Preparation method and application of novel flame-retardant solid electrolyte

Abstract

The invention provides a preparation method and application of a novel flame-retardant solid electrolyte, the solid electrolyte material comprises a lithium salt, a polymer matrix and a flame-retardant additive, and the flame-retardant additive comprises polyaromatic nitro cyclotriphosphazene. The flame retardant property and the ionic conductivity of the solid electrolyte material can be improved at the same time.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemistry, in particular to a preparation method of a novel flame-retardant solid-state electrolyte and application thereof. BACKGROUND

[0002] Lithium batteries have become the core energy devices in the fields of consumer electronics, electric vehicles, energy storage systems, etc. due to their advantages of high energy density, high power density and long cycle life, which greatly promote the development of new energy industry. However, the traditional lithium battery generally uses liquid electrolyte with organic solvent as carrier. Such electrolyte has inherent defects of flammability and liquid leakage, and is prone to thermal runaway under extreme conditions such as overcharge, short circuit and high temperature, which may cause fire and explosion accidents.

[0003] In order to fundamentally improve the safety of the battery, researchers have focused on solid-state electrolyte. The solid-state electrolyte itself has non-flammable characteristics, which can not only effectively avoid the risk of thermal runaway of liquid electrolyte, but also inhibit the growth of lithium dendrites, thereby prolonging the battery life. However, the traditional solid-state electrolyte still faces problems of insufficient thermal stability and low ionic conductivity under extreme high temperature environment, which leads to safety hazards of the battery under high temperature or thermal runaway scenarios. In addition, as the key medium for ion transmission, the conductivity of the solid-state electrolyte directly affects the power density and cycle efficiency of the battery. Therefore, the development of solid-state electrolyte materials with high flame retardant performance, excellent thermal stability and high ionic conductivity is a key technical breakthrough for promoting the commercial application of all-solid-state lithium batteries.

[0004] At present, the research of solid-state electrolyte mainly focuses on two directions of polymer-based solid-state electrolyte (SPE) and inorganic solid-state electrolyte. Among them, the polymer-based solid-state electrolyte is widely used due to its good flexibility and easy processing characteristics, but still has the following technical bottlenecks: first, the traditional polymer-based solid-state electrolyte is prone to degradation at high temperature, which leads to electrolyte failure and even thermal runaway, and the thermal stability is insufficient; second, due to the high crystallinity of the polymer matrix and other factors, the transmission path of lithium ions is limited, resulting in low ionic conductivity, which is difficult to meet the demand of high-power batteries. In order to improve its performance, some studies have tried to introduce small molecule flame retardant additives such as phosphate ester and organic phosphorus nitride. However, such small molecule flame retardant agents are prone to migration, and may decompose to generate electrochemically inert products at high temperature, covering the electrode or causing side reactions, thereby damaging the performance of the battery.

[0005] In view of the above technical problems, cyclotriphosphazene, as a phosphorus-based flame retardant with strong structure customization, has become an important research object for improving the comprehensive performance of solid-state electrolytes. Currently, the chemical modification strategies for cyclotriphosphazene mainly include three categories: first, by replacing the chlorine atoms on the cyclotriphosphazene with functional groups such as phenoxy and nitro groups, small molecule derivatives are formed, for example, phenoxy cyclotriphosphazene can interact with the polymer matrix through hydrogen bonds to improve the flame retardant performance, but its molecular weight is relatively low and it is easy to migrate from the electrolyte system, resulting in a decrease in flame retardant effect over time; second, using multifunctional molecules such as pentaerythritol to bridge multiple cyclotriphosphazene units to form a dendritic structure, although this structure can increase the crosslinking density of the flame retardant, the synthesis process is complex, and the introduction of the dendritic structure may further hinder the transport of lithium ions; third, cyclotriphosphazene molecules are crosslinked into a network structure by using curing agents such as epoxy groups and amine groups. For example, after linear phosphazene polymer reacts with epoxy resin to form a crosslinked network, the thermal stability can be improved, but the existing crosslinked structure is mostly linear or low crosslinking degree, which is difficult to form a stable carbonized layer at high temperature, and the regulation effect on the crystallinity of the polymer matrix is limited.

[0006] Although the existing modification strategies have improved the flame retardant performance of solid-state electrolytes to some extent, there are still the following common problems: small molecule flame retardants are prone to migration, resulting in poor long-term stability; the introduction of crosslinked structures may introduce byproducts, affecting the uniformity of the electrolyte. In addition, the addition of traditional flame retardants often accompanies a decrease in ionic conductivity, for example, crosslinked networks may limit the dissociation of lithium salts or the migration path of lithium ions. Finally, the existing flame retardant mechanism mainly relies on free radical capture or carbonized layer oxygen isolation, but lacks a synergistic mechanism.

[0007] In summary, there is still a lack of cyclotriphosphazene-based flame retardant additives that can simultaneously achieve high efficiency and high ionic conductivity in the existing technology. Therefore, how to significantly improve the flame retardant performance of solid-state electrolytes while ensuring that their ionic conductivity is not affected is a technical problem that needs to be solved in the field. SUMMARY

[0008] The present application provides a novel preparation method of flame-retardant solid-state electrolyte and its application, which can significantly improve the flame retardant performance of solid-state electrolyte while ensuring that its ionic conductivity is not affected, effectively overcoming the defects existing in the prior art.

[0009] The present application provides a flame-retardant solid-state electrolyte, which comprises a lithium salt, a polymer matrix and a flame-retardant additive, wherein the flame-retardant additive comprises a polyarylnitro cyclotriphosphazene.

[0010] In the embodiments of the present application, the polyarylnitro cyclotriphosphazene has the structure shown in the following formula 1 or formula 2:

[0011] Formula 1

[0012] Formula 2

[0013] each R in Formula 1 and Formula 2 is independently selected from wherein, represents a connection site with P in Formula 1 or Formula 2;

[0014] each R' in Formula 1 and Formula 2 is independently selected from wherein, represents a connection site with P in Formula 1 or Formula 2.

