Bisfluorosulfonimide lithium salts containing cesium ions or rubidium ions

Abstract

The present invention relates to an electrolyte additive composition comprising at least one selected from the group consisting of Cs + ions and Rb + ions and a lithium bisfluorosulfonylimide salt.

Description

Technical Field

[0001] This invention relates to a lithium bis(fluorosulfonyl)imide salt for use in lithium secondary battery electrolytes. Background Technology

[0002] In recent years, with the increasing demand in the secondary battery industry for medium and large-sized products, the importance of battery output and safety has become increasingly apparent. Furthermore, people are naturally paying more attention to battery lifespan. Although battery stability and lifespan are affected by other factors, they are significantly influenced by the SEI (solid electrolyte interphase) film.

[0003] The SEI film formed on the negative electrode performs ion tunneling, allowing only lithium ions to pass through. Due to this ion tunneling effect, the SEI film prevents high-molecular-weight organic solvent molecules that move with lithium ions in the electrolyte from inserting into the negative electrode active material layers and disrupting the negative electrode structure. Therefore, by preventing contact between the electrolyte and the negative electrode active material, electrolyte decomposition does not occur, and the amount of lithium ions in the electrolyte is reversibly maintained, thereby ensuring stable charging and discharging.

[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 great advantages in solving and improving the problems of lifespan, output, and stability of existing lithium salts. Summary of the Invention

[0005] However, existing LiFSIs have limitations in forming an SEI film and improving their electrical properties such as lifetime and output. Therefore, additional SEI film improvers must be used in the electrolyte, which leads to more complex processes and increased electrolyte costs.

[0006] The purpose of this invention is to provide an improved LiFSI salt that helps to form a thin and stable SEI film on the surface of the positive or negative electrode of a lithium battery.

[0007] To achieve the aforementioned objective, the present invention provides a lithium bis(fluorosulfonyl)imide salt, wherein the bis(fluorosulfonyl)imide salt comprises Cs selected from Cs. + Ions and Rb + At least one of the groups consisting of ions.

[0008] Furthermore, the present invention provides a composition for use as an electrolyte additive, wherein the composition comprises Cs selected from Cs + Ions and Rb+ At least one of the group consisting of ions and lithium bis(fluorosulfonyl)imide.

[0009] Invention Effects

[0010] The lithium bisfluorosulfonylimide (LiFSI) or a composition containing LiFSI prepared according to embodiments of the present invention, when added to an electrolyte, has the function of forming a thin and stable SEI film on the positive and negative electrodes of a lithium battery, thereby improving the high and low temperature output of the lithium battery and enhancing battery life and stability. Attached Figure Description

[0011] Figure 1 This is the output evaluation result of a LiFSI battery containing 5,000 ppm by weight of cesium ions.

[0012] Figure 2 This is the output evaluation result of a LiFSI battery containing 6,000 ppm by weight of rubidium ions. Detailed Implementation

[0013] The present invention will now be described in detail. The terms or words used in this specification and claims should not be construed as limited to their ordinary or dictionary meanings. Based on the principle that the inventors may appropriately define the concepts of terms in order to best illustrate their invention, they should be interpreted as meanings and concepts consistent with the technical spirit of the present invention.

[0014] The inventors recognized the potential of existing LiFSI to form thinner and more stable SEI films and attempted to address this issue, confirming that when using Cs-containing... + Ions and / or Rb + LiFSI containing ions, or containing Cs together with LiFSI + Ions and / or Rb + When ions are combined, the battery life and output can be improved by forming a thinner and more stable SEI (solid electrolyte interphase) film on the surface of the positive or negative electrode of the lithium battery, thus completing the present invention.

[0015] This invention provides a Cs-containing additive for use as an electrolyte in lithium batteries. + Ions and / or Rb + LiFSI containing ions, or containing Cs together with LiFSI + Ions and / or Rb + A composition for use as an electrolyte additive for ions.

