A method for preparing a lithium difluorodioxalate phosphate concentrate

Abstract

The application relates to a preparation method of a lithium difluorodioxalate phosphate concentrated solution, the lithium difluorodioxalate phosphate concentrated solution is composed of lithium difluorodioxalate phosphate and an aprotic solvent, the aprotic solvent includes any one or a combination of at least two of diethyl carbonate, methyl ethyl carbonate, ethylene carbonate or propylene carbonate, and the concentration of lithium difluorodioxalate phosphate in the lithium difluorodioxalate phosphate concentrated solution is 10-35 wt%. The lithium difluorodioxalate phosphate concentrated solution provided by the application exists in the state of an aprotic electrolyte, an evaporation crystallization process is omitted, and the production cost is reduced; the product can be transported through a pipeline, and the product transportation cost is reduced; compared with lithium difluorodioxalate phosphate solid, the process of re-dissolving during use is omitted, the risk of impurity introduction is avoided, and the use cost is reduced.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of battery manufacturing, in particular to a preparation method of a lithium difluorophosphate lithium oxalate concentrate. BACKGROUND

[0002] Lithium difluorophosphate lithium oxalate is an important electrolyte and is mainly applied to non-aqueous electrolyte of lithium (sodium) ion batteries, so that the purity and impurities are extremely high. The content of impurities in lithium difluorophosphate lithium oxalate, such as water, alkali metal, heavy metal, chloride ion, sulfate radical or free acid, must be strictly controlled, otherwise the problems of increased internal resistance of the battery, fast capacity attenuation of the battery, shortened cycle life and the like will be caused, and the safety of the battery is affected.

[0003] Therefore, it has important practical significance to obtain lithium difluorophosphate lithium oxalate products with high purity and low content of harmful impurities.

[0004] In addition, the lithium difluorophosphate lithium oxalate solid needs to be dissolved again in the use process, and part of impurities will be introduced in the dissolution process, so that the use cost is increased. Therefore, a new scheme needs to be provided to directly obtain lithium difluorophosphate lithium oxalate solution products with high purity and low impurity content, simplify the preparation process steps and realize direct application in lithium (sodium) ion batteries. SUMMARY

[0005] To solve the above technical problems, the application provides a lithium difluorophosphate lithium oxalate concentrate, which exists in the form of an aprotic electrolyte, has low acidity, low chlorine content and high purity and can be directly used for lithium ion battery or sodium ion battery electrolyte preparation. Compared with the process mentioned in the patent of Central Glass, by improving the feeding conditions and mode of lithium hexafluorophosphate, interval dissolution is carried out, the decomposition of lithium hexafluorophosphate caused by a large amount of heat generated due to a large amount of dissolution of lithium hexafluorophosphate is avoided, the increase of the acidity of the system is caused, a large amount of time is saved under low temperature conditions, the production efficiency is effectively improved, meanwhile, by reducing the water content of oxalic acid, the side reaction in the reaction process is reduced, the decomposition of the product is effectively reduced, and the product purity is improved. In addition, by optimizing the feeding mode of silicon tetrachloride, the silicon tetrachloride is added dropwise from below, the amount of silicon tetrachloride is reduced, the equipment cleaning cost caused by the treatment of silicon tetrachloride is reduced, the production efficiency is greatly improved, and the production cost is reduced. At the same time, the lithium difluorophosphate lithium oxalate concentrate prepared saves the evaporation crystallization process, and the energy consumption is greatly reduced. In transportation, the product can be transported through a pipeline, the product transportation cost is further reduced, and the safety problem in the transportation process is improved. Compared with the lithium difluorophosphate lithium oxalate solid, the process of re-dissolution in use is omitted, the risk of impurity introduction is avoided, and the use cost is greatly reduced.

[0006] To achieve the above object, the present application adopts the following technical solutions:

[0007] In a first aspect, the present application provides a lithium difluorodioxalate phosphate concentrate, which is composed of lithium difluorodioxalate phosphate and an aprotic solvent, and the aprotic solvent includes any one of diethyl carbonate, methyl ethyl carbonate, ethylene carbonate or propylene carbonate or a combination of at least two of them.

[0008] The concentration of lithium difluorodioxalate phosphate in the lithium difluorodioxalate phosphate concentrate is 10-35wt%, for example, 10wt%, 14wt%, 18wt%, 20wt%, 22wt%, 24wt%, 26wt%, 28wt%, 30wt%, 32wt%, 34wt% or 35wt% and the like.

[0009] The lithium difluorodioxalate phosphate concentrate provided by the present application exists in the form of an aprotic electrolyte, compared with lithium difluorodioxalate phosphate solid, the process of re-dissolving when used is omitted, the risk of introducing impurities is avoided, and the use cost is reduced.

[0010] The following is a preferred technical solution of the present application, but not as a limitation of the technical solutions provided by the present application, through the following preferred technical solution, the technical purpose and beneficial effect of the present application can be better achieved and realized.

[0011] Preferably, the acidity of the lithium difluorodioxalate phosphate concentrate is <100ppm, for example, 90ppm, 80ppm, 70ppm, 60ppm, 50ppm, 40ppm, 30ppm, 20ppm, 10ppm or 1ppm and the like, the water content is <50ppm, for example, 40ppm, 35ppm, 30ppm, 25ppm, 20ppm, 15ppm, 10ppm, 5ppm or 1ppm and the like, the chloride ion concentration is <20ppm, for example, 19ppm, 18ppm, 17ppm, 16ppm, 15ppm, 14ppm, 13ppm, 12ppm, 11ppm, 10ppm, 9ppm, 8ppm, 7ppm, 6ppm, 5ppm, 4ppm, 3ppm, 2ppm or 1ppm and the like.

[0012] In the present application, the acidity, water content and chloride ion concentration in the lithium difluorodioxalate phosphate concentrate are all low, which avoids the influence of impurities on the performance of the electrolyte during use, and achieves the use standard of battery-grade electrolyte.

[0013] In a second aspect, the present application further provides a preparation method of the lithium difluorodioxalate phosphate concentrate according to the first aspect, which comprises the following steps:

[0014] (1) In inert dry atmosphere, lithium hexafluorophosphate, aprotic solvent and oxalic acid are mixed uniformly to obtain a reaction solution (water content of oxalic acid after drying treatment is required to be ≤200ppm);

[0015] (2) In inert dry atmosphere, silicon tetrachloride is added dropwise into the reaction solution in step (1) to react, and then degassed to obtain a concentrated liquid precursor;

[0016] (3) In inert dry atmosphere, the concentrated liquid precursor in step (2) is treated by ion exchange resin to remove acid to obtain a lithium difluorophosphate oxalate concentrated solution.

