Method for producing lithium carbonate and lithium sulfide from lithium methanesulfonate

Abstract

The invention relates to chemical technology for the combined production of lithium sulfide and lithium carbonate from lithium methanesulfonate-containing materials and can be used for producing lithium compounds for use in batteries, glasses and ceramics, as well as in other fields in which lithium compounds are required to have a high degree of purity and specific chemical properties. The possibility of the combined production of lithium sulfide and lithium carbonate from lithium methanesulfonate allows for more efficient use of feedstock material and also for process optimization by using the same feedstock materials and equipment to produce two target products and reducing the need for separate infrastructure for each product, while at the same time decreasing the amount of waste and emissions and diminishing the impact on the environment.

Description

[0001] A method for producing lithium carbonate and lithium sulfide from lithium methanesulfonate

[0002] Field of technology

[0003] The invention relates to chemical technology for producing lithium sulfide and lithium carbonate from materials containing lithium methanesulfonate, and can be used to produce lithium compounds that are used in batteries, glass and ceramics, as well as in other areas where a high degree of purity and specific chemical properties of lithium compounds are required.

[0004] State of the art

[0005] Lithium sulfide (Li2S) and lithium carbonate (E12CO3) are important inorganic lithium compounds used:

[0006] - in the production of key components of lithium-ion, including lithium-sulfur batteries, including electrolytes, cathode and anode materials. Lithium sulfide is the main active material for the cathodes of lithium-sulfur batteries. It participates in the reactions of energy storage and release, which allows batteries to achieve high capacity and helps stabilize electrochemical processes in the battery, reducing the risk of short circuits and thermal runaway, which increases the safety of using lithium-sulfur batteries [Yang Y., Tian R., Zhang H., etc. / / Green Chemistry - 2024. - V.26. - P.7231- 7245; Ting LKJ, Gao Y., Wang H„ etc. / / ACS Omega - 2022. - V. 45 (7). - P. 40682-40700; Klein, S., Harte, P., Henschel, J. etc. / / Advanced Energy Materials. -2021 - V. 11 (10). P. 2003756; US20150014184A1];

[0007] - in the production of special glasses, ceramics and in other areas of industry [US9017582B2; US7892995B2; Garcia LV, Ho, Y.-C., Myo Thant, etc. / / Processes - 2023. V.77. - 418].

[0008] Lithium sulfide is rarely found in nature in its pure form, so it is obtained by synthetic methods, of which the following are known:

[0009] 1) Metathesis reactions - reduction of lithium sulfate (Li2SO4) upon heating with organic substances such as sucrose or starch in an inert gas atmosphere or vacuum [US20210261411A1; Fang L., Zhang Q., Na A, Zhao Z., etc. / / Chemical Communications - 2022. - V.58 (36). - P. 5498-5501].

[0010] A method for thermal reduction of lithium sulfate with carbon black or graphite powder is known [JP5770675B2; US20230343996A1]. The general chemical equation for the interaction of lithium sulfide is: The disadvantages of this method are:

[0011] - difficulty in process control; organic substances decompose uncontrollably when heated, which complicates control over the purity and yield of the final product;

[0012] - environmental aspects, the use of organic substances can lead to carbon emissions and other pollutants, which requires additional measures for their disposal.

[0013] 2) Exothermic method - interaction of metallic lithium with sulfur vapor at normal or increased pressure [US20230365407A1], the direct reaction is as follows:

[0014] Li° + 2S = Li2S.

[0015] The disadvantages of this method are:

[0016] - uncontrolled exothermic reaction;

[0017] - fire hazard when working with sulfur vapors;

[0018] - difficulty in process control – ensuring stable temperature and pressure.

[0019] 3) Solid-phase reaction of interaction of lithium hydroxide (LiOH) and sulfur in air at 200°C.

[0020] The process leads to the formation of by-products such as lithium sulfite (Li2SO3) and lithium thiosulfate (Li2SO3), so this method is practically not used in industry [Yang Sh., Hu X., Xu Sh., etc. Synthesis of Deliquescent Lithium Sulfide in Air / / ACS Applied Materials & Interfaces - 2023. - V.15 (34). -P. 34,].

[0021] 4) Interaction of lithium hydroxide with hydrogen sulfide in an aprotic organic solvent [US11542162B2]:

[0022] 2LiOH + H2S = Li2S + 2H2O.

