) Then discharging to the end voltage of 2.75VV by constant current of 0.2C, and standing for 10min after the discharge is finished. (6) Repeating steps (4) and (5), wherein the given current of step (4) is 0.5C, 1.0C, 2.0C, 3.0C, respectively.

Multiplying power discharge: (1) discharge to 2.75V at a given current of 0.2C, rest for 10min. (2) Charging to cut-off voltage of 4.2V with constant current of 0.2C, charging to cut-off current of 0.025C with constant voltage of 4.2V, and standing for 10min. (3) Discharging to a termination voltage of 2.75V at a given current of 0.2C, and standing for 10min after the discharge is finished; recorded as initial cell capacity. (4) Charging to 4.2V with charging current of 0.2C and constant voltage, cutting off current of 0.025C, and standing for 10min. (5) Then discharging with given current to a final voltage of 2.75V, and standing for 10min after discharging is finished. (6) Repeating steps (4) and (5), wherein the given current of step (5) is 0.5C, 1.0C, 2.0C, 3.0C, 5.0C, 7C, respectively.

(6) Soft package battery gas production test

The volume of the cell was tested by archimedes principle (drainage method): (1) the density of the medium (silicone oil) was tested. (2) The battery measurement assembly is placed onto the load cell. (3) And (3) controlling and displaying the numerical value of the weighing module through APW software, and peeling after the numerical value is stable. (4) Reading out the battery mass m ₁ Then adding medium, reading m after the sensor is stable ₂ Battery volume v= (m ₁ -m ₂ ) 1000/0.95;0.95 is the density of the silicone oil and the unit of gas volume V is mL.

By the method, the volumes of the battery before and after gas production are tested to obtain the gas production delta V. And carrying out normalization treatment to obtain the unit gas yield delta VQ= [ delta ] V/Q, wherein Q is the discharge capacity (unit Ah) of the battery, and the unit of [ delta ] V ] and [ m ] is mL/Ah.

(7) Hot box test

(1) The assembled battery was charged at a constant current and constant voltage of 1C to the upper limit cutoff voltage of the battery, and the cutoff current was set to 0.05C. (2) The fully charged battery is put into a 25+/-2 ℃ condition test box by adopting a programmed cold-hot circulation temperature impact box (BTT-150 CS), the test box is heated at the temperature rising rate of (5+/-2) DEG C/min, and the temperature is kept constant for 30min after the temperature in the box reaches 130+/-2 ℃. (3) After the steps are finished, the battery is observed for 60min in an experimental environment, and the battery is judged to pass the hot box test without fire, explosion or liquid leakage, or else, the battery is judged to not pass the hot box test.

FIG. 1 is a comparative graph of the solid electrolyte pre-polymer solutions of example 1 and comparative example 1 of the present invention after curing; as can be seen from FIG. 1, the precipitation liquid of example 1 was smaller, indicating that the shrinkage after polymerization of the alicyclic epoxy monomer having an ester group having a plurality of (at least three) epoxy groups was small.

FIG. 2 is an elastic modulus test chart of the solid electrolyte in example 1 and comparative example 1 of the present invention; the elastic modulus of example 1 was 0.75MPa and the elastic modulus of comparative example 1 was 0.55MPa, which indicates that the solid electrolyte of example 1 had better mechanical properties.

FIG. 3 is a graph showing DSC test results of a solid electrolyte and a corresponding liquid plasticizer in example 1 of the present invention; as can be seen from fig. 3, the peak exothermic temperature of the solid electrolyte in example 1 was raised from 218 ℃ to 278 ℃ compared to the corresponding liquid plasticizer, which indicates that the solid electrolyte in example 1 has better heat resistance and the corresponding semi-solid battery has better safety performance.

FIG. 4 is an infrared spectrum of the solid electrolyte pre-polymer solution before and after curing in example 1 of the present invention; the solid electrolyte prepolymer in example 1 was subjected to infrared spectroscopic test by a different sample preparation method by removing the low boiling point solvent by rotary evaporation or volatilization, 910cm ^-1 Is a characteristic peak of the first monomer; as can be seen from FIG. 4, after curing, the characteristic peak is 910cm ^-1 The disappearance indicates that the first monomer has been completely converted to polymer, and the system has no problem of influence of monomer residue on battery performance.

FIG. 5 is a graph showing the gram capacity distribution of a parallel sample finished battery in example 1 of the present invention; as can be seen from fig. 5, the 0.5C gram capacity of the battery of example 1 exhibited 150mAh/g, and the stability between parallel samples was good.

FIG. 6 is a graph showing a cycle of 0.5C/0.5C at 0deg.C for the finished cell of example 1 of the present invention; as can be seen from fig. 6, the finished battery in example 1 was reduced to 80% in discharge capacity after 73 cycles at 0C with 0.5C/0.5C charge-discharge cycles, and had a good low-temperature cycle performance.

Fig. 7 is a rate graph of the finished battery in example 1 of the present invention; as can be seen from fig. 7, the finished battery in example 1 had a 3C/0.2C rate charge retention of 73.2% and a 7C/0.2C rate discharge retention of 92.3%.

Table 1 shows the test results of the 0.5C gram capacity performance, low temperature cycle performance, rate capability, battery gassing test and hot box test of each of the examples and comparative examples of the present invention.

