Method for producing ultra-high purity bis(chlorosulfonyl)imide

Abstract

The present invention relates to a method for preparing ultra-high purity (UP) grade bis(chlorosulfonyl)imide (HCSI) having a purity of at least 99.0 mol% based on the total moles of HCSI. The present invention further relates to the UP grade HCSI obtained from the method, and the use of the UP grade HCSI for preparing lithium bis(fluorosulfonyl)imide (LiFSI). The present invention also relates to a method for preparing LiFSI, comprising preparing UP grade HCSI by the method of the present invention. The present invention relates to a composition containing LiFSI having a purity of at least 99.99 mol% based on the total moles of LiFSI in the composition, and the use of the composition containing LiFSI obtained from the method of the present invention in a lithium ion secondary battery.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED PATENT APPLICATIONS This application claims priority to European application No. 21315166.5, filed September 23, 2021, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to a method for preparing ultra-high purity (UP) grade bis(chlorosulfonyl)imide (HCSI) having a purity of at least 99.0 mol% based on the total moles of HCSI. The present invention further relates to the UP grade HCSI obtained from this method, and to the use of the UP grade HCSI for preparing lithium bis(fluorosulfonyl)imide (LiFSI). The present invention also relates to a method for preparing LiFSI, comprising the preparation of UP grade HCSI by the method according to the present invention. The present invention relates to a composition containing LiFSI having a purity of at least 99.99 mol% based on the total moles of LiFSI in the composition, and to the use of LiFSI obtained from the method of the present invention in a lithium ion secondary battery. [Background technology]

[0003] For over several decades, lithium secondary batteries, including lithium-ion batteries, have held a dominant position in the market for rechargeable energy storage devices due to their many advantages, including light weight, moderate energy density, and good cycle life.

[0004] Nevertheless, current lithium secondary batteries still suffer from a relatively low energy density relative to the ever-increasing required energy densities for high-power applications such as electric vehicles (EVs), hybrid electric vehicles (HEVs), grid energy storage, and the like.

[0005] Therefore, there is an increasing need for high purity electrolytes to obtain high power batteries, since high purity electrolytes can increase the nominal voltage of lithium ion batteries. In particular, since impurities in salts and / or electrolytes can have a detrimental effect on the overall performance and stability of lithium ion batteries, identifying and quantifying impurities in salts and / or electrolytes and elucidating their mechanism of action on battery performance continues to attract high interest in the battery field. In particular, various approaches have been investigated to develop salts and / or electrolytes with minimal amounts of impurities and very low residual water content.

[0006] In the field of lithium-ion batteries, LiPF 6 has been widely used due to its high solubility in non-aqueous polar solvents, especially organic carbonates, despite other drawbacks such as relatively low thermal stability and high sensitivity to water. As a result, bis(fluorosulfonyl)imide salts, especially LiFSI, have been favored over LiPF due to their excellent ionic conductivity and good hydrolysis resistance. 6 LiFSI has attracted a lot of attention from the battery community as a promising candidate to replace LiFSI. In this regard, various processes, reactants, and intermediates leading to LiFSI have been described in the literature.

[0007] Considering that LiFSI is intended to be used in lithium ion secondary batteries, and that impurities present in LiFSI can cause degradation of the performance and stability of the resulting lithium ion battery, it is important to keep the amount of impurities present in LiFSI as low as possible.

[0008] Most of the existing processes for producing LiFSI include multiple steps, which inevitably result in the production of many by-products or other contaminants, such as residual organic solvents, water, etc. The removal of these by-products and / or contaminants is costly and time-consuming, leading to reduced yields and purity of the final LiFSI. In some cases, the purification methods are hardly scalable to industrial levels, making the environmental footprint of the corresponding processes insufficient.

[0009] EP 3381923 B1 (CLS Inc. and Solvay Fluoro GmbH) relates to a method for producing LiFSI, inter alia, by using HCSI, which is reacted with anhydrous ammonium fluoride with a water content of 0.01-3,000 ppm as a fluorination reagent, and then directly treated with an alkaline reagent without further purification.

[0010] A typical LiFSI purification process almost always involves at least one liquid / liquid extraction technique to separate the aqueous and organic phases, and the choice of the solvent used is critical. However, extraction always comes with several drawbacks. For example, multiple extraction steps are often required to obtain optimal yields, which inherently requires large amounts of organic solvents, ultimately increasing their processing / recycling costs.

[0011] US 2019 / 0292053 A1 (Arkema) describes a method for producing LiFSI with reduced water and sulfate content, which is dried and purified by a drying and purification step, which is carried out in particular by using a short-path thin-film evaporator under specific conditions to remove the solvent used without decomposing the target product, i.e. LiFSI. Nevertheless, the LiFSI salt so prepared contains Cl - , S.O. 4 2- , F - , FSO 3 Li - , CO 3 2- , ClO 3 - , ClO 4 - , NO 2 - , NO 3 - It still contains a certain amount of impurities, including

[0012] Heating LiFSI at high temperatures and / or for long periods of time reduces the yield and purity of the product, making it quite difficult to concentrate, and increasing the production costs due to multiple additional purification steps afterwards, especially in the presence of organic solvents (and / or other contaminants).Furthermore, the boiling point of the reaction solvent increases due to the formation of alkali metal salts of bis(fluorosulfonyl)imides, as well as the increased solvation of LiFSI with solvent molecules.

[0013] US Patent No. 9985317B2 (Nippon Shokubai Co., Ltd.) relates to a method for producing alkali metal fluorosulfonylimides and alkali metal salts of fluorosulfonylimides having excellent heat resistance and reduced content of specific impurities and water content, in which the solvent can be easily removed from the reaction solution by bubbling a gas into the reaction solution containing the alkali metal salt of fluorosulfonylimides and / or by concentrating the solution of the alkali metal salt of fluorosulfonylimides by thin-layer distillation.

[0014] Overall, the complexity of the LiFSI manufacturing process, which includes multiple purification steps that are time-consuming and costly, is usually caused by the occurrence of side reactions that occur during the manufacturing process and the need to remove these formed by-products through purification and / or drying steps. This complexity still needs to be addressed in order to obtain LiFSI with excellent heat resistance and electrochemical performance. In short, there is still a need for a novel method for preparing LiFSI with minimal amounts of impurities and very low residual water content, which can be more easily scaled for industrialization in a sufficiently economical manner.

[0015] One of the known intermediates leading to LiFSI is HCSI, which is usually isolated after synthesis by classical batch or semi-batch distillation techniques.

[0016] WO 2015 / 004220 (Lonza Ltd.) relates to a process for preparing bis(halide sulfonyl)imide compounds, in particular bis(chlorosulfonyl)imides, in a continuous manner through three successive steps at elevated temperatures compared to the batchwise reactions of conventional processes.

[0017] Although many prior art documents describe HCSI intermediates as pure materials, they provide single analytical results with little concrete evidence of the exact purity / yield or no absolute reference of the HCSI material for comparison. Therefore, it is difficult to distinguish the quality of HCSI used in the various LiFSI manufacturing processes that use HCSI as a feedstock. Therefore, without a quantitative analytical method that provides strong evidence of the purity of HCSI, the reported yield of HCSI cannot be considered accurate.

