Flame-retardant fluorinated ultrahigh-voltage-resistant electrolyte as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium metal batteries, and particularly relates to a flame-retardant fluorinated ultrahigh-voltage-resistant electrolyte and a preparation method and application thereof, the flame-retardant fluorinated ultrahigh-voltage-resistant electrolyte comprises a fluorinated solvent and a lithium salt, and the fluorinated solvent comprises a fluorinated cyclic ester solvent and a fluorinated linear ester solvent. The flame-retardant fluorinated ultrahigh-voltage-resistant electrolyte has the advantages that the flame-retardant performance is good, the wettability to a diaphragm and an electrode material is good, the electrochemical window is wide, the stable charge-discharge cycle performance is maintained under the ultrahigh voltage of 4.8-5.2 V, and the cycle performance of a battery is excellent; the composite material has excellent compatibility with a high-voltage positive electrode and a lithium metal negative electrode, and a compact CEI layer rich in fluorine and boron elements can be effectively formed on the true electrode side; the preparation method of the flame-retardant fluorinated ultrahigh-voltage-resistant electrolyte is simple to operate and easy to control, and the flame-retardant fluorinated ultrahigh-voltage-resistant electrolyte can be immediately used after being prepared in a water-free and oxygen-free environment, is non-flammable and can be stored at normal temperature.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium metal batteries, and particularly relates to a flame-retardant fluorinated ultra-high voltage resistant electrolyte and a preparation method and application thereof. Background Art

[0002] Driven by the global energy structure transformation and the strategic goals of "carbon peak and carbon neutrality", emerging industries such as electric vehicles and smart grids have put forward higher requirements for energy storage systems. Developing new battery technologies with high energy density (>400 Wh / kg), long cycle life and intrinsic safety characteristics has become the core breakthrough point to promote the new energy revolution and achieve the dual-carbon strategy.

[0003] Currently, commercial lithium-ion batteries are limited by the intrinsic characteristics of graphite anodes and layered oxide cathode materials, and their energy density has approached the theoretical limit, making it difficult to meet the growing demand for high specific energy applications. The lithium metal anode, with its ultra-high theoretical capacity (3860 mAh / g) and low electrochemical potential (-3.04 V vs. SHE), when paired with high-voltage cathode materials (such as lithium nickel manganese oxide, lithium-rich manganese-based materials, etc.) to construct a lithium metal battery system, can theoretically achieve an energy density breakthrough of 500 Wh / kg, showing great application prospects. However, this system faces multiple technical challenges: (1) Traditional carbonate electrolytes have a low flash point (<40 °C), are flammable and explosive, posing serious safety hazards; (2) Side reactions at the electrolyte / lithium metal interface lead to dendrite growth and Coulombic efficiency decay; (3) High-voltage cathode materials cause oxidation and decomposition of the electrolyte in the deeply delithiated state. These key scientific issues have severely hindered the industrialization process of high-voltage lithium metal batteries and urgently require breakthrough innovations in material systems and interface regulation.

[0004] In response to the above technical bottlenecks, the research and development of new electrolyte systems with high working voltages has become the focus of attention in the academic and industrial communities. Among them, fluorinated electrolytes have shown great potential due to their unique molecular structure and performance advantages and have received extensive attention from researchers in recent years. Existing studies have shown that the stable working window of conventional high-voltage electrolytes is mostly limited to the range of 4.2 V - 4.7 V (vs. Li+ / Li), and there are still few reports on electrolyte systems that can maintain long-term stable cycling under extremely high voltages exceeding 5.0 V. Developing new electrolytes with a wide electrochemical window (>5.0 V) and good interface stability has become a key scientific issue to promote the development of next-generation high-energy density batteries. The breakthrough of this technical bottleneck will promote the commercial application development of high-voltage lithium metal batteries and has important research value and practical significance. Summary of the Invention

[0005] In view of the above deficiencies in the prior art, the present invention provides a flame-retardant fluorinated ultra-high voltage resistant electrolyte and a preparation method and application thereof. The specific technical solutions are as follows: The first object of the present invention is to provide a flame-retardant fluorinated ultra-high voltage resistant electrolyte, comprising a fluorinated solvent and a lithium salt, wherein the fluorinated solvent comprises a fluorinated cyclic ester solvent and a fluorinated linear ester solvent.

