Methylsulfate-containing lithium bis(fluorosulfonyl)imides

Abstract

The present invention relates to a bis(fluorosulfonyl)imide lithium salt (LiFSI) having a methyl sulfate content of 100 ppm by weight or less, a composition comprising same, and a method for preparing same. The lithium bis(fluorosulfonyl) imide having a methyl sulfate content of 100 ppm by weight or less according to the present invention suppresses side reactions occurring on the surface of an electrode and improves the voltage stability of a lithium-ion secondary battery, thereby increasing the lifespan of the battery.

Description

Lithium bis(fluorosulfonyl)imide containing methyl sulfate

[0001] The present invention relates to a bis(fluorosulfonyl)imide lithium salt (LiFSI) containing 100 ppm by weight or less of methylsulfate and a method for manufacturing the same.

[0002] With the popularization of mobile devices, the commercialization of electric vehicles, and the increasing demand for energy storage devices, secondary batteries equipped with performance capabilities such as high power output, high energy density, and high discharge voltage are being developed.

[0003] A lithium-ion secondary battery includes a negative electrode, a positive electrode, a separator, and an electrolyte.

[0004] The above electrolyte serves as a medium for the movement of lithium ions between the anode and the cathode and functions to improve the thermal, electrical, and physical safety of the battery; it consists of a solvent, an electrolyte salt, and various additives.

[0005] Solvents play a role in dissociating electrolyte salts, and carbonate and ester-based solvents are mainly used; the type of solvent used determines the bulk ionic conductivity, viscosity, density, and wettability. There are countless additives, and they are related to the formation of the solid electrolyte interphase (SEI). Lithium hexafluorophosphate (LiPF6), which possesses excellent performance and is relatively inexpensive, is mainly used as an electrolyte salt; however, LiPF6 has the disadvantage of decomposing into a gaseous form of hydrofluoric acid at room temperature.

[0006] To overcome the above disadvantages, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI) were developed. These salts exhibit little to no spontaneous decomposition and are more stable against hydrolysis than LiPF6.

[0007] Meanwhile, LiTFSI is known to have the disadvantage of causing corrosion to aluminum current collectors, whereas LiFSI is attracting attention as a useful salt because it does not have such significant drawbacks and possesses excellent performance compared to other conventional salts. In particular, since LiFSI has high dielectric strength and conductivity, it is expected that various high-performance electrochemical devices can be obtained by using LiFSI as an electrolyte salt.

[0008] LiFSI has the property of maintaining stability even at high temperatures, which helps prevent the electrolyte from decomposing even under demanding thermal conditions. As a result, it can reduce the rate of battery degradation and extend battery life.

[0009] Meanwhile, the inventors, in using LiFSI as an electrolyte salt for a secondary battery, note that conventional LiFSI contains methylsulfate (CH3OSO3) as an impurity. - It contains ) and it was discovered that using LiFSI containing methyl sulfate in the electrolyte of a secondary battery does not extend the life of the secondary battery but rather shortens it.

[0010] Accordingly, the purpose of the present invention is to provide lithium bis(fluorosulfonyl)imide that does not shorten the lifespan of a secondary battery.

[0011] The purpose of the present invention is to provide a lithium bis(fluorosulfonyl)imide containing composition that can prevent the degradation of the lifespan of a secondary battery.

[0012] In an effort to achieve the above objective, the inventors discovered that when the content of methyl sulfate contained in lithium bis(fluorosulfonyl)imide (LiFSI) is 100 ppm by weight or less, using the LiFSI in the electrolyte does not shorten the lifespan of the battery, and thus completed the present invention.

[0013] The present invention provides a lithium bis(fluorosulfonyl)imide having a methyl sulfate content of 100 ppm by weight or less.

[0014] The present invention provides an electrolyte composition for preventing the degradation of the lifespan of a lithium secondary battery, comprising 100 ppm by weight or less of lithium bis(fluorosulfonyl)imide and methyl sulfate, which can prevent the degradation of the lifespan of a lithium secondary battery.

