Fluorine-containing sulfonyl compounds, methods for preparing the same, and use thereof in batteries

Abstract

The application provides a fluorine-containing sulfonyl compound and a preparation method and application thereof in a battery. The lithium ion battery electrolyte comprises a non-water organic solvent, an electrolyte salt and an additive. The additive comprises the fluorine-containing sulfonyl compound, the fluorine-containing sulfonyl compound is compound 1, and the fluorine-containing sulfonyl compound accounts for 0.1-5.0% of the mass of the lithium ion battery electrolyte. The fluorine-containing sulfonyl compound can be used in the lithium ion battery, can capture oxygen free radicals generated in the use process of the lithium ion battery, and thus plays a function of protecting the positive and negative electrodes, so as to improve the cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of materials synthesis technology, and more particularly to a compound used in batteries, and even more particularly to fluorosulfonyl compounds, their preparation methods, and their applications in batteries. Background Technology

[0002] During high-voltage cycling, lithium cobalt oxide cathode active materials are prone to generating oxygen free radicals, which leads to instability at the electrolyte and electrode interface and severe gas generation during cycling, resulting in low battery cycle life. Therefore, overcoming the damage caused by oxygen free radicals during battery cycling can improve battery cycle life.

[0003] To overcome the destructive effects of oxygen free radicals, we can approach it from two aspects: first, we can inhibit the generation of oxygen free radicals at the source; second, we can remove oxygen free radicals in a timely manner once they are generated. Although there are many electrolyte additives on the market that can improve the cycle performance of batteries, they usually form a stable SEI film, while additives that overcome the destructive effects of oxygen free radicals are rare. Summary of the Invention

[0004] Based on the above problems, the purpose of this invention is to provide a new fluorosulfonyl compound and its preparation method. This fluorosulfonyl compound can be used in lithium-ion batteries to capture oxygen free radicals generated during the use of lithium-ion batteries, thereby protecting the positive and negative electrodes and improving the cycle performance of the battery.

[0005] To achieve the above objectives, the first aspect of the present invention provides a fluorosulfonyl compound, namely compound 1.

[0006]

[0007] Compound 1 in the fluorosulfonyl compounds of the present invention is a novel fluorosulfonyl compound containing an intracyclic sulfur group, which has strong reducing properties and many empty orbitals. It can capture oxygen free radicals generated during the use of lithium-ion batteries, thereby protecting the positive and negative electrodes and improving the cycle performance of the battery.

[0008] As a technical solution of the present invention, the gas chromatography purity of the fluorosulfonyl compound is 99.0-99.5%, the water content is 50-60 ppm, and the acid value is 8-15 ppm.

[0009] The second aspect of the present invention provides a method for preparing fluorosulfonyl compounds, comprising the steps of: adding thiomorpholine, acetonitrile and triethylamine to a reaction vessel, stirring evenly in an ice-water bath at 0-5°C, then slowly introducing a prescribed amount of thiosulfonyl fluoride to react, concentrating to remove the acetonitrile, and then distilling under reduced pressure.

[0010] The preparation method of this invention is simple. It utilizes thiomorpholine and thiomorpholine to carry out a nucleophilic addition reaction at low temperature under the action of triethylamine. The resulting fluorosulfonyl compound can improve the cycle performance of the battery.

[0011] A third aspect of the present invention provides the application of fluorosulfonyl compounds in batteries.

[0012] The fourth aspect of the present invention provides a lithium-ion battery electrolyte comprising a non-aqueous organic solvent, an electrolyte salt, and an additive, wherein the additive comprises the aforementioned fluorosulfonyl compound or a fluorosulfonyl compound prepared by the aforementioned method for preparing fluorosulfonyl compounds, wherein the fluorosulfonyl compound accounts for 0.1 to 5.0% of the mass of the lithium-ion battery electrolyte.

[0013] The structure of this fluorosulfonyl compound contains an intracyclic sulfur group, which has strong reducing properties and more empty orbitals. Compared with the extracyclic sulfur group or sulfonyl group, it can capture oxygen free radicals generated during the use of lithium-ion batteries, thereby protecting the positive and negative electrodes and improving the cycle performance of the battery.

