Method for measuring content of lithium sulfide based on gravimetric method

Abstract

The invention discloses a method for determining the content of lithium sulfide based on a gravimetric method, and belongs to the field of battery material detection. The invention discloses a method for determining the content of lithium sulfide based on a gravimetric method. The method comprises the following steps: A, oxidizing lithium sulfide into lithium sulfate at high temperature; b, converting lithium sulfate into barium sulfate precipitate; c, burning the precipitate at high temperature and keeping the weight constant; and D, calculating the content of lithium sulfide according to barium sulfate. According to the method, the content of lithium sulfide is measured through a gravimetric method, the problem that the content of lithium sulfide cannot be accurately measured in the industry is solved, and the method is easy to operate, high in accuracy, good in precision and safer.

Description

Technical Field

[0001] The present invention relates to the field of battery material detection, and in particular to a method for determining lithium sulfide content based on a weight method. Background Art

[0002] In recent years, lithium-ion batteries have been increasingly used in consumer electronics, transportation and other fields. However, most commercial lithium-ion secondary batteries currently use organic electrolytes as electrolytes, which pose safety risks such as flammability and leakage. Replacing electrolytes with solid electrolytes is one of the effective measures to solve the above problems, so research on solid-state lithium-ion batteries has received widespread attention.

[0003] Sulfide solid electrolytes, as a key component of all-solid-state batteries, have become the most promising technology route due to their high ionic conductivity, easy processing characteristics, good electrochemical stability, etc. Lithium sulfide (Li2S) is a key precursor material for synthesizing sulfide solid electrolytes. Currently, there are no relevant industry standards or relevant literature reports to evaluate its purity. The industry mainly evaluates its purity based on the content of physical-combination impurity elements, which has poor accuracy. Therefore, the present invention has developed a method for determining the content of lithium sulfide based on the gravimetric method.

[0004] For example, the Chinese patent number CN116754349B discloses a method for digesting lithium sulfide impurity elements based on ICP-OES and a method for determining their content, which includes the following steps: removing H2S: weighing a lithium sulfide sample, adding ultrapure water to obtain a sample aqueous solution; heating the sample aqueous solution to preliminarily remove the H2S generated in the sample aqueous solution to obtain a sample from which H2S has been removed; adjusting to acidity: dripping a non-oxidizing acid into the sample from which H2S has been removed to obtain an acidic turbid liquid; performing oxidation and precipitation removal: dripping an oxidant into the acidic turbid liquid until a clear solution is obtained, and the clear solution is the sample solution to be treated. Then, the impurity elements are determined by inductively coupled plasma emission spectrometry; this method mainly involves the determination of impurity elements in lithium sulfide, and does not involve the determination of lithium sulfide content.

[0005] Since lithium sulfide is very sensitive to air, it produces toxic hydrogen sulfide gas when dissolved in water, and it dissolves violently in acid, producing not only hydrogen sulfide gas but also sulfur precipitation. Therefore, conventional methods for testing lithium sulfide content are not feasible. Therefore, it is of positive significance to provide a safer and more accurate detection method. Summary of the invention

[0006] Based on this, in order to solve the technical problem of poor accuracy in the detection of lithium sulfide content in the prior art, the present invention provides a method for determining the content of lithium sulfide based on a weight method, which will not generate hydrogen sulfide or sulfur dioxide toxic gas during the oxidation process, and the method is simple to operate, very accurate, precise and safer. The specific technical solution is as follows: A method for determining lithium sulfide content based on a gravimetric method, the method comprising the following steps: A. High-temperature oxidation of lithium sulfide to lithium sulfate: Weigh a lithium sulfide sample in a dry environment and place it in a porcelain crucible. Place the porcelain crucible in a high-temperature furnace in an oxygen atmosphere and oxidize it at high temperature to obtain lithium sulfate. B. Converting lithium sulfate into barium sulfate precipitate: dissolving the lithium sulfate in hot water, adjusting the solution to be acidic, then adding barium chloride solution, and slightly boiling to obtain barium sulfate precipitate; C. High temperature calcination of barium sulfate precipitate and constant weight: After cooling or overnight, filter the solution, wash the barium sulfate precipitate, then place the barium sulfate precipitate and filter paper in a porcelain crucible of known mass, and then calcine at high temperature and constant weight; D. Calculate the lithium sulfide content based on the weight of barium sulfate: The mass of sulfur is calculated based on the mass of barium sulfate precipitate according to the conversion formula, and then the lithium sulfide content is calculated based on the mass of sulfur.

