Non-aqueous electrolyte for lithium ion battery and lithium ion battery

Abstract

The invention is applied to the technical field of lithium ion batteries, and discloses a non-aqueous electrolyte for a lithium ion battery, which comprises the following substances in percentage by weight: 1-20% of electrolyte lithium salt, 70-90% of organic solvent and 0.1-10% of functional additive, the electrolyte lithium salt is composed of a lithium salt A and a lithium salt B, and the weight fraction of the lithium salt A is greater than that of the lithium salt B; the organic solvent is composed of a solvent C and a solvent D, the weight fraction of the solvent C is 3%-20%, and the weight fraction of the solvent D is 50%-88%. According to the non-aqueous electrolyte for the lithium ion battery, the lithium fluorosulfonyl difluoroacetate is adopted as the main lithium salt to prepare the non-aqueous electrolyte, so that the electrolyte has the advantages of high ionic conductivity, stability in air and good thermal stability, and the performance of the lithium battery is more excellent.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, in particular to a non-aqueous electrolyte for lithium ion batteries and a lithium ion battery. Background Art

[0002] As one of the four major components of a battery, the electrolyte (liquid electrolyte) plays a pivotal role. The positive and negative electrodes in a lithium-ion battery need to conduct lithium ions inside the battery through the electrolyte to complete the conversion of electrical energy, and lithium salts play the role of ion conduction in the electrolyte. Lithium ions are relatively small and can be conducted faster in the electrolyte than other ions. The fast conduction speed of lithium ions can improve the discharge and charging efficiency of the battery and extend the battery's service life.

[0003] Lithium salts can affect the voltage of the battery by adjusting the ion concentration in the electrolyte, making it easier to maintain the battery voltage within the appropriate range. When a lithium-ion battery is discharged, the lithium ions in the positive electrode material move toward the negative electrode, and the electrons move from the negative electrode to the positive electrode, thereby generating electrical energy. When charging, the process is exactly the opposite. The lithium ions in the positive electrode material move toward the positive electrode, thereby storing electrical energy. By controlling the concentration of lithium salts, the battery voltage can be smoothly controlled to achieve the optimal working state.

[0004] In lithium-ion batteries, the presence of lithium salts in the electrolyte can inhibit the occurrence of electrochemical side reactions. Electrochemical side reactions refer to physical or chemical changes produced by the battery during the charging and discharging process. If the reaction is too strong, it will lead to the loss of active materials in the battery and shorten the battery life, thereby affecting the performance of the battery. Lithium salts can form a stable solid electrolyte film (SEI and CEI), thereby inhibiting the electrochemical reaction process inside the battery and ensuring long-term reliable use of the battery.

[0005] The most widely used lithium salt is lithium hexafluorophosphate (LiPF6), which has been widely used in lithium-ion batteries due to its good ionic conductivity, relatively low cost and the ability to form a stable passivation film on aluminum foil. As the most widely used lithium hexafluorophosphate, it has strong deliquescent properties and is easily decomposed when exposed to air or heated. When exposed to air or heated, lithium hexafluorophosphate decomposes rapidly in the air due to the action of water vapor, releasing phosphorus pentafluoride (PF5) and producing white smoke.

[0006] There are many main production methods for lithium hexafluorophosphate, namely organic solvent method, hydrogen fluoride solvent method, gas-solid reaction method, rheological phase method, solid-solid method and ion exchange method. Among them, the hydrogen fluoride solvent method and organic solvent method are more commonly used in the market. The other four production processes have not achieved large-scale industrial production, and the synthesis conditions are relatively harsh. The hydrogen fluoride solvent method is to dissolve lithium fluoride LiF in anhydrous hydrogen fluoride HF to form a LiF·HF solution, and then pass high-purity PF5 gas to react to obtain LiPF6 crystals, and then separate and dry to obtain LiPF6 products. The organic solvent method is to dissolve LiF solid in an organic solvent, and then pass high-purity PF5 gas. The LiPF6 generated by the reaction is directly dissolved in the organic solvent, and the resulting solvent can be directly used as the electrolyte of lithium-ion batteries.

