GB2626595A

GB2626595A - Compound

Info

Publication number: GB2626595A
Application number: GB2301239.6A
Authority: GB
Inventors: Bourcet Florence
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2023-01-27
Filing date: 2023-01-27
Publication date: 2024-07-31
Also published as: GB2628866A; GB202301239D0; WO2024156914A1; GB202306869D0

Abstract

A compound of formula (I): wherein X is aluminium or boron; R1 in each occurrence is independently a monovalent substituent; R2 is a divalent organic group; and M+ is a cation. Preferably, X is boron, M+ is a lithium ion, each R1 is independently selected from C1-20 alkyl wherein one or more C atoms other than the C atom bound to O of OR1 or a terminal C atom may be replaced with O, and one or more H atoms may be replaced by F, and R2 is a divalent organic group of formula (II): wherein R3 in each occurrence is independently H or a substituent and Ar1 is a C6-20 arylene group or heteroarylene group. More preferably, X is boron, M+ is a lithium ion, Ar1 is unsubstituted or substituted 1,2-phenylene, each R1 is 2,2,3,3,4,4,5,5-octafluoropentyl, Ar1 is unsubstituted 1,2-phenylene, and each R3 is trifluoromethyl. The compound of formula (I) may be used as an electrolyte in a metal battery or a metal ion battery.

Description

COMPOUND BACKGROUND

WO 00/53611 discloses a compound comprising a monoanion of formula (II): WO 99/12938 discloses a polyfluorinated alkoxide coordinated to a transition metal, or a Group BL IV or V element. Use of the compound in batteries is disclosed.

Nolan et al, -Nonaqueous Lithium Battery Electrolytes Based on Bis(polylluorodiolato)borates" 2003 J. Electrochem. Soc. 150 A1726 discloses lithium salts for use as battery electrolytes.

JP2002/260734 discloses electrolytes of formula (1): A pq+ ( 1) US6783896 discloses compounds of formula (I): (1) EP1075036 discloses compounds of formula (1): R2 \ b-XL-K(R3),1\ \ 0 inlk (I) W02022/243470 discloses an electrolyte comprising solvated lithium ions.

SUMMARY

The present disclosure provides a compound of formula (I): 0 OR1 / R2 x \ / \ 0 oR1 (I) wherein X is Al or B; RI in each occurrence is independently a monovalent substituent; R2 is a divalent organic group; and M* is a cation.

Optionally, R2 is a group of formula (II): (R3)2C Arl (1) wherein R3 in each occurrence is independently H or a substituent and Arl is a C6-20 arylene group or heteroarylene group.

Optionally, Ar is unsubstituted or substituted 1,2-phenylene.

Optionally, each RI is independently selected from C1-90 alkyl wherein one or more C atoms other than the C atom bound to 0 of OR1 or a terminal C atom may be replaced with 0, and one or more H atoms may be replaced by F. Optionally, X is B. Optionally, IVI* is a lithium ion.

The present disclosure provides an electrolyte comprising a compound of formula (I) and at least one of a solvent and a polymer.

Optionally, the electrolyte comprises a solvent selected from C2_10 alkylene carbonates; di(Ci_ 10 alkyl) carbonates; linear, branched or cyclic compounds containing two or more ether groups; and mixtures thereof.

The present disclosure provides a metal battery or a metal ion battery comprising an anode, a cathode and an electrolyte as described herein disposed between the anode and the cathode.

DESCRIPTION OF DRAWINGS

Figure I is a schematic illustration of a battery comprising a compound as described herein; Figure 2 shows illustrative initial and steady state Nyquist plots for a cell containing Comparative Compound 1; and Figure 3 shows linear sweep voltarnmograms for Compound Example I and Comparative Compounds 1 and 2.

DETAILED DESCRIPTION

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context penults, words in the Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word "or," in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. References to a layer "over" another layer when used in this application means that the layers may be in direct contact or one or more intervening layers may be present. References to a layer "on" another layer when used in this application means that the layers arc in direct contact. References to an element of the Periodic Table include any isotopes of that element.

The teachings of the technology provided herein can be applied to other systems, not necessarily the system described below. The elements and acts of the various examples described below can be combined to provide further implementations of the technology. Some alternative implementations of the technology may include not only additional elements to those implementations noted below, but also may include fewer elements.

