Method for preparing high-purity lithium difluoro (oxalato) borate solid by low-temperature melting method

Abstract

The invention relates to a method for preparing a high-purity lithium difluoro (oxalato) borate solid through a low-temperature melting method, and belongs to the technical field of lithium battery electrolyte additives. The preparation method comprises the following steps: under the protection of argon, adding lithium oxalate, boric acid and lithium fluoride into a reaction kettle, uniformly stirring and mixing, and carrying out a low-temperature melting reaction to form a molten reaction product; naturally cooling the molten reaction product to room temperature, cooling and crystallizing, and separating out solid crystals; washing the solid crystals with absolute ethyl alcohol, performing centrifugal separation, and removing surface impurities through a modified resin adsorbent; drying the washed solid crystals in a vacuum drying oven to obtain a high-purity lithium difluoro (oxalato) borate solid; the modified resin adsorbent is prepared from styrene-divinylbenzene copolymer resin, dichloroethane, allyl phosphine dichloride, benzoyl peroxide and tetraallyl silicate. The lithium difluoro (oxalato) borate prepared by the method is high in purity and high in yield, and meets the use requirements of a high-energy-density lithium ion battery electrolyte.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium battery electrolyte additives, and in particular to a method for preparing high-purity lithium difluorooxalate borate solid by a low-temperature melting method. BACKGROUND

[0002] Lithium difluorooxalate borate is a new type of lithium ion battery electrolyte salt, has excellent electrochemical stability, high and low temperature performance and ionic conductivity, can effectively inhibit the dissolution of the positive electrode material of the battery and the decomposition of the electrolyte, significantly improves the cycle life and safety performance of the lithium ion battery, and has a wide application prospect in the fields of power batteries and energy storage batteries.

[0003] Chinese patent CN119751491A provides a preparation method of lithium difluorooxalate borate, and belongs to the technical field of lithium battery electrolyte additives. A methyl chlorosilane compound is subjected to a substitution reaction with oxalic acid to obtain a bis (methyl silyl) oxalate compound, which is mixed with lithium oxalate, a boron trifluoride complex and an organic solvent to obtain lithium difluorooxalate borate through reaction.

[0004] Chinese patent CN120209010A discloses a synthesis method of lithium difluorooxalate borate, which comprises the following operation steps: S1, passing a negative ion SF6- into a triethyl boron (CH2CH3) 3B solution to perform a preliminary reaction; S2, adding oxalic acid to perform an intermediate reaction; S3, adding lithium hydroxide to perform a final reaction to generate the final reaction product lithium difluorooxalate borate LiC2O4BF2.

[0005] The existing preparation method of lithium difluorooxalate borate mainly adopts a solvent method. The method has obvious defects: on the one hand, the organic solvent is easy to remain in the product, so that the purity of the product is difficult to break through 99.9%, and the residual solvent will affect the performance of the battery electrolyte; on the other hand, the solvent recovery process has high energy consumption, and is easy to produce organic wastewater, pollutes the environment, and does not meet the green production requirements. SUMMARY

[0006] In order to solve the above problems, the application provides a method for preparing high-purity lithium difluorooxalate borate solid by a low-temperature melting method, and the operation steps are as follows, and the mass fraction is as follows: S1, low-temperature melting reaction: under the protection of argon, 70-100 parts of lithium oxalate, 60-74 parts of boric acid and 45-57 parts of lithium fluoride are added into a reaction kettle and uniformly stirred and mixed, and then low-temperature melting reaction is performed to form a molten reaction product; S2, cooling and crystallization: the molten reaction product is naturally cooled to room temperature, and cooling and crystallization are performed to precipitate solid crystals; S3, washing and purification: the solid crystals are washed and centrifuged for 2-3 times, and then a modified resin adsorbent is used to remove surface impurities. S4 vacuum drying: the washed solid crystals are placed in a vacuum drying oven to dry, obtaining high-purity lithium difluorophosphate solid.