[0018] As the main raw material in many LiFSI production processes, the quality of HCSI obviously has a strong influence on the generation of undesired by-products during the LiFSI production process based on HCSI, so it is very advantageous to obtain HCSI with extremely high purity as a key intermediate.

[0019] Under these circumstances, the present inventors have intensively studied the optimal process for obtaining higher purity HCSI at the same yield under milder conditions, and as a result, have found that it is possible to obtain higher purity LiFSI by reducing the labor required for purification while reducing the environmental impact of the LiFSI production process obtained. It has also been confirmed that higher purity HCSI can be obtained while reducing thermal stress by applying appropriate continuous distillation conditions. Summary of the Invention

[0020] The first object of the present invention is a method for preparing ultra-high purity (UP) grade bis(chlorosulfonyl)imide (HCSI), comprising the steps of: (i) providing a crude HCSI mixture (I) comprising HCSI, a heavy fraction, and a light fraction; (ii) removing the light fraction from the crude HSCI mixture (I) to obtain a HCSI mixture (II); (iii) transferring the HCSI mixture (II) to a thin film evaporator; and (iv) distilling the HCSI mixture (II) to isolate UP-grade HCSI; Including, The method, wherein the UP-grade HCSI exhibits a purity of at least 99.0 mole %, based on the total moles of HCSI, as determined by differential scanning calorimetry (DSC) in accordance with ASTM E928-19.

[0021] A second object of the present invention is an upgraded HCSI obtained by the above method.

[0022] A third object of the present invention is the use of the upgraded HCSI obtained from the above-mentioned process for preparing lithium bis(fluorosulfonyl)imide (LiFSI).

[0023] A fourth object of the present invention is a method for producing lithium bis(fluorosulfonyl)imide (LiFSI), which comprises preparing upgraded HCSI by the above-mentioned method.

[0024] The fifth object of the present invention is to provide a composition having a purity of at least 99.99 mol% based on the total moles of LiFSI in the composition, with the remainder being water, remaining raw materials, and F. - , Cl - , S.O. 4 2- , and FSO 3 - The present invention relates to a composition comprising LiFSI, an impurity comprising:

[0025] A sixth object of the present invention is the use of LiFSI obtained by the above mentioned method in a lithium ion secondary battery.

[0026] Surprisingly, the upgraded HCSI produced according to the method of the present invention can be used in subsequent processes to produce LiFSI, such as crude NH 4The inventors have found that the performance of the fluorination step for producing FSI is improved, resulting in a higher yield and purity of LiFSI produced as the final product by the lithiation step. Furthermore, the inventors have found that the synthesis of LiFSI using upgraded HCSI reduces the need for purification and positively impacts the impurity profile of the final LiFSI without compromising the yield. In addition, the heavy fraction can be reused for subsequent distillation to recover HCSI. That is, no yield loss occurs with the process according to the invention. [Brief description of the drawings]

[0027] [Figure 1] 1 shows the DSC curve of UP grade HCSI after WFSP distillation, where the 4th melting peak is integrated and the 3rd crystallization peak is visible above. [Diagram 2] 1 shows a comparison of DSC results between an UP-grade HCSI (shown as a solid line with 24 cumulative cycles) and a batch-distilled HCSI (shown as a dotted line with 4 cumulative cycles). [Diagram 3] The DSC curve of HCSI after batch distillation followed by WFSP distillation is shown, where the 4th melting peak is integrated and the 3rd crystallization peak is visible above. No UPgrade HCSI was obtained by this approach. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] definition Throughout this specification, unless the context requires otherwise, the terms "comprise" or "include" or variations such as "comprises," "comprising," "includes," "including" will be understood to imply the inclusion of a stated element or method step or group of elements or method steps, but not the exclusion of any other element or method step or group of elements or method steps. According to a preferred embodiment, the terms "comprise" and "comprises" and variations thereof mean "consisting only of".

[0029] As used herein, the singular forms "a", "an" and "the" include plural embodiments unless the context clearly indicates otherwise. The term "and / or" includes the meaning "and", "or" and also all other possible combinations of the elements associated with this term.

[0030] The term "~" should be understood to be inclusive.

[0031] In this application, any description is made in relation to a particular embodiment, but is applicable to and interchangeable with other embodiments of the present disclosure. Furthermore, when an element or component is said to be included and / or selected from a list of recited elements or components, in the relevant embodiments expressly contemplated herein, the element or component may be any one of the individually recited elements or components, or may be selected from a group consisting of any two or more of the explicitly recited elements or components; it should be understood that any element or component recited in a list of elements or components may be omitted from such a list. In addition, any recitation herein of numerical ranges by endpoints includes all numbers subsumed within the recited ranges, as well as the endpoints and equivalents of the ranges.

[0032] In the present invention, the term "batch process" is intended to refer to a process in which all reactants are fed to a reactor at the beginning of the process and products are removed when the reaction is complete. No reactants are fed to the reactor and no products are removed during the process.

[0033] In the present invention, the term "semi-batch process" is intended to refer to a process that allows for the additional feeding of reactants and / or removal of products in time.

[0034] In the present invention, the term "ppm" means 1 part per million (1,000,000) parts, i.e. 10 -6 is intended to represent.

[0035] Ratios, concentrations, amounts, and other numerical data may be presented in a range format herein. It should be understood that such range formats are used merely for convenience and brevity, and should be interpreted flexibly to include not only the numerical values ​​explicitly recited as the limits of the range, but also to include all the individual numerical values ​​or subranges contained within the range, as if each numerical value and subrange were explicitly recited. For example, a temperature range of about 120°C to about 150°C should be interpreted to include not only the explicitly recited limits of about 120°C to about 150°C, but also subranges such as 125°C to 145°C, 130°C to 150°C, etc., and individual amounts such as decimal points within the stated range, for example, 122.2°C, 140.6°C, and 141.3°C.

[0036] Unless otherwise specified, in the context of the present invention, the amount of a component in a composition is indicated as the ratio of the weight of the component to the total weight of the composition multiplied by 100, i.e., weight % (wt%), or the ratio of the volume of the component to the total volume of the composition multiplied by 100, i.e., volume % (vol%). It should be understood that both the foregoing summary and the following detailed description are exemplary and intended to provide further explanation of the invention as claimed. Thus, various changes and modifications described herein will be apparent to those skilled in the art. Furthermore, descriptions of well-known functions and structures may be omitted for clarity and brevity.

[0037] The first object of the present invention is to provide a method for preparing upgraded bis(chlorosulfonyl)imide (HCSI), comprising the steps of: (i) providing a crude HCSI mixture (I) comprising HCSI, a heavy fraction, and a light fraction; (ii) removing the light fraction from the crude HSCI mixture (I) to obtain a HCSI mixture (II); (iii) transferring the HCSI mixture (II) to a thin film evaporator; and (iv) distilling the HCSI mixture (II) to isolate UP-grade HCSI; wherein the UP-grade HCSI exhibits a purity of at least 99.0 mole %, based on the total moles of HCSI, as determined by differential scanning calorimetry (DSC) in accordance with ASTM E928-19.

