Lithium bisfluorosulfonylimide salts containing cesium ions or rubidium ions

Abstract

To provide an improved LiFSI salt that helps to form a thin and stable SEI film on the surface of a positive or negative electrode of a lithium battery.SOLUTION: The present invention provides an electrolyte additive composition comprising a lithium salt of bisfluorosulfonylimide and at least one selected from the group consisting of a Cs+ ion and a Rb+ ion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a lithium bisfluorosulfonylimide salt used in lithium secondary battery electrolytes. [Background technology]

[0002] Recently, with the increasing demand for secondary batteries in medium and large-sized products, the importance of battery output and safety is constantly emerging. Furthermore, there is growing concern about battery life. While battery stability and lifespan are influenced by other factors, they are significantly affected by the SEI (solid electrolyte interphase) membrane.

[0003] The SEI film formed on the negative electrode acts as an ion tunnel, allowing only lithium ions to pass through. As an effect of this ion tunnel, the SEI film prevents large organic solvent molecules that move with lithium ions in the electrolyte from being inserted between the layers of the negative electrode active material, thus preventing the destruction of the negative electrode structure. Therefore, by preventing contact between the electrolyte and the negative electrode active material, the decomposition of the electrolyte does not occur, the amount of lithium ions in the electrolyte is reversibly maintained, and stable charging and discharging are maintained.

[0004] LiFSI (lithium salt of bisfluorosulfonylimide), as a component of the electrolyte, forms an effective SEI (solid electrolyte interphase) layer on the electrode surface. Therefore, LiFSI has significant advantages in that it resolves and improves upon the problems of lifespan, output, and stability associated with existing lithium salts. [Overview of the project] [Problems that the invention aims to solve]

[0005] However, conventional LiFSI has limitations in improving electrical properties such as the formation and lifespan of the SEI film and output. Due to such reasons, there is no choice but to use a separate SEI film improvement additive in the electrolyte, which leads to complex processes and an increase in the cost of the electrolyte.

[0006] An object of the present invention is to provide an improved LiFSI salt that can help generate a thin and stable SEI film on the surface of the positive or negative electrode of a lithium battery.

Means for Solving the Problems

[0007] To achieve the above object, the present invention provides a lithium bis(fluorosulfonyl)imide salt containing one or more selected from the group consisting of Cs , [Figure 1] ,

[0010] ions and Rb + ions.

[0008] Further, the present invention provides a composition for an electrolyte additive containing one or more selected from the group consisting of Cs + ions and Rb + ions and a lithium bis(fluorosulfonyl)imide salt.

Advantages of the Invention

[0009] The lithium bis(fluorosulfonyl)imide salt (LiFSI) or the LiFSI-containing composition produced according to an embodiment of the present invention includes a function of forming a thin and stable SEI film on the positive and negative electrodes of a lithium battery when added to the electrolyte. As a result, there is an effect of improving the high-temperature and low-temperature output of the lithium battery and enhancing the battery lifespan and stability.

Brief Description of the Drawings

[0010] [Figure 1] It is the output evaluation result of a battery containing LiFSI containing 5,000 weight ppm of cesium ions. [Figure 2] It is the output evaluation result of a battery containing LiFSI containing 6,000 weight ppm of rubidium ions.

Best Mode for Carrying Out the Invention

[0011] The present invention will be described in detail below. Terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. The inventor should interpret them in accordance with the meaning and concept that conforms to the technical idea of the present invention in accordance with the principle that the inventor can appropriately define the concept of the terms in order to explain his invention in the best way.

[0012] The inventors recognized the possibility that the SEI film formed by conventional LiFSI can be formed thinner and more stably, and tried to solve this problem. Cs + ions and / or Rb + ions containing LiFSI, or Cs together with LiFSI + ions and / or Rb + When using a composition containing ions, it was confirmed that a thinner and more stable SEI (solid electrolyte interphase) film can be formed on the surface of the positive or negative electrode of a lithium battery, improving the battery life and output, and thus the present invention was completed.

[0013] The present invention provides a composition for an electrolyte additive used as an additive for a lithium battery electrolyte, which contains Cs + ions and / or Rb + ions containing LiFSI, or Cs together with LiFSI + ions and / or Rb + ions.

