Composition containing lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate

Abstract

The present invention relates to a composition for stabilizing lithium bis(fluorosulfonyl)imide over time, the composition comprising lithium bis(fluorosulfonyl)imide and lithium fluoroborate (MFSO3). In addition, the present invention relates to a composition for a lithium secondary battery electrolyte, comprising lithium bis(fluorosulfonyl)imide, lithium fluorosulfonate, and a carbonate solvent.

Description

Composition containing lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate

[0001] The present invention relates to a composition for stability of lithium bis(fluorosulfonyl)imide over time, and more particularly, to a composition for stability of lithium bis(fluorosulfonyl)imide over time, comprising lithium fluorosulfonate (LiFSO3, also referred to as LiFSA) and lithium bis(fluorosulfonyl)imide (also referred to as LiFSI) with a moisture content of 100 ppm by weight or less.

[0002] With the popularization of mobile devices, the commercialization of electric vehicles, and the growing demand for energy storage devices, lithium secondary batteries with non-aqueous electrolytes are being developed for a wide range of applications. Furthermore, demand for higher performance in non-aqueous electrolyte secondary batteries is increasing, necessitating the achievement of superior battery characteristics, such as high capacity, high output, high-temperature storage characteristics, and high cycle performance.

[0003] Therefore, numerous technologies are being examined for various battery components, including the active materials of the positive or negative electrodes, the electrolytes of the non-aqueous electrolyte, or additives, as a means to improve the input / output characteristics, impedance characteristics, high-temperature cycle characteristics, and high-temperature storage characteristics of non-aqueous electrolyte lithium secondary batteries.

[0004] For example, Patent Document 1 describes that alkali metal salts of bis(fluorosulfonyl)imide exhibit high withstand voltage and conductivity, and thus, when used as electrolytes, various high-performance electrochemical devices can be obtained. In particular, lithium bis(fluorosulfonyl)imide possesses outstanding properties such as excellent low-temperature performance, instantaneous high output, and low resistance, and is expected to be useful as a salt in non-aqueous electrolytes for lithium secondary batteries.

[0005] However, lithium bis(fluorosulfonyl)imide is vulnerable to moisture, and can decompose and generate HF and other gases if it comes into contact with a certain amount of moisture during storage or distribution after manufacturing. In other words, lithium bis(fluorosulfonyl)imide has the disadvantage of low stability over time.

[0006] Accordingly, the purpose of the present invention is to provide a method for improving the storage stability of lithium bis(fluorosulfonyl)imide over time.

[0007] To achieve the above object, the present invention provides a composition for stabilizing lithium bis(fluorosulfonyl)imide, comprising 100 ppm by weight or less of moisture, 100 ppm by weight to less than 10% by weight of lithium fluorosulfonate, and 90% by weight or more of lithium bis(fluorosulfonyl)imide.

[0008] The present invention provides a lithium bis(fluorosulfonyl)imide stability composition having an HF content of 50 wt ppm or less after being left at 50°C for 7 days.

[0009] The present invention provides a composition for a lithium secondary battery electrolyte comprising 100 ppm by weight or less of moisture, 100 ppm by weight to less than 10% by weight of lithium fluorosulfonate, and 90% by weight or more of lithium bis(fluorosulfonyl)imide.

[0010] In addition, the present invention provides a composition for a lithium secondary battery electrolyte comprising lithium bis(fluorosulfonyl)imide, lithium fluorosulfonate, and carbonate, wherein the composition contains moisture in an amount of 100 ppm by weight or less, and contains 0.01 to 10 parts by weight of lithium fluorosulfonate relative to 100 parts by weight of lithium bis(fluorosulfonyl)imide.

[0011] The composition for stability of lithium bis(fluorosulfonyl)imide according to the present invention contains lithium fluorosulfonate together with lithium bis(fluorosulfonyl)imide, thereby maintaining moisture at 100 ppm by weight or less, and preventing moisture from decomposing lithium bis(fluorosulfonyl)imide during storage and distribution, thereby having the effect of increasing stability of lithium bis(fluorosulfonyl)imide over time.