[0038] In particular, the inventors have found that in order to produce an upgraded HCSI by distillation, the light fraction should first be removed from the crude HCSI mixture (I) before transferring the HCSI mixture (II) to a thin-film evaporator to obtain an HCSI mixture (II). In contrast, if the thin-film evaporator is applied without removing the light fraction from the crude HCSI mixture (I), an upgraded HCSI cannot be obtained under the same conditions. Furthermore, the HCSI mixture (II) should be transferred to the thin-film evaporator, i.e., after the HCSI mixture (II) is obtained from step (ii). The inventors have found that if an additional distillation is performed in a batch manner instead of transferring the HCSI mixture (II) to a thin-film evaporator, a trace amount of the light fraction will still be present even after step (ii) due to the long time of the batch distillation that causes thermal decomposition, resulting in a mixture of a trace amount of the light fraction, a heavy fraction, and HCSI. Since thin film evaporators, especially WFSP, are more effective at separating mixtures of two compounds, such mixtures containing a heavy fraction and HCSI plus a trace of a light fraction reduced the molar purity of the HCSI even after distillation by thin film evaporators.

[0039] In one embodiment, the process for producing an UP-grade HCSI is carried out in a sequence, i.e., from step (i) to step (iv), and the sequence of steps (i) to (iv) can be carried out continuously or stepwise.

[0040] In another embodiment, the HCSI mixture (II) is transferred in molten form to a distillation boiler before being transferred to a thin film evaporator.

[0041] In the context of the present invention, the HCSI used in the method of the present invention is, for example, Chlorosulfonyl isocyanate (ClSO 2 NCO) to chlorosulfonic acid (ClSO 2 OH) to give Cyanogen chloride (CNCl), sulfuric anhydride (SO 3 ), and chlorosulfonic acid (ClSO 2 OH) to give Sulfamic acid (NH 2 SO 2 OH), thionyl chloride (SOCl 2 ), and chlorosulfonic acid (ClSO 2 OH) to give It can be produced by known methods.

[0042] In certain embodiments, HCSIs are prepared by either the so-called isocyanate route or the sulfamic acid route.

[0043] In one embodiment, the reaction mixture comprises chlorosulfonic acid (ClSO 2 OH) and chlorosulfonyl isocyanate (ClSO 2 According to this embodiment, step (i) is to provide a crude HCSI mixture (I) comprising HCSI, a heavy fraction, and a light fraction, and such crude HCSI mixture (I) is prepared by reacting chlorosulfonyl isocyanate (ClSO 2 NCO) to chlorosulfonic acid (ClSO 2 OH) to give

[0044] In another embodiment, the reaction mixture comprises sulfamic acid (NH 2 SO 2 OH), chlorosulfonic acid (ClSO 2 OH), and thionyl chloride (SOCl 2 According to this embodiment, step (i) is to provide a crude HCSI mixture (I) comprising HCSI, a heavy fraction, and a light fraction, and such crude HCSI mixture (I) is prepared by reacting sulfamic acid (NH 2 SO 2 OH), chlorosulfonic acid (ClSO 2 OH), and thionyl chloride (SOCl 2 ) is obtained by reacting

[0045] In another embodiment, crude HCSI is prepared by reacting cyanogen chloride, CNCl, with sulfuric anhydride (SO3 ) and chlorosulfonic acid (ClSO 2 According to this embodiment, step (i) is to provide a crude HCSI mixture (I) comprising HCSI, a heavy fraction, and a light fraction, and such crude HCSI mixture (I) is prepared by reacting cyanogen chloride, CNCl, with sulfuric anhydride (SO 3 ) and chlorosulfonic acid (ClSO 2 OH) to give

[0046] The method of the present invention also applies to commercially available HCSI, especially when such commercially available HCSI does not exhibit the expected purity. In this embodiment, step (i) can be defined as providing a "crude HCSI mixture (I)" comprising HCSI, a heavy fraction, and a light fraction.

[0047] In some embodiments, step (ii) is heating the HCSI mixture (I) above 40° C. to remove the light fraction in gaseous form from the remainder of the mixture. In a preferred embodiment, step (ii) is carried out at a temperature in the range of 40° C. to 150° C., preferably 60° C. to 120° C., more preferably 90° C. to 120° C.

[0048] In some embodiments, step (ii) is carried out at atmospheric pressure or at reduced pressure. In certain embodiments, step (ii) is carried out at a pressure of less than 500 mbar abs., preferably less than 200 mbar abs., more preferably less than 100 mbar abs., and even more preferably less than 10 mbar abs.

[0049] In some embodiments, the HCSI mixture (II) comprising the HCSI and the heavy fraction is transferred to a distillation boiler or temporary vessel before being transferred to the thin film evaporator, i.e., before step (iii), but without additional distillation in a batchwise manner.

[0050] In one embodiment, step (iii) is carried out at a temperature in the range of 40°C to 150°C, preferably 40°C to 120°C, more preferably 40°C to 100°C, even more preferably 40°C to 80°C, and most preferably 40°C to 70°C.

[0051] In one preferred embodiment, the HCSI mixture (II) is maintained in molten form during the transition phase by heating in the temperature range of 40-70° C. In another preferred embodiment, in case of solidification, the intermediate product or the final product, i.e., the HCSI mixture (II) or the UP-grade HCSI, is melted until completely melted by heating in the temperature range of 40-70° C. without significantly affecting the quality of the final product, i.e., the UP-grade HCSI.

[0052] In one embodiment, step (iii) is carried out at atmospheric pressure or under reduced pressure. In a preferred embodiment, step (iii) is carried out at atmospheric pressure.

[0053] In the present invention, the term "thin film evaporator", also called "thin layer evaporator", is intended to denote an apparatus used to purify temperature-sensitive products by evaporation that allows short residence times, which allows the processing of many heat-sensitive and difficult-to-distill products. Other terms such as falling film evaporator, rising film evaporator, wiped film evaporator, short path evaporator, flash evaporator, agitated thin film evaporator, wiped film short path (WFSP) evaporator can also be used.

[0054] In one embodiment, the thin film evaporator is a short-path thin film evaporator, a WFSP evaporator (with an external condenser), or a falling film evaporator. Such evaporators generate vapor during evaporation that covers a short path, i.e. travels a short distance, before being condensed in a condenser.

[0055] Typically, short-path thin-film evaporators have a condenser for the solvent vapor internal to the device, while other types of thin-film evaporators that are not short-path evaporators have a condenser external to the device.

[0056] In a short-path thin-film evaporator, a thin film of the product to be distilled is formed on the hot inner surface of the evaporator by continuously depositing the product to be distilled on the inner surface of the evaporator. In one embodiment, the short-path thin-film evaporator comprises a cylindrical heated body and an (axial) rotor that serves to distribute the product to be distilled as a thin film on the inner surface of the evaporator evenly. As the product spirals down the wall, the high rotor tip speed creates a large turbulence, forming waves and creating optimal heat flux and mass transfer conditions. The volatile components are then rapidly evaporated by conductive heat transfer, and the vapor becomes condensable, while the non-volatile components are discharged at the outlet. One of the main problems that can occur during evaporation is fouling, which occurs when hard deposits form on the surface of the heating medium in the evaporator. This type of undesirable phenomenon can be minimized by continuous stirring and mixing, which is associated with a sufficient flow rate of the crude mixture to form a stable film. This sufficient flow rate is dictated by the type and size of the thin-film evaporator used. For example, in the case of a thin-film evaporator of the type KD1 available from UIC GmbH, a flow rate of about 120-125 g / h is sufficient to obtain a stable film.

[0057] In the present invention, the term "residence time" is intended to denote the time that elapses between when the remaining reaction mixture enters the evaporator and when the first drop of solution leaves the evaporator.