[0014] In the composition containing Cs + ions and / or Rb + ions containing LiFSI, or Cs together with LiFSI + ions and / or Rb + ions, Cs + ions and / or Rb + ions can preferably be contained in an amount of more than 0 to 100,000 weight ppm or less, and more preferably 5 to 10,000 weight ppm. Cs+ Ions and / or Rb + When LiFSI containing ions in the aforementioned proportions is used as an electrolyte additive, a more stable SEI film can be formed in the battery.

[0015] Cs of the present invention + Ions and / or Rb + LiFSI or LiFSI-containing compositions containing ions can be produced by the method of the following reaction formula 1, but are not limited thereto. That is, the Cs of the present invention + Ions and / or Rb + LiFSI containing ions can be produced by adding a cesium salt or a rubidium salt during an ion exchange reaction between a compound of chemical formula 1 and a lithium salt under a solvent.

[0016] [ka]

[0017] In chemical formula 1, M1 + This is an onium ion containing H, Na, K, Ca, Zn, Cs, Rb or N, or S, and the ionic additive is a cesium salt or rubidium salt.

[0018] In chemical formula 2, M2 + This consists of a Li ion and one or more ions selected from Cs and Rb.

[0019] The present invention provides a cesium and / or rubidium ion-containing LiFSI that, when produced by a cation substitution reaction involving the reaction of a bisfluorosulfonylimide or bisfluorosulfonyl salt (excluding lithium salt) with a lithium salt, can ultimately produce LiFSI containing cesium and / or rubidium ions when a cesium salt and / or rubidium salt is added separately as an additive.

[0020] The present invention relates to a cesium and / or rubidium ion-containing LiFSI or LiFSI-containing composition, characterized by adding a cesium salt or rubidium salt to a solvent-containing LiFSI solution and stirring. + Ions and Rb + It can be manufactured by a method that includes one or more ions selected from a group of ions.

[0021] The onium ion containing N or S is preferably NH4 + It is an ion.

[0022] The lithium salt may be lithium hydroxide (LiOH), its hydrate (LiOH·H2O), Li2CO3, LiNH2, LiHCO3, BuLi, LiF, LiCl, LiBr, LiI, or LiClO4. The lithium salt is preferably lithium hydroxide, which is commercially useful and highly stable.

[0023] The cesium salt may be CsF, CsCl, CsBr, CsI, CsCN, CsClO4, CsH, CsNO3, CsOH, Cs2CO3, CsHCO3, Cs2SO4, Cs2S, CsC2H3O2, Cs2O, or CsHSO4. The cesium salt is preferably cesium hydroxide, which is commercially useful and highly stable.

[0024] The rubidium salt may be RbF, RbCl, RbBr, RbI, RbCN, RbClO4, RbH, RbNO3, RbOH, Rb2CO3, RbHCO3, Rb2SO4, Rb2S, RbC2H3O2, Rb2O, or RbHSO4. The rubidium salt is preferably rubidium hydroxide, which is commercially useful and highly stable.

[0025] The ion exchange reaction or the addition of cesium salt and / or rubidium salt can be carried out under a solvent capable of dissolving LiFSI.

[0026] The aforementioned solvents include water, alcohols such as methanol, ethanol, propanol, butanol, and isopropyl alcohol, hydrocarbons such as pentane, hexane, heptane, and cyclohexane, aromatic hydrocarbons such as benzene and toluene, acetone, acetates such as methyl acetate, ethyl acetate, and butyl acetate, methylene chloride, chloroform, ethers such as diisopropyl ether, methyl-t-butyl ether, and 1,2-dimethoxyethane, and ethylene carbonate, 1,2-butylene carbonate, and 2,3-butylene carbonate. Examples include at least one cyclic carbonate system selected from the group consisting of 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, and fluoroethylene carbonate (FEC); acetonitrile; linear carbonate systems such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate; and glycols such as ethylene glycol, propylene glycol, and butylene glycol. These can be used individually or in combination of two or more.

[0027] The reaction solvent may preferably be 1,2-dimethoxyethane, butyl acetate, acetonitrile, water, or a mixture thereof.

[0028] The solvent can be 10 to 50 mL per gram of M1FSI or M2FSI, preferably 15 to 40 mL. When the solvent is used in the above amounts, the reactants can be sufficiently dissolved and the reaction can proceed.