[0014] As one technical solution of the present invention, the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium methanesulfonate, lithium trifluoromethanesulfonate, lithium di(oxalate)borate, lithium di(fluorooxalate)borate, difluorophosphate, and lithium di(fluorobis(oxalate))phosphate.

[0015] As one technical solution of the present invention, the non-aqueous organic solvent includes one or more of chain carbonate compounds, cyclic carbonate compounds, carboxylic acid ester compounds and ether compounds.

[0016] As one technical solution of the present invention, the non-aqueous organic solvent includes one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, butyl acetate, ethyl butyrate, propyl propionate, and ethylene glycol dimethyl ether.

[0017] As a technical solution of the present invention, the additive further includes one or more of vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonic acid lactone and vinyl sulfate.

[0018] The fifth aspect of the present invention provides a lithium-ion battery, comprising a positive electrode active material, a negative electrode active material, and the aforementioned lithium-ion battery electrolyte. Attached Figure Description

[0019] Figure 1 The image shows the fluorine spectrum of the fluorinated sulfonyl compound from Example 1.

[0020] Figure 2This is the hydrogen spectrum of the fluorosulfonyl compound from Example 1. Detailed Implementation

[0021] The fluorosulfonyl compounds of this invention can be used in material synthesis and batteries. In particular, the fluorosulfonyl compounds are used in secondary batteries such as lithium-ion batteries, where they can improve the cycle performance of secondary batteries as electrolyte additives.

[0022] Secondary batteries consist of a positive electrode active material, a negative electrode active material, and an electrolyte. In lithium-ion batteries, the positive electrode active material can be a layered transition metal lithium oxide or an olivine-type lithium compound. Layered transition metal lithium oxides can be, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (with the chemical formula LiNi). x Co y Mn (1-x-y) M z O2, where 0.6≤x<0.9, x+y<1, 0≤z<0.08, and M is at least one of Al, Mg, Zr, and Ti, and coatings and dopants of the above materials. Olivine-type lithium compounds are lithium phosphates with an olivine structure, and may be, but are not limited to, lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, and coatings and dopants of the above materials. These positive electrode active materials can be used alone or in combination. Preferably, the positive electrode active material is lithium cobalt oxide, and fluorosulfonyl compounds can solve the problem of electrode damage caused by oxygen free radicals generated by lithium cobalt oxide.

[0023] The negative electrode active material includes at least one of carbon-based materials, silicon-based materials, and tin-based materials. The carbon-based material may include, but is not limited to, at least one of artificial graphite, natural graphite, hard carbon, soft carbon, graphene, and mesophase carbon microspheres. The silicon-based material may include, but is not limited to, at least one of elemental silicon, silicon-oxygen composite materials, silicon-carbon composite materials, and silicon alloy materials. The tin-based material may include elemental tin, tin-carbon composite materials, tin-oxygen composite materials, and tin alloy compounds.

[0024] Lithium-ion battery electrolytes include electrolyte salts, non-aqueous organic solvents, and additives.

[0025] The electrolyte salt may be, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium di(oxalate)borate (C4BLiO8), lithium di(fluorooxalate)borate (C2BF2LiO4), lithium difluorophosphate (LiPO2F2), and lithium di(fluorobis(oxalate))phosphate (LiDFBP).

[0026] Non-aqueous organic solvents include one or more of chain carbonates, cyclic carbonates, carboxylic acid esters, and ethers. Further, the non-aqueous organic solvent is selected from one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (PC), propylene carbonate (PC), ethyl acetate, ethyl propionate, propyl propionate, butyl acetate, ethyl butyrate, propyl propionate, and ethylene glycol dimethyl ether.

[0027] The additive includes fluorosulfonyl compounds, and more specifically, the additive is compound 1. The fluorosulfonyl compounds constitute 0.1% to 5.0% of the electrolyte mass. For example, the percentage of fluorosulfonyl compounds may be, but is not limited to, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, and 5.0%. Furthermore, the additive also includes one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), 1,3-propanesulfonyl lactone (PS), and vinyl sulfate (DTD).