[0006] The flame-retardant fluorinated ultra-high voltage resistant electrolyte of the present invention has good flame-retardant performance, good wettability to the separator and electrode materials, and a wide electrochemical window (>5.0V). It has stable charge-discharge cycle performance under ultra-high voltage of 4.8V - 5.2V, and the battery has excellent cycle performance, filling the domestic blank of ultra-high voltage resistant electrolytes.

[0007] Further, the fluorinated cyclic ester solvent is one or more of vinylene carbonate fluoride, 4,4-bis(fluorocarbonyl)ethylene, 4,5-bis(fluorocarbonyl)ethylene, fluoropropylene carbonate, and 3,3,3-trifluoropropylene carbonate; preferably vinylene carbonate fluoride.

[0008] Further, the fluorinated linear ester solvent is one or more of (2-fluoroethyl) ethyl carbonate, 2,2-difluoroethyl ethyl carbonate, methyl trifluoroethyl carbonate, 2,2-difluoroethyl methyl carbonate, and 2,2,2-trifluoroethyl ethyl carbonate; preferably 2,2,2-trifluoroethyl ethyl carbonate.

[0009] Further, the lithium salt is one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorophosphate, lithium difluoro(dioxalato)phosphate, and lithium tetrafluoroborate; preferably lithium bis(trifluoromethanesulfonyl)imide and / or lithium difluoro(oxalato)borate.

[0010] Further, the mass percentage content of the fluorinated solvent is 80 - 90wt%, and the mass percentage content of the lithium salt is 10 - 20wt%.

[0011] Further, the mass percentage content of the fluorinated solvent is 85wt%, and the mass percentage content of the lithium salt is 15wt%.

[0012] Further, the fluorinated cyclic ester solvent is vinylene carbonate fluoride with a mass percentage content of 45wt%; the fluorinated linear ester solvent is 2,2,2-trifluoroethyl ethyl carbonate with a mass percentage content of 40wt%.

[0013] Further, the mass percentage content of lithium bis(trifluoromethanesulfonyl)imide in the lithium salt is 10wt%, and the mass percentage content of lithium difluoro(oxalato)borate is 5wt%.

[0014] The second object of the present invention is to provide a preparation method of the above-mentioned flame-retardant fluorinated ultra-high voltage resistant electrolyte, comprising the following steps: (1)Dehydrate the fluorinated cyclic ester solvent and the fluorinated linear ester solvent, and store them in an anhydrous and anaerobic environment; (2)In an anhydrous and anaerobic environment, add a lithium salt to the fluorinated cyclic ester solvent and the fluorinated linear ester solvent dehydrated in step (1), stir for more than 10 h until clear, and then stand for 12 - 24 h to obtain the product.

[0015] Furthermore, the fluorinated cyclic ester solvent and the fluorinated linear ester solvent are dehydrated using activated 4A molecular sieve.

[0016] Furthermore, the water content in the fluorinated cyclic ester solvent and the fluorinated linear ester solvent is less than 10 ppm.

[0017] Furthermore, the anhydrous and anaerobic environment is a glove box filled with a protective gas, with oxygen < 0.01 ppm and water < 0.01 ppm.

[0018] Furthermore, the protective gas is at least one or more of argon, nitrogen, or helium.

[0019] The third object of the present invention is to provide an ultra-high pressure resistant lithium battery, including the above-mentioned flame-retardant fluorinated ultra-high pressure resistant electrolyte.

[0020] Furthermore, the positive electrode of the ultra-high pressure resistant lithium battery is a high-voltage positive electrode material, such as a ternary nickel cobalt manganese material or a lithium-rich manganese material, the negative electrode is a lithium sheet, and a polyethylene separator is provided between the positive and negative electrodes.

