Flame-retardant electrolyte and preparation method and application thereof

Abstract

The application discloses a kind of flame-retardant electrolyte and its preparation method and application, including the following preparation raw materials: lithium salt, polymer, flame-retardant filler;The mass ratio of lithium salt, polymer and flame-retardant filler is 1: (1-1.2) : (0.05-0.15). The flame-retardant electrolyte in the application has solid-state wide temperature range, good thermal stability, high ionic conductivity, high thermal conductivity, good cycle and rate performance by the synergistic effect of lithium salt, polymer and flame-retardant filler, can inhibit lithium dendrite, wider electrochemical window, higher lithium ion migration number and other characteristics, can make lithium ion battery have greater capacity, longer working time and higher safety, so that solid-state battery containing the flame-retardant electrolyte in the application meets the demand of new energy storage, new energy vehicles, mobile devices and other fields on the basis of high performance, high safety and reliability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of batteries, and particularly relates to a flame-retardant electrolyte and a preparation method and application thereof. BACKGROUND

[0002] The liquid electrolyte commonly used in traditional lithium ion batteries is prone to heat up during the operation of the battery, thereby causing excessive heat to accumulate inside the battery, bringing potential safety hazards such as combustion or explosion. In the case of improper use of the lithium ion battery, the temperature inside the battery rapidly rises, at this time, the high-oxidizing positive electrode material usually has poor thermal stability and is prone to decompose to generate oxygen radicals (O·). Alkyl radicals (RH·) and hydrogen radicals (H·) are also slowly decomposed from the polymer electrolyte, and then react with oxygen radicals in a chain combustion reaction to cause the temperature inside the battery to rise sharply, and the severe combustion may even cause the lithium battery to explode. In addition, the organic liquid electrolyte in the battery is toxic, flammable, easy to leak and has poor thermal stability, and there are serious safety hazards. Compared with the currently widely used electrolyte, the high-salt composite solid-state electrolyte has higher ionic conductivity, energy density, cycle rate performance and stress-strain capacity, and has attracted more attention.

[0003] The high-lithium salt polymer solid-state electrolyte is generally composed of lithium salt and organic solvent, and is usually flammable. When the battery is short-circuited, the electrolyte as fuel will burn rapidly. The existing high-lithium salt polymer solid-state electrolyte technology has the following problems: (1) A large amount of polymers exist in the high-lithium salt polymer solid-state electrolyte, which makes them flammable and have poor thermal stability. The existing technology fails to effectively solve the problem of flame retardation under the high-salt system, thereby limiting the safety and reliability of the application of the high-lithium salt polymer solid-state electrolyte. (2) The ionic conductivity is low, which cannot meet the commercial demand, affecting the battery performance and power density. (3) The lithium ion conduction rate is high, and the thermal conductivity is low, which causes the battery to heat up during charging and discharging, and has safety hazards. (4) The cycle and rate performance are insufficient, which causes the battery to have a short service life and slow charging and discharging. (5) Lithium dendrite growth cannot be effectively inhibited, which easily causes the battery to short-circuit and accidents such as explosion. (6) The electrochemical window is not wide enough, the electrolyte is prone to oxidative decomposition, and the applicable range is not wide enough. (7) The energy density needs to be improved, which is insufficient to meet the power supply demand of new energy vehicles, mobile devices and the like. (8) The manufacturing cost and difficulty are too high, which is not conducive to large-scale industrial production and commercial promotion. The above problems existing in the high-lithium salt polymer solid-state electrolyte greatly limit its application and promotion. SUMMARY

[0004] In order to overcome the problems existing in the prior art, one of the purposes of the present application is to provide a flame-retardant electrolyte.

[0005] The second purpose of the present application is to provide a preparation method of the flame-retardant electrolyte.

[0006] The third object of the present application is to provide a lithium ion battery.

[0007] The fourth object of the present application is to provide an application of the flame-retardant electrolyte in the field of batteries.

[0008] To achieve the above objects, the technical solution adopted by the present application is:

[0009] The first aspect of the present application provides a flame-retardant electrolyte comprising the following raw materials: lithium salt, polymer, flame-retardant filler; the mass ratio of the lithium salt, polymer and flame-retardant filler is 1:(1-1.2):(0.05-0.15).

