Flame-retardant lithium ion battery electrolyte and preparation method thereof

Abstract

The application discloses a kind of flame-retardant lithium ion battery electrolyte and preparation method thereof, belong to lithium ion battery electrolyte technical field, raw material includes diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, lithium hexafluorophosphate, lithium difluoro (oxalato) borate and flame-retardant additive, wherein, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate are solvent together, lithium hexafluorophosphate is lithium salt, lithium difluoro (oxalato) borate is lithium salt additive;Flame-retardant additive is with methyl methacrylate as shell material, with phosphoric acid ester flame retardant doped with heptafluorocyclopentane nano-capsule as core material, is prepared by suspension polymerization, can be uniformly dispersed in electrode liquid matrix, realizes that flame retardant and electrode surface are physically isolated, avoid phosphoric acid ester compound and negative electrode material sustained direct contact and interface side reaction, help to reduce the influence on lithium ion battery cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrolyte technology, specifically a flame-retardant lithium-ion battery electrolyte and its preparation method. Background Technology

[0002] With the widespread adoption of smartphones, laptops, and other electronic products, as well as the development of new energy vehicles, lithium-ion batteries, as recyclable energy supply devices, have gradually entered the public eye. Lithium-ion batteries mainly consist of four core components: the positive electrode, the negative electrode, the electrolyte, and the separator. Their working principle involves the insertion and extraction of lithium ions between the positive and negative electrodes to achieve charging and discharging. This charging and discharging process is highly reversible, giving lithium-ion batteries excellent cycle performance. Electrolyte is one of the core components of a lithium-ion battery. Its functions include serving as a medium for lithium-ion transport between the positive and negative electrodes to achieve charge balance, and acting as an insulator to prevent direct contact between the positive and negative electrodes, thus preventing short circuits. Lithium-ion battery electrolytes typically use carbonate-based organic solvents. While these solvents possess excellent ionic conductivity and electrochemical stability, they have low flash points and are flammable. Under conditions of abuse such as overcharging and short circuits, they are highly susceptible to combustion or even explosion. Therefore, lithium-ion batteries require extremely high safety standards in their applications.

[0003] Phosphate ester flame retardants have been widely studied due to their high flame retardant efficiency and low cost, and are commonly used flame retardant additives in lithium-ion batteries. However, phosphate ester flame retardants have poor compatibility with graphite anodes, easily co-intercalating and reducing on the anode surface, leading to a significant decrease in battery cycle performance.

[0004] Chinese patent application CN111146502A discloses a composite flame-retardant electrolyte and lithium-ion battery. It uses phosphate esters and cyclic phosphazene compounds as composite flame-retardant additives and introduces metal ion compounds as film-forming promoters. The solvation effect of metal ions and cyclic compounds promotes ring-opening polymerization on the electrode surface, thereby improving the compatibility between phosphate ester flame retardants and the electrode to some extent. However, in this scheme, the flame retardant is directly dissolved in the electrolyte in a free state, and the phosphate ester compounds continue to be in contact with the electrode material. Long-term cycling may trigger continuous interfacial side reactions, leading to interfacial film rupture and battery capacity decay. Therefore, while ensuring the flame-retardant effect of the lithium-ion battery electrolyte, how to reduce the continuous contact between phosphate ester flame retardants and the electrode to avoid affecting the cycle performance of the lithium-ion battery has become a hot topic in lithium-ion battery safety research. Summary of the Invention

[0005] The purpose of this invention is to provide a flame-retardant lithium-ion battery electrolyte and its preparation method, which encapsulates a carbonate-based flame retardant in the form of microcapsules to achieve physical isolation between the flame retardant and the electrode surface, thereby reducing the impact on the cycle performance of the lithium-ion battery.

[0006] The objective of this invention can be achieved through the following technical solutions: A flame-retardant lithium-ion battery electrolyte comprises diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, lithium hexafluorophosphate, lithium difluorooxalate borate, and flame-retardant additives. Diethyl carbonate, methyl ethyl carbonate, and ethylene carbonate are used as solvents, lithium hexafluorophosphate is a lithium salt, and lithium difluorooxalate borate is a lithium salt additive.