[0007] Further, the stirring rate of S1 is 200-500 r / min.

[0008] Further, the low-temperature melting reaction temperature of S1 is 120-180℃, and the time is 3-8h.

[0009] Further, the cooling crystallization temperature of S2 is 0-5℃, and the time is 2-4h.

[0010] Further, the centrifugal separation speed of S3 is 3000-5000 r / min, and the time is 5-10 min.

[0011] Further, the vacuum drying of S4 adopts a stepwise heating method: first drying at 60-70℃ for 2-3h, then heating to 70-80℃ for 4-6h, and finally heating to 90-100℃ for 2-3h.

[0012] Further, the preparation method of the modified resin adsorbent is: A1: according to the mass fraction, 100-120 parts of styrene-divinylbenzene copolymer resin, 1000-1200 parts of dichloroethane, 10-20 parts of allyl dichlorophosphine, 0.8-2.3 parts of benzoyl peroxide, 0.01-0.3 parts of tetraallylsilicate are added to an argon-protected stirred reactor, and stirred and heated to react; A2: after the reaction is completed, washed with anhydrous ethanol for 3-4 times, centrifuged, and then subjected to stepwise vacuum drying to obtain a modified resin adsorbent.

[0013] Further, the stirring rate of A1 is 200-500 r / min.

[0014] Further, the stirring rate of A1 is 200-500 r / min.

[0015] Further, the stepwise vacuum drying of A2 is: first drying at 60-70℃ for 2-3h, then drying at 70-80℃ for 4-6h, and finally drying at 90-100℃ for 2-3h.

[0016] I. Reaction mechanism of modified sulfur ion stabilizer Ethylenediamine as a basic catalyst can abstract the proton of -SLi in 2,5-dimercaptothiadiazole dilithium salt to generate a more nucleophilic thiolate. The thiolate will actively attack the electrophilic site of the epoxy ring on the pentaerythritol glycidyl ether molecule, causing the ring-opening reaction of the epoxy ring to form an oxygen anion intermediate; then the intermediate is converted into a stable hydroxyl group through proton transfer, completing a single addition reaction. Since the pentaerythritol glycidyl ether molecule contains multiple epoxy groups, and there are multiple -SLi groups in the 2,5-dimercaptothiadiazole dilithium salt molecule that can participate in the reaction, the active functional groups remaining after a single reaction will continue to undergo addition reactions, ultimately forming a three-dimensional cross-linked polymer type modified sulfur ion stabilizer containing C-S bonds, hydroxyl groups and thiazole heterocyclic structures.

[0017] II. Technical effects The modified sulfur ion stabilizer can effectively anchor S 2- in the molten reaction system through coordination or hydrogen bonding, avoiding the reaction of S 2- with oxygen in the system to form oxidation impurities; at the same time, the polymer structure can form physical wrapping for S 2- , reducing the volatilization loss of S 2- during the reaction. In addition, the hydroxyl groups in the stabilizer molecule can also coordinate with metal ions in the system to prevent the formation of inorganic impurities, reducing the types and total amount of impurities in lithium sulfide products from multiple aspects.

[0018] The modified sulfur ion stabilizer has good thermal stability and can adapt to the temperature range of low-temperature molten reaction. It will not decompose during the reaction and can continuously play a role and inhibit the occurrence of various side reactions. At the same time, the stabilizer is an organic polymer, which is significantly different from the physical properties of inorganic product lithium sulfide. It can be completely separated from lithium sulfide by conventional separation methods and will not be left in the lithium sulfide product, effectively ensuring and improving the purity of lithium sulfide.

