WO2014127977A1

WO2014127977A1 - Low-temperature method for producing lithium from poorly soluble lithium salts

Info

Publication number: WO2014127977A1
Application number: PCT/EP2014/052000
Authority: WO
Inventors: Günter Schmid; Dan Taroata
Original assignee: Siemens Aktiengesellschaft
Priority date: 2013-02-22
Filing date: 2014-02-03
Publication date: 2014-08-28
Also published as: DE102013202976A1

Abstract

The invention relates to a continuous method of low-temperature lithium electrolysis for producing elementary lithium by means of an electrolyser comprising a current source, an anode chamber, a cathode chamber and an Li-ion permeable membrane which separates the anode chamber from the cathode chamber. The method is characterised in that the electrolyte in the anode and cathode chambers comprises an aprotic solvent, the anions in the cathode chamber cannot be reduced by elementary lithium and the poorly-soluble lithium salt is continuously metered into the anode chamber.

Description

description

Low-temperature process for the production of lithium from poorly soluble lithium salts

The present invention relates to a continuous lithium low-temperature electrolysis process for producing elemental lithium by means of an electrolytic cell comprising a current source, an anode compartment, a cathode compartment and a Li-ion permeable membrane which separates the anode from the cathode compartment, characterized in that the electrolyte in the Anode and cathode compartment comprises an aprotic solvent, the anions in the cathode compartment can not be reduced by elemental lithium and the sparingly soluble

Lithium salt is metered continuously into the anode compartment.

In addition to a broad use of lithium and its compounds in the context of the storage of electrical energy can be increasingly think of industrial applications in which elemental lithium is used as a highly potent reactant or as a thermal energy source. Possible fields of application are, for example, the desulphurisation of flue gases and the conversion and fixation of carbon dioxide. In addition to the resulting heat of reaction, relatively easily recoverable raw materials such as methanol and acetylene can be obtained from the reaction products of these reactions, which in addition to environmental protection aspects can also lead to sustainable process economics. As a direct by-product of these reactions or as a consequence of a subsequent hydrolysis, relatively pure, poorly soluble lithium carbonate Li ₂ C0 _{3 is} generally obtained, which hitherto could only be recycled into the process cycle by means of energy-intensive and hence cost-intensive processes.

In the prior art, in principle known and used on an industrial scale is an electrolysis process, which starting from lithium chloride elemental lithium at the cathode a Downs electrolysis cell separates. Lithium carbonate as a lithium source can only be used via an additional chemical treatment step. In a pretreatment, therefore, the lithium carbonate must first be converted to LiCl by means of hydrochloric acid or Cl ₂ . For example, CA 2340528-A1 describes one possible methodology with chlorine gas.

To avoid the complicated reaction step with potentially dangerous gases, however, a direct electrochemical reduction of lithium carbonate to lithium would be desirable. However, as described in WO2010052714, the electrolysis of a lithium carbonate melt gives carbon monoxide and oxygen on account of the electrode potentials of the reactants present. Elemental lithium is not available in this way (see also Kaplan, V. et al., J. of the Electrochemical Society 157 (4) (2010) B552-B556 "Conversion of CO ₂ to CO by electrolysis of molten lithium carbonates").

In order to suppress CO deposition from the electrolysis solution, an anion which is not reducible under reaction conditions, such as e.g. Chloride or fluoride. This can be achieved, for example, by mechanically separating the anode and cathode compartments from each other by an ion-selective membrane which is permeable only to lithium ions. By a different

Anionenzusammensetzung in the cathode and anode space can prevent the formation of gaseous by-products at the cathode. Possible procedural embodiments of this type of melt electrolysis are described for example in US 498817 and JP 2003049291-A.

A disadvantage of these methods, however, is that they are cumbersome and expensive due to the required process temperatures in the context of electrolysis. Typical temperatures of the melt electrolysis in this case move in a range of above 800 ° C. It is therefore the object of the present invention to provide a continuous electrolysis process for the production of elemental lithium directly from poorly soluble lithium salts, which can be operated with a significantly lower energy consumption. Furthermore, it is within the scope of this invention to provide an apparatus with which the inventive method can be operated. This problem is solved by the features of claim 1. Particular embodiments of the invention are given in the dependent claims.