[0021] The beneficial effects of the present invention are as follows: (1)The flame-retardant fluorinated ultra-high pressure resistant electrolyte of the present invention has good flame-retardant performance, good wettability to the separator and the electrode material, and a wide electrochemical window (> 5.0 V). It has excellent cycling performance under ultra-high pressure, can maintain the stable cycling of a ternary coin-type lithium battery, and can provide an initial discharge capacity of nearly 200 mAh g −1 at 5.2 V ultra-high pressure, and shows good cycling stability. After 200 cycles, the discharge capacity is still 131.5 mAh g −1 , and the capacity retention rate is 66.4%. It demonstrates excellent long-term cycling stability and rate performance, effectively proving that the electrolyte has excellent cycling performance under ultra-high pressure and has good application prospects.

[0022] (2)The flame-retardant fluorinated ultra-high pressure resistant electrolyte of the present invention has excellent compatibility with both the high-voltage positive electrode and the lithium metal negative electrode, and can effectively form a dense CEI layer rich in fluorine and boron elements on the cathode side.

[0023] (3)The preparation method of the flame-retardant fluorinated ultra-high pressure resistant electrolyte of the present invention is simple and easy to control. It can be used immediately after being prepared in an anhydrous and anaerobic environment, is not flammable, and can be stored at room temperature. Description of the Drawings

[0024] Figure 1 This is the capacity-voltage curve of the ultra-high pressure resistant fluorinated electrolyte of Example 1 of the present invention in the Li / NCM811 full cell system at a rate of 0.5C.

[0025] Figure 2 This is the long cycle performance graph of the ultra-high pressure resistant fluorinated electrolyte of Example 1 of the present invention in the Li / NCM811 full cell system at a rate of 0.5C.

[0026] Figure 3 This is the TEM electron micrograph of the positive electrode plate after 200 cycles of the electrolyte prepared in Example 1 of the present invention. Detailed Description of the Invention

[0027] The principles and features of the present invention will be described below in conjunction with examples. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. The raw materials involved in the present invention are all ordinary commercially available products unless otherwise specified. Examples

[0028] A flame-retardant fluorinated ultra-high pressure resistant electrolyte, comprising a fluorinated cyclic ester solvent, a fluorinated linear ester solvent and a lithium salt; Weigh lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluoro(oxalato)borate (LiDFOB) required for preparation according to a molar ratio of 4:1, and the total concentration of the electrolyte is 1.0 - 1.2 mol / L -1 ; The volume ratio of fluoroethylene carbonate (FEC) to ethyl 2,2,2-trifluoroethyl carbonate (FDEC) is 1:1.

[0029] The preparation method of the above-mentioned flame-retardant fluorinated ultra-high pressure resistant electrolyte comprises the following steps: (1) Dehydrate the fluorinated cyclic ester solvent and the fluorinated linear ester solvent, and store them in a glove workbox filled with argon (oxygen < 0.01 ppm, water < 0.01 ppm); (2) In the glove workbox, add the lithium salt to the fluorinated cyclic ester solvent and the fluorinated linear ester solvent dehydrated in step (1), stir for more than 12 h until clear, and then let it stand for 12 h to obtain.

[0030] Assemble a lithium battery: Select a CR2032 type positive and negative battery case, a polypropylene separator, a stainless steel gasket, and a corrugated spring sheet. The positive electrode uses an NCM811 electrode plate, the negative electrode uses a lithium sheet with a thickness of 100 μm, place the polyethylene separator in the middle of the positive and negative electrodes, and drop 20 μL of the flame-retardant fluorinated ultra-high pressure resistant electrolyte on both sides respectively, and finally perform encapsulation to obtain a Li / NCM811 full cell.