[0023] The disadvantages of this method are:

[0024] - toxicity and danger of hydrogen sulfide;

[0025] - Corrosivity, requiring specialized equipment and increased maintenance and replacement costs; the use of an aprotic organic solvent, such as tetrahydrofuran (THF), requires special storage and handling conditions due to its flammability and toxicity, as well as ensuring complete solvent removal after the reaction, necessitating additional purification steps. The above-mentioned disadvantages make this method of reacting lithium hydroxide with hydrogen sulfide in an aprotic organic solvent less attractive than other methods for synthesizing lithium sulfide.

[0026] There are many methods for the synthesis of lithium carbonate, each with its own advantages depending on the starting materials and conditions used. These technologies cover various methods and approaches to obtaining lithium carbonate from various raw material sources, including lithium-containing minerals, brines, and secondary materials (salts) [Marcinov V., Klimko J., Takacova Z., etc. / / Metals - 2023. - V. 13. - No. 7. - P. 1213; Zhao H., Wang Y., Cheng H., / / Hydrometallurgy. - 2023. -V.217. -P.106025; US9255012B2; Chen Y., Tian Q., Chen B., etc. Preparation of lithium carbonate from spodumene by a sodium carbonate autoclave process / / Hydrometallurgy -2011 / - V.109 (1-2). P.43-46; RU 2659968С1].

[0027] Hydrometallurgical processes (technologies) for producing lithium carbonate are the most widely used in industry. These processes involve the use of acids to leach lithium from ores and concentrates, followed by precipitation of lithium carbonate [Yelatontsev D., Mukhachev A. / / Hydrometallurgy. - 2021. -V. 201. -R. 105578].

[0028] A method for producing lithium carbonate from spodumene concentrate is known from the prior art, in which the process is carried out by the hydrothermal method in an autoclave. Lithium conversion is at least 94% under optimal conditions. The resulting lithium carbonate has a purity of up to 99.6% [US9255012B2; Chen Y., Tian Q., Chen B., etc. / / Hydrometallurgy -2011. - V.109 (1-2). P.43-46].

[0029] The disadvantages of this method are: autoclaves require the use of associated capital-intensive and expensive equipment;

[0030] - complexity of control, the need to control pressure and temperature in the autoclave requires complex automation systems;

[0031] - processes in autoclaves can take a significant amount of time, which reduces productivity;

[0032] - emissions and waste that require disposal and may pose an environmental hazard.

[0033] A method [RU2796628C2] is known from the prior art, in which the process of chemical reduction of lithium methanesulfonate upon interaction with a carbon material at up to 400 °C proceeds according to the reaction:

[0034] 2CH3SO3Li + C Li2S + 3CO + 3H2O. The disadvantages of this method are:

[0035] - during the reaction, carbon monoxide (CO) and water vapor (H2O) are formed, their interaction at high temperatures creates additional products in the form of hydrocarbon gases, which requires an additional gas purification system and increases the cost of production;

[0036] - the formation of toxic gases can lead to environmental pollution.

[0037] Therefore, there remains a need to develop new and efficient methods for producing lithium carbonate and lithium sulfide.

[0038] Disclosure of invention

[0039] The technical objective of the present invention is to develop a method for the joint production of lithium sulfide and lithium carbonate from lithium methanesulfonate.

[0040] The stated problem is solved by implementing a method for producing lithium sulfide and lithium carbonate from lithium methanesulfonate, which includes a stage of thermal decomposition of lithium methanesulfonate in the presence of lithium oxide or lithium hydroxide at a temperature of 350-700 °C and a pressure of 5 Pa - 5 MPa.

[0041] In particular embodiments of the invention, the method according to the invention includes the following stages: a) mixing lithium methanesulfonate with lithium oxide or lithium hydroxide; b) heating the mixture obtained in stage a) to a temperature of 350-700 °C at a pressure of 5 Pa - 5 MPa with the formation of the target products lithium sulfide and lithium carbonate; c) separating the lithium sulfide and lithium carbonate obtained in stage b), their isolation and purification, wherein lithium sulfide is isolated from the mixture with lithium carbonate by extraction in an organic solvent, lithium sulfide is purified by recrystallization in an organic solvent, and lithium carbonate is purified by washing with deionized water, then filtered and dried.