[0058] Compatibility with thin film evaporators depends heavily on the product properties, especially the thermal stability of the product being purified.

[0059] The method according to the invention is advantageous mainly because it allows for a shorter time at milder conditions to obtain UP-grade HCSI after the distillation step. Usually, after a 15-25 hour reaction step at a reaction temperature range of 120°C-140°C to produce the HCSI crude mixture, the HCSI distillation step requires a longer time at a temperature range of 100°C-145°C, possibly ranging from a few hours on a laboratory scale to more than 20 hours on an industrial scale. Combining both the reaction and distillation steps results in a cumulative time of thermal stress of the HCSI of about 35-45 hours or more, which causes a substantial color change of the reaction mixture, from colorless to transparent yellow, often even brown, which suggests a significant formation of heavy non-value-added by-products. However, by using the method according to the invention, the inventors have made it substantially possible to lower the temperature and shorten the residence time of the distillation step while still reducing the overall thermal stress of the heat-sensitive HCSI.

[0060] In a particular embodiment, the distillation step (iv) is carried out at a temperature of at most 100°C, preferably at most 90°C, more preferably at most 80°C, even more preferably at most 70°C.

[0061] In another particular embodiment, the distillation step (iv) is carried out at a pressure of at most 10 mbar abs., preferably at most 5 mbar abs., more preferably at most 3 mbar abs., even more preferably at most 0.5 mbar abs.

[0062] In another particular embodiment, the residence time in distillation step (iv) is at most 5 minutes, preferably at most 3 minutes, more preferably at most 1 minute, even more preferably at most 30 seconds.

[0063] In a preferred embodiment, the distillation step (iv) is carried out in a short-path thin-film evaporator at a temperature varying between 80° C. and 100° C. and / or a pressure varying between 0.1 and 10 mbar abs., with a residence time of less than or equal to 30 seconds.

[0064] In the present invention, the purity of the UP grade HCSI obtained after step (iv) is evaluated, more precisely by Differential Scanning Calorimetry (DSC) according to ASTM E928-19. In order to minimize or completely avoid possible decomposition during characterization, specific sampling protocols and defined temperature profiles are applied, as described in the experimental section.

[0065] In a particular embodiment, the onset temperature is 34° C. or higher, the peak temperature is 38° C. or higher, and the melting temperature is 37.5° C. or higher. In another particular embodiment, the normalized integral ranges from about −58 J / g to about −65 J / g. In another particular embodiment, the apex temperature of the crystallization peak is 20° C. or higher.

[0066] In a preferred embodiment, the UP-grade HCSI exhibits a purity of at least 99.3 mole %, based on the total moles of HCSI, as determined by DSC according to ASTM E928-19.

[0067] In a more preferred embodiment, the UP-grade HCSI exhibits a purity of at least 99.5 mole %, based on the total moles of HCSI, as determined by DSC according to ASTM E928-19.

[0068] In a more preferred embodiment, the UP grade HCSI has a purity of at least 99.7 mole %, based on the total moles of HCSI, as determined by DSC according to ASTM E928-19.

[0069] In a most preferred embodiment, the UP-grade HCSI exhibits a purity of at least 99.9 mole %, based on total moles of HCSI, as determined by DSC according to ASTM E928-19.

[0070] The inventors have also found that in order to produce UP-grade HCSI, the light fraction should first be removed from the reaction mixture before transferring the crude HCSI and the heavy fraction to the thin film evaporator. In comparison, when the thin film evaporator is applied without removing the light fraction from the reactor, UP-grade HCSI is not obtained under the same conditions. This is probably due to the smaller number of theoretical plates provided by such a distillation apparatus compared to the more separating types of distillation apparatus known to those skilled in the art. Moreover, when the thin film evaporator is applied to the HCSI previously distilled in batch mode, UP-grade HCSI is not obtained under the same conditions.

[0071] In the present invention, the expression "light fraction" is intended to denote the fraction obtained by distillation, either batchwise, semi-batchwise or continuous, of the crude HCSI mixture obtained from the reaction stage by applying the distillation conditions described for step (iii).

[0072] Non-limiting examples of components from the light fraction include chlorosulfonic acid, chlorosulfonyl isocyanate, and / or thionyl chloride that remain unreacted after the reaction.

[0073] In the present invention, the expression "heavy fraction" is intended to denote the fraction obtained after either batch, semi-batch or continuous distillation of the HCSI from the crude mixture (previously separated from its light fraction) by applying the distillation conditions described for step (v).

[0074] Non-limiting examples of components from the heavy fraction include residual undistilled HCSI and associated by-products including dimers, trimers, and other oligomers that may be formed from HCSI and other reactants by hydrolysis or other side reactions. The heavy fraction is difficult to value and often ultimately must be disposed of as a corrosive chemical waste.

[0075] A second object of the present invention is an upgraded HCSI obtainable by the above method.

[0076] A third object of the present invention is the use of the UPGRADE HCSI obtainable from the above-mentioned method for preparing LiFSI.

[0077] A fourth object of the present invention is a method for producing lithium bis(fluorosulfonyl)imide (LiFSI), which comprises preparing upgraded HCSI by the above-mentioned method.

[0078] In one embodiment, the method for producing LiFSI comprises the following successive steps: (i) providing an UP-grade HCSI obtained by the above-mentioned method; (ii) Fluorination of UP grade HCSI with a fluorinating agent to give ammonium bis(fluorosulfonyl)imide (NH 4 forming a FSI; (iii) optionally, reacting NH obtained from step (ii) 4 purifying the FSI; and (iv) optionally at least one solvent S 2 In the form of a solvate with NH 4 Lithiating FSI with a lithiating agent to form LiFSI.

[0079] In some embodiments, the NH 4 FSIs are in the form of solvates, and optionally crystalline forms, including the following: 50-98% by weight of NH 4 FSI salt, and 2 to 50% by weight of a solvent S selected from the group consisting of cyclic and acyclic ethers 2 .

[0080] Preferably, NH 4 The FSI solvate is preferably 51 to 90% by weight, more preferably 78 to 83% by weight, of NH 4 Contains FSI salts.

[0081] Preferably, NH 4The FSI solvate is preferably a solvate of 10 to 49% by weight, more preferably 17 to 22% by weight, of solvent S. 2 Includes.

[0082] In some embodiments, step (iii) of the method for preparing LiFSI described above comprises: (iii 1 ) the NH from step (ii) 4 FSI is mixed with at least one solvent S 1 Dissolving in; (iii 2 ) at least one solvent S 2 Thus, step (iii) 1 ) from NH 4 Crystallizing the FSI; and (iii 3 ) Solvent S 1 and S 2 At least a portion of NH 4 The FSI salt is separated, preferably by filtration, and NH 4 Preparing an FSI solvate; Includes.

[0083] According to these embodiments, NH from step (ii) 4 FSI is a 4 The content of FSI salt may be 80 to 97% by weight, preferably 85 to 95% by weight, and more preferably 90 to 95% by weight, with the remainder being impurities.