[0015] The present invention provides an electrolyte composition for preventing degradation of the lifespan of a lithium secondary battery, comprising 100 ppm by weight or less of methyl sulfate, 20 to 60% by weight of lithium bis(fluorosulfonyl)imide, and the remainder being a solvent.

[0016] The present invention is characterized by being able to reduce methyl sulfate by contacting lithium bis(fluorosulfonyl)imide with polyvinylpyridine (PVP).

[0017] Contact between lithium bis(fluorosulfonyl)imide and polyvinylpyridine can be achieved by dissolving solid lithium bis(fluorosulfonyl)imide in a solvent and then adding PVP.

[0018] In addition, contact between lithium bis(fluorosulfonyl)imide and polyvinylpyridine can be achieved by preparing lithium bis(fluorosulfonyl)imide in a solvent and then adding PVP to a solution containing lithium bis(fluorosulfonyl)imide.

[0019] In addition, the present invention provides a method for producing lithium bis(fluorosulfonyl)imide with reduced methyl sulfate, characterized by including the steps of adding polyvinylpyridine to a solution containing lithium bis(fluorosulfonyl)imide and filtering the solution.

[0020] The lithium bis(fluorosulfonyl)imide of the present invention, having a methyl sulfate content of 100 ppm by weight or less, has the effect of preventing the degradation of battery life when used as an electrolyte salt for a lithium secondary battery.

[0021] When the lithium bis(fluorosulfonyl)imide of the present invention, which has a methyl sulfate content of 100 ppm by weight or less, is used as an electrolyte salt for a lithium secondary battery, it improves the ionic conductivity of the battery electrolyte, thereby increasing the charging / discharging speed of the battery and improving long-term charge / discharge cycle performance.

[0022] The lithium bis(fluorosulfonyl)imide of the present invention, having a methyl sulfate content of 100 ppm by weight or less, has the effect of suppressing side reactions occurring on the electrode surface and improving the voltage stability of the lithium-ion secondary battery, thereby extending the battery's lifespan.

[0023] The present invention has the effect of economically producing lithium bis(fluorosulfonyl)imide with a methyl sulfate content of 100 ppm by weight or less.

[0024] The present invention will be described in detail below. Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, and should be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0025] The present invention relates to lithium bis(fluorosulfonyl)imide having a methyl sulfate content of 100 ppm by weight or less.

[0026] The present invention relates to a composition for a lithium secondary battery electrolyte comprising methyl sulfate and lithium bis(fluorosulfonyl)imide in an amount of 100 ppm by weight or less.

[0027] The above lithium bis(fluorosulfonyl)imide can be prepared by a reaction using bis(fluorosulfonyl)imide and a lithium salt.

[0028] The inventors recognized that in the conventional step of producing lithium bis(fluorosulfonyl)imide (LiFSI) by reacting bis(fluorosulfonyl)imide (HFSI) and a lithium salt containing LiF, methyl sulfate is generated as a by-reaction and remains in the final LiFSI. Furthermore, they discovered that using LiFSI containing a large amount of methyl sulfate in the electrolyte of a secondary battery results in a greater degradation of the secondary battery's lifespan.

[0029] Furthermore, the inventors confirmed that when lithium bis(fluorosulfonyl)imide containing 100 ppm by weight or less, which is most preferably without methyl sulfate, is used in a secondary battery electrolyte, there is no significant decrease in the battery's lifespan, and thus completed the present invention.

[0030] [Methylsulfate]

[0031]

[0032] The present invention provides a lithium bis(fluorosulfonyl)imide having a methyl sulfate content of 100 ppm by weight or less, obtained by measuring the lithium bis(fluorosulfonyl)imide containing methyl sulfate using liquid chromatography (LC).

