Process for obtaining hydrofluoric acid from lithium hexafluorophosphate and from lithium hexafluorophosphate-containing electrolytes

Abstract

The invention relates to a method for obtaining hydrofluoric acid from an electrolyte of a lithium-ion battery. The method comprises the steps (a) thermal treatment of the electrolyte to obtain phosphorus pentafluoride; (b) Contacting phosphorus pentafluoride with an absorbent to obtain a first solution containing hydrofluoric acid and phosphoric acid, wherein the first solution additionally contains monofluorophosphoric acid and / or difluorophosphoric acid; (c) Reaction of monofluorophosphoric acid and / or difluorophosphoric acid with an inorganic base to obtain a fluoride and a phosphate; and (d) Contacting the fluoride with a cation exchanger to convert the fluoride into hydrofluoric acid.

Description

[0001] The invention relates to a process for obtaining hydrofluoric acid from lithium hexafluorophosphate. It further relates to a process for obtaining hydrofluoric acid from an electrolyte of a lithium-ion battery.

[0002] Lithium-ion batteries (LIBs) are secondary batteries, also known as accumulators. They consist of several interconnected cells, called LIB cells, each essentially comprising a negative electrode (also called the anode), a positive electrode (also called the cathode), and an ion-conducting electrolyte. The electrolyte contains a conducting salt that carries lithium ions. This conducting salt can be a perfluorinated lithium compound. Lithium hexafluorophosphate (LiPF6) is predominantly used as the conducting salt. The conducting salt is dissolved in an electrolyte matrix, which is typically a mixture of organic carbonates and various additives, and enables the flow of current between the anode and cathode of an LIB cell. The conducting salt is therefore essential for the production of LIB cells.

[0003] The recovery and / or recycling of valuable materials from used lithium-ion batteries is currently of enormous economic interest. This stems primarily from the ongoing trend of societal electrification, which is reflected, among other things, in the widespread expansion of global e-mobility. As a result, securing the raw material base for LIB cells is of paramount importance. Accordingly, EU member states are obligated, among other things, to achieve a lithium recovery rate of 65% by 2025 and 70% by 2030. [1] These requirements are particularly challenging because the conducting salt of the LIB electrolyte, preferably LiPF6, has not yet been considered in established recycling processes. A process for recovering precisely this compound was described in DE 10 2023 116 962 A1. [2]

[0004] In the case of established recycling processes, the recovery of LIB materials relies on the processing of the solid electrode material in the form of LIB black mass. This represents the non-magnetic fraction of the coating and electrode materials obtained after mechanical processing. At the beginning of the process chain for generating the LIB black mass, which forms the starting material for LIB recycling processes, the electrolyte of an LIB cell is removed.

[0005] The in Fig.The prior art LIB recycling process (100) shown begins with the preparation of the used LIB cells (101) to obtain LIB material. This preparation can involve comminution of the LIB cells, optionally under inert gas or aqueous conditions. In the next step, the optionally comminuted LIB material (104) undergoes thermal pretreatment. During this process, the electrolyte (102) is removed by decomposing the conducting salt (103). The electrolyte does not participate in the further processing of the LIB cells. After the optional comminution (101) and thermal pretreatment of the LIB cells (104), the LIB black mass (105) is obtained. This mass contains all LIB components that were not removed by the thermal pretreatment. This therefore includes casing residues that could not be separated during mechanical processing, electrode material, and collector foils.Excluded are the original conducting salt, i.e., the perfluorinated lithium compound, and (depending on the process parameters of the thermal pretreatment) the organic components of the electrolyte. The LIB black mass undergoes hydrometallurgical processing (107). For this purpose, one of the following processes can be used, for example: the Accurec process, the Duesenfeld process, the Primobius process, or the COOL process. These processes provide access to secondary lithium sources (108), which can be used together with primary lithium sources (109) for LIB production (110). For this purpose, the primary and secondary lithium sources (109, 108) can first be converted into lithium carbonate (111), which can then be used in LIB production (110). The use of lithium from secondary lithium sources (108) is associated with a reduction in greenhouse gas emissions (112).The lithium-ion batteries obtained in LIB production (110) by adding elements such as C, Mn, Fe, Co and Ni (113) are recycled again (arrow A) after their use (114), for example for the electrification of vehicles, as storage for renewable energies, etc. In this process, the electrolyte is destroyed again.

[0006] However, the electrolyte contains valuable Li compounds, which make up to 2 wt% of an entire EV-LIB cell and are pyrolyzed during removal and fed into an exhaust gas stream and scrubber. [3] These washing solutions are usually alkaline, calcium-based. 2+ -containing aqueous solutions which bind the fluorinated compounds in the form of CaF2. If the production of hydrofluoric acid from the CaF2 is the goal, this is generally carried out with H2SO4 at 350 to 450 °C in a rotary kiln, as described in DE 10 031 562 A1. [4]This can be described as extremely energy-intensive due to the comparatively high temperatures. Another problematic aspect of this approach to F - Immobilization and RF recovery is the reduction of F - -Yields from the formation of partially fluorinated phosphoric acids upon contact of the LiPF6 decomposition gas with aqueous solutions (see also equations 2 to 5 below). The F - The proportion of these compounds (H2PO2F2, HPOF3) cannot be completely bound in the form of CaF2. Therefore, these highly toxic compounds remain in the system and cannot be used in the hydrofluoric acid production process.

[0007] From CN 1 14 388 920 A a recovery method and a recovery system for spent lithium battery electrolytes are known.

[0008] The object of the invention is to eliminate the disadvantages of the prior art. In particular, a process for obtaining hydrofluoric acid from lithium hexafluorophosphate is to be provided, which enables higher fluoride ion yields. The lithium hexafluorophosphate can be derived from the electrolyte of a lithium-ion battery.

[0009] This problem is solved by the features of claim 1 and claim 15. Advantageous embodiments of the inventions result from the features of the dependent claims.

[0010] According to the invention, a process for obtaining hydrofluoric acid from lithium hexafluorophosphate is provided, comprising the following steps: (a) thermal treatment of lithium hexafluorophosphate to obtain phosphorus pentafluoride; (b) Contacting phosphorus pentafluoride with an absorbent to obtain a first solution containing hydrofluoric acid and phosphoric acid, wherein the first solution additionally contains monofluorophosphoric acid and / or difluorophosphoric acid; (c) Reaction of monofluorophosphoric acid and / or difluorophosphoric acid with an inorganic base to obtain a fluoride and a phosphate; and (d) Contacting the fluoride with a cation exchanger to convert the fluoride into hydrofluoric acid.