[0029] In one embodiment of the present invention, the lithium salt may be 0.5 equivalents or more and 2 equivalents or less based on the reaction equivalent ratio of the bisfluorosulfonylimide salt, and preferably 1 equivalent or more and 1.5 equivalents or less.

[0030] When lithium salt is included in the aforementioned equivalent range, the yield can be increased in the subsequent purification process, and after the reaction is complete, no residue remains, resulting in a superior effect of increasing purity.

[0031] The cesium salt or rubidium salt added to the ion exchange reaction or LiFSI is present in the final LiFSI salt or LiFSI-containing composition. + Ions and / or Rb + The ions are added so that they are greater than 0 and exceed 100,000 ppm by weight.

[0032] In one embodiment of the present invention, a filtration or purification step may be further included to remove unreacted products, by-reactants, and other foreign substances generated in the step of reacting the bisfluorosulfonylimide salt with the lithium salt.

[0033] For the purification of LiFSI, aqueous cesium hydroxide solution can be used, which removes acid by-products that may cause changes in LiFSI over time.

[0034] In one embodiment of the present invention, the reaction temperature may be -50°C to 100°C, preferably -20°C to 50°C, and more preferably -10°C to 30°C or lower.

[0035] When the reaction temperature is within the aforementioned range, it is possible to prevent the suppression of by-products and to prevent changes in the color of the product. Furthermore, in the step of concentrating the filtrate to form a concentrate, crystallization can be easily performed without using expensive equipment such as a thin-film evaporator, which is considered an advantage of one embodiment of the present invention.

[0036] (Modes for carrying out the invention) The present invention will be described in detail below with reference to a preferred embodiment, but the present invention is not limited thereto.

[0037] <Example 1-1: Cs+ Method for producing LiFSI using a mixed solvent containing ions > 10 g (0.05 mole) of NH4FSI, 20 ml of butyl acetate, and 10 ml of distilled water were added to a reactor and allowed to dissolve completely. The reactor was then cooled to 0°C. 0.05 g of cesium hydroxide monohydrate was added to the cooled reactor and stirred at room temperature for 30 minutes. Then, 2.75 g (0.066 mole) of lithium hydroxide monohydrate was added and reacted at room temperature for 1 hour. After the reaction was complete, the organic layer was separated and collected. The process was repeated twice, with 30 ml of butyl acetate added to the aqueous layer. The resulting organic layer was concentrated under reduced pressure at 50°C to obtain 6.14 g (0.033 mole) of LiFSI crystals. (LiFSI purity 99%, cesium ion content 5,000 ppm by weight, yield 65%)

[0038] <Example 1-2: Cs + Method for producing LiFSI using a mixed solvent containing ions > The preparation was carried out in the same manner as in Example 1-1, except that 0.03 g of cesium hydroxide monohydrate used in Example 1-1 was used. 5.95 g of LiFSI crystals were obtained in white solid form. (LiFSI purity 99%, cesium ions 3,000 ppm by weight, yield 63%)

[0039] <Examples 1-3: Cs + Method for producing LiFSI using a mixed solvent containing ions > The preparation was carried out in the same manner as in Example 1-1, except that 0.01 g of cesium hydroxide monohydrate used in Example 1-1 was used. 6.23 g of LiFSI crystals were obtained in white solid form. (LiFSI purity 99%, cesium ions 1,000 ppm by weight, yield 66%)

[0040] <Example 2-1: Cs + Method for producing an aqueous solution of LiFSI containing ions > At room temperature, 10 g (0.05 mole) of NH4FSI and 20 ml of distilled water were added to a reactor and completely dissolved. Then, 0.05 g of cesium hydroxide monohydrate was added and the mixture was stirred for 10 minutes. Next, 2.75 g (0.066 mole) of lithium hydroxide monohydrate was added and the reaction was allowed to proceed at room temperature for 1 hour. After the reaction was complete, the mixture was completely concentrated at 40°C, and then recrystallized with 50 ml of toluene. The crystals obtained by filtration were dissolved in 40 ml of 1,2-dimethoxyethane, and insoluble matter was removed. The filtrate was concentrated under reduced pressure at 50°C to obtain 8.5 g (0.045 mole) of LiFSI crystals. (LiFSI purity 99%, cesium ion 5,000 ppm by weight, yield 90%)