[0033] The above methyl sulfate is CH3O of methanol in the presence of methanol and water, as in the reaction pathway shown in formula (1) below. - It is expected that the fluorine of HFSI is substituted and subsequently hydrolyzed to form. Furthermore, it is expected to exist as a lithium salt when lithium ions are present due to the supply of LiF, but is not limited thereto.

[0034] Equation (1)

[0035]

[0036] The inventors of the present invention have made efforts to reduce the methyl sulfate content contained in lithium bis(fluorosulfonyl)imide and discovered that when lithium bis(fluorosulfonyl)imide is contacted with polyvinylpyridine (PVP), the methyl sulfate content is reduced to 100 ppm by weight or less.

[0037] The methyl sulfate content included in the lithium bis(fluorosulfonyl)imide of the present invention is preferably 50 ppm by weight or less, more preferably 25 ppm by weight or less, and the lower limit may be greater than 0 ppm by weight.

[0038] Contact between lithium bis(fluorosulfonyl)imide and polyvinylpyridine can be achieved by dissolving solid lithium bis(fluorosulfonyl)imide in a solvent and then adding polyvinylpyridine.

[0039] In addition, contact between lithium bis(fluorosulfonyl)imide and polyvinylpyridine can be achieved by preparing lithium bis(fluorosulfonyl)imide in a solvent and then adding PVP to a solution containing lithium bis(fluorosulfonyl)imide.

[0040] The present invention relates to a composition for a lithium secondary battery electrolyte comprising methyl sulfate at a weight ppm or less of 100 ppm and lithium bis(fluorosulfonyl)imide. The composition for a lithium secondary battery electrolyte is intended to prevent degradation of the lifespan of a secondary battery.

[0041] The composition for a lithium secondary battery electrolyte of the present invention may contain methyl sulfate in an amount greater than 0 ppm by weight to 100 ppm by weight, preferably 3 ppm by weight to 50 ppm by weight, more preferably 5 ppm by weight to 20 ppm by weight.

[0042] The electrolyte composition of the present invention may contain 99% by weight or more, preferably 99.9% by weight or more, lithium bis(fluorosulfonyl)imide, while containing 100 ppm by weight or less, preferably 50 ppm by weight or less, more preferably 25% by weight or less. When a composition containing methyl sulfate and lithium bis(fluorosulfonyl)imide in the above amounts is used as a secondary battery electrolyte, it has the effect of preventing the shortening of the lifespan of the secondary battery at room temperature and at high temperatures.

[0043] The present invention provides an electrolyte composition for preventing degradation of the lifespan of a lithium secondary battery, comprising 100 ppm by weight or less of methyl sulfate, 20 to 60% by weight of lithium bis(fluorosulfonyl)imide, and the remainder being a solvent.

[0044] The present invention provides a method for producing lithium bis(fluorosulfonyl)imide with reduced methyl sulfate, characterized by comprising the steps of adding polyvinylpyridine to a solution containing lithium bis(fluorosulfonyl)imide and filtering the solution.

[0045] The present invention can produce lithium bis(fluorosulfonyl)imide with reduced methyl sulfate by including the steps of dissolving lithium bis(fluorosulfonyl) produced by a conventional manufacturing method in a solvent, adding polyvinylpyridine, and filtering the solution.

[0046] The above solvent may be a carbonate solvent.

[0047] In addition, the present invention can produce lithium bis(fluorosulfonyl)imide with reduced methyl sulfate by including the steps of reacting bis(fluorosulfonyl)imide with a lithium salt in a solvent to produce lithium bis(fluorosulfonyl)imide, adding polyvinylpyridine to the solution, and filtering the solution.