[0012] The composition for a lithium secondary battery electrolyte comprising lithium fluorosulfonate together with lithium bis(fluorosulfonyl)imide of the present invention can improve the stability of lithium bis(fluorosulfonyl)imide over time and reduce the content of decomposition byproducts, so that when used in an electrolyte of a secondary battery, it can impart the effect of improving the lifespan of the battery along with high output characteristics to the lithium secondary battery.

[0013] The present invention provides a composition comprising lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate together with a carbonate, which is a solvent for a non-aqueous electrolyte, thereby enabling the composition to be used as is in a non-aqueous electrolyte of a lithium secondary battery, and has the effect of improving the lifespan of the battery along with high output characteristics of the lithium secondary battery.

[0014] Hereinafter, the present invention will be described in detail. Terms and words used in this specification and claims should not be interpreted as limited to their conventional or dictionary meanings. Rather, they should be interpreted with meanings and concepts consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of a term to best explain his or her invention.

[0015] Lithium bis(fluorosulfonyl)imide has excellent performance such as excellent low-temperature performance, instantaneous high output, and low resistance value, making it useful as a salt for non-aqueous electrolytes in lithium secondary batteries. However, it is soluble in water and may be decomposed by water, so there is a concern that changes may occur over time during storage after manufacturing lithium bis(fluorosulfonyl)imide.

[0016] Accordingly, the inventors of the present invention have tried to develop a method for preventing changes in lithium bis(fluorosulfonyl)imide over time, and have found that when lithium bis(fluorosulfonyl)imide is left together with lithium fluorosulfonate, the moisture content that may exist is managed to be 100 ppm by weight or less, and the moisture is prevented from reacting with lithium bis(fluorosulfonyl)imide, thereby preventing lithium bis(fluorosulfonyl)imide from being decomposed, thereby reducing the changes in lithium bis(fluorosulfonyl)imide over time, and have completed the present invention.

[0017] The present invention provides a composition for stabilizing lithium bis(fluorosulfonyl)imide, comprising 100 ppm by weight or less of moisture, 100 ppm to less than 10% by weight of lithium fluorosulfonate, and 90% by weight or more of lithium bis(fluorosulfonyl)imide.

[0018] The present invention provides a composition for a lithium secondary battery electrolyte comprising 100 ppm by weight or less of moisture, 100 ppm by weight to less than 10% by weight of lithium fluorosulfonate, and 90% by weight or more of lithium bis(fluorosulfonyl)imide.

[0019] In the composition of the present invention, lithium fluorosulfonate is thought to form a hydrogen bond with moisture, thereby inhibiting the decomposition of lithium bis(fluorosulfonyl)imide by moisture, thereby reducing the content of HF, which is a decomposition byproduct, but the present invention is not limited thereto.

[0020]

[0021] In the composition of the present invention, lithium fluorosulfonate is preferably included in an amount of 100 ppm to less than 10% by weight for the above role, preferably 500 ppm to 9% by weight, 900 ppm to 8% by weight, or 0.1% to 7% by weight.

[0022] The composition for stability of lithium bis(fluorosulfonyl)imide according to the present invention is most preferably free of moisture, but may preferably contain more than 0 and less than 100 ppm by weight, more preferably more than 0 and less than 50 ppm by weight. By containing moisture in an amount of less than 100 ppm by weight, changes in lithium bis(fluorosulfonyl)imide over time can be suppressed.

[0023] The lithium bis(fluorosulfonyl)imide stability composition of the present invention, which comprises 100 ppm by weight or less of moisture, 100 ppm to less than 10% by weight of lithium fluorosulfonate, and 90% by weight or more of lithium bis(fluorosulfonyl)imide, is characterized in that the HF content is 50 ppm by weight or less, preferably 30 ppm by weight or less, when the HF content is measured after being left at 50°C for 7 days.

[0024] In addition, the present invention provides a composition for a lithium secondary battery electrolyte comprising lithium bis(fluorosulfonyl)imide, lithium fluorosulfonate, and a carbonate, wherein the composition contains moisture in an amount of 100 ppm by weight or less, and contains 0.01 to 10 parts by weight, 0.05 to 10 parts by weight, 0.1 to 10 parts by weight, or 1 to 9 parts by weight of lithium fluorosulfonate relative to 100 parts by weight of lithium bis(fluorosulfonyl)imide.