According to the invention, a continuous lithium low-temperature electrolysis process for the production of elemental lithium by means of an electrolytic cell comprising a current source, an anode compartment, a cathode compartment and a Li-ion permeable membrane which separates the anode from the cathode compartment, characterized in that the electrolyte comprises an aprotic solvent in the anode and cathode compartment, the anions in the cathode compartment can not be reduced by elemental lithium and the sparingly soluble lithium salt is metered continuously into the anode compartment. This process can be carried out directly from a sparingly soluble lithium salt without complicated chemical reaction steps

Electrolysis represent elemental lithium within a continuous manufacturing process. The occurring by-products are not toxic and by using the intended anions in the cathode and anode space and the use of the aprotic solvent process temperatures can be realized, which are well below the previously performed, continuous operated electrolysis. Without being bound by theory, the use of the aprotic solvent in the electrolyte increases the mobility of the ions involved in such a way that sufficient mobility for electrolysis is already achieved at significantly lower temperatures compared with the melt flow method mentioned in the prior art comes about. As a result, a significantly energy-efficient production process can be ensured.

Suitable Li-ion-permeable membranes are the membranes or separators which are known in the prior art and are selectively permeable to Li ions. These are usually polymeric films, which may also consist of several layers or microporous ceramic separators. Furthermore, ceramic-coated nonwovens such as, for example, Separion or Celgard membranes can also be used. Examples of possible types of membranes are listed in Pankaj A. et al, Chem. Rev. 2004, 104, 4419-4462.

Because of the low process temperatures, ceramic-coated polymeric membranes can preferably be used as the Li-ion permeable membrane. This can contribute to the extended life of the electrolysis cell by the higher mechanical load capacity of the polymer-based membranes. The anions in the cathode compartment are stable to reduction with lithium if they do not exchange electrons with elemental lithium under the given reaction conditions. If lithium-reducible anions were introduced into the cathode space, they would be reduced by the elemental lithium formed and, if appropriate, removed from the process as gaseous reaction products. The anions which are inert to an undesired redox reaction can be added to the aprotic solvent in the cathode space at the start of the process in the form of a lithium salt. It is also possible to use mixtures of different anions in the cathode space, provided that each of these anions is stable to reduction by elemental lithium. In particular, these are to be understood as those anions whose normal potential, including any overvoltage that may occur, is greater than or equal to 1.0 V.

Non-inventive anions in the cathode region are, for example, the carbonates, oxides or hydroxides. A continuous production and a continuous supply in the sense of the presented method means in particular that the method is not designed as a pure batch operation, but that during the ongoing process from the outside further reactants of the electrolysis cell fed and formed products can be removed from the electrolysis cell. The supply of the educts and the discharge of the products formed can take place either continuously or else sequentially at certain regular or irregular points in time. The delivery of the sparingly soluble

Lithium salt can be obtained either by introducing the pure lithium salt or by introducing a solution or suspension of the sparingly soluble lithium salt in one

aprotic solvents can be achieved.

As anode material, all those used in lithium battery technology electrically conductive materials can be used, which can be formed to sufficiently mechanically stable anodes and which are chemically stable to any redox products occurring. These may be simple precious metals, stainless steels, graphite, Li ₄ Ti ₅ 0i ₂ in the form of nets, rods or cylinders. The cathode material can consist of cathode materials of the lithium ion accumulator usually used in the prior art, which generally have low overvoltages for lithium. Cited here are, for example, carbonaceous materials such as graphite or carbonaceous intercalation compounds, nanocrystalline, amorphous silicon, Li ₄ Ti ₅ 0i ₂ , LiCoO ₂ , LiNiO ₂ , LiNii_ _x Co _x O ₂ , LiNio, 85COO, ₁ Al ₀ , 050 ₂ , LiNio, 33Co ₀ , 33Mn ₀ , 330 ₂ , LiMnO ₄ , spinel, SnO ₂ and LiFePO ₄ . Other usable cathode materials are described, for example, in Mansour, J. et al. J. Electrochem. Soc. 146 (1999), p. 2799 and Applied Surface Science 253: 10 (March 15, 2007), pp. 4782-4791. Furthermore, it is also possible to use stainless steel, iron, copper, nickel or their alloys. Less preferred is the use of Precious metals such as gold, silver, platinum or their alloys. Advantageously, all of these cathode materials have a low overvoltage to lithium. It is also possible to use inert, conductive carrier materials which are provided only with a thin metal layer. The use of these coated materials can lead to cost savings.