[0010] Preferably, the mass ratio of the lithium salt, polymer and flame-retardant filler is 1:(1-1.2):(0.06-0.1); further preferably, the mass ratio of the lithium salt, polymer and flame-retardant filler is 1:1.1:(0.06-0.1). The solid flame-retardant electrolyte is prepared according to the above ratio, and the flame-retardant filler is introduced into the high-salt electrolyte in a specific ratio, so that the system becomes more stable, and the flame-retardant effect of the polymer solid-state electrolyte is achieved on the basis of maintaining the high conductivity of the battery.

[0011] Preferably, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate.

[0012] Preferably, the polymer is selected from at least one of poly(vinylidene fluoride-co-hexafluoropropylene), poly(ethylene oxide), poly(vinylidene fluoride).

[0013] Preferably, the flame-retardant filler is selected from at least one of polybenzimidazole, benzimidazole-linked polymer, aluminum hydroxide, dimethyl phosphate. The present application introduces polybenzimidazole polymer flame-retardant filler into the high-salt system, thereby preparing an electrolyte with flame-retardant performance, and maintaining good electrochemical performance in a wide temperature range, which has better performance than most electrolytes. The application of the electrolyte to lithium ion batteries is conducive to the development of lithium ion batteries with higher performance. The flame-retardant filler selected by the present application has excellent flame-retardant ability, which reduces the preparation cost and difficulty while improving the performance of the battery, and provides a more promising solution for large-scale industrial production and commercialization.

[0014] Preferably, the flame-retardant electrolyte is a solid-state electrolyte.

[0015] Preferably, the ionic conductivity of the flame-retardant electrolyte is 3.2x10 -4 -8.3x10 -4 S / cm.

[0016] Preferably, the electrochemical window of the flame-retardant electrolyte is 4.5-4.8V (vs. Li + / Li).

[0017] Preferably, the lithium ion transference number of the flame-retardant electrolyte accounts for 50-60% of the total ion transference number.

[0018] Preferably, the thickness of the flame-retardant electrolyte is 80-120nm. The thickness of the flame-retardant electrolyte in the present application determines the difficulty of forming the flame-retardant electrolyte film. If the thickness is too small, it is not easy to form a film.

[0019] Preferably, the preparation raw material further comprises a solvent.

[0020] Preferably, the solvent is at least one selected from DMF, a mixture of DMF and THF.

[0021] The second aspect of the present application provides a preparation method of the flame-retardant electrolyte provided in the first aspect of the present application, comprising the following steps:

[0022] S1: mixing a lithium salt, a polymer and a solvent A to obtain a mixed solution A; mixing a flame-retardant filler and a solvent B to obtain a mixed solution B;

[0023] S2: mixing the mixed solution A and the mixed solution B;

[0024] S3: removing bubbles and then forming a film; pre-drying and then secondary drying to obtain the flame-retardant electrolyte.

[0025] In the present application, the flame-retardant electrolyte is prepared by first mixing a lithium salt and a polymer to form a high salt system and then adding a flame-retardant filler. Compared with mixing all raw materials at one time, the preparation method in the present application makes the PVDF-HFP in the system partially lose hydrogen fluoride, thereby increasing the proportion of the amorphous phase of the polymer and fully dissociating LiTFSI to ensure the excellent performance of the high salt electrolyte.

[0026] Preferably, the temperature of the pre-drying step is 20-30℃, and the humidity of the pre-drying step is 75-85%. In the present application, too high pre-drying temperature and too high humidity will result in too long forming time of the flame-retardant electrolyte or difficulty in forming; too low pre-drying temperature or too low humidity will result in difficulty in controlling the forming time of the flame-retardant electrolyte film.

[0027] Preferably, the secondary drying temperature is 55-65℃, and the secondary drying time is 15-30h.

[0028] Preferably, the solvent A is DMF.

[0029] Preferably, the solvent B is a mixture of DMF and THF. The present application uses polybenzimidazole polymer flame-retardant filler as a flame-retardant additive and uses THF as a cosolvent, which greatly improves the flame-retardant performance of the flame-retardant electrolyte.