[0015] In some embodiments, the mass fraction of the polymer matrix is 50%-90%, the mass fraction of the lithium salt is 10%-40%, and the mass fraction of the polyarylnitrocyclotriphosphazene is 1%-25%, based on the total mass of the solid-state electrolyte material.

[0016] In some embodiments, the polymer matrix comprises one or more of polyethylene oxide (PEO), polyethylene glycol (PEG), polyethylene glycol dimethyl ether (PEGDME), polyvinylidene fluoride (PVDF), and polymethyl methacrylate (PMMA).

[0017] In some embodiments, the lithium salt comprises one or more of lithium hexafluorophosphate LiPF6, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB), lithium bisfluorophosphate (LiPO2F2).

[0018] In some embodiments, the solid-state electrolyte material is a solid-state electrolyte film, and the thickness of the solid-state electrolyte film is 5-20 μm.

[0019] In another aspect of the present application, a preparation method of a solid-state electrolyte material is provided, comprising the following preparation steps: mixing raw materials comprising a lithium salt, a polymer matrix, and a flame-retardant additive to obtain the solid-state electrolyte material.

[0020] In some embodiments, the solid-state electrolyte material is a solid-state electrolyte film, and the process of mixing the raw materials comprising the lithium salt, the polymer matrix, and the flame-retardant additive comprises: S1: mixing the polymer matrix with a solvent, and after first stirring, obtaining a first mixed solution; S2: adding the lithium salt to the first mixed solution, and after second stirring, obtaining a second mixed solution; S3: adding the flame-retardant additive to the second mixed solution, and after third stirring, obtaining a third mixed solution; S4: casting the third mixed solution into a film and drying to obtain the solid-state electrolyte film.

[0021] In some embodiments, the solvent in S1 comprises a polar solvent comprising one or more of N-methylpyrrolidone (NMP), tetrahydrofuran, dichloromethane, acetone, dimethylformamide (DMF), anhydrous acetonitrile; and / or, the first stirring temperature is 40-100 ℃; and / or, the second stirring temperature is 40-100 ℃; and / or, the third stirring temperature is 40-100 ℃; and / or, the drying temperature of S4 is 60-120 ℃.

[0022] In another aspect of the present application, a secondary battery is provided, which comprises a positive electrode layer, an electrolyte layer, and a negative electrode layer, the electrolyte layer being located between the positive electrode layer and the negative electrode layer, at least one of the positive electrode layer, the electrolyte layer, and the negative electrode layer containing the solid-state electrolyte material according to any one of claims 1 to 6 or the solid-state electrolyte material prepared according to the method for preparing a solid-state electrolyte material according to claims 7 to 9.

[0023] The present application has at least the following beneficial effects: the flame-retardant solid-state electrolyte provided by the present application comprises polyaryl nitro cyclotriphosphazene flame-retardant additives, which can release phosphorus-containing radicals (to interrupt the combustion chain reaction) and form a dense carbon layer (to isolate oxygen and heat) at high temperatures, thereby achieving gas-phase-solid-phase synergistic flame retardation; on the other hand, the polyaryl nitro cyclotriphosphazene flame-retardant additives can destroy the regular arrangement of the original polymer matrix, reduce the crystallinity of the matrix, thereby increasing the proportion of amorphous regions of the system, providing more transmission paths for lithium ions, thereby improving the ionic conductivity, and ultimately achieving simultaneous optimization of the flame-retardant performance and ionic conductivity of the solid-state electrolyte material. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Impedance spectra of stainless steel symmetric cells assembled for Examples 1-9 and Comparative Examples 1-2 of the present application. DETAILED DESCRIPTION

[0025] In order for those skilled in the art to better understand the scheme of the present application, the present application is further described in detail as follows. The following specific embodiments are only used to describe the principles and characteristics of the present application, and the examples are used to explain the present application, but not to limit the scope of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0026] The present application provides a flame-retardant solid-state electrolyte, which comprises a lithium salt, a polymer matrix, and a flame-retardant additive, the flame-retardant additive comprising polyaryl nitro cyclotriphosphazene.

[0027] According to the research of the inventor, the introduction of a flame-retardant additive in a solid-state electrolyte generally causes an increase in the crystallinity of the solid-state electrolyte or hinders the dissociation of lithium salt, thereby reducing the ionic conductivity of the solid-state electrolyte, making it difficult to balance the flame-retardant performance and the conductive performance; in addition, existing flame-retardant additives mostly rely on a single mechanism, such as gas-phase free radical capture or solid-phase carbon layer oxygen isolation, and lack the synergistic effect of multiple mechanisms, limiting the comprehensive flame-retardant efficiency. However, in the above-mentioned solid-state electrolyte composition system of the embodiments of the present application, by introducing a polyaromatic nitro cyclotriphosphazene flame-retardant additive, the synergistic effect of the flame-retardant mechanism is achieved. The flame-retardant additive can release phosphorus-containing free radicals at high temperatures, effectively block the combustion chain reaction, and form a dense carbon layer on the surface of the material to isolate oxygen and heat, thereby synergistically playing a flame-retardant role at the gas and solid phases.

[0028] In addition, the polyaromatic nitro cyclotriphosphazene flame-retardant additive can destroy the regular arrangement of the original polymer matrix, reduce the crystallinity of the matrix, thereby increasing the proportion of amorphous regions in the system, providing more transmission paths for lithium ions, thereby effectively improving the ionic conductivity of the solid-state electrolyte while ensuring the flame-retardant performance, and ultimately realizing the simultaneous optimization of the flame-retardant performance and the conductive performance of the solid-state electrolyte material.

[0029] In the embodiments of the present application, the polyaromatic nitro cyclotriphosphazene has the structure shown in Formula 1 or Formula 2:

[0030] Formula 1

[0031] Formula 2

[0032] In Formula 1 and Formula 2, R is each independently selected from , wherein, represents the connection site with P in Formula 1 or Formula 2;

[0033] In Formula 1 and Formula 2, R' is each independently selected from , wherein, represents the connection site with P in Formula 1 or Formula 2.