[0048] The above lithium salt may be used without limitation as long as it is a salt capable of providing lithium ions, and preferably, it may be one or more selected from the group consisting of lithium hydroxide (LiOH), lithium hydroxide hydrate (LiOH·H2O), lithium carbonate (Li2CO3), lithium bicarbonate (LiHCO3), lithium chloride (LiCl), lithium fluoride (LiF), lithium alkoxide compounds such as CH3OLi and lithium ethoxide (EtOLi), alkyl lithium compounds, lithium acetate (CH3COOLi), and lithium oxalate. More preferably, the above lithium salt is one or more selected from the group consisting of lithium hydroxide (LiOH), lithium hydroxide hydrate (LiOH·H2O), lithium carbonate (Li2CO3), lithium bicarbonate (LiHCO3), and lithium fluoride (LiF). The above lithium salt may be a solid and may be added to the reaction solution.

[0049] The above solvent may be a carbonate solvent.

[0050] When LiF is used in the reaction with bis(fluorosulfonyl)imide, HF is produced as a byproduct; however, since HF has a low boiling point, it is easy to remove through volatilization, allowing for the production of pure lithium bis(fluorosulfonyl)imide. When lithium bis(fluorosulfonyl)imide is prepared by reacting bis(fluorosulfonyl)imide (HFSI) with LiOH, Li2CO3, etc., water is produced as a byproduct, and the present invention may include a process for removing the water produced as a byproduct during the reaction by volatilization or by using a dehydrating agent. Furthermore, since the metal is Li, the battery characteristics are excellent when used in lithium-ion secondary batteries.

[0051] In the present invention, for every 1 mole of bis(fluorosulfonyl)imide, 0.9 to 2.0 moles of lithium salt, preferably 1 to 1.5 moles, and more preferably more than 1 to 1.3 moles can be reacted. When the molar ratio of lithium salt to bis(fluorosulfonyl)imide is excessive, the lithium salt remaining after the reaction can be removed by filtration, while the possibility of unreacted bis(fluorosulfonyl)imide remaining in the resulting lithium bis(fluorosulfonyl)imide can be sufficiently reduced. If unreacted bis(fluorosulfonyl)imide remains and is contained in the electrolyte, it can destroy the SEI (solid electrolyte interphase) membrane. On the other hand, when using a lithium salt with a molar ratio of 2 or more, it does not help improve the reaction yield, but there are disadvantages such as the time required to remove the lithium salt after the reaction and the increased manufacturing cost.

[0052] The reaction temperature of bis(fluorosulfonyl)imide and lithium salt is 0°C to 200°C, preferably 10°C to 100°C. If the reaction temperature is lower than 0°C, the reaction rate decreases, and if the reaction temperature is higher than the above, it is undesirable as there is a risk of by-products being formed. The time required for the reaction varies depending on the scale of the reaction, but is preferably 0.1 to 48 hours, more preferably 0.5 to 24 hours.

[0053] The reaction can be carried out under atmospheric pressure, but if carried out under reduced pressure, it is easier to remove by-products such as HF and CO2, making it easier to synthesize the target product. The reaction pressure is not particularly limited, but less than atmospheric pressure - 0.01 atm is preferred, and a reduced pressure such that the solvent refluxes at 0°C - 100°C is more preferred.

[0054] The manufacturing method of the present invention may include a step of removing volatile substances or water from the reaction solution by reduced pressure and / or heating. In the present invention, HF generated as a byproduct is a substance that exists as a gas at 19.5°C or higher and can be removed by reduced pressure and heating. In addition, CO2, H2O, etc., can be removed.

[0055] Meanwhile, if there is an excess amount of water in the lithium salt used to manufacture lithium bis(fluorosulfonyl)imide, the water decomposes the reactant bis(fluorosulfonyl)imide to produce fluorosulfonic acid.

[0056] Accordingly, the present invention uses a lithium salt having a moisture content of 200 ppm by weight or less for the manufacture of lithium bis(fluorosulfonyl)imide.

[0057] The above lithium salt having a moisture content of 200 ppm by weight or less, preferably 100 ppm by weight or less, may be a commercially available lithium salt with reduced moisture, or a lithium salt containing 200 ppm by weight or more of moisture may be used after further removing moisture. The method for removing moisture may utilize known methods for removing moisture from salts, and as an example, a method of drying by heating may be used.