[0042] In particular embodiments of the invention, the organic solvent is selected from methanol, ethanol, propanol, butyl alcohol, N-methyl-2-pyrrolidone, dioxane, acetonitrile, tetrahydrofuran.

[0043] In particular embodiments of the invention, the ratio of lithium methanesulfonate to lithium oxide in step a) is 2:3.

[0044] In particular embodiments of the invention, the ratio of lithium methanesulfonate to lithium hydroxide in step a) is 1:3. As a result of implementing the invention, the following technical results are achieved

[0045] - a new and effective method for the joint production of lithium sulfide and lithium carbonate has been developed;

[0046] - the developed method allows for the joint production of lithium sulfide and lithium carbonate in one technological stage without the use of catalysts, under conditions of medium and high temperatures, low and high pressures;

[0047] - the method developed according to the invention is not accompanied by the formation of toxic gases, in particular, it is not accompanied by the formation of carbon monoxide (CO);

[0048] - the method developed according to the invention helps to reduce the amount of waste and reduce the impact on the environment and reduce emissions;

[0049] - the method developed according to the invention eliminates the need for a separate infrastructure for obtaining each product separately, which optimizes and simplifies production;

[0050] - the developed method expands the arsenal of available means for obtaining lithium sulfide and lithium carbonate.

[0051] Detailed disclosure of the invention

[0052] Brief description of the drawings

[0053] Figure 1. Technological equipment for implementing the method according to the invention: pos. 1 - electric mixer at 14,000 revolutions per minute (rpm); pos. 2 - mixing tank; pos. 3 - overhead drive motor; pos. 4 - screw mixer at 300-900 rpm; pos. 5 - electric or induction furnace; pos. 6 - gas outlet; pos. 7 - outlet of final products Li S / L2CO3.

[0054] Figure 2. Schemes for producing lithium carbonate and lithium sulfide from lithium methanesulfonate using the method according to the invention: element A is a flow chart for producing lithium methanesulfonate; element B is a flow chart for producing lithium carbonate and lithium sulfide by thermal decomposition in a lithium methanesulfonate - lithium oxide mixture, in the high temperature range of 350 - 700 °C, at low and high pressure from 5 Pa to 5 MPa; element C is a flow chart for producing lithium carbonate and lithium sulfide by thermal decomposition in a lithium methanesulfonate - lithium hydroxide mixture, in the high temperature range of 350 - 700 °C, at low and high pressure from 5 Pa to 5 MPa. Figure 3. Results of thermal analysis of the decomposition of lithium methanesulfonate formed from lithium hydroxide: 1 - thermogravimetric analysis (TGA) curve and - differential thermal analysis (DTA) curve.

[0055] Figure 4. X-ray diffraction pattern of the starting lithium methanesulfonate.

[0056] Figure 5. Diffraction patterns of lithium carbonate, lithium hydroxide and lithium oxide.

[0057] Figure 6. Phase X-ray diffraction patterns of lithium sulfide formed as a result of the decomposition of mixtures of lithium methanesulfonate - lithium (I) oxide, lithium methanesulfonate - lithium (II) hydroxide.

[0058] Definitions (terms)

[0059] For a better understanding of the present invention, certain terms used in this description of the invention are provided below. The following definitions apply throughout this document unless otherwise specified.

[0060] In this description and in the following claims, unless the context otherwise requires, the words "have," "include," and "contain," or variations thereof, such as "has," "having," "includes," "including," "contains," or "comprising," are to be understood as including the stated whole or group of wholes, but not excluding any other whole or group of wholes. These terms are not intended to be construed as "consists solely of."

[0061] Also here, listing numeric ranges by endpoints includes all numbers within that range.

[0062] DTA - differential thermal analysis;

[0063] TG - thermogravimetry;

[0064] 12Х18Н10Т is a steel alloy grade where the letters represent chemical elements and the numbers represent their percentage content: 12 is a number and indicates the carbon content of no more than 0.12%; XI 8 is the chromium content of no more than 18%, which protects steel from corrosion and oxidation and increases strength without sacrificing alloy ductility; НЮ indicates the nickel content of no more than 10%, which increases thermal strengthening and toughness of steel; T is the letter that denotes the titanium content, approximately equal to 1, which contributes to corrosion resistance, strengthens the metal, increases ductility and affects hardenability.

[0065] 40X is a grade of alloy steel containing 0.40% carbon and less than 1.5% chromium, the rest being iron.