[0011] This method will also be referred to below as the first method according to the invention.

[0012] In this application, hydrofluoric acid is also referred to as HF. Unless otherwise specified, HF refers to hydrofluoric acid as an aqueous solution of HF and not to hydrogen fluoride gas. Monofluorophosphoric acid (H₂PO₃F) and difluorophosphoric acid (HPO₂F₂) are hereinafter referred to, individually and collectively, as partially fluorinated phosphoric acids or PFP. Phosphoric acid (H₃PO₄), monofluorophosphoric acid (H₂PO₃F), and difluorophosphoric acid (HPO₂F₂) are also referred to, individually and collectively, as phosphorus compounds. Fluoride refers to a salt containing fluoride ions. Phosphate refers, unless otherwise specified, to a salt containing phosphate ions.

[0013] The first process according to the invention achieves higher fluoride ion yields because the partially fluorinated phosphoric acids, i.e., monofluorophosphoric acid and difluorophosphoric acid, are converted into a fluoride and a phosphate. The fluoride obtained in this way is converted into hydrofluoric acid in step (d) together with the fluoride obtained from the hydrofluoric acid in step (c). Hydrofluoric acid is a fluorinating reagent.

[0014] Since there is no large-scale industrial application of the PFP compounds, the first process according to the invention provides in step (c) for the reaction of PFP with an inorganic base, such as NaOH or KOH. Step (a)

[0015] Step (a) involves the thermal treatment of lithium hexafluorophosphate (LiPF6). This involves the thermal decomposition of lithium hexafluorophosphate. The thermal decomposition of LiPF6 is described in equation (1). The thermal treatment in step (a) yields phosphorus pentafluoride (PF5). LiPF6 → LiF↓ + PF3↑ (1)

[0016] The direct conversion of LiPF6 means that significantly lower temperatures are required in the following steps, especially step (b), compared to the calcination of CaF2 within established processes.

[0017] The thermal treatment is preferably carried out at a temperature in the range of 40 °C to 200 °C and particularly preferably at a temperature greater than 40 °C and less than 200 °C. The thermal treatment can be carried out at ambient pressure, for example 101325 Pa. At ambient pressure, PF5 is a gas. It is possible to carry out step (a) in an inert gas. The inert gas can be, for example, nitrogen or argon, with nitrogen being preferred. The inert gas used need not be anhydrous.

[0018] It may be provided that step (a) includes the thermal treatment of a material containing LiPF6 as a conducting salt. This material may be the electrolyte originating from one or more lithium-ion batteries, for example, from one or more LIB cells. As is known per se, the thermal decomposition of the conducting salt occurs during the thermal treatment of the material containing LiPF6 as a conducting salt. [5-9]Preferably, a plurality of lithium-ion batteries are used to obtain the electrolyte. The term "electrolyte" refers to the material containing the conducting salt, including the conducting salt itself. In other words, the electrolyte used in step (a) comprises the conducting salt and the material containing the conducting salt. This material is the electrolyte matrix. The electrolyte used in step (a) can be obtained by dismantling and / or comminuting one or more lithium-ion batteries. The dismantling and / or comminuting is known from the prior art per se (see Fig.1, reference numeral 101). In this process, the electrolyte is separated from the other components of the lithium-ion battery by opening the LIB cells. The electrolyte is obtained as a liquid. To obtain the electrolyte, the lithium-ion batteries can first be completely discharged. The lithium-ion batteries can then be disassembled by removing components that do not belong to the LIB cells, such as housings, electronic circuits (e.g., the battery management system), as well as cables, busbars, and screws. The remaining LIB cells can then be shredded. This can be done, for example, by shredding, resulting in shredded material. The shredded material preferably has a particle size of 10 to 50 µm. If necessary, the shredded material can be sieved. The liquid components can then be separated from the solid components.The liquid components are the electrolyte, while the solid components may be thermally untreated black mass. Step (b)

[0019] Step (b) of the first process according to the invention provides for bringing the phosphorus pentafluoride obtained in step (a) into contact with an absorbent to obtain a first solution containing hydrofluoric acid and one or more of the phosphorus compounds phosphoric acid (H3PO4), monofluorophosphoric acid (H2PO3F), difluorophosphoric acid (HPO2F2).

[0020] The gaseous phosphorus pentafluoride PF5 obtained in step (a) can be fed into an absorption reactor using an inert gas stream. The inert gas can be argon or nitrogen, with nitrogen being preferred. The inert gas stream serves as a transport gas for the gaseous phosphorus pentafluoride PF5 obtained in step (a). It does not need to be anhydrous. The phosphorus pentafluoride PF5 obtained in step (a) is diluted by the inert gas.

[0021] The first process according to the invention can be carried out as a continuous process. The phosphorus pentafluoride PF5 produced in step (a) can be continuously fed to the absorption reactor.

[0022] The absorption reactor preferably consists of an RF-resistant material. Alternatively, the reaction chamber of the absorption reactor, containing the absorbent, may be coated with the RF-resistant material. The RF-resistant material may be, for example, a perfluoroalkoxy polymer (PFA), polytetrafluoroethylene (PTFE), or a combination of PFA and PTFE. The alkoxy group of the perfluoroalkoxy polymer may be a perfluorinated alkoxy group with 1 to 6 carbon atoms, for example, -O-CF3. The absorbent is preferably water.

[0023] When PF5 is introduced into water, it hydrolyzes according to equations 2 to 5. [7,10] PF5 + H2O → 2HF + POF3 (2) POF3 + H2O → HF + HPO2F2 (3) HPO2F2 + H2O → HF + H2PO3F (4) H2PO3F + H2O → HF + H3PO4 (5)

[0024] The hydrolysis of the introduced PF5 is strongly exothermic. Therefore, cooling of the absorbent may be necessary. Cooling the absorbent solution also improves the solubility of PF5 in water and simultaneously reduces the release of gaseous reaction products.