[0017] The preparation method of the lithium difluorophosphate oxalate concentrated solution provided by the application avoids using hydrogen fluoride as a raw material, and also avoids the risks brought by hydrogen fluoride, and further improves the yield; the impurities are removed by degassing and concentration and resin treatment, and the obtained lithium difluorophosphate oxalate concentrated solution has high purity.

[0018] In the application, the whole reaction needs to be carried out in an inert dry atmosphere, otherwise the acidity, chloride ion and water content in the prepared lithium difluorophosphate oxalate concentrated solution system will be high.

[0019] Preferably, the inert dry atmosphere includes dry nitrogen or dry argon;

[0020] Preferably, a method for secondary purification of the inert dry atmosphere is as follows:

[0021] First stage: most of the water in the gas is removed by silica gel desiccant;

[0022] Second stage: the water in the gas is reduced to ≤5ppm by using the porous structure and copper ion coordination of the metal organic framework material HKUST-1 adsorption column to selectively adsorb water;

[0023] The specific operation is as follows:

[0024] First stage silica gel drying: coarse pore (pore size 60-100Å) or fine pore (pore size 20-30Å) silica gel with a bulk density of 0.6-0.8g / cm³ is selected; the initial water content ≤50ppm is pretreated to ≤20ppm at a gas flow rate of 4-10L / min.

[0025] Second stage HKUST-1 adsorption: the HKUST-1 adsorption column is filled with 20%-40% of the adsorption column volume at a gas flow rate of 5-10L / min; the adsorption capacity is ≥0.5g / g MOF under the adsorption conditions of flow rate ≤5L / min and temperature 20-30℃;

[0026] The target purity of the secondary purification process is moisture ≤5ppm, oxygen content ≤10ppm,

[0027] Preferably, the mass ratio of the lithium hexafluorophosphate to the aprotic solvent in step (1) is 1:(2-20), for example 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19 or 1:20, etc., preferably 1:(8-18).

[0028] When the mass ratio of the lithium hexafluorophosphate to the aprotic solvent in the present application is 1:(8-18), the prepared lithium difluorophosphate dioxalate concentrated solution not only has low acidity, but also has high purity.

[0029] Preferably, the molar ratio of the lithium hexafluorophosphate to the oxalic acid in step (1) is 1:(1.995-2.1000), for example 1:1.995, 1:1.997, 1:1.999, 1:2.004, 1:1, 1:2.009, 1:2.014, 1:2.019 or 1:2.1000, etc., preferably 1:(1.995-2.015).

[0030] When the molar ratio of the lithium hexafluorophosphate to the oxalic acid in the present application is 1:(0.995-2.015), the prepared lithium difluorophosphate dioxalate concentrated solution not only has low acidity, but also has high purity.

[0031] Preferably, the mixing in step (1) comprises: first mixing and dissolving the lithium hexafluorophosphate with the aprotic solvent, and then adding the oxalic acid.

[0032] Preferably, the mixing and dissolving mode comprises stirring the intermediate process to maintain the temperature.

[0033] Preferably, the stirring time is 5-15min, for example 5min, 6min, 7min, 8min, 9min, 10min, 11min, 12min, 13min, 14min or 15min, etc.

[0034] Preferably, the temperature for dissolving the lithium hexafluorophosphate is -10-10℃, for example -10℃, -5℃, 0℃, 5℃, 10℃, etc.

[0035] Preferably, the temperature for dissolving the oxalic acid is 0-40℃, for example 0℃, 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, etc.

[0036] Preferably, the molar ratio of the lithium hexafluorophosphate in step (1) to the silicon tetrachloride in step (2) is 1:(0.995-1.100), for example 1:0.995, 1:0.997, 1:1.000, 1:1.005, 1:1.010, 1:1.020, 1:1.030, 1:1.040, 1:1.050, 1:1.080, or 1:1.100, etc., preferably 1:(0.998-1.015).

[0037] When the molar ratio of the lithium hexafluorophosphate in step (1) to the silicon tetrachloride in step (2) is 1:(0.998-1.015) in the present application, the prepared lithium difluorophosphate dioxalate concentrated solution has low acidity and high purity.

[0038] Preferably, the temperature of the reaction solution in step (1) is -5-40℃, for example -5℃, 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, etc.

[0039] Preferably, the temperature of the reaction in step (2) is 0-50℃, for example 0℃, 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, etc.

[0040] In the present application, when the temperature of the reaction is 0-50℃, the silicon tetrachloride can effectively participate in the reaction. If the temperature is too high, the silicon tetrachloride volatilizes seriously and cannot participate in the reaction. If the temperature is too low, the reaction speed is slow and the reaction is incomplete.

[0041] Preferably, the reaction time is 1-8h, for example 1h, 2h, 3h, 4h, 5h, 6h, 7h, or 8h, etc.

[0042] In the present application, when the face-down dripping method is used, the silicon tetrachloride can effectively participate in the reaction. If the liquid-up dripping method is used, the silicon tetrachloride volatilizes seriously and cannot participate in the reaction, and the amount of silicon tetrachloride used is too much and the subsequent impurity ions are difficult to remove. If the temperature is too low, the reaction speed is slow and the reaction is incomplete, causing energy waste and cost increase.

[0043] It should be noted that the temperature of the reaction in step (2) is consistent with the temperature of the reaction solution in step (1).

[0044] Preferably, the degassing in step (2) includes positive pressure inert gas degassing or negative pressure degassing.

[0045] It should be noted that the positive pressure inert gas degassing or the negative pressure degassing can remove hydrogen chloride and silicon tetrafluoride in the system after the reaction is completed, but the positive pressure inert gas degassing takes a little longer time.

[0046] In the present application, the degassing method is used to further reduce the hydrogen chloride and silicon tetrafluoride in the system after the reaction, and to reduce the acidity and chloride ion concentration of the system.

[0047] Preferably, the pressure of the degassing in step (2) is 0.5-10 kPa, such as 0.5 kPa, 1 kPa, 1.5 kPa, 2 kPa, 2.5 kPa, 3 kPa, 3.5 kPa, 4 kPa, 4.5 kPa, 5 kPa, 5.5 kPa, 6 kPa, 6.5 kPa, 7 kPa, 7.5 kPa, 8 kPa, 8.5 kPa, 9 kPa, 9.5 kPa, or 10 kPa, etc.

[0048] Preferably, the temperature of the degassing in step (2) is 0-50℃, such as 0℃, 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, etc., and the optimal temperature is 20-40℃. If the temperature is too high, the product will be finely decomposed, the color and purity will be reduced accordingly, and the product performance will be affected.