[0007] Furthermore, the drying environment in step A has a water content of less than 0.0002%; the oxygen atmosphere is to use high-purity oxygen to replace the air in the high-temperature furnace and exhaust the air, and the oxygen atmosphere must be maintained throughout the process.

[0008] Furthermore, the temperature of the high temperature oxidation in step A is 300° C. to 500° C., and the time of the high temperature oxidation is 30 min to 90 min.

[0009] Furthermore, the temperature of the high temperature oxidation in step A is 350° C., and the time of the high temperature oxidation is 60 minutes.

[0010] Furthermore, in step B, methyl orange is used as an indicator, hydrochloric acid is used to adjust the solution to be acidic, and the concentration of the hydrochloric acid is 2 mol / L to 6 mol / L, and the pH value is less than 3.1.

[0011] Furthermore, the concentration of the barium chloride solution in step B is 100 g / L.

[0012] Furthermore, the temperature of the slight boiling treatment in step B is 80° C. to 100° C., and the time of the slight boiling treatment is 1 h to 3 h.

[0013] Furthermore, in step C, dense ash-free quantitative filter paper is used, and the ash content of the quantitative filter paper is required to be less than 0.1 mg.

[0014] Furthermore, the temperature of the high-temperature calcination in step C is 800°C~900°C, and the time of the high-temperature calcination is 20min~40min; wherein, the crucible of known mass also needs to be high-temperature calcined at 800°C~900°C for 20min~40min in advance, cooled to room temperature and constant weight.

[0015] Furthermore, the formula for calculating the sulfur mass from the weight of barium sulfate in step D is: , where m s is the mass of sulfur, in g; m1 is the mass of barium sulfate precipitate and filter paper placed in a porcelain crucible of known mass, then calcined at high temperature and weighed to a constant value, in g; m2 is the blank mass, i.e. the mass of the porcelain crucible with a constant weight after calcination at high temperature, in g; M s is the molar mass of sulfur, in g / moL; M BaSO4 is the molar mass of barium sulfate, in g / moL; The calculation formula for calculating the lithium sulfide content based on the mass of sulfur is: ωLi2S is the percentage of lithium sulfide, in units of %; m s is the mass of sulfur, in g; M Li2S is the molar mass of lithium sulfide, in g / moL; m is the mass of the lithium sulfide sample, in g; M s is the molar mass of sulfur, in g / moL.

[0016] Compared with the prior art, this application has the following beneficial effects: The present invention provides a method for determining the content of lithium sulfide based on a gravimetric method. The present invention adopts a high-temperature furnace to carry out high-temperature calcination of lithium oxide in an oxygen-rich atmosphere. The reaction is relatively mild, safe and controllable, no toxic hydrogen sulfide gas is generated, the operation is safe, and the lithium sulfate generated by the high-temperature calcination has stable properties. At the same time, a barium sulfate gravimetric method is adopted, which is simple to operate, highly accurate, precise, and safer. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 It is a schematic flow chart of a method for determining lithium sulfide content based on a weight method in Example 1 of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with its embodiments. It should be understood that the specific implementation methods described herein are only used to explain the present invention and do not limit the protection scope of the present invention.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0019] A method for determining the content of lithium sulfide based on a weight method in one embodiment of the present invention comprises the following steps: A. High-temperature oxidation of lithium sulfide to lithium sulfate: Weigh a lithium sulfide sample in a dry environment and place it in a porcelain crucible. Place the porcelain crucible in a high-temperature furnace in an oxygen atmosphere and oxidize it at high temperature to obtain lithium sulfate. B. Converting lithium sulfate into barium sulfate precipitate: dissolving the lithium sulfate in hot water, adjusting the solution to be acidic, then adding barium chloride solution, and slightly boiling to obtain barium sulfate precipitate; C. High temperature calcination of barium sulfate precipitate and constant weight: After cooling or overnight, filter the solution, wash the barium sulfate precipitate, then place the barium sulfate precipitate and filter paper in a porcelain crucible of known mass, and then calcine at high temperature and constant weight; D. Calculate the lithium sulfide content based on the weight of barium sulfate: The mass of sulfur is calculated based on the mass of barium sulfate precipitate according to the conversion formula, and then the lithium sulfide content is calculated based on the mass of sulfur.