[0016] In the present invention, Cs is included + Ions and / or Rb+ LiFSI containing ions, or containing Cs together with LiFSI + Ions and / or Rb + In the ionic composition, Cs + Ions and / or Rb + The ions, preferably, may contain more than 0 to 100,000 ppm by weight, more preferably, may contain 5 to 10,000 ppm by weight. When Cs contains the above-mentioned amounts... + Ions and / or Rb + When ionic LiFSI is used as an electrolyte additive, a more stable SEI film can be formed in the battery.

[0017] The present invention includes Cs + Ions and / or Rb + The ionic LiFSI or compositions containing LiFSI are not limited thereto, and can be prepared by the method of the following reaction formula 1. That is, the Cs-containing LiFSI of the present invention + Ions and / or Rb + LiFSI of ions can be prepared by adding cesium or rubidium salts when a compound of chemical formula 1 and a lithium salt undergo an ion exchange reaction in the presence of a solvent.

[0018] [Reaction Formula 1]

[0019]

[0020] In chemical formula 1, M 1+ It 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 a rubidium salt.

[0021] In chemical formula 2, M2 + It is a Li ion, and at least one ion selected from Cs and Rb.

[0022] The LiFSI containing cesium and / or rubidium ions of the present invention is prepared by reacting a bis(fluorosulfonyl)imide or a bis(fluorosulfonyl) salt (excluding lithium salt) with a lithium salt via a cation substitution reaction. When cesium salt and / or rubidium salt are added as additives, LiFSI containing cesium ions and / or rubidium ions can be finally prepared.

[0023] The LiFSI containing cesium and / or rubidium ions or the composition containing LiFSI of the present invention can be made by including Cs-selected LiFSI. + Ions and Rb + Prepared by a method comprising at least one of the group consisting of ions, characterized in that a cesium salt or a rubidium salt is added to a LiFSI solution containing a solvent and then stirred.

[0024] The N or S-containing onium ion is preferably NH4+. + ion.

[0025] The lithium salt may be lithium hydroxide (LiOH), its hydrate (LiOH·H2O), Li2CO3, LiNH2, LiHCO3, BuLi, LiF, LiCl, LiBr, LiI, or LiClO4. Preferably, the lithium salt is commercially available and highly stable lithium hydroxide.

[0026] The cesium salt can be CsF, CsCl, CsBr, CsI, CsCN, CsClO4, CsH, CsNO3, CsOH, Cs2CO3, CsHCO3, Cs2SO4, Cs2S, CsC2H3O2, Cs2O, or CsHSO4. The preferred cesium salt is commercially available and highly stable cesium hydroxide.

[0027] The rubidium salt can be RbF, RbCl, RbBr, RbI, RbCN, RbClO4, RbH, RbNO3, RbOH, Rb2CO3, RbHCO3, Rb2SO4, Rb2S, RbC2H3O2, Rb2O, or RbHSO4. The preferred rubidium salt is commercially available and highly stable rubidium hydroxide.

[0028] The ion exchange reaction or the addition reaction of cesium salt and / or rubidium salt can be carried out in a solvent capable of dissolving LiFSI.

[0029] The solvent is water; alcohols such as methanol, ethanol, propanol, butanol, and isopropanol; 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; dichloromethane; chloroform; ethers such as diisopropyl ether, methyl tert-butyl ether, and 1,2-dimethoxyethane; or ethylene carbonate and 1,2-dimethoxyethane. Cyclic carbonates comprising at least one of the following groups: butyl acetate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, and fluoroethylene carbonate (FEC); acetonitrile; linear carbonates such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate; and diols such as ethylene glycol, propylene glycol, and butanediol, which may be used alone or in combination of two or more.

[0030] The preferred reaction solvents are 1,2-dimethoxyethane, butyl acetate, acetonitrile, water, or mixtures thereof.

[0031] The solvent used per 1g of M1FSI or M2FSI is 10 to 50 mL, preferably 15 to 40 mL. When using the solvent at the above concentration, the reactants should be fully dissolved before proceeding with the reaction.

[0032] In one embodiment of the present invention, based on the reaction equivalence ratio of the bis(fluorosulfonyl)imide salt, the lithium salt can be from 0.5 equivalents to less than 2 equivalents, preferably from 1 equivalent to less than 1.5 equivalents.