[0007] The fluoride ions in lithium bis(fluorosulfonyl)imide (LiFSI) have strong electron-withdrawing properties, which weaken the coordination between anions and cations of lithium salts. The lithium ions are very active, and have high ionic conductivity, thermal stability and electrochemical stability. There are basically no side reactions, and the expansion effect can be suppressed. However, the synthesis cost of LiFSI is high, the synthesis route is prone to corrode the reaction equipment, and when used in the electrolyte, it is easy to corrode the negative electrode current collector, and the production process is complicated. Therefore, at present, LiFSI is mainly in the form of additives and compounded with LiF6, and cannot significantly replace lithium hexafluorophosphate. Summary of the invention

[0008] The object of the present invention is to provide a non-aqueous electrolyte for lithium ion batteries and lithium ion batteries, so as to solve the problems mentioned in the above background technology that LiPF6 has poor thermal stability and is easy to hydrolyze, and LiFSI has complex preparation and corrosive current collector and high cost, and cannot replace lithium hexafluorophosphate to a large extent.

[0009] To achieve the above object, the present invention provides the following technical solution: a non-aqueous electrolyte for lithium ion batteries, comprising the following substances by weight: 1-20% of electrolyte lithium salt, 70-90% of organic solvent and 0.1%-10% of functional additives;

[0010] The electrolyte lithium salt consists of lithium salt A and lithium salt B, and the weight fraction of lithium salt A is greater than that of lithium salt B;

[0011] The organic solvent consists of solvent C and solvent D, wherein the weight fraction of solvent C is 3%-20%, and the weight fraction of solvent D is 50%-88%.

[0012] Preferably, the lithium salt A is lithium 2-fluorosulfonyldifluoroacetate, and the lithium salt B is one or a mixture of lithium tetrafluoroborate, lithium hexafluorophosphate, lithium bisfluorosulfonamide, lithium bis(trifluoromethylsulfonyl)imide, lithium oxalate borate, lithium difluorooxalate borate, lithium difluorobisoxalate phosphate, lithium fluoromalonate borate, lithium 2-trifluoromethyl-4,5-dicyanoimidazole and lithium difluorophosphate.

[0013] Preferably, the solvent C is one or more of sulfoxide, sulfone or cyclic sulfone solvents, specifically dimethyl sulfoxide, diphenyl sulfoxide, ethyl methyl sulfone, ethyl methoxyethyl sulfone, cyclopentane, dimethyl sulfone, ethyl isopropyl sulfone, ethyl isobutyl sulfone and methyl isopropyl sulfone or a mixture of one or more of them.

[0014] Preferably, the solvent D is a mixture of one or more cyclic carbonate compounds or chain carbonate compounds, wherein the cyclic carbonate compound is a mixture of one or more of ethylene carbonate, propylene carbonate, and γ-butyrolactone, and the chain carbonate compound is a mixture of one or more of diethyl carbonate, methyl ethyl carbonate, and a carbonate derivative synthesized from a straight-chain or branched fatty monoalcohol having a carbon number of 3-8 and carbonic acid.

[0015] Preferably, the functional additive is tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, fluoroethylene carbonate, difluoroethylene carbonate, vinyl sulfite, vinyl sulfate, propylene sulfate, methylene disulfonate, vinyl ethylene carbonate, 1,4-butane sultone, 1,3-propane sultone, 1-propylene-1,3-sultone, 1,3-propylene sultone, vinyl carbonate, vinyl ethylene carbonate, ethoxy pentafluorocyclotriphosphazene, 1-propyl phosphoric acid cyclic anhydride, 1-n-butyl cyclic phosphoric acid anhydride, Succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,2,3-tris-(2-cyanoethoxy)propane, ethylene glycol bis(propionitrile) ether, 1,2-bis(cyanoethoxy)ethane, pentaerythritol bicyclic sulfate, methyl trifluoroethyl carbonate, 3,3,3-trifluoropropylene carbonate, 4-trifluoromethylethylene carbonate, tris(2,2,2-trifluoroethyl)phosphate, tris(2,2,2-trifluoroethyl)carbonate, 2-fluorobiphenyl, 2,4-difluorobiphenyl, 4-methylethylene sulfate, 4-propylethylene sulfate and tripropargyl phosphate or a mixture of any of them.

[0016] Preferably, the specific steps for preparing the non-aqueous electrolyte are as follows:

[0017] S1: lithium salt A and solvent C are mixed and dissolved to form solution 1;

[0018] S2: lithium salt B and solvent D are mixed and dissolved to form solution 2;

[0019] S3: Solution 1 and solution 2 are mixed and functional additives are added, and the mixture is fully mixed to form a non-aqueous electrolyte.

[0020] Preferably, the synthesis method of the lithium salt A comprises the following steps:

[0021] Step 1: Purchase commercially available 99% or more pure fluorosulfonyl difluoroacetic acid and dissolve it in a solvent;

[0022] Step 2: Then react with an appropriate amount of lithium carbonate to release carbon dioxide gas, and then distill to remove water or organic solvent to obtain anhydrous lithium fluorosulfonyl difluoroacetate.