[0020] In one of the embodiments, in step A, due to different synthesis methods and different purities of lithium sulfide, other sulfide impurities may appear. If other sulfide impurities are contained, the lithium sulfide sample is dissolved in water to drive out hydrogen sulfide, and then a hydrochloric acid solution is added to acidify it, and then hydrogen peroxide is added to oxidize and dissolve the precipitate. At this time, only sulfur among other sulfide impurities remains in the solution. The standard curve method is used on an inductively coupled plasma atomic emission spectrometer to test the impurity sulfur content, and the lithium sulfide content is obtained by subtracting the impurity sulfur content from the test result of the present invention.

[0021] In one embodiment, the dry environment in step A has a water content of less than 0.0002%; the oxygen atmosphere is to use high-purity oxygen to replace the air in the high-temperature furnace and exhaust the air, and the oxygen atmosphere must be maintained throughout the process.

[0022] In one embodiment, sampling is performed in a glove box, which is beneficial for controlling the water content.

[0023] In one embodiment, lithium sulfide is very sensitive to air, which may lead to low test results. The high-temperature oxidation in step A is carried out in a high-temperature furnace, and maintaining an oxygen environment is conducive to the smooth progress of the lithium sulfide oxidation reaction.

[0024] In one embodiment, the temperature of the high temperature oxidation in step A is 300° C. to 500° C., and the time of the high temperature oxidation is 30 min to 90 min.

[0025] In one embodiment, the temperature of the high temperature oxidation in step A is 350° C., and the time of the high temperature oxidation is 60 minutes.

[0026] In one embodiment, the lithium sulfate obtained after high-temperature oxidation is cooled naturally or by passing an inert gas for cooling.

[0027] In one embodiment, methyl orange is used as an indicator in step B, and hydrochloric acid is used to adjust the solution to be acidic, and the concentration of the hydrochloric acid is 2 mol / L to 6 mol / L, and the pH value is less than 3.1. Using methyl orange as an indicator is conducive to controlling the acidity of the solution. The acidic solution is red and the pH value of the solution is less than 3.1 because the acidic environment is more conducive to the precipitation of barium sulfate and eliminates the interference of other possible precipitations.

[0028] In one embodiment, the hydrochloric acid concentration is 6 mol / L.

[0029] In one embodiment, the concentration of the barium chloride solution in step B is 100 g / L.

[0030] In one embodiment, the temperature of the slight boiling treatment in step B is 80° C. to 100° C., and the time of the slight boiling treatment is 1 h to 3 h.

[0031] In one embodiment, the temperature of the slight boiling treatment in step B is 95° C. and the time is 2 hours.

[0032] In one embodiment, dense ash-free quantitative filter paper is used in step C, and the ash content of the quantitative filter paper is required to be less than 0.1 mg. The quantitative filter paper used has a negligible effect on the results, and the pore size of the slow filter paper is preferably smaller, so as not to cause the loss of barium sulfate precipitation.

[0033] In one embodiment, the high temperature calcination in step C is performed at a temperature of 800° C. to 900° C., and the high temperature calcination time is 20 min to 40 min.

[0034] In one embodiment, the high temperature calcination in step C is performed at a temperature of 850° C. and for a time of 30 minutes.

[0035] In one embodiment, the porcelain crucible needs to be calcined at a high temperature in advance, the calcination temperature is 800°C to 900°C, preferably 850°C, and cooled to constant weight at room temperature, so as to eliminate the difference between the weight of the crucible at room temperature and the weight after high temperature calcination, thus causing inaccurate results.

[0036] In one embodiment, the formula for calculating the sulfur mass from the weight of barium sulfate in step D is: ; Among them, m s is the mass of sulfur, in g; m1 is the mass of barium sulfate precipitate and filter paper placed in a porcelain crucible of known mass, then calcined at high temperature and weighed to a constant value, in g; m2 is the blank mass, i.e. the mass of the porcelain crucible with a constant weight after calcination at high temperature, in g; M s is the molar mass of sulfur, in g / moL; M BaSO4 is the molar mass of barium sulfate, in g / moL; The calculation formula for calculating the lithium sulfide content based on the mass of sulfur is: ; Among them, ωLi2S is the percentage of lithium sulfide, unit is %; m s is the mass of sulfur, in g; M Li2S is the molar mass of lithium sulfide, in g / moL; m is the mass of the lithium sulfide sample, in g; M s is the molar mass of sulfur, in g / moL.

[0037] In one embodiment, the electronic balance used in step D is a 1 / 10,000 balance with a resolution of 0.1 mg.

[0038] The above scheme provides overall safety and controllability, and can detect the content of lithium sulfide with high accuracy and excellent precision.

