Preparation method of high-purity lithium selenide

Abstract

The invention discloses a preparation method of high-purity lithium selenide, which comprises the following specific steps: S1, adding amorphous selenium Se into a CS2 solvent; s2, adding 5-30 vol% of a viscosity reducing solvent; s3, adding LiH powder into the solvent according to the molar ratio, and stirring and heating; and S4, collecting reaction precipitates, washing, drying, and carrying out high-temperature heat treatment to obtain Li2Se with the purity not lower than 99.9%. Compared with the prior art, the preparation method has the advantages that the liquid-phase reaction is adopted to replace the ball-milling solid-phase reaction which is tedious in operation, the preparation steps are simplified, the potential of continuous batch preparation is achieved, reactant molecules can be quickly diffused and uniformly mixed through the liquid-phase reaction, the reaction rate and uniformity are remarkably improved, and the preparation method is simple and convenient. The method has the advantages that residual elemental selenium in a final product is reduced, CS2 is mixed with a low-consistency solvent, the consistency of a solvent system is reduced, the solubility of elemental selenium is further improved, and the reaction rate is increased.

Description

TECHNICAL FIELD

[0001] The application relates to the chemical industry field, in particular to a preparation method of high-purity lithium selenide. BACKGROUND

[0002] Lithium selenide is a compound with a certain selenization rate, and its chemical formula is LiSe. Lithium selenide is mainly used in the field of lithium batteries. The lithium battery is a rechargeable battery, has the advantages of high energy density, light weight and long service life, and is widely used in mobile communication equipment, electric vehicles and other fields.

[0003] Lithium selenide can be prepared by reacting lithium hydride LiH and elemental selenium Se. The commonly used preparation method is to mix the two and then perform high-energy ball milling treatment, but since the Mohs hardness of elemental selenium is low, wall sticking is serious during high-energy ball milling, and the materials are difficult to achieve a fully mixed state. In order to make LiH fully react, 1-3% of elemental selenium in excess of the molar ratio needs to be added, and the wall sticking materials are scraped off multiple times during ball milling, which makes the manufacturing difficult, the product impure (with residual elemental selenium) and batch production impossible.

[0004] The disadvantages of the prior art using high-energy ball milling solid-phase reaction are as follows:

[0005] (1) The preparation is difficult, wall sticking is serious during high-energy ball milling, and multiple wall scraping treatments are needed.

[0006] (2) The product is impure. In order to make LiH fully react, excess elemental selenium needs to be added, so that a certain amount of elemental selenium is left in the final product.

[0007] (3) Batch continuous production is impossible. Ball milling needs to be carried out in a sealed space, H2 gas is generated during the reaction, which has safety hazards, and the safety performance requirement of the equipment is high. SUMMARY

[0008] The purpose of the present application is to provide a preparation method of high-purity lithium selenide which solves the above problems.

[0009] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: a preparation method of high-purity lithium selenide, the specific steps are as follows:

[0010] S1, amorphous selenium Se is added into CS2 solvent;

[0011] Elemental selenium exists in various forms, including amorphous Se, alpha-Se, beta-Se and gamma-selenium. Amorphous selenium has a stronger solubility due to the absence of long-range ordered structure in atomic arrangement, so the present application selects amorphous selenium with better solubility.

[0012] The reason for choosing CS2 as the solvent is that the non-polar CS2 molecules interact with the selenium chains / clusters through dispersion forces, breaking the weak van der Waals forces between the selenium chains, allowing the selenium to disperse in the form of molecules or chain clusters in the CS2;

[0013] S2, adding a thickening solvent;

[0014] The purpose of adding a thickening solvent is to further improve the solubility of Se in the solvent system, and the added solvent is a low-viscosity non-polar solvent;

[0015] S3, according to the addition of LiH powder to the solvent of step S2, stirring and heating, the heating temperature is 40-200℃, the heating and stirring time is 1-10h, the heating and stirring is to improve the reaction rate;

[0016] S4, collecting the reaction precipitate and washing and drying, high temperature heat treatment, heat treatment temperature is 400-750℃, heat treatment time is 0.5-8h, to obtain Li2Se with purity not less than 99.9%, and the purpose of heat treatment is to improve the crystallinity of the product, on the other hand, high temperature treatment can further remove impurities.