[0034] In the present application, the polyaromatic nitro cyclotriphosphazene can be obtained by conventional methods, such as being commercially available or being self-made by conventional methods or based on the principle of conventional chemical reactions.

[0035] For example, the polyaryl nitrocyclotriphosphazene shown in formula 1 can be prepared by reacting the aryl nitrocyclotriphosphazene A and the bisphenol A, and the preparation process can specifically include: reacting the aryl nitrocyclotriphosphazene A and the bisphenol A in a first solvent to obtain the polyaryl nitrocyclotriphosphazene shown in formula 1. The reaction time can be 10-60 min, for example, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, or any two ranges thereof, and the first solvent can include anhydrous methanol.

[0036] The aryl nitrocyclotriphosphazene A

[0037] Specifically, the aryl nitrocyclotriphosphazene A can be prepared by a conventional method, for example, the preparation process of the aryl nitrocyclotriphosphazene A can include mixing hexachlorocyclotriphosphazene, phenol, and a base in a second solvent, and then performing a first reflux reaction, the reaction time can be 4-48 h, for example, 4 h, 12 h, 20 h, 28 h, 36 h, 42 h, 48 h, or any two ranges thereof, to obtain a first mixed solution; mixing the first mixed solution, 4-nitrophenol, and sodium cyanide, and then performing a second reflux reaction, the reaction time can be 8-72 h, for example, 8 h, 16 h, 24 h, 32 h, 40 h, 48 h, 56 h, 64 h, 72 h, or any two ranges thereof, to obtain a second mixed solution; filtering the second mixed solution, concentrating and cooling the obtained filtrate to obtain a milky substance, and then washing the milky substance with lye, water, and methanol in sequence to obtain a solid product; and recrystallizing the solid product to obtain the aryl nitrocyclotriphosphazene A.

[0038] For example, the polyaryl nitrocyclotriphosphazene shown in formula 2 can be prepared by reacting the aryl nitrocyclotriphosphazene B and the bisphenol A, and the preparation process can specifically include: reacting the aryl nitrocyclotriphosphazene A and the bisphenol A in a third solvent to obtain the polyaryl nitrocyclotriphosphazene shown in formula 2. The reaction time can be 10-60 min, for example, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, or any two ranges thereof, and the third solvent can include anhydrous methanol.

[0039] The aryl nitrocyclotriphosphazene B

[0040] In some embodiments, the mass fraction of the polymer matrix can be 50-90%, for example 50%, 60%, 70%, 80%, 90%, or a range consisting of any two of them, based on the total mass of the solid electrolyte material, so that the mass fraction of the polymer matrix is not less than 50%, which helps the polymer matrix itself to form a continuous and stable electrolyte skeleton, thereby providing sufficient mechanical strength for the entire solid electrolyte system to inhibit the growth of lithium dendrites and improve the film-forming performance of the solid electrolyte; the mass fraction of the polymer matrix is not more than 90%, which helps to reserve more sufficient space for lithium salt and flame retardant additives in the finally formed electrolyte system, avoiding the occupation of ion migration channels due to excessive matrix, so that the electrolyte system has higher ionic conductivity and stable and durable flame retardant function. Therefore, maintaining the mass fraction of the polymer matrix in the range of 50-90% helps to balance the internal high ionic conductivity and excellent safety of the solid electrolyte while ensuring the integrity of the solid electrolyte structure.

[0041] In some embodiments, the mass fraction of the lithium salt can be 10-40%, for example 10%, 20%, 30%, 40%, or a range consisting of any two of them, based on the total mass of the solid electrolyte material, so that the mass fraction of the lithium salt is not less than 10%, which helps to provide a sufficient number of free lithium ions to further improve the ionic conductivity of the solid electrolyte material; the mass fraction of the lithium salt is not more than 40%, which helps to prevent aggregation and crystallization due to excessive concentration of lithium salt, avoiding the destruction of the continuity of the polymer matrix and its interface compatibility with the electrode, thereby further improving the structural stability and electrochemical stability of the solid electrolyte material. Therefore, maintaining the mass fraction of the lithium salt in the range of 10-40% helps to further improve the long-term stability of the electrolyte body and interface while ensuring the high ion migration ability of the solid electrolyte material.

[0042] In some embodiments, the mass fraction of the polyarylnitrocyclotriphosphazene can be 1-25%, for example 1%, 5%, 10%, 15%, 20%, 23%, 25%, or a range consisting of any two of them, based on the total mass of the solid electrolyte material, so that the mass fraction of the polyarylnitrocyclotriphosphazene is not less than 1%, which helps to establish an effective three-dimensional flame retardant network in the polymer matrix, ensuring that it can significantly capture free radicals and promote the formation of a dense carbon layer under thermal runaway conditions, and play a key flame retardant synergistic role; the mass fraction of the polyarylnitrocyclotriphosphazene is not more than 25%, which helps to give the solid electrolyte material excellent flame retardant performance while avoiding excessive addition to hinder ion migration paths or introduce unnecessary electrochemical side reactions, ensuring that the core electrochemical performance is not negatively affected. Therefore, maintaining the mass fraction of the polyarylnitrocyclotriphosphazene in the range of 1-25% helps to balance the flame retardant performance and electrochemical performance of the solid electrolyte material.

[0043] wherein the mass fraction (wt%) of each component refers to the percentage of the mass of the component in the total mass of the flame-retardant solid-state electrolyte material. For example, the mass fraction (wt%) of the polymer matrix is equal to [mass of the polymer matrix / (mass of the polymer matrix + mass of the lithium salt + mass of the polymeric aryl-nitrocyclotriphosphazene)].

[0044] In some embodiments, the polymer matrix comprises one or more of polyethylene oxide (PEO), polyethylene glycol (PEG), polyethylene glycol dimethyl ether (PEGDME), polyvinylidene fluoride (PVDF), and polymethyl methacrylate (PMMA).