[0019] The modified sulfur ion stabilizer has a targeted control effect on the possible introduction of sodium, chlorine and other impurities in the reaction system. Through the specific adsorption or blocking effect of its molecular structure, the retention of sodium, chlorine and other impurities in the lithium sulfide product is reduced; compared with the scheme of not using the stabilizer or using a single component stabilizer, the content of key impurities can be further reduced, providing additional protection for the lithium sulfide product to achieve high-purity standards. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 F-NMR nuclear magnetic spectrum of high-purity lithium difluoroborate oxalate prepared in Example 6. DETAILED DESCRIPTION

[0021] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined object of the present application, the following embodiments and comparative examples are described in detail. 1. Purity of lithium difluorooxalate borate: determined by a JNM-ECZ600R / S1 nuclear magnetic resonance instrument of Zhejiang University; 2. Yield of lithium difluorooxalate borate: yield (%) = actual product mass / theoretical product mass x 100%.

[0022] Example 1 A method for preparing high-purity lithium difluorooxalate borate solid by a low-temperature melting method, the operation steps of which are as follows: S1. Low-temperature melting reaction: 70 g of lithium oxalate, 60 g of boric acid, and 45 g of lithium fluoride were added into a reaction kettle under the protection of argon, stirred and mixed uniformly, and subjected to low-temperature melting reaction to form a molten reaction product; S2. Cooling crystallization: the molten reaction product was naturally cooled to room temperature to form solid crystals by cooling crystallization; S3. Washing and purification: the solid crystals were washed and centrifuged twice with anhydrous ethanol, and then subjected to adsorption by a modified resin adsorbent to remove surface impurities; S4. Vacuum drying: the washed solid crystals were dried in a vacuum drying oven to obtain high-purity lithium difluorooxalate borate solid.

[0023] The stirring rate of S1 is 200 r / min.

[0024] The low-temperature melting reaction temperature of S1 is 120℃, and the time is 3 h.

[0025] The cooling crystallization temperature of S2 is 0℃, and the time is 2 h.

[0026] The centrifugation speed of S3 is 3000 r / min, and the time is 5 min.

[0027] The vacuum drying of S4 is performed by a stepwise heating method: first dried at 60℃ for 2 h, then heated to 70℃ for 4 h, and finally heated to 90℃ for 2 h.

[0028] The preparation method of the modified resin adsorbent is as follows: A1: 100 g of styrene-divinylbenzene copolymer resin, 1000 g of dichloroethane, 10 g of allyl phosphine dichloride, 0.8 g of benzoyl peroxide, and 0.01 g of tetraallylsilicate CAS: 1067-43-2 were added into an argon-protected stirring reaction kettle, and subjected to stirring and temperature rising reaction; A2: after the reaction was completed, the reaction product was washed with anhydrous ethanol for 3 times, centrifuged, and then subjected to stepwise vacuum drying to obtain the modified resin adsorbent.

[0029] The stirring rate of A1 is 200 r / min.

[0030] The reaction temperature of A1 is 70℃, and the time is 8h.

[0031] The step of A2 segment vacuum drying is: first drying at 60℃ for 2h, then drying at 70℃ for 4h, and finally drying at 90℃ for 2h.

[0032] Example 2 A method for preparing high-purity lithium difluorophosphate solid by low-temperature melting method, the operation steps are: S1 low-temperature melting reaction: under the protection of argon, 80g lithium oxalate, 65g boric acid, 49g lithium fluoride are added to the reaction kettle and stirred to mix uniformly, and then low-temperature melting reaction is carried out to form a molten reaction product; S2 cooling crystallization: the molten reaction product is naturally cooled to room temperature, and then cooling crystallization is carried out to precipitate solid crystals; S3 washing and purification: the solid crystals are washed and centrifuged twice with anhydrous ethanol, and then a modified resin adsorbent is used to remove surface impurities; S4 vacuum drying: the washed solid crystals are placed in a vacuum drying oven to obtain high-purity lithium difluorophosphate solid.

[0033] The stirring rate of S1 is 300 r / min.

[0034] The low-temperature melting reaction temperature of S1 is 140℃, and the time is 4h.

[0035] The cooling crystallization temperature of S2 is 0℃, and the time is 3h.

