The present invention relates to cation exchange membranes, especially cation exchange membranes having a high selectivity for lithium ions, to electrodialysis stacks comprising these cation exchange membranes and to their use in production, purification, and concentration of lithium salts.

Ion exchange membranes are generally categorized as cation exchange membranes (“CEM”s) or anion exchange membranes (“AEM”s), depending on their predominant charge. CEMs comprise negatively charged groups that allow the passage of cations but reject anions, while AEMs comprise positively charged groups that allow the passage of anions but reject cations. Some ion exchange membranes comprise a porous support which provides mechanical strength. Such membranes are often called “composite membranes” due to the presence of both an ionically charged polymer which discriminates between oppositely charged ions and the porous support which provides mechanical strength.

The production of lithium salts, especially lithium hydroxide, generally requires several stages, including pre-concentration, e.g. by evaporation in evaporation ponds, and pre-treatment, e.g. the removal of multivalent cations such as magnesium and calcium ions.

EP3326974 describes a process for producing lithium hydroxide using bipolar membranes. However first divalent ions are to be removed by injecting NaOH, Na2COs, Ca(OH)2, Na2SO4, and the like sequentially.

EP3061518 describes a process for the production of lithium hydroxide- containing aqueous solutions wherein multivalent metal hydroxides are removed by filtration.

EP2365867 discloses a method for recovering lithium as lithium hydroxide wherein phosphates and other impurities are removed by increasing the pH of the feed prior to bipolar electrodialysis.

JP2009270189 describes the use of acid type chelating resins and cation exchange resins to remove unwanted ions from lithium hydroxide solutions.

It is an object of the present invention to produce lithium hydroxide in high purity without the need for pre-treatment of the feed liquid. It is a further object of the present invention to provide a process for highly efficient production of lithium hydroxide with minimal use of water and low amount of waste chemicals.

According to a first aspect of the present invention there is provided a cation exchange membrane comprising a lithium-ion selective layer and a base layer obtainable by curing a composition comprising:

(a) a first crosslinking agent comprising a bissulphonylimide group and at least two polymerisable groups; (b) a second crosslinking agent comprising at least two polymerisable groups and being free from ionic groups.

In this document (including its claims), the verb "comprise" and its conjugations is used in its non-limiting sense to mean that items following this word are included, but items not specifically mentioned are not excluded. In addition, reference to an element by the indefinite article "a" or "an" does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article "a" or "an" thus usually mean "at least one".

The cation exchange membrane comprising a lithium-ion selective layer is also referred to as lithium-ion selective membrane or Li-selective membrane.

BRIEF DESCRIPTION OF THE DRAWINGS:

Fig 1 illustrates one embodiment of the Li-selective membrane according to the present invention.

Fig 2 illustrates another embodiment of the Li-selective membrane according to the present invention.

Fig 3 illustrates a cross section of the Li-selective layer according to the present invention.

Fig 4 schematically shows an electrodialysis device comprising an electrodialysis cell comprising the Li-selective membrane according to the present invention.

In Fig 1 10 is a base layer and 20 is a Li-selective layer.

In Fig 2 10 is a base layer, 20 is a Li-selective layer and 30 is a protective layer.

In Fig 3 21 is a MOF particle and 22 is a matrix resin.

In Fig 4 40 is an electrical wire, 41 is an electrodialysis cell, 42 is an anode, 43 is a cathode, 44 is a power supply, 45 is a Feed tank, 46 is a Base tank, 47 is an Acid tank, 48 is an Electrolyte tank, 56 is an Electrolyte channel, 57 is a Feed channel, 58 is an Acid channel, 59 is a Base channel, A is an anion exchange membrane, BP is a bipolar membrane and Li is a Li-selective membrane.

Component (a) may contain one first crosslinking agent or more than one first crosslinking agent, e.g. 2, 3 or 4 first crosslinking agents, each comprising a bissulphonylimide group and at least two polymerisable groups. The first crosslinking agent preferably further comprises at least one aromatic group.

Preferred polymerisable groups comprise ethylenically unsaturated groups and thiol groups (e.g. alkylenethiol, preferably -C1-3-SH). Optionally the polymerisable groups further comprise an optionally substituted alkylene group (e.g. optionally substituted Ci-6-alkylene) and/or an optionally substituted arylene group (e.g. optionally substituted Ce-18-arylene). The preferred substituents, when present, include Ci-4-alkyl, Ci-4-alkoxy, sulpho, carboxy and hydroxyl groups.

Preferred ethylenically unsaturated groups include vinyl groups, (meth)acrylic groups (e.g. CH2=CR ¹ — C(O) — groups), especially (meth)acrylate groups (e.g. CH2=CR ¹ — C(O)O — groups) and (meth)acrylamide groups (e.g. CH2=CR ¹ — C(O)NR ¹ — groups), wherein each R ¹ independently is H or CH3). Most preferred ethylenically unsaturated groups comprise or are vinyl groups (CH2=CH- groups).

Preferably components (a) and (b) can be polymerised by exposure to actinic radiation, thermally and/or by electron beam initiation. When component (a) or (b) comprises an ethylenically unsaturated group (e.g. a vinyl group), such group is preferably attached to an aromatic carbon atom such as a benzene ring, e.g. as in divinylbenzene. When component (a) or (b) comprises a thiol group such group is preferably attached to a non-aromatic carbon atom.

Preferably the first crosslinking agent is free from fluoro groups. Fluoro groups are F atoms covalently bound to a carbon atom. Fluoro groups are not preferred because crosslinking agents having fluoro groups are less soluble in aqueous liquids and because of the environmental issue generally associated with fluorinated compounds.

Preferably the first crosslinking agent is free from chloro groups. Chloro groups are Cl atoms covalently bound to a carbon atom.

Preferably the first crosslinking agent is of Formula (I):

Formula (I) wherein: n' has a value of 1 or 2; m has a value of 1 or 2;

M ⁺ is a cation; each R is independently a polymerisable or non-polymerisable group; and

X is an optionally substituted amine group, an optionally substituted alkylene group (e.g. optionally substituted C-i-6-alkylene) or an optionally substituted arylene group (e.g. optionally substituted Ce-is-arylene); provided that the compound of Formula (I) comprises at least two polymerisable groups (and preferably is free from fluoro groups).

Preferably R or each R independently is a vinyl group or a (Ci-3-alkylene)thiol group, an amino group, an alkyl group (especially C- -alkyl) or an aryl group (especially phenyl or naphthyl).

For example, when m=1 and X is amino R is a polymerisable group and n’ is 2. Preferably R is a vinyl group or a (Ci-3-alkylene)thiol group. Thus R may be a vinyl group, an optionally substituted thiol group or non- polymerisable group (as defined above).

The preferred substituents in X, when present, include C- -alkyl, C-i-4-alkoxy, sulpho, carboxy, and hydroxyl groups.

In a preferred embodiment the compound of Formula (I) comprises 2, 3 or 4 polymerisable groups and especially 2 (and only 2) polymerisable groups.