[0066] Carrying out the invention Figure 1 shows a diagram of the main process equipment used to carry out the method according to the invention: pos. 1 in the figure is an electric mixer at 14,000 revolutions per minute (rpm), in which lithium methanesulfonate is mixed with lithium oxide or lithium hydroxide. Next, the feedstock enters the mixing tank (pos. 2, figure 1), which contains a screw mixer at 300-900 rpm (pos. 4, figure 1), driven by an overhead drive motor (pos. 3, figure The raw material is heated using an electric or induction furnace (item 5, figure 1). The resulting exhaust gases are sent for purification (item 6, figure 1). The final product is also sent for purification (item 7, figure 1). Figure 2 shows a flow chart of the method for producing lithium carbonate and lithium sulfide from lithium methanesulfonate according to the invention.

[0067] The material of the mixing tank must withstand high temperatures, be heat-resistant and acid-resistant, so it can be made of special steel (for example, 12X18H10T, 40X) or electrolytic steel, or titanium.

[0068] As a material for obtaining lithium methanesulfonate, which is used in the claimed method, a chemical reaction of a methanesulfonic acid solution with one of the lithium compounds can be used: lithium oxide (1), lithium hydroxide (2), lithium carbonate (3) and lithium chloride (4): 2CH3S(O)2OH + Li2O 2 CH3S(O)2OLi + H2O (1);

[0069] CH3S(O)2OH + LiOH - 2 CH3S(O)2OLi + H2O (2);

[0070] CH3S(O)2OH + Li2CO3— CH3S(O)2OLi +H2O+CO2t (3); CH3S(O)2OH + LiCl - CH3S(O)2OLi +HClf (4).

[0071] Figure 3 shows the results of differential thermal analysis (DTA) and thermogravimetry (TG) of lithium methanesulfonate decomposition. As can be seen in Figure 3, the decomposition temperature (Td) of lithium methanesulfonate is 370 °C, and the mass loss during decomposition was 63.81%. The endothermic region at 350-400 °C is associated with heat absorption of -276.9 J / g, while exothermic regions associated with heat release are observed at 410-460 °C and 530-590 °C.

[0072] Figure 4 shows the X-ray diffraction pattern of the starting lithium methanesulfonate.

[0073] Control of the final product purity in the process according to the invention directly depends on the chemical purity of the starting material—lithium methanesulfonate—as well as the purity of lithium oxide, lithium hydroxide, and non-aqueous solvents. Table 1 below shows the chemical composition of the starting material—lithium methanesulfonate—obtained by reacting a methanesulfonic acid solution with one of the lithium compounds: lithium oxide, lithium hydroxide, lithium carbonate, and lithium chloride. Table 1. Chemical composition data for lithium methanesulfonate.

[0074] As can be seen from Table 1, the highest purity of CFhSChLi is observed in samples obtained by the interaction of CH3SO3H with Li2O and LiOH.

[0075] Figure 5 shows X-ray diffraction patterns of lithium carbonate, lithium hydroxide, and lithium oxide compounds, which are used to produce lithium methanesulfonate.

[0076] Tables 2-4 show the chemical composition of lithium carbonate, lithium hydroxide and lithium oxide.

[0077] Table 2. Chemical composition data of lithium carbonate. The chemical composition of lithium carbonate (Table 2) complies with TU 6-09-3728-83.

[0078] Other impurities may include trace amounts of Fe 2+ , Fe 3+ , Ni 2+ , Al 3+ , Zn 2+ and others.

[0079] Table 3. Chemical composition data of lithium hydroxide.

[0080] The chemical composition of the lithium hydroxide used (Table 3) complies with GOST 8595-83 grade LGO-1.

[0081] Table 4. Chemical composition data of lithium oxide.

[0082] The chemical composition of lithium oxide (Table 4) corresponds to the chemically pure grade, CAS 12057-24-8.

[0083] Figure 6 shows the phase X-ray diffraction pattern of lithium sulfide formed as a result of the decomposition of mixtures of lithium methanesulfonate - lithium (I) oxide, lithium methanesulfonate - lithium (II) hydroxide, at atmospheric pressure and a temperature of 500 °C.