[0030] Preferably, the mixing temperature of step S1 is 55-65℃.

[0031] Preferably, the mixing temperature of step S2 is 55-65℃.

[0032] Preferably, the film-forming step uses blade coating film-forming or spin coating film-forming.

[0033] Preferably, the blade coating film-forming is done by using a doctor blade.

[0034] Preferably, the step of removing bubbles is done by using vacuum to remove bubbles. The step of removing bubbles makes the surface and the inside of the flame-retardant electrolyte free of macroscopic bubbles, ensuring the integrity of the solid-state flame-retardant electrolyte, and at the same time making the surface of the flame-retardant electrolyte smooth enough to reduce the interfacial impedance and enable the flame-retardant electrolyte to fully contact the electrode, thereby increasing the effective area.

[0035] The third aspect of the present application provides a lithium ion battery comprising the flame-retardant electrolyte provided by the first aspect of the present application.

[0036] The fourth aspect of the present application provides the use of the flame-retardant electrolyte provided by the first aspect of the present application in the field of batteries.

[0037] The beneficial effects of the present application are: the flame-retardant electrolyte in the present application has the characteristics of solid-state wide temperature range, good thermal stability, high ionic conductivity, high thermal conductivity, good cycle and rate performance, can inhibit lithium dendrites, has a wider electrochemical window, higher lithium ion migration number, etc., can make the lithium ion battery have greater capacity, longer working time and higher safety, so that the solid-state battery containing the flame-retardant electrolyte in the present application meets the needs of the fields of new energy storage, new energy vehicles, mobile devices, etc. on the basis of high performance, high safety and reliability. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 The preparation process flow chart of the flame-retardant electrolyte in the embodiments of the present application.

[0039] Figure 2 The AC impedance test chart of the flame-retardant electrolyte in Example 1.

[0040] Figure 3 The AC impedance test chart of the flame-retardant electrolyte in Example 2.

[0041] Figure 4 Impedance plot for the flame retardant electrolyte in Example 1.

[0042] Figure 5 Impedance plot for the flame retardant electrolyte in Example 1.

[0043] Figure 6 Impedance plot for the flame retardant electrolyte in Example 2.

[0044] Figure 7 Impedance plot for the flame retardant electrolyte in Example 3.

[0045] Figure 8 Charge-discharge cycling plot for the lithium iron phosphate battery assembled with the flame retardant electrolyte in Example 1.

[0046] Figure 9 Charge-discharge cycling plot for the lithium iron phosphate battery assembled with the flame retardant electrolyte in Example 2.

[0047] Figure 10 Charge-discharge cycling plot for the lithium iron phosphate battery assembled with the flame retardant electrolyte in Example 3.

[0048] Figure 11 Stress-strain plot for the flame retardant electrolyte in Example 3.

[0049] Figure 12 Stress-strain plot for the flame retardant electrolyte in Comparative Example 1.

[0050] Figure 13 Physical burning test plot for the flame retardant electrolyte in Example 1.

[0051] Figure 14 Physical burning test plot for the flame retardant electrolyte in Example 2.

[0052] Figure 15 Physical burning test plot for the flame retardant electrolyte in Example 3. DETAILED DESCRIPTION

[0053] The specific embodiments of the present application will be further described in the following with reference to the drawings and examples, but the implementation and protection of the present application are not limited thereto. It should be noted that if the following processes are not specifically described in detail, they can be implemented or understood by those skilled in the art with reference to the prior art. If the reagents or instruments used are not marked with the manufacturer, they are conventional products that can be purchased on the market.