[0017] As a preferred, in step S1, the molar ratio of Se and CS2 is 1:5-1:20, based on the consideration of reaction concentration, too high Se concentration is not conducive to full reaction, and too low Se concentration is not conducive to reaction, this molar ratio is the best; Because the water in CS2 will react with lithium hydride or lithium selenide, the water content needs to be controlled below 30PPM, and the reaction needs to be carried out in an inert gas protection environment.

[0018] As a preferred, in step S2, the thickening solvent is at least one of benzene, toluene, xylene, ethylbenzene, nitrobenzene, carbon tetrachloride, n-heptane, petroleum ether, and cyclohexane.

[0019] As a preferred, in step S2, the molar ratio of Se and CS2 is the best molar ratio of 1:15, at this time, 6 hours can be fully reacted, and the purity of Li2Se can reach 99.93%.

[0020] As a preferred, in step S2, the thickening solvent addition ratio is 5-20% of the volume of CS2 solvent, in principle, the more the better, but considering the cost, through experiments, when the ratio of thickening solvent to CS2 solvent is 5-20%, the solubility of Se can meet the needs, and when it is higher than 20%, the solubility of Se can be further improved, but the improvement is small, and the input and output are not proportional.

[0021] As preferred, in step S3, the amount of LiH added is in a molar ratio of 2:1-2:1.05 to Se, the heating temperature is 40-200℃, and the heating and stirring time is 1-10h, so as to make the LiH and Se fully react completely.

[0022] As preferred, in step S3, the molar ratio of the LiH and Se is the optimal molar ratio of 2:1.01, so as to ensure that the LiH fully reacts completely and the purity of Li2Se reaches 99.95%.

[0023] As preferred, in step S4, after the reaction is completed, the reaction precipitate is washed with a CS2 solvent, so as to remove the elemental Se possibly remaining in the reaction, and the molar ratio of the reaction precipitate to CS2 is 1:0.5-1:3.

[0024] As preferred, in step S4, for safety consideration, the heat treatment needs to be carried out in an inert atmosphere, the heat treatment temperature is 400-750℃, and the heat treatment time is 0.5-8h.

[0025] Compared with the prior art, the present application has the following advantages:

[0026] (1) The present application adopts a liquid phase reaction to replace a complicated ball-milling solid phase reaction, so as to simplify the preparation steps, and the scheme does not need to be carried out in a high ball-milling solid phase reaction, and has the potential of continuous batch preparation.

[0027] (2) The present application makes the reactant molecules quickly diffuse and uniformly mix through the liquid phase reaction, significantly improves the reaction rate and uniformity, does not need to add excessive elemental Se, and reduces the residual elemental Se in the final product.

[0028] (3) The present application mixes CS2 with a low-concentration solvent, reduces the concentration of the solvent system, further improves the solubility of the elemental Se, and improves the reaction rate. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The present application is a method flow chart. DETAILED DESCRIPTION

[0030] The present application will be further described below, and comparative experiments of different methods will be carried out.

[0031] Example 1: Li2Se is prepared by using LiH and elemental Se for high-energy ball milling, 15.90g of LiH and 85.05g of elemental Se are added into a 1000ML ball mill tank, the ball-to-material ratio is 5:1, the rotation speed is 600rmp / min, and the ball milling time is 4h.

[0032] Example 2: Preparation of Li2Se by high-energy ball milling with LiH and elemental Se, 3.18 g of LiH and 17.01 g of elemental Se were added to a 1000 mL ball mill jar, ball-to-charge ratio of 5:1, rotation speed of 600 rmp / min, and ball milling for 4 h.

[0033] Example 3: Preparation of high-purity lithium selenide according to the method of the present application, see Figure 1 , the preparation method is as follows:

[0034] S1: 85.05 g of amorphous selenium was added to 1000 mL of CS2 solvent;

[0035] S2: 200 mL of dimethylbenzene was added;

[0036] S3: 15.90 g of LiH powder was added, heated to 60°C, and stirred for 5 h.