In a preferred embodiment of the invention, the temperature of the low-temperature electrolysis process during the electrolysis may be greater than or equal to 20 ° C and less than or equal to 500 ° C. Further preferably, the temperature of the low-temperature electrolysis process may be greater than or equal to 20 ° C and less than or equal to 300 ° C, and most preferably greater than or equal to 20 ° C and less than or equal to 200 ° C. Due to the method according to the invention, sufficient electrochemical mobilities of the Li ions can be adjusted by this temperature range, which are present in the previously known electrolysis process only at significantly higher temperatures. For this reason, the process temperature can be lowered significantly and thus a significant cost reduction in the manufacturing process can be achieved.

In a further embodiment, the aprotic solvent used in the low-temperature electrolysis process can be selected from the group consisting of polycarbonates, ionic liquids, ethers, polyethers, aliphatic and aromatic amines, C 2 -C 5 -alkyl carbonates, C 2 -C 5 -dialkyl carbonates, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropene and crown ethers are selected. These aprotic solvents show a sufficiently good solubility with respect to the sparingly soluble lithium compounds used and are also chemically and electrochemically inert. By means of these solvents, even in a low temperature range, a sufficiently low viscosity of the electrolyte solution with correspondingly high mobilities of the lithium ions can be achieved. This can contribute to a cost reduction of the manufacturing process. The solvents can be used alone or as a mixture. different solvents are used. Potentially higher viscosity solvents such as polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropene can be used as low molecular weight compounds as sole solvents. Should higher molecular compounds of this type for

When used, these solvents can preferably be used with further, low-viscosity solvents. Furthermore, the actual solvent composition of the anode and the cathode compartment may differ in principle. For the purposes of the present invention, ionic liquids are, for example, salt-like compounds as described in Trans. Nonferrous Met. Soc. China 19, 2009 are described.

In a particular embodiment of the invention, the aprotic solvents used are anhydrous, i. they either have no or only a negligible amount of water of, for example, less than 10 ppm. The water content of the aprotic solvents can be determined by the method known in the art, for example Karl Fischer titration.

In an additional embodiment of the invention, the sparingly soluble lithium salt in aqueous solution at a temperature of 20 ° C have a solubility of less than or equal to 30 g / liter. It is precisely the lithium salts which are sparingly soluble in aqueous solution which can preferably be used in the process according to the invention, since these generally exhibit a sufficiently high solubility in the aprotic solvents used according to the invention. This facilitates process management and can contribute to time and energy savings. However, it is also within the meaning of the invention that the poorly soluble lithium salt in the electrolyte of the anode compartment is only suspended and dissolves further in the course of the electrolysis process. The solubility of the sparingly soluble salts in water can be determined by conventional methods such as, for example, conductometry. Lithium sparingly soluble salts of lithium include, for example, lithium carbonate and lithium phosphate. In an additional aspect of the invention, the sparingly soluble lithium salt used in the low temperature electrolysis process may comprise lithium carbonate. Lithium carbonate may be particularly preferred as starting material of the process according to the invention, since the base material is obtained in large quantities, at reasonable prices and sufficiently pure, so that expensive preparative pretreatment steps can be dispensed with. This can thus contribute to the implementation of a low-cost process. Preferably, dry, ie anhydrous lithium carbonate is metered into the anode compartment. This can counteract unwanted electrochemical decomposition of the water at the anode. In another aspect of the invention, the aprotic solvent in the anode compartment may additionally comprise anions selected from the group of sulfates, chlorides, phosphates, fluorophosphates, fluoroborates. The addition of further anions to the anode compartment can be accomplished, for example, by an initial addition of the corresponding lithium salts. The addition can generally increase the conductivity of the electrolyte and thus lead to a faster and more efficient electrolysis process. The anions added as additional conductive salt (eg PF ₆ ^" , BF ₄ ^" ) should be electrochemically stable and in particular not anodically oxidizable under the given process conditions.