[0033] When lithium salts fall within the above equivalent range, the yield can be increased during subsequent purification processes, and no residue remains after the reaction is completed. Therefore, it can have an excellent effect of improving purity.

[0034] Cesium or rubidium salts added in ion exchange reactions or LiFSIs may contain Cs+ and / or Rb+ ions in the final LiFSI salt or LiFSI-containing composition, where the Cs+ and / or Rb+ ions may contain more than 0 to 100,000 ppm by weight.

[0035] In one embodiment of the present invention, a filtration or purification step may be further included to remove unreacted substances, by-reactants, and other foreign substances generated during the reaction of the bis(fluorosulfonyl)imide salt with the lithium salt.

[0036] To purify LiFSI, an aqueous solution of cesium hydroxide can be used, in which acid byproducts that may cause LiFSI to change over time can be removed.

[0037] In one embodiment of the present invention, the reaction temperature can be from -50°C to 100°C, preferably from -20°C to 50°C, and more preferably from -10°C to below 30°C.

[0038] When the reaction temperature is within the above-mentioned range, it not only prevents the inhibition of by-products but also prevents color changes in the product. Furthermore, in the step of concentrating the filtrate to form a concentrate, crystallization can be easily carried out without the need for an expensive thin-film evaporator, which can be considered an advantage according to an embodiment of the present invention.

[0039] Implementation

[0040] The present invention will now be described in detail with reference to a preferred embodiment, but the present invention is not limited thereto.

[0041] Example 1-1: In a system containing Cs + Preparation method of ionic LiFSI in mixed solvents >

[0042] 10 g (0.05 mol) of NH4FSI, 20 ml of butyl acetate, and 10 ml of distilled water were added to a reactor and completely dissolved. 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 mol) of lithium hydroxide monohydrate was added, and the reaction was carried out at room temperature for 1 hour. After the reaction was complete, the organic layer was separated and recovered. Then, 30 ml of butyl acetate was added to the aqueous layer again, and this process was repeated twice. The resulting organic layer was concentrated under reduced pressure at 50°C to obtain 6.14 g (0.033 mol) of LiFSI crystals. (LiFSI purity 99%, cesium ion 5,000 ppm by weight, yield 65%)

[0043] Example 1-2: In the case of Cs + Preparation method of ionic LiFSI in mixed solvents >

[0044] Except for using 0.03 g of cesium hydroxide monohydrate as used in Example 1-1, LiFSI was prepared using the same method as in Example 1-1. 5.95 g of white solid LiFSI crystals were obtained. (LiFSI purity 99%, cesium ion 3,000 ppm by weight, yield 63%)

[0045] Example 1-3: In the case of Cs + Preparation method of ions in LiFSI mixed solvents >

[0046] The LiFSI was prepared in the same manner as in Example 1-1, except that 0.01 g of cesium hydroxide monohydrate was used in Example 1-1. 6.23 g of white solid LiFSI crystals were obtained. (LiFSI purity 99%, cesium ion 1,000 ppm by weight, yield 66%)

[0047] Example 2-1: Containing Cs + Preparation method of LiFSI ions in aqueous solution >

[0048] At room temperature, 10 g (0.05 mol) 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 mol) 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 recrystallized by adding 50 mL of toluene. The filtered crystals were dissolved in 40 mL of 1,2-dimethoxyethane to remove insoluble matter. The filtrate was concentrated under reduced pressure at 50 °C to obtain 8.5 g (0.045 mol) of LiFSI crystals. (LiFSI purity 99%, cesium ion concentration 5,000 ppm by weight, yield 90%)

[0049] Example 2-2: Containing Cs + Preparation method of ionized LiFSI in aqueous solution >

[0050] Except for using 0.03 g of cesium hydroxide monohydrate as used in Example 2-1, LiFSI was prepared using the same method as in Example 2-1. 8.12 g of white solid LiFSI crystals were obtained. (LiFSI purity 99%, cesium ion 3,000 ppm by weight, yield 86%)