[0045] In some embodiments, the average molecular weight of the polymer matrix is in the range of 400-1000000, for example, 400, 100000, 400000, 600000, 800000, 1000000, or a range defined by any two of them. In this way, the average molecular weight of the polymer matrix is not less than 400, and the molecular chains of the polymer matrix can intertwine with each other, which is conducive to forming a continuous electrolyte film with self-supporting ability. The average molecular weight of the polymer matrix is not more than 1000000, which is conducive to maintaining moderate system viscosity and improving the uniformity and film quality of the casting process. Therefore, maintaining the average molecular weight of the polymer matrix in the range of 400-1000000 helps to strike a balance between the integrity of the matrix structure and the processability.

[0046] wherein the average molecular weight is the number average molecular weight.

[0047] In some embodiments, the lithium salt comprises one or more of lithium hexafluorophosphate LiPF6, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB), lithium bisfluorophosphate (LiPO2F2).

[0048] In some embodiments, the solid-state electrolyte material is a solid-state electrolyte film, and the thickness of the solid-state electrolyte film can be in the range of 5-20 μm, for example, 5 μm, 10 μm, 15 μm, 20 μm, or a range defined by any two of them. In this way, the thickness of the solid-state electrolyte film is not less than 5 μm, which is conducive to maintaining the mechanical integrity of the film structure and reducing the risk of short circuit of the battery. The thickness of the solid-state electrolyte film is not more than 20 μm, which is conducive to controlling the ion transport path length and improving the volumetric energy density and rate performance of the battery. Therefore, maintaining the thickness of the solid-state electrolyte film in the range of 5 μm-20 μm helps to strike a balance between the safety of the battery and the overall electrochemical performance.

[0049] In another aspect of the present application, a preparation method of a solid-state electrolyte material is provided, comprising the following preparation steps: mixing raw materials including a lithium salt, a polymer matrix and a flame-retardant additive to obtain the solid-state electrolyte material.

[0050] In some embodiments, the solid-state electrolyte material is a solid-state electrolyte film, and the process of mixing the raw materials including the lithium salt, the polymer matrix and the flame-retardant additive comprises: S1: mixing the polymer matrix with a solvent, and after first stirring, obtaining a first mixed solution; S2: adding the lithium salt to the first mixed solution, and after second stirring, obtaining a second mixed solution; S3: adding the flame-retardant additive to the second mixed solution, and after third stirring, obtaining a third mixed solution; S4: casting the third mixed solution into a film and drying to obtain the solid-state electrolyte film.

[0051] In some embodiments, the solvent in S1 comprises a polar solvent, and the polar solvent comprises one or more of N-methyl pyrrolidone (NMP), tetrahydrofuran, dichloromethane, acetone, dimethylformamide (DMF), anhydrous acetonitrile.

[0052] In some embodiments, the first stirring temperature can be 40-100 ℃, for example, 40 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃, 90 ℃, 100 ℃ or a range formed by any two of them.

[0053] In some embodiments, the second stirring temperature can be 40-100 ℃, for example, 40 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃, 90 ℃, 100 ℃ or a range formed by any two of them.

[0054] In some embodiments, the third stirring temperature can be 40-100 ℃, for example, 40 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃, 90 ℃, 100 ℃ or a range formed by any two of them.

[0055] In some embodiments, the drying temperature can be 60-120 ℃, for example, 60 ℃, 70 ℃, 80 ℃, 90 ℃, 100 ℃, 110 ℃, 120 ℃ or a range formed by any two of them, which is helpful for the solvent to volatilize sufficiently to form a structural dense electrolyte film, while maintaining the molecular structure stability of the polymer matrix, avoiding the degradation of the main chain or the deactivation of the flame-retardant additive due to the excessively high temperature, and this drying condition is conducive to obtaining a solid-state electrolyte film with good interface contact and mechanical strength, which provides support for its cycle stability in the battery.

[0056] Specifically, in step S4, the above drying can be vacuum drying, which can be performed under the above drying temperature condition.

[0057] In another aspect of the present application, a secondary battery is provided, which includes a positive electrode layer, an electrolyte layer, and a negative electrode layer, the electrolyte layer being located between the positive electrode layer and the negative electrode layer, at least one of the positive electrode layer, the electrolyte layer, and the negative electrode layer containing a solid electrolyte material or a solid electrolyte material prepared according to a preparation method of the solid electrolyte material.

[0058] The present application is further described below through specific examples.

[0059] Example 1

[0060] The solid electrolyte material of this example 1 includes a lithium salt, a polymer matrix, and a flame retardant additive, the flame retardant additive including a polyarylnitrocyclotriphosphazene.

[0061] The solid electrolyte material is prepared according to the following process.

[0062] 1. Preparation of polyarylnitrocyclotriphosphazene A

[0063] (1) 6.952 g of hexachlorocyclotriphosphazene was weighed and dissolved in 60 mL of tetrahydrofuran to obtain solution 1, 6.647 g of phenol and 2.88 g of sodium hydroxide were weighed and dissolved in 60 mL of tetrahydrofuran to obtain solution 2, solution 2 was added dropwise to solution 1, and the mixture was condensed and refluxed under nitrogen protection for 48 h to obtain solution 3;

[0064] (2) 12.51 g of 4-nitrophenol and 2.64 g of sodium hydroxide were weighed and dissolved in 80 mL of tetrahydrofuran to obtain solution 4, solution 4 was added dropwise to solution 3, and the mixture was condensed and refluxed under N2 protection for 3 days (72 h) to obtain solution 5;

[0065] (3) The tetrahydrofuran solution was obtained by filtering solution 5, the tetrahydrofuran solution was concentrated, cooled, poured into crushed ice and soaked for 24 h to obtain a thick cream-like substance, the cream-like substance was washed with 10% KOH aqueous solution, water, and methanol to obtain a solid product, the solid product was recrystallized with acetonitrile-methanol and dried under vacuum at 90 ℃ to obtain polyarylnitrocyclotriphosphazene A.