[0054] The three components have a synergistic effect. The polybenzimidazole polymer is introduced as a flame-retardant filler to modify the PVDF-HFP / LiTFSI to enhance the flame-retardant performance, and a composite solid-state flame-retardant electrolyte with higher safety is obtained. The lithium ion battery assembled from the composite solid-state flame-retardant electrolyte can enhance the practicability of the battery, and is helpful to the storage and conversion of renewable energy and the safe development thereof, and has good strategic and commercial values. + move on the polymer chain. At the same time, due to the polarization effect of fluorine atoms on the polymer, the dissociation of the added LiTFSI is promoted, resulting in an increase in Li + , and the number of Li + migration is increased, and the ion clusters are combined with TFSI — under this proportion, and the ion clusters are sequentially arranged to form new ion channels. Therefore, the electrolyte in the high-salt system in the application has high ionic conductivity. First, the existence of the high-salt polymer system improves the electrochemical performance of the flame-retardant electrolyte, and second, the addition of the flame-retardant filler will catalyze and induce the pyrolysis of PVDF-HFP at high temperatures to promote the formation of fluorine radicals, hydrogen radicals and carbon-carbon double bonds, and also induce the TFSI-anion clusters rich in fluorine to release fluorine radicals. The hydrogen radicals generated in the system will generate water with oxygen, and the large amount of fluorine radicals released in the system will undergo fluorination addition reaction with the carbon-carbon double bonds in PVDF-HFP to generate carbon-fluorine bonds. The process of repeated defluorination and dehydrogenation, fluorination addition will make PVDF-HFP become a polymer chain rich in F atoms, thereby enhancing the thermal stability of the polymer and realizing the flame retardation of the system. Therefore, the introduction of the flame-retardant filler makes the electrolyte in the high-salt system have high flame-retardant performance.

[0055] The instruments and materials used in examples 1-3 of the application are as follows:

[0056] The instruments used are: ① glove box, ② constant temperature stirring pot, ③ constant temperature and humidity box, ④ vacuum drying oven, ⑤ slicing machine, ⑥ pressure machine.

[0057] The materials used are: LiTFSI is lithium bis(trifluoromethanesulfonyl)imide; PVDF-HFP is polyvinylidene fluoride-hexafluoropropylene copolymer; PBI is polybenzimidazole; BILP is benzimidazole-linked polymer.

[0058] Example 1

[0059] Reference Figure 1Preparation flow chart in the preparation process, the example of the flame retardant electrolyte is prepared by the following preparation method, the specific steps are as follows:

[0060] 1. First, weigh 1.250g of DMF and 0.330g of LiTFSI in bottle A in the glove box, shake slightly until the LiTFSI is dissolved, then add 0.300g of PVDF-HFP to bottle A, wherein DMF is used as a solvent, and the ratio of lithium salt LiTFSI to polymer PVDF-HFP is controlled to be 1:1.1 to form a high-salt system.

[0061] 2. Secondly, weigh 6% PVDF-HFP flame retardant filler polybenzimidazole polymer (PBI) (i.e. the mass ratio of PVDF-HFP to PBI is 100:6), 0.500g of DMF and 0.600g of THF in bottle B, wherein DMF and THF are used as solvents to dissolve the flame retardant filler.

[0062] 3. Then, put bottles A and B in a 60℃ water bath and stir overnight to preliminarily form a high-salt polymer system, and dissolve the filler into a liquid state to facilitate further mixing.

[0063] 4. After stirring, add the dissolved flame retardant filler in bottle B to the high-salt system in bottle A in the glove box. Then put the mixed bottle A in a 60℃ water bath and stir for 6h.

[0064] 5. After the solution in bottle A is uniformly stirred, an electrolyte precursor is obtained, which is placed in a glove box to remove bubbles by vacuumizing (the purpose of removing bubbles is to prevent high interfacial impedance caused by bubbles in the electrolyte precursor leading to a rough electrolyte surface). Then, the solution is poured onto a clean glass plate and coated into a film using a 400μm high stainless steel scraper. Then, the glass plate is immediately placed in a constant temperature and humidity chamber at 25℃ and 80% humidity for 3 hours to obtain a preliminarily shaped electrolyte film. (In this example, the specific temperature and humidity are more conducive to electrolyte shaping, and at this time the electrolyte still contains part of the solvent which needs to be dried to obtain a solid electrolyte.)

[0065] 6. After the film is removed from the glass plate, it is placed in a 60℃ vacuum drying oven for 24h to remove residual solvents, and an electrolyte film with a thickness of about 100μm is obtained. (Evaporation of the solvent makes the electrolyte present in a solid state, and the fine pores left after evaporation of the solvent are conducive to increasing the ionic conductivity.)