[0028]

[0029] The preparation method of fluorosulfonyl compounds includes the following steps: adding thiomorpholine, acetonitrile and triethylamine to a reaction vessel, stirring evenly in an ice-water bath at 0-5°C, then slowly introducing the prescribed amount of thiosulfate fluoride to react, concentrating to remove acetonitrile, and then distilling under reduced pressure. The reaction formula is as follows.

[0030]

[0031] The reaction time can be 3–10 h, the concentration temperature can be 40–60 °C, and the distillation can be carried out at 100–140 °C. The obtained fluorosulfonyl compounds have a gas chromatography purity of 99.0–99.5%, a water content of 50–60 ppm, and an acid value of 8–15 ppm.

[0032] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0033] Part 1: Preparation of Fluorosulfonyl Compounds

[0034] Example 1

[0035] This embodiment describes the preparation of compound 1, which includes the following steps: 103.2 g of thiomorpholine, 258 g of acetonitrile, and 101.2 g of triethylamine are added sequentially to a three-necked flask filled with nitrogen atmosphere. The mixture is stirred evenly in an ice-water bath at 0–5 °C. Then, 102.1 g of thioyl fluoride is slowly introduced. After the thioyl fluoride is completely introduced, the reaction proceeds for 4 hours, yielding a light yellow solution. The solution is concentrated at 45 °C to remove the reaction solvent acetonitrile, and then distilled under reduced pressure at 120 °C to obtain 156.2 g of colorless and transparent product with a gas chromatography purity of 99.1%, a water content of 53 ppm, an acid value of 12 ppm, and a yield of 84.3%.

[0036] The product was analyzed by mass spectrometry, and the results are as follows: Figure 1 and Figure 2 As shown, the NMR (60MHz) data are F19: 47.4, H19: 4.2, 3.2. The description indicates the presence of one fluorine and two hydrogen atoms, consistent with the target structure, indicating the synthesis of compound 1.

[0037] Part Two: Applications of Fluorosulfonyl Compounds in Batteries

[0038] 1.1 Preparation of non-aqueous electrolyte

[0039] In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 10 ppm, nitrogen purity > 99.9999%), 85 g of a mixed solvent obtained by uniformly mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a mass ratio of 3:7 was used as the organic solvent. Then, 1 g of compound 1 prepared in Example 1 was added to each solvent to obtain a mixed solution. The mixed solution was sealed and packaged and frozen in a freezer (-4°C) for 2 hours. After being removed, 14 g of lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution in a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm). After uniform mixing, non-aqueous electrolyte 1# was prepared.

[0040] The formulations of non-aqueous electrolytes 2# to 21# are shown in Table 1, and their preparation process is the same as that of non-aqueous electrolytes in Section 1.1.

[0041] Table 1 Formulations of Non-Aqueous Electrolytes 2# to 21#

[0042]

[0043]

[0044] 1.2 Preparation of the positive electrode

[0045] LiCoO2, PVDF and conductive carbon black were mixed in a weight ratio of 96:2:2, and an equal weight of N-methylpyrrolidone (NMP) was added. After stirring evenly, the mixture was coated onto aluminum foil and dried at 120°C to obtain a positive electrode sheet with a moisture content of <100ppm.

[0046] 1.3 Preparation of negative electrode

[0047] Graphite, styrene-butadiene rubber, and carbon black were mixed in a weight ratio of 96:3:1, and an equal weight of deionized oil was added to form a slurry. The slurry was then evenly coated onto copper foil and dried at a programmed temperature of 90°C to obtain a negative electrode sheet with a moisture content of <300ppm.

[0048] 1.4 Preparation of Lithium-ion Batteries

[0049] The positive electrode, negative electrode, and separator prepared according to the above process are stacked to form lithium-ion batteries with a thickness of 4.7 mm, a width of 55 mm, a length of 60 mm, and a total capacity of 2 Ah. These batteries are then vacuum-baked at 75°C for 10 hours and injected with non-aqueous electrolytes #1 to #21. After standing for 24 hours, they are charged to 3.65 V using a constant current of 0.1 C (200 mA), then charged at a constant voltage of 3.65 V until the current drops to 0.05 C (100 mA). They are then discharged to 2.5 V at 0.2 C (400 mA), and this charge-discharge cycle is repeated twice. Finally, the batteries are charged to 3.65 V at 0.1 C (200 mA), completing the fabrication of lithium-ion batteries #1 to #21.