[0049] Preferably, the time of the degassing in step (2) is 2-6 h, such as 2 h, 3 h, 4 h, 5 h, or 6 h, etc.

[0050] Preferably, the resin in the acid removal treatment in step (3) includes strong basic anion resin and / or weak basic anion resin.

[0051] Preferably, before the resin treatment in step (3), a non-protic solvent is further added.

[0052] It should be noted that before the resin treatment in step (3), the concentration of the concentrated liquid precursor in step (2) needs to be 0.5-2 wt% higher than the target lithium bis(difluorodioxalato)phosphate concentrated liquid product concentration. If the concentration of the concentrated liquid precursor in step (2) is too high, that is, the difference from the target lithium bis(difluorodioxalato)phosphate concentrated liquid product concentration exceeds 0.5-2 wt%, a non-protic solvent needs to be further added.

[0053] In the present application, the resin treatment of the concentrated liquid precursor can further effectively reduce the acid, chloride ion, and water content in the system, and meet the use standard of battery-grade electrolyte.

[0054] As a preferred technical solution, the preparation method comprises the following steps:

[0055] (1) In an inert dry atmosphere, lithium hexafluorophosphate and a non-protic solvent are mixed and stirred for 5-15 min to dissolve, and then oxalic acid is added and uniformly mixed, and the temperature of the obtained reaction solution is controlled to be -5-40℃;

[0056] The mass ratio of the lithium hexafluorophosphate to the aprotic solvent is 1: (8-18), the molar ratio of the lithium hexafluorophosphate to the oxalic acid is 1: (1.995-2.015), and the inert dry atmosphere comprises dry nitrogen or dry argon.

[0057] (2) The silicon tetrachloride is added dropwise into the reaction solution in step (1), after the dropwise addition is completed, the reaction is carried out at 0-50 DEG C for 1-8 hours, and the degassing is carried out under the conditions of a pressure of 0.5-10 kPa and a temperature of 20-40 DEG C for 2-6 hours to obtain a precursor concentrate;

[0058] The molar ratio of the lithium hexafluorophosphate in step (1) to the silicon tetrachloride in step (2) is 1: (0.995-1.015), and the degassing comprises positive pressure inert gas degassing or negative pressure degassing.

[0059] (3) The concentrate precursor in step (2) is subjected to ion exchange resin treatment to obtain a lithium difluoride dioxalate phosphate concentrate;

[0060] If the concentration of the concentrate precursor in step (2) is too high, that is, the difference between the concentration and the target lithium difluoride dioxalate phosphate concentrate product concentration exceeds 0.5-2 wt%, before the resin treatment, non-protic solvent is additionally added to the product concentration which is 0.5-2 wt% higher than the target lithium difluoride dioxalate phosphate concentrate product concentration, and the resin in the resin treatment comprises strong basic anion resin and / or weak basic anion resin.

[0061] Further, a fluoracylation treatment method of strong basic anion resin is provided to prepare a fluoropyridyl strong basic anion resin, and the method is as follows:

[0062] According to mass parts, 100-120 parts of strong basic anion resin, 10-20 parts of o-fluorobenzoyl chloride, 0.05-0.4 parts of 2-fluoro-6-pyridine formyl chloride (CAS: 64197-03-1), 1000-1500 parts of dichloroethane, and 2-4 parts of zinc chloride are added into a polymerization kettle, the reaction temperature is controlled at 40-50 DEG C, the reaction is carried out in the dark for 10-20 hours, filtration is carried out, dichloroethane is washed until there is no chloride ion, drying is carried out, and a fluoropyridyl strong basic anion resin is obtained.

[0063] The strong basic anion resin comprises: D201: macroporous strong basic styrene anion exchange resin, D202: macroporous type II strong basic anion resin, and 201x7 anion exchange resin.

[0064] The weak basic anion resin comprises: D301 macroporous weak basic anion exchange resin, D311 macroporous weak basic acrylic anion exchange resin, and Amberlite IRA-45 macroporous weak basic anion exchange resin.

[0065] The anion resin reaction mechanism is as follows:

[0066] Coordination substitution reaction: in step (1), lithium hexafluorophosphate is dissociated into ions in an aprotic solvent, oxalic acid acts as a bidentate ligand, and PF6 - occurs a coordination exchange reaction, gradually replaces the fluoride ion to form an intermediate complex; in step (2), silicon tetrachloride as a Lewis acid promotes the reaction, so that the oxalate completely replaces the two fluorine atoms in PF6 - , generates difluorodioxalate phosphate, and combines with lithium ions to form lithium difluorodioxalate phosphate.

[0067] Ion exchange purification: in step (3), strong and weak basic anion resins are used to adsorb residual PF6 - , Cl - and other anions and acidic impurities through electrostatic interaction, hydrogen bonding or coordination; after fluoracylation treatment of the fluoropyridyl strong basic anion resin, the selective adsorption of fluorinated impurity ions is enhanced, and the purification effect is further improved.

[0068] In a third aspect, the application also provides an application of the lithium difluorodioxalate phosphate concentrate, wherein the lithium difluorodioxalate phosphate concentrate prepared by the preparation method of the second aspect is applied to prepare a non-aqueous electrolyte for lithium ion batteries or sodium ion batteries.

[0069] Compared with the prior art, the application has at least the following beneficial effects:

[0070] 1) The lithium difluorodioxalate phosphate concentrate provided by the application exists in the form of an aprotic electrolyte, has low acidity, low chlorine content and high purity, and can be directly used for electrolyte preparation for lithium ion batteries or sodium ion batteries;

[0071] 2) The application improves the feeding conditions and methods of lithium hexafluorophosphate, and performs interval dissolution, which avoids the decomposition of lithium hexafluorophosphate due to the generation of a large amount of heat caused by the dissolution of lithium hexafluorophosphate, thereby increasing the acidity of the system, and saves a large amount of time under low temperature conditions, and effectively improves the production efficiency;

[0072] 3) The application optimizes the water content of oxalic acid, reduces side reactions in the reaction process, effectively reduces the decomposition of the product, and improves the product purity;

[0073] 4) The application optimizes the feeding method of silicon tetrachloride, and through the method of dropping from the surface, not only reduces the amount of silicon tetrachloride, but also reduces the equipment cleaning cost caused by the treatment of silicon tetrachloride, greatly improves the production efficiency and reduces the production cost;

[0074] 5) The lithium difluorodioxalate phosphate concentrated solution provided by the application can be transported through a pipeline, thereby reducing the product transportation cost; compared with the lithium difluorodioxalate phosphate solid, the process of re-dissolving during use is omitted, the risk of impurity introduction is avoided, and the use cost is greatly reduced;

[0075] 6) The preparation of the lithium difluorodioxalate phosphate concentrated solution provided by the application omits the evaporation crystallization process, thereby reducing the production cost;

[0076] 7) The lithium difluorodioxalate phosphate solution is prepared through a simple and efficient one-step reaction, thereby reducing the production capacity loss; by controlling the raw material ratio, the lithium difluorodioxalate phosphate solution prepared has a low initial acidity and a low chloride ion concentration; through subsequent treatment, the impurity content in the system is quickly and efficiently reduced, and the lithium difluorodioxalate phosphate concentrated solution meeting the battery electrolyte use standard is obtained.