[0007] This invention also provides a method for preparing a flame-retardant lithium-ion battery electrolyte, comprising the following steps: In an argon atmosphere glove box with moisture and oxygen content both <0.1ppm, diethyl carbonate, methyl ethyl carbonate, and ethylene carbonate are added to a flask and magnetically stirred at 200-500 rpm until homogeneous. Then, lithium hexafluorophosphate and lithium difluorooxalate borate are added and magnetically stirred until homogeneous. Finally, flame retardant additives are added, and the mixture is ultrasonically separated for 3-5 minutes and then magnetically stirred until homogeneous to obtain a flame-retardant lithium-ion battery electrolyte.

[0008] Furthermore, the ratio of diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, lithium hexafluorophosphate, lithium difluorooxalate borate, and flame retardant additive is 30-35 mL: 35 mL: 30 mL: 20-24: 2.5-3.5 g: 5-15 g.

[0009] Furthermore, the flame retardant additive is prepared by suspension polymerization using methyl methacrylate as the shell material and a phosphate ester flame retardant doped with heptafluorocyclopentane nanocapsules as the core material. Specifically, it is prepared through the following steps: Step 1: Add zinc nitrate hexahydrate, cerium nitrate hexahydrate, and anhydrous methanol to a reaction vessel and stir to dissolve. Then, add an 8% (w / w) methanol solution of 2-methylimidazole to the reaction vessel and stir and mix for 5-8 min with ultrasonic assistance at a speed of 300-500 r / min. Then, stir and react at 20-30℃ for 4-6 h. Centrifuge the reaction product at 8000 r / min for 10 min. Then, wash the precipitate with methanol by centrifugation 2-3 times and dry it at 50-60℃ to constant weight to obtain cerium-doped nano-adsorbent material with an average particle size of 270-285 nm. Step 2: Add heptafluorocyclopentane and cerium-doped nano-adsorbent material to the flask and ultrasonically disperse at 30-35℃ for 5-8 min. Then place the flask containing the dispersion in a vacuum chamber, evacuate to 0.09 MPa and vacuum impregnate for 1-1.5 h. Then centrifuge the product at 8000 r / min for 10 min, take the precipitate, store the precipitate at 5-10℃ and grind it to obtain heptafluorocyclopentane nanocapsules.

[0010] Step 3: Add the phosphate ester flame retardant and heptafluorocyclopentane nanocapsules to the reaction vessel and stir at 300-500 r / min for 10-15 min. Then add a 1% (w / w) aqueous solution of sodium dodecyl sulfonate to the reaction vessel and stir at 1000-1200 r / min for 10-15 min to obtain an emulsion. Add methyl methacrylate and pentaerythritol triacrylate to a flask and ultrasonically disperse for 20-30 min. Then add the mixture to the reaction vessel containing the emulsion and stir at 1000-1200 r / min for 15-20 min. Add azobisisobutyronitrile (AIBN) as an initiator to the reaction vessel and stir at 75℃ and 300-400 r / min for 6-8 h. Centrifuge the product at 8000 r / min for 10 min, wash 2-3 times with a 30% (w / w) ethanol solution, and vacuum dry at 50-60℃ to constant weight to obtain the flame retardant additive.

[0011] Furthermore, in step 1, the ratio of the amounts of zinc nitrate hexahydrate, cerium nitrate hexahydrate, anhydrous methanol, and 2-methylimidazole methanol solution is 1.25g:0.36-0.37g:50mL:50mL.

[0012] Furthermore, in step 2, the ratio of heptafluorocyclopentane to cerium-doped nano-adsorbent material is 20 mL: 1-2 g.

[0013] Furthermore, in step 3, the ratio of the amounts of phosphate ester flame retardant, heptafluorocyclopentane nanocapsules, sodium dodecyl sulfonate aqueous solution, methyl methacrylate, pentaerythritol triacrylate, and azobisisobutyronitrile is 0.5-1g: 9-9.5g: 90-100mL: 10g: 1-1.2g: 0.1g.

[0014] Furthermore, the phosphate ester flame retardant is trimethyl phosphate or triethyl phosphate.

[0015] Furthermore, both the ultrasonic-assisted and ultrasonic-dispersed frequencies are 20kHz, and the power is 300W.

[0016] The beneficial effects of this invention are: 1. The flame-retardant lithium-ion battery electrolyte of this invention contains a flame-retardant additive in the form of microcapsules. The particle size of the flame-retardant additive is 2.5±0.5μm, which has good interfacial compatibility and dispersibility. It can be uniformly dispersed in the electrode liquid matrix, realizing the physical isolation between the flame retardant and the electrode surface, avoiding continuous direct contact and interfacial side reactions between phosphate ester compounds and negative electrode materials, and helping to reduce the impact on the cycle performance of lithium-ion batteries.