[0066] 7. After drying is completed, the electrolyte is quickly taken out and cut into a circular piece with a radius of 8mm or the required size using a slicer, then sealed and stored to prevent water absorption, and the flame retardant electrolyte in this example is prepared, which is denoted as: PSPBI 0.06 .

[0067] Example 2

[0068] Referring to Figure 1 the preparation flowchart in the figure, the flame-retardant electrolyte in this example is prepared by the following method, and the specific steps are as follows:

[0069] 1. First, 1.250 g of DMF and 0.330 g of LiTFSI were weighed into bottle A in a glove box, and after the LiTFSI was dissolved by slight shaking, 0.300 g of PVDF-HFP was added to bottle A, wherein DMF was used as a solvent, and the ratio of lithium salt LiTFSI to polymer PVDF-HFP was controlled to be 1:1.1 to form a high-salt system.

[0070] 2. Next, 8% PVDF-HFP flame-retardant filler polybenzimidazole polymer (PBI) (i.e. the mass ratio of PVDF-HFP to PBI is 100:8), 0.500 g of DMF and 0.600 g of THF were weighed into bottle B, wherein DMF and THF were used as solvents to dissolve the flame-retardant filler.

[0071] 3. Then, bottle A and bottle B were placed in a 60°C water bath and stirred overnight to preliminarily form a high-salt polymer system, and the filler was dissolved into a liquid state to facilitate further mixing.

[0072] 4. After stirring, the dissolved flame-retardant filler in bottle B was added to the high-salt system in bottle A in the glove box. The mixed bottle A was then placed in a 60°C water bath and stirred for 6h.

[0073] 5. After the solution in bottle A was stirred uniformly, an electrolyte precursor solution was obtained, which was placed in a glove box to remove bubbles after vacuum degassing, and then poured onto a clean glass plate and coated into a film with a 400μm high stainless steel scraper. Then the glass plate was immediately placed in a constant temperature and humidity chamber at 25°C and 80% humidity for 3 hours to obtain a preliminarily shaped electrolyte film.

[0074] 6. After the film was removed from the glass plate and placed in a 60°C vacuum drying oven for 24h to remove residual solvents, an electrolyte film with a thickness of about 100μm was obtained.

[0075] 7. After drying was completed, the electrolyte was quickly removed and cut into a circular piece with a radius of 8mm or the required size using a slicer, and then sealed and stored to prevent the electrolyte from absorbing water, thereby obtaining the flame-retardant electrolyte in this example, which is denoted as: PSPBI 0.08 .

[0076] Example 3

[0077] Referring to Figure 1 the preparation flowchart in the figure, the flame-retardant electrolyte in this example is prepared by the following method, and the specific steps are as follows:

[0078] 1. First, 1.250 g DMF and 0.330 g LiTFSI were weighed into bottle A in a glove box, and after the LiTFSI was dissolved by slight shaking, 0.300 g PVDF-HFP was added to bottle A, wherein DMF was used as a solvent, and the ratio of lithium salt LiTFSI to polymer PVDF-HFP was controlled to be 1:1.1 to form a high-salt system.

[0079] 2. Second, 10% PVDF-HFP flame-retardant filler polybenzimidazole polymer (PBI) (i.e., the mass ratio of PVDF-HFP to PBI was 100:10), 0.500 g DMF, and 0.600 g THF were weighed into bottle B, wherein DMF and THF were used as solvents to dissolve the flame-retardant filler.

[0080] 3. Then, bottles A and B were placed in a 60°C water bath and stirred overnight to preliminarily form a high-salt polymer system, and the filler was dissolved into a liquid state to facilitate further mixing.

[0081] 4. After the stirring was completed, the dissolved flame-retardant filler in bottle B was added to the high-salt system in bottle A in the glove box. The mixed bottle A was then placed in a 60°C water bath and stirred for 6 h.