[0025] The composition for the lithium secondary battery electrolyte is characterized in that the HF content measured after leaving the composition at 50°C for 7 days is 50 ppm by weight or less.

[0026] Since the composition for the lithium secondary battery electrolyte contains lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate in the above ratio and a carbonate solvent as a secondary battery electrolyte solvent, the composition can be used as is for the secondary battery electrolyte, and further, the high output characteristics of the secondary battery can be improved while improving the battery life.

[0027] The above carbonate may be at least one selected from the group consisting of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl propyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate, and preferably may be ethyl methyl carbonate, propylene carbonate, ethylene carbonate, and dimethyl carbonate.

[0028] In a composition comprising lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate together with a carbonate solvent, the carbonate may be included in an amount of 40 to 80 wt%, preferably 50 to 70 wt%, based on the total weight of the composition. In addition, lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate may be included in an amount of 20 to 60 wt%, preferably 30 to 50 wt%, based on the total weight of the composition. When the composition comprising lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate together with a carbonate solvent of the present invention contains lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate and a carbonate solvent in the above amounts, it has the advantage of blocking moisture contact of lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate, increasing storage stability, and facilitating the manufacture of an electrolyte by using it as an electrolyte. In addition, it is possible to improve the high-output characteristics of a secondary battery while enhancing the battery life.

[0029] The composition comprising lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate of the present invention together with a carbonate solvent may further comprise at least one selected from the group consisting of fluorinated carbonates, fluorinated ethers, fluorinated ethers, and unsaturated carbonates. When at least one selected from the group consisting of fluorinated carbonates, fluorinated ethers, fluorinated nitriles, and unsaturated carbonates is further comprised, the oxidation resistance or reduction resistance of the electrolyte may be affected, thereby improving the stability of the battery and extending its lifespan.

[0030] The composition of the present invention comprising a carbonate solvent together with lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate may contain at least one selected from the group consisting of fluorinated carbonates, fluorinated ethers, fluorinated ethers, and unsaturated carbonates in an amount of 0.5 to 20 wt%, 1 to 20 wt%, or 1 to 10 wt% based on the total weight of the composition. When the composition of the present invention contains at least one selected from the group consisting of fluorinated carbonates, fluorinated ethers, fluorinated ethers, and unsaturated carbonates in the above amount, the stability of the battery can be sufficiently improved and the lifespan can be enhanced.

[0031] Examples of the above fluorinated carbonates include 4-fluoroethylene carbonate, 4,5-difluoroethylene carbonate, methyl 2,2,2-trifluoroethyl carbonate, bis(2,2,2-trifluoroethyl) carbonate, fluoromethyl-(2,2,2-trifluoroethyl) carbonate or (1-fluoroethyl)-(2,2,2-trifluoroethyl) carbonate.

[0032] Examples of the above fluorinated ethers include HCF2CF2OCH2CF3, HCF2CF2OCF2CHF2, It may be at least one selected from the group consisting of CF3CH2OCH2CF3, HCF2CF2CH2OCF2CF2H, HCF2CF2CH2OCF2CF2CF2H, HCF2CF2OCH2CH2OCF2CF2H, HCF2CF2OCH2CH2OCF2CF2H, HCF2CF2OCH2CH2OCF2CF2H, HCF2CF2OCH2CH2CH2OCF2CF2H, HCF2CF2OCF2CF2CF2H, HCF2CF2OCH2CH2OCF2CF2CF2H, HCF2CF2OCH2CH2OCF2CF2CF2H, and HCF2CF2OCH2CH2CH2OCF2CF2CF2H.

[0033] Examples of the above fluorinated ether solvents are as follows.

[0034] ,

[0035] An example of the above unsaturated carbonate is vinylene carbonate.

[0036] The composition of the present invention, which contains 100 ppm by weight or less of moisture and includes lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate together with a carbonate solvent, can be produced by reacting bis(fluorosulfonyl)imide (HFSI) and LiF in a carbonate solvent to produce lithium bis(fluorosulfonyl)imide and then adding lithium fluorosulfonate thereto.

