WO2020221918A2

WO2020221918A2 - Electrolyte

Info

Publication number: WO2020221918A2
Application number: PCT/EP2020/062186
Authority: WO
Inventors: Bijpost ERIK ALEXANDER; Alexander Maslow; Wasil Maslow
Original assignee: Novochem Green Additives 1 B.V.
Priority date: 2019-05-01
Filing date: 2020-05-01
Publication date: 2020-11-05
Also published as: WO2020221918A3

Abstract

The invention pertains to a electrolyte comprising a solute and a eutectic composition comprising a lactam and a eutecting agent and to a battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises a solute and a eutectic composition comprising a lactam and a eutecting agent.

Description

ELECTROLYTE

The present invention relates to electrolytes.

Electrolytes are used in various batteries to enable ion transport. Such electrolytes can be aqueous and non-aqueous. In commercial lithium-ion batteries the non-aqueous electrolytes are based on cyclic carbonates. In particular, the solvents in the non-aqueous electrolyte comprises dimethyl carbonate (DMC), ethylene carbonate (EC) and propylene carbonate (PC). The chosen solvents combine a relatively high solubility of the lithium salt with an acceptable viscosity over a narrow temperature range. At low temperatures the viscosity becomes too high, which leads to a considerably lower battery capacity. These carbonates have a limited stability as they have a tendency to form radicals, hydrolyse, may form polycarbonates and may develop gaseous products (like C0₂). Moreover, these carbonates are volatile, toxic and flammable.

The objective of the present invention is to provide novel electrolytes.

The present invention pertains to an electrolyte comprising a solute and a eutectic composition comprising a lactam and a eutecting agent. The eutecting agent is a compound capable of forming a eutectic mixture with the lactam of the invention. The eutectic composition of the invention generally has a lower viscosity as the known carbonate solvents used in conventional electrolytes. In particular, when used in combination with a solute the viscosity observed is lower than observed with a conventional electrolyte. Moreover, the solute can generally be dissolved at a higher concentration compared to the cyclic carbonate electrolytes, while maintaining a low(er) viscosity. Solute concentrations exceeding 40 wt%, of for example LiPF₆, have been observed. In this way, the ion mobility of the solute is generally improved. Also the capacity of the resulting battery is significantly improved. The electrolytes of the invention further exhibit a good thermostability, a relatively low conductivity, and a low vapour pressure. It is further noted that the eutectic composition of the invention can be prepared using components, i.e. the lactam and the eutecting agent, that are both solid at room temperature. Upon forming a eutecting composition of these solid components the resulting composition may be liquid at room temperature, like for example a eutectic composition of e-caprolactam and salicylic acid, g- butyrolactam and salicylic acid, and g-butyrolactam and maleic anhydride. Also compositions comprised of a component that is solid at room temperature and a component that is liquid at room temperature may form a liquid eutectic composition, like for example g-butyrolactam and PEG 200 (polyethylene glycol), g-butyrolactam and citraconic anhydride, and e-caprolactam and citraconic anhydride. Also compositions comprised of components that are liquid at room temperature are contemplated. In all the aforementioned eutectic compositions of the invention the melting point of the resulting eutectic composition is lower than the melting point of each of the individual components. The eutectic compositions of the invention may remain liquid at temperatures as low as -30°C. Consequently, the electrolyte of the invention exhibits a wide temperature range, e.g. from -30°C to 100°C, in which the electrolyte remains liquid. The eutectic composition of the invention generally is non-toxic, affordable, non-hazardous and readily bio-degradable.

In a preferred embodiment, the eutectic composition of the invention has a melting point below 0°C. In this way, the inventive compositions are liquid at room temperature, rendering an easier processing and use of the eutectic composition of the invention. Preferably, the melting point of the eutectic composition of the invention is at most -5°C, more preferably at most -10°C, even more preferably at most -15°C, and most preferably at most -20°C, and preferably at

least -100°C, more preferably at least -90°C, even more preferably at least -80°C, and most preferably at least -75°C.

In one embodiment, the electrolyte generally has a (dynamic) viscosity at 20°C of at most 50 cP, preferably at most 10 cP, more preferably at most 5 cP, even more preferably at most 3 cP and most preferably at most 2 cP, and preferably at least 0.1 cP, more preferably at least 0.2 cP and most preferably at least 0.5 cP. Such a viscosity can be measured using techniques

conventionally used in the art.

In a preferred embodiment, the electrolyte of the invention has a water content of at most 20 ppm, preferably at most 10 ppm, more preferably at most 5 ppm and most preferably at most 1 ppm. When the electrolyte comprises a cyclic anhydride such as maleic anhydride, itaconic anhydride and/or citraconic anhydride the water content can be diminished even further as these cyclic anhydrides react with water. A water-free electrolyte can even be obtained. Also, when water enters the battery during storage or operation and contacts the electrolyte, the cyclic anhydride readily reacts with water present, thereby preventing the detrimental effect of water.