[0025] The absorption reactor may be equipped with a condenser. It may have a gas inlet and a gas outlet. The inert gas stream containing gaseous PF5 is introduced into the absorption reactor via the gas inlet. After passing through the absorbent and absorbing the PF5, the inert gas stream is discharged from the absorption reactor via the gas outlet. The condenser may be located at the gas outlet of the absorption reactor. The condenser reduces the discharge of the resulting hydrofluoric acid via the gas phase. The condensate collected in the condenser can be recycled back into the absorption reactor. This improves the hydrofluoric acid recovery yield.

[0026] It can be provided that the contacting of PF5 with the absorbent in step (b) is carried out at a temperature in the range of 1 °C to 30 °C, preferably in the range of 1 °C to 10 °C, and particularly preferably in the range greater than 1 °C and less than 10 °C. It can be provided that the absorbent and the absorption mixture obtained from contacting PF5 with the absorbent are cooled to a temperature in the range of 1 °C to 30 °C, preferably in the range of 1 °C to 10 °C, and preferably in the range greater than 1 °C and less than 10 °C. For this purpose, the absorption reactor can include a cooling device. The contacting of PF5 with the absorbent in step (b) can be carried out at ambient pressure, for example, 101325 Pa.

[0027] Equations 2 to 5 illustrate the formation of an aqueous product mixture of hydrofluoric acid (HF), phosphoric acid (H3PO4), and the partially fluorinated phosphoric acids (PFP), i.e., HPO2F2 and H2PO3F. Due to its decomposition stoichiometry, HF is the dominant compound. The aqueous product mixture is obtained by contacting PF5 with water, which serves as the absorbent, as described in step (b). The aqueous product mixture is obtained in step (b) by the hydrolysis of PF5.

[0028] When PF5 comes into contact with the absorbent, a first solution containing hydrofluoric acid is obtained. If hydrofluoric acid is only required in a low purity, the first solution can be used directly as a fluorinating agent. This solution therefore represents a crude product, also referred to as a crude solution. The first solution is a mixture containing the absorbent and the phosphorus compounds HPO₂F₂, H₂PO₃F, and H₃PO₄ obtained when PF5 comes into contact with the absorbent. If the absorbent is water, the first solution is an aqueous solution of hydrofluoric acid and one or more of the following components: HPO₂F₂, H₂PO₃F, and H₃PO₄. If PF5 absorption occurs within the specified temperature range, HPO₂F₂ is predominantly obtained from the partially fluorinated phosphoric acids.However, the use of the first solution as a fluorinating agent is only advantageous if none of the phosphorus-containing components interferes with the intended application. H3PO4, however, is a phosphorus compound of economic interest. Therefore, H3PO4 is also considered a valuable phosphorus resource. Isolating H3PO4 from the absorbent mixture is thus beneficial. Furthermore, HPO2F2 and H2PO3F bind fluoride ions, resulting in a loss of fluoride ions and reducing the yield of hydrofluoric acid obtainable by the first process according to the invention. Therefore, purification of the first solution can be provided according to the invention. Step (c) and (d)

[0029] Steps (c) and (d) concern the purification of the first solution obtained in step (b). Two possibilities exist. In a first embodiment, an inorganic base is added to the first solution. In a second embodiment, the first solution is subjected to a work-up process, and only then is an inorganic base added. In the first embodiment, the polyphenols (PFPs) are destroyed, and then the solution is worked up. In the second embodiment, the first solution is worked up without destroying the PFPs, then the PFPs are destroyed by adding the inorganic base, and finally, a further work-up process is carried out. First embodiment: Addition of an inorganic base to the first solution; Step (c) according to the first embodiment

[0030] Step (c) of the first process according to the invention, in the first embodiment, involves adding an inorganic base to the first solution, thereby converting hydrofluoric acid and phosphorus compound(s) into a fluoride and a phosphate, yielding a second solution. Preferably, the inorganic base is a strong base. A strong base is a base that exists in aqueous solutions in a completely ionized form. The inorganic base can be, for example, an alkali hydroxide or an alkaline earth hydroxide. A particularly preferred inorganic base is sodium hydroxide (NaOH) or potassium hydroxide (KOH). The choice of the inorganic base is primarily determined by the solubility of the respective fluorides formed during the reaction of hydrofluoric acid with the inorganic base. The fluorides formed should exhibit sufficient water solubility.Sufficient water solubility of the formed fluorides should ensure that the fluorides do not precipitate.

[0031] The addition of the inorganic base hydrolyzes HPO₂F₂ and H₂PO₃F, which are not of major industrial importance. Equations 6 to 8 illustrate the reaction of HPO₂F₂ and H₂PO₃F using NaOH as the inorganic base. When NaOH is used as the inorganic base, HPO₂F₂ and H₂PO₃F react to form NaF and Na₃PO₄. In step (c), a second solution is obtained containing a fluoride and a phosphate. HPO2F2 + NaOH → NaF + H2PO3F (6) H2PO3F + NaOH → NaF + H3PO4 (7) H3PO4 + 3NaOH → Na3PO4 + 3H2O (8)

[0032] The reaction is carried out by adding the inorganic base to the first solution obtained in step (b). The inorganic base can be added to the first solution as a solid or as an aqueous solution. The reaction is preferably carried out at a temperature of 20 °C to 100 °C, more preferably at a temperature of 20 °C to 25 °C, and particularly preferably at a temperature greater than 20 °C and less than 25 °C. Preferably, HPO₂F₂ and H₂PO₃F are reacted with the inorganic base at a temperature of 20 °C to 100 °C, more preferably at a temperature of 20 °C to 25 °C, and particularly preferably at a temperature greater than 20 °C and less than 25 °C. Step (d) according to the first embodiment

[0033] In step (c), a second solution is obtained containing a fluoride and a phosphate. This second solution contains a mixture of the fluoride and the phosphate. Both the fluoride and the phosphate are salts. The second solution thus contains a salt mixture. Step (d) involves contacting the fluoride obtained in step (c) with a cation exchanger to convert the fluoride into hydrofluoric acid. In one variant, this can be achieved by contacting the second solution obtained in step (c), which contains a mixture of the fluoride and the phosphate, with the cation exchanger. This converts the fluoride into hydrofluoric acid and the phosphate into phosphoric acid, resulting in a third solution containing hydrofluoric acid and phosphoric acid.In a second variant, the salts fluoride and phosphate contained in the second solution are first separated from each other before the salts are brought into contact with the cation exchanger separately in order to convert fluoride into hydrofluoric acid and phosphate into phosphoric acid.