[0017] 2. The wall material of the flame retardant additive of this invention is polymethyl methacrylate, which has good affinity with carbonate solvents such as diethyl carbonate, helping to avoid a surge in electrolyte viscosity that could affect the electrochemical performance of the lithium-ion battery. The core material of the flame retardant additive is mainly composed of phosphate ester flame retardants, and also contains heptafluorocyclopentane nanocapsules as an expansion component. When the lithium-ion battery overheats or experiences thermal runaway, the heptafluorocyclopentane in the nanocapsules can vaporize to generate internal pressure, causing the microcapsule shell of the flame retardant additive to rupture, which helps to rapidly release the flame retardant substance and makes the flame retardant effect more timely.

[0018] 3. The cerium-doped nano-adsorbent material of this invention is a cerium-doped zinc MOF with an internal hollow structure, which can effectively adsorb heptafluorocyclopentane to form heptafluorocyclopentane nanocapsules; the cerium element therein can promote the decomposition of phosphate ester flame retardants, help promote char formation, and further improve the flame retardant effect. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1: This example provides a flame-retardant lithium-ion battery electrolyte, prepared by the following method: S1: 12.5 g of zinc nitrate hexahydrate, 3.6 g of cerium nitrate hexahydrate, and 500 mL of anhydrous methanol were added to a reaction vessel and stirred until dissolved. Then, 500 mL of a methanol solution containing 8% (w / w) 2-methylimidazole was added to the reaction vessel. The mixture was stirred for 5 min under ultrasonic assistance at 300 rpm, and then stirred and reacted at 20 °C for 4 h. The reaction product was centrifuged at 8000 rpm for 10 min, and the precipitate was washed twice with methanol by centrifugation and dried at 50 °C to constant weight to obtain cerium-doped nano-adsorbent material with an average particle size of 270 nm. The ultrasonic assistance frequency was 20 kHz and the power was 300 W.

[0021] S2: Add 60 mL of heptafluorocyclopentane and 3 g of cerium-doped nano-adsorbent material to a flask, and ultrasonically disperse it for 5 min at 30 °C. Then, place the flask containing the dispersion in a vacuum chamber, evacuate it to 0.09 MPa and vacuum impregnate it for 1 h. Then, centrifuge the product at 8000 r / min for 10 min, take the precipitate, store the precipitate at 5 °C and grind it to obtain heptafluorocyclopentane nanocapsules.

[0022] S3: 18g of trimethyl phosphate and 2g of heptafluorocyclopentane nanocapsules were added to a reaction vessel and stirred at 300r / min for 10min. Then, 180mL of a 1% sodium dodecyl sulfonate aqueous solution was added to the reaction vessel and stirred at 1000r / min for 10min to obtain an emulsion. 20g of methyl methacrylate and 2g of pentaerythritol triacrylate were added to a flask and ultrasonically dispersed for 20min. Then, the mixture was added to the reaction vessel containing the emulsion and stirred at 1000r / min for 15min. 0.2g of azobisisobutyronitrile (AIBN) as an initiator was added to the reaction vessel and stirred at 75℃ and 300r / min for 6h. The product was centrifuged at 8000r / min for 10min, washed twice with a 30% ethanol solution, and vacuum dried at 50℃ to constant weight to obtain a flame retardant additive with an average particle size of 2.5±0.5μm.

[0023] S4: In an argon atmosphere glove box with moisture and oxygen content both <0.1ppm, add 30mL of diethyl carbonate, 35mL of methyl ethyl carbonate and 30mL of ethylene carbonate to a flask, and mix thoroughly by magnetic stirring at 200r / min. Then add 20g of lithium hexafluorophosphate and 2.5g of lithium difluorooxalate borate and mix thoroughly by magnetic stirring. Finally, add 5g of flame retardant additive, sonicate for 3min and mix thoroughly by magnetic stirring to obtain a flame retardant lithium-ion battery electrolyte.

[0024] Example 2: This example provides a flame-retardant lithium-ion battery electrolyte, prepared by the following method: S1: 12.5 g of zinc nitrate hexahydrate, 3.65 g of cerium nitrate hexahydrate, and 500 mL of anhydrous methanol were added to a reaction vessel and stirred until dissolved. Then, 500 mL of a methanol solution containing 8% (w / w) 2-methylimidazole was added to the reaction vessel. The mixture was stirred and mixed for 6.5 min under ultrasonic assistance at 400 r / min, and then stirred and reacted at 25 °C for 5 h. The reaction product was centrifuged at 8000 r / min for 10 min, and the precipitate was washed twice with methanol by centrifugation and dried at 55 °C to constant weight to obtain cerium-doped nano-adsorbent material with an average particle size of 276 nm. The ultrasonic assistance frequency was 20 kHz and the power was 300 W.