Within another embodiment of the low-temperature electrolysis process, the aprotic solvent may be in the Ka Thode space anions selected from the group consisting BF ₄ ^", PF _^6" comprise, Cl ^", CF ₃ -SO _^3". Due to their electrochemical mobility, electrochemical stability and chemical inertness, this group of anions can contribute to a stable electrolyte process without the occurrence of undesired, possibly toxic, by-products. In particular, these anions can not be electrochemically reduced by lithium, so that advantageously a subsequent metering of these anions in Form of their salts can be omitted due to potential losses during the course of the process.

Furthermore, according to the invention, a continuously operating, low-temperature electrochemical cell for producing elemental lithium comprising an anode, a cathode, a Li-ion permeable membrane which separates the anode and cathode region and a current source, characterized in that the poorly soluble lithium salt can be fed to the anode compartment and elemental lithium is removable from the cathode compartment. This arrangement of the electrolytic cell enables continuous and safe production of elemental lithium at low temperatures. The embodiments of the device for continuously supplying the sparingly soluble

Lithium salt can be directed either to the supply of a pure, dry solid or to the supply of a suspension or solution. In the case of solid feed, this can be realized by a feed screw, a chute or a hopper, if necessary. The metering of liquid or pasty starting materials can be accomplished by the common methods known in the art. Furthermore, it can be provided that the anode compartment can be stirred in a special embodiment of the electrolysis cell. A device for removing the metallic lithium from the cathode space may expediently be directed to the selected process temperature. If the electrolysis is carried out above about 180.degree. C., the lithium can be separated off as a liquid, below 180.degree. C., purely mechanically as a solid and removed from the cathode compartment. In particular, the delivery of the poorly soluble lithium salt and the removal of the elemental lithium can take place without interrupting the electrolysis process. In a further embodiment, the anode material of the low-temperature electrochemical cell may be selected from the group comprising graphite and stainless steel. In contrast to the anode materials described in the prior art battery technology For example, the anode material of this electrolysis cell can be made of a material which is unable to reversibly bind lithium. Chemical resistance to potentially occurring reaction products, such as oxygen, and sufficiently high conductivity may be sufficient. This makes it possible to realize a simple and inexpensive cell structure and save production costs.

In an additional aspect of the invention, the anode of the low temperature electrochemical cell may have a thin exterior

Layer of a metal selected from the group of Edelstäh- le, iron, copper, nickel, gold, platinum, silver on a conductive support material. This anode construction allows an effective electrochemical conversion of the anions present in the anode compartment and can contribute to a cost reduction of the overall method by the thin metal layer only. The outer layer may conveniently have a layer thickness of greater than or equal to 1 μπι and less than or equal to 5 cm, preferably greater than or equal to 10 μπι and less than or equal to 3 cm and further preferably greater than or equal to 50 μπι and less than or equal to 1 cm. The conductive substrate may be selected from the group consisting of stainless steels, copper, aluminum and graphite.

In a further embodiment of the low-temperature electrochemical cell, poorly soluble lithium salt can be supplied to the anode compartment via a pump. In this case, the sparingly soluble lithium salt can be dissolved or suspended as such or in an aprotic solvent and can be metered in via conveying or metering pumps known in the prior art. The metering can be carried out continuously, pulsed or discontinuously in the anode compartment. In general, displacers such as rotary piston, rotary vane, rotary piston, eccentric screw, impeller, tubular or rotary piston pumps or flow pumps can be used for this purpose. The preliminary dissolution and subsequent dosing of the sparingly soluble lithium salt can influence the weight setting of the dissolution process favorably and thus contribute to a lower concentration of conductive salts in the anode compartment. In an additional embodiment of the low-temperature electrochemical cell, the low-temperature cell may be closed by a mechanical barrier from the external environment gas and moisture sealed. This embodiment can prevent the ingress of moisture and oxygen into the region of the electrolysis cell and thus lead to a smaller number of side reactions. Furthermore, the barrier can be designed so that the entire electrolysis cell can be pressurized. The pressurization may favorably influence the solubility product of the sparingly soluble lithium compounds in the aprotic solvent. A preferred range of the compressive strength of the mechanical barrier is between greater than or equal to 1 bar and less than or equal to 500 bar, more preferably between greater than or equal to 1 bar and less than or equal to 400 bar and even more preferably between greater than or equal to 1 bar and smaller or equal to 300 bar.