Alternatively or additionally, the electrolyte of the invention has an oxygen content of at most 20 ppm, preferably at most 10 ppm, more preferably at most 5 ppm and most preferably at most 1 ppm. When the electrolyte comprises a cyclic anhydride such as itaconic anhydride and/or citraconic anhydride the oxygen content can be diminished even further as these cyclic anhydrides react with oxygen. An oxygen-free electrolyte can even be obtained. Also, when oxygen enters the battery during storage or operation and contacts the electrolyte, the cyclic anhydride readily reacts with the oxygen present, thereby preventing the detrimental effect of oxygen.

The electrolyte of the invention comprises the eutectic composition comprising a lactam and a eutecting agent. The electrolyte of the invention comprises the eutectic composition in an amount of at most 90 % by weight (wt%), based on the total weight of the electrolyte.

Preferably, the eutectic composition is present in an amount of at most 85 wt%, more preferably at most 80 wt%, even more preferably at most 75 wt%, even more preferably at most 70 wt%, even more preferably at most 60 wt% and even most preferably at most 50 wt%, and preferably at least 10 wt%, more preferably at least 15 wt%, even more preferably at least 20 wt%, even more preferably at least 25 wt%, even more preferably at least 30 wt% and most preferably at least 35 wt%, based on the total weight of the electrolyte.

The electrolyte of the invention comprises the solute in an amount of at least 10 % by weight (wt%), based on the total weight of the electrolyte. Preferably, the solute is present in an amount of at least 15 wt%, more preferably at least 20 wt%, even more preferably at least 25 wt%, even more preferably at least 30 wt%, even more preferably at least 40 wt% and even most preferably at least 50 wt%, and preferably at most 90 wt%, more preferably at most 85 wt%, even more preferably at most 80 wt%, even more preferably at most 75 wt%, even more preferably at most 70 wt% and most preferably at most 65 wt%, based on the total weight of the electrolyte.

The lactam of the invention is well known in the art and refers to a cyclic amide. Typically and preferably, the lactam is not substituted on the nitrogen in the ring. Most preferably, the lactam is not substituted. Examples of lactams include b-lactam, g-lactam, d-lactam and e-lactam. The lactam may be substituted, e.g. with C1 -C4 alkyl or vinyl, or unsubstituted. Unsubstituted lactams are preferred. Examples of unsubstituted lactams include 2-azetidinone, g-butyrolactam, 2- piperidinone, e-caprolactam and caprylolactam. Preferably, the lactam is selected from g- butyrolactam and e-caprolactam. Most preferably, the lactam is e-caprolactam. It is

contemplated that two or more lactams are used in the eutectic composition of the invention.

The lactam may also be an oligomer of the lactam, preferably the oligomer is a cyclic oligomer. The oligomer can be a dimer, trimer, tetramer, pentamer of hexamer of lactam. Examples of the oligomers of lactam can be found in Abe et al. (Abe, Y. et al (2016) Isolation and Quantification of Polyamide Cyclic Oligomers in Kitchen Utensils and Their Migration into various Food Stimulants, PLoS ONE 1 1 (7): e0159547, doi:10.1371/journal. pone.0159547). Preferably, the oligomer is a dimer of lactam, even more preferably the dimer is a dimer of caprolactam, preferably 1 ,8-diaxacyclodecane-2,9-dione.

In a further preferred embodiment, the lactam of the invention is a combination of g-butyrolactam and e-caprolactam. The invention encompasses a eutectic composition comprising g- butyrolactam and e-caprolactam, as well as a eutectic composition comprising g-butyrolactam and e-caprolactam and a eutecting agent. In one embodiment, the eutectic composition comprises g-butyrolactam and e-caprolactam. In either the eutectic composition or the lactam combination, the molar ratio between g-butyrolactam and e-caprolactam is at least 0.01.

Preferably, the ratio is at least 0.05, more preferably at least 0.1 , even more preferably at least 0.2, even more preferably at least 0.5, and most preferably at least 1 , and preferably at most 100, more preferably at most 75, even more preferably at most 50, and most preferably at most 40.

The eutectic composition of the invention comprises the lactam in an amount of at most 90 % by weight (wt%), based on the total weight of the eutectic composition. Preferably, the lactam is present in an amount of at most 85 wt%, more preferably at most 80 wt%, even more preferably at most 70 wt%, even more preferably at most 60 wt%, even more preferably at most 50 wt% and even most preferably at most 40 wt%, and preferably at least 1 wt%, more preferably at least 2 wt%, even more preferably at least 5 wt%, even more preferably at least 10 wt%, even more preferably at least 15 wt% and most preferably at least 20 wt%, based on the total weight of the eutectic composition.

The eutecting agent in the eutectic composition of the invention can be any eutecting agent capable of forming a eutectic mixture with the lactam. Typically, the eutecting agent has an ionic part. The ionic part can be cationic, anionic or amphiphilic, preferably the ionic part is amphiphilic. The eutecting agent can be a hydrogen-bond donor, an electron pair donor, hydrogen-bond acceptor, an electron pair acceptor or a metal salt. In one embodiment, the eutecting agent is a hydrogen-bond donor or acceptor comprising a functional group selected from, but not limited to, acids, anhydrides, (poly)ethers, polysaccharides, functionalized polymers, amines, amides, imides, alcohols, quaternary ammonium salts. Preferably, the eutecting agent is selected from the group consisting of cyclic acids, aliphatic acids, cyclic acid anhydrides, aliphatic acid anhydrides, (poly)ethers, polysaccharides, functionalized polymers, amines, amides, imides and alcohols. Most preferably, the eutecting agent is selected from the group consisting of cyclic acids and cyclic anhydrides. In the context of the present description, the term“cyclic acid” refers to a ring-containing molecule comprising an acid group; the ring can be a phenyl group or a cycloalkyl group, for example and the acid group can be a carboxylic acid or a sulphonic acid group, for instance.