[0031] A lithium battery containing a flame-retardant fluorinated ultra-high-voltage electrolyte was placed in a Blue Energy Test System to test its high-voltage charge-discharge cycle performance. The charge-discharge voltage range was set to 2.8 - 5.2 V, and the charge-discharge rate was 0.5 C. At room temperature of 25 °C, the test results are as Figure 1 shown. After 200 cycles, the discharge capacity was 132.5 mAh g −1 , and the capacity retention rate was 66.4%; Figure 2 Its electrochemical stability can be seen more intuitively; TEM characterization was performed on the positive electrode after cycling. As Figure 3 shown, a dense and smooth CEI layer was formed in the high-voltage-resistant fluorinated electrolyte system, enabling the battery to exhibit extremely excellent electrochemical performance even under ultra-high-voltage conditions. Example

[0032] A flame-retardant fluorinated ultra-high-voltage electrolyte includes a fluorinated cyclic ester solvent, a fluorinated linear ester solvent, and a lithium salt; An electrolyte with a total lithium salt concentration of 1.0 - 1.2 mol L -1 was prepared. The lithium salt was lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluoro(oxalato)borate (LiDFOB) with a molar ratio of 4:1; the volume ratio of the fluorinated solvents fluoroethylene carbonate (FEC) and ethyl 2,2,2-trifluoroethyl carbonate (FDEC) was 1:1.

[0033] The preparation method of the flame-retardant fluorinated ultra-high-voltage electrolyte in this example and the assembly method of the lithium metal full battery are the same as those in Example 1 and will not be elaborated here.

[0034] The cycle performance of the obtained Li / NCM811 full battery was tested, and the charge-discharge rate was 0.5 C. At room temperature of 25 °C and a cut-off voltage of 5.2 V, after 200 charge-discharge processes, the high-voltage-resistant fluorinated electrolyte in this example has excellent room-temperature cycle performance. The initial discharge specific capacity was 199.5 mAh g -1 , and the discharge specific capacity was still as high as 132.1 mAh g after 200 cycles -1 . Example

[0035] A flame-retardant fluorinated ultra-high-voltage electrolyte includes a fluorinated cyclic ester solvent, a fluorinated linear ester solvent, and a lithium salt; An electrolyte with a total lithium salt concentration of 1.0 - 1.2 mol L-1 was prepared. Lithium bis(trifluoromethanesulfonyl)imide and lithium difluoro(oxalato)borate with a molar ratio of 8:1 were weighed; the volume ratio of the fluorinated solvents fluoroethylene carbonate (FEC) and ethyl 2,2,2-trifluoroethyl carbonate (FDEC) was 1:1.

[0036] The preparation method of the flame-retardant fluorinated ultra-high voltage resistant electrolyte in this example is the same as that in Example 1, and will not be elaborated here.

[0037] Assemble a lithium battery: Select a CR2032 type stainless steel battery case as the positive and negative electrode case, place a polypropylene separator between an NCM811 positive electrode sheet with a diameter of 12 mm and a lithium sheet with a thickness of 100 μm, and drop 25 μL of the prepared flame-retardant fluorinated ultra-high voltage resistant electrolyte on both sides respectively, and then encapsulate to obtain a button-type lithium metal battery.

[0038] Place the encapsulated button-type lithium battery in a BlueTEC test system and set the parameters, and perform cyclic charge and discharge tests at a charge and discharge current density of 0.5C and an ultra-high cut-off voltage of 5.2V. The Li / NCM811 battery obtained an initial discharge capacity close to 200 mAh g −1 After 200 cycles of charge and discharge tests, a discharge specific capacity of 133.7 mAh g −1 and an excellent performance of a discharge specific capacity retention rate of 66.4% were obtained. Example

[0039] A flame-retardant fluorinated ultra-high voltage resistant electrolyte, comprising a fluorinated cyclic ester solvent, a fluorinated linear ester solvent and a lithium salt; Prepare an electrolyte with a total lithium salt concentration of 1.0 - 1.2 mol L-1, weigh and mix LiTFSI and LiDFOB with a molar ratio of 8:1 evenly, and fluorinated solvents FEC and FDEC with a volume ratio of 1:1.

[0040] The preparation method of the flame-retardant fluorinated ultra-high voltage resistant electrolyte in this example is the same as that in Example 1, and will not be elaborated here.

