Preparation method of binary fluorosulfonylimide alkali metal salt and application of alkali metal salt

Abstract

The present invention provides a preparation method of a binary fluorosulfonylimide alkali metal salt and the application of the alkali metal salt. The preparation method of the binary fluorosulfonylimide alkali metal salt comprises step (1) and step (2). In step (1), fluorosulfonyl isocyanate reacts with a diol to generate a binary fluorosulfonyl carbamate compound. In step (2), the binary fluorosulfonyl carbamate compound undergoes a substitution reaction with a metal source. The present invention uses fluorosulfonyl isocyanate and a diol as raw materials to react to obtain an intermediate product with two sulfonylimide groups, and then undergoes a substitution reaction with a metal source to obtain a binary fluorosulfonylimide alkali metal salt. This preparation method is simple and controllable, which is conducive to promoting its application in electrolytes and secondary batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of material synthesis, and particularly to the preparation of organic alkali metal salts, and more particularly to the preparation method of binary fluorosulfonylimide alkali metal salts and the application of alkali metal salts. Background Art

[0002] Fluorosulfonylimide and its alkali metal salts, especially lithium salts and sodium salts, are important fluorinated organic ionic compounds. They have important industrial application values in the fields of new and efficient catalysts, secondary lithium-ion (or sodium-ion) batteries, supercapacitors, and aluminum electrolytic capacitors and other clean energy devices. Therefore, people have been committed to carrying out research on the synthesis and application of new fluorosulfonylimide and its derivatives.

[0003] At present, the research on fluorosulfonylimide and its derivatives focuses on monofluorinated sulfonylimide (that is, the molecule contains only one sulfonylimide group -SO2-N-), such as perfluoroalkylsulfonylimide and its alkali metals, and its representative substances are lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide. However, there are few research reports on binary or polyfluorosulfonylimide and its alkali metal salts, especially the application of binary or polyfluorosulfonylimide and its alkali metal salts as electrolyte materials in secondary lithium-ion (or sodium-ion) batteries. Therefore, it is extremely important and promising to develop a preparation method of binary or polyfluorosulfonylimide and its alkali metal salts to prepare related materials and determine their electrochemical properties as electrolyte materials. Summary of the Invention

[0004] In view of the above problems, the purpose of the present invention is to provide a preparation method of binary fluorosulfonylimide alkali metal salts, which can effectively synthesize binary fluorosulfonylimide alkali metal salts and can effectively improve the battery performance when used as electrolyte materials in lithium-ion batteries (or sodium-ion batteries).

[0005] To achieve the above purpose, the first aspect of the present invention provides a preparation method of binary fluorosulfonylimide alkali metal salts, including step (1) and step (2).

[0006] Step (1): Fluorosulfonyl isocyanate reacts with diol to form binary fluorosulfonyl carbamate compounds.

[0007] Step (2): The binary fluorosulfonyl carbamate compounds undergo a substitution reaction with a metal source.

[0008] The present invention uses fluorosulfonyl isocyanate and diol as raw materials to react to obtain an intermediate product with two sulfonylimide groups, and then undergoes a substitution reaction with a metal source to obtain a binary fluorosulfonylimide alkali metal salt. This preparation method is simple and controllable, which is conducive to promoting its application in electrolytes and secondary batteries.

[0009] As a technical solution of the present invention, the structural formula of the binary fluorosulfonylimide alkali metal salt is as shown in Structural Formula I,

[0010]

[0011] wherein, A + is a lithium ion or a sodium ion, and R is a C1-C12 hydrocarbon group, a C2-C6 cycloalkyl group, a C1-C12 hydrocarbon group containing a heteroatom, or a C2-C6 cycloalkyl group containing a heteroatom. Further, the binary fluorosulfonylimide alkali metal salt is at least one of Compounds 1 to 9,

[0012]

[0013] wherein, A + is a lithium ion or a sodium ion.

[0014] Fluorosulfonyl isocyanate can be obtained by fluorination of chlorosulfonyl isocyanate, and its reaction process is as shown in Reaction Formula I.

[0015]

[0016] The structural formula of the diol is as shown in Structural Formula II, wherein R is a C1-C12 hydrocarbon group, a C2-C6 cycloalkyl group, a C1-C12 hydrocarbon group containing a heteroatom, or a C2-C6 cycloalkyl group containing a heteroatom.