[0036] The centrifugal separation speed of S3 is 4000 r / min, and the time is 5min.

[0037] The step of S4 vacuum drying adopts a segmented heating mode: first drying at 65℃ for 2.5h, then heating to 75℃ for 5h, and finally heating to 95℃ for 2.5h.

[0038] The preparation method of the modified resin adsorbent is: A1: 105g of styrene-divinylbenzene copolymer resin, 1050g of dichloroethane, 14g of dichloroallyl phosphine, 1.3g of benzoyl peroxide, and 0.1g of tetraallylsilicate CAS: 1067-43-2 are added to an argon-protected stirring reaction kettle, and then stirring and heating reaction are carried out; A2: after the reaction is completed, the mixture is washed with anhydrous ethanol for 3 times, and then centrifuged and separated, and then segmental vacuum drying is carried out to obtain the modified resin adsorbent.

[0039] The stirring rate of A1 is 300 r / min.

[0040] The reaction temperature of A1 is 70℃, and the time is 9h.

[0041] The step of A2 segment vacuum drying is: first drying at 65℃ for 2.5h, then drying at 75℃ for 5h, and finally drying at 95℃ for 2.5h.

[0042] Example 3 A method for preparing high-purity lithium difluorophosphate solid by low-temperature melting method, the operation steps are: S1 low-temperature melting reaction: under the protection of argon, 90g lithium oxalate, 70g boric acid, 53g lithium fluoride are added into a reaction kettle and stirred to mix uniformly, then low-temperature melting reaction is carried out to form a molten reaction product; S2 cooling crystallization: the molten reaction product is naturally cooled to room temperature to form solid crystals by cooling crystallization; S3 washing and purification: the solid crystals are washed and centrifuged for 3 times, and then modified resin adsorbent is used to remove surface impurities; S4 vacuum drying: the washed solid crystals are dried in a vacuum drying oven to obtain high-purity lithium difluorophosphate solid.

[0043] The stirring rate of S1 is 400 r / min.

[0044] The low-temperature melting reaction temperature of S1 is 160℃, and the time is 7h.

[0045] The cooling crystallization temperature of S2 is 5℃, and the time is 3h.

[0046] The centrifugal separation speed of S3 is 4000 r / min, and the time is 10 min.

[0047] The vacuum drying of S4 adopts a stepwise heating mode: first drying at 65℃ for 2.5h, then heating to 75℃ for 5h, and finally heating to 95℃ for 2.5h.

[0048] The preparation method of the modified resin adsorbent is: A1: 115g of styrene-divinylbenzene copolymer resin, 1150g of dichloroethane, 18g of allyl phosphine dichloride, 2g of benzoyl peroxide, and 0.2g of tetraallylsilicate CAS: 1067-43-2 are added into an argon-protected stirring reaction kettle, and then stirring and heating reaction are carried out; A2: after the reaction is completed, the mixture is washed with anhydrous ethanol for 4 times, and then centrifuged and dried to obtain the modified resin adsorbent.

[0049] The stirring rate of A1 is 400 r / min.

[0050] The reaction temperature of A1 is 75℃, and the time is 9h.

[0051] The step of A2 segmental vacuum drying is: first drying at 65℃ for 2.5h, then drying at 75℃ for 5h, and finally drying at 95℃ for 2.5h.

[0052] Example 4 A method for preparing high-purity lithium difluorophosphate solid by low-temperature melting method, the operation steps are: S1 low-temperature melting reaction: under the protection of argon, 100g lithium oxalate, 74g boric acid, 57g lithium fluoride are added into a reaction kettle and stirred to mix uniformly, then low-temperature melting reaction is carried out to form a molten reaction product; S2 cooling crystallization: the molten reaction product is naturally cooled to room temperature to carry out cooling crystallization, and solid crystals are precipitated; S3 washing and purification: the solid crystals are washed and centrifuged for 3 times, and then modified resin adsorbent is used to remove surface impurities; S4 vacuum drying: the washed solid crystals are placed in a vacuum drying oven to obtain high-purity lithium difluorophosphate solid.