[0066] 2. Preparation of polyarylnitrocyclotriphosphazene A

[0067] (1) 0.69 g of metallic sodium was weighed and placed in a round-bottom flask, 40 mL of anhydrous methanol was added and stirred until completely dissolved, then 3.42 g of bisphenol A was added, a magnetic stirrer was put in and stirred at room temperature for 30 min, and the reaction system was distilled to remove the methanol solvent;

[0068] (2) Connect the round bottom flask to the Dean-Stark apparatus, and after warming to 120 °C, add 15 mL of toluene, and collect the distilled toluene; then add 10 mL of toluene and 10 mL of dimethyl sulfoxide, and continue to warm to 140 °C, and again distill and collect the toluene;

[0069] (3) Cool the reaction solution in the round bottom flask to 40 °C, and add 8.28 g of aryl nitro cyclotriphosphazene A, 10 mL of toluene and 10 mL of dimethyl sulfoxide, and continue to stir at 80 °C for 72 h to obtain a fourth mixed solution;

[0070] (4) Pour the fourth mixed solution into cold water to precipitate a solid brown powder, wash the brown powder with ethanol three times, and then dry under vacuum at 80 °C to obtain polyaryl nitro cyclotriphosphazene A.

[0071] 3. Preparation of a solid electrolyte membrane

[0072] (1) Under argon protection, sequentially mix 0.8 g of lithium bis(trifluoromethanesulfonyl)imide, 1.2 g of polyethylene oxide with a number average molecular weight of 600000 and 15 mL of anhydrous acetonitrile, and stir at 80 °C until completely dissolved; then add 0.105 g of the polyaryl nitro cyclotriphosphazene A prepared above, and continue to stir until the system is uniformly mixed to obtain a solid electrolyte precursor solution (i.e., the third mixed solution described above);

[0073] (2) Pour the solid electrolyte precursor solution into a polytetrafluoroethylene mold to form a film, and dry under vacuum at 80 °C, and after cutting, obtain a solid electrolyte membrane.

[0074] 4. Assembly of a stainless steel symmetric structure button cell (i.e., the secondary battery described above)

[0075] Transfer the solid electrolyte to a glove box filled with high-purity argon (H2O < 0.01 ppm, O2 < 0.01 ppm) for assembly. First, cut the solid electrolyte membrane into a circle with a diameter of 16.2 mm, and then select two pieces of stainless steel (SS) as inert electrodes, and place the cut circular solid electrolyte membrane between the two pieces of stainless steel with a diameter of 16.2 mm to form a symmetric structure of SS / SPE / SS. Then, place the structure into a CR2032 type button cell shell, add a spring, and use a battery packaging machine to package and form at a pressure of about 50 kg / cm 2 to ensure that the electrodes are in full contact with the solid electrolyte membrane and avoid interface gaps.

[0076] 5. Test of ionic conductivity

[0077] The impedance spectrum of the above assembled stainless steel symmetric structure button cell was tested by an electrochemical workstation (model Zennium Pro), the test used a perturbation voltage of 10 mV, the test frequency scanning range was 1 Hz-8 MHz, and the impedance spectrum of the stainless steel symmetric cell of Example 1 was as shown in Figure 1 .

[0078] The intersection of the high frequency region (frequency ≥ 1 MHz, and imaginary part-Z''≤0.1 Ω) and the real axis (Z' axis) in the impedance spectrum was taken as the bulk resistance (R) of the solid-state electrolyte, and the ionic conductivity (σ, unit mS / cm) of the solid-state electrolyte film = L / (R×A), wherein L is the thickness of the solid-state electrolyte film, and A is the effective contact area of the stainless steel sheet (i.e. the inert electrode) and the solid-state electrolyte, since the diameter of the stainless steel sheet and the solid-state electrolyte film is both 16.2 mm, A=π×(16.2 mm / 2) 2 ≈2.06 cm 2 .

[0079] 6. Flame retardant performance test

[0080] The cone calorimeter method was used to test the flame retardant performance of the solid-state electrolyte film: a solid-state electrolyte film sample with a size of 10×10 cm and a thickness of 20 microns was placed in a cone calorimeter (model IKAC6000 Calorimeter), and a point ignition experiment was performed under a set heat flux, and the ignition time, total heat release, and other parameters during the sample combustion process were automatically recorded by the instrument to characterize the combustion behavior and flame retardant effect.

[0081] Example 2

[0082] The solid-state electrolyte material of this Example 2 includes a lithium salt, a polymer matrix, and a flame retardant additive, and the flame retardant additive includes a polyaryl nitro cyclotriphosphazene.

[0083] The solid-state electrolyte material was prepared according to the following process.

[0084] 1. Preparation of aryl nitro cyclotriphosphazene A

[0085] The preparation process and conditions were the same as in Example 1.

[0086] 2. Preparation of polyaryl nitro cyclotriphosphazene A

[0087] The preparation process and conditions were the same as in Example 1.

[0088] 3. Preparation of solid-state electrolyte film

[0089] (1) Under argon protection, 0.8 g lithium bistrifluoromethanesulfonimide, 1.2 g polyvinylidene fluoride with a number average molecular weight of 900000 and 15 mL NMP were sequentially mixed, and stirred at 80°C until completely dissolved; then 0.222 g polyarylnitrocyclotriphosphazene A prepared in Example 1 was added, and the stirring was continued until the system was uniformly mixed to obtain a solid electrolyte precursor solution;

[0090] (2) The solid electrolyte precursor solution was cast into a film in a polytetrafluoroethylene mold, and vacuum dried at 100°C, and after cutting, a solid electrolyte film was obtained.

[0091] 4. Assembly of a stainless steel symmetrical structure button cell

[0092] The assembly process was the same as in Example 1.

[0093] 5. Test of ionic conductivity

[0094] The test process was the same as in Example 1.

[0095] 6. Test of flame retardant performance

[0096] The test process was the same as in Example 1.

[0097] Example 3

[0098] The solid electrolyte material of this Example 3 comprises a lithium salt, a polymer matrix and a flame retardant additive, and the flame retardant additive comprises polyarylnitrocyclotriphosphazene.

[0099] The solid electrolyte material was prepared according to the following process.

[0100] 1. Preparation of aryl nitro cyclotriphosphazene A

[0101] The preparation process and conditions were the same as in Example 1.

[0102] 2. Preparation of polyarylnitrocyclotriphosphazene A

[0103] The preparation process and conditions were the same as in Example 1.