In a preferred embodiment, component (a) is of Formula (I) wherein m and n’ both have a value of 1 , X is a phenylene group carrying a vinyl group and R is a polymerisable group, preferably a vinyl group or a (Ci-3-alkylene)thiol group, and M ⁺ is as herein before defined.

In another preferred embodiment, component (a) is of Formula (I) wherein m has a value of 2, X is a C-i-6-alkylene, or Ce-is-arylene group or X is a group of the formula NR” wherein each R” independently is H or Ci- alkyl and R and M ⁺ are as hereinbefore defined.

In a preferred embodiment, the first crosslinking agent is of Formula (I) wherein m has a value of 1 , n’ has a value of 2, X is a Ci -e-alkyl, or Ce-is-aryl group or a group of the formula N(R”)2 wherein each R” independently is H or C-i-4-alkyl and R is a polymerisable group, preferably a vinyl group or a (Ci-3-alkylene)thiol group, and R and M ⁺ is as herein before defined.

Illustrative synthesis methods for the first crosslinking agent can be found in the examples section below. Furthermore, many of the first crosslinking agents may be prepared by a process comprising the steps of:

(i) providing a sulphonyl halide (e.g. chloride, bromide or fluoride) compound;

(ii) reacting the sulphonyl halide group of component (i) with a compound comprising a sulphonamide group to obtain component (a) (e.g. of Formula (I)); wherein at least one of component (i) and component (ii) comprises at least one polymerisable group or a precursor thereof, preferably a vinyl group or thiol group. Preferably either component (i) or component (ii) comprises an aryl group, e.g. a phenylene group. For instance, component (i) may be a benzenesulphonyl chloride and component (ii) a sulphonamide.

In the illustrative synthesis method described above typically the vinyl group or (Ci-3-alkylene)thiol group is attached to a benzene ring of component (i) and/or (if present) of component (ii). In a preferred embodiment the sulphonyl halide compound used in the process comprises one or more vinyl groups, more preferably one or two vinyl groups, e.g. vinylbenzenesulphonyl halide or divinylbenzenesulphonyl halide.

The composition preferably comprises 40 to 70wt%, more preferably 45 to 65wt% of component (a) (i.e. first crosslinking agent(s)), especially 55 to 62wt%.

Examples of the first crosslinking agents which may be used alone or in combination as component (a) include the following compounds:

As the second crosslinking agent is free from ionic groups it does not comprise any carboxylic acid, bissulphonylimide, sulphonic acid or sulphonate groups.

The second crosslinking agent may be a curable compound of Formula (II):

R -ArrBrrrCq-R

Formula (II) wherein:

A is [CH ₂ CH=CHCH ₂ ];

B is [CH ₂ CH(CH=CH ₂ )];

C is [CH ₂ CH(C ₆ H ₅ )]; n has a value of from 5 to 80% of the sum of (n+m+q); m has a value of from 20 to 95% of the sum of (n+m+q); q has a value of from 0 to 30% of the sum of (n+m+q); and each R’ independently is H or OH; wherein the curable compound of Formula (II) preferably comprises at least 5 vinyl groups and is free from ionic groups.

In Formula (II) groups represented by A are each independently in the cis or the trans configuration.

Preferably the curable compound of Formula (II) is a random, linear copolymer. The groups shown in brackets in Formula (II) (i.e. [CH2CH=CHCH2]n, [CH2CH(CH=CH2)]m and [CH2CH(CeH5)]q) are preferably distributed randomly in Formula (II). Thus the groups shown in brackets in Formula (II) are preferably not in the form of continuous blocks and the curable compound of Formula (II) is preferably not a diblock or triblock copolymer.

Groups A and B in Formula (II) comprise ethenyl groups derived from butadiene. Thus in one embodiment component (b) may be obtained by a process comprising polymerisation of a composition comprising butadiene monomers (and optionally styrene monomers, the latter being represented by group C in Formula (II).

Preferably the second crosslinking agent of Formula (II) comprises at least 8 vinyl groups, more preferably at least 10 and especially at least 12 vinyl groups.

Preferably the second crosslinking agent of Formula (II) comprises less than 75 vinyl groups, more preferably less than 70, especially less than 60 vinyl groups.

The values of n, m and q define the proportion, numerically, of each of the groups A, B and C respectively in the compound of Formula (II) relative to the total amount of the groups A, B and C (i.e. (n+m+q)) in the compound of Formula (II).

Preferably n has a value 5% to 80%, more preferably 10% to 75% and especially 15% to 72% of the sum of (n+m+q).

Preferably m has a value 20% to 95%, more preferably 25% to 90% and especially 28% to 85% of the sum of (n+m+q).

Preferably q has a value 0 to 25% of the sum of (n+m+q).

The values of n, m and q are therefore numbers and herein they are expressed as a % relative to the total number of (n+m+q) groups. In each molecule of Formula (II) n, m and q are integers, although typically component (b) comprises a mixture of compounds of Formula (II) and so the average value of n, m and q for component (b) as a whole will typically not be an integer.

Preferably the absolute value of (n+m+q) is 5 to 270, more preferably 10 to 145, especially 19 to 130.

The absolute value of m is preferably 5 to 75, more preferably 6 to 70, especially 8 to 60.

The absolute value of n is preferably 1 to 250, more preferably 2 to 170, especially 2 to 100.

The absolute value of q is preferably 0 to 80, more preferably 0 to 50, especially 0 to 40.

In a preferred embodiment, the second crosslinking agent is of the Formula (III):

Formula (III) wherein n, m, q and each R’ independently are as hereinbefore defined and preferred in relation to Formula (II).

Optionally, the second crosslinking agent comprises styrene groups. Such styrene groups are preferably distributed randomly within the second crosslinking agent.

Examples of the second crosslinking agents of Formula (II) which may be used as or in component (b) include polybutadiene polymers (especially through predominantly 1 ,2-addition), styrene-butadiene copolymers (especially through predominantly 1 ,2-addition) such polymers carrying one or more (especially two) OH groups, provided that such polymers comprise at least 5 vinyl groups and are free from ionic groups. Such materials can be obtained from commercial sources, e.g. from Cray Valley Technologies (e.g. under the names of Ricon®, Krasol®, Poly bd®) or Nippon Soda Co, Ltd (e.g. under the name of Nisso-PB ^TM ).

The second crosslinking agents of Formula (II) preferably have a viscosity not higher than 600 Poise, more preferably less than 400 Poise, especially lower than 200 Poise, more especially below 100 Poise, when measured at 25°C by a suitable viscosity meter such as a Brookfield DVII viscosity meter equipped with a SC4-18 conical spindle and operated at 60 rpm. When the second crosslinking agent has the above preferred viscosity then manufacturing of the base layer of the cation exchange membrane is facilitated.