[0082] 5. After the solution in bottle A was uniformly stirred, an electrolyte precursor solution was obtained. After the solution was degassed by vacuumizing in a glove box, it was poured onto a clean glass plate and coated into a film by using a 400-μm-high stainless steel doctor blade. The glass plate was then immediately placed in a constant-temperature and constant-humidity box at 25°C and 80% humidity for 3 h to obtain a preliminarily shaped electrolyte film.

[0083] 6. After the film was removed from the glass plate, it was placed in a 60°C vacuum drying box for 24 h to remove residual solvents, and an electrolyte film with a thickness of about 100 μm was obtained.

[0084] 7. After the drying was completed, the electrolyte was quickly removed and cut into a circular sheet with a radius of 8 mm or a desired size by using a slicer, and then sealed and stored to prevent the electrolyte from absorbing water, thereby obtaining the flame-retardant electrolyte in this example, which is recorded as: PSPBI 0.10 .

[0085] Example 4

[0086] The difference between the preparation method of the flame-retardant electrolyte in this example and the preparation method in Example 1 is that the same amount of BILP is used to replace PBI in this example.

[0087] Example 5

[0088] The difference between the preparation method of the flame-retardant electrolyte in this example and the preparation method in Example 2 is that the same amount of BILP is used to replace PBI in this example.

[0089] Example 6

[0090] The difference between the preparation method of the flame-retardant electrolyte in this example and the preparation method in Example 3 is that the same amount of BILP is used to replace PBI.

[0091] The flame-retardant electrolytes in Examples 1-6 of the present application are all in solid state, with a slightly yellow surface, and are extremely easy to absorb water, so they must be stored in a sealed manner.

[0092] Comparative Example 1

[0093] The electrolyte in this example is prepared by the following preparation method, and the specific steps are as follows:

[0094] 1. First, 1.250 g of DMF and 0.330 g of LiTFSI were weighed into bottle A in a glove box, and after the LiTFSI was dissolved by slight shaking, 0.300 g of PVDF-HFP was added to bottle A and stirred overnight in a 60°C water bath, wherein DMF was used as a solvent, and the ratio of lithium salt LiTFSI to polymer PVDF-HFP was controlled to be 1:1.1, thereby forming a high-salt system.

[0095] 2. After the above solution was stirred uniformly, an electrolyte precursor solution was obtained, which was placed in a glove box to remove bubbles under vacuum, then poured onto a clean glass plate, and coated into a film with a 400 μm high stainless steel scraper. Then the glass plate was immediately placed in a constant temperature and humidity chamber at 25°C and 80% humidity for 3 hours to obtain a preliminarily shaped electrolyte film.

[0096] 3. After the above film was removed from the glass plate and placed in a 60°C vacuum drying box for 24 h to remove residual solvent, an electrolyte film with a thickness of about 100 μm was obtained.

[0097] 4. After drying was completed, the electrolyte was quickly removed and cut into a circular piece with a radius of 8 mm or the required size using a slicer, then sealed and stored to prevent the electrolyte from absorbing water, thereby obtaining the electrolyte in this example.

[0098] Performance test:

[0099] (1) AC impedance, linear voltammetry and flame retardant performance test

[0100] The fire-retardant electrolytes in Examples 1-3 were assembled into batteries according to the corresponding test requirements for performance testing, wherein the positive electrode was LiFePO4. Lithium ion batteries for ion alternating current impedance spectrum testing were assembled according to the anode shell, spring, gasket, electrolyte film, gasket, and cathode shell. Lithium ion batteries for measuring charge-discharge cycles were assembled according to the anode shell, spring, gasket, LiFePO4, electrolyte film, lithium sheet, and cathode shell. All batteries were pressurized under a press machine at 50 N, and linear voltammetry scanning (LSV) and alternating current impedance spectrum tests were performed using a CHI660E electrochemical workstation. The voltage range for LSV testing was 2 V-5.5 V, and the scanning speed was 0.1 mV / s. The frequency for alternating current impedance spectrum testing was 106 Hz, and the amplitude was 5 mV. The above tests were all performed at 25°C. The ion conductivity was calculated from the measured impedance value according to the following formula:

[0101]

[0102] wherein R is the alternating current impedance of the electrolyte film obtained from the impedance diagram, L is the thickness of the electrolyte film, and S is the effective contact area between the electrolyte and the electrode. Considering that the film will be thinned under pressure when assembling the battery, the actual L of the film needs to be measured after disassembling the test battery.