[0104] 3. Preparation of a solid electrolyte film

[0105] (1) Under argon protection, 0.8 g lithium bistrifluoromethanesulfonimide, 1.2 g polyvinylidene fluoride with a number average molecular weight of 900000 and 15 mL NMP were sequentially mixed, and stirred at 80°C until completely dissolved; then 0.222 g polyarylnitrocyclotriphosphazene A prepared in Example 1 was added, and the stirring was continued until the system was uniformly mixed to obtain a solid electrolyte precursor solution;

[0106] (2) The solid electrolyte precursor solution is cast into a film in a polytetrafluoroethylene mold and vacuum dried at 100°C, and after cutting, a solid electrolyte film is obtained.

[0107] 4. Assembly of a symmetrical structure stainless steel button cell

[0108] The assembly process is the same as in Example 1.

[0109] 5. Test of ionic conductivity

[0110] The test process is the same as in Example 1.

[0111] 6. Test of flame retardant performance

[0112] The test process is the same as in Example 1.

[0113] Example 4

[0114] The solid electrolyte material of this Example 4 includes a lithium salt, a polymer matrix, and a flame retardant additive, and the flame retardant additive includes a polyaryl nitro cyclotriphosphazene.

[0115] The solid electrolyte material is prepared according to the following process.

[0116] 1. Preparation of polyaryl nitro cyclotriphosphazene B

[0117] (1) 25.02 g of nitrophenol and 10.8 g of KOH were weighed and dissolved in 150 mL of dimethylbenzene, a magnet was added to stir at 100 r / min and slowly heated to 80°C to obtain solution A; 6.96 g of hexachlorocyclotriphosphazene was dissolved in 150 mL of dimethylbenzene to obtain solution B; solution B was slowly added dropwise to solution A within 1 h, and solution A was then condensed and refluxed for 24 h to obtain precipitate A;

[0118] (2) The precipitate A was washed with a 50°C potassium hydroxide aqueous solution and deionized water, and recrystallized with dimethylformamide as a solvent to obtain dry yellow crystalline polyaryl nitro cyclotriphosphazene B. The concentration of the above-mentioned potassium hydroxide aqueous solution is 10%, i.e., the mass of the solute potassium hydroxide accounts for 10% of the total mass of the solution, and the total mass of the solution is the mass of potassium hydroxide + the mass of water.

[0119] 2. Preparation of polyaryl nitro cyclotriphosphazene B

[0120] (1) 0.69 g of metallic sodium was weighed into a round-bottom flask, 40 mL of anhydrous methanol was added and stirred until completely dissolved, then 2.257 g of bisphenol A was added, a magnet was inserted and stirred at room temperature for 30 min, and the reaction system was distilled to remove the methanol solvent;

[0121] (2) The round bottom flask was connected to a Dean-Stark apparatus, and after being warmed to 120 °C, 15 mL of toluene was added, and the distilled toluene was collected; then 10 mL of toluene and 10 mL of dimethyl sulfoxide were added, and the temperature was increased to 140 °C, and the toluene was distilled and collected again;

[0122] (3) The reaction solution in the round bottom flask was cooled to 40 °C, 3.177 g of aryl nitro cyclotriphosphazene, 10 mL of dimethyl sulfoxide were added, and the stirring was continued at 75 °C for 72 h to obtain a fifth mixed solution;

[0123] (4) The fifth mixed solution was poured into cold water to precipitate a solid brown powder, which was washed with ethanol three times and dried at 80 °C under vacuum to obtain polyaryl nitro cyclotriphosphazene B.

[0124] 3. Preparation of a solid electrolyte membrane

[0125] (1) Under argon protection, 0.8 g of lithium bis(trifluoromethanesulfonyl)imide, 1.2 g of polyethylene oxide with a number average molecular weight of 600000, and 15 mL of anhydrous acetonitrile were sequentially mixed, and stirred at 80 °C until completely dissolved; then 0.353 g of the above-prepared polyaryl nitro cyclotriphosphazene B was added, and the stirring was continued until the system was uniformly mixed to obtain a solid electrolyte precursor solution;

[0126] (2) The solid electrolyte precursor solution was cast into a film in a polytetrafluoroethylene mold, and dried at 100 °C under vacuum, and after cutting, a solid electrolyte membrane was obtained.

[0127] 4. Assembly of a stainless steel symmetrical structure button cell

[0128] The assembly process was the same as in Example 1.

[0129] 5. Test of ionic conductivity

[0130] The test process was the same as in Example 1.

[0131] 6. Test of flame retardant performance

[0132] The test process was the same as in Example 1.

[0133] Example 5

[0134] The solid electrolyte material of this Example 5 comprises a lithium salt, a polymer matrix, and a flame retardant additive, and the flame retardant additive comprises polyaryl nitro cyclotriphosphazene.

[0135] The solid electrolyte material was prepared according to the following process.

[0136] 1. Preparation of polyaryl nitro cyclotriphosphazene B

[0137] The preparation process and conditions were the same as in Example 4.

[0138] 2. Preparation of polyaromatic nitrocyclotriphosphazene B

[0139] The preparation process and conditions are the same as those of Example 4.

[0140] 3. Preparation of solid electrolyte film

[0141] (1) Under the protection of argon, 0.6 g of lithium hexafluorophosphate, 1.2 g of polyvinylidene fluoride with a number average molecular weight of 900000, and 15 mL of NMP were sequentially mixed and stirred at 80°C until completely dissolved; then 0.5 g of polyaromatic nitrocyclotriphosphazene B prepared in Example 4 was added, and the stirring was continued until the system was uniformly mixed, to obtain a solid electrolyte precursor solution;

[0142] (2) The solid electrolyte precursor solution was cast into a film in a polytetrafluoroethylene mold and vacuum dried at 80°C, and after cutting, a solid electrolyte film was obtained.

[0143] 4. Assembly of stainless steel symmetrical structure button cell

[0144] The assembly process is the same as that of Example 1.

[0145] 5. Test of ionic conductivity

[0146] The test process is the same as that of Example 1.