[0041] <Example 2-2: Cs + Method for producing an aqueous solution of LiFSI containing ions > The preparation was carried out in the same manner as in Example 2-1, except that 0.03 g of cesium hydroxide monohydrate used in Example 2-1 was used. 8.12 g of LiFSI crystals were obtained in a white solid form. (LiFSI purity 99%, cesium ions 3,000 ppm by weight, yield 86%)

[0042] <Example 2-3: Cs + Method for producing an aqueous solution of LiFSI containing ions > The preparation was carried out in the same manner as in Example 2-1, except that 0.01 g of cesium hydroxide monohydrate used in Example 2-1 was used. 8.40 g of LiFSI crystals were obtained in white solid form. (LiFSI purity 99%, cesium ions 1,000 ppm by weight, yield 89%)

[0043] <Example 3-1: Cs + Method for producing LiFSI containing ions in organic solvents > At room temperature, 10 g (0.05 mole) of NH4FSI, 20 ml of acetonitrile, and 0.05 g of cesium hydroxide monohydrate were added to a reactor and stirred for 1 hour. Then, 2.75 g (0.066 mole) of lithium hydroxide monohydrate was added and the reaction was allowed to proceed at room temperature for 3 hours. After the reaction was complete, the mixture was filtered to remove insoluble matter, and the filtrate was concentrated under reduced pressure at 50°C to obtain 9.16 g (0.049 mole) of LiFSI crystals. (LiFSI purity 99%, cesium ion 5,000 ppm by weight, yield 97%)

[0044] <Example 3-2: Cs + Method for producing LiFSI containing ions in organic solvents > The preparation was carried out in the same manner as in Example 3-1, except that 0.03 g of cesium hydroxide monohydrate used in Example 3-1 was used. 8.97 g of LiFSI crystals were obtained in a white solid form. (LiFSI purity 99%, cesium ions 3,000 ppm by weight, yield 95%)

[0045] <Example 3-3: Cs + Method for producing LiFSI containing ions in organic solvents > The preparation was carried out in the same manner as in Example 3-1, except that 0.01 g of cesium hydroxide monohydrate used in Example 3-1 was used. 9.25 g of LiFSI crystals were obtained in a white solid form. (LiFSI purity 99%, cesium ions 1,000 ppm by weight, yield 98%)

[0046] <Example 4-1: Adding cesium salt to LiFSI-containing solution to Cs + LiFSI manufacturing containing ions > 10 g (0.053 moles) of LiFSI was dissolved in 20 ml of 1,2-dimethoxyethane in a reactor, then 0.05 g of cesium hydroxide monohydrate was added and the mixture was stirred at 40°C for 24 hours. After the reaction was complete, the mixture was filtered to completely remove any remaining insoluble matter. The filtered filtrate was concentrated under reduced pressure at 50°C to its maximum concentration, and then 30 ml of toluene was added to allow recrystallization to proceed. The resulting crystals were completely dried at 50°C to obtain 9.35 g (0.050 moles) of LiFSI crystals. (LiFSI purity 99%, cesium ion 5,000 ppm by weight, yield 99%)

[0047] <Example 4-2: Adding cesium salt to LiFSI-containing solution to Cs + LiFSI manufacturing containing ions > The preparation was carried out in the same manner as in Example 4-1, except that 0.03 g of cesium hydroxide monohydrate used in Example 4-1 was used. 9.35 g of LiFSI crystals were obtained in a white solid form. (LiFSI purity 99%, cesium ions 3,000 ppm by weight, yield 99%)

[0048] <Example 4-3: Adding cesium salt to LiFSI-containing solution to Cs + LiFSI manufacturing containing ions > The preparation was carried out in the same manner as in Example 4-1, except that 0.01 g of cesium hydroxide monohydrate used in Example 4-1 was used. 9.35 g of LiFSI crystals were obtained in a white solid form. (LiFSI purity 99%, cesium ions 1,000 ppm by weight, yield 99%)

[0049] <Examples 5-8: Rb + Manufacturing of LiFSI containing ions > The reaction products and solvents listed in Table 1 below were used to carry out the procedure as described in Examples 1 to 4, respectively, and Rb + LiFSI containing ions was manufactured, and the LiFSI content obtained is shown in Table 1 below.