[0053] The stirring rate of S1 is 500 r / min.

[0054] The low-temperature melting reaction temperature of S1 is 180℃, and the time is 8h.

[0055] The cooling crystallization temperature of S2 is 5℃, and the time is 4h.

[0056] The centrifugal separation speed of S3 is 5000 r / min, and the time is 10 min.

[0057] The step of S4 vacuum drying adopts a segmented heating mode: first drying at 70℃ for 3h, then heating to 80℃ for 6h, and finally heating to 100℃ for 3h.

[0058] The preparation method of the modified resin adsorbent is: A1: 120g of styrene-divinylbenzene copolymer resin, 1200g of dichloroethane, 20g of allyl dichlorophosphine, 2.3g of benzoyl peroxide, and 0.3g of tetraallylsilicate CAS: 1067-43-2 are added into an argon-protected stirring reaction kettle, and stirring and heating reaction are carried out; A2: after the reaction is completed, the mixture is washed with anhydrous ethanol for 4 times, and then centrifuged and subjected to segmental vacuum drying to obtain the modified resin adsorbent.

[0059] The stirring rate of A1 is 500 r / min.

[0060] The reaction temperature of A1 is 75℃, and the time is 10h.

[0061] The step of A2 segment vacuum drying is: first drying at 70℃ for 3h, then drying at 80℃ for 6h, and finally drying at 100℃ for 3h.

[0062] Comparative Example 1 A method for preparing high-purity lithium difluorophosphate solid by low-temperature melting method, the operation steps are: S1 low-temperature melting reaction: under the protection of argon, 70g of lithium oxalate, 60g of boric acid, and 45g of lithium fluoride are added to a reaction kettle and stirred and mixed uniformly to perform low-temperature melting reaction to form a molten reaction product; S2 cooling crystallization: the molten reaction product is naturally cooled to room temperature to perform cooling crystallization to precipitate solid crystals; S3 washing and purification: the solid crystals are washed with anhydrous ethanol and centrifuged twice to remove surface impurities; S4 vacuum drying: the washed solid crystals are placed in a vacuum drying oven to obtain high-purity lithium difluorophosphate solid.

[0063] The stirring rate of S1 is 200 r / min.

[0064] The low-temperature melting reaction temperature of S1 is 120℃, and the time is 3h.

[0065] The cooling crystallization temperature of S2 is 0℃, and the time is 2h.

[0066] The centrifugation speed of S3 is 3000 r / min, and the time is 5min.

[0067] The step of S4 vacuum drying adopts a segmented heating mode: first drying at 60℃ for 2h, then heating to 70℃ for 4h, and finally heating to 90℃ for 2h.

[0068] Comparative Example 2 A method for preparing high-purity lithium difluorophosphate solid by low-temperature melting method, the operation steps are: S1 low-temperature melting reaction: under the protection of argon, 70g of lithium oxalate, 60g of boric acid, and 45g of lithium fluoride are added to a reaction kettle and stirred and mixed uniformly to perform low-temperature melting reaction to form a molten reaction product; S2 cooling crystallization: the molten reaction product is naturally cooled to room temperature to perform cooling crystallization to precipitate solid crystals; S3 washing and purification: the solid crystal is washed and centrifuged twice with anhydrous ethanol, and then adsorbed by a modified resin adsorbent to remove surface impurities; S4 vacuum drying: the washed solid crystal is dried in a vacuum drying oven to obtain high-purity lithium difluorophosphate solid.

[0069] The stirring rate of S1 is 200 r / min.

[0070] The low-temperature melting reaction temperature of S1 is 120 DEG C, and the time is 3 h.

[0071] The cooling crystallization temperature of S2 is 0 DEG C, and the time is 2 h.