The second crosslinking agent may also be a compound of Formula (IV):

R ”’n-A’

Formula (IV) wherein: each R’” independently comprises a polymerisable group or a non- polymerisable group; n has a value of 2, 3 or 4; and

A’ is a linking group; wherein the compound of Formula (IV) preferably comprises 2, 3 or 4 polymerisable groups and is free from ionic groups.

The polymerisable groups present in R’” in Formula (IV) include ethylenically unsaturated groups and thiol groups (e.g. alkylenethiol, preferably -C1-3-SH). Preferred ethylenically unsaturated groups are as described above in relation to the first crosslinking agent.

The non-polymerisable groups in R’” include amino, alkyl (especially C- -alkyl) and aryl (especially phenyl or naphthyl), each of which is unsubstituted or carries one or more non-polymerisable substituents, e.g. Ci-4-alkyl, C-i-4-alkoxy, amino, C1-4- alkyamine, sulpho, carboxy, or hydroxyl group.

Preferably in Formula (IV) each R’” is a vinyl group, an allyl group or a C0-3- alkylene-thiol group.

The second crosslinking agent of Formula (IV) may be obtained commercially or by methods known in the art.

Preferably the second crosslinking agent of Formula (IV) is free from fluoro and/or chloro groups.

In Formula (IV) the group A’ is preferably N (a nitrogen atom) or an optionally substituted alkylene group (e.g. optionally substituted C-i-6-alkylene) or an optionally substituted arylene group (e.g. optionally substituted Ce-is-arylene). The preferred substituents, when present, include C- -alkyl, C- -alkoxy and hydroxyl groups.

In a preferred embodiment, in Formula (IV):

(i) each R’” independently comprises a polymerisable group, n has a value of 2, 3 or 4 and A’ is C-i-6-alkylene or Ce-is-arylene; or

(ii) A’ is N, n has a value of 3 and either all three of the groups represented by R’” comprise a polymerisable group or two of the groups represented by R’” comprise a polymerisable group and the third group represented by R’” is H or C1-4 alkyl; or

(iii) A’ is a triazine group or a cyanuric acid derivative, n has a value of 3 and either all three of the groups represented by R’” comprise a polymerisable group or two of the groups represented by R’” comprise a polymerisable group and the third group represented by R’” is C1-4 alkoxy or C1-4 alkyl.

The second crosslinking agent of Formula (IV) preferably has a molecular weight below 500 Da, more preferably below 400 Da, especially below 300 Da, more especially below 260. By keeping the molecular weight of the second crosslinking agent low the ion exchange capacity of the base layer of the present invention is not reduced significantly.

Examples of the second crosslinking agents of Formula (IV) which may be used alone or in combination as component (b) include the following compounds.

Preferably the second crosslinking agent of Formula (IV) comprises divinylbenzene, 2,4,6-triallyloxy-1 ,3,5-triazine, 1 ,3,5-triallylisocyanurate, triallylamine, 1 ,2,4-trivinylcyclohexane, tetra(allyloxy)ethane, pentaerythritol tetraallyl ether, 2,3- dimercapto-1 -propanol, dithioerythritol, trithiocyanuric acid, 1 ,3 or 1 ,4- benzenedimethanethiol or a combination thereof. The second crosslinking agent preferably comprises vinyl groups.

Preferably the composition comprises 1 to 25wt%, most preferably 2 to 20wt% of component (b), i.e. the second crosslinking agent(s).

Component (b) may contain one second crosslinking agent or more than one second crosslinking agent, e.g. 2, 3 or 4 second crosslinking agents, each comprising at least 2 crosslinkable groups and being free from ionic groups and may be selected from a crosslinking agent comprising 2, 3 or 4 polymerisable groups and having a molecular weight of less than 500 Da (a compound of Formula (IV)), a crosslinking agent comprising at least 5 vinyl groups (a compound of Formula (II)), or combinations of two or more thereof.

In a preferred embodiment the second crosslinking agent is a liquid at the temperature at which the base layer is prepared. Preferably the second crosslinking agent has a melting point below 80°C, more preferably below 50°C, especially below 30°C.

Preferably the polymerisable groups present in the first crosslinking agent(s) are copolymerisable with the polymerisable groups present in the second crosslinking agent(s). For example:

- the polymerisable groups in the first and second crosslinking agents are each independently selected from ethylenically unsaturated groups;

- the polymerisable groups in one of the first or second crosslinking agents are/comprise thiol groups and the polymerisable groups in the other of the first and second crosslinking agents are groups which are reactive with thiol groups, e.g. ethylenically unsaturated groups.

The molar ratio of component (a) to the molar amount of component (b) is preferably in the range 2 to 12 (i.e. 2:1 to 12:1 ).

The base layer of the cation exchange membrane according to the first aspect of the present invention is preferably obtainable by curing a composition comprising:

(a) component (a) as defined above;

(b) component (b) as defined above; optionally (c) a compound comprising one and only one polymerisable group; optionally (d) a radical initiator; and optionally (e) a solvent.

The abovementioned composition forms a second aspect of the present invention.

The preferred amounts of components (a) and (b) are as described above in relation to the first aspect of the present invention.

Preferably the composition comprises 0 to 40 wt%, more preferably 5 to 30% wt%, most preferably 6 to 25 wt%, of component (c).

Preferably the composition comprises 0 to 10 wt%, more preferably 0.001 to 5 wt%, most preferably 0.005 to 2 wt%, of component (d). Preferably the composition comprises 0 to 40 wt%, more preferably 10 to 40 wt%, most preferably 15 to 35 wt%, of component (e).

Component (c) may contain one a compound comprising one and only one polymerisable group or more than one compound comprising one and only one polymerisable group. Preferably component (c) comprises an anionic group.

The preferred polymerisable group which may be present in the compound(s) comprising one and only one polymerisable group is as defined above in relation to component (a), especially a vinyl group, e.g. in the form of allylic or styrenic group. Styrenic groups are preferred over e.g. (meth)acrylic groups because the resultant base layer has particularly good stability over a wide pH range.

Examples of compounds which comprise one and only one polymerisable group include the following compounds of Formula (MB-a), (AM-B) and Formula (V): wherein in Formula (MB-a),

R ^A2 represents a hydrogen atom or an alkyl group;

R ^A4 represents an organic group comprising a sulpho group in free acid or salt form and having no ethylenically unsaturated group; and

Z ² represents -(C=O)NRa- wherein Ra represents a hydrogen atom or an alkyl group preferably a hydrogen atom.

Examples of compounds of Formula (MB-a) include: Synthesis methods for compounds of Formula (MB-a) can be found in e.g. US2015/0353696.

Synthesis methods for the above compounds can be found in e.g. LIS2016/0369017.

Formula (AM-B) wherein in Formula (AM-B): LL ² represents a single bond or a bivalent linking group; and

A represents a sulpho group in free acid or salt form; and m represents 1 or 2.

Examples of compounds of Formula (AM-B) include:

Such compounds of Formula (AM-B) are commercially available, e.g. from Tosoh Chemicals and Sigma-Aldrich.