[0034] The cation exchanger can be an H + trade in -loaded cation exchangers. First variant of step (d) according to the first embodiment

[0035] In the first variant, the second solution obtained in step (c) is treated directly with the cation exchanger, yielding the corresponding acid mixture of hydrofluoric acid and phosphoric acid. The term "directly" means that the second solution is brought into contact with the cation exchanger without any further intermediate steps.

[0036] The acid mixture of hydrofluoric acid and phosphoric acid can then be separated, yielding hydrofluoric acid and phosphoric acid separately. This separation can be achieved, for example, by distillation or by the addition of a silicon-containing compound. The distillation and the addition of a silicon-containing compound are described in detail in the following section, "Second Embodiment." The distillation described there corresponds to the distillation provided here, with the difference that the acid mixture does not contain any phosphoric acid (PFP). The addition of a silicon-containing compound described there corresponds to the addition of a silicon-containing compound provided here, with the difference that the acid mixture does not contain any PFP. Second variant of step (d) according to the first embodiment

[0037] In the second variant, it is provided that the salts fluoride and phosphate contained in the second solution are first separated from each other before the salts are brought into contact with the cation exchanger separately in order to convert fluoride into hydrofluoric acid and phosphate into phosphoric acid.

[0038] In the second variant, step (d) can be the sub-steps (d1) Enrichment of fluoride and phosphate; and (d2) Separation of the fluoride from the phosphate; include.

[0039] To separate the two salts, the second solution can first undergo one or more enrichment processes (step (d1)). The aim of the enrichment process(s) is to increase the concentration of fluoride and phosphate in the second solution. Subsequently, the fluoride can be separated from the phosphate (step (d2)). For example, the precipitation of the fluoride and / or the phosphate can be carried out. Fractional precipitation of the fluoride and phosphate can be performed. Following the fractional precipitation of the fluoride, the fluoride can be contacted with the cation exchanger, yielding hydrofluoric acid. Similarly, following the fractional precipitation of the phosphate, the phosphate can be contacted with the cation exchanger, yielding phosphoric acid.

[0040] It is possible that the fluoride is already separated from the phosphate by the enrichment of the fluoride and phosphate in step (d1). A separate step (d2) is then not necessary.

[0041] The enrichment process can, for example, involve one of the following methods: recycling of the material streams in the process, electrodialysis, solvent evaporation, and other methods may also be used. The enrichment process(s) increase the salt concentration in the second solution. Furthermore, the enrichment process(s) can separate the fluoride from the phosphate. This separation is due to differences in solubility between the fluoride and the phosphate. Fluorides are generally less soluble than phosphates. After the solubility-based separation of the fluoride from the phosphate, the conversion of the fluoride to hydrofluoric acid can be carried out separately from the conversion of the phosphate to phosphoric acid. For this purpose, a solution of the fluoride can be treated with the cation exchanger, preferably H₂. +-loaded cation exchanger, is brought into contact. Additionally, a solution of the phosphate can be combined with another cation exchanger, preferably another H + The fluoride-loaded cation exchanger is brought into contact with the solution. In this way, hydrofluoric acid and phosphoric acid are obtained separately. The term "other cation exchanger" refers to a cation exchanger that is not brought into contact with the fluoride solution. In both cases, it can be the same chemically identical cation exchanger.

[0042] Enrichment of the fluoride and / or phosphate in the second solution is not absolutely necessary. Second embodiment: Work-up of the first solution before addition of an inorganic base

[0043] The first solution obtained in step (b) can be worked up before an inorganic base is used to destroy the PFP. This workup can be carried out, for example, by distilling the first solution in one procedure or by adding a silicon-containing compound to the first solution in a second procedure. Following this workup, an inorganic base is used to destroy the PFP. First method of the second embodiment: Distillation of the first solution according to the first method

[0044] The first solution can be purified by distillation. Distillation can be single- or multi-stage. During distillation, phosphoric acid can be obtained as the bottom product and hydrofluoric acid together with PFP as the top product. The hydrofluoric acid is obtained as an azeotropic mixture of hydrogen fluoride in water.

[0045] Depending on the distillation parameters, due to the similar boiling points of hydrofluoric acid on the one hand and HPO₂F₂ and / or H₂PO₃F on the other, HPO₂F₂ and / or H₂PO₃F are also obtained in the overhead product in addition to the hydrofluoric acid. Therefore, a multi-stage distillation may be required to separate the hydrofluoric acid from the initial solution. Alternatively, the separation of hydrofluoric acid on the one hand and HPO₂F₂ and H₂PO₃F on the other can be achieved in a single distillation run, i.e., by means of a single-stage distillation.

[0046] Distillation yields a first fraction containing phosphoric acid and a second fraction containing hydrofluoric acid and PFP. The second fraction can then be further processed to obtain hydrofluoric acid, either by adding a silicon-containing compound or by treating it with an inorganic base. Addition of an inorganic base to the second fraction according to the first procedure. Step (c) according to the first procedure

[0047] Step (c) of the first method according to the invention provides in the first method of the second embodiment for the addition of an inorganic base to the second fraction, whereby hydrofluoric acid and PFP are converted into a fluoride and a phosphate to obtain a second solution.

[0048] Further details regarding step (c) of the first procedure of the second embodiment have already been explained in connection with step (c) of the first embodiment. Reference is made to these explanations. Step (d) according to the first procedure

[0049] In step (c), a second solution is obtained containing a fluoride and a phosphate. This second solution contains a mixture of the fluoride and the phosphate. Both the fluoride and the phosphate are salts. The second solution thus contains a salt mixture. Step (d) involves contacting the fluoride obtained in step (c) with a cation exchanger to convert the fluoride into hydrofluoric acid. In one variant, this can be achieved by contacting the second solution obtained in step (c), which contains a mixture of the fluoride and the phosphate, with the cation exchanger. This converts the fluoride into hydrofluoric acid and the phosphate into phosphoric acid, resulting in a third solution containing hydrofluoric acid and phosphoric acid.In a second variant, the salts fluoride and phosphate contained in the second solution are first separated from each other before the salts are brought into contact with the cation exchanger separately in order to convert fluoride into hydrofluoric acid and phosphate into phosphoric acid.

