LITHIUM SALT OF BISFLUOROSULFONYLIMIDE COMPRISING CESIUM ION OR RUBIDIUM ION

Abstract

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

Claims

1. A bisfluorosulfonylimide lithium salt, comprising one or more selected from the group consisting of Cs.sup.+ ion and Rb.sup.+ ion.

2. The lithium salt according to claim 1, wherein the one or more selected from the group consisting of Cs.sup.+ ion and Rb.sup.+ ion is included in an amount of more than 0 to 100,000 ppm per weight (wt. ppm) or less.

3. A composition for an electrolyte additive, comprising a bisfluorosulfonylimide lithium salt as well as one or more selected from the group consisting of Cs.sup.+ ion and Rb.sup.+ ion.

4. The composition according to claim 3, wherein the one or more selected from the group consisting of Cs.sup.+ ion and Rb.sup.+ ion is included in an amount of more than 0 to 100,000 wt. ppm or less.

5. A method for preparation of a bisfluorosulfonylimide lithium salt which includes one or more selected from the group consisting of Cs.sup.+ ion and Rb.sup.+ ion, comprising adding a cesium salt or rubidium salt when a compound represented by Formula 1 below and a lithium salt are subjected to ion exchange reaction in a solvent. ##STR00002## wherein, in Formula 1, M.sub.1.sup.+ is H, Na, K, Ca, Zn, Cs, Rb, or an onium ion including N or S, and an ion additive is a cesium salt or a rubidium salt, and wherein, in Formula 2, M.sub.2.sup.+ is a Li ion and one or more ions selected from Cs and Rb.

6. A method for preparation of a bisfluorosulfonylimide lithium salt which includes one or more selected from the group consisting of Cs.sup.+ ion and Rb.sup.+ ion, comprising adding a cesium salt or rubidium salt to a solvent-including LiFSI solution and then stirring the same.

7. The method according to claim 5, wherein the lithium salt is lithium hydroxide (LiOH), lithium hydroxide hydrate (LiOH.Math.H.sub.2O), Li.sub.2CO.sub.3, LiNH.sub.2, LiHCO.sub.3, BuLi, LiF, LiCl, LiBr, LiI, or LiClO.sub.4.

8. The method according to claim 5, wherein the cesium salt is CsF, CsCl, CsBr, CsI, CsCN, CsClO.sub.4, CsH, CsNO.sub.3, CsOH, Cs.sub.2CO.sub.3, CsHCO.sub.3, Cs.sub.2SO.sub.4, Cs.sub.2S, CsC.sub.2H.sub.3O.sub.2, Cs.sub.2O or CsHSO.sub.4, and the rubidium salt is RbF, RbCl, RbBr, RbI, RbCN, RbClO.sub.4, RbH, RbNO.sub.3, RbOH, Rb.sub.2CO.sub.3, RbHCO.sub.3, Rb.sub.2SO.sub.4, Rb.sub.2S, RbC.sub.2H.sub.3O.sub.2, Rb.sub.2O or RbHSO.sub.4.

9. The method according to claim 6, wherein the cesium salt is CsF, CsCl, CsBr, CsI, CsCN, CsClO.sub.4, CsH, CsNO.sub.3, CsOH, Cs.sub.2CO.sub.3, CsHCO.sub.3, Cs.sub.2SO.sub.4, Cs.sub.2S, CsC.sub.2H.sub.3O.sub.2, Cs.sub.2O or CsHSO.sub.4, and the rubidium salt is RbF, RbCl, RbBr, RbI, RbCN, RbClO.sub.4, RbH, RbNO.sub.3, RbOH, Rb.sub.2CO.sub.3, RbHCO.sub.3, Rb.sub.2SO.sub.4, Rb.sub.2S, RbC.sub.2H.sub.3O.sub.2, Rb.sub.2O or RbHSO.sub.4.

10. The method according to claim 5, wherein the solvent is one or a combination of two or more selected from the group consisting of: water; alcohols; hydrocarbons; hydrocarbons: acetates; methylene chloride; chloroform; ethers; cyclic carbonates; acetonitrile; linear carbonates; and glycols.