[0037] When LiF is used in a reaction with bis(fluorosulfonyl)imide, HF is produced as a by-product. However, since HF has a low boiling point, it is easy to remove by volatilization, thereby obtaining pure lithium bis(fluorosulfonyl)imide. In addition, since the metal is Li, it has excellent battery characteristics when used in lithium secondary batteries.

[0038] In the present invention, 0.9-2.0 moles of LiF, preferably 1-1.5 moles, and more preferably more than 1-1.3 moles, can be reacted with respect to 1 mole of bis(fluorosulfonyl)imide. When the molar ratio of LiF to bis(fluorosulfonyl)imide is excessive, the LiF remaining after the reaction can be easily removed by filtration.

[0039] The reaction temperature of bis(fluorosulfonyl)imide and LiF is 0°C-200°C, preferably 10°C-100°C. If the reaction temperature is lower than 0°C, the reaction rate decreases, and if the reaction temperature is higher than that, by-products may be generated, which is not preferred. The time required for the reaction varies depending on the reaction scale, but is preferably 0.1 hour-48 hours, and more preferably 0.5 hour-24 hours.

[0040] The reaction can be carried out under atmospheric pressure, but if carried out under reduced pressure, the by-product HF is removed, making it easier to synthesize the target product. The reaction pressure is not particularly limited, but a pressure below atmospheric pressure - 0.01 atm is preferable, and a reduced pressure that allows the solvent to reflux at 0°C - 100°C is more preferable.

[0041] The manufacturing method of the present invention may include a step of removing volatile substances in the reaction solution by depressurization and / or heating. HF, which is produced as a by-product in the present invention, is a substance that exists as a gas at temperatures above 19.5°C and can be removed by depressurization and heating.

[0042] The present invention uses a carbonate solvent in the reaction of bis(fluorosulfonyl)imide and LiF.

[0043] The above carbonate solvent is used as a secondary battery electrolyte solvent, and the present invention prepares lithium bis(fluorosulfonyl)imide in a carbonate solvent, adds lithium fluorosulfonate, and uses the solution as is or after adding some solvent as a secondary battery electrolyte. Using carbonate solvents as an electrolyte for a secondary battery can effectively stabilize the positive and negative electrodes, increase the electrochemical stability of the electrolyte, suppress consumption, and improve the efficiency of a lithium secondary battery.

[0044] In the manufacturing method of the present invention, the carbonate solvent for bis(fluorosulfonyl)imide may be used in an amount of 1 to 5 weight, preferably 1.5 to 4 weight, and more preferably 1.5 to 3 weight, relative to 1 weight of bis(fluorosulfonyl)imide. When the carbonate solvent is used in the above amount, LiF and HFSI can be sufficiently dissolved to sufficiently progress the lithium bis(fluorosulfonyl)imide manufacturing reaction, and after the reaction, lithium fluorosulfonate can be added without removing the solvent to manufacture an electrolyte composition.

[0045]

[0046] The present invention provides a lithium secondary battery comprising the composition for lithium secondary battery electrolyte.

[0047] The lithium secondary battery of the present invention includes a positive electrode and a negative electrode.

[0048] The positive electrode includes a positive electrode active material capable of absorbing and desorbing lithium ions, and the positive electrode active material is preferably a composite metal oxide comprising at least one selected from cobalt, manganese, and nickel and lithium. The solid solution ratio between the metals can be varied, and in addition to these metals, an element selected from the group consisting of Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V, and rare earth elements can be further included. A specific example of the positive electrode active material may be a compound represented by any one of the following chemical formulas:

[0049] Li a A 1-b B b D2 (in the above formula, 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5); Li a E 1-b B b O 2-c D c (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE 2-b B b O 4-c D c (In the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b B c D α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Co b B c O 2-α Fα (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Co b B c O 2-α F2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B c D α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Mn b B c O 2-α F α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B c O 2-α F2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni b E c G d O2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn d GeO2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li a NiG bO2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a MnG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3(0 ≤ f ≤ 2); Li (3-f) Fe2(PO4)3(0 ≤ f ≤ 2); and LiFePO4.