[0072] The centrifugal separation speed of S3 is 3000 r / min, and the time is 5 min.

[0073] The vacuum drying of S4 adopts a stepwise heating mode: first dried at 60 DEG C for 2 h, then heated to 70 DEG C for 4 h, and finally heated to 90 DEG C for 2 h.

[0074] The preparation method of the modified resin adsorbent is: A1: 100 g of styrene-divinylbenzene copolymer resin, 1000 g of dichloroethane, 0.8 g of benzoyl peroxide, and 0.01 g of tetraallylsilicate CAS: 1067-43-2 are added to an argon-protected stirred reaction kettle, and the stirring is heated and reacted; A2: after the reaction is completed, the mixture is washed with anhydrous ethanol for 3 times, centrifuged, and then subjected to stepwise vacuum drying to obtain a modified resin adsorbent.

[0075] The stirring rate of A1 is 200 r / min.

[0076] The reaction temperature of A1 is 70 DEG C, and the time is 8 h.

[0077] The stepwise vacuum drying of A2 is: first dried at 60 DEG C for 2 h, then dried at 70 DEG C for 4 h, and finally dried at 90 DEG C for 2 h.

[0078] Comparative Example 3 A method for preparing high-purity lithium difluorophosphate solid by low-temperature melting method, the operation steps are: S1 low-temperature melting reaction: under the protection of argon, 70 g of lithium oxalate, 60 g of boric acid, and 45 g of lithium fluoride are added to a reaction kettle, stirred and mixed uniformly, and subjected to low-temperature melting reaction to form a molten reaction product; S2 cooling and crystallization: the molten reaction product is naturally cooled to room temperature, and the solid crystal is precipitated by cooling and crystallization; S3 washing and purification: the solid crystal is washed and centrifuged twice with anhydrous ethanol, and then adsorbed by a modified resin adsorbent to remove surface impurities; S4 vacuum drying: the washed solid crystal is dried in a vacuum drying oven to obtain high-purity lithium difluoroboric acid oxalate solid.

[0079] The stirring rate in S1 is 200 r / min.

[0080] The low-temperature melting reaction temperature in S1 is 120 DEG C, and the time is 3 h.

[0081] The cooling crystallization temperature in S2 is 0 DEG C, and the time is 2 h.

[0082] The centrifugal separation speed in S3 is 3000 r / min, and the time is 5 min.

[0083] The vacuum drying in S4 adopts a stepwise heating mode: first drying at 60 DEG C for 2 h, then heating to 70 DEG C for 4 h, and finally heating to 90 DEG C for 2 h.

[0084] The preparation method of the modified resin adsorbent is as follows: A1: 100 g of styrene-divinylbenzene copolymer resin, 1000 g of dichloroethane, 10 g of allyl dichlorophosphine, and 0.8 g of benzoyl peroxide are added to an argon-protected stirring reaction kettle, and the mixture is stirred and heated to react; A2: after the reaction is completed, the mixture is washed with anhydrous ethanol for 3 times, centrifuged, and then subjected to stepwise vacuum drying to obtain the modified resin adsorbent.

[0085] The stirring rate in A1 is 200 r / min.

[0086] The reaction temperature in A1 is 70 DEG C, and the time is 8 h.

[0087] The stepwise vacuum drying in A2 is as follows: first drying at 60 DEG C for 2 h, then drying at 70 DEG C for 4 h, and finally drying at 90 DEG C for 2 h.

[0088] Table 1 shows the detection results of the purity and yield of high-purity lithium difluoroboric acid oxalate solid in the examples and comparative examples.

[0089] As can be seen from the data in Table 1, the present application (Examples 1-4) has significant advantages over Comparative Examples 1-3 in terms of core indicators: in terms of purity, the purity of the product of the examples is much higher than that of the comparative examples, and the overall level is maintained at a high level.