11. The method according to claim 6, wherein the solvent is one or a combination of two or more selected from the group consisting of: water; alcohols; hydrocarbons; hydrocarbons: acetates; methylene chloride; chloroform; ethers; cyclic carbonates; acetonitrile; linear carbonates; and glycols.

12. The method according to claim 5, wherein the reaction temperature ranges from ?50 to 100? C.

13. The method according to claim 6, wherein the reaction temperature ranges from ?50 to 100? C.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0010] FIG. 1 illustrates an output evaluation result of a battery including LiFSI, which contains 5,000 ppm by weight of cesium ions.

[0011] FIG. 2 illustrates an output evaluation result of a battery including LiFSI, which contains 6,000 ppm by weight of rubidium ions.

BEST MODE FOR CARRYING OUT INVENTION

[0012] Hereinafter, the present invention will be described in detail. The terms or words used in the present specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, instead, on the basis of the principle that the inventor may appropriately define the concepts of the terms in order to best describe his invention by the best method, it should be interpreted as meanings and concepts consistent with the technical idea of the present invention.

[0013] The present inventors recognized the possibility of forming a thinner and more stable SEI film than that formed using conventional LiFSI, and tried to solve the problem. Therefore, it was confirmed that, when LiFSI including Cs.sup.+ ions and/or Rb.sup.+ ions, or a composition including Cs.sup.+ and/or Rb.sup.+ ions as well as LiFSI is used, 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 to improve battery life and output, thereby completing the present invention.

[0014] The present invention provides LiFSI including Cs.sup.+ ions and/or Rb.sup.+ ions, which is used as a lithium battery electrolyte additive, or a composition for an electrolyte additive, which includes Cs.sup.+ and/or Rb.sup.+ ions as well as LiFSI.

[0015] In the inventive LiFSI including Cs.sup.+ ions and/or Rb.sup.+ ions, or the composition including Cs.sup.+ ions and/or Rb.sup.+ ions as well as LiFSI, the Cs.sup.+ ions and/or Rb.sup.+ ions may be included in an amount of more than 0 to 100,000 ppm by weight (wt. ppm) or less, more preferably, 5 to 10,000 wt. ppm. When LiFSI including Cs.sup.+ ions and/or Rb.sup.+ ions in the above content are used as an electrolyte additive, a more stable SEI film may be formed in the battery.

[0016] The LiFSI or LiFSI-containing composition including Cs.sup.+ ions and/or Rb.sup.+ ions of the present invention is not limited thereto, but may be prepared by a method of Scheme 1 below. That is, the LiFSI containing Cs.sup.+ ions and/or Rb.sup.+ ions of the present invention may be prepared by adding a cesium salt or a rubidium salt when the compound of Formula 1 and a lithium salt are ion-exchanged in a solvent.

##STR00001##

[0017] In Formula 1, M.sub.1.sup.+ is H, Na, K, Ca, Zn, Cs, Rb, or an onium ion including N or S, and the ion additive is a cesium salt or a rubidium salt.

[0018] In Formula 2, M.sub.2.sup.+ is a Li ion and one or more ions selected from Cs and Rb.

[0019] With regard to LiFSI containing cesium and/or rubidium ions of the present invention, when LiFSI is prepared by reacting bisfluorosulfonylimide or a salt of bisfluorosulfonyl (except lithium salt) with a lithium salt and then conducting cation substitution, LiFSI finally including cesium ions and/or rubidium ions may be prepared if adding a cesium salt and/or rubidium salt as a separate additive.

[0020] When the cesium and/or rubidium ion-containing LiFSI or LiFSI-including composition may be produced by adding a cesium salt and/or a rubidium salt to a LiFSI solution including a solvent and then stirring the same, wherein one or more selected from the group consisting of Cs.sup.+ ions and Rb.sup.+ ions is included.

[0021] The onium ion including N or S is preferably an NH.sub.4.sup.+ ion.