Formula (V) wherein

R _a in Formula (V) is C1-4 alkyl, NH2 or Ce-12-aryl; and M ⁺ is a cation, preferably H ⁺ , Li ⁺ , Na ⁺ , K ⁺ or Nl_4 ⁺ wherein each L independently is H or C-i-3-alkyl.

Examples of compounds of Formula (V) include:

Synthesis methods for the above compounds having the MM prefix are known from literature.

Preferably component (c) comprises one or more compounds of Formula (AM-B) and/or Formula (V) because this can result in a base layer having especially good stability in the pH range 0 to 14.

Component (d) may contain one radical initiator or more than one radical initiator. Preferred radical initiators include thermal initiators and photoinitiators.

Examples of suitable thermal initiators which may be used as component (d) include 2,2’-azobis(2-methylpropionitrile) (AIBN), 4,4’-azobis(4-cyanovaleric acid), 2,2’- azobis(2,4-dimethyl valeronitrile), 2,2’-azobis(2-methylbutyronitrile), 1 ,1’- azobis(cyclohexane-1 -carbonitrile), 2,2’-azobis(4-methoxy-2,4-dimethyl valeron itri le) , dimethyl 2,2’-azobis(2-methylpropionate), 2,2’-azobis[N-(2-propenyl)-2- methylpropionamide, 1-[(1-cyano-1 -methylethyl)azo]formamide, 2,2'-Azobis(N-butyl-2- methylpropionamide), 2,2'-Azobis(N-cyclohexyl-2-methylpropionamide), 2,2'-Azobis(2- methylpropionamidine) dihydrochloride, 2,2'-Azobis[2-(2-imidazolin-2- yl)propane]dihydrochloride, 2,2'-Azobis[2-(2-imidazolin-2-yl)propane]disulphate dihydrate, 2,2'-Azobis[N-(2-carboxyethyl)-2-methylpropionamidine] hydrate, 2,2'- Azobis{2-[1 -(2-hydroxyethyl)-2-imidazolin-2-yl]propane} dihydrochloride, 2,2'-Azobis[2- (2-imidazolin-2-yl)propane], 2,2'-Azobis(1 -imino-1 -pyrrolidino-2-ethylpropane) dihydrochloride, 2,2'-Azobis{2-methyl-N-[1 , 1 -bis(hydroxymethyl)-2- hydroxyethl]propionamide}, 2,2'-Azobis[2-methyl-N-(2-hydroxyethyl)propionamide] and combinations of two or more thereof.

Examples of suitable photoinitiators which may be included in the composition as component (d) include aromatic ketones, acylphosphine compounds, aromatic onium salt compounds, organic peroxides, thio compounds, hexa-arylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon halogen bond, and an alkyl amine compounds. Preferred examples of the aromatic ketones, the acylphosphine oxide compound, and the thio-compound include compounds having a benzophenone skeleton or a thioxanthone skeleton described in "RADIATION CURING IN POLYMER SCIENCE AND TECHNOLOGY", pp.77-117 (1993) and combinations of two or more thereof. More preferred examples thereof include an alphathiobenzophenone compound described in JP1972-6416B (JP-S47-6416B), a benzoin ether compound described in JP1972-3981 B (JP-S47-3981 B), an alpha-substituted benzoin compound described in JP1972-22326B (JP-S47-22326B), a benzoin derivative described in JP1972-23664B (JP-S47-23664B), an aroylphosphonic acid ester described in JP1982-30704A (JP-S57-30704A), dialkoxybenzophenone described in JP1985-26483B (JP-S60-26483B), benzoin ethers described in JP1985-26403B (JP- S60-26403B) and JP1987-81345A (JPS62-81345A), alpha-amino benzophenones described in JP1989-34242B (JP H01 -34242B), U.S. Pat. No. 4,318,791A, and EP0284561A1 , p-di(dimethylaminobenzoyl) benzene described in JP1990-211452A (JP-H02- 211452A), a thio substituted aromatic ketone described in JP1986-194062A (JPS61 -194062A), an acylphosphine sulphide described in JP1990-9597B (JP-H02- 9597B), an acylphosphine described in JP1990-9596B (JP-H02-9596B), thioxanthones described in JP1988-61950B (JP-S63-61950B), and coumarins described in JP1984- 42864B (JP-S59-42864B). In addition, the photoinitiators described in JP2008-105379A and JP2009-114290A are also preferable. In addition, photoinitiators described in pp. 65 to 148 of "Ultraviolet Curing System" written by Kato Kiyomi (published by Research Center Co., Ltd., 1989) may be used.

Preferred photoinitiators include Norrish Type II photoinitiators having an absorption maximum at a wavelength longer than 380nm, when measured in one or more of the following solvents at a temperature of 23°C: water, ethanol and toluene. Examples include a xanthene, flavin, curcumin, porphyrin, anthraquinone, phenoxazine, camphorquinone, phenazine, acridine, phenothiazine, xanthone, thioxanthone, thioxanthene, acridone, flavone, coumarin, fluorenone, quinoline, quinolone, naphtaquinone, quinolinone, arylmethane, azo, benzophenone, carotenoid, cyanine, phtalocyanine, dipyrrin, squarine, stilbene, styryl, triazine, anthocyanin-derived photoinitiator and combinations of two or more thereof.

Component (e) may contain one solvent or, more typically, more than one solvent.

Preferably the solvent(s) used as component (e) are inert solvents. In other words, preferably the solvent does not react with any of the other components of the composition. In one preferred embodiment component (e) comprises water and optionally an organic solvent, especially where some or all of the organic solvent is water-miscible. The water is useful for dissolving component (a) and possibly also component (c) and the organic solvent is useful for dissolving component (b) and any other organic components present in the composition.

Component (e) is useful for reducing the viscosity and/or surface tension of the composition.

Examples of inert solvents which may be used as or in component (e) include water, alcohol-based solvents, ether-based solvents, amide-based solvents, ketone- based solvents, sulphoxide-based solvents, sulphone-based solvents, nitrile-based solvents and organic phosphorus-based solvents. Examples of alcohol-based solvents which may be used as or in component (e) (especially in combination with water) include methanol, ethanol, isopropanol, n-butanol, diacetone alcohol, methoxypropanol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol and mixtures comprising two or more thereof. In addition, preferred inert, organic solvents which may be used in component (e) include dimethyl sulphoxide, dimethyl imidazolidinone, sulpholane, N-methylpyrrolidone, dimethyl formamide, acetonitrile, acetone, 1 ,4- dioxane, 1 ,3-dioxolane, tetramethyl urea, hexamethyl phosphoramide, hexamethyl phosphorotriamide, pyridine, propionitrile, butanone, cyclohexanone, tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran, ethylene glycol diacetate, cyclopentylmethylether, methylethylketone, ethyl acetate, y-butyrolactone and mixtures comprising two or more thereof.