[0041] Assemble a lithium battery: Assemble the positive and negative electrode cases, NCM811 electrode sheets, and lithium sheets. Use a pipette to take 20 μL of the prepared flame-retardant fluorinated ultra-high voltage resistant electrolyte and drop it into the contact surfaces of the positive electrode sheet, lithium sheet and polyethylene separator respectively, and then encapsulate to obtain a button-type lithium metal battery.

[0042] Place the encapsulated lithium metal battery in a BlueTEC instrument for testing. The test conditions are cyclic charge and discharge tests at a cut-off working voltage of 5.2V and a current of 1C. The test results show that the average Coulomb efficiency remains at 99.2% after 200 cycles of charge and discharge, and the discharge specific capacity is 132.7 mAh g −1 , and the capacity retention rate is 66.3%.

[0043] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A flame retardant fluorinated ultrahigh voltage resistant electrolyte, characterized in that: The invention comprises a fluorinated solvent and a lithium salt, wherein the fluorinated solvent comprises a fluorinated cyclic ester solvent and a fluorinated linear ester solvent.

2. The flame-retardant fluorinated ultrahigh voltage resistant electrolyte according to claim 1, characterized in that: The fluorinated cyclic ester solvent is one or more of fluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, trifluoropropylene carbonate and 3,3,3-trifluoropropylene carbonate.

3. The flame-retardant fluorinated ultrahigh voltage resistant electrolyte according to claim 1, characterized in that: The fluorinated linear ester solvent is one or more of ethyl carbonate (2-fluoroethyl), 2,2-difluoroethyl ethyl carbonate, methyl trifluoroethyl carbonate, 2,2-difluoroethyl methyl carbonate, and 2,2,2-trifluoroethyl ethyl carbonate.

4. The flame-retardant fluorinated ultrahigh voltage resistant electrolyte according to claim 1, characterized in that: The lithium salt is one or more of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl imide), lithium bis(fluorosulfonyl imide), lithium perchlorate, lithium difluorooxalatoborate, lithium bis(oxalatoborate), lithium difluorophosphate, lithium difluorobis(oxalatophosphate), and lithium tetrafluoroborate.

5. The flame-retardant fluorinated ultrahigh voltage resistant electrolyte according to claim 1, characterized in that: The mass percentage of the fluorinated solvent is 80-90wt%, and the mass percentage of the lithium salt is 10-20wt%.

6. The flame-retardant fluorinated ultrahigh voltage resistant electrolyte according to claim 5, characterized in that: The mass percentage of the fluorinated solvent is 85 wt %, and the mass percentage of the lithium salt is 15 wt %.

7. The flame-retardant fluorinated ultrahigh voltage resistant electrolyte according to claim 6, characterized in that: The fluorinated cyclic ester solvent is fluoroethylene carbonate, and its mass percentage is 45wt%; the fluorinated linear ester solvent is 2,2,2-trifluoroethyl ethyl carbonate, and its mass percentage is 40wt%.

8. The flame-retardant fluorinated ultrahigh-voltage resistant electrolyte according to claim 6, characterized in that: The mass percentage of lithium bis(trifluoromethylsulfonyl)imide in the lithium salt is 10 wt %, and the mass percentage of lithium difluorooxalatoborate is 5 wt %.

9. A method for preparing a flame-retardant fluorinated ultrahigh voltage resistant electrolyte according to any one of claims 1 to 8, characterized in that: The steps include: (1) removing water from the fluorinated cyclic ester solvent and the fluorinated linear ester solvent and storing them in an anhydrous and oxygen-free environment; (2) In an anhydrous and oxygen-free environment, lithium salt is added to the fluorinated cyclic ester solvent and the fluorinated linear ester solvent after the water is removed in step (1), stirred for more than 10 hours until the solvent becomes clear, and then allowed to stand for 12-24 hours to obtain the product.

10. An ultra-high voltage lithium battery, characterized in that: It comprises the flame retardant fluorinated ultra-high voltage resistant electrolyte as described in any one of claims 1 to 8.

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