[0022] The lithium salt may be lithium hydroxide (LiOH), a hydrate thereof (LiOH.Math.H.sub.2O), Li.sub.2CO.sub.3, LiNH.sub.2, LiHCO.sub.3, BuLi, LiF, LiCl, LiBr, LiI, or LiClO.sub.4. The lithium salt is preferably lithium hydroxide that is commercially useful and has high stability.

[0023] The cesium salt may be CsF, CsCl, CsBr, CsI, CsCN, CsClO.sub.4, CsH, CsNO.sub.3, CsOH, CS.sub.2CO.sub.3, CsHCO.sub.3, CS.sub.2SO.sub.4, Cs.sub.2S, CsC.sub.2H.sub.3O.sub.2, CS.sub.2O or CsHSO.sub.4. The cesium salt is preferably cesium hydroxide that is commercially available and has high stability.

[0024] The rubidium salt may be RbF, RbCl, RbBr, RbI, RbCN, RbClO.sub.4, RbH, RbNO.sub.3, RbOH, Rb.sub.2CO.sub.3, RbHCO.sub.3, Rb.sub.2SO.sub.4, Rb.sub.2S, RbC.sub.2H.sub.3O.sub.2, Rb.sub.2O or RbHSO.sub.4. The rubidium salt is preferably rubidium hydroxide that is commercially useful and has high stability.

[0025] The ion exchange reaction or the cesium salt and/or rubidium salt addition reaction may be performed in a solvent capable of dissolving LiFSI.

[0026] The solvent may be, for example: 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; at least one cyclic carbonates selected from the group consisting of ethylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate and fluoroethylene carbonate (FEC); acetonitrile;

[0027] linear carbonates such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, and ethylpropyl carbonate; and glycols such as ethylene glycol, propylene glycol and butylene glycol, and these may be used alone or in combination of two or more thereof.

[0028] The reaction solvent is preferably 1,2-dimethoxyethane, butyl acetate, acetonitrile, water, or a mixture thereof.

[0029] The solvent may be used in an amount of 10 to 50 mL, preferably, 15 to 40 mL per 1 g of M.sub.1FSI or M.sub.2FSI. When the solvent is used in the above content, the reaction may proceed by sufficiently dissolving the reactants.

[0030] In an exemplary embodiment of the present invention, the lithium salt may be 0.5 equivalent or more and 2 equivalents or less, preferably, 1 equivalent or more and 1.5 equivalents or less based on the reaction equivalent ratio of the bisfluorosulfonylimide salt.

[0031] When the lithium salt is included in the above equivalent range, a yield can be increased in a purification process to be carried out later and, after the reaction is completed, no residue is left, thereby achieving excellent effects of increasing the purity.

[0032] The cesium salt or rubidium salt added to the ion exchange reaction or LiFSI may be added so that Cs+ ions and/or Rb+ ions can be included in the final LiFSI salt or LiFSI-containing composition in the range of more than 0 to 100,000 wt. ppm

[0033] In an exemplary embodiment of the present invention, a filtration or purification step may be further included in order to remove unreacted substances, side reactants, and other foreign substances generated in the step of reacting the bisfluorosulfonylimide salt with the lithium salt.

[0034] For the purification of LiFSI, an aqueous solution of cesium hydroxide, etc. may be used, and in this case, acid by-products possibly causing a change in LiFSI over time may be removed.

[0035] In one embodiment of the present invention, a reaction temperature may be ?50 to 100? C., preferably ?20 to 50? C., more preferably ?10 to 30? C. or less.

[0036] When the reaction temperature is in the above range, suppression of by-products can be prevented and color change of the product can be prevented. Further, in the step of concentrating the filtrate to form a concentrate, it may be easily crystallized without using any expensive equipment, that is, a thin-film evaporator, and this may be an advantage according to an exemplary embodiment of the present invention.

Mode for Carrying Out Preferred Embodiment of Invention

[0037] Hereinafter, the present invention will be described in detail with reference to preferred embodiments of the present invention, but the present invention is not limited thereto.