[0051] Example 2-3: Containing Cs + Preparation method of ionized LiFSI in aqueous solution >

[0052] Except for using 0.01 g of cesium hydroxide monohydrate as used in Example 2-1, LiFSI was prepared using the same method as in Example 2-1. 8.40 g of white solid LiFSI crystals were obtained. (LiFSI purity 99%, cesium ion 1,000 ppm by weight, yield 89%)

[0053] Example 3-1: Containing Cs + Preparation method of ionic LiFSI in organic solvents >

[0054] At room temperature, 10 g (0.05 mol) 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 mol) of lithium hydroxide monohydrate was added, and the reaction was carried out at room temperature for 3 hours. After the reaction was complete, insoluble matter was removed by filtration, and the filtrate was concentrated under reduced pressure at 50 °C to obtain 9.16 g (0.049 mol) of LiFSI crystals. (LiFSI purity 99%, cesium ion concentration 5,000 ppm by weight, yield 97%)

[0055] Example 3-2: Containing Cs +Preparation method of ionic LiFSI in organic solvents >

[0056] Except for using 0.03 g of cesium hydroxide monohydrate as used in Example 3-1, LiFSI was prepared using the same method as in Example 3-1. 8.97 g of white solid LiFSI crystals were obtained. (LiFSI purity 99%, cesium ion 3,000 ppm by weight, yield 95%)

[0057] Example 3-3: Containing Cs + Preparation method of ionic LiFSI in organic solvents >

[0058] Except for using 0.01 g of cesium hydroxide monohydrate as used in Example 3-1, LiFSI was prepared using the same method as in Example 3-1. 9.25 g of white solid LiFSI crystals were obtained. (LiFSI purity 99%, cesium ion 1,000 ppm by weight, yield 98%)

[0059] Example 4-1: Preparation of Cs-containing solution by adding cesium salt to LiFSI-containing solution + LiFSI ions>

[0060] 10 g (0.053 mol) of LiFSI and 20 mL of 1,2-dimethoxyethane were dissolved in a reactor, followed by the addition of 0.05 g of cesium hydroxide monohydrate. The mixture was stirred at 40 °C for 24 hours. After the reaction was complete, the residue was completely removed by filtration. The filtrate was concentrated under reduced pressure at 50 °C, and after further concentration, recrystallization was performed by adding 30 mL of toluene. The resulting crystals were then completely dried at 50 °C to obtain 9.35 g (0.050 mol) of LiFSI crystals. (LiFSI purity 99%, cesium ion concentration 5,000 ppm by weight, yield 99%)

[0061] Example 4-2: Preparation of Cs-containing solution by adding cesium salt to LiFSI-containing solution + LiFSI ions>

[0062] The LiFSI was prepared in the same manner as in Example 4-1, except that 0.03 g of cesium hydroxide monohydrate was used in Example 4-1. 9.35 g of white solid LiFSI crystals were obtained. (LiFSI purity 99%, cesium ion 3,000 ppm by weight, yield 99%)

[0063] Example 4-3: Preparation of Cs-containing solutions by adding cesium salts to LiFSI-containing solutions + LiFSI ions>

[0064] Except for using 0.01 g of cesium hydroxide monohydrate as used in Example 4-1, LiFSI was prepared using the same method as in Example 4-1. 9.35 g of white solid LiFSI crystals were obtained. (LiFSI purity 99%, cesium ion 1,000 ppm by weight, yield 99%)

[0065] Examples 5 to 8: Preparation of Rb + LiFSI ions>

[0066] Using the reactants and solvents listed in Table 1 below, preparations containing Rb were performed as described in Examples 1 through 4. + The LiFSI of the ions is shown in Table 1 below.

[0067] [Table 1]

[0068]

[0069] <Experimental Example 1>

[0070] The batteries used for evaluation were pouch cells, using NCM811 as the positive electrode and graphite as the negative electrode. A mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate was used as the electrolyte solvent. The batteries were manufactured using an electrolyte containing 1.15M LiPF6 and VC (vinylene carbonate) and LiFSI as additives in the weight ratios shown in Table 2 below. Battery output was evaluated, followed by evaluation of battery output after exposure to high temperature (70°C) for one week. The evaluation results are shown in... Figure 1 .