In a preferred embodiment, the eutecting agent comprises at least 2 functional groups. The functional groups may be the same or different. The advantage of a eutecting agent having at least two functional groups is that the resulting eutecting composition when combined with the lactam of the invention is more stable and less dependent on pH, temperature and/or concentration. Preferably, the eutecting agent comprises at least 2 functional groups in which at least two functional groups are separated by at most 3 atoms, preferably at most 2 atoms.

Preferably, the polyfunctional compound comprises at least one of the substituents selected from the group consisting of carboxylic acid and ether. The other group(s) may be any known functional group.

In one embodiment, the eutecting agent is an oligomer or polymer having a plurality of functional groups. When a molar ratio is indicated and it relates to an oligomer or polymer, the molar ratio should be calculated based on the number of monomers present in the oligomer or polymer. In other words, a polymer comprising 500 monomer units should be contacted with 500 lactam molecules to reach a molar ratio between polymer and lactam of 1 or 1 :1. This is different from the molar ratio or 1 :1 molar complexes as disclosed in US 4,319,881 , which refers to a molar ratio of 1 molecule of lactam per polyethylene glycol oligomer (e.g. PEG 300). At such molar ratios, a eutectic composition is not obtained.

In one embodiment, the eutecting agent has a pKa (i.e. the acid dissociation constant) of at most 14, preferably a pKa of at most 10, more preferably a pKa of at most 8, even more preferably a pKa of at most 5 and most preferably a pKa value of at most 4, and preferably a pKa of at least 0, more preferably a pKa of at least 0.5 and most preferably a pKa of at least 1.

Examples of suitable acids include aliphatic monoacids such as formic acid, acetic acid, lactic acid and butyric acid; aliphatic polyacids such as oxalic acid, citric acid, citraconic acid, itaconic acid and maleic acid; and cyclic acids such as salicylic acid, 2-phenol phosphinic acid, 2-phenol phosphonic acid and 2-phenol sulphonic acid. Preferably, the acid is a cyclic acid, more preferably the acid is salicylic acid. Examples of suitable acid anhydrides include aliphatic acid anhydrides such as formic anhydride, acetic anhydride, propanoic anhydride, butyric anhydride, crotonic anhydride and benzoic anhydride; and cyclic acid anhydrides such as maleic anhydride, citraconic anhydride, phthalic anhydride, trimellitic anhydride, hexahydrophthalic anhydride, methyl hexahydrophthalic anhydride, tetrahydrophthalic anhydride, methyl tetrahydrophthalic anhydride,

tetrachlorophthalic anhydride, pyromellitic dianhydride, himic anhydride, succinic anhydride, dodecenylsuccinic anhydride, chlorendic anhydride and tetrabromophthalic anhydride.

Preferably, the acid anhydride is a cyclic acid anhydride. More preferably, the cyclic acid anhydride is selected from the group consisting of maleic anhydride, citraconic anhydride, itaconic anhydride and phthalic anhydride, even more preferably the cyclic acid anhydride is maleic anhydride, itaconic anhydride or citraconic anhydride, and most preferably, the acid anhydride is maleic anhydride. The advantage of maleic anhydride, itaconic anhydride and citraconic anhydride is their potential to react with water, oxygen and radicals. These anhydrides are further advantageous in ternary or quaternary eutectic compositions to reduce the viscosity of the resulting eutectic composition. Especially when a solute is dissolved in the eutectic composition of the invention its viscosity may increase at higher solute concentrations - which tend to be higher than the solubility in conventional solvents - the cyclic anhydride, and in particular maleic anhydride and/or citraconic anhydride, significantly reduces the viscosity of the eutectic composition.

Examples of suitable ethers include monomeric ethers such as methyl ethyl ether, methyl phenyl ether, diethylene glycol, triethylene glycol, dibutyl ether, and dihexyl ether; and polyethers such as paraformaldehyde, polyethylene glycol (PEG), polypropylene glycol (PPG), polytetramethylene glycol (PTMG), polytetramethylene ether glycol (PTMEG),

polytatrahydrofuran (PTHF), polyoxymethylene (POM), polyethylene oxide (PEO),

polypropylene oxide (PPOX) and polyethyleneglycol-polypropyleneglycol (EO/PO block copolymers). Aromatic ethers, such as phenolic and benzylic ethers, are also suitable.