[0050] Further details regarding step (d) of the first procedure of the second embodiment have already been explained in connection with step (d) of the first embodiment. Reference is made to these explanations, including the explanations of the first and second variants of step (d). Second method of the second embodiment: Addition of a silicon-containing compound to the first solution

[0051] The first solution can be purified by adding a silicon-containing compound. This addition isolates the hydrofluoric acid present in the first solution. The silicon-containing compound can be silicon dioxide (SiO₂). Alternatively, another silicon source can be used. For example, quartz can be used as the silicon-containing compound.

[0052] Equations 9 to 11 show the reaction of hydrofluoric acid with SiO2. Gaseous SiF4 is formed (Equation 9), which can be separated from the liquid residue. The resulting SiF4 can be used as a fluorination reagent. Alternatively, it can be introduced into concentrated hydrofluoric acid to form hexafluorosilicic acid (H2SiF6) (Equation 10). This process of hydrofluoric acid storage is known in the literature and is reversible, with hydrofluoric acid release being induced by increasing the temperature.

[11] The formation of hydrofluoric acid from H2SiF6 results from hydrolysis (equation 11). 4 HF + SiO2 → SiF4+ 2 H2O (9) SiF4 + 2 HF ⇌ H2SiF6 (10) H2SiF6 + 2 H2O → 6 HF + SiO2 (11)

[0053] Phosphoric acid and, necessarily, PFP remain as residues from the hydrofluoric acid reaction with SiO₂ or another silicon source. A reaction of PFP with corresponding silicon sources cannot be observed at 1 bar in aqueous solutions within the temperature range of 20 °C to 100 °C. The residue can be worked up by distillation, allowing the respective PFP and H₃PO₄ to be isolated. The distillation can be carried out as described above in the section "Distillation of the First Solution," with the residue appearing instead of the first solution. The residue differs from the first solution in that it does not contain hydrofluoric acid.

[0054] The distillation can be followed by the destruction of PFP by the addition of an inorganic base, as already explained in the section “Distillation of the first solution according to the first procedure”.

[0055] As an alternative to distilling the residue, an inorganic base can be added to the residue. Addition of an inorganic base to the residue according to the second procedure, step (c) according to the second procedure

[0056] Step (c) of the first method according to the invention provides, in the second method of the second embodiment, for the residue obtained from the hydrofluoric acid reaction with SiO2 to be treated with an inorganic base, whereby PFP is converted into a fluoride and a phosphate to obtain a second solution.

[0057] Further details regarding step (c) of the second procedure of the second embodiment have already been explained in connection with step (c) of the first embodiment. Reference is made to these explanations. Step (d) according to the second procedure

[0058] In step (c), a second solution is obtained containing a fluoride and a phosphate. This second solution contains a mixture of the fluoride and the phosphate. Both the fluoride and the phosphate are salts. The second solution thus contains a salt mixture. Step (d) involves contacting the fluoride obtained in step (c) with a cation exchanger to convert the fluoride into hydrofluoric acid. In one variant, this can be achieved by contacting the second solution obtained in step (c), which contains a mixture of the fluoride and the phosphate, with the cation exchanger. This converts the fluoride into hydrofluoric acid and the phosphate into phosphoric acid, resulting in a third solution containing hydrofluoric acid and phosphoric acid.In a second variant, the salts fluoride and phosphate contained in the second solution are first separated from each other before the salts are brought into contact with the cation exchanger separately in order to convert fluoride into hydrofluoric acid and phosphate into phosphoric acid.

[0059] Further details regarding step (d) of the first procedure of the second embodiment have already been explained in connection with step (d) of the first embodiment. Reference is made to these explanations, including the explanations of the first and second variants of step (d).

[0060] According to the invention, a process for obtaining hydrofluoric acid from an electrolyte of a lithium-ion battery containing lithium hexafluorophosphate is further provided. The process comprises the following steps: (a) thermal treatment of the electrolyte to obtain phosphorus pentafluoride; (b) Contacting phosphorus pentafluoride with an absorbent to obtain a first solution containing hydrofluoric acid and phosphoric acid, wherein the first solution additionally contains monofluorophosphoric acid and / or difluorophosphoric acid; (c) Reaction of monofluorophosphoric acid and / or difluorophosphoric acid with an inorganic base to obtain a fluoride and a phosphate; and (d) Contacting the fluoride with a cation exchanger to convert the fluoride into hydrofluoric acid.

[0061] This process is hereinafter also referred to as the second process according to the invention. The second process according to the invention corresponds to the first process according to the invention, except that lithium hexafluorophosphate is contained in an electrolyte. For this reason, step (a) provides for a thermal treatment of the electrolyte, whereby phosphorus pentafluoride is obtained from the electrolyte, which contains the lithium hexafluorophosphate as a conducting salt.

[0062] Further details of the second method according to the invention have already been explained in connection with the first method according to the invention. Reference is made to this explanation.

[0063] Since LIB cells are recycled at different stages of their lifespan, and aging processes partially hydrolyze the LiPF6-containing electrolyte to hydrofluoric acid, PFP, and H3PO4 within the LIB cell itself, LiPF6 recovery from such cells and purification to restore battery-grade quality has been costly to date. In contrast, the targeted conversion of LiPF6 to hydrofluoric acid using the second process according to the invention is independent of the aging state of the LIB cells being recycled. This results from the material utilization of the PFP compounds and the isolation of the respective individual components (hydrofluoric acid and phosphoric acid) within the process. Furthermore, the second process according to the invention is characterized by its independence from the different types of LIB cells being recycled, as the cathode and anode materials used are irrelevant for the conversion of the LiPF6 electrolyte.

[0064] The invention is explained in more detail below with reference to exemplary embodiments, which are not intended to limit the invention, and with reference to the drawings. Fig. 1. A flowchart illustrating the state-of-the-art recycling of lithium-ion batteries; Fig. 2 a flowchart showing the first, common part of a first embodiment and a second embodiment of the second method according to the invention; Fig. 3 a flow diagram illustrating the second part of the first embodiment of the second method according to the invention, in which the inorganic base is added to the first solution; and Fig. 4 a flow diagram illustrating the second part of the second embodiment of the second method according to the invention, in which the first solution is worked up before the inorganic base is added.