Example 1-1: Preparation Method of LiFSI Containing Cs.SUP.+ Ions in a Mixed Solvent

[0038] 10 g (0.05 mole) of NH.sub.4FSI, 20 ml of butyl acetate, and 10 ml of distilled water were added to a reactor, completely dissolved, and then cooled to 0? C. After adding 0.05 g of cesium hydroxide monohydrate to the cooled reactor while stirring at room temperature for 30 minutes, 2.75 g (0.066 mole) of lithium hydroxide monohydrate was added and reacted at room temperature for 1 hour. After the reaction was completed, an organic layer was separated and recovered. After that, 30 ml of butyl acetate was added again to an aqueous layer and the reaction was repeated twice. The obtained organic layer was concentrated under reduced pressure at 50? ? C. to yield 6.14 g (0.033 mole) of LiFSI crystals (LiFSI purity 99%, cesium ion 5,000 wt. ppm, yield 65%).

Example 1-2: Preparation Method of LiFSI Containing Cs.SUP.+ Ions in a Mixed Solvent

[0039] A desired product was prepared in the same manner as in Example 1-1, except that cesium hydroxide monohydrate used in Example 1-1 was used in an amount of 0.03 g. As a result, 5.95 g of LiFSI crystals were obtained as a white solid (LiFSI purity 99%, cesium ion 3,000 wt. ppm, yield 63%).

Example 1-3: Preparation Method of LiFSI Containing Cs.SUP.+ Ions in a Mixed Solvent

[0040] A desired product was prepared in the same manner as in Example 1-1, except that cesium hydroxide monohydrate used in Example 1-1 was used in an amount of 0.01 g. As a result, 6.23 g of LiFSI crystals were obtained as a white solid (LiFSI purity 99%, cesium ion 1,000 wt. ppm, yield 66%)

Example 2-1: Preparation Method of LiFSI Containing Cs.SUP.+ Ions in an Aqueous Solution

[0041] 10 g (0.05 mole) of NH.sub.4FSI and 20 ml of distilled water were added to a reactor at room temperature, completely dissolved, and then 0.05 g of cesium hydroxide monohydrate was added and stirred for 10 minutes. Then, 2.75 g (0.066 mole) of lithium hydroxide monohydrate was added and the reaction proceeded at room temperature for 1 hour. After the reaction was completed, it was completely concentrated at 40? C., and then 50 ml of toluene was added, followed by recrystallization. The crystals obtained by filtration were dissolved in 40 ml of 1,2-dimethoxyethane, and then insoluble matter was removed. The filtrate was concentrated under reduced pressure at 50? ? C. to yield 8.5 g (0.045 moles) of LiFSI crystals (LiFSI purity 99%, cesium ion 5,000 wt. ppm, yield 90%).

Example 2-2: Preparation Method of LiFSI Containing Cs.SUP.+ Ions in an Aqueous Solution

[0042] A desired product was prepared in the same manner as in Example 2-1, except that cesium hydroxide monohydrate used in Example 2-1 was used in an amount of 0.03 g. 8.12 g of LiFSI crystals were obtained as a white solid (LiFSI purity 99%, cesium ion 3,000 wt. ppm, yield 86%).

Example 2-3: Preparation Method of LiFSI Containing Cs.SUP.+ Ions in an Aqueous Solution

[0043] A desired product was prepared in the same manner as in Example 2-1, except that cesium hydroxide monohydrate used in Example 2-1 was used in an amount of 0.01 g. 8.40 g of LiFSI crystals were obtained as a white solid (LiFSI purity 99%, cesium ion 1,000 wt. ppm, yield 89%).