[0147] 6. Test of flame retardant performance

[0148] The test process is the same as that of Example 1.

[0149] Example 6

[0150] The solid electrolyte material of this Example 6 includes a lithium salt, a polymer matrix, and a flame retardant additive, and the flame retardant additive includes a polyaromatic nitrocyclotriphosphazene.

[0151] The solid electrolyte material is prepared according to the following process.

[0152] 1. Preparation of aromatic nitrocyclotriphosphazene B

[0153] The preparation process and conditions are the same as those of Example 4.

[0154] 2. Preparation of polyaromatic nitrocyclotriphosphazene B

[0155] The preparation process and conditions are the same as those of Example 4.

[0156] 3. Preparation of solid electrolyte film

[0157] (1) Under argon protection, 0.5 g of lithium bisfluorosulfonylimide, 1.2 g of polymethyl methacrylate with a number average molecular weight of 500000 and 15 mL of anhydrous acetonitrile were sequentially mixed and stirred at 80°C until completely dissolved; then 0.5 g of polyarylnitrocyclotriphosphazene B prepared in Example 4 was added, and the stirring was continued until the system was uniformly mixed to obtain a solid electrolyte precursor solution;

[0158] (2) The solid electrolyte precursor solution was cast into a film in a polytetrafluoroethylene mold and vacuum dried at 60°C, and after cutting, a solid electrolyte film was obtained.

[0159] 4. Assembly of a stainless steel symmetrical structure button cell

[0160] The assembly process was the same as in Example 1.

[0161] 5. Test of ionic conductivity

[0162] The test process was the same as in Example 1.

[0163] 6. Test of flame retardant performance

[0164] The test process was the same as in Example 1.

[0165] Example 7

[0166] The solid electrolyte material of this Example 7 includes a lithium salt, a polymer matrix and a flame retardant additive, and the flame retardant additive includes a polyarylnitrocyclotriphosphazene.

[0167] The solid electrolyte material was prepared according to the following process.

[0168] 1. Preparation of aryl nitro cyclotriphosphazene A

[0169] The preparation process and conditions were the same as in Example 1.

[0170] 2. Preparation of polyarylnitrocyclotriphosphazene A

[0171] The preparation process and conditions were the same as in Example 1.

[0172] 3. Preparation of a solid electrolyte film

[0173] The amount of lithium bis(trifluoromethanesulfonyl)imide was changed to 0.02 g, and the other processes and conditions were the same as in Example 1.

[0174] 4. Assembly of a stainless steel symmetrical structure button cell

[0175] The assembly process was the same as in Example 1.

[0176] 5. Test of ionic conductivity

[0177] The test process was the same as in Example 1.

[0178] 6. Flame Retardant Performance Test

[0179] The test procedure was the same as in Example 1.

[0180] Example 8

[0181] The solid state electrolyte material of this Example 8 included a lithium salt, a polymer matrix, and a flame retardant additive including a polymeric aryl-nitro cyclotriphosphazene.

[0182] The solid state electrolyte material was prepared according to the following procedure.

[0183] 1. Preparation of aryl-nitro cyclotriphosphazene A

[0184] The preparation procedure and conditions were the same as in Example 1.

[0185] 2. Preparation of polymeric aryl-nitro cyclotriphosphazene A

[0186] The preparation procedure and conditions were the same as in Example 1.

[0187] 3. Preparation of solid state electrolyte film

[0188] The amount of lithium bis-trifluoromethanesulfonimide was changed to 0.014 g, and the other procedure and conditions were the same as in Example 1.

[0189] 4. Assembly of stainless steel symmetric structure button cell

[0190] The assembly procedure was the same as in Example 1.

[0191] 5. Test of ionic conductivity

[0192] The test procedure was the same as in Example 1.

[0193] 6. Flame Retardant Performance Test

[0194] The test procedure was the same as in Example 1.

[0195] Example 9

[0196] The solid state electrolyte material of this Example 9 included a lithium salt, a polymer matrix, and a flame retardant additive including a polymeric aryl-nitro cyclotriphosphazene.

[0197] The solid state electrolyte material was prepared according to the following procedure.

[0198] 1. Preparation of aryl-nitro cyclotriphosphazene A

[0199] The preparation procedure and conditions were the same as in Example 1.

[0200] 2. Preparation of polymeric aryl-nitro cyclotriphosphazene A

[0201] The preparation procedure and conditions were the same as in Example 1.

[0202] 3. Preparation of solid electrolyte membrane

[0203] The amount of lithium bis-trifluoromethanesulfonimide was changed to 0.74 g, and other procedures and conditions were the same as in Example 1.

[0204] 4. Assembly of stainless steel symmetrical structure button cell

[0205] The assembly procedure was the same as in Example 1.

[0206] 5. Test of ionic conductivity

[0207] The test procedure was the same as in Example 1.

[0208] 6. Test of flame retardant property

[0209] The test procedure was the same as in Example 1.

[0210] Comparative Example 1

[0211] No polymeric aryl-nitro cyclotriphosphazene A flame retardant additive was added, and other preparation procedures and conditions and test methods were the same as in Example 1.

[0212] Comparative Example 2

[0213] No polymeric aryl-nitro cyclotriphosphazene A flame retardant additive was added, and other preparation procedures and conditions and test methods were the same as in Example 2.

[0214] Table 1: Solid electrolyte materials and their preparation conditions

[0215]

[0216] Table 2: Solid electrolyte materials and their preparation conditions

[0217]

[0218] The ionic conductivity, ignition time and total heat release of the solid electrolyte materials prepared in the Examples and Comparative Examples were tested, and the results are shown in Table 3.

[0219] Table 3: Ionic conductivity, ignition time and total heat release of solid electrolyte in Examples 1-6 and Comparative Examples 1-2

[0220]

[0221] Note: “Not ignited (within 1800 s)” in Table 3 means not ignited within 1800 s.