[0077] 8) The patent realizes comprehensive control of acidity, moisture and chloride ions through secondary gas purification (silica gel + HKUST-1), accurate raw material ratio and resin acid removal, and the product performance reaches the industry leading level.

[0078] 9) The lithium difluorodioxalate phosphate concentrated solution prepared by the application can form a stable SEI film on the electrode surface when used for preparing an electrolyte, thereby improving the battery cycle life; the lithium difluorodioxalate phosphate concentrated solution is suitable for lithium ion batteries and sodium ion batteries, thereby expanding the application scenarios and exhibiting good performance under special conditions such as low temperature environment. BRIEF DESCRIPTION OF DRAWINGS

[0079] Figure 1 is the 19F-NMR spectrum of the lithium difluorodioxalate phosphate concentrated solution prepared in Example 1 of the application. DETAILED DESCRIPTION

[0080] The characteristics of the application will be further described through the following examples, but the protection scope of the patent is not limited by the examples.

[0081] The technical solutions of the application will be further described through specific embodiments in combination with the drawings. However, the following examples are only simple examples of the application, and do not represent or limit the protection scope of the application, and the protection scope of the application is subject to the claims.

[0082] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0083] Example 1

[0084] The embodiment provides a preparation method of a lithium difluorodioxalate phosphate concentrate liquid, the lithium difluorodioxalate phosphate concentrate liquid is composed of lithium difluorodioxalate phosphate and methyl ethyl carbonate; and the concentration of lithium difluorodioxalate phosphate in the lithium difluorodioxalate phosphate concentrate liquid is 20 wt%.

[0085] The preparation method of the lithium difluorodioxalate phosphate concentrate liquid comprises the following steps:

[0086] (1) under a dry nitrogen atmosphere, 100.8 g of methyl ethyl carbonate is added, the solvent temperature is set to 10 DEG C, 15.19 g of lithium hexafluorophosphate is weighed into a reaction bottle, stirring is carried out for 15 min to completely dissolve the lithium hexafluorophosphate, 18.05 g of oxalic acid is added into the reaction bottle, and the obtained reaction liquid is kept at 40 DEG C;

[0087] (2) after the temperature is kept constant, 16.99 g of silicon tetrachloride is slowly added into the reaction liquid in a face-down manner (a large amount of acidic gas is generated during the adding process), after the adding is completed, 40 DEG C reaction is carried out for 4 h, and 3 h of negative pressure degassing is carried out at 5 kPa and 30 DEG C, to obtain a concentrate liquid precursor;

[0088] (3) the inert dry atmosphere is kept, the concentrate liquid precursor is supplemented with methyl ethyl carbonate, chromatography is carried out by using a fluoropyridyl strong basic anion resin, to obtain the lithium difluorodioxalate phosphate concentrate liquid.

[0089] 100 g of strong basic anion resin (D201: macroporous strong basic styrene anion exchange resin), 10 g of o-fluorobenzoyl chloride, 0.2 g of 2-fluoro-6-pyridinecarboxyl chloride (CAS: 64197-03-1) are added into a polymerization kettle, 1000 g of dichloroethane, 2 g of zinc chloride are added, the reaction temperature is controlled at 40 DEG C, and dark reaction is carried out for 20 h, then filtration, dichloroethane washing until no chlorine ion is generated, and drying are carried out, to obtain the fluoropyridyl strong basic anion resin.

[0090] The method for secondary purification of the inert dry atmosphere is as follows:

[0091] First-stage silica gel drying: fine-pore (pore size 20-30 angstrom) silica gel is selected, the bulk density is 0.6 g / cm3, and the initial moisture content ≤50 ppm is pretreated to ≤20 ppm under a gas flow of 10 L / min.

[0092] Second-stage HKUST-1 adsorption: an HKUST-1 adsorption column is used, the gas flow is 10 L / min, and the adsorption column volume is filled by 20%; the adsorption condition is that the flow rate is ≤5 L / min, the temperature is 20 DEG C, and the adsorption capacity is ≥0.5 g / g MOF.

[0093] After the secondary purification, the moisture content is 4.2 ppm, and the oxygen content is 8.5 ppm.

[0094] The filtrate was taken to a NMR tube, and an internal standard was added. Deuterated acetonitrile was added to dissolve the filtrate, and NMR measurement (F spectrum) was performed. The content ratio of the filtrate was calculated from the proportion integral of NMR. The integral ratio of lithium difluorodioxalate phosphate was 93%, the integral ratio of lithium tetrafluorodioxalate phosphate was 6%, and the integral ratio of lithium difluorophosphate was 1%. In order to measure the concentration of the contained acid, a titration method was used, and the measurement result was 20 ppm. The concentration of the contained chloride ion was measured by silver nitrate titration under ice water bath conditions, and the measurement result was 5 ppm. The moisture was measured by a moisture meter, and the measurement result was 15 ppm.

[0095] Example 2

[0096] The present embodiment provides a preparation method of lithium difluorodioxalate phosphate concentrate, which is composed of lithium difluorodioxalate phosphate and methyl ethyl carbonate; the concentration of lithium difluorodioxalate phosphate in the lithium difluorodioxalate phosphate concentrate is 20 wt%.

[0097] The preparation method of the lithium difluorodioxalate phosphate concentrate comprises the following steps:

[0098] (1) In a dry nitrogen atmosphere, 100.8 g of methyl ethyl carbonate was added, the solvent temperature was set to 10°C, 15.19 g of lithium hexafluorophosphate was weighed into a reaction bottle, and the lithium hexafluorophosphate was completely dissolved by stirring for 15 min. 18.05 g of oxalic acid was added to the reaction bottle, and the obtained reaction liquid was kept at 40°C;

[0099] (2) After the temperature was kept constant, 16.99 g of silicon tetrachloride was slowly added dropwise to the reaction liquid by the face method (a large amount of acidic gas was generated during the dropwise addition process), after the dropwise addition was completed, the reaction was carried out at 40°C for 4 h, and the concentrate precursor was obtained by degassing at 5 kPa and 30°C for 3 h;

[0100] (3) The concentrate precursor was supplemented with methyl ethyl carbonate under a dry inert atmosphere, and chromatography was performed using a fluoropyridyl strong basic anion resin to obtain the lithium difluorodioxalate phosphate concentrate.