[0071] [Table 2]

[0072]

[0073] Depend on Figure 1 It can be seen that, in the case of battery (A) without added VC and LiFSI, the battery output before high-temperature exposure was 53.31, but after high-temperature exposure, the battery output was 21.7, a decrease of less than 50% compared to before high-temperature exposure. On the other hand, battery D with added VC and LiFSI containing cesium ions had a battery output of 54.48 before high-temperature exposure, higher than battery A. Although the output decreased after high-temperature exposure, it still remained at 51.5% of the pre-exposure level. Furthermore, it can be seen that battery D has a higher battery output both before and after high-temperature exposure compared to battery C, where battery C has added VC and LiFSI without cesium ions.

[0074] <Experimental Example 2>

[0075] A battery was prepared as in Example 1 using an electrolyte containing 1.15 M LiPF6 and VC (vinylene carbonate) and LiFSI as additives in the weight ratios shown in Table 3. The battery output was then evaluated before and after one week of exposure to high temperature (70°C), and the results are presented below. Figure 2 .

[0076] [Table 3]

[0077]

[0078] Depend on Figure 2 It can be seen that, in the case of battery F without added VC and LiFSI, the battery output before high-temperature exposure was 53.12, but after high-temperature exposure, the battery output was 21.26, a decrease of less than 50% compared to before high-temperature exposure. On the other hand, battery I with added VC and LiFSI containing rubidium ions had a higher battery output than battery F before high-temperature exposure, at 54.42. Although the output decreased after high-temperature exposure, it still remained at 50.4% of the pre-exposure level. Furthermore, it can be seen that battery I has a higher battery output both before and after high-temperature exposure compared to battery H, where battery H has added VC and does not contain LiFSI containing rubidium ions.

[0079] Based on the above results, when the LiFSI containing cesium or rubidium ions prepared in this invention is used as an electrolyte, improved results can be obtained in terms of long-term battery stability and high-temperature output compared with the existing methods.

[0080] Industrial application potential

[0081] When the LiFSI containing cesium or rubidium ions prepared in this invention is used as an electrolyte, improved results can be obtained in terms of long-term battery stability and high-temperature output compared with existing methods.

Claims

1. A Cs containing 1000 to 10000 ppm by weight + Ions or 6000 to 10000 ppm by weight of Rb + A method for preparing lithium bis(fluorosulfonyl)imide salts, characterized in that, When a compound of formula 1 undergoes an ion exchange reaction with a lithium salt in the presence of a solvent, a cesium salt or a rubidium salt is added: In chemical formula 1, M1 + It is an onium ion containing H, Na, K, Ca, Zn, Cs, Rb or N or S, with ionic additives being cesium salts or rubidium salts. In chemical formula 2, M2 + It consists of Li ions and one ion selected from Cs and Rb.

2. The preparation method according to claim 1, characterized in that, The lithium salt is lithium hydroxide, lithium hydroxide hydrate, Li2CO3, LiHCO3, LiF, LiCl, LiBr, LiI or LiClO4.

3. The method according to claim 1, characterized in that, The cesium salts are CsF, CsCl, CsBr, CsI, CsCN, CsClO4, CsNO3, CsOH, Cs2CO3, CsHCO3, Cs2SO4, and CsHSO4; the rubidium salts are RbF, RbCl, RbBr, RbI, RbCN, RbClO4, RbNO3, RbOH, Rb2CO3, RbHCO3, Rb2SO4, and RbHSO4.

4. The method according to claim 1, characterized in that, The solvent is one or more selected from the group consisting of water, alcohols, hydrocarbons, acetates, dichloromethane, chloroform, ethers, cyclic carbonates, acetonitrile, and straight-chain carbonates.

5. The preparation method according to claim 1, characterized in that, The reaction temperature ranges from -50℃ to 100℃.

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