[0039] The embodiments of the present invention will be described in detail below with reference to specific examples.

[0040] Embodiment 1: A method for determining lithium sulfide content based on a gravimetric method, the method comprising the following steps: (1) In a glove box (water and oxygen content less than 0.01 ppm), weigh 0.1 g (accurate to 0.0001 g) of lithium sulfide and place it in a 30 mL porcelain crucible, and cover the crucible with a lid; seal the crucible containing lithium sulfide and transfer it to a high-temperature furnace that has been evacuated with high-purity oxygen, then gradually heat it to 350°C and maintain it at this temperature for 30 min. During the entire process, maintain an oxygen atmosphere in the high-temperature furnace; (2) After the reaction is completed, cool naturally to room temperature, remove the crucible from the high-temperature furnace and transfer it to a 400mL beaker. Soak the crucible in hot water, wash the crucible, then heat the water to 300mL, and heat to dissolve until clear; add (2~3) drops of methyl orange indicator (2g / L) to the solution, neutralize with 6mol / L hydrochloric acid solution and add excess to make the pH value of the solution less than 3.1. Heat the solution to boiling, slowly add 10mL of barium chloride solution (100g / L) while stirring continuously, and keep it at a slight boiling state for about 1h. The final volume of the solution is about 100mL; (3) After the solution is cooled and allowed to stand overnight, it is filtered with dense ash-free quantitative slow filter paper and washed with hot water until there is no chloride ion (silver nitrate solution (10 g / L) is tested to be turbid); the filter paper with the precipitate is transferred to a porcelain crucible of known mass, the filter paper is incinerated at low temperature, and then burned in a high-temperature furnace at 800°C for 20 min. The crucible is taken out, cooled slightly in the air, and then placed in a desiccator to cool to room temperature before weighing; (4) According to the formula: , calculate the mass of sulfur; where m s is the mass of sulfur, in g; m1 is the mass of barium sulfate precipitate and filter paper placed in a porcelain crucible of known mass, then calcined at high temperature and weighed to a constant value, in g; m2 is the blank mass, i.e. the mass of the porcelain crucible with a constant weight after calcination at high temperature, in g; M s is the molar mass of sulfur, in g / moL; M BaSO4 is the molar mass of barium sulfate, in g / moL; according to the formula: , calculate the mass of lithium sulfide, where ωLi2S is the percentage of lithium sulfide, unit is %; m s is the mass of sulfur, in g; M Li2S is the molar mass of lithium sulfide, in g / moL; m is the mass of the lithium sulfide sample, in g; M s is the molar mass of sulfur, in g / moL.

[0041] Embodiment 2: A method for determining lithium sulfide content based on a gravimetric method, the method comprising the following steps: (1) In a glove box (water and oxygen content less than 0.01 ppm), weigh 0.1 g (accurate to 0.0001 g) of lithium sulfide and place it in a 30 mL porcelain crucible, and cover the crucible with a lid; seal the crucible containing lithium sulfide and transfer it to a high-temperature furnace that has been evacuated with high-purity oxygen, then gradually heat it to 400°C and maintain it at this temperature for 60 min. During the entire process, maintain an oxygen atmosphere in the high-temperature furnace; (2) After the reaction is completed, cool naturally to room temperature, remove the crucible from the high-temperature furnace and transfer it to a 400mL beaker. Soak the crucible in hot water, wash the crucible, then heat the water to 300mL, and heat to dissolve until clear; add (2~3) drops of methyl orange indicator (2g / L) to the solution, neutralize with 4mol / L hydrochloric acid solution and add excess to make the pH value of the solution less than 3.1. Heat the solution to boiling, slowly add 10mL of barium chloride solution (100g / L) while stirring continuously, and boil it slightly for 2h. The final volume of the solution is about 100mL; (3) After the solution is cooled and allowed to stand overnight, it is filtered with dense ash-free quantitative slow filter paper and washed with hot water until there is no chloride ion (silver nitrate solution (10 g / L) is tested to be turbid); the filter paper with the precipitate is transferred to a porcelain crucible of known mass, the filter paper is incinerated at low temperature, and then burned in a high-temperature furnace at 850°C for 30 min. The crucible is taken out, cooled slightly in the air, and then placed in a desiccator to cool to room temperature before weighing; (4) According to the formula: , calculate the mass of sulfur; where m s is the mass of sulfur, in g; m1 is the mass of barium sulfate precipitate and filter paper placed in a porcelain crucible of known mass, then calcined at high temperature and weighed to a constant value, in g; m2 is the blank mass, i.e. the mass of the porcelain crucible with a constant weight after calcination at high temperature, in g; M s is the molar mass of sulfur, in g / moL; M BaSO4 is the molar mass of barium sulfate, in g / moL; according to the formula: , calculate the mass of lithium sulfide, where ωLi2S is the percentage of lithium sulfide, unit is %; m s is the mass of sulfur, in g; M Li2S is the molar mass of lithium sulfide, in g / moL; m is the mass of the lithium sulfide sample, in g; M s is the molar mass of sulfur, in g / moL.