[0084] In step (ii), the fluorinating agent is preferably a lithium compound, more preferably lithium hydroxide LiOH, lithium hydroxide hydrate LiOH·H 2 O, Lithium carbonate Li 2 CO 3 , Lithium hydrogen carbonate LiHCO 3 , Lithium chloride LiCl, Lithium fluoride LiF, CH 3 Alkoxide compounds such as OLi and EtOLi, alkyllithium compounds such as EtLi, BuLi and t-BuLi, lithium acetate, CH 3 COOLi and lithium oxalate Li 2 C 2 O4 , more preferably LiOH H 2 O or Li 2 CO 3 is selected from the group consisting of:

[0085] Solvent S 1 is preferably selected from the group consisting of acetonitrile, valeronitrile, adiponitrile, benzonitrile, methanol, ethanol, 1-propanol, 2-propanol, 2,2,2-trifluoroethanol, n-butyl acetate, isopropyl acetate, and mixtures thereof, preferably 2,2,2-trifluoroethanol.

[0086] Solvent S 2 is preferably selected from the group consisting of diethyl ether, diisopropyl ether, methyl t-butyl ether, dimethoxymethane, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxane, 4-methyl-1,3-dioxane, 1,4-dioxane, and mixtures thereof, more preferably from the list consisting of diethyl ether, diisopropyl ether, methyl t-butyl ether, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, and mixtures thereof, even more preferably 1,3-dioxane or 1,4-dioxane.

[0087] In some preferred embodiments, the fluorinating agent in step (ii) is NH 4 It is added to the FSI.

[0088] In another embodiment, a method for producing LiFSI comprises the following successive steps: (i) providing an UP-grade HCSI by the method described above; (ii) Neutralizing UP grade HCSI with an onium halide having a water content of 500 ppm or less, preferably 400 ppm or less, more preferably 300 ppm or less, to produce ammonium bis(chlorosulfonyl)imide (NH 4forming a CSI; (iii)NH 4 CSI was fluorinated with a fluorinating agent to give ammonium bis(fluorosulfonyl)imide (NH 4 forming a FSI; (iv) optionally, reacting NH obtained from step (iii) 4 purifying the FSI; and (v)NH 4 lithiating FSI with a fluorinating agent to form LiFSI.

[0089] In another embodiment, a method for producing LiFSI comprises the following successive steps: (i) providing an UP-grade HCSI by the method described above; (ii) lithiating the UP grade HCSI with a lithiating agent to form lithium bis(chlorosulfonyl)imide (LiCSI); (iii) optionally purifying the LiCSI obtained from step (ii); and (iv) fluorinating LiCSI with a fluorinating agent to form LiFSI.

[0090] In certain embodiments, the lithiating agent is a lithium halide, including LiF, LiCl, LiBr, and LiI.

[0091] In another particular embodiment, the lithiating agent is LiOH, LiOH·H 2 O or LiNH 2 It is.

[0092] In another particular embodiment, the fluorinating agent is HF, NH 4 F·(HF) n (n=0~10), NaF, KF, CsF, AgF, LiBF 4 , NaBF 4 , K.B.F. 4 , or AgBF 4 It is.

[0093] In a preferred embodiment, the fluorinating agent is HF.

[0094] In another preferred embodiment, the fluorinating agent is NH 4 It's F.

[0095] A fifth object of the present invention is a composition containing LiFSI having a purity of at least 99.99 mole % based on the total moles of LiFSI in the composition. The remainder is F. - , Cl - , S.O. 4 2- , and FSO 3 - The residual raw materials or by-products may contain impurities such as dimethylformamide, water, and residual solvents.

[0096] In a preferred embodiment, the composition comprises LiFSI having a purity of at least 99.99 mole %, based on the total moles of LiFSI in the composition, with the remainder being residual raw materials or by-products.

[0097] In one embodiment, the impurity content is 50 ppm or less based on the total weight of the composition.

[0098] In a preferred embodiment, the water and impurity content is less than or equal to 20 ppm based on the total weight of the composition.

[0099] In a more preferred embodiment, the water and impurity content is less than or equal to 10 ppm based on the total weight of the composition.

[0100] In a particularly preferred embodiment, the composition comprises LiFSI having a purity of at least 99.99 mole %, based on the total moles of LiFSI, and the composition is in solid form.

[0101] In another particularly preferred embodiment, the composition comprises LiFSI having a purity of at least 99.99 mole %, based on the total moles of LiFSI, and the composition is in the form of a solution comprising an organic solvent, such as an organic carbonate.

[0102] In a further particularly preferred embodiment, the composition comprises LiFSI having a purity of at least 99.99 mole %, based on the total moles of LiFSI, and the composition is in the form of a solution comprising ethyl methyl carbonate (EMC).

[0103] The present invention also relates to the use of LiFSI obtained by the above-mentioned method in a lithium-ion secondary battery.

[0104] To the extent that the disclosures of the patents, patent applications and publications incorporated herein by reference conflict with the statements of this application to the extent that certain terms may be unclear, this statement will control.

[0105] The present invention will now be described in detail with reference to the following examples, the purpose of which is merely illustrative and is not intended to limit the scope of the invention.

[0106] Raw materials and equipment Chlorosulfonyl isocyanate (ClSO 2 NCO): Commercially available from Lonza Ltd. or synthesized in-house at Solvay. Chlorosulfonic acid (ClSO 3 H): Commercially available from Sigma Aldrich Sulfamic acid (NH 2 SO 3 H): Commercially available from Sigma Aldrich. Thionyl chloride (SOCl 2 ): commercially available from Sigma Aldrich Ammonium chloride (NH 4 Cl): commercially available from Sigma Aldrich Ammonium fluoride (NH 4 F): commercially available from Sigma Aldrich Ethyl methyl carbonate (EMC): commercially available from Sigma Aldrich Lithium hydroxide monohydrate (LiOH 2 O): commercially available from Sigma Aldrich Short-path thin film evaporator: KD1, available from UIC GmbH.

[0107] Test Method Differential Scanning Calorimetry (DSC): For purity determination by DSC, ASTM E928-19 was followed with some optimization of the measurement conditions. Sampling of HCSI must be performed in a strictly inert atmosphere using stainless steel or gold-plated pressure-resistant crucibles. DSC is performed with samples in the range of 10-30 mg. The melting peaks obtained after at least two, and possibly up to four melting / crystallization cycles, are integrated by the DSC software. As an example, the DSC method used was specified as follows: N at 50 mL / min. 2 One cycle (4 melts / 3 crystallizations) from -30°C to 150°C at 5°C / min (duration 4h 12m) in gas flow. As another example, a Mettler Toledo DSC instrument was used for the analytical development. For this instrument, the software commanding the device and performing the data analysis was STARe software, Version 11.00a (Build 4393), also from Mettler Toledo. Other DSC instruments can be used as well. The crucibles and membranes used for the HCSI DSC analysis can be selected from a variety of reference numbers, such as the following from Mettler Toledo: HP Steel Crucible: 51140404 HP Gold Plated Crucible: 51140405 Disposable gold plating film: 51140403

[0108] The molar purity can be estimated by the "Purity" or "Purity Plus" function of the software by applying the Van't Hoff law equation known to those skilled in the art. Purity determination by DSC can be considered as the determination of the super melting point. Purity determination by DSC is based on the fact that impurities lower the melting point of a eutectic system. This effect is described by the Van't Hoff equation, as explained on the website of the DSC equipment supplier at https: / / www.mt.com / de / en / home / supportive_content / matchar_apps / MatChar_UC101.html.