[0037] S4: The reaction precipitate was collected, washed and dried, and heat treated in an inert atmosphere, with a sintering temperature of 600°C and a sintering time of 4 h, to obtain high-purity lithium selenide after the reaction.

[0038] Case Phase Purity Remark Example 1 - - Because the reaction is large, the generated H2causes the tank to explode Example 2 No obvious impurity peak 99.1% Unreacted impurities exist Example 3 No obvious impurity peak 99.9% Large reaction amount, good safety, and less impurities

[0039] Conclusion: By comparing Example 1 and Example 3, it can be seen that the same amount of 85.05 g of selenium is reacted, and the safety of the reaction in 1000 mL of CS2 solvent is much higher than that in a 1000 mL ball mill jar.

[0040] By comparing Example 2 and Example 1, it can be seen that Example 2 reduces the amount of Se to improve safety, and only 17.01 g of elemental Se is added, which greatly reduces the production efficiency.

[0041] By comparing Example 3 and Example 1, the present application adds 85.05 g of amorphous selenium, which not only has a large reaction amount, high production efficiency, but also good safety, and the purity of lithium selenide reaches 99.9%, which is higher than 99.1% of Example 2.

[0042] Example 4, experimental comparison of Se to CS2 molar ratio in the range of 1:5-1:20, based on the same reaction conditions (LiH:Se = 2:1.05, 10 Vol% toluene as a thickening solvent, reaction temperature 120°C, heat treatment 650°C / 3h), see Table 1:

[0043] Table 1:

[0044] Se:CS2 molar ratio Reaction system state Product Li2Se Purity (%) Reaction completion time (h) Remark 1:3 Light brown solution, with unsolved Se 99.32 - Incomplete reaction 1:15 Yellow solution / yellow precipitate at the bottom 99.93 6 Complete reaction 1:30 Yellow solution / yellow precipitate at the bottom 99.88 15 Complete reaction time delay

[0045] Se:CS2 molar ratio of 1:3, Se concentration is higher: Se in CS2 may occur in the case of incomplete dissolution, the formation of viscous system lead to mass transfer resistance, product due to residual unreacted Se and LiH lead to purity decline (99.52%), and a small amount of particle agglomeration.

[0046] Se:CS2 molar ratio of 1:30, Se concentration is low: although completely dissolved, but the concentration of reactants in unit volume is insufficient, leading to the reaction time is extended to.

[0047] Se:CS2 molar ratio of 1:15: the system has good flowability, the fastest reaction rate (4h complete reaction), purity 99.93%, the best comprehensive performance.

[0048] Conclusion: Se and CS2 molar ratio is too high or too low, the balance of reaction efficiency, product purity and process economy will be affected.

[0049] Example 5, compared with example 1, the variable is to adjust the ratio of LiH and Se.

[0050] The following is the experimental data comparison of LiH:Se molar ratio in the range of 2:0.95 to 2:1.1, the experimental results:

[0051] Molar ratio of LiH:Se Product Li2Se Purity (%) Reaction system state 2:0.90 95.28 Deep yellow solution / yellow-white precipitate at the bottom 2:1.00 99.92 Deep yellow solution / yellow precipitate at the bottom 2:1.01 99.95 Deep yellow solution / yellow precipitate at the bottom 2:1.05 99.91 Deep yellow solution / yellow precipitate at the bottom 2:1.10 99.3 Brown solution / yellow-brown precipitate at the bottom

[0052] LiH:Se molar ratio of 2:0.9, LiH excess, it is difficult to separate LiH and target product, resulting in Li2Se purity;

[0053] LiH:Se molar ratio of 2:1.00-2:1.05, slightly Se excess, Li2Se purity is ≥99.9%, among them 2:1.01 up to 99.95%, the best value; yellow solution shows that Se is fully dissolved, the yellow precipitate at the bottom is pure Li2Se, no mixed color impurities, indicating that the selectivity of the reaction is high, Se slightly excess 1%-3% can ensure the complete reaction of LiH (no white / yellow white precipitate of LiH residue), at the same time, excess Se is dissolved in CS2 in molecular state, which is easy to remove in subsequent washing;

[0054] LiH:Se molar ratio of 2:1.10, Se excess, Li2Se purity is ≥99.3%; brown solution and yellow brown precipitate suggest the formation of polyselenide (such as Li2Se3, Li2Se5), which is difficult to completely convert to Li2Se in heat treatment, resulting in purity decline.