The lithium selective layer preferably comprises a metal-organic-framework (MOF) in the form of particles. MOFs generally comprise one or more metal ions and organic ligands. Examples of MOFs include Zeolitic Imidazolate Frameworks (ZIF) (e.g. ZIF-7, ZIF-8, ZIF-11 , ZIF-22, ZIF- 69, ZIF-90, ZIF-94 aka SIM-1 ), Isoreticular Metal Organic Frameworks (IRMOF) (e.g. IRMOF-1 , IRMOF-3), zirconium-ion based MOFs (e.g. UiO-66 and derivatives thereof), copper based MOFs (e.g. CuBTC, also known as HKUST-1 or MOF-199, wherein BTC stands for benzene-1 ,3,5-tricarboxylate), chromium(lll)-ion based MOFs (e.g. MIL-53), vanadium-ion based MOFs (e.g. MIL-47), titanium-ion based MOFs (e.g. MIL125), aluminium-ion based MOFs (e.g. MIL-96), and combinations thereof. Also Mixed Metal Organic Frameworks (MMOFs) may be used. In most MOFs the metal ion may be replaced as well as the organic ligand. Metal ions that may be used include e.g. Cu, Zn, Zr, Co, In, Al, Fe, V, Mg, Mn, Ni, Ru, Mo, Cr, W, Rh and Pd, preferably Cu, Zn, Co, In, Al, Fe, and Zr, and most preferably Cu, Zn or Zr. The metal ions may be introduced in the form of salts, e.g. as metal nitrates, metal sulfates, metal chlorides, metal bromides, metal iodides, metal fluorides, metal carbonates, metal acid salts, metal phosphates, metal sulfides and metal hydroxides. Preferred are metal nitrates and metal chlorides.

In a preferred embodiment crown ether MOFs (CEMOFs) are used comprising: a porous metal organic framework (MOF) structure having a first surface with a first pore window and a second surface with a second pore window and a channel therebetween, the MOF structure being functionalized by one or more crown ether (CE) structures contained within or on the channel; the MOF structure comprising a material selected from the group consisting of UiO-66, ZIF-7, ZIF- 8, MIL-121 , ZJU-24, NU-125-IPA, and NU-125-HBTC; and the CE structure comprising a compound selected from the group consisting of 12-crown-4, 15-crown-5, 18-crown-6, 21 -crown-7, 24-crown-8, 27-crown- 9, and 30-crown-10 are preferred.

The organic ligand preferably comprises a dicarboxylic acid, tricarboxylic acid, imidazole, benzimidazole, azabenzoimidazole and/or derivatives thereof. Examples of dicarboxylic acid include isophthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, 1 ,4-naphthalenedicarboxylic acid and biphenylenedicarboxylic acid. Examples of tricarboxylic acid include 1 ,2,3-benzenetricarboxylic acid and 1 ,3,5-benzenetricarboxylic acid. Examples of tetracarboxylic acid include 1 ,2,3,4-benzenetetracarboxylic acid and 1 ,2,4,5-benzenetetracarboxylic acid. These organic ligands may optionally be substituted by one or more hydroxyl groups, amino groups, methoxy groups, methyl groups, nitro groups, methylamino groups, dimethylamino groups, cyano groups, chloro groups, bromo groups, fluoro groups and combinations thereof.

The particle size of the MOF is preferably from 1 nm to 10 pm, more preferably from 5 to 1000 nm. The particle size may be uniform or not uniform, i.e. the MOF may be a mixture of particles having a different size.

The shape of the particles is not limited, and may be a sphere, a cube, a polyhedron, a rectangular parallelepiped, a plate, or a rod. In case of a plate shape, the width of the flat plate surface is preferably 50 nm or more, more preferably 100 nm-5pm, the length is preferably 50 nm or more, more preferably 100 nm-5pm, and the aspect ratio (width I thickness, or length /thickness) is preferably 5 or more, more preferably 10 or more. The larger the aspect ratio the larger the contact area between the particles is. Therefore the Li permeablity of the Li-selective layer may be increased.

The average pore size of the MOF particles is preferably from 0.1 to 2 nm, more preferably from 0.3 to 0.9 nm, e.g. around 0.4 nm, around 0.5 nm, around 0.6 nm or around 0.7 nm. In one embodiment the average pore size of the MOF particles is between 0.38 and 0.65 nm.

MOF particles may be prepared as described in e.g. J. Am. Chem. Soc., 130, 13950-13951 (2008).

The MOF particles are preferably embedded in a matrix resin which may be cationically charged, or non-charged and preferably hydrophobic. The cationically charged matrix is preferred as it repels multivalent cations and enhances the separation of Li-ions over multivalent cations.

In one embodiment the matrix resin comprises poly(amide imide), poly(ether-b- amide), polysulfone, a polymer derived from bisphenylsulfone, polyimide, polyether sulfone, polyphenylsulfone, polyvinylidene difluoride (PVDF), polybenzimidazole (PBI), polyamide, polyimide, cellulose acetate, derivatives thereof, or combinations thereof. Examples include MATRIMID® maleimide thermoset and thermoplastic polyimide resins from Huntsman Corporation and Torlon® polyamide-imide (PAI) from Solvay.

In another embodiment the matrix resin comprises cationic charges. In a preferred embodiment the cationically charged matrix resin is obtained by curing a composition comprising a curable compound comprising two or more polymerizable groups and a cationic group, preferably a quaternary ammonium group or a pyridinium group. The polymerizable group is preferably an ethylenically unsaturated group, an epoxy group, or oxetane group, more preferably an ethylenically unsaturated group, such as a (meth)acrylic group or a vinyl group. The curable compound comprising two or more polymerizable groups and a cationic group is preferably a monomer of General Formula (CCL-A), (CCL-B) or (CCL- C): wherein each of R and R ¹ independently represents a hydrogen atom or an alkyl group; each of R ¹ , R ¹ ’, R ² and R ² ' independently represents an alkyl group or an aryl group; each of L, L ¹ , L ² , and L ² ' independently represents an alkylene group, an arylene group, or a bivalent linking group comprising an alkylene and an arylene group; at least two of R ¹ , R ¹ ', R ² , and R ² ' may be bonded to each other to form a ring, together with L;

X represents a counter anion; n1 represents an integer of 2 to 6, preferably 2 or 3, and more preferably 2.

The ring mentioned above is preferably a 5-membered or 6-membered ring, e.g. a piperazine ring or a 1 ,4-diazabicyclo[2,2,2]octane ring.

The number of alkyl groups in R, R', R ¹ , R ¹ ', R ² and R ² ' is preferably 1 to 3, more preferably 1 or 2, and even more preferably 1. Examples of the alkyl group include methyl, ethyl, propyl, and isopropyl, a methyl group is preferred. The number of carbon atoms of the aryl group in R ¹ , R ¹ ', R ² and R ² ' is preferably 6 to 10, more preferably 6 or 8, and even more preferably 6. Examples of the aryl group include phenyl and naphthyl groups, and a phenyl group is preferred. For R and R' hydrogen is preferred.