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[0109] Example 1: Provision of upgraded HCSI according to the present invention (CSI route) Chlorosulfonic acid (814.1 g) was cannulated into a pre-dried, mechanically stirred, double-jacketed, glass, stirred-tank reactor equipped with four baffles, a stirring shaft, a distillation apparatus (including a condenser (cooled by a cryostat) and a fraction separator), two temperature probes connected to a thermostat (double jacket), and a KOH scrubber (to neutralize acid vapors) at room temperature under a nitrogen flow, followed by chlorosulfonic acid (814.1 g) followed by chlorosulfonyl isocyanate (989 g). The mixture was heated from room temperature to reflux over 17 hours and maintained at reflux until gas evolution ceased. The clear brown mixture obtained from such a reaction contains HCSI, a heavy fraction, and a light fraction, i.e., crude HCSI mixture (I). The crude HCSI mixture (I) was pre-distilled under reduced pressure (T set = 90-120 °C; P = 4 mbar abs.), and 263 g of a light fraction (T head = 90-107 °C). The resulting HCSI mixture (II) was cooled to 50 °C and transferred under inert conditions to a pre-dried WFSP distillation apparatus via a pre-dried double-jacketed glass addition funnel. The WFSP apparatus parameters were set as follows: T boiler =80℃ T inner condenser =35℃ T funnel =50℃ P WFSP ≦1mbar Rotational speed:=400rpm

[0110] The HCSI mixture (II) (332.8 g) was introduced at a constant rate (approximately 120-125 g / h) to allow the formation of a stable film at the given distillation parameters. The vapors were rapidly condensed on the surface of the internal condenser and collected in a collection flask. The flow rate was set to give a condensed vapor / mother liquor ratio of approximately 6 / 4. The isolated pure material was withdrawn from the WFSP. The obtained mother liquor was reintroduced into a second WFSP distillation stage using the same distillation parameters. Another pure fraction was collected and combined with the first fraction of pure material. The distillation was stopped at this stage. The total mass of purified HCSI withdrawn from the WFSP (249.5 g) was approximately 75% without further optimization. The residence time in the WFSP was less than 30 seconds. The isolated HCSI was allowed to solidify in an inert atmosphere in a refrigerator for 12 hours before placing the crystallized material in a glove box.

[0111] Example 2: DSC analysis of UP grade HCSI DSC samples of the products isolated in Example 1 were prepared in a glove box using stainless steel pressure crucibles and appropriate presses (both from Mettler Toledo). Sealed crucibles containing approximately 10 mg of ground solid were removed from the glove box for DSC analysis. The DSC method used a N 2 The procedure included four meltings and three crystallizations from -30 to 150 °C at 5 °C / min in a stream (4 h 12 min). UP-grade HCSI isolated and characterized by DSC showed a very sharp and symmetrical melting peak. The purity of UP-grade HCSI was determined by applying the "Purity" function of STARe software, version 11.00a (Mettler Toledo) software. A sample of UP-grade HCSI showed the following DSC results (see also Figure 1): ·Start: 34.7℃ Peak: 38.3°C Melting temperature: 37.7℃ ·Purity: Approx. 99.3% ·Normalized integral: Approx. 62J / g · Top of crystallization peak: about 23°C.

[0112] The criteria for being UPgrade were defined internally based on cumulative observations of the HCSI of the UPgrade samples and the batch distilled HCSI (Comparative Example 1) as follows: ·Start:>34℃ Peak: >38℃ Melting temperature: >37.5℃ ·Purity:>99.0% ·Normalized integral: -58 <x<-65J / g · Apex of crystallization peak: >20°C.

[0113] A comparison of UP-grade HCSI (solid line) and batch-distilled HCSI (dotted line) is shown in Figure 2.

[0114] Example 3: NH of HCSI with upgraded grade 4 Neutralizing CSI UP-grade HCSI (100.3 g) obtained according to the protocol described in Example 1 was placed in molten form in a pre-dried, double-jacketed, mechanically stirred, 0.1 L glass reactor equipped with four baffles and a condenser under inert atmosphere and heated at 60° C. The reactor was connected to a KOH scrubber to neutralize acid vapors. Powdered NH 4 Cl (24.9 g) was slowly introduced into the UP-grade molten HCSI in an inert atmosphere over a period of 15 min. The mixture was heated and maintained at 75-80 °C until gas evolution ceased. A viscous colorless liquid was quantitatively obtained. Chloride analysis (IC, DIONEX ICS-3000) from the scrubber confirmed quantitative neutralization of the released HCSI. The isolated NH 4 The CSI was used as is in the following Example 4.

[0115] Example 4: NH from Example 3 4 CSI's NH 4 Fluorination with F A pre-dried PTFE 0.5 L mechanically stirred reactor equipped with a four-blade stirring shaft, four baffles, a PTFE condenser, a PFA-based internal piping system connected to a thermostat (for internal heating), and an insulating outer layer was purged with NH under nitrogen. 4 F (38.7 g) and anhydrous EMC (283.2 g). The resulting slurry was preheated to 60° C. NH 4 CSI (97.1 g) was preheated to 60° C. and introduced in molten form at a constant flow rate. After addition, the mixture was heated from 60° C. to 84° C. for 1 h, the temperature was maintained at 84° C. for an additional 3 h, and then cooled to room temperature. The suspension was transferred under a nitrogen flow to a Buchner-type filter equipped with a 0.22 μm PTFE membrane. The emptied reactor was washed with additional EMC (164.2 g) and used for further washing of the solid cake. The combined filtrate obtained (563 g) was 19 F NMR (Bruker Avance400 NMR) showed that 4 The yield was 91.3% in FSI (76 g). Table 1 below shows the major impurities (F - , Cl - , S.O. 4 2- , FSO 3 - ) was reduced and no additional impurities were present, as shown by IC results (DIONEX ICS-3000).

[0116] [Table 1]

[0117] Example 5: Crude NH in solid 4 FSI Precipitation The EMC prepared in Example 4 was mixed with NH 4 The filtrate containing FSI was transferred to a magnetically stirred PTFE flask. Water (14.6 g) and 25% NH 4 Aqueous OH solution (0.21 g) was added to the mixture and stirred at room temperature for 1 h. The solution was concentrated under reduced pressure to give NH 4A 60 wt% solution of FSI was obtained. The concentrate obtained was transferred to a pre-dried, mechanically stirred, double-jacketed, 0.3 L glass reactor equipped with four baffles and a condenser. Dichloromethane (DCM) (74.2 g) was introduced using a pump over 1 h, and the mixture was then cooled to 0° C. over 1 h. DCM (73.3 g) was added again over 1 h, and the mixture was maintained at 0° C. for another 1 h. Under nitrogen flush, the suspension obtained was transferred to a Buchner filter equipped with a 0.22 μm PTFE membrane. Crude NH 4 The resulting solid cake, consisting of FSI, was washed with DCM (78.9 g). The resulting solid was dried under reduced pressure. The isolated solid, crude NH 4 The unoptimized overall deposition yield of FSI was 85.2%.