[0050] [Table 1]

[0051] <Experimental Example 1> The batteries used for evaluation were pouch cells, with NCM811 used for the positive electrode and graphite for the negative electrode. A mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate was used as the electrolyte solvent. The electrolyte contained 1.15 M LiPF6 electrolyte, and the batteries were manufactured using an electrolyte containing VC (Vinylene Carbonate) and LiFSI as additives in the weight ratios shown in Table 2 below. The battery output was evaluated for the aforementioned batteries, and then evaluated again after exposure to high temperature (70°C) for one week. The evaluation results are shown in Figure 1.

[0052] [Table 2]

[0053] As shown in Figure 1, in the case of battery A, which does not have VC or LiFSI added, the battery output before high-temperature exposure was 53.31, but the battery output after high-temperature exposure was 21.7, a decrease of less than 50% compared to before high-temperature exposure. In contrast, battery D, which has VC and cesium ion-containing LiFSI added, had a battery output of 54.48 before high-temperature exposure, which was higher than battery A, and although the output decreased after high-temperature exposure, it remained at 51.5% compared to before exposure. Furthermore, it can be seen that battery D has higher battery output both before and after high-temperature exposure compared to battery C, which has VC and LiFSI without cesium added.

[0054] <Experimental Example 2> A battery was manufactured as in Experimental Example 1 using an electrolyte containing 1.15M LiPF6 electrolyte and VC (Vinylene Carbonate) and LiFSI as additives in the weight ratios shown in Table 3 below. The battery output was evaluated before and after exposure to high temperature (70°C) for one week. The results are shown in Figure 2.

[0055] [Table 3]

[0056] As shown in Figure 2, in the case of battery F, which does not contain VC or LiFSI, the battery output before high-temperature exposure was 53.12, but the battery output after high-temperature exposure was 21.26, a decrease of less than 50% compared to before high-temperature exposure. In contrast, battery I, which contains VC and rubidium ion-containing LiFSI, had a higher battery output of 54.42 before high-temperature exposure compared to battery F, and although the output decreased after high-temperature exposure, it remained at 50.4% compared to before exposure. Furthermore, it can be seen that battery I has higher battery output both before and after high-temperature exposure compared to battery H, which contains VC and LiFSI without rubidium.

[0057] According to the results described above, using LiFSI containing cesium ions or rubidium ions produced by the present invention as an electrolyte yielded improved long-term battery stability and high-temperature output compared to existing solutions. [Industrial applicability]

[0058] By using LiFSI containing cesium ions or rubidium ions produced by this invention as the electrolyte, improved long-term stability and high-temperature output of the battery can be obtained compared to existing systems.

Claims

1. A Cs ＋ Ions and Rb ＋ A method for producing a lithium bisfluorosulfonylimide salt containing 5 to 10,000 ppm by weight of one or more ions selected from a group of ions. 【Chemistry 1】 In chemical formula 1, M １ ＋ This is an onium ion containing H, Na, K, Ca, Zn, Cs, Rb or N, or S, and the ionic additive is a cesium salt or rubidium salt. In chemical formula 2, M ２ ＋ This is a Li ion and one or more ions selected from Cs and Rb.

2. The lithium salt is lithium hydroxide (LiOH), lithium hydroxide hydrate (LiOH·H ２ O), Li ２ CO ３ , LiNH ２ , LiHCO ３ , BuLi, LiF, LiCl, LiBr, LiI or LiClO ４ The production method according to claim 1, which is as described above.

3. The aforementioned cesium salts are CsF, CsCl, CsBr, CsI, CsCN, and CsClO ４ , CsH, CsNO ３ , CsOH, Cs ２ CO ３ , CsHCO ３ , Cs ２ SO ４ , Cs ２ S, CsC ２ H ３ O ２ , Cs ２ O or CsHSO ４ The rubidium salts are RbF, RbCl, RbBr, RbI, RbCN, and RbClO. ４ , RbH, RbNO ３ , RbOH, Rb ２ CO ３ , RbHCO ３ , Rb ２ SO ４ , Rb ２ S, RbC ２ H ３ O ２ , Rb ２ O or RbHSO ４ The manufacturing method according to claim 1.

4. The manufacturing method according to claim 1, characterized in that the solvent is one or more selected from the group consisting of water, alcohols, hydrocarbons, acetates, methylene chloride, chloroform, ethers, cyclic carbonates, acetonitrile, linear carbonates, and glycols.

5. The manufacturing method according to claim 1, wherein the reaction temperature is -50°C to 100°C.

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