These and other changes can be made to the technology in light of the following detailed description. While the description describes certain examples of the technology, and describes the best mode contemplated, no matter how detailed the description appears, the technology can be practiced in many ways. As noted above, particular terminology used when describing certain features or aspects of the technology should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the technology with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the technology to the specific examples disclosed in the specification, unless the Detailed Description section explicitly defines such terms. Accordingly, the actual scope of the technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the claims.

To reduce the number of claims, certain aspects of the technology arc presented below in certain claim forms, but the applicant contemplates the various aspects of the technology in any number of clai in forms.

In the following description, for the purposes of explanation, numerous specific details are set. forth in order to provide a thorough understanding of implementations of the disclosed technology. It will be apparent, however, to one skilled in the art that embodiments of the disclosed technology may be practiced without some of these specific details.

Compounds of Formula (I) The present inventors have surprisingly found that compounds of formula (I) may possess both high electrochemical stability as well as high ionic conductivity and / or a high lithium transference number.

0\/OR1 R2 X \ / \ 0 OR1 (I) Xis Al or B. RI in each occurrence is independently a monovalent substituent and wherein RI is bound to 0 of OR' by a carbon atom of RI.

Preferably, each R1 is independently selected from linear, branched or cyclic CI-40 alkyl in which one or more C atoms of the C140 alkyl, other than the C atom bound to 0 of OR' or a terminal C atom of the CI40 alkyl may be replaced with 0, and one or more H atoms may be replaced by F. By "terminal C atom" of an alkyl group as used herein is meant the methyl C atom of an ii-alkyl chain or the methyl C atoms of a branched alkyl chain.

Preferred groups RI are: -(CH2CH20)n-R5 wherein R5 is a C1-4 alkyl and n is 1-15, and wherein one or more H atoms may be replaced with F; and C,,2 alkyl wherein one or more H atoms may be replaced by F. In some embodiments, the RI groups are the same. In some embodiments, the RI groups are different.

R2 is a divalent organic group wherein each 0 of 0-R2-0 is bound to a carbon atom of R2. Preferably, R2 is a group of formula (II): (R3)2C Ari (II) wherein R3 in each occurrence is independently H or a substituent and Ari is a Co_20 arylene group or heteroarylene group.

Preferably, Ai' is unsubstituted or substituted 1,2-phenylene or an unsubstituted or substituted 5-or 6-membered heteroaromatic ring. A particularly preferred heteroaromatic group Arl is a 6-membered heteroaromatic ring in which the ring atoms consist of C and N atoms only, for example pyridine or pyrimidine.

Where present, substituents of Arl are preferably and independently selected from F and Chp alkyl wherein one or more non-adjacent, non-terminal C atoms of the C1-12 alkyl may be replaced with 0, S. N R4, CO COO or CONR4 wherein R4 in each occurrence is independently a Ci_12 hydrocarbyl group, and one or more H atoms of the CI-12 alkyl group may be replaced with F. A C,.42 hydrocarbyl group as described anywhere herein is preferably selected from C1-12 alkyl; phenyl; and phenyl substituted with one or more C1-6 alkyl groups.

Preferably, R3 in each occurrence is independently H, F or a C1-12 alkyl group in which one or more H atoms may be replaced with F and one or more non-terminal C atoms may be replaced with 0. In a preferred embodiment, at least one R3, optionally each 123, is a Choperfluoroalkyl group.

W is a cation. W is preferably an alkali metal cation, more preferably Lit The compound of formula (I) may be formed by reacting a compound of formula (HI) with a compound selected from formulae °VIA) and (IVb) and a compound selected from formulae (Va), (Vb) and (Ye): XH4-M+ (111) R1-0H (IV a) 0 0 R2/OH

NH NH

(Va) (Vb) (Vc) The compound of formula (IVa) may he a primary, secondary or tertiary alcohol. The compound of formula (IVb) may he an aldehyde or a ketone.

Exemplary compounds of formula (III) include, without limitation, lithium aluminium hydride (LiAIHI) and lithium borohydride (L1BH4).