[0103] All the above experimental steps were performed in a glove box under an argon atmosphere, so as to avoid the influence of water and oxygen on the experimental results.

[0104] The fire-retardant electrolytes in Examples 1-3 were subjected to alternating current impedance tests, linear voltammetry scanning (LSV) tests, and fire-retardant performance tests according to the above test methods, and the specific test results are shown in Figures 2-10 , wherein Figure 2 , Figure 3 , Figure 4 are the alternating current impedance test diagrams of Examples 1, 2, and 3, respectively. Figure 5 , Figure 6 , Figure 7 are the linear voltammetry test diagrams of Examples 1, 2, and 3, respectively. Figure 8 , Figure 9 , Figure 10 are the charge-discharge cycle test diagrams of the lithium iron phosphate batteries assembled from the fire-retardant electrolytes in Examples 1, 2, and 3, respectively. As can be seen from Figures 8-10 , the fire-retardant electrolytes in Examples 1-3 perform normally under long-term work, are not prone to heat, and have good thermal conductivity. As can be seen from Figures 2-10 , compared with Examples 1-2, Example 3 has better ion conductivity, electrochemical window, and fire-retardant performance, wherein the test data of the ion conductivity and electrochemical window are shown in Table 1 below.

[0105] Table 1. Ionic conductivity and electrochemical window test results of the flame-retardant electrolytes in Examples 1-3.

[0106]

[0107]

[0108] As shown in Table 1, the ionic conductivity of the flame-retardant electrolytes in Examples 1-3 of this invention is 3.2 × 10⁻⁶. -4 ~8.3×10 -4 S / cm, electrochemical window is 4.5-4.8V.

[0109] (2) Mechanical property testing

[0110] The stress-strain tests of the flame-retardant electrolytes in Example 3 and Comparative Example 1 were conducted using an electronic tensile testing machine. The specific test results are as follows: Figures 11-12 As shown, by Figures 11-12 It can be seen that the flame-retardant electrolytes in Example 3 all have excellent mechanical properties and can effectively inhibit the growth of lithium dendrites.

[0111] (3) Flame retardant performance test

[0112] The combustion performance of the electrolytes in Examples 1-3 and Comparative Example 1 was tested respectively, and the specific test results are as follows: Figures 13-15 As shown, where, Figure 13 (a) Figure 13 (b) and Figure 13 (c) are actual photos of the flame-retardant electrolyte in Example 1 before, during and after combustion; Figure 14 (a) Figure 14 (b) and Figure 14 (c) are actual photos of the flame-retardant electrolyte in Example 2 before, during and after combustion; Figure 15 (a) Figure 15 (b) and Figure 15 (c) Images of the flame-retardant electrolyte in Example 3 before, during, and after combustion are shown in Table 2. The self-extinguishing time of the electrolytes in Examples 1-3 and Comparative Example 1 during combustion is recorded.

[0113] Table 2 shows the flame retardant performance test results of the electrolytes in Examples 1-3 and Comparative Example 1 during combustion.

[0114]

[0115] Depend on Figures 13-15Compared with the comparative example 1, the filling material PBI is introduced in the inventive examples 1-3, so that the prepared electrolyte has excellent flame retardant effect and excellent thermal stability, the electrolyte can be self-extinguished within 8s, and the self-extinguishing time gradually shortens with the increase of the PBI content.

[0116] In summary, the flame-retardant electrolyte in the application has the following advantages:

[0117] 1. Good thermal stability, solving the problem of flame retardation in high salt system. On the basis of the synthesis of high salt system solid electrolyte, the application creatively uses polybenzimidazole polymer as a flame-retardant filler, and uses THF as a solvent, which greatly improves the flame-retardant performance of the flame-retardant electrolyte.

[0118] 2. High ionic conductivity. On the basis of using polymer PVDF-HFP and high content lithium salt LiTFSI, the flame-retardant electrolyte in the application uses THF to assist the flame-retardant filler PBI, and forms an additional polymer in the formed high salt system, and the ionic conductivity reaches 8.3*10 -4 S / cm.