[0058] The present invention allows the use of a carbonate solvent in the reaction between bis(fluorosulfonyl)imide and a lithium salt.

[0059] The above carbonate solvent is used as a solvent for a secondary battery electrolyte. The present invention allows lithium bis(fluorosulfonyl)imide to be prepared in a carbonate solvent, and the solution can be used as a secondary battery electrolyte either as is or with the addition of some solvent. Using carbonate solvents as an electrolyte for a secondary battery effectively stabilizes both the positive and negative electrodes, increases the electrochemical stability of the electrolyte to suppress consumption, and improves the efficiency of the lithium secondary battery.

[0060] In the manufacturing method of the present invention, the carbonate solvent for bis(fluorosulfonyl)imide can be used in an amount of 1 to 5 weights, preferably 1.5 to 4 weights, and more preferably 1.5 to 3 weights per 1 weight of bis(fluorosulfonyl)imide. When the carbonate solvent is used in the above amounts, the lithium salt and HFSI can be sufficiently dissolved to allow the lithium bis(fluorosulfonyl)imide manufacturing reaction to proceed sufficiently, and there is an advantage that it can be used as a secondary battery electrolyte containing LiFSI of an appropriate concentration without removing the solvent after the reaction.

[0061] The above carbonate may be one or more selected from the group consisting of ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylpropyl carbonate, methylpropyl 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 ethylmethyl carbonate, propylene carbonate, ethylene carbonate, and dimethyl carbonate.

[0062] The present invention uses a carbonate solvent having a moisture content of 100 ppm by weight or less, preferably 50 ppm by weight or less, for the manufacture of lithium bis(fluorosulfonyl)imide.

[0063] The above carbonate solvent having a moisture content of 100 ppm by weight or less may be a commercially available carbonate solvent with a moisture content reduced to 100 ppm by weight or less, or a carbonate solvent containing 100 ppm by weight or more of moisture may be used after additionally removing moisture.

[0064] The manufacturing method of the present invention may perform a filtration process to remove unreacted materials, etc., after the step of reacting bis(fluorosulfonyl)imide with a lithium salt. The filtration step may be carried out at atmospheric pressure, pressurized, or reduced pressure, but the filtration time can be shortened if reduced pressure filtration is performed at a pressure of 0.1 atm or less. The process may also be carried out by pressurizing at the reaction solution injection side and reducing pressure at the filtrate side.

[0065] The present invention can reduce methyl sulfate by adding polyvinylpyridine to a lithium bis(fluorosulfonyl)imide-containing solution prepared by the above method.

[0066] If methyl sulfate remains in the solution, the methyl sulfate reacts with solid polyvinylpyridine to produce solid polyvinylpyridine containing methyl sulfate, which can be easily removed by a filter.

[0067] In one embodiment, the above polyvinylpyridine may have a weight-average molecular weight (Mw) of 10,000 to 10,000,000, preferably 10,000 to 1,000,000.

[0068] The above polyvinylpyridine can be used in an amount of preferably 1 to 10 g, more preferably 3 to 9 g, per 1 mole of bis(fluorosulfonyl)imide. When polyvinylpyridine is used in the above amount, residual methyl sulfate can be sufficiently removed, and residual polyvinylpyridine after the removal of methyl sulfate can also be easily removed.

[0069] By treating the solid polyvinylpyridine of the present invention, a carbonate solution of lithium bis(fluorosulfonyl)imide (LiFSI) with a pH of 6.5 to 7.5 can be obtained.

[0070] The present invention provides a composition for a lithium secondary battery electrolyte prepared by the method of the present invention, comprising 100 ppm by weight or less of methyl sulfate, 20 to 60% by weight of lithium bis(fluorosulfonyl)imide, preferably 35 to 50% by weight, and the remainder being a solvent.