[0050] In the above chemical formula, A is Ni, Co, Mn or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; F is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; I is Cr, V, Fe, Sc, Y or a combination thereof; J may be V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0051] The negative electrode includes a negative electrode active material capable of absorbing and desorbing lithium ions, and as such a negative electrode active material, carbon materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers, silicon, lithium metal, alloys of lithium and other elements, etc. can be used. For example, amorphous carbon includes hard carbon, coke, mesocarbon microbeads (MCMB) calcined at 1500℃ or lower, and mesophase pitch-based carbon fiber (MPCF). Crystalline carbon includes graphite materials, and specifically, natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. The carbon material is preferably a material having an interplanar distance of 3.35 to 3.38Å and an Lc (crystallite size) by X-ray diffraction of at least 20㎚ or more. Other elements that may be used to form alloys with lithium include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0052] The positive or negative electrode can be manufactured by dispersing an electrode active material, a binder, a conductive agent, and, if necessary, a thickener in a solvent to prepare an electrode slurry composition, and then applying this slurry composition to an electrode current collector. Aluminum or an aluminum alloy can commonly be used as the positive current collector, and copper or a copper alloy can commonly be used as the negative current collector. Examples of the forms of the positive and negative current collectors include foil or mesh.

[0053] Binders are substances that play a role in the formation of pastes of active materials, their mutual adhesion, adhesion to the current collector, and cushioning against expansion and contraction of the active materials. When a battery is repeatedly charged and discharged, volume changes in the negative electrode material can reduce battery performance, including battery life and charging time. They also enhance the bonding strength of electrode materials.

[0054] Examples of binders include polyvinylidene fluoride (PVdF), copolymers of polyhexafluoropropylene-polyvinylidene fluoride (PVdF / HFP)), poly(vinylacetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, polyvinyl ether, poly(methyl methacrylate), poly(ethyl acrylate), polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, and acrylonitrile-butadiene rubber. The binder content is 0.1 to 30 wt%, preferably 1 to 10 wt%, based on the electrode active material. If the content of the above binder is too low, the adhesive strength between the electrode active material and the current collector is insufficient, and if the content of the binder is too high, the adhesive strength is improved, but the content of the electrode active material is reduced accordingly, which is disadvantageous for increasing the battery capacity.

[0055] The conductive material is used to provide conductivity to the electrode, and in the battery to be constructed, any electronically conductive material that does not cause a chemical change can be used, and at least one selected from the group consisting of a graphite-based conductive material, a carbon black-based conductive material, and a metal or metal compound-based conductive material can be used. Examples of the graphite-based conductive material include artificial graphite, natural graphite, etc., and examples of the carbon black-based conductive material include acetylene black, ketjen black, denkablack, thermal black, channel black, etc., and CNT (Carbon Nanotube) can be used. Examples of the metal-based or metal compound-based conductive material include perovskite materials such as tin, tin oxide, tin phosphate (SnPO4), titanium oxide, potassium titanate, LaSrCoO3, and LaSrMnO3. However, the present invention is not limited to the conductive materials listed above.

[0056] The content of the conductive agent is preferably 0.1 to 10 wt% with respect to the electrode active material. If the content of the conductive agent is less than 0.1 wt%, the electrochemical properties deteriorate, and if it exceeds 10 wt%, the energy density per weight decreases.

[0057] The thickener is not particularly limited as long as it can play a role in controlling the viscosity of the active material slurry, but examples of thickeners that can be used include carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose.

[0058] Non-aqueous or aqueous solvents are used as solvents in which electrode active materials, binders, and conductive agents are dispersed. Non-aqueous solvents include N-methyl-2-pyrrolidinone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran.

[0059] The lithium secondary battery of the present invention may include a separator that prevents short circuits between the positive and negative electrodes and provides a passage for lithium ions. As the separator, a polyolefin-based polymer film such as polypropylene, polyethylene, polyethylene / polypropylene, polyethylene / polypropylene / polyethylene, polypropylene / polyethylene / polypropylene, or a multi-film thereof, a microporous film, a woven fabric, or a non-woven fabric may be used. In addition, a film in which a porous polyolefin film is coated with a resin having excellent stability may be used.