[0050] Performance tests were conducted on lithium-ion batteries #1 to #21. The test results are shown in Table 1. The test conditions are as follows.

[0051] (1) High temperature cycling test

[0052] Under high temperature (45℃) conditions, the lithium-ion battery was charged and discharged at 1.0C / 1.0C (the average discharge capacity of the first three batteries is C0), with a charging cut-off current of 0.05C and a discharge cut-off current of 3.0V. The battery was charged and discharged at 1.0C / 1.0C for 500 cycles at 45℃ (the battery discharge capacity is C1).

[0053] Capacity retention rate = (C1 / C0) * 100%

[0054] (2) Low temperature cycling test

[0055] Under low temperature (15℃) conditions, the lithium-ion battery was charged and discharged at 1.0C / 1.0C (the average discharge capacity of the first three batteries is C0), with a charging cut-off current of 0.05C and a discharge cut-off current of 3.0V. The battery was charged and discharged at 1.0C / 1.0C for 500 cycles at 15℃ (the battery discharge capacity is C1).

[0056] Capacity retention rate = (C1 / C0) * 100%

[0057] Table 2 shows the cycle performance test results for each example.

[0058]

[0059] As shown in Table 2, the cycle performance of lithium-ion batteries 1# to 14# is better than that of lithium-ion batteries 15# to 19#. This is because lithium-ion batteries 1# to 14# use compound 1 as an additive, which contains intracyclic sulfur groups, has strong reducing properties, and has more empty orbitals. It can capture oxygen free radicals generated during the use of lithium-ion batteries, thereby protecting the positive and negative electrodes and improving the cycle performance of the batteries.

[0060] Comparing lithium-ion batteries #7 to #14, it can be seen that the battery with VC, FEC, PS, and DTD added to compound 1 has better cycle performance.

[0061] Comparing the results of lithium-ion batteries 2# to 3# and lithium-ion batteries 20# to 21#, it can be seen that although the structure of compound 2 is somewhat similar to that of compound 1, compound 2 is an oxygen atom within a ring, which has weak reducing power and does not have empty orbitals. Therefore, it cannot capture oxygen free radicals generated during the use of lithium-ion batteries, and its improvement on cycle performance is limited.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. The application of fluorosulfonyl compounds as electrolyte additives in batteries, characterized in that, The fluorosulfonyl compound is compound 1.

2. The application according to claim 1, characterized in that, The fluorosulfonyl compounds have a gas chromatography purity of 99.0–99.5%, a water content of 50–60 ppm, and an acid value of 8–15 ppm.

3. A lithium-ion battery electrolyte, comprising a non-aqueous organic solvent, an electrolyte salt, and additives, characterized in that, The additive includes a fluorosulfonyl compound, which accounts for 0.1% to 5.0% of the mass of the lithium-ion battery electrolyte, and the fluorosulfonyl compound is compound 1.

4. The lithium-ion battery electrolyte according to claim 3, characterized in that, The electrolyte salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium methanesulfonate, lithium trifluoromethanesulfonate, lithium di(oxalate)borate, lithium di(fluorooxalate)borate, difluorophosphate, and lithium di(fluorobis(oxalate))phosphate.

5. The lithium-ion battery electrolyte according to claim 3, characterized in that: The non-aqueous organic solvent includes one or more of the following: chain carbonates, cyclic carbonates, carboxylic acid esters, and ethers.

6. The lithium-ion battery electrolyte according to claim 5, characterized in that: The non-aqueous organic solvent includes one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, butyl acetate, ethyl butyrate, propyl propionate, and ethylene glycol dimethyl ether.

7. The lithium-ion battery electrolyte according to claim 3, characterized in that: The additives also include one or more of vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonic acid lactone, and vinyl sulfate.

8. A lithium-ion battery, characterized in that: It includes positive electrode active material, negative electrode active material and lithium-ion battery electrolyte as described in any one of claims 3 to 7.

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