Exemplary compounds of formula (I) include without limitation:

F F

0"0,B, cEc7.78 Lit + Li

F F

Cy3, 7 7. 8 0, ;0 0 0 \

F

F ( F F L i+ Li+ CF3 0 Al L 0\ 0 CF3 Li+ d b c1. CF3 C F3 CF3 L L.+ Li+ F3C F3C Electrolyte An electrolyte comprising a compound of formula (I) suitably further comprises at least one of a polymer and a solvent. If a polymer and solvent are both present, the electrolyte may be a gel.

The polymer may be selected from any known ion-conducting polymers including, without limitation: poly(alkylene oxide), for example poly(ethylene oxide) and poly(propylene oxide); and fluorinated polymers such as PVDF, PVDF-HFP; PMMA; polyacrylonitrile; polycarbonate; polyethylene; polypropylene; poly(vinyl methyl ketone); polyvinylpyrrolidone; polyether ether ketone; polyisoprene; polybutadiene; polystyrene-block-polyisoprene-blockpolystyrene; poly(1-vinylpyrrolidone-co-vinyl acetate); polystyrene-block-polybutadieneblock-polystyrene; polystyrene-block-poly(ethylene oxide)-block-polystyrene; co-polymer and mixtures thereof.

The polymer is suitably a neutral polymer, i.e., not a polymer substituted with ionic groups, and in particular is suitably not a single-ion conducting polymer comprising anionic groups.

The electrolyte may comprise one or more solvents. Solvents are preferably selected from et ID alkylene carbonates, di(Ci_io alkyl) carbonates, for example propylene carbonate, ethylene carbonate, di methyl carbonate, diethyl carbonate; linear, branched or cyclic compounds containing two or more ether groups, for example 1,3-dioxolane, 2,5dimethoxy tetrahydrofuran, glyme (dimethoxyethane), diglyme, trialyme and tetraglyme; cyclic lactones and mixtures thereof.

The compound of formula (I) may comprise a solvated M± cation.

Optionally, the electrolyte as present in a battery contains no more than 10 solvent molecules per M+ cation. The solvent / M+ ratio may be as determined from a 1H NMR spectrum of the electrolyte prior to its incorporation into a battery.

Battery Figure 1 illustrates a battery comprising a compound of formula (I). The battery may be a metal battery or a metal ion battery, preferably a lithium battery or a lithium ion battery.

The battery comprises an anode current collector 101 carrying an anode 103 on a surface thereof; a cathode current collector 109 having a cathode 107 disposed on a surface thereof; and a layer 105 comprising an electrolyte comprising a compound as described herein disposed between the anode and the cathode.

The layer 105 may comprise a porous separator in which the electrolyte, e.g., a liquid or gel electrolyte, is absorbed. If the electrolyte comprises a solid, e.g., a gel comprising a polymer and the compound of formula (I), then a porous separator may or may not be present.

In the case of a metal battery, the anode is a layer of metal (e.g., lithium) which is formed over the anode current collector during charging of the battery and which is stripped during discharge of the battery.

In the case of a metal ion battery, e.g., a lithium ion battery, the anode comprises an active material, e.g., graphite, for absorption of the metal ions.

The cathode may be selected from any cathode known to the skilled person.

The anode and cathode current collectors may be any suitable conductive material known to the skilled person, e.g., one or more layers of metal or metal alloy such as aluminium or copper.

A battery may be formed by providing an electrolyte as described herein on a surface of one of an anode and a cathode and providing the other of an anode and cathode, and associated current collector, over the electrolyte.

A metal battery precursor may be formed by providing an electrolyte as described herein on a surface of an anode current collector; and providing the cathode and a cathode current collector over the electrolyte. Upon application of a charging bias, a metal anode may be formed between the electrolyte and the anode current collector.

Figure 1 illustrates a battery in which the anode and cathode are separated only by a single layer comprising or consisting of the electrolyte, for example a separator comprising the electrolyte. In other embodiments, one or more further layers may be disposed between the anode and the cathode.

For simplicity. Figure 1 illustrates a battery in which the anode and cathode are separated only by a single layer 105, however it will be understood that in use a solid-electrolyte interphase will typically form on the anode surface.