Examples of polysaccharides include celluloses such as cellulose, methyl cellulose (MC), ethyl cellulose (EC), hydroxyethyl cellulose (HEC), ethyl hydroxyethyl cellulose (EHEC), methyl ethyl hydroxyethyl cellulose (MEHEC), carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose (HPMC); and starches such as starch, oxidized starch, hydroxyethyl starch, hydroxypropyl starch and carboxymethyl starch; chitin and arabinoxylans. The polysaccharide can have any degree of polymerization (DP) and degree of substitution (DS) known in the art. Examples of functionalized polymers include polyvinyl alcohol (PVA), polyvinyl acetate, polyvinylbutyral (PVB), polyvinylamine, polyvinylamides, polyurethanes, polyamides, polyimides, polycarbonates, polyesters, poly lactic acid (PLA), poly(lactic-co-glycolic acid) (PLGA), and polyvinyl pyrrolidone (PVP).

Examples of suitable amines include aliphatic polyamines include EDA homologues such as linear, branched and cyclic EDA homologues including tetraethylene pentamine (TEPA), triethylene tetramine (TETA), diethylene triamine (DETA), hexaethylene pentamine (HEPA) and N-aminoethyl piperazine (NAEP); propylene homologues such as dipropylene triamine (DPTA; methylene homologues such as hexamethylene pentamine (HMPA); polyether monoamines such as Jeffamine® M-600 amine, Jeffamine® M-1000 amine, Jeffamine® M-2005 amine and Jeffamine® M-2070 amine; polyether diamines such as Jeffamine® D-230 amine, Jeffamine® D-2300 amine, Jeffamine® D-400 amine, Jeffamine® D-4000 amine, Jeffamine® ED-600 amine, Jeffamine® ED-900 amine, Jeffamine® ED-2003 amine, Jeffamine® EDR-148 amine and Jeffamine® EDR-176 amine; polyether triamines such as Jeffamine® T-403 amine, Jeffamine® T-3000 amine and Jeffamine® T-5000 amine; alkylated polyamines include propylene diamines such as coco propylene diamine, oleyl propylene diamine, arachidyl behenyl propylene diamine, soya propylene diamine, (partially) hydrogenated tallow propylene diamine, N,N,N’-trimethyl-N’-tallow propylene diamine and tallow propylene diamine;

dipropylene triamines such as dodecyl dipropylene triamine, oleyl dipropylene triamine, octyl dipropylene triamine, stearyl dipropylene triamine and tallow dipropylene triamine and other polyamines such as N-tallowalkyl dipropylene tetramine, N-tallowalkyl tripropylene triamine, N- (3-aminopropyl)-N-cocoalkyl propylene diamine, N-(3-aminopropyl)-N-tallowalkyl propylene diamine, N-(3-aminopropyl)-N-cocoalkyl trimethylenediamine, N-(3-aminopropyl)-N-tallowalkyl trimethylenediamine and dendrimers containing propylene diamines; bisalkylated amines such as di(dodecyl) amine, di(oleyl) amine, di(arachidyl behenyl) amine, di(tallow) amine, di(octyl) amine, di(stearyl) amine and di(coco) amine; alkylated primary amines such as dodecyl amine, oleyl amine, hexadecyl amine, arachidyl behenyl amine, hydrogenated tallowalkyl amine, tallowalkyl amine, rapeseedalkyl amine, hydrogenated rapeseedalkyl amine, soyaalkyl amine, octyl amine, octadecyl amine, stearyl amine, coco amine and polyvinyl amine; alkoxylated polyamines such as propylene diamines such as octyl/decyloxypropyl-1 ,3-diaminopropane, isodecyloxypropyl-1 ,3-diaminopropane, isododecyloxypropyl-1 ,3-diaminopropane,

dodecyl/tetradecyloxypropyl-1 ,3-diaminopropane, isotridecyloxypropyl-1 ,3-diaminopropane and tetradecyloxypropyl-1 ,3-diaminopropane; and dipropylene triamines such as dodecyl dipropylene triamine, dodecyl dipropylene triamine, octyl/decyl dipropylene triamine, isotridecyl dipropylene triamine and tetradecyl dipropylene triamine; bisalkoxylated amines such as di(dodecyloxypropyl) amine, di(oleyloxypropyl) amine, di(arachidyl behenyloxypropyl) amine, di(tallowoxypropyl) amine, di(octyloxypropyl) amine, di(stearyloxypropyl) amine and

di(cocoalkyloxy) amine; and alkoxylated amines such as isopropyloxypropyl amine,

hexyloxypropyl amine, 2-ethylhexyloxypropyl amine, octyl/decyloxypropyl amine,

isodecyloxypropyl amine, dodecyl/tetradecyloxypropyl amine, isotridecyloxypropyl amine, tetradecyloxypropyl amine, tetradecyl/dodecyloxypropyl amine, linear alkyloxypropyl amine and octadecyl/hexadecyloxypropyl amine.

Examples of suitable amides include aliphatic unsubstituted amides such as urea, formamide, acetamide, propanamide, butanamide, pentanamide, hexanamide and heptanamide; substituted aliphatic amides such as N-methylpropanamide, N-ethylpropanamide, N-methylbutanamide, N- ethylbutanamide, N-acetyl-3-oxopentanamide, N-acetyl butanamide, N-acetyl propanamide, N- Acetyl-2-amino-5-(diaminomethylideneamino) pentanamide, N-acetyl benzamide, N- methylpentanamide, N-ethylpentanamide; aromatic amides such as benzamide, ethenzamide and salicylamide.