[0065] In the Fig. 3 and Fig. Four compounds suitable as fluorination reagents are highlighted in bold and within a frame. This highlighting is intended to emphasize the term "fluorination reagent" in the Fig. 3 and Fig. 4 illustrate. Abbreviations used DMC Dimethyl carbonate EC Ethylene carbonate sccm Standard cubic centimeters per minute PFA Perfluoroalkoxy copolymer PFP partially fluorinated phosphoric acids PTFE Polytetrafluoroethylene Example 1

[0066] The Fig. 2 and Fig. Figure 3 illustrates a first embodiment of the second process according to the invention for obtaining hydrofluoric acid from the electrolyte of a lithium-ion battery. For this purpose, LIB cells are provided which have an electrolyte containing LiPF6 as a conducting salt. In a step (a) preceding the second process according to the invention, the LIB cells are disassembled and comminuted (2).

[0067] Following the dismantling and comminution of the LIB cells, the thermal treatment according to step (a) is carried out (3), resulting in the decomposition of the conducting salt LiPF6 (Box 51). The thermal treatment is performed under an inert gas atmosphere and at a temperature ranging from 40 °C to 200 °C. PF5 is recovered as a gas (4). LiF is also recovered (5). Steps (2) and (3), shown in Box 91, are compatible with established LIB recycling processes.

[0068] The PF5 obtained in step (a) is now used to prepare a crude product (Box 52). The crude product is the first solution obtained in step (b) of the second process according to the invention. The first solution is also referred to as crude solution (12) in view of the subsequent purification (Box 53). However, it can also be used as a fluorinating agent without purification.

[0069] To prepare the crude solution (12), the gaseous PF5 obtained in step (a) is fed to an absorption reactor using an inert gas stream, which need not be anhydrous. There, the PF5 is absorbed using water as the absorbent (11). The inert gas stream serves as the transport gas for the PF5. The absorption reactor contains the absorbent. The absorption of PF5 is carried out at a temperature in the range of 1 °C to 10 °C. For this purpose, the absorbent is cooled. By introducing PF5, the crude solution (12) is obtained. The crude solution (12) is an aqueous solution of hydrofluoric acid, H3PO4, HPO2F2, and H2PO3F.

[0070] The crude solution is now subjected to purification (Box 53). The aim of the purification is to obtain hydrofluoric acid in high yield. For this purpose, HPO₂F₂ and H₂PO₃F are to be reacted to form hydrofluoric acid and phosphoric acid. The hydrofluoric acid is to be obtained separately from the phosphoric acid. The crude solution (12) obtained in step (b) (Box 52) is brought into contact with an inorganic base (step (c) of the second process according to the invention). For this purpose, the inorganic base, for example NaOH or KOH, is added to the crude solution (12) (13). The reaction with the inorganic base is carried out at a temperature greater than 20 °C and less than 25 °C. The addition of the inorganic base yields an aqueous solution of the salts fluoride and phosphate; in the case of the addition of NaOH, the salts are NaF and NaPO₃ (14). This aqueous solution of the salts fluoride and phosphate is the second solution. First option

[0071] In a first variant (arrow A), the second solution is brought into contact with a cation exchanger (step (d) of the process according to the invention). The cation exchanger is a H + -loaded cation exchanger. Treatment (15) of the second solution, which contains the two salts fluoride and phosphate, leads to an exchange of the cations, giving an aqueous solution containing hydrofluoric acid and phosphoric acid (16) (arrow C). This solution is a third solution.

[0072] The third solution is now further purified. Further purification can be carried out by distillation (21) (arrow D) or by adding a silicon-containing compound (31) (arrow E).

[0073] The distillation (21) can be single-stage or multi-stage. Through distillation, hydrofluoric acid (22) is obtained separately from phosphoric acid (23). The hydrofluoric acid (23) obtained can then be used as a fluorination reagent.

[0074] Instead of purifying the third solution by distillation (21), purification can be carried out by adding a silicon-containing compound (31). The silicon-containing compound can be SiO2 or another silicon source. Upon addition of SiO2 or the other silicon source, gaseous SiF4 (32) is formed. The gaseous SiF4 is separated from the liquid residue (37). It is then introduced into concentrated hydrofluoric acid to form H2SiF6 (34) (33). This process is called SiF4 absorption. The resulting H2SiF6 (34) is then introduced into water (35). Hydrofluoric acid (36) is obtained by hydrolysis of H2SiF6.

[0075] The liquid residue (37) obtained in (31) is phosphoric acid. Second option

[0076] In a second variant (arrow B), the second solution (14), containing the salts NaF and NaPO3, is enriched (17) (step (d1) of the second process according to the invention). The enrichment enables fractional separation of the two salts (step (d2) of the second process according to the invention), yielding NaF (18) as the first fraction and NaPO3 (19) as the second fraction. The first fraction and the second fraction are then brought into contact with a cation exchanger (15) separately (step (d) of the second process according to the invention). The cation exchanger is a hydrogen peroxide (H₂O₂). + -loaded cation exchanger. The treatment (15) leads to an exchange of the cations in each case. An aqueous solution containing hydrofluoric acid (181) is obtained, and separately an aqueous solution containing phosphoric acid (191) is obtained. Example 2

[0077] The Fig. 2 and Fig. Figure 4 illustrates a second embodiment of the second process according to the invention for obtaining hydrofluoric acid from the electrolyte of a lithium-ion battery. For this purpose, LIB cells are provided which have an electrolyte containing LiPF6 as a conducting salt. In a step (a) preceding the second process according to the invention, the LIB cells are disassembled and comminuted (2).

[0078] Following the dismantling and comminution of the LIB cells, the thermal treatment according to step (a) is carried out (3), resulting in the decomposition of the conducting salt LiPF6 (Box 51). The thermal treatment is performed under an inert gas atmosphere and at a temperature ranging from 40 °C to 200 °C. PF5 is recovered as a gas (4). LiF is also recovered (5). Steps (2) and (3), shown in Box 91, are compatible with established LIB recycling processes.

[0079] The PF5 obtained in step (a) is now used to prepare a crude product (Box 52). The crude product is the first solution obtained in step (b) of the second process according to the invention. The first solution is also referred to as crude solution (12) in view of the subsequent purification (Box 53). However, it can also be used as a fluorinating agent without purification.

[0080] To prepare the crude solution (12), the gaseous PF5 obtained in step (a) is fed to an absorption reactor using an inert gas stream, which need not be anhydrous. There, the PF5 is absorbed using water as the absorbent (11). The inert gas stream serves as the transport gas for the PF5. The absorption reactor contains the absorbent. The absorption of PF5 is carried out at a temperature in the range of 1 °C to 10 °C. For this purpose, the absorbent is cooled. By introducing PF5, the crude solution (12) is obtained. The crude solution (12) is an aqueous solution of hydrofluoric acid, H3PO4, HPO2F2, and H2PO3F.