Example 3-1: Preparation Method of LiFSI Containing Cs.SUP.+ Ions in an Organic Solvent

[0044] 10 g (0.05 mole) of NH.sub.4FSI, 20 ml of acetonitrile and 0.05 g of cesium hydroxide monohydrate were added to a reactor at room temperature and stirred for 1 hour. Then, 2.75 g (0.066 mole) of lithium hydroxide monohydrate was added and the reaction proceeded at room temperature for 3 hours. After the reaction was completed, it was filtered to remove insoluble matter, and the filtrate was concentrated under reduced pressure at 50? ? C. to yield 9.16 g (0.049 moles) of LiFSI crystals (LiFSI purity 99%, cesium ion 5,000 wt. ppm, yield 97%).

Example 3-2: Preparation Method of LiFSI Containing Cs.SUP.+ Ions in an Organic Solvent

[0045] A desired product was prepared in the same manner as in Example 3-1, except that cesium hydroxide monohydrate used in Example 3-1 was used in an amount of 0.03 g. 8.97 g of LiFSI crystals were obtained as a white solid. (LiFSI purity 99%, cesium ion 3,000 wt. ppm, yield 95%).

Example 3-3: Preparation Method of LiFSI Containing Cs.SUP.+ Ions in an Organic Solvent

[0046] A desired product was prepared in the same manner as in Example 3-1, except that cesium hydroxide monohydrate used in Example 3-1 was used in an amount of 0.01 g. 9.25 g of LiFSI crystals were obtained as a white solid. (LiFSI purity 99%, cesium ion 1,000 wt. ppm, yield 98%).

Example 4-1: Preparation of LiFSI Containing Cs.SUP.+ Ions by Adding Cesium Salt to a LiFSI-Containing Solution

[0047] After dissolving 10 g (0.053 mole) of LiFSI in 20 ml of 1,2-dimethoxyethane in a reactor, 0.05 g of cesium hydroxide monohydrate was added thereto and stirred at 40? C. for 24 hours. When the reaction was completed, the remaining insoluble matter was completely removed by filtration. Then, the filtrate was concentrated under reduced pressure at 50? C., and recrystallization proceeded by adding 30 ml of toluene. The obtained crystals were completely dried with the residual solvent at 50? C. to yield 9.35 g (0.050 moles) of LiFSI crystals (LiFSI purity 99%, cesium ion 5,000 wt. ppm, yield 99%).

Example 4-2: Preparation of LiFSI Containing Cs.SUP.+ Ions by Adding Cesium Salt to a LiFSI-Containing Solution

[0048] A desired product was prepared in the same manner as in Example 4-1, except that cesium hydroxide monohydrate used in Example 4-1 was used in an amount of 0.03 g. 9.35 g of LiFSI crystals were obtained as a white solid (LiFSI purity 99%, cesium ion 3,000 wt. ppm, yield 99%).

Example 4-3: Preparation of LiFSI Containing Cs.SUP.+ Ions by Adding Cesium Salt to a LiFSI-Containing Solution

[0049] A desired product was prepared in the same manner as in Example 4-1, except that cesium hydroxide monohydrate used in Example 4-1 was used in an amount of 0.01 g. 9.35 g of LiFSI crystals were obtained as a white solid (LiFSI purity 99%, cesium ion 1,000 wt. ppm, yield 99%).

Examples 5 to 8: Preparation of LiFSI Containing Rb+ Ions

[0050] LiFSI including Rb.sup.+ ions was prepared in the same manner as in Examples 1 to 4 using the reactants and solvents in Table 1 below, and the obtained LiFSI content is shown in Table 1 below.

TABLE-US-00001 TABLE 1 Example 5 Example 6 Example 7 Example 8 NH.sub.4FSI 10 g (0.05 10 g (0.05 10 g (0.05 mole) mole) mole) LiFSI 10 g (0.053 mole) RbOHH.sub.2O 0.06 g 0.06 g 0.06 g 0.06 g LiOHH.sub.2O 2.75 g 2.75 g 2.75 g Medium Butyl distilled Acetonitrile 1,2- acetate 20 mL water 20 mL 20 mL dimethoxy- distilled ethane 20 ml water 10 mL LiFSI 5.66 g 8.50 g 9.25 g 9.35 g content (yield 60%) (yield 90%) (yield 98%) (yield 99%) (yield) Rb ion 6,000 wt. 6,000 wt. 6,000 wt. 6,000 wt. content ppm ppm ppm ppm