[0084] The process of decomposition of a mixture of methanesulfonate and lithium oxide is carried out in accordance with the chemical reaction equation (5):

[0085] The process of decomposition of a mixture of methanesulfonate and lithium hydroxide is carried out in accordance with the chemical reaction equation (6):

[0086] The present invention is further illustrated by the following examples, but is not limited thereto.

[0087] Example 1. The decomposition of a mixture of lithium methanesulfonate and lithium oxide is carried out at low pressure. For this purpose, 100 g of lithium methanesulfonate and 44.5 g of lithium oxide are loaded into a 300.0 ml flask and mixed, and stirred at 14,000 rpm. Next, the resulting mixture is heated to 350 °C and a pressure of 5 Pa. The raw material is heated using an electric or induction furnace. Under these conditions, lithium methanesulfonate undergoes thermal decomposition, with the formation of lithium carbonate (48.49% by weight), lithium sulfide (30.16%), and water (16.8%). The decomposition conversion of CH3S03Il is 95%. The resulting final reaction products, lithium sulfide and lithium carbonate, are separated by extraction with L12S in anhydrous ethanol. The recovered lithium sulfide was then recrystallized in ethanol and subjected to vacuum distillation at T = 50 °C and P = 5 Pa. The distilled ethanol was transferred to a suitable container and recycled.

[0088] After the thermolysis process, lithium methanesulfonate may be present as an impurity, so lithium carbonate is purified by dissolving the unreacted lithium methanesulfonate impurity through repeated rinsing with deionized water. The Li2CO3 is then filtered and dried. If significant lithium methanesulfonate impurities remain after the initial decomposition, reheating to a higher temperature (approximately 500°C) at atmospheric pressure is performed to complete the decomposition of the lithium methanesulfonate. The main products of lithium methanesulfonate decomposition at atmospheric pressure are lithium carbonate and hydrogen sulfide or sublimed sulfur.

[0089] It is important to prevent lithium sulfide from coming into contact with air and moisture, as I 2S undergoes hydrolysis to form lithium hydroxide and hydrogen sulfide gas. Therefore, lithium sulfide should be stored in a sealed, moisture-free container (e.g., glass, plastic, or metal).

[0090] Example 2. The decomposition of a mixture of lithium methanesulfonate and lithium oxide is carried out at high pressure. For this purpose, 20 g of lithium methanesulfonate and 44.5 g of lithium oxide are charged into a 100.0 ml flask. The resulting mixture is then heated to 500 °C and a pressure of 0.1 MPa. The raw material is heated using an electric or induction furnace. Under these conditions, lithium methanesulfonate undergoes thermal decomposition, leading to the formation of lithium carbonate (32.67% by weight), lithium sulfide (20.32%) and water (11.32%). The decomposition conversion of CH3SO3IJ is 64%. The process occurs at high pressure without the use of catalysts. The resulting end products of the reaction - lithium sulfide and lithium carbonate - are separated, isolated and purified according to Example 1.

[0091] The recovered lithium sulfide was then recrystallized in tetrahydrofuran after extraction, and the resulting solution was subjected to vacuum distillation at T = 50 °C and P = 5 Pa. The tetrahydrofuran distilled in this manner was transferred to a suitable container and recycled.

[0092] Example 3. The decomposition of a mixture of lithium methanesulfonate and lithium hydroxide is carried out at low pressure. For this purpose, 100 g of lithium methanesulfonate and 75.5 g of lithium hydroxide are placed in a 1000.0 ml flask. The resulting mixture is then heated to 350 °C and a pressure of 5 Pa. The feedstock is heated using an electric or induction furnace. Under these conditions, lithium methanesulfonate undergoes thermal decomposition, leading to the formation of lithium carbonate (38.06% by weight), lithium sulfide (25.65%), and water (26.4%). The decomposition conversion of CHjSChLi is 93%. The process occurs at low pressure, without the need for catalysts.

[0093] The resulting final reaction products, lithium sulfide and lithium carbonate, are separated, isolated and purified according to Example 1.

[0094] The extracted lithium sulfide solution was recrystallized in N-methyl-2-pyrrolidone and subjected to vacuum distillation under conditions of T = 70 °C, P = 5 Pa. The N-methyl-2-pyrrolidone distilled in this manner was transferred to an appropriate container and returned for recycling.