[0042] Embodiment 3: A method for determining lithium sulfide content based on a gravimetric method, the method comprising the following steps: (1) In a glove box (water and oxygen content less than 0.01 ppm), weigh 0.1 g (accurate to 0.0001 g) of lithium sulfide and place it in a 30 mL porcelain crucible, and cover the crucible with a lid; seal the crucible containing lithium sulfide and transfer it to a high-temperature furnace that has been evacuated with high-purity oxygen, then gradually heat it to 500°C and maintain it at this temperature for 90 min. During the entire process, the oxygen atmosphere in the high-temperature furnace is maintained; (2) After the reaction is completed, cool naturally to room temperature, remove the crucible from the high-temperature furnace and transfer it to a 400mL beaker. Soak the crucible in hot water, wash the crucible, heat the water to 300mL, and heat to dissolve until clear; add (2~3) drops of methyl orange indicator (2g / L) to the solution, neutralize with 2mol / L hydrochloric acid solution and add excess to make the pH value of the solution less than 3.1. Heat the solution to boiling, slowly add 10mL of barium chloride solution (100g / L) while stirring continuously, and treat at a slight boil for 3h. The final volume of the solution is about 100mL; (3) After the solution is cooled and allowed to stand overnight, it is filtered with dense ash-free quantitative slow filter paper and washed with hot water until there is no chloride ion (silver nitrate solution (10 g / L) is tested to be turbid); the filter paper with the precipitate is transferred to a porcelain crucible of known mass, the filter paper is incinerated at low temperature, and then burned in a high-temperature furnace at 900°C for 40 min. The crucible is taken out, cooled slightly in the air, and then placed in a desiccator to cool to room temperature before weighing; (4) According to the formula: , calculate the mass of sulfur; where m s is the mass of sulfur, in g; m1 is the mass of barium sulfate precipitate and filter paper placed in a porcelain crucible of known mass, then calcined at high temperature and weighed to a constant value, in g; m2 is the blank mass, i.e. the mass of the porcelain crucible with a constant weight after calcination at high temperature, in g; M s is the molar mass of sulfur, in g / moL; M BaSO4 is the molar mass of barium sulfate, in g / moL; according to the formula: , calculate the mass of lithium sulfide, where ωLi2S is the percentage of lithium sulfide, unit is %; m s is the mass of sulfur, in g; M Li2S is the molar mass of lithium sulfide, in g / moL; m is the mass of the lithium sulfide sample, in g; M s is the molar mass of sulfur, in g / moL.

[0043] Comparative Example 1: Comparative Example 1 provides a method for determining the content of lithium sulfide, which is an impurity reduction method, wherein the lithium sulfide sample is dissolved in ultrapure water to remove hydrogen sulfide, then dissolved and acidified with hydrochloric acid, and oxidized and dissolved with hydrogen peroxide to precipitate; in a hydrochloric acid medium, a standard curve method is used on an inductively coupled plasma atomic emission spectrometer to determine the content of impurity elements in lithium sulfide, and then combined with the lithium sulfide phase (XRD diagram), the impurity element content is subtracted from 100% to obtain the content of lithium sulfide.

[0044] The results of the determination of the lithium sulfide content in Examples 1 to 3 and Comparative Example 1 are recorded as shown in Table 1.

[0045] Table 1: Lithium sulfide content

[0046] As can be seen from Table 1, the content result of lithium sulfide obtained by the impurity reduction method is significantly higher than the test result of the present invention. The reason is that a small amount of unknown impurities are often introduced in the synthesis process of lithium sulfide, and it is impossible to test all the impurity elements at the same time. Therefore, the impurity reduction method often leads to a high result, which is often inconsistent with the actual situation and is not conducive to the optimization and improvement of the production process. The present invention converts the sulfur ions in lithium sulfide into sulfate ions in an oxygen-rich environment, and then converts the sulfate ions into barium sulfate precipitates, and determines the content of lithium sulfide by a gravimetric method. The method is simple to operate, highly accurate, reproducible, and safer. It solves the problem that the content of lithium sulfide cannot be accurately determined in the current industry, fills the gap in the method for determining the content of lithium sulfide, and promotes the development of the sulfide solid electrolyte industry.