[0071] The present invention provides a composition for a lithium secondary battery electrolyte prepared by the method of the present invention, comprising more than 0 ppm by weight and less than or equal to 100 ppm by weight of methyl sulfate, 20 to 60% by weight of lithium bis(fluorosulfonyl)imide, preferably 35 to 50% by weight, and the remainder being a solvent.

[0072] The above solvent may be a carbonate.

[0073] The present invention provides a composition for a lithium secondary battery electrolyte comprising 100 ppm by weight or less of methyl sulfate and 99% by weight or more of lithium bis(fluorosulfonyl)imide.

[0074] When lithium bis(fluorosulfonyl)imide or a solution containing lithium bis(fluorosulfonyl)imide having a methyl sulfate content of 100 ppm by weight or less obtained according to the manufacturing method of the present invention is used in the electrolyte of a secondary battery, it can stabilize the electrolyte and also extend the lifespan of the secondary battery. In addition, the lithium bis(fluorosulfonyl)imide of the present invention stabilizes carbonate-based solvents. Therefore, it can be preferably used as a material for ion conductors constituting electrochemical devices such as primary batteries, secondary batteries such as lithium-ion secondary batteries, electrolytic capacitors, electric double-layer capacitors, fuel cells, solar cells, and electrochromic devices.

[0075] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, the following embodiments are merely illustrative of the invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the invention, and that such changes and modifications fall within the scope of the claims of the present invention.

[0076] Example 1

[0077] In a four-neck Teflon reaction vessel, 362 g (weight ratio 2) of distilled and purified ethyl methyl carbonate (EMC) containing 15 ppm by weight of moisture was mixed with 28.6 g (1.1 mol) of LiF containing 15 ppm by weight of moisture and 181 g (1.0 mol) of HFSI [bis(fluorosulfonyl)imide], which had been heat-treated and depressurized in a vacuum oven. The mixture was then reacted under atmospheric pressure at 25°C for 5 hours while stirring. Afterward, the pressure was reduced to 0.1 atm to remove residual HF for 0.5 hours. After the reaction, the reaction product was pressure-filtered using PTFE filter paper to obtain 431 g of a lithium bis(fluorosulfonyl)imide carbonate solution. 6 g of polyvinylpyridine was added to the above solution, stirred at room temperature for 1 hour, and filtered to remove the polyvinylpyridine, yielding 417 g of LiFSI solution. The LiFSI content contained was 182 g.

[0078] The LiFSI content was calculated by F-NMR.

[0079] pH was measured with a pH meter.

[0080] The methyl sulfate content was measured by ion chromatography.

[0081] Example 2

[0082] 413 g of a solution of lithium bis(fluorosulfonyl)imide was obtained by proceeding in the same manner as in Example 1, except that 362 g of a dimethyl carbonate solvent containing 10 ppm by weight of water was used instead of ethylmethyl carbonate.

[0083] Example 3

[0084] Using 4g of polyvinylpyridine, the process was carried out in the same manner as in Example 1 above to obtain 415g of a solution of lithium bis(fluorosulfonyl)imide.

[0085] Example 4

[0086] Using 4g of polyvinylpyridine, the same procedure as in Example 2 was carried out to obtain 406g of a solution of lithium bis(fluorosulfonyl)imide.

[0087] Example 5

[0088] 409 g of a solution of lithium bis(fluorosulfonyl)imide was obtained by proceeding in the same manner as in Example 1, except that 181 g (weight ratio 1) of ethylmethyl carbonate (EMC) containing 15 ppm by weight of moisture and 181 g (weight ratio 1) of dimethyl carbonate (DMC) containing 10 ppm by weight of moisture were used.

[0089] Comparative Example 1

[0090] In a four-neck Teflon reaction vessel, 362 g of ethylmethyl carbonate (EMC) containing 110 ppm by weight of moisture was mixed with 28.6 g (1.1 mol) of LiF containing 250 ppm by weight of moisture and 181 g (1.0 mol) of the HFSI [bis(fluorosulfonyl)imide], and the reaction was carried out under atmospheric pressure at 25°C for 5 hours while stirring. After the reaction, the reaction product was pressure-filtered using PTFE filter paper to obtain 428 g of a lithium bis(fluorosulfonyl)imide carbonate solution.