[0095] Example 4. The decomposition of a mixture of lithium methanesulfonate and lithium hydroxide is carried out at high pressure. The process occurs at high pressure, without the need for catalysts. For this, 100 g of lithium methanesulfonate and 75.5 g of lithium hydroxide are charged into a 1000.0 ml flask. Next, the resulting mixture is heated to 700 °C and a pressure of 5 MPa. The feedstock is heated using an electric or induction furnace. Under these conditions, lithium methanesulfonate undergoes thermal decomposition, leading to the formation of lithium carbonate (37.29% by weight), lithium sulfide (23.07%), and water (24.1%). The conversion of CH3SO4 decomposition is 72%.

[0096] The resulting final reaction products - lithium sulfide and lithium carbonate - are separated, isolated and purified according to Example 1.

[0097] The extracted lithium sulfide solution was recrystallized in dioxane and subjected to vacuum distillation at T = 60 °C, P = 5 Pa. The dioxane distilled in this manner was transferred to an appropriate container and recycled.

[0098] Table 5 shows the chemical composition of the final products—lithium carbonate and lithium sulfide—obtained by the method according to the invention. Other impurities may include lithium polysulfides and trace amounts of Fe ions. 2+ , Fe 3+ , Ni 2+ , Al 3+ , Zn 2+ and others. Table 5. Data on the chemical composition of purified final decomposition products of CH3SO3LL

[0099] Data on the yield of final products, conversion of starting materials, as well as the amount of by-products obtained during the implementation of the method according to the invention under different variants of conditions are presented in Table 6. The measurement error of the yield of final products is ± 3-5%.

[0100] As can be seen from Table 6, the maximum yield of lithium carbonate (48.49% by weight) is observed as a result of thermal decomposition of the lithium metasulfonate - lithium oxide mixture, as well as the maximum yield of lithium sulfide (31.71% by weight).

[0101] At atmospheric and high pressure (up to 5 MPa) by-products are formed: LiOH, H2S, H2O and S.

[0102] Table 6. Data on the yields of products from the thermal decomposition of lithium methanesulfonate by the method according to the invention.

[0103] Thus, the advantages of the declared technology are:

[0104] - the possibility of jointly producing lithium sulfide and lithium carbonate from lithium methanesulfonate, which increases the efficiency of using the starting material, allows for the optimization of processes and the reduction of costs;

[0105] - in one technological stage it is possible to obtain lithium sulfide and lithium carbonate;

[0106] - joint production of lithium sulfide and lithium carbonate eliminates the need for separate infrastructure for the production of each product, which optimizes and simplifies production, and reduces capital costs;

[0107] - Minimizing cross-contamination: the technology reduces the risk of cross-contamination of products, which is important to ensure their cleanliness and compliance with standards;

[0108] - environmental benefits: reduced waste and reduced harmful impact on the environment and reduced emissions.

[0109] Although the invention has been described with reference to the disclosed embodiments, it will be apparent to those skilled in the art that the specific experiments described in detail are provided merely for the purpose of illustrating the present invention and should not be construed as limiting the scope of the invention in any way. It should be understood that various modifications are possible without departing from the spirit of the present invention.

Claims

Invention formula 1. A method for producing lithium sulfide and lithium carbonate from lithium methanesulfonate, including a stage of thermal decomposition of lithium methanesulfonate in the presence of lithium oxide or lithium hydroxide at a temperature of 350-700 °C and a pressure of 5 Pa - 5 MPa.

2. The method according to claim 1, comprising the following steps: a) mixing lithium methanesulfonate with lithium oxide or lithium hydroxide; b) heating the mixture obtained in step a) to a temperature of 350-700 °C at a pressure of 5 Pa - 5 MPa with the formation of the target products lithium sulfide and lithium carbonate; c) separating the lithium sulfide and lithium carbonate obtained in step b), isolating and purifying them, wherein lithium sulfide is isolated from the mixture with lithium carbonate by extraction in an organic solvent, lithium sulfide is purified by recrystallization in an organic solvent, and lithium carbonate is purified by washing with deionized water, then filtered and dried.

3. The method according to claim 2, wherein the organic solvent is selected from methanol, ethanol, propanol, butyl alcohol, N-methyl-2-pyrrolidone, dioxane, acetonitrile, tetrahydrofuran.

4. The method according to claim 2, wherein the ratio of lithium methanesulfonate to lithium oxide in step a) is 2:

3.

5. The method according to claim 2, wherein the ratio of lithium methanesulfonate and lithium hydroxide in step a) is 1:3.

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