[0025] S2: Add 60 mL of heptafluorocyclopentane and 4.5 g of cerium-doped nano-adsorbent material to a flask, and ultrasonically disperse at 32.5 °C for 6.5 min. Then, place the flask containing the dispersion in a vacuum chamber, evacuate to 0.09 MPa and vacuum impregnate for 1.25 h. Then, centrifuge the product at 8000 r / min for 10 min, collect the precipitate, store the precipitate at 7.5 °C and grind it to obtain heptafluorocyclopentane nanocapsules.

[0026] S3: 18.5g of triethyl phosphate and 1.5g of heptafluorocyclopentane nanocapsules were added to a reaction vessel and stirred at 400r / min for 12.5min. Then, 190mL of a 1% sodium dodecyl sulfonate aqueous solution was added to the reaction vessel and stirred at 1100r / min for 12.5min to obtain an emulsion. 20g of methyl methacrylate and 2.2g of pentaerythritol triacrylate were added to a flask and ultrasonically dispersed for 25min. Then, the mixture was added to the reaction vessel containing the emulsion and stirred at 1100r / min for 17.5min. 0.2g of azobisisobutyronitrile (AIBN) as an initiator was added to the reaction vessel and stirred at 75℃ and 350r / min for 7h. The product was centrifuged at 8000r / min for 10min, washed twice with a 30% ethanol solution, and vacuum dried at 55℃ to constant weight to obtain a flame retardant additive with an average particle size of 2.5±0.5μm.

[0027] S4: In an argon atmosphere glove box with moisture and oxygen content both <0.1ppm, add 33mL of diethyl carbonate, 35mL of methyl ethyl carbonate and 30mL of ethylene carbonate to a flask, and mix thoroughly by magnetic stirring at 350r / min. Then add 22g of lithium hexafluorophosphate and 3.0g of lithium difluorooxalate borate and mix thoroughly by magnetic stirring. Finally, add 10g of flame retardant additive, sonicate for 4min and mix thoroughly by magnetic stirring to obtain a flame retardant lithium-ion battery electrolyte.

[0028] Example 3: This example provides a flame-retardant lithium-ion battery electrolyte, prepared by the following method: S1: 12.5 g of zinc nitrate hexahydrate, 3.7 g of cerium nitrate hexahydrate, and 500 mL of anhydrous methanol were added to a reaction vessel and stirred until dissolved. Then, 500 mL of a methanol solution containing 8% (w / w) 2-methylimidazole was added to the reaction vessel. The mixture was stirred for 8 min under ultrasonic assistance at 500 rpm, and then stirred and reacted at 30 °C for 6 h. The reaction product was centrifuged at 8000 rpm for 10 min, and the precipitate was washed three times with methanol by centrifugation. It was then dried at 60 °C to constant weight to obtain cerium-doped nano-adsorbent material with an average particle size of 285 nm. The ultrasonic assistance frequency was 20 kHz and the power was 300 W.

[0029] S2: Add 60 mL of heptafluorocyclopentane and 6 g of cerium-doped nano-adsorbent material to a flask, and ultrasonically disperse at 35 °C for 8 min. Then place the flask containing the dispersion in a vacuum chamber, evacuate to 0.09 MPa and vacuum impregnate for 1.5 h. Then centrifuge the product at 8000 r / min for 10 min, take the precipitate, store the precipitate at 10 °C and grind it to obtain heptafluorocyclopentane nanocapsules.

[0030] S3: 19g of trimethyl phosphate and 1g of heptafluorocyclopentane nanocapsules were added to a reaction vessel and stirred at 500r / min for 15min. Then, 200mL of a 1% sodium dodecyl sulfonate aqueous solution was added to the reaction vessel and stirred at 1200r / min for 15min to obtain an emulsion. 20g of methyl methacrylate and 2.4g of pentaerythritol triacrylate were added to a flask and ultrasonically dispersed for 30min. Then, the mixture was added to the reaction vessel containing the emulsion and stirred at 1200r / min for 20min. 0.2g of azobisisobutyronitrile (AIBN) as an initiator was added to the reaction vessel and stirred at 75℃ and 400r / min for 8h. The product was centrifuged at 8000r / min for 10min, washed three times with a 30% ethanol solution, and vacuum dried at 60℃ to constant weight to obtain a flame retardant additive with an average particle size of 2.5±0.5μm.