[0023] Preferably, the solvent in step 1 is water, methanol, acetone or ethyl acetate.

[0024] The present invention also provides a lithium ion battery, which comprises a positive electrode, a negative electrode and the non-aqueous electrolyte described above.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The non-aqueous electrolyte prepared by using lithium fluorosulfonyl difluoroacetate (FSO2CF2COOLi) as one of the lithium salts has the advantages of high ion conductivity, stability in air and high decomposition temperature, so that the performance of the lithium battery is more excellent. At the same time, since the preparation of lithium fluorosulfonyl difluoroacetate is simpler, the preparation cost is reduced, making the application range of the non-aqueous electrolyte wider. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the process route for preparing the non-aqueous electrolyte of the present invention. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] The present invention provides a technical solution: a non-aqueous electrolyte for a lithium ion battery.

[0030] The specific steps for preparing the non-aqueous electrolyte are as follows:

[0031] S1: lithium salt A and solvent C are mixed and dissolved to form solution 1;

[0032] S2: lithium salt B and solvent D are mixed and dissolved to form solution 2;

[0033] S3: Solution 1 and solution 2 are mixed and functional additives are added, and after thorough mixing, a non-aqueous electrolyte is finally formed.

[0034] Table 1 Specific electrolyte formulas for the examples and comparative examples in the full battery performance test

[0035]

[0036] Among them, the Chinese names of the abbreviations of lithium salts, solvents, additives, etc. in Table 1 are:

[0037] EC: ethylene carbonate; EMC: ethyl methyl carbonate; DMC: dimethyl carbonate; DEC: diethyl carbonate; PC: propylene carbonate; GBL: γ-butyrolactone; EA: ethyl acetate; VC: vinylene carbonate; VEC: vinylene carbonate; FEC: fluoroethylene carbonate; PS: propenyl sulfite; PST: propenyl-1,3-sultone; BSA: N,O-bis( Trimethylsilyl )acetamide; TMSB: tris(trimethylsilylphosphate); LiTDI: lithium 2-trifluoromethyl-4,5-dicyanoimidazole; LiFSI: lithium bis(trifluoromethylsulfonyl)imide; LiTFSI: lithium bis(trifluoromethylsulfonyl)imide; MMDS: methylene methanedisulfonate.

[0038] Full battery process parameters:

[0039] Laminated soft-pack battery 856006, N / P ratio 1.10, injection volume 3.2g / Ah, design capacity 2.0Ah.

[0040] 1) The positive electrode active material is 96% of Rongbai Technology's high nickel ternary S83RY, the binder is 2.0% of Solvey polyvinylidene fluoride Solif 5130, the conductive agent carbon black Super P Li (Swiss Temmega) is 2.0%, and the pole piece is compacted at 3.4g / cm 3 , single-sided loading 21.3mg / cm 2 .

[0041] 2) The negative electrode graphite is AML-400 from Dongguan Kaijin, and the single-sided loading of the negative electrode is 14.1 mg / cm 2 , the compacted density of the pole piece is 1.55g / cm 2 The formula is 96.0% active matter, 2.0% CMC / SBR binder (Dacel 2200 / Aiyulong 3001), and 2.0% Super P Li conductive carbon black (by weight).

[0042] Soft pack battery production process: The specification is 2.0Ah NMC811 / graphite 856006 battery. The electrolyte dosage is 3.2g / Ah, and the electrolyte formula is as shown in Table 1. Use Shenzhen Kejing Battery Sealing Machine (MSK-115A) to pre-seal the battery at -90kPa pressure and let it stand for 24 hours. Then, the battery is transferred to the pressure formation cabinet and connected to the Xinwei automatic testing system. It is formed under 2.8-4.3V and C / 10 conditions. After one cycle, it is charged to 3.8V and stopped. Then, the battery airbag is cut and sealed with a second sealing machine to remove the gas generated during the formation process. Finally, the battery is taken out for cycle testing (Xinwei) and thermal storage experiments.

[0043] Table 2 Test data of the embodiment and comparative example in the full battery performance test

[0044]

[0045] It can be clearly seen from Tables 1 and 2 that Example 3 has the highest capacity retention rate after 28 days at 60°C, while Example 5 has the highest capacity recovery rate after 28 days at 60°C, Example 1 has the highest capacity retention rate after 500 cycles at room temperature, and Example 2 has the highest capacity retention rate after 500 cycles at 45°C. At the same time, by comparing Examples 1-5 with Comparative Examples 1-2, it can be found that the technical solution of the present application has greatly improved safety and stability.