[0091] Comparative Example 2

[0092] Except for using 362 g of a dimethyl carbonate solvent containing 10 ppm by weight of moisture, the process was carried out in the same manner as Comparative Example 1 above to obtain 432 g of a solution of lithium bis(fluorosulfonyl)imide.

[0093] Classification Solvent Polyvinylpyridine Used LiFSI Content (g) LiFSI Concentration (wt%) pH Sulfate Content (wt ppm) Example 1 EMC 6g 182g 43.6 wt% 7.09 ppm Example 2 DMC 6g 181g 43.8 wt% 7.011 ppm Example 3 EMC 4g 184g 44.3 wt% 6.817 ppm Example 4 DMC 4g 180g 44.3 wt% 6.922 ppm Example 5 EMC / DMC 6g 183g 44.7 wt% 7.013 ppm Comparative Example 1 EMC-182g 42.5 wt% 6.2125 ppm Comparative Example 2 DMC-184g 42.6 wt% 6.3109 ppm

[0094] According to the table above, in the case of the present invention, methyl sulfate is removed and the pH becomes neutral by treating the solution with polyvinylpyridine after the preparation of LiFSI.

[0095] On the other hand, in the case of the lithium bis(fluorosulfonyl)imide of the comparative example, it was confirmed that the methyl sulfate content exceeded 100 ppm by weight.

[0096] Experimental Example 2. Preparation of Non-Aqueous Electrolyte

[0097] Experimental Example 2-1.

[0098] A 0.5M LiFSI solution was prepared by mixing a solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 with the lithium bis(fluorosulfonyl)imide carbonate solution of Example 1. LiPF6 was added to the solution at a concentration of 0.5M, and LiPO2F2 was added as an additive in an amount of 1% by weight relative to 100% by weight of the total electrolyte, and then mixed to prepare a non-aqueous electrolyte.

[0099] Experimental Examples 2-2 to 2-5

[0100] A non-aqueous electrolyte was prepared in the same manner as in Experimental Example 2-1 using the lithium bis(fluorosulfonyl)imide-containing solutions of Examples 2 to 5, respectively.

[0101] Comparative Experiment Examples 2-1 and 2-2

[0102] A non-aqueous electrolyte was prepared in the same manner as in Experimental Example 2-1 using the lithium bis(fluorosulfonyl)imide-containing solutions of Comparative Example 1 and Comparative Example 2, respectively.

[0103] Experimental Example 3. Verification of Lithium Secondary Battery Life Characteristics

[0104] A 1.4 Ah pouch battery was assembled using a conventional method by using a positive electrode material with LiNi / Co / Mn as the positive active material and a negative electrode material with artificial graphite and natural graphite in a 1:1 weight ratio, and the secondary battery was completed by injecting 6.0 g of the electrolyte prepared in Experimental Example 2 into each.

[0105] (1) Room temperature lifespan

[0106] The above secondary battery was charged at room temperature (25℃) to 4.5V and discharged at 1C to 2.75V to measure the initial capacity, and the capacity was measured after repeating this 100 times to calculate the life retention rate (%) using the following mathematical formula 1.

[0107] [Mathematical Formula 1]

[0108] Life retention rate = (Discharge capacity after 100 cycles / Initial discharge capacity) × 100

[0109] (2) High temperature lifespan retention rate

[0110] The above secondary battery was charged at a high temperature (45℃) to 4.5V and discharged at a high temperature (45℃) to 2.75V to measure the initial capacity, and the capacity was measured after repeating this 100 times to calculate the life retention rate (%) using the above mathematical formula 1.