[0090] The above merely describes the preferred embodiments of the present application, and is not intended to limit the present application in any form. Although the present application has been disclosed with the preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, as long as the changes or modifications do not deviate from the technical solution of the present application. Any modification, change, equivalent change and modification of the above embodiments made according to the technical essence of the present application still belong to the scope of the technical solution of the present application.

Claims

1. A method for preparing high-purity lithium difluoro(oxalato)borate solid by low-temperature melting method, the operation steps being as follows, in terms of mass fraction: S1, low-temperature melting reaction: under the protection of argon, 70-100 parts of lithium oxalate, 60-74 parts of boric acid and 45-57 parts of lithium fluoride are added into a reaction kettle and stirred to mix uniformly, and then low-temperature melting reaction is carried out to form a molten reaction product; S2, cooling crystallization: the molten reaction product is naturally cooled to room temperature to carry out cooling crystallization, and solid crystals are precipitated; S3, washing and purification: the solid crystals are washed with anhydrous ethanol, centrifuged, and then adsorbed by a modified resin adsorbent to remove surface impurities; S4, vacuum drying: the washed solid crystals are placed in a vacuum drying oven to obtain high-purity lithium difluoro(oxalato)borate solid; The modified resin adsorbent is prepared by reaction of styrene-divinylbenzene copolymer resin, allyl phosphine dichloride, benzoyl peroxide and tetraallylsilicate.

2. A process for the preparation of high purity lithium bisfluorosulfonyl imide solid by low temperature melt method as claimed in claim 1, wherein: The stirring rate in S1 is 200-500 r / min.

3. A process for the preparation of high purity lithium bisfluorosulfonyl imide solid by low temperature melt method as claimed in claim 1, wherein: The low-temperature melting reaction temperature in S1 is 120-180℃, and the time is 3-8 h.

4. A process for the preparation of high purity lithium bisfluorosulfonyl imide solid by low temperature melt method as claimed in claim 1, wherein: The cooling crystallization temperature in S2 is 0-5℃, and the time is 2-4 h.

5. A process for the preparation of high purity lithium bisfluorosulfonyl imide solid by low temperature melt method as claimed in claim 1, wherein: The centrifugation speed in S3 is 3000-5000 r / min, and the time is 5-10 min.

6. A process for the preparation of high purity lithium bisfluorosulfonyl imide solid by low temperature melt method as claimed in claim 1, wherein: The vacuum drying in S4 is carried out in a stepwise heating mode: first drying at 60-70℃ for 2-3 h, then drying at 70-80℃ for 4-6 h, and finally drying at 90-100℃ for 2-3 h.

7. The method for preparing high-purity lithium difluorooxalate borate solid by low-temperature melting according to claim 1, characterized in that: The preparation method of the modified resin adsorbent is as follows: A1: 100-120 parts of styrene-divinylbenzene copolymer resin, 1000-1200 parts of dichloroethane, 10-20 parts of allyl phosphine dichloride, 0.8-2.3 parts of benzoyl peroxide and 0.01-0.3 parts of tetraallylsilicate are added into an argon-protected stirring reaction kettle, and stirring and heating reaction are carried out; A2: after the reaction is completed, the product is washed with anhydrous ethanol for 3-4 times, centrifuged, and then subjected to stepwise vacuum drying to obtain the modified resin adsorbent.

8. A process for the preparation of high purity lithium bisfluorosulfonyl imide solid by low temperature melt method as claimed in claim 7, wherein: The stirring rate in A1 is 200-500 r / min.

9. The method for preparing high-purity lithium difluorooxalate borate solid by low-temperature melting according to claim 7, characterized in that: The reaction temperature in A1 is 70-75℃, and the time is 8-10 h.

10. The method for preparing high-purity lithium difluorooxalate borate solid by low-temperature melting according to claim 7, characterized in that: The stepwise vacuum drying in A2 is as follows: first drying at 60-70℃ for 2-3 h, then drying at 70-80℃ for 4-6 h, and finally drying at 90-100℃ for 2-3 h.

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