[0047] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0048] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for determining the content of lithium sulfide based on a gravimetric method, characterized in that: The method comprises the following steps: A. High-temperature oxidation of lithium sulfide to lithium sulfate: Weigh a lithium sulfide sample in a dry environment and place it in a porcelain crucible. Place the porcelain crucible in a high-temperature furnace in an oxygen atmosphere and oxidize it at high temperature to obtain lithium sulfate. B. Converting lithium sulfate into barium sulfate precipitate: dissolving the lithium sulfate in hot water, adjusting the solution to be acidic, then adding barium chloride solution, and slightly boiling to obtain barium sulfate precipitate; C. High temperature calcination of barium sulfate precipitate and constant weight: After cooling or overnight, filter the solution, wash the barium sulfate precipitate, then place the barium sulfate precipitate and filter paper in a porcelain crucible of known mass, and then calcine at high temperature and constant weight; D. Calculate the lithium sulfide content based on the weight of barium sulfate: the mass of sulfur is calculated based on the conversion formula from the mass of barium sulfate precipitate, and then the lithium sulfide content is calculated based on the mass of sulfur.

2. The method for determining the content of lithium sulfide based on the weight method according to claim 1, characterized in that: The dry environment in step A has a water content of less than 0.0002%; the oxygen atmosphere is to use high-purity oxygen to replace the air in the high-temperature furnace and exhaust the air, and the oxygen atmosphere must be maintained throughout the process.

3. The method for determining the content of lithium sulfide based on the weight method according to claim 1, characterized in that: The temperature of the high temperature oxidation in step A is 300° C. to 500° C., and the time of the high temperature oxidation is 30 min to 90 min.

4. The method for determining the content of lithium sulfide based on the weight method according to claim 3, characterized in that: The temperature of the high temperature oxidation in step A is 350° C., and the time of the high temperature oxidation is 60 minutes.

5. The method for determining the content of lithium sulfide based on the weight method according to claim 1, characterized in that: In step B, methyl orange is used as an indicator, and hydrochloric acid is used to adjust the solution to be acidic, and the concentration of the hydrochloric acid is 2 mol / L to 6 mol / L, and the pH value is less than 3.

1.

6. The method for determining the content of lithium sulfide based on the weight method according to claim 1, characterized in that: The concentration of the barium chloride solution in step B is 100 g / L.

7. The method for determining the content of lithium sulfide based on the weight method according to claim 1, characterized in that: The temperature of the slight boiling treatment in step B is 80° C. to 100° C., and the time of the slight boiling treatment is 1 h to 3 h.

8. The method for determining the content of lithium sulfide based on the weight method according to claim 1, characterized in that: In step C, dense ash-free quantitative filter paper is used, and the ash content of the quantitative filter paper is required to be less than 0.1 mg.

9. The method for determining the content of lithium sulfide based on the weight method according to claim 1, characterized in that: The temperature of the high-temperature calcination in step C is 800°C~900°C, and the time of the high-temperature calcination is 20min~40min; wherein, the porcelain crucible of known mass also needs to be high-temperature calcined at 800°C~900°C for 20min~40min in advance, cooled to room temperature and constant weight.

10. The method for determining the content of lithium sulfide based on the weight method according to any one of claims 1 to 9, characterized in that: The formula for calculating the sulfur mass from the weight of barium sulfate in step D is: , where m s is the mass of sulfur, in g; m1 is the mass of barium sulfate precipitate and filter paper placed in a porcelain crucible of known mass, then calcined at high temperature and weighed to a constant value, in g; m2 is the blank mass, i.e. the mass of the porcelain crucible with a constant weight after calcination at high temperature, in g; M s is the molar mass of sulfur, in g / moL; M BaSO4 is the molar mass of barium sulfate, in g / moL; The calculation formula for calculating the lithium sulfide content based on the mass of sulfur is: , where ωLi2S is the percentage of lithium sulfide, in units of %; m s is the mass of sulfur, in g; M Li2S is the molar mass of lithium sulfide, in g / moL; m is the mass of the lithium sulfide sample, in g; M s is the molar mass of sulfur, in g / moL.

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