The number of carbon atoms of the alkylene group in L, L ¹ , L ² , and L ² ' is preferably 1 to 10, more preferably 1 to 6, especially 1 to 4 and more especially 1 to 3. The number of carbon atoms of the arylene group in L, L ¹ , L ² , and L ² ' is preferably 6 to 10 and more preferably 6 to 8. The arylene group preferably includes phenylene or naphthylene; phenylene is preferable.

X is preferably a halogen ion, e.g. a chloride or bromide ion. The curable compound of Formula (CCL-A), (CCL-B) or (CCL-C) may further comprise one or more substituents. Preferred substituents include alkyl groups, cycloalkyl groups, alkenyl groups, alkynyl groups, aryl groups, amino groups, alkoxy groups, aryloxy groups, cyano groups, nitro groups, halide groups, and combinations thereof. Specific examples of the monomer expressed by any one of General formulae

(CCL-A) to (CCL-C) are provided below.

The composition for preparing the cationically charged matrix resin may further comprise a monofunctional monomer that is preferably cationically charged and/or a multifunctional monomer being free from ionic groups. In addition to the components described above, the composition may further comprise a surface tension adjuster, a surfactant, a high molecular weight dispersant, a viscosity improver, a preservative, and/or an anti-crater agent.

Preferably the monofunctional monomer is of General Formula (CM-A) or (CM-B). wherein, in General formulae (CM-A) and (CM-B), R and X have the same meanings as R and X in General formulae (CCL-A) to (CCL-C), and the preferable scopes thereof are also the same; each of R ¹⁰ to R ¹² independently represents an alkyl group or an aryl group; at least two of R ¹⁰ to R ¹² may be bonded to each other to form a ring; and each of L ¹⁰ and L ²⁰ independently represents an alkylene group, an arylene group, or a bivalent linking group comprising an alkylene and an arylene group.

The ring mentioned above is preferably a 5-membered or 6-membered ring, e.g. a piperidine ring, a piperazine ring, a morpholine ring, and a thiomorpholine ring.

Examples of the monovalent monomer include the following compounds. The amount of the monofunctional monomer is preferably 0 parts by mass to 120 parts by mass, more preferably 0 parts by mass to 100 parts by mass, and even more preferably 0 parts by mass to 80 parts by mass with respect to 100 parts by mass of the curable compound comprising two or more polymerizable groups and a cationic group.

The weight fraction of MOF particles in the Li-selective layer is preferably at least 0.7, more preferably at least 0.8, e.g. at least 0.9. A high weight fraction is preferred to achieve a high selectivity of lithium over other metal ions.

The selectivity of lithium to sodium is preferably at least 4 more preferably at least 20.

The thickness of the Li-selective layer is preferably 0.1 pm to 50 pm, more preferably 0.2 pm to 30 pm, and especially 0.2 pm to 10 pm.

If the Li-selective layer is too thick, the Li permeability is lowered, so that the electric resistance is increased and the operating voltage of the electrodialysis apparatus is increased, which is not preferable. On the other hand, if the Li-selective layer is too thin, the permeability of impurities will increase and the purity of the product will decrease, which is not preferable.

In one embodiment the thickness of the Li-selective layer is preferably less than 1 pm, e.g. between 0.2 and 0.9 pm, to achieve a high permeability of lithium ions and reduce costs. A very thin Li-selective layer may be vulnerable to damaging during handling resulting in a reduced selectivity. In this embodiment a protective layer on the Li-selective layer on the side opposite to the base layer is preferred.

As protective layer the same material which is applied in the base layer may be used. Alternatively, a polymeric resin bearing cationic charges is applied, e.g. the same materials as described above for the matrix resin in the Li-selective layer.

In another embodiment the protective layer comprises an anionic resin and a thin monovalent cation selective layer on top.

The thickness of the protective layer is preferably 0.1 -50 pm, more preferably 0.5- 20 pm from the viewpoint of permeability and stress relaxation.

According to a third aspect of the present invention there is provided a process for preparing a base layer comprising curing the composition defined in relation to the first aspect of the present invention to form a base layer and subsequently applying a lithium-ion selective layer.

The composition which is cured in the process according to the third aspect of the present invention is preferably as defined in relation to the second aspect of the present invention.

The process for preparing the cation exchange membrane preferably comprises the steps of: i. providing a porous support; ii. impregnating the porous support with the composition (preferably the composition of the second aspect of the present invention); iii. curing the composition; iv. applying and curing a composition comprising MOF particles to form the lithium- ion selective layer; and v. optionally applying a protective layer.

The preferences for the composition used in the process of the third aspect of the present invention are as described herein in relation to the first and second aspects of the present invention.

Preferably the process according to the third aspect of the present invention comprises two different curing methods (dual curing). In a preferred embodiment the compositions are cured first by photocuring, e.g. by irradiating the compositions by ultraviolet or visible light, or by gamma or electron beam radiation, and thereby causing curable components present in the compositions to polymerise, and then applying a third curing step. The third curing step preferably comprises thermal curing, gamma irradiation or EB irradiation (thereby causing curable components present in the compositions to further polymerise thereby increasing the network density). When gamma or electron beam irradiation is used in the first and second curing steps preferably a dose of 60 to 120 kGy, more preferably a dose of 80 to 100 kGy is applied.

In one embodiment the process according to the third aspect of the present invention comprises curing the composition of the second aspect of the present invention in a first curing step (e.g. UV curing or electron beam (EB) curing) to form a base layer, applying and curing a composition comprising MOF particles to form the lithium-ion selective layer on the base layer (in a second curing step), winding the resulting membrane onto a core (optionally together with an inert polymer foil) and then performing a third curing step (e.g. thermal curing). In another embodiment the process comprises curing the composition of the second aspect of the present invention in a first curing step (e.g. UV curing) to form a base layer, applying and curing a composition comprising MOF particles to form the lithium-ion selective layer on the base layer in a second curing step, performing a third curing step (e.g. EB curing) and then winding the resulting membrane onto a core (optionally together with an inert polymer foil).

In a preferred embodiment the first, second and third curing steps are respectively selected from (i) UV curing, UV curing then thermal curing; (ii) UV curing, UV curing then electron beam curing; (iii) electron beam curing, electron beam curing then thermal curing, and (iv) electron beam curing, UV curing then thermal curing.

The composition preferably comprises 0.05 to 5wt% of radical initiator for the first and second curing steps. The compositions optionally further comprise 0 to 5 wt% of a second radical initiator for the third curing step. When it is intended to cure the composition thermally or using light (e.g. UV or visible light) the compositions preferably comprise 0.001 to 2wt%, depending on the selected radical initiator(s), in some embodiments 0.005 to 0.9wt%, of component (d). As mentioned above, component (d) may comprise more than one radical initiator, e.g. a mixture of several photoinitiators (for UV curing) or a mixture of photoinitiators and thermal initiators (for UV and thermal curing). Alternatively a second curing step is performed using gamma or EB irradiation. For the third curing step by gamma or EB irradiation preferably a dose of 20 to 100 kGy is applied, more preferably a dose of 40 to 80 kGy is applied.