TABLE 1 Performance test results for each of the examples and comparative examples of the present invention

From the results of the performance tests shown in Table 1, it is evident from the comparison of examples 1 to 5 of the present invention and comparative examples 1 to 2 that the battery properties obtained in examples 1 to 5 of the present invention are significantly better than those of comparative examples 1 to 2, indicating that excellent battery properties can be obtained by using an ester group-containing alicyclic epoxy monomer having at least three epoxy groups as a polymerization monomer.

From the performance test results shown in table 1, it is clear from comparison of the present invention in example 1 and examples 6 to 15 that the first monomer alone was added in example 1 to form a polymer having a high degree of crosslinking and a good heat resistance, and thus being advantageous in obtaining a good safety performance and passing through a hot box. However, the polymerization of the first monomer with high functionality has steric hindrance, so that the crosslinked network with high functionality has weak anti-telescoping capability and is unfavorable for movement of lithium ions, and therefore, the electrochemical performance is poor, and the gram exertion is 152.6mAh/g. Examples 6-15 are the compounding of the first monomer and the second monomer, and a small amount of chain monomers are introduced into the second monomer with high functionality, so that the crosslinking degree of the polymer is reduced, the performance elastic network is facilitated, and the migration rate of lithium ions is improved. Therefore, the electrochemical performance is improved, and the gram performance is improved by 1-2mAh/g. However, when the second monomer is added in excess, for example, examples 9, 11 and 13, the safety performance is lowered and the hot box test cannot be passed. In addition, although excess chain monomers promote the elasticity of the polymer, electrochemical performance is not advantageous because the polar functional groups of the first monomer still determine the conductivity of the formed electrolyte.

In conclusion, the pure first monomer has high crosslinking degree and good heat resistance, and is beneficial to safety performance. The chain-shaped second monomer is compounded, so that the elasticity of the polymer is improved, the electrochemical performance is improved, but the safety performance is reduced. In addition, the simple second monomer has no polar function in the first monomer, so that the electrochemical performance is still poor. Therefore, a small amount of the second monomer is added to the first monomer, and a solution which combines safety performance and electrochemical performance can be obtained.

The foregoing descriptions of specific exemplary embodiments of the present invention are presented for purposes of illustration and description. It is not intended to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application to thereby enable one skilled in the art to make and utilize the invention in various exemplary embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims and their equivalents.

Claims

1. A solid electrolyte pre-polymerization solution, characterized in that the solid electrolyte pre-polymerization solution comprises a first monomer, an initiator and a plasticizer solution;

The first monomer includes at least one of an alicyclic epoxy monomer containing an ester group, an epoxy monomer containing an ester group and a heterocyclic group, and the first monomer contains at least three epoxy groups.

2. The solid state electrolyte pre-polymer solution of claim 1 wherein the first monomer is selected from the group consisting of compounds of formula i-a or formula i-B:

3. The solid state electrolyte pre-polymer solution of claim 1 wherein the initiator is lithium tetrafluoroborate.

4. The solid state electrolyte pre-polymerization solution of claim 1, wherein the plasticizer solution comprises a solvent, an additive, and a lithium salt;

the mass fraction of the solvent in the plasticizer solution is 50-70%, the mass fraction of the additive in the plasticizer solution is 5-15%, and the mass fraction of the lithium salt in the plasticizer solution is 20-40%.

5. The solid state electrolyte pre-polymer solution according to claim 4, wherein the solvent comprises at least one of ethyl propionate, diethyl carbonate, fluoroethylene carbonate, and ethylene carbonate; and/or

The additive comprises at least one of 1, 3-propane sultone, adiponitrile, ethylene glycol bis (propionitrile) ether and 1,3, 6-hexane trinitrile; and/or

The lithium salt comprises at least one of lithium hexafluorophosphate and lithium difluorosulfonimide.

6. The solid state electrolyte pre-polymerization solution of claim 1, further comprising a second monomer comprising at least one of a heterocyclic compound, a vinyl ether compound, and a polyvinyl alcohol nitrile compound.

7. The solid state electrolyte pre-polymerization solution according to claim 6, wherein the heterocyclic compound comprises at least one of an epoxy compound, an oxetane compound, an isopentane compound, a furan compound, and a pyridine compound; and/or

The vinyl ether compound comprises at least one of vinyl methyl ether, vinyl ethyl ether and vinyl phenyl ether; and/or

The polyvinyl alcohol nitrile compound comprises at least one of polyvinyl alcohol acetonitrile, polyvinyl alcohol malononitrile, polyvinyl alcohol acrylonitrile, polyvinyl alcohol isovaleronitrile and polyvinyl alcohol cyclopentyl propionitrile.

8. The solid electrolyte pre-polymerization solution according to claim 6, wherein in the solid electrolyte pre-polymerization solution, the mass fraction of the first monomer is 5 to 15%, and the molar ratio of the first monomer to the second monomer is 1 (0.2 to 3).

9. A solid electrolyte, characterized in that the solid electrolyte is formed by solidifying the solid electrolyte prepolymer liquid according to any one of claims 1 to 8 by means of cationic polymerization.

10. The solid state electrolyte of claim 9, wherein the solid state electrolyte comprises a polymer molecular chain of the structure of formula iii:

11. An electrochemical device comprising the solid electrolyte according to claim 9 or 10.