[0017]

[0018] The structural formula of the binary fluorosulfonyl carbamate compound is as shown in Structural Formula III, wherein R is a C1-C12 hydrocarbon group, a C2-C6 cycloalkyl group, a C1-C12 hydrocarbon group containing a heteroatom, or a C2-C6 cycloalkyl group containing a heteroatom.

[0019]

[0020] The reaction process of fluorosulfonyl isocyanate and diol can be as shown in Reaction Formula II.

[0021]

[0022] As a technical solution of the present invention, the metal source is lithium hydroxide, lithium carbonate, sodium hydroxide or sodium carbonate. Taking the metal source as a hydroxide as an example, the reaction process of the binary fluorosulfonyl carbamate compound and the metal source can be as shown in Reaction Formula III.

[0023]

[0024] The second aspect of the present invention provides an application of the binary fluorosulfonylimide alkali metal salt in an electrolyte.

[0025] In the third aspect of the present invention, an electrolyte is provided, which includes an electrolyte salt, a solvent, and a binary fluorosulfonylimide alkali metal salt. The binary fluorosulfonylimide alkali metal salt can be used as an additive in the electrolyte. As a technical solution of the present invention, the proportion of the binary fluorosulfonylimide alkali metal salt in the electrolyte is 0.01 - 5 wt.%. Specific Embodiments

[0026] To better illustrate the purpose, technical solution, and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the methods described in the following embodiments are further explanatory descriptions of the present invention and should not be construed as limitations on the present invention.

[0027] Part 1: Preparation of Binary Fluorosulfonylimide Alkali Metal Salt

[0028] The preparation of Compound 1 includes the following steps.

[0029] ① Synthesize fluorosulfonyl isocyanate with reference to Reaction Scheme 1

[0030] Add 210 g of antimony trifluoride to a dry 1 L three-necked flask, dropwise add 500 g of chlorosulfonyl isocyanate thereto, and allow the reaction system to react at 70 °C for 48 h. After the reaction is completed, distill out the target product fluorosulfonyl isocyanate (402 g) at 80 °C.

[0031] ② Synthesize binary fluorosulfonyl carbamate compounds with reference to Reaction Scheme 2

[0032] Add 20 g of ethylene glycol to a dry 500 mL three-necked flask, add 150 g of dichloromethane as a solvent, and place it in a 0 °C water bath. Dropwise add 80 g of fluorosulfonyl isocyanate thereto. After the addition is completed, allow the reaction system to continue reacting for 12 h. After the reaction is completed, filter the reaction mixture and wash it with dichloromethane to obtain 85 g of an intermediate product, which is in the form of a white solid.

[0033] ③ Synthesize binary fluorosulfonylimide alkali metal salt with reference to Reaction Scheme 3

[0034] Add 20 g of the intermediate product and 3 g of lithium hydroxide (or 5.12 g of sodium hydroxide) to a dry 500 ml three-necked flask, add 100 g of absolute ethanol as a solvent, and allow the reaction system to react in a 0 °C water bath for 12 h. After the reaction is completed, concentrate the reaction solution, add the recrystallization solvent dichloromethane to the reaction solution, and filter the reaction mixture to obtain the target product (A + When A is lithium ion, 18.7 g of the product is obtained, A + When A is sodium ion, 20.5 g of the product is obtained), which is in the form of a white solid.

[0035] The preparation of Compound 8 includes the following steps.

[0036] ①Synthesis of fluorosulfonyl isocyanate with reference to Reaction Scheme 1

[0037] Add 210 g of antimony trifluoride to a dry 1 L three-necked flask, dropwise add 500 g of chlorosulfonyl isocyanate thereto, and allow the reaction system to react at 70 °C for 48 h. After the reaction is completed, distill out the target product fluorosulfonyl isocyanate (402 g) at 80 °C.

[0038] ②Synthesis of binary fluorosulfonyl carbamate compounds with reference to Reaction Scheme 2

[0039] Add 20 g of butynediol to a dry 500 mL three-necked flask, add 150 g of dichloromethane as a solvent, and place it in a 0 °C water bath. Dropwise add 58 g of fluorosulfonyl isocyanate thereto. After the addition is completed, allow the reaction system to continue reacting for 12 h. After the reaction is completed, filter the reaction mixture and wash it with dichloromethane to obtain 67 g of an intermediate product, which is in the form of a white solid.