For the third curing step, thermal curing is preferred. The thermal curing is preferably performed at a temperature between 50 and 100°C, more preferably between 60 and 90°C. The thermal curing is preferably performed for a period between 2 and 48 hours, e.g. between 8 and 16 hours, e.g. about 10 hours. Optionally after the first and second curing steps a polymer foil is applied to the cation exchange membrane before winding (this reduces oxygen inhibition and/or sticking of the membrane onto itself).

Optionally a protective layer is applied and cured in an additional curing step between the second and the third curing step. Preferably for the curing of the protective layer the same curing method is used as for the first or second curing steps.

In another embodiment the first and second curing steps are combined into one curing step whereby the lithium selective layer is applied prior to the combined curing step.

Preferably the process according to the third aspect of the present invention is performed in the presence of a porous support. For example, the composition is present in and/or on a porous support when it is cured. The porous support provides mechanical strength to the cation exchange membrane resulting from curing the composition.

As examples of porous supports which may be used there may be mentioned woven and non-woven synthetic fabrics and extruded films. Examples include wetlaid and drylaid non-woven material, spunbond and meltblown fabrics and nanofiber webs made from, e.g. polyethylene, polypropylene, polyacrylonitrile, polyvinyl chloride, polyphenylenesulphide, polyester, polyamide, polyaryletherketones such as polyether ether ketone and copolymers thereof. Porous supports may also be porous membranes, e.g. polysulphone, polyethersulphone, polyphenylenesulphone, polyphenylenesulphide, polyimide, polyethermide, polyamide, polyamideimide, polyacrylonitrile, polycarbonate, polyacrylate, cellulose acetate, polypropylene, poly(4- methyl 1 -pentene), polyinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene and polychlorotrifluoroethylene membranes and derivatives thereof.

The porous support preferably has an average thickness of between 10 and 800pm, more preferably between 15 and 300pm, especially between 20 and 150pm, more especially between 30 and 130pm, e.g. around 60pm or around 100pm.

Preferably the porous support has a porosity of 30 and 95%. The free volume of the porous support, prior to making the membrane, may be calculated from thickness and weight (g/m ² ) and fiber density (g/m ³ ) data. The porous support, when present, may be treated to modify its surface energy, e.g. to values above 45 mN/m, preferably above 55mN/m. Suitable treatments include corona discharge treatment, plasma glow discharge treatment, flame treatment, ultraviolet light irradiation treatment, chemical treatment or the like, e.g. for the purpose of improving the wettability of and the adhesiveness to the porous support to the cation exchange membrane.

Commercially available porous supports are available from a number of sources, e.g. from Freudenberg Filtration Technologies (Novatexx materials), Lydall Performance Materials, Celgard LLC, APorous Inc., SWM (Conwed Plastics, DelStar Technologies), Teijin, Hirose, Mitsubishi Paper Mills Ltd and Sefar AG.

Preferably the porous support is a porous polymeric support. Preferably the porous support is a woven or non-woven synthetic fabric or an extruded film without covalently bound ionic groups.

In a preferred process according to the third aspect of the present invention, the composition may be applied continuously to a moving (porous) support, preferably by means of a manufacturing unit comprising a composition application station, one or more irradiation source(s) for curing the composition, a membrane collecting station and a means for moving the support from the composition application station to the irradiation source(s) and to the membrane collecting station.

The composition application station may be located at an upstream position relative to the irradiation source(s) and the irradiation source(s) is/are located at an upstream position relative to the membrane collecting station.

Examples of suitable coating techniques for applying the composition to a porous support include slot die coating, slide coating, air knife coating, roller coating, screenprinting, and dipping. Depending on the used technique and the desired end specifications, it might be desirable to remove excess coating from the substrate by, for example, roll-to-roll squeeze, roll-to-blade or blade-to-roll squeeze, blade-to-blade squeeze or removal using coating bars. Curing by light is preferably done for the first curing step, preferably at a wavelength between 300 nm and 800 nm using a dose between 40 and 20,000 mJ/cm ² In some cases additional drying might be needed for which temperatures between 40°C and 200°C could be employed. When gamma or EB curing is used irradiation may take place under low oxygen conditions, e.g. below 200 ppm oxygen.

The cation exchange membrane of the present invention is very suitable for use in a lithium-ion concentration system comprising an electrodialysis apparatus.

According to a fourth aspect of the present invention there is provided an electrodialysis apparatus comprising:

(i) the cation exchange membrane according to the first aspect of the present invention;

(ii) a bipolar membrane; and

(iii) optionally an anion exchange membrane. Preferably the electrodialysis apparatus comprises a unit cell having two compartments placed between an anode and a cathode comprising:

(A1 ). a first compartment defined by the cation exchange membrane of the present invention and a first bipolar membrane; and

(B1 ). a second compartment defined by the cation exchange membrane of the present invention and a second bipolar membrane.

Alternatively the electrodialysis apparatus comprises a unit cell having three compartments placed between an anode and a cathode comprising:

(A2). a first compartment defined by the cation exchange membrane of the present invention and an anion exchange membrane;

(B2). a second compartment defined by the cation exchange membrane of the present invention and a first bipolar membrane; and

(C2). a third compartment defined by the anion exchange membrane and a second bipolar membrane.

This embodiment is depicted in Fig 4.

Preferably in the electrodialysis apparatus a current density of between 10 and 100 A/m ² is applied. A low current density is preferred to achieve a high purity of lithium hydroxide.

According to a fifth aspect of the present invention there is provided a process for concentrating lithium ions comprising the steps of:

I. feeding a liquid comprising lithium ions to a first compartment of the electrodialysis apparatus defined by the cation exchange membrane of the present invention and a first bipolar membrane;

II. applying electrical power to the electrodialysis apparatus (preferably resulting in a current density of between 10 and 100 A/m ² );

III. retrieving a solution of lithium hydroxide from a second compartment defined by the cation exchange membrane of the present invention and a second bipolar membrane.

In an alternative process the process comprises the steps of:

I. feeding a liquid comprising lithium ions to a first compartment of the electrodialysis apparatus defined by the cation exchange membrane of the present invention and an anion exchange membrane;

II. circulating an acid stream through a second compartment defined by the anion exchange membrane and a first bipolar membrane;

III. applying electrical power to the electrodialysis apparatus (preferably resulting in a current density of between 10 and 100 A/m ² );

IV. retrieving a solution of lithium hydroxide from a third compartment defined by the cation exchange membrane of the present invention and a second bipolar membrane. The cation exchange membrane of the present invention may be used for the production, purification and/or concentration of lithium hydroxide.

Preferably the process for concentrating lithium ions provides a solution of lithium hydroxide having a concentration of at least 5wt%.