Examples of suitable imides include aliphatic imides such as trifluoromethylsulfonyl imide, pentafluoroethylsulfonyl imide, methylsulfonyl imide and ethylsulfonyl imide; cyclic imides such as succinimide, maleimide, citraconimide, glutarimide, phthalimide, tetrahydrophthalimide, hexahydrophthalimide, pyromellitic diimide, 1 ,8-naphthalimide, cyclohexane-1 ,2-dicarboximide and 1 ,3-bis(citraconimidomethyl) benzene (Perkalink® 900). Preferably, the imide is 1 ,3- bis(citraconimidomethyl) benzene.

Examples of suitable alcohols include aliphatic polyols such as 1 ,2-ethanediol, 1 ,3-propanediol, 1 ,4-butanediol, glycerol, ethylene glycol, propylene glycol, mannitol and trimethylol propane (TMP); and cyclic alcohols such as ascorbic acid, glucuronic acid, catechol and salicylic acid; monosaccharides such as glucose, altrose, fructose, mannose, iodose, talose, allose, gulose, galactose, ribose, arabinose, xylose, lyxose and glucosamine; and disaccharides such as sucrose, lactose, lactulose, trehalose, cellobiose and chitobiose.

In one embodiment of the invention, the eutectic composition comprises g-butyrolactam, e- caprolactam and a cyclic acid anhydride. The cyclic acid anhydride is selected from the group consisting of maleic anhydride, itaconic anhydride, citraconic anhydride and phthalic anhydride. In one embodiment, the eutectic composition comprises g-butyrolactam, e-caprolactam and maleic anhydride. In a further embodiment, the eutectic composition comprises g-butyrolactam, e-caprolactam and citraconic anhydride. In a further embodiment, the eutectic composition comprises g-butyrolactam, e-caprolactam and itaconic anhydride. The advantage of the use of these eutectic compositions in the electrolyte of the invention is its improved stability and/or lower reactivity. Moreover, the likelihood of radical formation from any of the aforementioned constituents is significantly lower than in conventional carbonate-based electrolytes.

Furthermore, the viscosity of the electrolyte can be significantly decreased, especially when higher concentrations of the solute are used.

The eutectic composition of the invention comprises the lactam in an amount of at least 10 % by weight (wt%), based on the total weight of the eutectic composition. Preferably, the lactam is present in an amount of at least 15 wt%, more preferably at least 80 wt%, even more preferably at least 30 wt%, even more preferably at least 40 wt%, even more preferably at least 50 wt% and even most preferably at least 60 wt%, and preferably at most 99 wt%, more preferably at most 98 wt%, even more preferably at most 95 wt%, even more preferably at most 90 wt%, even more preferably at most 85 wt% and most preferably at most 80 wt%, based on the total weight of the eutectic composition.

The molar ratio between lactam and the eutecting agent is at least 0.01. Preferably, the ratio is at least 0.05, more preferably at least 0.1 , even more preferably at least 0.2, even more preferably at least 0.5, and most preferably at least 1 , and preferably at most 100, more preferably at most 75, even more preferably at most 50, even more preferably at most 40, even more preferably at most 20, even more preferably at most 10 and most preferably at most 5.

When the lactam is a combination of 2 or more lactams, the molar ratio between lactam and the eutecting agent is at least 0.01. Preferably, the ratio is at least 0.05, more preferably at least 0.1 , even more preferably at least 0.2, even more preferably at least 0.5, and most preferably at least 1 , and preferably at most 100, more preferably at most 75, even more preferably at most 50, even more preferably at most 40, even more preferably at most 20, even more preferably at most 10 and most preferably at most 5.

The solute in the electrolyte of the invention can be any solute known in the art. The solute generally is a lithium-based solute, preferably a lithium salt. The lithium-based solute, preferably a lithium salt, may be any lithium-based solute known in the art. In one embodiment, the solute is a lithium salt selected from the group consisting of lithium fluoride (LiF), lithium chloride (LiCI), lithium bromide (LiBr), lithium iodide (Lil), lithium nitrate (LiN0₃), lithium carbonate (Li₂C0₃), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethane sulfonate (LiTFS), lithium hexafluorophosphate (LiPF₆), lithium hexafluoroarsenate (LiAsF₆), lithium

tetrafluoroborate (LiBF₄), lithium perchlorate (LiCI0₄), lithium

tris(pentafluoroethyl)trifluorophosphate (LiFAP), lithium bis(fluorosulfonyl)imide (LiFSI), lithium cyclo-difluoromethane-1 ,1-bis(sulfonyl)imide (LiDMSI), lithium cyclo-difluoropropane-1 ,1- bis(sulfonyl)imide (LiHPSI), lithium bis(perfluoroethanesulfonyl)imide (LiBETI), lithium bis(oxalate)borate (LiBOB), lithium difluoro(oxalate)borate (LiDFOB), lithium

bis(fluoromalonato)borate (LiBFMB), lithium dicyanotriazolate (LiDCTA), lithium dicyano- pentafluoroethyl-imidazole (LiPDI), lithium tetracyanoborate (LiBison) and lithium dicyano- trifluoromethyl-imidazole (LiTDI). Preferably, the solute is a lithium salt selected from the group consisting of LiTFSI, LiTFS, LiPF₆, LiAsF₆, LiBF₄ and LiCI0₄.