[0101] In a polymerization kettle, 110 g of strong basic anion resin (D202: macroporous type II strong basic anion resin), 15 g of o-fluorobenzoyl chloride, and 0.3 g of 2-fluoro-6-pyridinecarbonyl chloride (CAS: 64197-03-1) were added. 1250 g of dichloroethane, 3 g of zinc chloride, and the reaction temperature was controlled at 45°C. The reaction was carried out in the dark for 15 hours. After filtration, dichloroethane was washed until no chloride ion was detected. After drying, the fluoropyridyl strong basic anion resin was obtained.

[0102] The method for secondary purification of the inert dry atmosphere introduced is as follows:

[0103] First-stage silica gel drying: fine-pore (pore size 20-30 A) silica gel with a bulk density of 0.7 g / cm3 is selected; the gas flow rate is 8 L / min, and the initial moisture content of ≤50 ppm can be pretreated to ≤20 ppm.

[0104] Second-stage HKUST-1 adsorption: HKUST-1 adsorption column, 30% of the adsorption column volume is filled at a gas flow rate of 8 L / min; the adsorption capacity is ≥0.5 g / g MOF at a flow rate of ≤5 L / min and a temperature of 25℃.

[0105] After secondary purification, the moisture content is 4.0 ppm, and the oxygen content is 8.1 ppm.

[0106] The filtrate was taken to a nuclear magnetic tube, and an internal standard was added. Deuterated acetonitrile was added to dissolve it, and nuclear magnetic determination (F spectrum) was performed. The content of the filtrate was calculated by the proportion of the integral of nuclear magnetic resonance. The integral ratio of lithium difluorodioxalatophosphate was 85%, the integral ratio of lithium tetrafluorodioxalatophosphate was 8%, the integral ratio of lithium difluorophosphate was 5%, and the integral ratio of lithium hexafluorophosphate was 2%. In order to determine the concentration of the contained acid, a titration method was used, and the determination result was 26 ppm. The silver nitrate titration method was used to determine the concentration of the contained chloride ions under the condition of ice water bath, and the determination result was 7 ppm. The moisture content was measured by a moisture meter, and the determination result was 24 ppm.

[0107] Example 3

[0108] The embodiment provides a preparation method of lithium difluorodioxalatophosphate concentrate liquid, the lithium difluorodioxalatophosphate concentrate liquid is composed of lithium difluorodioxalatophosphate and methyl ethyl carbonate; the concentration of lithium difluorodioxalatophosphate in the lithium difluorodioxalatophosphate concentrate liquid is 10 wt%.

[0109] The preparation method of the lithium difluorodioxalatophosphate concentrate liquid comprises the following steps:

[0110] (1) 100.8 g of methyl ethyl carbonate is added in a dry nitrogen atmosphere, the solvent temperature is set to 10℃, 6.03 g of lithium hexafluorophosphate is weighed and added into a reaction bottle, stirring for 15 min to completely dissolve lithium hexafluorophosphate, 7.17 g of oxalic acid is added into the reaction bottle, and the obtained reaction liquid is kept at 40℃;

[0111] (2) after the temperature is kept constant, 6.74 g of silicon tetrachloride is slowly added dropwise into the reaction liquid in a face-down manner (a large amount of acidic gas is generated during the dropwise addition process), after the dropwise addition is completed, 40℃ reaction is performed for 4 h, and then the reaction liquid is degassed under a negative pressure of 5 kPa at 30℃ for 3 h, to obtain a concentrate liquid precursor;

[0112] (3) the inert dry atmosphere is kept, the concentrate liquid precursor is supplemented with methyl ethyl carbonate, chromatography is performed on the concentrate liquid precursor by using a fluoropyridyl strong basic anion resin, and a lithium difluorodioxalatophosphate concentrate liquid is obtained.

[0113] Into the polymerization kettle, 110 g of strong basic anion resin (201x7 anion exchange resin), 15 g of o-fluorobenzoyl chloride, 0.3 g of 2-fluoro-6-pyridinecarboxyl chloride (CAS: 64197-03-1); 1250 g of dichloroethane, 3 g of zinc chloride, control the reaction temperature at 45℃, avoid light reaction for 15 hours, filter, dichloroethane wash until no chloride ion, dry, get fluoropyridyl strong basic anion resin.

[0114] The method for secondary purification of the inert dry atmosphere is as follows:

[0115] First-stage silica gel drying: fine-pore (pore size 20-30 Å) silica gel is selected, the bulk density is 0.7 g / cm3; the gas flow is 6 L / min, and the initial moisture ≤50 ppm can be pretreated to ≤20 ppm.

[0116] Second-stage HKUST-1 adsorption: the HKUST-1 adsorption column is filled with 30% of the adsorption column volume at a gas flow of 6 L / min; the adsorption conditions are a flow rate ≤5 L / min and a temperature of 25℃, and the adsorption capacity is ≥0.5 g / g MOF.

[0117] After secondary purification, the moisture is 3.9 ppm, and the oxygen content is 7.8 ppm.

[0118] Take a few drops of the filtrate into a nuclear magnetic tube, add an internal standard, add deuterated acetonitrile to dissolve, and perform nuclear magnetic determination (F spectrum). The content of the filtrate is calculated from the proportion of the integral of the nuclear magnetic. The integral ratio of lithium difluorodioxalatophosphate is 90%, the integral ratio of tetrafluorodioxalatophosphate lithium phosphate is 8%, and the integral ratio of lithium difluorophosphate is 2%. In order to measure the concentration of the contained acid, a titration method is used, and the measurement result is 28 ppm. The concentration of the contained chloride ion is measured by silver nitrate titration method under ice water bath condition, and the measurement result is 18 ppm. The moisture is measured by a moisture meter, and the measurement result is 22 ppm.

[0119] Example 4

[0120] The embodiment provides a preparation method of lithium difluorodioxalatophosphate concentrated solution, the lithium difluorodioxalatophosphate concentrated solution is composed of lithium difluorodioxalatophosphate and methyl ethyl carbonate; the concentration of lithium difluorodioxalatophosphate in the lithium difluorodioxalatophosphate concentrated solution is 35 wt%.