[0118] Example 6: Precipitated crude NH 4 Purification of FSI The resulting solid, NH 4 FSI (64.7 g) was transferred to a pre-dried, mechanically stirred, double-jacketed, 0.3 L glass reactor equipped with four baffles and a condenser. Then, 291 g of 2,2,2-trifluoroethanol (TFE) was added. The overhead stirrer was set at 350 rpm. The temperature of the solution was set at 60 °C and NH 4 Complete dissolution of the FSI in the TFE was ensured. Then, 291 g of 1,4-dioxane was added dropwise to the reactor over a period of 3 hours. After the addition of 1,4-dioxane was completed, the solution temperature was maintained at 60° C. for an additional 3 hours. The resulting slurry was allowed to cool to room temperature in about 3 hours and maintained stirring for about 12 hours. The slurry was filtered using a 0.22 μm PTFE membrane to remove the solid NH 4 FSI was recovered. The recovered solid cake was washed with 131 g of 1,4-dioxane. The recovered wet solid, 156.7 g, was dried using a rotary evaporator at 70° C. and 20 mbar abs. until no more solvent evaporated, yielding 72.7 g of a white solid, which was 80.5 wt % NH 4 NH containing FSI and 19.5% by weight of 1,4-dioxane 4Crystallization solvate of FSI (NH 4 FSI-S1) 19 The purification yield was 90.4%. The 70.1 g of product recovered from the first precipitation was run through this process a second time with the following amounts of chemicals: 255.1 g TFE, 242.4 g 1,4-dioxane for crystallization, and 132 g 1,4-dioxane for washing. After drying, 66.6 g of a white solid was obtained, which was 79.6 wt% NH 4 NH containing FSI and 20.4% by weight of 1,4-dioxane 4 Crystallization solvate of FSI (NH 4 FSI-S2) 19 The purification yield was 94% after the second purification run, as confirmed by F-NMR (Bruker Avance 400 NMR).

[0119] Table 2 below shows the crude NH 4 FSI and the product, i.e., NH obtained after the first and second purification. 4 FSI solvate (NH 4 FSI-S1 and NH 4 The IC (DIONEXICS-3000) results of FSI-S2 are shown.

[0120] [Table 2]

[0121] Example 7: Purified NH 4 Lithiation of FSI 65 g of NH obtained in Example 6 4 FSI-S2 was dissolved in 217 g of butyl acetate, followed by 48.2 g of 25 wt% LiOH H 2 Aqueous O solution was added. The biphasic mixture was stirred at room temperature for 5 hours and then decanted. The organic phase was collected and placed in a thin film evaporator at 60 °C under reduced pressure (0.1 bar abs.). The resulting lithium bis(fluorosulfonyl)imide (LiFSI) 19The purity determined by F-NMR (Bruker Avance 400 NMR) is greater than 99.99 mol%, the chlorine and fluorine contents are less than 20 ppm, the metal element contents are less than 3 ppm, and the SO detected by IC (DIONEX ICS-3000) is 4 2- or FSO 3 - No other impurities such as

[0122] Comparative Example 1: Preparation of HCSI using batch distillation Chlorosulfonic acid (868.8 g) was cannulated into a pre-dried, mechanically stirred, double-jacketed, glass, stirred-tank reactor equipped with four baffles, a stirring shaft, a distillation apparatus (including a condenser (cooled by a cryostat) and a fraction separator), two temperature probes connected to a thermostat (double jacket), and a KOH scrubber (to neutralize acid vapors) at room temperature under a nitrogen sweep, followed by chlorosulfonic acid (1011.9 g), followed by chlorosulfonyl isocyanate (1011.9 g). The mixture was heated from room temperature to reflux over 17 hours and maintained at reflux until gas evolution ceased. The resulting clear brown HCSI mixture (I) contained HCSI, a heavy fraction, and a light fraction. The mixture was pre-distilled under reduced pressure (T set = 95-120 °C; P = 6-7 mbar abs.), and after about 2 hours, 330.1 g of a light fraction (T head = 90-115 °C). The resulting HCSI mixture (II) was further distilled in the first vessel to separate two HCSI fractions (T set =120~145℃;T head = 115-118 °C, P = about 6-7 mbar abs.) were isolated. During this time, due to further pyrolysis, in addition to the heavy fraction and HCSI, trace amounts of light fractions appeared. The resulting fractions were combined to give 896.3 g of distilled HCSI. The DSC analysis of the batch-distilled HCSI is shown in Figure 3.

[0123] Comparative Example 2: WFSP Distillation of Pre-Batch Distilled HCSI The distilled HCSI obtained in Comparative Example 1 was transferred under inert conditions via a pre-dried double-jacketed glass addition funnel to a pre-dried WFSP distillation apparatus at 50° C. The WFSP apparatus parameters were set as follows: T boiler : 80℃ T inner condenser : 35℃ T funnel : 50℃ P WFSP ;Less than 1mbar abs. Rotational speed: 400 rpm

[0124] The distilled HCSI (122.7 g) was introduced at a constant rate (approximately 120-125 g / h) to allow the formation of a stable film at the given distillation parameters. The vapors were rapidly condensed on the surface of the internal condenser and collected in a collection flask. The flow rate was set to give a condensed vapor / mother liquor ratio of approximately 8 / 2. The isolated material was withdrawn from the WFSP. The distillation was stopped at this stage. The total mass of the distilled HCSI withdrawn from the WFSP (101.2 g) was approximately 82% without further optimization. The isolated HCSI was allowed to solidify in an inert atmosphere in a refrigerator for 12 h before the crystallized material was carefully placed in a glove box for DSC analysis. The results can be seen in Figure 3. The shape of the melting peak was broad and asymmetric, with a melting temperature of 30.2 °C. The molar purity was evaluated to be approximately 95.5%. A comparison of the UP-grade HCSI and the batch-distilled HCSI is shown in Figure 2.

[0125] Comparative example 3:NH 4 Direct fluorination of batch-distilled HCSI with F A pre-dried PTFE 0.5 L mechanically stirred reactor equipped with a four-blade stirring shaft, four baffles, a PTFE condenser, a PFA-based internal piping system connected to a thermostat (for internal heating), and an insulating outer layer was purged with NH under nitrogen. 4F (77.1 g) and anhydrous EMC (307.9 g) were charged. The resulting slurry was preheated to 60° C. NHCSI (97.1 g) obtained according to Comparative Example 1 was preheated to 60° C. and introduced in molten form at a constant flow rate. After the addition, the mixture was maintained at 84° C. for 3 hours and then cooled to room temperature. Under a nitrogen flow, the suspension was transferred to a Büchner-type filter equipped with a 0.22 μm PTFE membrane. The emptied reactor was washed with additional EMC (164.7 g) and used for further washing of the solid cake. The combined filtrate obtained (474.7 g) was 19 F NMR (Bruker Avance 400 NMR) showed that 4 The yield was 93% in FSI (83.6 g). IC (DIONEX ICS-3000) results showed that the main impurities (F-, Cl-, SO 4 2- , N.H. 2 SO 3 - , FSO 3 - ) and additional impurities were present, demonstrating a better impurity profile than Example 4.

[0126] Comparative Example 4: NH of HCSI distilled in batch mode 4 Neutralizing CSI HCSI (100.7 g) obtained according to Comparative Example 1 was placed in a molten state at 60° C. in a pre-dried, double-jacketed, mechanically stirred, 0.1 L glass reactor equipped with four baffles and a condenser under an inert atmosphere and heated at 60° C. The reactor was connected to a KOH scrubber to neutralize acid vapors. Powdered NH 4 Cl (24.9 g) was slowly introduced into the molten HCSI UP in an inert atmosphere over a period of 15 min. The mixture was heated and maintained at 75-80 °C until gas evolution ceased. A viscous colorless liquid was quantitatively obtained. Chloride analysis (IC, DIONEXICS-3000) from the scrubber confirmed quantitative neutralization of the released HCSI. The isolated NH 4 CSI was used as is in the following comparative examples.