In a further embodiment, the electrolyte of the invention comprises the solute, preferably the lithium salt, in an amount of at most 85 % by weight (wt%), based on the total weight of the electrolyte. Preferably, the solute is present in an amount of at most 70 wt%, more preferably at most 60 wt%, even more preferably at most 50 wt%, even more preferably at most 40 wt% and most preferably at most 30 wt%, and preferably at least 1 wt%, more preferably at least 2 wt%, even more preferably at least 5 wt% and most preferably at least 10 wt%, based on the total weight of the electrolyte.

In one embodiment of the invention, the eutectic composition of the invention comprises water in an amount of at most 1 % by weight (wt%), based on the total weight of the eutectic composition. Preferably, the water is present in an amount of at most 0.5 wt%, more preferably at most 0.2 wt%, even more preferably at most 0.1 wt%, even more preferably at most 0.05 wt% and most preferably at most 0.01 wt%, and preferably at least 0.0001 wt%, more preferably at least 0.0005 wt, and most preferably at least 0.001 wt%, based on the total weight of the eutectic composition. In a preferred embodiment, the eutectic composition of the invention is substantially free from water. More preferably, the eutectic composition of the invention is completely free from water. The term“substantially free from water” means that less than 100 parts per million of water is present in the eutectic composition. The term“completely free” means that the eutectic composition contains less than 20 parts per billion (ppb) of water.

The remaining part of the electrolyte may be comprised of other components commonly or not commonly used in electrolyte. With the lactam, the eutecting agent and the solute, the other components add up to 100 wt% of the total weight of the electrolyte. In one embodiment, the electrolyte further comprises an additive. The additive can be any additive known in the art and suitably used in electrolytes. Examples of such additives include SEI film-forming additives such as vinylene carbonate (VC), ethylene sulphite (ES), vinyl ethylene carbonate (VEC), catechol carbonate (CC) and succinimide; flame-retardant additives such as halogenated alkyl phosphates like tris(2,2,2-trifluoroethyl)phosphate, phosphazanes like hexamethoxycyclotriophosphazane and halogenated alkyl phosphites like tris(2,2,2- trifluoroethyl)phosphite; shutdown additives such as xylene, cyclohexylbenzene, biphenyl, 2,2- diphenylpropane and phenyl-tertbutylcarbonate; and redox shuttle additives such as 10-methyl- phenothiazine (MPT) and 2,5-di-tertbutyl-1 ,4-dimethoxybenzene (DBDMB).

In a further embodiment, the electrolyte of the invention comprises the additive in an amount of at most 30 % by weight (wt%), based on the total weight of the electrolyte. Preferably, the solute is present in an amount of at most 25 wt%, more preferably at most 20 wt%, even more preferably at most 15 wt%, even more preferably at most 10 wt% and most preferably at most 5 wt%, and preferably at least 0.1 wt%, more preferably at least 0.2 wt%, even more preferably at least 0.5 wt% and most preferably at least 1 wt%, based on the total weight of the electrolyte.

The invention further pertains to an electrolyte comprising a eutectic composition comprising a lactam and a lithium salt. The lactam and the lithium salt form a eutectic mixture and are liquid at room temperature. Such eutectic compositions can be used per se or further diluted with a solvent and/or the eutectic composition comprising a lactam and a eutecting agent as described above.

The lithium salt can be any lithium salt known in the art. Preferably, the eutecting agent is a metal salt wherein the amount of water is at most 5 wt%, preferably at most 2 wt%, more preferably at most 1 wt% and most preferably at most 0.1 wt%, based on the total weight of metal salt and water. The water can be crystal water and/or water adsorbed to the metal salt. In a preferred embodiment, water is absent in the metal salt. With the lower levels of water, the metal salt can more easily form a eutectic composition with the lactam of the invention. Not being bound by theory, it is believed that the metal salt does not dissociate when a eutectic solvent is formed with the lactam rendering the resulting eutectic mixture to be different from a solution in water in which the metal salt dissociates. This allows for a high concentration of the metal salt in the deep eutectic solvent. Examples of lithium salts include lithium fluoride (LiF), lithium chloride (LiCI), lithium bromide (LiBr), lithium iodide (Lil), lithium nitrate (LiN0₃), lithium carbonate (Li₂C0₃), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethane sulfonate (LiTFS), lithium hexafluorophosphate (LiPF₆), lithium hexafluoroarsenate (LiAsF₆), lithium tetrafluoroborate (LiBF₄), lithium perchlorate (LiCI0₄), lithium

bis(fluoromalonato)borate (LiBFMB), lithium dicyanotriazolate (LiDCTA), lithium dicyano- pentafluoroethyl-imidazole (LiPDI), lithium tetracyanoborate (LiBison) and lithium dicyano- trifluoromethyl-imidazole (LiTDI). Preferably, the solute is a lithium salt selected from the group consisting of LiF, LiCI, LiBr, Lil, LiN0₃, LiTFSI, LiTFS, LiPF₆, LiAsF₆, LiBF₄ and LiCI0₄. More preferably, the lithium salt is selected from the group consisting of LiF, LiCI, LiBr, Lil and LiN0₃. Even more preferably, the lithium salt is selected from the group consisting of LiF, LiCI and LiN0₃.With these simpler lithium salts, higher concentrations of lithium can be achieved which in turn may lead to a higher capacity of the battery. Moreover, the stability of these salts is better than of e.g. LiPF₆, as less side reactions may occur, especially with the organic anion.