[0121] The preparation method of the lithium difluorodioxalatophosphate concentrated solution comprises the following steps:

[0122] (1) In a dry nitrogen atmosphere, 100.8 g of methyl ethyl carbonate was added, the solvent temperature was set to 10°C, 32.72 g of lithium hexafluorophosphate was weighed into the reaction bottle, stirred for 15 min to completely dissolve the lithium hexafluorophosphate, 38.88 g of oxalic acid was added to the reaction bottle, and the obtained reaction liquid was kept at 40°C;

[0123] (2) After the temperature was constant, 36.59 g of silicon tetrachloride was slowly added to the reaction liquid by face-down method (a large amount of acidic gas was generated during the dropwise addition process), after the dropwise addition was completed, the reaction was carried out at 40°C for 4 h, and then the concentrated liquid precursor was obtained by degassing at 5 kPa and 30°C for 3 h;

[0124] (3) The concentrated liquid precursor was supplemented with methyl ethyl carbonate, and chromatography was carried out with fluoropyridyl strong basic anion resin to obtain lithium difluorodioxalatophosphate concentrated liquid.

[0125] In the polymerization kettle, 120 g of strong basic anion resin (201x7 anion exchange resin), 20 g of o-fluorobenzoyl chloride, and 0.4 g of 2-fluoro-6-pyridinecarbonyl chloride (CAS: 64197-03-1) were added; 1500 g of dichloroethane, 4 g of zinc chloride, the reaction temperature was controlled at 50°C, and the reaction was carried out in the dark for 10 hours. After filtration, dichloroethane was washed until there was no chloride ion, and then it was dried to obtain fluoropyridyl strong basic anion resin.

[0126] The method for secondary purification of the inert dry atmosphere is as follows:

[0127] First-stage silica gel drying: fine-pore (pore size 20-30 Å) silica gel with a bulk density of 0.8 g / cm³ was used, and the initial moisture content ≤50 ppm was pretreated to ≤20 ppm at a gas flow rate of 5 L / min.

[0128] Second-stage HKUST-1 adsorption: HKUST-1 adsorption column, 40% of the adsorption column volume was filled at a gas flow rate of 5 L / min, and the adsorption capacity was ≥0.5 g / g MOF under the conditions of a flow rate ≤5 L / min and a temperature of 30°C.

[0129] After secondary purification, the moisture content was 3.7 ppm and the oxygen content was 7.8 ppm.

[0130] The filtrate was taken to a nuclear magnetic tube, and an internal standard was added. Deuterated acetonitrile was added to dissolve the filtrate, and nuclear magnetic measurement (F spectrum) was performed. The content ratio contained in the filtrate was calculated from the proportion integral of nuclear magnetic. The integral ratio of lithium difluorodioxalate phosphate was 88%, the integral ratio of lithium tetrafluorodioxalate phosphate was 9%, and the integral ratio of lithium difluorophosphate was 2%. In order to determine the concentration of the contained acid, a titration method was used, and the determination result was 35 ppm. The concentration of the contained chloride ion was determined by silver nitrate titration method under ice water bath condition, and the determination result was 14 ppm. The moisture was determined by using a moisture meter, and the determination result was 19 ppm.

[0131] Example 5

[0132] The present embodiment provides a preparation method of lithium difluorodioxalate phosphate concentrate solution, the concentration and composition of lithium difluorodioxalate phosphate in the lithium difluorodioxalate phosphate concentrate solution are consistent with those of Example 1, and the difference from Example 1 is that in the preparation method of the lithium difluorodioxalate phosphate concentrate solution, the reaction solution in step (2) is heated to 50°C, and the rest of the preparation method and parameters are consistent with those of Example 1.

[0133] The filtrate was taken to a nuclear magnetic tube, and an internal standard was added. Deuterated acetonitrile was added to dissolve the filtrate, and nuclear magnetic measurement (F spectrum) was performed. The content ratio contained in the filtrate was calculated from the proportion integral of nuclear magnetic. The integral ratio of lithium difluorodioxalate phosphate was 88%, the integral ratio of lithium tetrafluorodioxalate phosphate was 9%, and the integral ratio of lithium difluorophosphate was 2%. In order to determine the concentration of the contained acid, a titration method was used, and the determination result was 35 ppm. The concentration of the contained chloride ion was determined by silver nitrate titration method under ice water bath condition, and the determination result was 14 ppm. The moisture was determined by using a moisture meter, and the determination result was 19 ppm.

[0134] Example 6

[0135] The present embodiment provides a preparation method of lithium difluorodioxalate phosphate concentrate solution, the concentration and composition of lithium difluorodioxalate phosphate in the lithium difluorodioxalate phosphate concentrate solution are consistent with those of Example 1, and the difference from Example 1 is that in the preparation method of the lithium difluorodioxalate phosphate concentrate solution, the reaction solution in step (2) is heated to 50°C, and the rest of the preparation method and parameters are consistent with those of Example 1.

[0136] The filtrate was taken to a nuclear magnetic tube, and an internal standard was added. Deuterated acetonitrile was added to dissolve the filtrate, and nuclear magnetic measurement (F spectrum) was performed. The content ratio contained in the filtrate was calculated from the proportion integral of nuclear magnetic. The integral ratio of lithium difluorodioxalate phosphate was 88%, the integral ratio of lithium tetrafluorodioxalate phosphate was 9%, and the integral ratio of lithium difluorophosphate was 2%. In order to determine the concentration of the contained acid, a titration method was used, and the determination result was 35 ppm. The concentration of the contained chloride ion was determined by silver nitrate titration method under ice water bath condition, and the determination result was 14 ppm. The moisture was determined by using a moisture meter, and the determination result was 19 ppm.

[0137] Example 7

[0138] The present example provides a preparation method of a lithium difluorodioxalate phosphate concentrate solution, the concentration of lithium difluorodioxalate phosphate in the lithium difluorodioxalate phosphate concentrate solution is consistent with that of Example 1, and the difference from Example 1 is that in the preparation method of the lithium difluorodioxalate phosphate concentrate solution, the addition amount of silicon tetrachloride in step (2) is 16.90 g, and the rest of the preparation method and parameters are consistent with those of Example 1.

[0139] The filtrate was taken to a nuclear magnetic tube, an internal standard was added, deuterated acetonitrile was added for dissolution, and nuclear magnetic measurement (F spectrum) was performed. The content ratio contained in the filtrate was calculated from the proportion integral of nuclear magnetic. The integral ratio of lithium difluorodioxalate phosphate was 89%, the integral ratio of lithium tetrafluorodioxalate phosphate was 8%, and the integral ratio of lithium difluorophosphate was 3%. In order to determine the concentration of the contained acid, a titration method was used, and the measurement result was 100 ppm. The concentration of chloride ions contained was measured by silver nitrate titration method under ice water bath condition, and the measurement result was 6 ppm. The moisture was measured by using a moisture measuring instrument, and the measurement result was 14 ppm.