[0081] The crude solution is now subjected to purification (Box 53). The aim of the purification is to obtain hydrofluoric acid in high yield. For this purpose, HPO₂F₂ and H₂PO₃F are to be reacted to form hydrofluoric acid and phosphoric acid. The hydrofluoric acid is to be obtained separately from the phosphoric acid. The crude solution (12) obtained in step (b) (Box 52) is subjected to distillation (21) (arrow F), or a silicon-containing compound (31) (arrow G) is added to it.

[0082] During distillation (21), a first fraction, which is phosphoric acid (23), and a second fraction (24), containing hydrofluoric acid and PFP, are obtained. The second fraction (24) can then be subjected to further distillation to obtain hydrofluoric acid and separate it from PFP. This yields hydrofluoric acid (25) separately from an aqueous PFP solution (26). The aqueous PFP solution (26) is an aqueous solution of HPO₂F₂ and H₂PO₃F.

[0083] The aqueous PFP solution (26) is now brought into contact with an inorganic base to convert HPO₂F₂ and H₂PO₃F into hydrofluoric acid and phosphoric acid (step (c) of the second process according to the invention). For this purpose, the inorganic base, for example NaOH or KOH, is added to the aqueous PFP solution (26) (27). The reaction with the inorganic base is carried out at a temperature greater than 20 °C and less than 25 °C. The addition of the inorganic base yields an aqueous solution of the salts fluoride and phosphate; in the case of the addition of NaOH, these are the salts NaF and NaPO₃ (14). This aqueous solution of the salts fluoride and phosphate is the second solution.

[0084] If no distillative separation of hydrofluoric acid and PFP is provided (arrow Z), the fraction (24) containing hydrofluoric acid and PFP is brought into contact with an inorganic base (step (c) of the second process according to the invention) (27). The addition of the inorganic base yields an aqueous solution of the salts fluoride and phosphate; in the case of the addition of NaOH, the salts are NaF and NaPO3 (14). This aqueous solution of the salts fluoride and phosphate is also a second solution. First option

[0085] In a first variant (arrow H), the second solution (14) is brought into contact with a cation exchanger (step (d) of the method according to the invention). The cation exchanger is a H +-loaded cation exchanger. The treatment (15) of the second solution, which contains the two salts fluoride and phosphate, leads to an exchange of the cations, giving an aqueous solution containing hydrofluoric acid and phosphoric acid (16) (arrow L). This solution is a third solution.

[0086] The third solution is now further purified. Further purification can be achieved by adding a silicon-containing compound (31) (arrow M). The silicon-containing compound can be SiO2 or another silicon source. Upon addition of SiO2 or the other silicon source, gaseous SiF4 (32) is formed. The gaseous SiF4 is separated from the liquid residue (37). It is then introduced into concentrated hydrofluoric acid to form H2SiF6 (34) (33). This process is called SiF4 absorption. The resulting H2SiF6 (34) is finally introduced into water (35). Hydrofluoric acid (36) is obtained by hydrolysis of H2SiF6.

[0087] The liquid residue (38) obtained in (31) is phosphoric acid. Unlike in (31), it contains Fig. 4 indicated, no PFP. Further treatment of the liquid residue (38) according to arrow O or P is not planned. Second option

[0088] In a second variant (arrow K), the second solution (14), containing the salts NaF and NaPO3, is enriched (17) (step (d1) of the second process according to the invention). The enrichment enables fractional separation of the two salts (step (d2) of the second process according to the invention), yielding NaF (18) as the first fraction and NaPO3 (19) as the second fraction. The first fraction and the second fraction are then brought into contact with a cation exchanger (15) separately (step (d) of the second process according to the invention). The cation exchanger is a hydrogen peroxide (H₂O₂). +-loaded cation exchanger. The treatment (15) leads to an exchange of the cations in each case. An aqueous solution containing hydrofluoric acid (181) is obtained, and separately an aqueous solution containing phosphoric acid (191) is obtained.

[0089] Instead of purifying the crude solution by distillation (21), purification can be carried out by adding a silicon-containing compound (31). The silicon-containing compound can be SiO2 or another silicon source. Upon addition of SiO2 or the other silicon source, gaseous SiF4 (32) is formed. The gaseous SiF4 is separated from the liquid residue (37). It is then introduced into concentrated hydrofluoric acid to form H2SiF6 (34) (33). This process is called SiF4 absorption. The resulting H2SiF6 (34) is then introduced into water (35). Hydrofluoric acid (36) is obtained by hydrolysis of H2SiF6.

[0090] The liquid residue (38) obtained in (31) is a solution containing phosphoric acid and PFP. This solution is now subjected to distillation (21) (arrow O) or brought into contact with an inorganic base (step (c) of the second process according to the invention) (arrow P).

[0091] During distillation (21), a first fraction, which is phosphoric acid (23), and a second fraction (24), containing hydrofluoric acid and PFP, are obtained. The second fraction (24) can then be subjected to further distillation to obtain hydrofluoric acid and separate it from PFP. This yields hydrofluoric acid (25) separately from an aqueous PFP solution (26). The aqueous PFP solution (26) is an aqueous solution of HPO₂F₂ and H₂PO₃F.

[0092] The aqueous PFP solution (26) is now brought into contact with an inorganic base to convert HPO₂F₂ and H₂PO₃F into hydrofluoric acid and phosphoric acid (step (c) of the second process according to the invention). For this purpose, the inorganic base, for example NaOH or KOH, is added to the aqueous PFP solution (26) (27). The addition of the inorganic base yields an aqueous solution of the salts fluoride and phosphate; in the case of the addition of NaOH, the salts are NaF and NaPO₃ (14). This aqueous solution of the salts fluoride and phosphate is the second solution.

[0093] If no distillative separation of hydrofluoric acid and PFP is provided (arrow Z), the fraction (24) containing hydrofluoric acid and PFP is brought into contact with an inorganic base (step (c) of the second process according to the invention) (27). The addition of the inorganic base yields an aqueous solution of the salts fluoride and phosphate; in the case of the addition of NaOH, the salts are NaF and NaPO3 (14). This aqueous solution of the salts fluoride and phosphate is also a second solution.