In a further embodiment, the electrolyte of the invention comprises the lithium salt in an amount of at most 85 % by weight (wt%), based on the total weight of the electrolyte. Preferably, the lithium salt is present in an amount of at most 70 wt%, more preferably at most 60 wt%, even more preferably at most 50 wt%, even more preferably at most 40 wt% and most preferably at most 30 wt%, and preferably at least 1 wt%, more preferably at least 2 wt%, even more preferably at least 5 wt% and most preferably at least 10 wt%, based on the total weight of the electrolyte.

The molar ratio between lactam and the lithium salt is at least 0.01. Preferably, the ratio is at least 0.05, more preferably at least 0.1 , even more preferably at least 0.2, even more preferably at least 0.5, and most preferably at least 1 , and preferably at most 100, more preferably at most 75, even more preferably at most 50, even more preferably at most 40, even more preferably at most 20, even more preferably at most 10 and most preferably at most 5.

The invention further pertains to an electrolyte comprising a lithium salt of a lactam. Such lithium salts of lactam also referred to as lithium lactamates can be used per se or further diluted with a solvent and/or the eutectic composition comprising a lactam and a eutecting agent as described above. The advantage of using lithium lactamates in battery electrolytes is their improved conductivity and ion mobility. Moreover, a counter anion is absent, which increases the electrolyte and/or battery stability.

The lithium salt of lactam can be prepared using any suitable method known in the art, such as the methods described for sodium caprolactamate and potassium caprolactamate in US

3,574,938, US 3,875,121 , EP 0 238 143, GB 1 ,032,294 and US 8,710,217. The invention further pertains to a method of preparing a lithium salt of a lactam by (a) contacting metallic lithium to the lactam, (b)heating the mixture to a temperature of at least 70 °C, and (c) cooling the colored and transparent liquid to room temperature.

The invention further pertains to the use of a eutectic composition comprising a lactam and a eutecting agent in a battery. The invention further pertains to the use of a eutectic composition comprising a lactam and a lithium salt in a battery. The invention further pertains to the use of a lithium salt of lactam in a battery.

The invention further pertains to a battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises a solute and a eutectic composition comprising a lactam and a eutecting agent. The invention further pertains to a battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises a eutectic composition comprising a lactam and a lithium salt and optionally a solute. The invention further pertains to a battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises a lithium salt of lactam and optionally a solute and a solvent and/or a eutectic composition comprising a lactam and a eutecting agent.

The battery of the invention comprises a positive electrode. The positive electrode can be any positive electrode known in the art. Examples of suitable positive electrodes include lithium nickel manganese cobalt oxide (NMC or LiNi_xMn_yCO_z0₂), lithium manganese oxide (LMO or LiMn₂0 ). Lithium iron phosphate (LFP or LiFeP0₄), lithium cobalt oxide (LCO or LiCo0₂) and lithium nickel cobalt aluminum oxide (NCA or LiNiCoAI0₂). Preferably, the positive electrode is selected from the group consisting of lithium nickel manganese cobalt oxide, lithium manganese oxide and lithium cobalt oxide. The battery of the invention comprises a negative electrode. The negative electrode can be any negative electrode known in the art. Examples of suitable negative electrodes include graphite, lithium titanate (LTO or Li₄Ti₅0i₂), hard carbon, tin/cobalt alloy and silicon/carbon. Preferably, the negative electrode is graphtite.

The battery of the invention comprises a separator. The separator can be any separator known in the art. Examples of materials that can be suitably used in separators include non-woven fibers such as cotton, nylon, polyesters and glass; polymer films such as polyethylene (PE), polypropylene (PP), poly(tetrafluoroethylene) (PTFE) and polyvinyl chloride (PVC)

The invention is exemplified in the following Examples.

Examples Example 1 : g-butyrolactam, e-caprolactam (molar ratio 1 :1 ) and LiNQ₃

5 g of g-butyrolactam (solid) was mixed with 6.6 g e-caprolactam (solid). The mixture was heated to about 70°C until the mixture turns into a liquid. To the liquid, 1.3 g of LiN0₃ (10 wt%) was added. Subsequently, the liquid mixture was cooled to room temperature. A pourable, transparent liquid was obtained. Example 2: g-butyrolactam, e-caprolactam (molar ratio 1 :1 ) and LiNQ₃

5 g of g-butyrolactam (solid) was mixed with 6.6 g e-caprolactam (solid). The mixture was heated to about 70°C until the mixture turns into a liquid. To the liquid, 3.3 g of LiN0₃ (22 wt%) was added. Subsequently, the liquid mixture was cooled to room temperature. A pourable, transparent liquid was obtained. Addition of 10 wt% citraconic anhydride to the electrolyte of Example 2 results in an electrolyte with a considerably lower viscosity (water thin).