EXAMPLES

Compound Example I

Compound Example I was prepared according to the following reaction scheme: OH OH 1) LiBH4, THE -72°C to 0°C Li+ 2) F F

HO F

THF,0°C to 60°C

Compound Example 1

To a solution of lithium borohydride (9.2 ml, 4.6 mmol, 0.5M in THE) was added a solution of hexalluoro-2-(2-hydroxyphenyl)propan-2-ol (1 g in 8 ml of THF, 3.84 mmol) dropwise at -70°C. The mixture was stirred for 3 hours between -70°C and -60°C, then allowed to warm to 0°C. A solution of 2,2,3,3,4,4,5,5-octatluoropentanol (1 nil in 8m of THF, 7 68 mmol) was added dropwise to the mixture and solution was stirred for 1.75 hours at room temperature. The temperature was increased to 60°C and the mixture was stirred overnight. The reaction mixture was cooled down to room temperature and a solution of lithium borohydride (0.4 ml, 0.8 mmol, 2M in THF) was added dropwise. The mixture was stirred for 4 hours at 60°C and then cooled down to room temperature. Propylene carbonate (0.65m1, 7.66 mmol) was added. Excess solvent was removed under vacuum (3.1x10-2 mbar) at 25°C for 1 hour then at 40°C for 2 hours to yield a white thick oil. Additional propylene carbonate (0.6 ml 7 1 rnmol) was added to yield 3.8 g of white oil (86% yield).

From integration of NMR peaks, it was calculated that for one molecule of hexafluoro-2-(2-hydroxyphenyl)propan-2-ol corresponding to one molecule of lithium cation, there is 0.1 molecules of THF and 4.0 molecules of propylene carbonate (PC).

NMR (600 MHz) in deuterated THF: 6 (ppm), 1.39 (121-1, d, J = 6.2 Hz, Cl-l3 from PC), 1.78 (0.5H, m, CH2, from THF), 3.62 (0.5H, m, CH2 from THF, 3.90 (4H, m), 4.00 (4H, t, J = 8.0 Hz, CH from PC, 4H), 4.50(4H, t, J= 8.1 Hz, CH from PC), 4.80(m, CH from PC, 4H) 6.6-6.86 (4H, m), 7.15 (1H, td, J = 7.6 Hz. 1= 1.4 Hz), 7.32 (IN, d, J = 7.6 Hz).

Compound Example 2

Compound Example 2 was prepared according to the following reaction scheme: 1) LiBH4, THE -80°C to 0°C 2) 7 8C 7.78

HO

THF,0°C to 60°C p /47.78 7.V8

OH OH

Compound Example 2

Number of repeat unit was determined by 1H NMR.

To a solution of lithium borohydride (9.2 ml, 4.6 mmol, 0.5M in THF) was added a solution of hexalluoro-2-(2-hydroxyphenyl)propan-2-ol (1 a in 8 ml of THF, 3.84 mmol) dropwise between -90°C and -80°C. The mixture was stirred for 3 hours between -85°C and -70°C, then allowed to warm to 0°C. A solution of MPEG350 (2.87 g, in 8m of THF, 7.68 mmol) was added dropwise to the mixture and solution was stirred for 1 hour at room temperature. The temperature was increased to 60°C for 30 minutes and the mixture cooled down to room temperature overnight. Propylene carbonate (0.62m1, 7.31 mmol) was added. Excess solvent was removed under vacuum (3.2x10-2 mbar) at 25°C for 2 hours then at 40°C for 4 hours to yield 4.0 g of compound example 2 as a colourless oil (85% yield).

From integration of NMR peaks, it was calculated that for one molecule of hexatluoro-2-(2-hydroxyphenyl)propan-2-ol corresponding to one molecule of lithium cation there is 1.88 molecules of propylene carbonate (PC).

Compound Example 3

Compound Example 3 was prepared according to the following reaction scheme: F3C c F3 cF3 9)-CE3 F3C-ct CF3 Li+

Compound Example 3

FJF 1) L1BH4, THF HO -70°C to R.T.