In a further embodiment of the method, this can be used for the continuous production of elemental lithium.

The above-described characteristics, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the exemplary embodiments, which will be explained in more detail in conjunction with the drawings.

The construction of a low-temperature electrolysis cell according to the invention for the continuous recovery of elemental lithium from sparingly soluble lithium salts is explained in more detail below with reference to FIG. FIG. 1 shows by way of example the structure of a low-temperature electrolysis cell in which Lithium carbonate is converted to elemental lithium, carbon dioxide and oxygen. FIG. 1 shows in detail

Fig. 1, the low-temperature electrolysis cell (1) with the

Removal of elemental lithium (2), the cathode

(3), the cathode compartment (4), the lithium ion selective membrane (5), the anode compartment (6), the anode (7), a discharge of possible reaction products at the anode

(8) and a supply of the sparingly soluble

Lithium salt (for example Li ₂ C0 ₃ ) (9).

Claims

Continuous lithium low-temperature electrolysis process for producing elemental lithium by means of an electrolytic cell comprising a current source, an anode space, a cathode space and a Li-ion permeable membrane which separates the anode from the cathode space, characterized in that the electrolyte in the anode and Cathode space comprises an aprotic solvent, the anions in the cathode compartment can not be reduced by elemental lithium and the sparingly soluble lithium salt is continuously metered into the anode compartment.

A low temperature electrolytic process according to claim 1, wherein the temperature during the electrolysis is greater than or equal to 20 ° C and less than or equal to 500 ° C.

Low-temperature electrolysis process according to one of the preceding claims, wherein the aprotic solvent from the group comprising polycarbonates, ionic liquids, ethers, polyethers, aliphatic and aromatic amines, C 2 -C 5 -alkyl carbonates, C 2 -C 5 -dialkylcarbonates, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropene and crown ethers is selected.

Low-temperature electrolysis process according to one of the preceding claims, wherein the sparingly soluble

Lithium salt in aqueous solution at a temperature of 20 ° C has a solubility of less than or equal to 30 g / liter.

Lithium salt lithium carbonate.

6. Low-temperature electrolysis process according to one of

preceding claims, wherein the aprotic solvent In addition, anions selected from the group of sulfates, chlorides, phosphates, fluorophosphates, fluoroborates in the anode compartment.

Low-temperature electrolysis process according to one of the preceding claims, wherein the aprotic solvent in the cathode compartment anions selected from the group BF ₄ ^~ , PF ₆ ^~ , Cl ^" , CF ₃ -SO ₃ ^" comprises.

Continuously operating, low-temperature electrochemical cell for the production of elemental lithium having an anode, a cathode, an anode and cathode region separating Li-ion permeable membrane and a power source, characterized in that poorly soluble lithium salt can be supplied to the anode compartment and elemental lithium from the cathode compartment can be removed.

A low-temperature electrochemical cell according to claim 8, wherein the anode material is selected from the group comprising graphite and stainless steel.

A low-temperature electrochemical cell according to claim 8 or 9, wherein the anode comprises a thin outer layer of a metal selected from the group of stainless steels, iron, copper, nickel, gold, platinum, silver on a conductive support material.

Low-temperature electrochemical cell according to any one of claims 8-10, wherein poorly soluble lithium salt is supplied to the anode compartment via a pump.

Use of the method according to one of claims 1 to 7 for the continuous production of elemental lithium.