[0111] Experimental Example 3 Non-aqueous Electrolyte Room Temperature Life Retention Rate (%) High Temperature Life Retention Rate (%) Experimental Example 3-1 Experimental Example 2-193.587.4 Experimental Example 3-2 Experimental Example 2-292.885.3 Experimental Example 3-3 Experimental Example 2-393.183.5 Experimental Example 3-4 Experimental Example 2-492.684.1 Experimental Example 3-5 Experimental Example 2-592.584.1 Comparative Experimental Example 3-1 Comparative Experimental Example 2-188.175.7 Comparative Experimental Example 3-2 Comparative Experimental Example 2-288.076.1

[0112] It can be seen that the non-aqueous electrolyte using lithium bis(fluorosulfonyl)imide of the present invention has a reduced methyl sulfate content, and therefore has a higher room temperature life retention rate and a higher high temperature life retention rate compared to the non-aqueous electrolyte containing lithium bis(fluorosulfonyl)imide of the comparative example.

[0113] The lithium bis(fluorosulfonyl)imide of the present invention, having a methyl sulfate content of 100 ppm by weight or less, can be used in the manufacture of batteries because, when used as an electrolyte salt for a lithium secondary battery, it improves the ionic conductivity of the electrolyte without shortening the battery life, thereby increasing the charging / discharging speed of the battery and improving long-term charge / discharge cycle performance.

[0114] The lithium bis(fluorosulfonyl)imide composition of the present invention, having a methyl sulfate content of 100 ppm by weight or less, can be used in the manufacture of batteries because it has the effect of suppressing side reactions occurring on the electrode surface and improving the voltage stability of the lithium-ion secondary battery, thereby extending the lifespan of the battery.

Claims

1. Lithium bis(fluorosulfonyl)imide with a methyl sulfate content of 100 ppm by weight or less.

2. Lithium bis(fluorosulfonyl)imide according to claim 1, wherein the methyl sulfate content is measured by ion chromatography and the methyl sulfate content is 100 ppm by weight or less.

3. A composition for an electrolyte for preventing degradation of lithium secondary battery life, comprising 100 ppm by weight or less of methyl sulfate and 99% by weight or more of lithium bis(fluorosulfonyl)imide.

4. The lithium bis(fluorosulfonyl)imide having a methyl sulfate content of 100 ppm or less, characterized in that the lithium bis(fluorosulfonyl)imide containing more than 100 ppm by weight of methyl sulfate is obtained by contacting polyvinylpyridine (PVP).

5. Lithium bis(fluorosulfonyl)imide having a methyl sulfate content of 100 ppm by weight or less, wherein the contact between the lithium bis(fluorosulfonyl)imide and polyvinylpyridine (PVP) is formed by adding polyvinylpyridine to a solvent containing lithium bis(fluorosulfonyl)imide.

6. Lithium bis(fluorosulfonyl)imide having a methyl sulfate content of 100 ppm by weight or less, characterized in that the solvent of claim 5 is a carbonate. A method for producing lithium bis(fluorosulfonyl)imide containing 100 ppm by weight or less of methyl sulfate, characterized by comprising the steps of adding polyvinylpyridine to a solution containing lithium bis(fluorosulfonyl)imide containing more than 100 ppm by weight of methyl sulfate and filtering the solution.

8. A method for producing lithium bis(fluorosulfonyl)imide according to claim 7, wherein the lithium bis(fluorosulfonyl)imide containing solution containing more than 100 ppm by weight of methyl sulfate is a solution formed by the reaction of bis(fluorosulfonyl)imide and LiF under a carbonate solvent, containing 100 ppm by weight or less of methyl sulfate.

9. An electrolyte composition for preventing degradation of lithium secondary battery life, comprising 100 ppm by weight or less of methyl sulfate, 20 to 60% by weight of lithium bis(fluorosulfonyl)imide, and the remainder being a solvent.

10. An electrolyte composition for preventing degradation of lithium secondary battery life, wherein the solvent is a carbonate, in accordance with claim 9.

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