[0127] Comparative example 5:NH 4NH from Comparative Example 3 with F 4 Fluorination of CSI NH obtained in Comparative Example 4 4 The same fluorination conditions as described in Example 4 were applied to CSI (98.1 g) to give a combined filtrate (404.8 g), which was 19 F NMR reveals that 4 The yield was 92.2% in FSI (77.6 g). The IC (DIONEX ICS-3000) results showed that the main impurity (F - , Cl - , S.O. 4 2- , FSO 3 - ) and the presence of additional impurities.

[0128] [Table 3]

[0129] Comparative Example 6: Solid crude NH 4 FSI Precipitation The filtrate prepared in Comparative Example 5 was subjected to a series of steps strictly following the operating conditions of Examples 5 and 6 to obtain crude NH3 as a white solid. 4 FSI was obtained. The overall precipitation yield was comparable to that of Example 5 without optimization, as was the purification yield for the first and second purification runs of Example 6. After drying, 68 g of a white solid was obtained, which was 80.4 wt. % NH 4 NH containing FSI and 19.6% by weight of 1,4-dioxane 4 Crystallization solvate of FSI (NH 4 FSI-S2) 19 This was confirmed by F-NMR (Bruker Avance 400 NMR).

[0130] Table 4 below shows the crude NH 4 FSI and comparative NH obtained after the first and second purification 4 The IC (DIONEX ICS-3000) results of the FSI solvate are shown.

[0131] [Table 4]

[0132] Comparative Example 7: Purified NH 4 Lithiation of FSI 60 g of NH obtained in Comparative Example 6 4 FSI-S2 was dissolved in 200 g of butyl acetate. Then, 25 wt% LiOH H 2 44.5 g of aqueous O solution was added. The resulting two-phase mixture was stirred at room temperature for 5 hours and then decanted. The organic phase was collected and placed in a thin-film evaporator at 60° C. under reduced pressure (0.1 bar abs.). The resulting lithium bis(fluorosulfonyl)imide (LiFSI) 19 The purity determined by F-NMR (Bruker Avance 400 NMR) is greater than 99.99 mol%, the chlorine and fluorine contents are less than 40 ppm, and the SO 4 2- or FSO 3 - The content of other impurities such as tin, tin oxide ...

[0133] It has been clearly shown in the examples that the upgraded HCSI produced according to the method of the present invention can improve the performance of subsequent steps to ultimately produce high purity LiFSI in high yields, and in particular, HCSI can be obtained under milder conditions including temperature conditions and residence times required to purify the upgraded HCSI.

[0134] Furthermore, the inventors have found that the use of upgraded HCSI obtained according to the method of the present invention in the synthesis of LiFSI improves the impurity profile of the final LiFSI without compromising yield while reducing the need for purification. The reduced level of impurities obtained prior to the fluorination step reduces the need for purification steps, thereby reducing the overall environmental impact of the LiFSI process as a whole. Finally, the improved quality of the final LiFSI product allows for superior performance when used in lithium-ion secondary batteries.

Claims

1. 1. A method for producing ultra-high purity (UP) grade bis(chlorosulfonyl)imide (HCSI), comprising: (i) providing a crude HCSI mixture (I) comprising HCSI, a heavy fraction, and a light fraction; (ii) removing the light fraction from the crude HSCI mixture (I) to obtain an HSCI mixture (II); (iii) transferring the HCSI mixture (II) to a thin film evaporator; and (iv) distilling the HCSI mixture (II) to isolate the UP grade HCSI; Including, The method, wherein the UP grade HCSI exhibits a purity of at least 99.0 mole %, based on total moles of HCSI, as determined by differential scanning calorimetry (DSC) according to ASTM E928-19.

2. The crude HCSI mixture (I) is by reacting chlorosulfonic acid with chlorosulfonyl isocyanate, or By reacting sulfamic acid, chlorosulfonic acid, and thionyl chloride, The method of claim 1, wherein

3. 3. The method according to claim 1 or 2, wherein the purity of the UP grade HCSI is at least 99.3 mol %, preferably at least 99.5 mol %, more preferably at least 99.9 mol %, based on the total moles of HCSI.

4. 3. The method according to claim 1 or 2, wherein the thin film evaporator is a short-path thin film evaporator, a wiped film short-path (WFSP) evaporator (with or without an external condenser), or a falling film evaporator, preferably a short-path thin film evaporator.

5. 3. The process according to claim 1 or 2, wherein the distillation step (iv) is carried out at a temperature of from 60°C to 120°C, preferably from 70°C to 100°C, more preferably from 80°C to 90°C, even more preferably from 80°C to 85°C.

6. 3. The process according to claim 1 or 2, wherein the distillation step (iv) is carried out at a pressure of at most 10 mbar abs., preferably at most 5 mbar abs., more preferably at most 3 mbar abs., even more preferably at most 0.5 mbar abs.

7. 3. The process according to claim 1 or 2, wherein the distillation step (v) is carried out for 5 minutes or less, preferably 3 minutes or less, more preferably 1 minute or less, even more preferably 30 seconds or less.

8. 3. The method of claim 1 or 2, wherein the light fraction comprises chlorosulfonic acid, chlorosulfonyl isocyanate, and thionyl chloride.

9. 3. The process of claim 1 or 2, wherein the heavy fraction comprises by-products from the reaction mixture including dimers, trimers, and other oligomers.

10. 3. A UP grade HCSI obtained by the process of claim 1 or 2, exhibiting a purity of at least 99.0 mole %, based on the total moles of HCSI, as determined by differential scanning calorimetry (DSC) according to ASTM E928-19.

11. 11. Use of the UP grade HCSI according to claim 10 for preparing lithium bis(fluorosulfonyl)imide (LiFSI).

12. 3. A method for producing lithium bis(fluorosulfonyl)imide (LiFSI) comprising preparing the UP grade HCSI of claim 1 or 2.

13. (i) providing UP grade HCSI according to the method of claim 1; (ii) fluorinating the UP grade HCSI with a fluorinating agent to produce ammonium bis(fluorosulfonyl)imide (NH ４ forming a FSI; (iii) optionally, the NH obtained from step (ii) ４ purifying the FSI; and (iv) optionally at least one solvent S ２ in the form of a solvate with ４ lithiating FSI with a lithiating agent to form LiFSI; 13. The method of claim 12, comprising:

14. In step (iv), the NH ４ FSI, 50 to 98 wt.% NH ４ FSI salt, 2 to 50% by weight of a solvent S selected from the group consisting of cyclic and acyclic ethers ２ and, and optionally in a crystalline form.

15. Step (iii) is (iii) １ ) the NH from step (ii) ４ FSI is dissolved in at least one solvent S １ dissolving in; (iii) ２ ) at least one solvent S ２ Thus, step (iii) １ ) from NH ４ Crystallizing the FSI; and (iii) ３ ) The solvent S １ and S ２ from at least a portion of the NH ４ The FSI salt is preferably separated by filtration and NH ４ Preparing an FSI solvate; 14. The method of claim 13, comprising:

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