[0140] Example 8

[0141] The present example provides a preparation method of a lithium difluorodioxalate phosphate concentrate solution, the concentration of lithium difluorodioxalate phosphate in the lithium difluorodioxalate phosphate concentrate solution is consistent with that of Example 1, and the difference from Example 1 is that in the preparation method of the lithium difluorodioxalate phosphate concentrate solution, the addition amount of silicon tetrachloride in step (2) is 17.24 g, and the rest of the preparation method and parameters are consistent with those of Example 1.

[0142] The filtrate was taken to a nuclear magnetic tube, an internal standard was added, deuterated acetonitrile was added for dissolution, and nuclear magnetic measurement (F spectrum) was performed. The content ratio contained in the filtrate was calculated from the proportion integral of nuclear magnetic. The integral ratio of lithium difluorodioxalate phosphate was 89%, the integral ratio of lithium tetrafluorodioxalate phosphate was 8%, and the integral ratio of lithium difluorophosphate was 3%. In order to determine the concentration of the contained acid, a titration method was used, and the measurement result was 100 ppm. The concentration of chloride ions contained was measured by silver nitrate titration method under ice water bath condition, and the measurement result was 6 ppm. The moisture was measured by using a moisture measuring instrument, and the measurement result was 14 ppm.

[0143] Example 9

[0144] The present example provides a preparation method of a lithium difluorodioxalate phosphate concentrate solution, the concentration of lithium difluorodioxalate phosphate in the lithium difluorodioxalate phosphate concentrate solution is consistent with that of Example 1, and the difference from Example 1 is that in the preparation method of the lithium difluorodioxalate phosphate concentrate solution, the addition amount of silicon tetrachloride in step (2) is 17.24 g, and the rest of the preparation method and parameters are consistent with those of Example 1.

[0145] The filtrate was taken to a NMR tube, and an internal standard was added, deuterated acetonitrile was added to dissolve it, and NMR measurement (F spectrum) was performed. The content ratio contained in the filtrate was calculated from the integral ratio of NMR. The integral ratio of lithium difluorodioxalate phosphate was 91%, the integral ratio of lithium tetrafluorooxalate phosphate was 7%, and the integral ratio of lithium difluorophosphate was 2%. To measure the concentration of the contained acid, a titration method was used, and the measurement result was 20 ppm. The concentration of the contained chloride ion was measured using a silver nitrate titration method under ice water bath conditions, and the measurement result was 20 ppm. The moisture was measured using a moisture meter, and the measurement result was 22 ppm.

[0146] Example 10

[0147] The present example provides a preparation method of lithium difluorodioxalate phosphate concentrate solution, the concentration of lithium difluorodioxalate phosphate in the lithium difluorodioxalate phosphate concentrate solution is consistent with that of Example 1, and the difference from Example 1 is that in the preparation method of the lithium difluorodioxalate phosphate concentrate solution, the amount of added oxalic acid in step (2) is 18.91 g, and the rest of the preparation method and parameters are consistent with those of Example 1.

[0148] The filtrate was taken to a NMR tube, and an internal standard was added, deuterated acetonitrile was added to dissolve it, and NMR measurement (F spectrum) was performed. The content ratio contained in the filtrate was calculated from the integral ratio of NMR. The integral ratio of lithium difluorodioxalate phosphate was 91%, the integral ratio of lithium tetrafluorooxalate phosphate was 7%, and the integral ratio of lithium difluorophosphate was 2%. To measure the concentration of the contained acid, a titration method was used, and the measurement result was 20 ppm. The concentration of the contained chloride ion was measured using a silver nitrate titration method under ice water bath conditions, and the measurement result was 20 ppm. The moisture was measured using a moisture meter, and the measurement result was 22 ppm.

[0149] Example 11

[0150] The present example provides a preparation method of lithium difluorodioxalate phosphate concentrate solution, the concentration and composition of lithium difluorodioxalate phosphate in the lithium difluorodioxalate phosphate concentrate solution are consistent with those of Example 1, and the difference from Example 1 is that in the preparation method of the lithium difluorodioxalate phosphate concentrate solution, in step (1), when lithium hexafluorophosphate is added, the temperature of the solvent is 25°C.

[0151] The dropwise filtrate was taken to a nuclear magnetic tube, and an internal standard was added, deuterated acetonitrile was added to dissolve it, and nuclear magnetic determination (F spectrum) was performed. The content ratio contained in the filtrate was calculated by the integral ratio of nuclear magnetic. The integral ratio of lithium difluorodioxalate phosphate was 89%, the integral ratio of lithium tetrafluoroxalate phosphate was 9%, and the integral ratio of lithium difluorophosphate was 2%. In order to determine the concentration of the contained acid, a titration method was used, and the determination result was 97 ppm by calculation. The concentration of the contained chloride ion was determined by silver nitrate titration under ice water bath conditions, and the determination result was 11 ppm. The moisture was determined by using a moisture meter, and the determination result was 50 ppm.

[0152] Example 12

[0153] The present embodiment provides a preparation method of lithium difluorodioxalate phosphate concentrate, the concentration and composition of lithium difluorodioxalate phosphate in the lithium difluorodioxalate phosphate concentrate are consistent with those of Example 1, and the difference from Example 1 is that the temperature in step (2) is 50°C in the preparation method of the lithium difluorodioxalate phosphate concentrate.

[0154] The dropwise filtrate was taken to a nuclear magnetic tube, and an internal standard was added, deuterated acetonitrile was added to dissolve it, and nuclear magnetic determination (F spectrum) was performed. The content ratio contained in the filtrate was calculated by the integral ratio of nuclear magnetic. The integral ratio of lithium difluorodioxalate phosphate was 89%, the integral ratio of lithium tetrafluoroxalate phosphate was 9%, and the integral ratio of lithium difluorophosphate was 2%. In order to determine the concentration of the contained acid, a titration method was used, and the determination result was 97 ppm by calculation. The concentration of the contained chloride ion was determined by silver nitrate titration under ice water bath conditions, and the determination result was 11 ppm. The moisture was determined by using a moisture meter, and the determination result was 50 ppm.

[0155] It can be seen from the test results that:

[0156] (1) It can be seen from Examples 1 to 9 that the acidity of the lithium difluorodioxalate phosphate concentrate is ≤100 ppm, the chloride ion is ≤20 ppm, and the water content is ≤50 ppm. Further preferably, it can be seen from Examples 1 to 4 that the acidity of the lithium difluorodioxalate phosphate concentrate is ≤20 ppm, the chloride ion is ≤5 ppm, and the water content is ≤15 ppm by adjusting the addition amount of the reaction raw material and the reaction temperature.