[0119] 3. High lithium ion conduction rate and high thermal conductivity, the battery is not easy to heat during charging and discharging, effectively solving the safety hidden danger of the battery due to heating.

[0120] 4. Good cycle and rate performance, the electrolyte PSPBI 0.10 In the cycle test, the energy density remains stable, has a long cycle life and resistance to large current, and the charging and discharging is rapid.

[0121] 5. Effectively inhibits lithium dendrite growth. Since the added flame-retardant filler PBI has high mechanical strength, the strength of the electrolyte is improved, the growth of lithium dendrites is inhibited, the problem of battery short circuit caused by lithium dendrite piercing the electrolyte film is prevented, the related risks can be effectively reduced, the battery short circuit is reduced, and the explosion accident is avoided.

[0122] 6. Wide electrochemical window. The electrochemical window of the electrolyte PSPBI 0.10 after adding 10% PBI reaches 4.8V (vs. Li+ / Li), the electrolyte is not easy to oxidize and decompose, and the application range is wide.

[0123] 7. High energy density, can meet the power supply demand of new energy vehicles, mobile devices and the like.

[0124] 8. Simple preparation method, easy to operate, easy to popularize and apply, can realize industrialization, large-scale and commercial production.

[0125] 9. Good stress-strain performance, with the addition of PBI, the molecular interaction in the flame-retardant electrolyte is strengthened, the stress-strain ability of the electrolyte is improved, the flame-retardant electrolyte has good bending and stretching recovery performance, which is beneficial to the work of the battery in harsh environment, and even if partial deformation occurs, the safety and the ability to continue working of the equipment can be ensured.

[0126] The above describes the embodiments of the present application in detail, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the present application. In addition, the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

Claims

1. A flame-retardant electrolyte, characterized by: The preparation raw materials comprise a lithium salt, a polymer, and a flame-retardant filler; the mass ratio of the lithium salt to the polymer is 1:1.1; the mass ratio of the polymer to the flame-retardant filler is 100:10; The polymer is selected from polyvinylidene fluoride-hexafluoropropylene copolymer. The flame-retardant filler is selected from polybenzimidazole.

2. The flame retardant electrolyte of claim 1, wherein: The lithium salt is selected from at least one of lithium bis-trifluoromethanesulfonimide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium bisoxalate borate.

3. The flame retardant electrolyte of claim 1, wherein: The flame-retardant electrolyte is a solid-state electrolyte.

4. The flame retardant electrolyte of claim 1, wherein: The ionic conductivity of the flame-retardant electrolyte is 3.2 x 10 -4 ~8.3 x 10 -4 S / cm; and / or, the electrochemical window of the flame-retardant electrolyte is 4.5-4.8 V; and / or, the number of lithium ion transference accounts for 50-60% of the total number of ion transference in the flame-retardant electrolyte.

5. Process for the preparation of a flame-retardant electrolyte according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: S1: mixing a lithium salt, a polymer, and a solvent A to obtain a mixed solution A; mixing a flame-retardant filler and a solvent B to obtain a mixed solution B; S2: mixing the mixed solution A and the mixed solution B; S3: removing bubbles and then forming a film; pre-drying and then secondary drying to obtain the flame-retardant electrolyte.

6. The method of preparing a flame-retardant electrolyte according to claim 5, characterized in that: The pre-drying temperature is 20-30°C, and the pre-drying humidity is 75-85%; and / or, the secondary drying temperature is 55-65°C, and the secondary drying time is 15-30h.

7. The method of preparing a flame-retardant electrolyte according to claim 5, characterized in that: The solvent A is DMF; and / or, the solvent B is a mixture of DMF and THF.

8. The method of preparing a flame retardant electrolyte according to claim 5, characterized in that: The mixing temperature in step S1 is 55-65°C; and / or, the mixing temperature in step S2 is 55-65°C.

9. A lithium-ion battery, characterized by: The flame-retardant electrolyte according to any one of claims 1-4.

10. Application of the flame-retardant electrolyte according to any one of claims 1-4 in the field of batteries.

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