[0031] S4: In an argon atmosphere glove box with moisture and oxygen content both <0.1ppm, add 35mL of diethyl carbonate, 35mL of methyl ethyl carbonate and 30mL of ethylene carbonate to a flask, and mix thoroughly by magnetic stirring at 500r / min. Then add 24g of lithium hexafluorophosphate and 3.5g of lithium difluorooxalate borate and mix thoroughly by magnetic stirring. Finally, add 15g of flame retardant additive, sonicate for 5min and mix thoroughly by magnetic stirring to obtain a flame retardant lithium-ion battery electrolyte.

[0032] Comparative Example 1: The difference from Example 3 is that the heptafluorocyclopentane nanocapsules prepared in step S2 are not added in step S3, while the other steps remain unchanged, and a flame-retardant lithium-ion battery electrolyte is prepared.

[0033] Comparative Example 2: The difference from Example 3 is that in step S3, the heptafluorocyclopentane nanocapsules are directly replaced with an equal mass of raw material heptafluorocyclopentane, while the other steps remain unchanged, to prepare a flame-retardant lithium-ion battery electrolyte.

[0034] Comparative Example 3: The difference from Example 3 is that in step S5, the flame retardant additive is replaced with an equal mass of a mixture of trimethyl phosphate and ethoxypentafluorocyclotriphosphazene (the mass ratio of trimethyl phosphate to ethoxypentafluorocyclotriphosphazene is 3:1) to prepare a flame retardant lithium-ion battery electrolyte.

[0035] The performance of the flame-retardant lithium-ion battery electrolytes in Examples 1-3 and Comparative Examples 1-3 was tested. Coin cells (Li||NCM coin cells) were prepared using different flame-retardant lithium-ion battery electrolytes: lithium nickel cobalt manganese oxide electrode was used as the positive electrode, lithium sheet was used as the negative electrode, and Celgard 2400 was used as the separator. Each flame-retardant lithium-ion battery electrolyte was added during the assembly process. The charge-discharge range for electrochemical performance testing was 3V-4.5V, and the capacity retention rate of the battery was tested after 500 cycles at 1C. Flame retardancy test: A 0.5cm diameter fiberglass cotton ball was immersed in the electrolyte of each flame-retardant lithium-ion battery for 2 minutes. After removal, it was placed on a wire frame, ignited with an ignition gun, and the self-extinguishing time was observed. The results are shown in Table 1. Table 1 Performance results of electrolytes for various flame-retardant lithium-ion batteries As can be seen from Table 1, the button half-cells in Examples 1-3 still have a high capacity retention rate after 500 cycles, and the self-extinguishing time of the electrolyte in the flame-retardant lithium-ion battery is also relatively short.

[0036] The significantly increased self-extinguishing time in Comparative Example 1 is due to the lack of heptafluorocyclopentane nanocapsules. These nanocapsules can release vaporized heptafluorocyclopentane upon overheating, which promotes the rupture of the microcapsule-form flame retardant additive shell through gas expansion, thereby rapidly releasing the flame retardant substance and reducing the self-extinguishing time.

[0037] The lowest capacity retention rate after 500 cycles in Comparative Example 2 is likely due to the lack of cerium-doped nano-adsorbent loading. The direct addition of heptafluorocyclopentane to the microcapsule-form flame retardant additive led to decreased stability, making it prone to gas expansion during cycling and subsequent leakage, thus affecting the electrochemical performance of the coin cell. In contrast, the self-extinguishing time in Comparative Example 2 was shorter than in Examples 1 and 2, and longer than in Example 3. This is likely due to the lack of cerium-doped nano-adsorbent loading, resulting in volatilization loss during the preparation of the flame retardant additive. This indicates that heptafluorocyclopentane nanocapsules can increase the stability of the flame retardant additive.

[0038] The capacity retention rate after 500 cycles in Comparative Example 3 was lower than that in Example 3, and the self-extinguishing time was greater than that in Example 3, indicating that the microcapsule-form flame retardant additive in Example 1 has better compatibility with the lithium-ion battery electrolyte.