Example 3: g-butyrolactam, e-caprolactam (molar ratio 1 :1 ) and LiCI

5 g of g-butyrolactam (solid) was mixed with 6.6 g e-caprolactam (solid). The mixture was heated to about 70°C until the mixture turns into a liquid. To the liquid, 1.3 g of LiN0₃ (10 wt%) was added. Subsequently, the liquid mixture was cooled to room temperature. A pourable, transparent liquid was obtained.

Example 4: e-caprolactam and LiCI

6.6 g of e-caprolactam (solid) was mixed with 1.3 g of LiCI (16 wt%). The mixture was heated to about 70°C until the mixture turns into a liquid. Subsequently, the liquid mixture was cooled to room temperature. A pourable, transparent liquid was obtained.

Example 5: e-caprolactam and LiN0₃

6.6 g of e-caprolactam (solid) was mixed with 1.9 g of LiN0₃ (22 wt%). The mixture was heated to about 70°C until the mixture turns into a liquid. Subsequently, the liquid mixture was cooled to room temperature. A pourable, transparent liquid was obtained.

Addition of 10 wt% citraconic anhydride to the electrolyte of Example 5 results in an electrolyte with a considerably lower viscosity.

Example 6: g-butyrolactam, e-caprolactam (molar ratio 1 :1 ) and LiPFg

5 g of g-butyrolactam (solid) was mixed with 6.6 g e-caprolactam (solid). The mixture was heated to about 70°C until the mixture turns into a liquid. To the liquid, 7.7 g of LiPF₆ (40 wt%) was added. Subsequently, the liquid mixture was cooled to room temperature. A pourable, transparent, viscous liquid was obtained.

Addition of 10 wt% citraconic anhydride to the electrolyte of Example 5 results in an electrolyte with a considerably lower viscosity. Example 7: g-butyrolactam, e-caprolactam (molar ratio 1 :1 ) and LiPFg

5 g of g-butyrolactam (solid) was mixed with 6.6 g e-caprolactam (solid). The mixture was heated to about 70°C until the mixture turns into a liquid. To the liquid, 2.9 g of LiPF₆ (20 wt%) was added. Subsequently, the liquid mixture was cooled to room temperature. A pourable, transparent liquid was obtained. Example 8: g-butyrolactam and LiPFg

5 g of g-butyrolactam (solid) was mixed with 3.3 g of LiPF₆ (40 wt%). The mixture was heated to about 70°C until the mixture turns into a liquid. Subsequently, the liquid mixture was cooled to room temperature. A pourable, transparent, very viscous liquid was obtained. The viscosity of this liquid was higher than the electrolyte obtained in Example 6. Example 9: g-butyrolactam, e-ca pro lactam and glycerol (molar ratio 1 :1 :2) and LiPFg 5 g of g-butyrolactam (solid) was mixed with 6.6 g e-caprolactam (solid). The mixture was heated to about 70°C until the mixture turns into a liquid. To the liquid, 5.4 g of glycerol was added. To the resulting liquid various amounts of LiCI were added, viz. equivalent to 2, 4 and 6.4 wt% Li. Subsequently, the liquid mixture was cooled to room temperature. Pourable, transparent liquids were obtained with increasing viscosity: 2 wt% Li (thin) to 6.4 wt% Li (very viscous).

As a comparison, a mix of LiCI in glycerol was prepared with 4.1 wt% Li. This liquid exhibits a considerably higher viscosity than its comparable electrolyte comprising the eutectic

composition of the invention.

Claims

1. An electrolyte comprising a solute and a eutectic composition comprising a lactam and a eutecting agent.

2. Electrolyte according to claim 1 wherein the lactam is selected from the group of 2- azetidinone, g-butyrolactam, 2-piperidinone and e-caprolactam.

3. Electrolyte according to claim 1 or 2 wherein the lactam is g-butyrolactam.

4. Electrolyte according to any one of the preceding claims wherein the solute is a lithium salt.

5. Electrolyte comprising a solute and a eutectic composition comprising g-butyrolactam and e- caprolactam.

6. Electrolyte comprising a eutectic composition comprising a lactam and a lithium salt, and optionally a solute.

7. Electrolyte comprising a lithium salt of lactam, and optionally a solvent and/or eutectic

composition comprising a lactam and a eutecting agent.

8. Use of a eutectic composition comprising a lactam and a eutecting agent in a battery

9. Use of a eutectic composition comprising a lactam and a lithium salt in a battery.

10. Use of a lithium salt of a lactam in a battery.

11. A battery comprising a positive electrode, a negative electrode, a separator and an

electrolyte, wherein the electrolyte comprises a solute and a eutectic composition comprising a lactam and a eutecting agent.

12. Battery according to claim 11 wherein the battery is a lithium-ion battery.

13. Battery according to claim 12 wherein the solute is a lithium salt selected from the group consisting of LiF, LiCI, LiBr, Lil, LiN0₃, LiTFSI, LiTFS, LiPF₆, LiAsF₆, LiBF₄ and LiCI0₄.

14. A battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises a eutectic composition comprising a lactam and a lithium salt, and optionally a solute.

15. A battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises a lithium salt of a lactam, and optionally a solute and a solvent and/or a eutectic composition comprising a lactam and a eutecting agent.