[0094] The second solution can now be subjected to further processing according to the first variant described above (arrow H) or the second variant described above (arrow K). Example 3

[0095] Example 3 focuses on the production of hydrofluoric acid from LiPF6 using an electrolyte that is a LiPF6-EC-DMC solution. The electrolyte is thus a solution of LiPF6 in a mixture of EC and DMC. Such an electrolyte is an example of the type used in LIB cells.

[0096] 1 mL to 2 mL of a 1 mol / L LiPF6-EC-DMC solution (EC : DMC, 50:50 v / v) is heated to 200 °C in a tube furnace (heating rate: 15 K / min). The ceramic furnace tube is continuously perfused with N2 (purity 5.0) (volume flow rate: 200 sccm).

[0097] In a 50 mL PFA-PTFE reactor, 35 mL of deionized water were placed. The generated PF5 was introduced into this absorbent. The absorbent and the resulting solution were cooled to 4 °C and homogenized using a magnetic stirrer. The generated PF5 was introduced for 60 min. After this infusion time, a solution with an HF concentration of approximately 50 mmol / L was obtained (quantified by anion chromatography). The H3PO4 concentration was approximately 10 mmol / L (quantified by anion chromatography). The total concentration of PF5 compounds was approximately 1 mmol / L (quantified by anion chromatography and reaction with NaOH).

[0098] 10 mL of this crude solution were treated with 0.2261 g of solid NaOH at 25 °C. The complete conversion of the PFP compounds was verified by anion chromatography. The Na + -ions were removed by treatment with a H +-loaded cation exchanger (Lanxess, Lewatit S2568H) was removed. This was done discontinuously in an overhead shaker at a solid:liquid ratio of 1, a rotation speed of 20 rpm, and a duration of 20 min. This was repeated twice until the absence of Na was confirmed by cation chromatography. + -ions could be confirmed. literature [1] European Commission, Study on the Critical Raw Materials for the EU 2023. Final Report, Publications Office of the European Union, Luxembourg, 2023. [2] M. Bertau, B. Hansel, C. Pätzold, 10 2023 116 962.9. [3] DL Thompson, JM Hartley, SM Lambert, M Shiref, GDJ Harper, E Kendrick, P Anderson, KS Ryder, L Gaines, AP Abbott, Green Chem. 2020, 22, 7585. [4] A. Bulan, K. Esch, P. Strabel, DE10031562A1. [5] CL Campion, W. Li, BL Lucht, J. Electrochem. Soc. 2005, 152, A2327. [6] A. V. Plakhotnyk, L. Ernst, R. Schmutzler, J. Fluorine Chem. 2005, 126, 27. [7] T. Kawamura, S. Okada, J. Yamaki, J. Power Sources 2006, 156, 547. [8] U. Heider, R. Oesten, M. Jungnitz, J. Power Sources 1999, 81-82, 119. [9] D. Aurbach, A. Zaban, Y. Ein-Eli, I. Weissman, O. Chusid, B. Markovsky, M. Levi, E. Levi, A. Schechter, E. Granot, Recent studies on the correlation between surface chemistry, morphology, three-dimensional structures and performance of Li and Li-C intercalation anodes in several important electrolyte systems, 1997.

[10] V. Kraft, W. Weber, M. Grützke, M. Winter, S. Nowak, RSC Adv. 2015, 5, 80150.

[11] T. Dahlke, O. Ruffiner, R. Cant, Procedia Engineering 2016, 138, 231.

Claims

A process for obtaining hydrofluoric acid from lithium hexafluorophosphate, comprising the steps (a) thermal treatment of lithium hexafluorophosphate to obtain phosphorus pentafluoride; (b) contacting phosphorus pentafluoride with an absorbent to obtain a first solution containing hydrofluoric acid and phosphoric acid, the first solution additionally containing monofluorophosphoric acid and / or difluorophosphoric acid; (c) reacting monofluorophosphoric acid and / or difluorophosphoric acid with an inorganic base to obtain a fluoride and a phosphate; and (d) contacting the fluoride with a cation exchanger to convert the fluoride into hydrofluoric acid. Method according to claim 1, characterized in that in step (a) the thermal treatment is carried out at a temperature of 40 °C to 200 °C. Method according to claim 1 or claim 2, characterized in that water is used as an absorbent in step (b). Method according to one of the preceding claims, characterized in that in step (b) the contacting takes place at a temperature of 1 °C to 10 °C. Method according to one of the preceding claims, characterized in that in step (c) the inorganic base is an alkali hydroxide or an alkaline earth hydroxide. Method according to one of the preceding claims, characterized in that in step (c) a second solution is obtained which contains the fluoride and the phosphate. The method according to claim 6, characterized in that the second solution in step (d) is brought into contact with the cation exchanger to convert the fluoride to hydrofluoric acid and the phosphate to phosphoric acid, thereby obtaining a third solution. The method according to claim 7, characterized in that the hydrofluoric acid is separated from the phosphoric acid by means of a separation process. The method according to claim 8, characterized in that the separation is carried out by distillation or by the addition of a silicon-containing compound. Method according to any one of claims 1 to 6, characterized in that step (d) comprises the sub-steps (d1) enriching the fluoride and the phosphate; and (d2) separating the fluoride from the phosphate. Method according to claim 10, characterized in that in partial step (d2) a fractional precipitation of the fluoride and the phosphate takes place. Method according to claim 11, characterized in that the fluoride is brought into contact with the cation exchanger separately from the phosphate. Method according to one of the preceding claims, characterized in that in step (d) the contacting takes place at a temperature of 20 °C to 100 °C. Method according to one of claims 1 to 5, characterized in that the first solution is subjected to purification before monofluorophosphoric acid and / or difluorophosphoric acid are reacted with an inorganic base. A process for obtaining hydrofluoric acid from an electrolyte of a lithium-ion battery containing lithium hexafluorophosphate, comprising the steps (a) thermal treatment of the electrolyte to obtain phosphorus pentafluoride; (b) contacting phosphorus pentafluoride with an absorbent to obtain a first solution containing hydrofluoric acid and phosphoric acid, wherein the first solution additionally contains monofluorophosphoric acid and / or difluorophosphoric acid; (c) reacting monofluorophosphoric acid and / or difluorophosphoric acid with an inorganic base to obtain a fluoride and a phosphate; and (d) contacting the fluoride with a cation exchanger to convert the fluoride into hydrofluoric acid.

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