[0046] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and do not limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the protection scope of the present invention.

Claims

1. A non-aqueous electrolyte for a lithium ion battery, characterized in that: The following substances are included by weight: 1-20% of electrolyte lithium salt, 70-90% of organic solvent and 0.1%-10% of functional additives; The electrolyte lithium salt consists of lithium salt A and lithium salt B, and the weight fraction of lithium salt A is greater than that of lithium salt B; The organic solvent consists of solvent C and solvent D, wherein the weight fraction of solvent C is 3%-20%, and the weight fraction of solvent D is 50%-88%.

2. The non-aqueous electrolyte for lithium ion batteries according to claim 1, characterized in that: The lithium salt A is lithium 2-fluorosulfonyldifluoroacetate, and the lithium salt B is one or a mixture of lithium tetrafluoroborate, lithium hexafluorophosphate, lithium bisfluorosulfonamide, lithium bis(trifluoromethylsulfonyl)imide, lithium oxalate borate, lithium difluorooxalate borate, lithium difluorobisoxalate phosphate, lithium fluoromalonate borate, lithium 2-trifluoromethyl-4,5-dicyanoimidazole and lithium difluorophosphate.

3. The non-aqueous electrolyte for lithium ion batteries according to claim 1, characterized in that: The solvent C is one or a mixture of dimethyl sulfoxide, diphenyl sulfoxide, ethyl methyl sulfone, ethyl methoxyethyl sulfone, sulfolane, dimethyl sulfone, ethyl isopropyl sulfone, ethyl isobutyl sulfone and methyl isopropyl sulfone.

4. The non-aqueous electrolyte for lithium ion batteries according to claim 1, characterized in that: The solvent D is a mixture of one or more cyclic carbonate compounds or chain carbonate compounds, wherein the cyclic carbonate compound is a mixture of one or more ethylene carbonate, propylene carbonate, and γ-butyrolactone, and the chain carbonate compound is a mixture of one or more carbonate derivatives synthesized from diethyl carbonate, methyl ethyl carbonate, and a straight-chain or branched fatty monoalcohol with a carbon number of 3-8 and carbonic acid.

5. The non-aqueous electrolyte for lithium ion batteries according to claim 1, characterized in that: The functional additives are tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, fluoroethylene carbonate, difluoroethylene carbonate, vinyl sulfite, vinyl sulfate, propylene sulfate, methylene disulfonate, vinyl ethylene carbonate, 1,4-butane sultone, 1,3-propane sultone, 1-propylene-1,3-sultone, 1,3-propylene sultone, vinyl carbonate, vinyl ethylene carbonate, ethoxy pentafluorocyclotriphosphazene, 1-propyl phosphoric acid cyclic anhydride, 1-n-butyl phosphoric acid cyclic anhydride, butanediol The invention can be selected from the group consisting of nitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,2,3-tri-(2-cyanoethoxy)propane, ethylene glycol bis(propionitrile) ether, 1,2-bis(cyanoethoxy)ethane, pentaerythritol bicyclic sulfate, methyl trifluoroethyl carbonate, 3,3,3-trifluoropropylene carbonate, 4-trifluoromethylethylene carbonate, tris(2,2,2-trifluoroethyl)phosphate, tris(2,2,2-trifluoroethyl)carbonate, 2-fluorobiphenyl, 2,4-difluorobiphenyl, 4-methylethylene sulfate, 4-propylethylene sulfate and tripropargyl phosphate, or a mixture of the two or more thereof.

6. The non-aqueous electrolyte for lithium ion batteries according to claim 1, characterized in that: The specific steps of preparing the non-aqueous electrolyte are as follows: S1: lithium salt A and solvent C are mixed and dissolved to form solution 1; S2: lithium salt B and solvent D are mixed and dissolved to form solution 2; S3: Solution 1 and solution 2 are mixed and functional additives are added, and after thorough mixing, a non-aqueous electrolyte is finally formed.

7. The non-aqueous electrolyte for lithium ion batteries according to claim 1, characterized in that: The synthesis method of the lithium salt A comprises the following steps: Step 1: Purchase commercially available 99% or more pure fluorosulfonyl difluoroacetic acid and dissolve it in a solvent; Step 2: Then react with an appropriate amount of lithium carbonate to release carbon dioxide gas, and then distill to remove the solvent to obtain anhydrous lithium fluorosulfonyl difluoroacetate.

8. The non-aqueous electrolyte for lithium ion batteries according to claim 7, characterized in that: The solvent is water, methanol, acetone or ethyl acetate.

9. A lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode and the non-aqueous electrolyte according to any one of claims 1 to 8.

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