[0157] (2) It can be seen from Examples 7 and 8 that when the addition amount of silicon tetrafluoride is relatively large, a side reaction exists in the reaction system, which leads to a relatively high acidity of the prepared lithium difluorodioxalate phosphate concentrate, and the silicon tetrachloride in the concentrate cannot be completely removed, which leads to a relatively high content of chloride ion.

[0158] (3) It can be seen from Example 9 and Example 10 that when the addition amount of oxalic acid is small, part of the silicon tetrafluoride does not participate in the reaction, resulting in a high content of chloride ions in the prepared lithium difluorophosphate dioxalate concentrate; when the addition amount of oxalic acid is large, part of the oxalic acid does not participate in the reaction, and the remaining oxalic acid cannot be completely removed, resulting in a high acidity of the prepared lithium difluorophosphate dioxalate concentrate.

[0159] (4) It can be seen from Example 1 and Example 11 that when the temperature of adding lithium hexafluorophosphate is too high, the hydrolysis of lithium hexafluorophosphate will occur, resulting in an increase in its acidity, a high acidity of the prepared lithium difluorophosphate dioxalate concentrate, and a decrease in its purity.

[0160] (5) It can be seen from Example 1 and Example 12 that when the degassing temperature is too high, the prepared lithium difluorophosphate dioxalate concentrate has a high colority, and high temperature will cause the decomposition of lithium difluorophosphate dioxalate, resulting in an increase in its acidity and a decrease in its purity.

[0161] In summary, the lithium difluorophosphate dioxalate concentrate provided by the present application exists in the form of an aprotic electrolyte, has low acidity, low chlorine content, and high purity, and can be directly used for the preparation of electrolyte for lithium ion batteries or sodium ion batteries; the preparation of the lithium difluorophosphate dioxalate concentrate eliminates the evaporation crystallization process, thereby reducing the production cost; in addition, the lithium difluorophosphate dioxalate concentrate can be transported through a pipeline, further reducing the product transportation cost; compared with the lithium difluorophosphate dioxalate solid, the process of re-dissolving during use is omitted, the risk of introducing impurities is avoided, and the use cost is greatly reduced.

[0162] The applicant declares that the above description is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and those skilled in the art should understand that any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for preparing a lithium difluorodioxalate phosphate concentrate solution, characterized in that, The method comprises the following steps: (1) mixing lithium hexafluorophosphate, an aprotic solvent and oxalic acid uniformly in an inert dry atmosphere to obtain a reaction solution, wherein the water content of the oxalic acid is ≤200 ppm after drying treatment; (2) maintaining the inert dry atmosphere, adding silicon tetrachloride into the reaction solution in step (1) to perform a reaction, and degassing to obtain a concentrated liquid precursor; (3) maintaining the inert dry atmosphere, performing acid removal treatment on the concentrated liquid precursor in step (2) by ion exchange resin to obtain a lithium difluorodioxalate phosphate concentrated solution; The resin used in the acid removal treatment by ion exchange resin in step (3) is a fluoropyridyl strong basic anion resin, and the preparation process thereof is as follows: According to mass fraction, 100-120 parts of strong basic anion resin, 10-20 parts of o-fluorobenzoyl chloride and 0.05-0.4 parts of 2-fluoro-6-pyridine formyl chloride are added into a polymerization kettle, 1000-1500 parts of dichloroethane and 2-4 parts of zinc chloride are added, the reaction temperature is controlled at 40-50 DEG C, the reaction is performed for 10-20 hours in the dark, filtration is performed, dichloroethane is used for washing until no chlorine ions are present, drying is performed, and the fluoropyridyl strong basic anion resin is obtained. The strong basic anion resin is selected from the following: D201: macroporous strong basic styrene anion exchange resin, D202: macroporous type II strong basic anion resin, 201x7 anion exchange resin.

2. A process for the preparation of a concentrated solution of lithium difluorodioxalate phosphate according to claim 1, characterized in that: The mass ratio of lithium hexafluorophosphate to the aprotic solvent in step (1) is 1:(2-20).

3. A process for the preparation of a concentrated solution of lithium difluorodioxalate phosphate according to claim 1, characterized in that: The molar ratio of lithium hexafluorophosphate to oxalic acid in step (1) is 1:(1.995-2.100).

4. The method for preparing a lithium difluorodioxanol phosphate concentrate according to claim 1, characterized in that: The mixing in step (1) comprises: first mixing and dissolving lithium hexafluorophosphate and an aprotic solvent, and then adding oxalic acid. The temperature of the reaction solution in step (1) is-20-50 DEG C, and the temperature of the reaction system during the process of adding lithium hexafluorophosphate is-20-25 DEG C.

5. A process for the preparation of a concentrated solution of lithium difluorodioxalate phosphate as claimed in claim 1, wherein: The molar ratio of lithium hexafluorophosphate to silicon tetrachloride in step (1) to step (2) is 1:(0.995-1.100), and silicon tetrachloride is added in a face-down manner.

6. A process for the preparation of a lithium bisfluorodioxalate phosphate concentrate solution as claimed in claim 1, wherein: The temperature of the reaction in step (2) is-5-60 DEG C, and the reaction time is 1-8 hours.

7. A process for the preparation of a concentrated solution of lithium difluorodioxalate phosphate as claimed in claim 1, wherein: Before the reaction in step (3) starts, the inert dry atmosphere is subjected to secondary purification: First stage: most of the water in the gas is removed by a silica gel desiccant; Second stage: the water content in the gas is reduced to ≤5 ppm by using the porous structure and copper ion coordination of a metal organic framework material HKUST-1 adsorption column to selectively adsorb water. The specific surface area of the metal organic framework material HKUST-1 is ≥1500 m² / g, and the adsorption capacity is ≥0.5 g / g MOF.

8. A process for the preparation of a concentrated solution of lithium difluorodioxalate phosphate as claimed in claim 1, wherein: The lithium difluorodioxalate phosphate concentrated solution is composed of lithium difluorodioxalate phosphate and an aprotic solvent, the aprotic solvent is selected from any one or a combination of at least two of diethyl carbonate, methyl ethyl carbonate, ethylene carbonate or propylene carbonate, the concentration of lithium difluorodioxalate phosphate in the lithium difluorodioxalate phosphate concentrated solution is 10-35 wt%, the acidity of the lithium difluorodioxalate phosphate concentrated solution is <100 ppm, the water content is <50 ppm, and the chlorine ion concentration is <20 ppm.

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