[0060] The lithium secondary battery of the present invention may be formed in other shapes, such as a cylindrical shape, a pouch shape, etc., in addition to a square shape.

[0061] Hereinafter, preferred embodiments of the present invention will be described in detail. However, in describing the present invention, descriptions of already known conditions or configurations will be omitted to clarify the gist of the present invention.

[0062] Example 1

[0063] Composition 1 was prepared by mixing 100 g of lithium bis(fluorosulfonyl)imide and 0.3 g of lithium fluorosulfonate.

[0064] Example 2

[0065] Composition 2 was prepared by mixing 100 g of lithium bis(fluorosulfonyl)imide and 1 g of lithium fluorosulfonate.

[0066] Example 3

[0067] Composition 3 was prepared by mixing 100 g of lithium bis(fluorosulfonyl)imide and 0.1 g of lithium fluorosulfonate.

[0068] Example 4

[0069] In a four-neck Teflon-made reaction vessel, 362 g (weight ratio 2) of anhydrous ethyl methyl carbonate (EMC), 28.6 g (1.1 mol) of LiF, and 181 g (1.0 mol) of HFSI [bis(fluorosulfonyl)imide] were mixed, and the mixture was stirred at 25°C under atmospheric pressure for 5 hours to perform the reaction. Thereafter, the pressure was reduced to 0.1 atm to remove the remaining HF for 0.5 hours. After the reaction, the reactant was pressure-filtered using a PTFE filter paper, and 405 g of a carbonate solution of lithium bis(fluorosulfonyl)imide was obtained. 19 The LiFSI content in the solution was measured using F-NMR and confirmed to contain 183 g. 5 g of lithium fluorosulfonate was added to prepare electrolyte composition 4.

[0070] Example 5

[0071] Using 362 g (weight ratio 2) of dimethyl carbonate (DMC), 28.6 g (1.1 mol) of LiF, and 181 g (1.0 mol) of HFSI [bis(fluorosulfonyl)imide], a process was performed as in Example 4 to obtain 401 g of a carbonate solution containing 181 g of lithium bis(fluorosulfonyl)imide, and 4 g of lithium fluorosulfonate was added thereto to prepare an electrolyte composition 5.

[0072] Example 6

[0073] A method was performed as in Example 4 using 362 g (weight ratio 2) of a solvent containing ethylene carbonate and ethyl methyl carbonate in a 1:2 weight ratio, 28.6 g (1.1 mol) of LiF, and 181 g (1.0 mol) of HFSI [bis(fluorosulfonyl)imide] to obtain 452 g of a carbonate solution containing 184 g of lithium bis(fluorosulfonyl)imide, to which 5 g of lithium fluorosulfonate was added to prepare an electrolyte composition 6.

[0074] Comparative Example 1

[0075] Lithium fluorosulfonate was not added to the LiFSI carbonate solution prepared in Example 4, and this was used as Comparative Example Composition 1.

[0076] Comparative Example 2

[0077] Lithium fluorosulfonate was not added to the LiFSI carbonate solution prepared in Example 1, and water was added to prepare a comparative composition 2.

[0078] Experimental Example 1. Confirmation of LiFSI stability over time

[0079] The initial moisture content of the LiFSI or LiFSI-containing solutions prepared in Examples 1 to 6 and Comparative Examples 1 and 2 was measured and shown in Table 1 below. In addition, the HF content of the LiFSI or LiFSI-containing solutions prepared in Examples 1 to 6 and Comparative Examples 1 and 2 was measured after leaving them at 50°C for 7 days.

[0080] The above HF content is measured by ion chromatography of F ions.

[0081] According to the table below, it was confirmed that a large amount of HF was present in the lithium bis(fluorosulfonyl)imide solutions containing no lithium fluorosulfonate or water of Comparative Examples 1 and 2 when left at 50°C for 7 days. In contrast, only a small amount of HF was detected in the lithium bis(fluorosulfonyl)imide or its solutions prepared in Examples 1 to 6.