Examples

The invention will now be illustrated by the following, non-limiting example in which all parts and percentages are by weight unless specified otherwise. Table 1 : Ingredients used in the Examples Preparation of CI-SS

Thionyl chloride (109 mL, 178.46 g, 1 .5 mol, 3 moleq) was added dropwise to a solution of 4-vinylbenzenesulphonic acid lithium salt (95.08 g, 0.500 mol, 1 moleq) and 4OH-TEMPO (50 mg, 500 ppm) in DMF (300 mL) in a double-walled reactor that was actively cooled to 5°C. After the addition was completed, the solution was allowed to slowly heat to room temperature and was stirred for another 16 hours. Then the reaction mixture was poured into 1 liter of cold 1 M KCI in a separation funnel. The bottom layer was removed and dissolved in 500 mL diethylether. This solution was washed with a 1 M KCI-solution (300 mL). The organic layer was dried over sodium sulphate, filtered and concentrated in vacuum to give a yellow oil. The crude product was used without further purification in the next step. Typical yield was 89.5 g (88%). HPLC-MS purity > 98%; ¹ H- NMR: <2 wt% DMF, 0% diethyl ether. Preparation of NH2-SS

Thionyl chloride (109 mL, 178.46 g, 1 .5 mol, 3 moleq) was added dropwise to a solution of 4-vinylbenzene-sulphonic acid lithium salt (95.08 g, 0.500 mol, 1 moleq) and 4OH-TEMPO (50 mg, 500 ppm) in DMF (300 mL) in a double-walled reactor that was actively cooled to 5°C. After the addition was completed, the solution was allowed to slowly heat to room temperature and was stirred for another 16 hours. Then the reaction mixture was poured into 1 liter of cold 1 M KCI in a separation funnel. The bottom layer was removed and was added dropwise to a solution of ammonium hydroxide 25% in water (250 mL, 3.67 mol, 15 moleq) and 4OH-TEMPO (50 mg, 500 ppm) in a doublewalled reactor that was actively cooled to 5°C. After the addition was completed, the solution was stirred for 1 hour. The solution was then allowed to heat to room temperature and was stirred for one hour. Then the reaction mixture was cooled back to 5°C and the product was filtered off and washed with 50 mL of cold water. The product was dried overnight in vacuum at 30°C and used without further purification. Typical yield was 66.8 g (73%). HPLC-MS purity > 95%.

Preparation of XL-B

Before the synthesis, vinylbenzene sulphonamide (NH2-SS) was dried in a vacuum oven overnight (30°C, vac). To a solution of the dried vinylbenzene sulphonamide (11.12 g, 0.061 mol, 1 moleq) and 4OH-TEMPO (30 mg, 500 ppm) in THF (100 mL) was added LiH (1.06 g, 0.134 mol, 2.2 moleq) as a solid at once. The reaction mixture was stirred for 30 minutes at room temperature. Then, a solution of Cl- SS (12.3 g, 0.061 mol, 1 moleq) in THF (50 mL) was added to the reaction mixture. After addition, the reaction mixture was heated to 60°C (water bath temperature). After two days, the reaction mixture was filtrated over celite to remove the excess of LiH. Celite was added and the resulting slurry was stirred for 5 minutes. Then, the celite was filtered off and washed with 100 mL ethyl acetate. The solvent was then evaporated in vacuo and the resulting white foam was washed with 500 mL diethyl ether overnight. The resulting white powder was filtered off and dried in a vacuum oven at 30°C for 16h yielding a white solid. Typical yield was 11 g (51 %). HPLC-MS purity > 94%; ¹ H-NMR:<1 wt% residual solvents, <5 wt% styrene sulphonate or styrene sulphonamide; ICP-OES: 21 -26 g Li/kg product. Table 2: Preparation of the base membrane

The composition of Table 2 was applied at a temperature of 25°C to an aluminum plate using an 80 pm wire-wound (Mayer) rod followed by applying a porous support (non-woven fabric FO-2333-10 from Freudenberg Filtration Technologies) onto the applied layer of composition whereby the porous support became impregnated with the composition. Excess composition was removed using a 4 pm Mayer rod. A PET foil was applied to the impregnated porous support and the impregnated support was irradiated with a Light Hammer LH10 from Fusion UV Systems fitted with a D-bulb working at 50% intensity with a speed of 5 m/min to cure the composition. The exposure dose was 950 mJ/cm ² in the IIV-A region. Subsequently the cured composition was further cured thermally at 90°C for 8 hours. The PET foil was removed, and the resulting base membrane was removed from the aluminum plate and stored in a 0.5M NaCI solution for at least 12 hours.

Preparation of a lithium selective membrane

A lithium selective layer was prepared by mixing 15mL of a 4mM copper nitrate aqueous solution and 15mL of 1.4mM 2-aminoethanol aqueous solution at room temperature (21 °C) for 30min and then left at 21 °C for 24 hours without stirring. 1 mL of 0.03wt% polystyrene sulfonate sodium salt aqueous solution was added and mixed. The obtained solution was applied to a PET foil using a 40 pm Mayer bar and the applied layer was allowed to dry at 90°C for 5 minutes. The PET foil with the dried layer was kept immersed into a 50-50 vol% water-ethanol solution of 10mM 1 ,3,5- benzentricarboxylic acid at room temperature for 4hours. Subsequently the PET foil with the lithium selective layer was allowed to dry at room temperature for 8 hours. All used materials were obtained from Sigma-Aldrich.

A base membrane was prepared as described above except that the PET foil was replaced by the PET foil with the lithium selective layer which was applied with the lithium selective layer side to the impregnated porous support. Evaluation of the lithium selectivity

The Li selectivity was measured in a double compartment H-cell (Metrohm). A constant voltage of 0.4V was applied using an Autolab PGSTAT204 (Metrohm) for 24 hours at 40°C. The Li selective layer side of the membrane faced the anode side and the feed compartment. The feed compartment of the H-cell contained a mixture of 80mL of 0.5M LiOH and 80mL of 0.5M NaOH. The permeate compartment contained 160ml of pure water. Both solutions were stirred by a magnetic stirrer during the measurement. After 24 hours, the Li- and Na-ion concentrations in the permeate were quantified by ICP-MS. Li selectivity was calculated by dividing the concentration of Li by concentration of Na. The selectivity of Li selective membrane was 4.2.

Evaluation of LiOH productivity

LiOH was produced by a bipolar electrodialysis (BPED) device as shown in Fig 4. Feed solution was a mixture of 2L of 2M LiCI and 0.1 L of 2M NaCI having a Li/Na ratio of 95/5. The operating condition was 80 A/m ² for 5 hours. 1 L of 0.5M HCI was in acid tank (47). 1 L of 0.5M LiOH was in base tank (46). 2L of 0.5M LiOH was in electrolyte tank (48). Flow rate for all solutions was 40 L/min. Fumasep FAM was used as AEM and Fumasep FBM were used as BPM in the BPED device. The base membrane was compared with the lithium selective membrane. When the base membrane was used as lithium selective membrane the Li/Na ratio in the base tank was 95/5 after 5 hours as determined by ICP-MS, while when the lithium selective membrane was used the Li/Na ratio was 98/2.