[0055] Conclusion: The optimal molar ratio is determined: LiH:Se=2:1.01, which is the optimal ratio, at which the product has the highest purity (99.95%), and the reaction system is stable, and no obvious by-products are generated. Excessive LiH (≤2:0.90) will lead to unreacted LiH residue and side reactions, and significantly reduce the purity of the product. A slight excess of Se (1%-3%) can promote the complete reaction of LiH and improve the purity to more than 99.9%. Excessive Se (≥10%) will trigger polyselenide side reactions, resulting in a decrease in purity. Therefore, the process control is recommended: strictly control the excess ratio of Se to be 1%-2% (i.e., LiH:Se=2:1.01-2:1.02), balance the completeness of the reaction and the inhibition of by-products. For systems with a high Se ratio such as 2:1.10, the decomposition of polyselenides can be promoted by extending the heat treatment time (e.g., 650°C / 5h), but the purity is still difficult to reach the level of a slight excess group.

[0056] In summary, the above conclusions provide clear experimental evidence for the ratio control of LiH and Se in the preparation of high-purity Li2Se, which can directly guide the process optimization.

[0057] The above describes in detail a method for preparing high-purity lithium selenide provided by the present application, and the principles and implementation modes of the present application are described by applying specific examples. The above examples are only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed, and the modification and improvement of the present application will be possible, without exceeding the concept and scope defined in the appended claims. In summary, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A method for preparing high-purity lithium selenide, characterized in that, The specific steps are as follows: S1, amorphous selenium (Se) is added to the CS2 solvent to promote the dispersion of selenium in the form of molecules or chain clusters in the CS2 solvent; S2, add a thickening solvent to promote better dissolution of Se into the CS2 solvent; S3, add LiH powder to the solvent of step S2, and stir and heat to react; S4. The reaction precipitate is collected, washed, dried, and then subjected to high-temperature heat treatment to obtain Li2Se with a purity of not less than 99.9%.

2. The method for preparing high-purity lithium selenide according to claim 1, characterized in that: In step S1, the molar ratio of Se to CS2 is 1:5-1:20, wherein the water content in CS2 is less than 30 PPM, and the reaction needs to be carried out under an inert gas protective environment.

3. The method for preparing high-purity lithium selenide according to claim 2, characterized in that: The thickening solvent is added at a ratio of 5-20% of the volume of CS2 solvent.

4. The method for preparing high-purity lithium selenide according to claim 2, characterized in that: The optimal molar ratio of Se to CS2 is 1:

15.

5. The method for preparing high-purity lithium selenide according to claim 1, characterized in that: In step S2, the thickening solvent is at least one of benzene, toluene, xylene, ethylbenzene, nitrobenzene, carbon tetrachloride, n-heptane, petroleum ether, and cyclohexane.

6. The method for preparing high-purity lithium selenide according to claim 1, characterized in that: In step S3, the molar ratio of the added LiH to Se is 2:1 to 2:1.

05.

7. The method for preparing high-purity lithium selenide according to claim 6, characterized in that: In step S3, the optimal molar ratio of LiH to Se is 2:1.

01.

8. The method for preparing high-purity lithium selenide according to claim 1, characterized in that: In step S3, the heating temperature is 40-200℃, and the heating and stirring time is 1-10h.

9. The method for preparing high-purity lithium selenide according to claim 1, characterized in that: In step S4, after the reaction is complete, the reaction precipitate is washed with CS2 solvent to remove the residual elemental Se in the reaction. The molar ratio of the reaction precipitate to CS2 is 1:0.5-1:

3.

10. The method for preparing high-purity lithium selenide according to claim 1, characterized in that: In step S4, heat treatment is carried out under an inert atmosphere at a temperature of 400-750℃ for 0.5-8 hours.

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