[0040] ③Synthesis of binary fluorosulfonyl imide alkali metal salts with reference to Reaction Scheme 3

[0041] Add 20 g of the intermediate product and 2.73 g of lithium hydroxide (or 4.76 g of sodium hydroxide) to a dry 500 ml three-necked flask, add 100 g of absolute ethanol as a solvent, and allow the reaction system to react in a 0 °C water bath for 12 h. After the reaction is completed, concentrate the reaction solution, add the recrystallization solvent dichloromethane to the reaction solution, and filter the reaction mixture to obtain the target product (A + 17.1 g of the product is obtained when A is lithium ion, A + 19.28 g of the product is obtained when A is sodium ion), which is in the form of a brown solid.

[0042] The preparation of Compounds 2-7 and Compound 9 is the same as that in Example 1, except that different diols are used as raw materials, and the contents of fluorosulfonyl isocyanate and metal source are different. The specific diol to be used can be determined according to the group corresponding to R in Compounds 2-7 and Compound 9. Based on the same amount of diol, the contents of fluorosulfonyl isocyanate and metal source can be adjusted according to the molecular weight of the diol used by referring to the preparation of Compound 8.

[0043] The prepared Compounds 1-9 were subjected to nuclear magnetic resonance analysis, and the obtained hydrogen spectrum results are shown in Table 1. From the results in Table 1, it can be seen that Compounds 1-9 can be effectively synthesized by the preparation method of the present invention.

[0044] Table 1 Nuclear magnetic resonance hydrogen spectrum results of Compounds 1-9 (A + = Li + or Na + )

[0045]

[0046]

[0047] Part II: Applications of Binary Fluorosulfonylimide Alkali Metal Salt Compounds 1 - 9 (A + = Li + ) in Lithium - ion Secondary Batteries

[0048] (1) Fabrication of the Positive Electrode Sheet

[0049] Taking LiCoO₂ as the positive electrode material as an example: Mix the positive electrode LiCoO₂ powder, carbon black (particle size of 1000 nm), polyvinylidene fluoride (PVDF), and N,N - dimethylpyrrolidone (NMP) to form a homogeneous slurry. Coat the slurry evenly on an aluminum foil (15 μm) current collector, then dry it (bake at 120 °C for 12 h), and roll - press to obtain the LiCoO₂ electrode sheet, where LiCoO₂ accounts for 94 wt.%, PVDF accounts for 4 wt.%, and carbon black accounts for 2 wt.%. Then cut the obtained electrode sheet into circular pieces with a diameter of 8 mm as the positive electrode sheet.

[0050] (2) Fabrication of the Negative Electrode Sheet

[0051] Taking artificial graphite as the negative electrode material as an example: Mix artificial graphite, polyvinylidene fluoride (PVDF), and N,N - dimethylpyrrolidone (NMP) to form a homogeneous slurry. Coat the slurry evenly on a copper foil (15 μm) current collector, then dry it (bake at 120 °C for 12 h), and roll - press to obtain the carbon negative electrode sheet, where graphite accounts for 96.4 wt.% of the total coating, and PVDF accounts for 3.6 wt.%. Then cut the obtained electrode sheet into circular pieces with a diameter of 9 mm as the negative electrode sheet.

[0052] (3) Preparation of the Electrolyte

[0053] Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 30 / 40 / 30. Add LiPF₆ to this mixture at a concentration of 1.0 mol / L, and then add Compounds 1 - 9 at proportions of 0.01 wt.%, 1 wt.%, and 5 wt.% in the electrolyte respectively. After mixing, a non - aqueous electrolyte is prepared.

[0054] (4) Composition and Performance Evaluation of CR2032 Button - type Lithium - ion Batteries

[0055] Place the polyethylene porous membrane between the positive and negative electrode sheets prepared in the above steps (1) and (2), and drop the electrolyte prepared in the above step (3) respectively to submerge the electrode sheets, and assemble them into a CR2032 button cell. Perform the battery cycle performance test on a microcomputer-controlled automatic charge and discharge instrument (Land, CT2001A). Test conditions: charge rate is 0.5C, discharge rate is 0.2C, voltage is 3.0 - 4.2V, and test temperature is 25°C. The test results are shown in Table 2.

[0056] Table 2 Electrochemical performance of each button lithium-ion battery

[0057]

[0058]

[0059] As can be seen from the results in Table 2, when Compounds 1 - 9 prepared by the preparation method of the present invention are applied to lithium-ion batteries, the capacity retention rate can reach over 75% after 50 cycles with a content of only 0.01 wt.%, and the capacity retention rate can reach 81 - 93% after 50 cycles with an addition amount of 1 wt.%, indicating that it has a better application prospect in lithium-ion batteries.