[0082] Example Moisture content (ppm by weight) HF content (ppm by weight) after leaving at 50℃ for 7 days Example 13023 Example 22917 Example 33219 Example 42915 Example 53317 Example 63214 Comparative Example 13088 Comparative Example 213092

[0083] Experimental Example 2. Preparation of non-aqueous electrolyte

[0084] Experimental examples 2-1 to 2-3

[0085] A 0.5 M solution based on LiFSI was prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) 3:7 solvents with the lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate-containing compositions of Examples 1 to 3. LiPF6 was added to the solution at a concentration of 0.5 M, and LiPO2F2 was added as an additive in an amount of 1 wt% based on 100 wt% of the total electrolyte, and then mixed to prepare a non-aqueous electrolyte.

[0086] Experimental examples 2-4 to 2-6

[0087] A 0.5 M solution based on LiFSI was prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) 3:7 solvents with the lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate-containing carbonate solutions of Examples 4 to 6. LiPF6 was added to the solution at a concentration of 0.5 M, and LiPO2F2 was added as an additive in an amount of 1 wt% based on 100 wt% of the total electrolyte, and then mixed to prepare a non-aqueous electrolyte.

[0088] Experimental Example 2-7

[0089] A 0.5 M LiFSI solution was prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) 3:7 solvents with the carbonate solution of lithium bis(fluorosulfonyl)imide of Comparative Example 1. LiPF6 was added to the solution at a concentration of 0.5 M, and LiPO2F2 was added as an additive in an amount of 1 wt% based on 100 wt% of the total electrolyte, and then mixed to prepare a non-aqueous electrolyte.

[0090] Experimental Example 2-8

[0091] A non-aqueous electrolyte was prepared as in Experimental Example 2-7 using the carbonate solution of lithium bis(fluorosulfonyl)imide of Comparative Example 2.

[0092] Experimental Example 3. Confirmation of Lithium Secondary Battery Life Characteristics

[0093] A 1.4 Ah pouch battery was assembled using a conventional method using a cathode material using LiNi / Co / Mn as a cathode active material and an anode material using artificial graphite and natural graphite in a 1:1 weight ratio, and 6.0 g of the electrolyte prepared in Experimental Example 2 was injected to complete the secondary battery.

[0094] (1) Room temperature lifespan

[0095] The secondary battery was charged at room temperature (25°C) at 1C to 4.5V, then discharged at 1C to 2.75V to measure the initial capacity, and after repeating this 100 times, the capacity was measured to calculate the life maintenance rate (%) using the following mathematical formula 1.

[0096] [Mathematical Formula 1]

[0097] Life maintenance rate = (discharge capacity after 100 repetitions / initial discharge capacity) × 100

[0098] (2) High temperature lifespan maintenance rate

[0099] The secondary battery was charged at a high temperature (45°C) at 1C to 4.5V, then discharged at 1C to 2.75V to measure the initial capacity, and after repeating this 100 times, the capacity was measured to calculate the life maintenance rate (%) using the above mathematical formula 1.

[0100] Experimental Example 4. Confirmation of Lithium Secondary Battery Output Characteristics

[0101] The secondary battery was discharged from a fully charged state to 50% SOC (state of charge) at a constant current of 0.2 C, and after a rest time of 1 hour, it was discharged at a constant current of 1.5 C for 10 seconds. In the next process, after a rest time of 40 seconds, it was charged at a constant current of 1.125 C. Initial DC resistance (DC-IR, R dis ) was calculated from the discharge data using the following mathematical formula 2.

[0102] [Equation 2]

[0103] R dis = ΔV / I

[0104] In the above equation, ΔV is OCV dis (voltage just before the 10-second discharge starts)-V dis (10 second discharge end voltage), and I is the current value during discharge.