[0039] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0040] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a flame-retardant lithium-ion battery electrolyte, characterized in that, Includes the following steps: Diethyl carbonate, methyl ethyl carbonate, and ethylene carbonate were added to a flask in an argon-atmosphere glove box and magnetically stirred at 200-500 r / min until homogeneous. Then, lithium hexafluorophosphate and lithium difluorooxalate borate were added and magnetically stirred until homogeneous. Finally, flame retardant additives were added, and the mixture was ultrasonically separated for 3-5 min and magnetically stirred until homogeneous to obtain a flame-retardant lithium-ion battery electrolyte. The flame retardant additive is prepared by suspension polymerization using methyl methacrylate as the shell material and a phosphate ester flame retardant doped with heptafluorocyclopentane nanocapsules as the core material.

2. The method for preparing a flame-retardant lithium-ion battery electrolyte according to claim 1, characterized in that, The ratio of diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, lithium hexafluorophosphate, lithium difluorooxalate borate, and flame retardant additive is 30-35 mL: 35 mL: 30 mL: 20-24: 2.5-3.5 g: 5-15 g.

3. The method for preparing a flame-retardant lithium-ion battery electrolyte according to claim 1, characterized in that, The flame retardant additive is prepared through the following steps: Phosphate ester flame retardants and heptafluorocyclopentane nanocapsules were added to a reaction vessel and stirred at 300-500 r / min for 10-15 min. Then, 1 wt% sodium dodecyl sulfonate aqueous solution was added and stirred at 1000-1200 r / min for 10-15 min. Methyl methacrylate and pentaerythritol triacrylate were ultrasonically dispersed for 20-30 min and added to the reaction vessel. The mixture was stirred at 1000-1200 r / min for 15-20 min. Azobisisobutyronitrile was then added and the mixture was stirred at 75℃ and 300-400 r / min for 6-8 h. The mixture was centrifuged at 8000 r / min for 10 min, washed, and vacuum dried to constant weight to obtain the flame retardant additive.

4. The method for preparing a flame-retardant lithium-ion battery electrolyte according to claim 3, characterized in that, The ratio of the phosphate ester flame retardant, heptafluorocyclopentane nanocapsules, aqueous solution of sodium dodecyl sulfonate, methyl methacrylate, pentaerythritol triacrylate and azobisisobutyronitrile is 0.5-1g: 9-9.5g: 90-100mL: 10g: 1-1.2g: 0.1g.

5. The method for preparing a flame-retardant lithium-ion battery electrolyte according to claim 3, characterized in that, The phosphate ester flame retardant is trimethyl phosphate or triethyl phosphate.

6. The method for preparing a flame-retardant lithium-ion battery electrolyte according to claim 3, characterized in that, The heptafluorocyclopentane nanocapsules were prepared via the following steps: Add heptafluorocyclopentane and cerium-doped nano-adsorbent material to a flask, ultrasonically disperse at 30-35℃ for 5-8 min, place in a vacuum chamber, evacuate to 0.09 MPa and vacuum impregnate for 1-1.5 h, then centrifuge the product at 8000 r / min for 10 min, collect the precipitate, store the precipitate at 5-10℃ and grind it into fine particles to obtain heptafluorocyclopentane nanocapsules.

7. The method for preparing a flame-retardant lithium-ion battery electrolyte according to claim 6, characterized in that, The ratio of heptafluorocyclopentane to cerium-doped nano-adsorbent material is 20 mL: 1-2 g.

8. The method for preparing a flame-retardant lithium-ion battery electrolyte according to claim 6, characterized in that, The cerium-doped nano-adsorbent material is prepared by the following steps: Zinc nitrate hexahydrate, cerium nitrate hexahydrate, and anhydrous methanol were added to a reaction vessel and stirred to dissolve. Then, an 8 wt% methanol solution of 2-methylimidazole was added. The mixture was stirred at 300-500 rpm for 5-8 min with ultrasonic assistance and stirred at 20-30°C for 4-6 h. The reaction product was centrifuged at 8000 rpm for 10 min, and the precipitate was washed and dried to constant weight to obtain cerium-doped nano-adsorbent material.

9. The method for preparing a flame-retardant lithium-ion battery electrolyte according to claim 8, characterized in that, The ratio of the amount of zinc nitrate hexahydrate, cerium nitrate hexahydrate, anhydrous methanol, and 2-methylimidazole in the methanol solution is 1.25g:0.36-0.37g:50mL:50mL.

10. A flame-retardant lithium-ion battery electrolyte, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.

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