[0222] As can be seen from Table 3, compared with Comparative Example 1-Comparative Example 2, Example 1-Example 9, by introducing the flame-retardant additive polyaryl nitro cyclotriphosphazene into the solid-state electrolyte, the flame-retardant additive can destroy the regular arrangement of the original polymer matrix, reduce the crystallinity of the matrix, thereby increasing the proportion of the amorphous region of the system, providing more transmission paths for lithium ions, and effectively improving the ionic conductivity of the solid-state electrolyte; in addition, the flame-retardant additive can release phosphorus-containing free radicals at high temperatures, effectively block the combustion chain reaction, and form a dense carbon layer on the surface of the material, thereby isolating oxygen and heat, and thus synergistically playing a flame-retardant role in the gas and solid phases. As can be seen from Table 3, the ionic conductivity of Example 1-Example 9 is significantly higher than that of Comparative Example 1-Comparative Example 2, therefore, by introducing the flame-retardant additive polyaryl nitro cyclotriphosphazene into the solid-state electrolyte, the flame-retardant performance and conductivity of the solid-state electrolyte material can be effectively improved.

[0223] Further, taking Example 1 and Comparative Example 1 (not introducing the flame-retardant additive polyaryl nitro cyclotriphosphazene) as examples, the conductivity and flame-retardant performance of the solid-state electrolyte material prepared by the present application are compared. As can be seen from Table 3, compared with Comparative Example 1, polyaryl nitro cyclotriphosphazene additive A is added in Example 1, which can destroy the high crystallinity of the polymer matrix and reduce the crystallinity, thereby significantly improving the ionic conductivity of the polymer solid-state electrolyte, making it reach 0.56 mS / cm, while the ionic conductivity of Comparative Example 1 is only 0.29 mS / cm.

[0224] As can be seen from Table 3, the examples with polyaryl nitro cyclotriphosphazene are not ignited within 1800 s, while the comparative examples release a large amount of heat in a short time, indicating that the introduction of polyaryl nitro cyclotriphosphazene optimizes the flame-retardant performance of the solid-state electrolyte. This is because when the solid-state electrolyte material with polyaryl nitro cyclotriphosphazene is decomposed by heat, the phosphazene material can react with the polymer matrix, promoting the dehydration and crosslinking of the polymer, and forming a dense carbon layer on the surface of the material, thereby isolating oxygen and heat and preventing the escape of flammable gas. At the same time, the phosphorus-containing free radicals produced by the decomposition of polyaryl nitro cyclotriphosphazene can react with the high-activity free radicals in the chain reaction of the flame, making them lose activity.

[0225] Finally, it should be noted that other embodiments of the present application will be readily apparent to those skilled in the art upon considering the specification and practicing the present application as disclosed. The present application is intended to cover any variations, uses, or adaptations of the present application following, in general, the principles of the present application and including such variations, uses, or adaptations of the present application as come within the general scope of the present application and including the general principles of the present application as well as the best mode of practicing the present application disclosed herein, without limiting the present application to the precise construction and method disclosed herein, and as such claims the scope of the present application. The scope of the present application is limited only by the claims that follow.

Claims

1. A solid electrolyte material, characterized in that, It includes lithium salt, polymer matrix and flame retardant additive, wherein the flame retardant additive includes polyarylnitrocyclotriphosphazene.

2. The solid electrolyte material according to claim 1, characterized in that, The polyarylnitrocyclotriphosphazene has the structure shown in Formula 1 or Formula 2: Formula 1 Formula 2 In Equations 1 and 2, R is independently selected from... ,in, express The connection site with P in Equation 1 or Equation 2; R' in Equations 1 and 2 are each independently selected from ,in, express The connection site with P in Equation 1 or Equation 2.

3. The solid electrolyte material according to claim 1, characterized in that, Based on the total mass of the solid electrolyte material, the polymer matrix has a mass fraction of 50%-90%, the lithium salt has a mass fraction of 10%-40%, and the polyarylnitrocyclotriphosphazene has a mass fraction of 1%-25%.

4. The solid electrolyte material according to claim 1, characterized in that, The polymer matrix includes one or more of polyethylene oxide, polyethylene glycol, polyethylene glycol dimethyl ether, polyvinylidene fluoride, and polymethyl methacrylate.

5. The solid electrolyte material according to claim 1, characterized in that, The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalateborate), and lithium difluorophosphate.

6. The solid electrolyte material according to claim 1, characterized in that, The solid electrolyte material is a solid electrolyte membrane, and the thickness of the solid electrolyte membrane is 5-20 μm.

7. A method for preparing a solid electrolyte material according to any one of claims 1-6, characterized in that, The preparation process includes the following steps: mixing raw materials including lithium salt, polymer matrix and flame retardant additives to obtain the solid electrolyte material.

8. The method for preparing the solid electrolyte material according to claim 6, characterized in that, The solid electrolyte material is a solid electrolyte membrane, and the process of mixing raw materials including lithium salt, polymer matrix and flame retardant additives includes: S1: The polymer matrix is ​​mixed with a solvent, and after a first stirring, a first mixture is obtained; S2: Add the lithium salt to the first mixture, and after a second stirring, obtain a second mixture; S3: Add the flame retardant additive to the second mixture, and after a third stirring, obtain the third mixture; S4: The third mixture is cast into a film and dried to obtain the solid electrolyte membrane.

9. The method for preparing the solid electrolyte material according to claim 8, characterized in that, The solvent mentioned in S1 includes polar solvents, which include one or more of N-methylpyrrolidone, tetrahydrofuran, dichloromethane, acetone, dimethylformamide, and anhydrous acetonitrile. And / or, the temperature of the first stirring is 40-100 °C; And / or, the temperature of the second stirring is 40-100 °C; And / or, the temperature of the third stirring is 40-100 ℃; And / or, the drying temperature of S4 is 60-120 °C.

10. A secondary battery, characterized in that, It includes a positive electrode layer, an electrolyte layer, and a negative electrode layer, wherein the electrolyte layer is located between the positive electrode layer and the negative electrode layer; At least one of the positive electrode layer, electrolyte layer, and negative electrode layer contains the solid electrolyte material according to any one of claims 1 to 6 or the solid electrolyte material prepared according to the preparation method of the solid electrolyte material according to claims 7 to 9.

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