[0060] Part III: Application of Binary Fluorosulfonylimide Alkali Metal Salt Compounds 1 - 9 (A + = Na + ) in Sodium Ion Secondary Batteries

[0061] (1) Fabrication of the positive electrode sheet

[0062] Taking the Na 0.9 Cu 0.22 Fe 0.30 Mn 0.48 O2 positive electrode material as an example: Mix Na 0.9 Cu 0.22 Fe 0.30 Mn 0.48 O2, carbon nanotubes (CNTs), polyvinylidene fluoride (PVDF) and N,N-dimethylpyrrolidone (NMP) to make a uniform slurry. Among them, the mass ratio of Na 0.9 Cu 0.22 Fe 0.30 Mn 0.48 O2, carbon nanotubes and PVDF is 97.4:1.3:1.3. Coat the slurry evenly on an aluminum foil (15um) current collector, then dry it (bake at 120°C for 12h), roll it to obtain an electrode sheet, and then cut the obtained electrode sheet into 8mm diameter circular pieces as the positive electrode sheet.

[0063] (2) Fabrication of the negative electrode sheet

[0064] Taking hard carbon as an example: Hard carbon, sodium carboxymethyl cellulose (CMC), carbon nanotubes (CNTs), and styrene-butadiene rubber (SBR) are mixed to form a uniform slurry. Among them, the mass ratio of hard carbon, CMC, carbon nanotubes, and SBR is 95.8:1.4:0.8:2.0. The slurry is uniformly coated on a copper foil (15 μm) current collector, and then dried (baked at 120 °C for 12 h), and roll-pressed to obtain a negative electrode sheet. Then, the obtained sheet is cut into 9-mm-diameter circular pieces as the negative electrode sheets.

[0065] (3) Preparation of the electrolyte

[0066] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed at a volume ratio of 30 / 40 / 30. LiPF6 is added to this mixture at a concentration of 1.0 mol / L, and Compounds 1-9 with a proportion of 0.01 wt.%, 1 wt.%, and 5 wt.% in the electrolyte are respectively added. After mixing, a non-aqueous electrolyte is prepared.

[0067] (4) Composition and performance evaluation of small soft-pack batteries

[0068] The ceramic-coated polyethylene film (2-μm ceramic layer + 12-μm PE layer + 2-μm ceramic layer) is placed between the positive and negative electrode sheets prepared in the above steps (1) and (2). The electrolyte prepared in the above step (3) is respectively dropped to submerge the electrode sheets, and a 2-Ah small soft-pack battery is assembled. The battery cycle performance test is carried out on a microcomputer-controlled automatic charge and discharge instrument (Land, CT2001A). Test conditions: charging current is 0.5C, discharging current is 0.5C, voltage is 1.5 - 4.0V, and test temperature is 25 °C. The test results are shown in Table 3.

[0069] Table 3 Electrochemical performance of each small soft-pack battery

[0070]

[0071] As can be seen from the results in Table 3, when Compounds 1-9 prepared by the preparation method of the present invention are applied to sodium-ion batteries, the capacity retention rate can reach over 75% after 50 cycles with a content of only 0.01 wt.%, and the capacity retention rate can reach 81 - 93% after 50 cycles with an addition amount of 1 wt.%, indicating that it has a good application prospect in sodium-ion batteries.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it is not limited to only those listed in the embodiments. Those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An electrolyte, characterized in that, It includes an electrolyte salt, a solvent and an additive. The additive is an alkali metal salt of difluorosulfonylimide represented by Structural Formula 1. The alkali metal salt of difluorosulfonylimide is at least one of Compound 1 to Compound 9. Among them, A + is a lithium ion or a sodium ion.

2. The electrolyte according to claim 1, wherein The proportion of the binary fluorosulfonylimide alkali metal salt is 0.01 to 5 wt.%.

3. The electrolyte according to claim 1, wherein The preparation method of the binary fluorosulfonylimide alkali metal salt includes: Step (1) Fluorosulfonyl isocyanate reacts with diol to generate a binary fluorosulfonyl carbamate compound, and the reaction formula is as follows. Step (2) The binary fluorosulfonyl carbamate compound undergoes a substitution reaction with a metal source, and the reaction formula is as follows.

4. The electrolyte according to claim 3, wherein The fluorosulfonyl isocyanate is obtained by fluorinating chlorosulfonyl isocyanate.

5. The electrolyte according to claim 3, characterized in that, The metal source is lithium hydroxide, lithium carbonate, sodium hydroxide or sodium carbonate.

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