Experimental Example 1

[0051] The battery used for battery evaluation was a pouch cell, and NCM811 was used as a positive electrode while graphite was used as a negative electrode. Further, a mixed solvent of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate was used as the electrolyte solvent. The electrolyte was prepared using an electrolyte solution containing 1.15M LiPF.sub.6 electrolyte, as well as VC (Vinylene Carbonate) and LiFSI as additives in the weight ratio of Table 2 below. For the manufactured battery, a battery output was evaluated, and then the battery output was also evaluated after exposure to a high temperature (70? C.) for 1 week. The evaluation results are shown in FIG. 1

TABLE-US-00002 TABLE 2 Battery Electrolyte Additive A 1.15M LiPF.sub.6 NO add B 1.15M LiPF.sub.6 VC 1 wt. % C 1.15M LiPF.sub.6 VC 1 wt. % 0.5 wt. % LiFSI D 1.15M LiPF.sub.6 VC 1 wt. % 0.5 wt. % LiFSI containing 0.5 wt. % cesium ion E 1.15M LiPF.sub.6 VC 1 wt. % 0.1 wt. % LiFSI containing 0.5 wt % cesium ion

[0052] According to FIG. 1, in the case of the battery A to which VC and LiFSI were not added, the battery output before high temperature exposure was 53.31 whereas, after high temperature exposure, the battery output was 21.7, which decreased to less than 50% compared to before high temperature exposure. On the other hand, battery D, to which VC and LiFSI containing cesium ions were added, had a higher battery output of 54.48 compared to battery A before high temperature exposure. Further, although the output decreased after high temperature exposure, it was maintained to 51.5% compared to before exposure. In addition, it could be seen that battery D has higher battery output in both cases of before and after high temperature exposure compared to battery C, to which LiFSI not containing cesium was added together with VC.

Experimental Example 2

[0053] A battery was manufactured as in Experimental Example 1 using an electrolyte containing 1.15M LiPF.sub.6 electrolyte, as well as VC (Vinylene Carbonate) and LiFSI as additives in the weight ratio of Table 3 below, and was exposed at high temperature (70? C.) for 1 week. The manufactured battery was subjected to battery output evaluation before and after exposure. The results are shown in FIG. 2.

TABLE-US-00003 TABLE 3 Battery Electrolyte Additive F 1.15M LiPF.sub.6 No add G 1.15M LiPF.sub.6 VC 1 wt. % H 1.15M LiPF.sub.6 VC 1 wt. % 0.5 wt. % LiFSI I 1.15M LiPF.sub.6 VC 1 wt. % 0.5 wt. % LiFSI containing 0.6 wt. % rubidium ion J 1.15M LiPF.sub.6 VC 1 wt. % 0.1 wt. % LiFSI containing 0.6 wt. % rubidium ion

[0054] According to FIG. 2, in the case of the battery F to which VC and LiFSI were not added, the battery output before high temperature exposure was 53.12, whereas, after high temperature exposure, the battery output was 21.26, which decreased to less than 50% compared to before high temperature exposure. On the other hand, the battery I to which VC and LiFSI containing rubidium ions were added had a higher battery output of 54.42 than Battery F before high temperature exposure. Further, although the output decreased after high temperature exposure, it was maintained to 50.4% compared to before exposure. Further, it could be seen that battery I has higher battery output in both cases of before and after high temperature exposure compared to battery H, to which LiFSI not containing was added together with VC.

[0055] According to the above results, when the LiFSI containing cesium ions or rubidium ions prepared in the present invention is used in the electrolyte, improved results can be obtained in terms of long-term stability and high-temperature output of the battery.

INDUSTRIAL APPLICABILITY

[0056] When the LiFSI containing cesium ions or rubidium ions prepared in the present invention is used in the electrolyte, improved results can be obtained in terms of long-term stability and high-temperature output of the battery.