[0105] Experimental reserve electrolyte Room temperature life maintenance rate (%) High temperature life maintenance rate (%) Initial DC resistance (DC-IR) (mΩ) 3-1 Experimental example 2-191.78 3.73 9.43-2 Experimental example 2-292.48 5.23 8.13-3 Experimental example 2-392.186.5 39.53-4 Experimental example 2-493.48 6.74 0.33-5 Experimental example 2-593.186.34 0.73-6 Experimental example 2-692.58 5.34 0.53-7 Experimental example 2-788.08 0.34 5.73-8 Experimental example 2-887.27 9.54 6.3

[0106] It can be seen that the lithium secondary battery including the non-aqueous electrolyte using the lithium bis(fluorosulfonyl)imide or carbonate solution thereof of the present invention (Experimental Examples 2-1 to 2-6) has a higher room temperature life maintenance rate and a higher high temperature life maintenance rate than the lithium secondary battery including the non-aqueous electrolyte using the lithium bis(fluorosulfonyl)imide carbonate solution of Comparative Examples 1 and 2 (Experimental Examples 2-7 and 2-8).

[0107] In addition, as a result of measuring the initial DC resistance value of a lithium secondary battery, it can be seen that the lithium secondary battery including the non-aqueous electrolyte using the lithium bis(fluorosulfonyl)imide or its carbonate solution of the present invention (Experimental Examples 2-1 to 2-6) has a low initial DC resistance value. That is, it can be seen that the lithium secondary battery including the non-aqueous electrolyte using the lithium bis(fluorosulfonyl)imide or its carbonate solution of the present invention (Experimental Examples 2-1 to 2-6) has excellent output characteristics.

[0108] The composition for stability of lithium bis(fluorosulfonyl)imide of the present invention suppresses decomposition during the storage and distribution process of lithium bis(fluorosulfonyl)imide, and when used as an electrolyte salt of a secondary battery, it can improve the life characteristics and output characteristics of the secondary battery.

Claims

1. A composition for stability of lithium bis(fluorosulfonyl)imide, comprising 100 ppm by weight or less of moisture, 100 ppm by weight to less than 10% by weight of lithium fluorosulfonate, and 90% by weight or more of lithium bis(fluorosulfonyl)imide.

2. A lithium bis(fluorosulfonyl)imide stability composition according to claim 1, characterized in that the HF content measured after leaving the composition at 50°C for 7 days is 50 ppm by weight or less.

3. A composition for a lithium secondary battery electrolyte comprising lithium bis(fluorosulfonyl)imide, lithium fluorosulfonate, and carbonate, wherein the composition contains moisture in an amount of 100 ppm by weight or less, and contains 0.01 to 10 parts by weight of lithium fluorosulfonate relative to 100 parts by weight of lithium bis(fluorosulfonyl)imide.

4. A composition for a lithium secondary battery electrolyte, characterized in that the HF content measured after leaving the composition at 50°C for 7 days in claim 3 is 50 ppm by weight or less.

5. A composition for a lithium secondary battery electrolyte comprising 20 to 60 wt% of lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate based on the total composition according to claim 3.

6. A composition for a lithium secondary battery electrolyte comprising 40 to 80 wt% of carbonate relative to the total composition according to claim 3.

7. A composition for a lithium secondary battery electrolyte according to claim 3, further comprising at least one selected from the group consisting of fluorinated carbonates, fluorinated ethers, fluorinated ethers, and unsaturated carbonates.

8. A composition for a lithium secondary battery electrolyte, characterized in that, in claim 3, bis(fluorosulfonyl)imide (HFSI) and LiF are reacted in a carbonate solvent to produce a carbonate solution of lithium bis(fluorosulfonyl)imide, and lithium fluorosulfonate is added thereto.

9. A method for producing a composition for a lithium secondary battery electrolyte, comprising lithium bis(fluorosulfonyl)imide, lithium fluorosulfonate, and carbonate, comprising reacting bis(fluorosulfonyl)imide (HFSI) and LiF in a carbonate solvent to produce a carbonate solution of lithium bis(fluorosulfonyl)imide, and adding lithium fluorosulfonate thereto, wherein the composition contains moisture of 100 ppm or less by weight.

10. A method for producing a composition for a lithium secondary battery electrolyte comprising lithium bis(fluorosulfonyl)imide, lithium fluorosulfonate, and carbonate, characterized in that 0.9 to 2.0 moles of LiF react with 1 mole of bis(fluorosulfonyl)imide in claim 9.

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