THF, R.T. to 65°C To a solution of lithium borohydrkle (7.9 mL, 3.84 mmol 0 5M) in tetrahydrofuran was added dropwise a solution of 1,1,1,3,3,3-hexanuoropropan-2-ol (0.8 mL, 7.68 nunol) in 7 ml. of anhydrous tetrahydrofuran at -70"C.The mixture was then stirred for 1 hour between -70°C and -60°C, then allowed to warm to 0°C. A solution of hexafluoro-2-(2-hydroxyphenyl)propan-2-ol (1 g, 3.84 mmol) in 7 mL of anhydrous TI-IF was added dropwise to the reaction mixture at room temperature. The mixture was stirred at 65°C for 4 hours and overnight at room temperature. Additional lithium borohydrine (0.23 mL, 0.46 mmol) and hexafluoro-2-(2-hydroxyphenyl)propan-2-ol (0.1 g, 0.38 mmol) was added, and the reaction mixture was stirred at 65°C. for 2 hours. The mixture was cooled down to room temperature and propylene carbonate (0.96 mL, 11 5 mmol) was added. Further propylene carbonate was added to obtain a transparent liquid.

IFT NMR (600 MHz) in deuterated THF: 6 (ppm), 1.38 (d, CH3, from propylene carbonate 15.614), 3.97 (m, CH, from propylene carbonate, 5.11-1), 4.52 (t, CH, from propylene carbonate and CH from HFP, 6.8H), 4.81 (m, CH, from propylene carbonate 4.7H). 6.67 (m. 2H). 7.12 (td, J= 7.7Hz, J=1.6 Hz. 1H), 7.29 (d, J=7.9Hz, 1H).

From integration of NMR peaks, it was calculated that for one molecule of hexafluoro-2-(2-hydroxyphenyl)propan-2-ol corresponding to one molecule of lithium cation, there is 5.1 molecules of propylene carbonate.

Compound Example 4

Compound Example 4 was prepared according to the following reaction scheme: To a solution of lithium borohydride (7.9 mL, 3.84 nunol 0 5M) in tetrahydrofuran was added drop wise a solution of 2,2,3,3-tetrafluoropropan-1-ol (0.68 mL, 7 68 mmol) in 7 mL of anhydrous tetrahydrofuran at -70°C.The mixture was then stirred for 1 hour between -70°C and 1) LiBH4, THE -70°C to R.T.

Compound Example 4

THE, R.T. to 65°C Li+ -60°C, then allowed to warm to 0°C. A solution of hexafluoro-2-(2-hydroxyphenyl)propan-2-ol (1 g, 3.84 mmol) in 7 mL of anhydrous THF was added dropwise to the reaction mixture at room temperature. The mixture was stirred at 65°C for 4 hours and overnight at room temperature. Additional lithium borohydride (0.1 mL, 0 2 mmol) followed by hexalluoro-2-(2-hydroxyphenyl)propan-2-ol (0.06 g, 0.23 mmol) were added, and the reaction mixture was stirred at 65°C for 1 hour. The mixture was cooled down to room temperature and Propylene carbonate (0.96 mL, 11 5 mmol) was added. Further propylene carbonate was added to obtain a transparent liquid.

11-1 NMR (600 MHz) in deuterated THE: 13 (ppm), 1.38 (d, CH3, from propylene carbonate 11.6H), 3.77 (m, 4.2H), 3.97 (in, CH, from propylene carbonate 3.7H), 4.52 (t, CH, from propylene carbonate,3.7H), 4.80 (m, CH, from propylene carbonate 3.3H), 6.10 (tt, J=53.51 Hz, J= 5.97 Hz, 2H), 6.70(m, 2H), 7.14 (td, J= 7.7 Hz, J=1.6 Hz, 1H), 7.31 (d, J=8.0 Hz, 1H).

From integration of NMR peaks, it was calculated that for one molecule of hexalluoro-2-(2-hydroxyphenyl)propan-2-ol corresponding to one molecule of lithium cation, there is 3.70 molecules of propylene.

Compound Example 5

Compound Example 5 was prepared according to the following reaction scheme: F3c CF3 CF3 9 CF3 -6-0 F3C-

Compound Example 5 Li+

1) L1BH4, THF -70°C to R.T.

2) OH OH CF3 CF3 R.T. to 65°C To a solution of lithium borohydride (7.9 mL, 3.84 mmol 0 5M) in tetrahydrofuran was added drop wise a solution of 1,1,1,3,3,3-hexafluoro-2-methylpropan-2-ol (0.94 mL, 7 68 mmol) in 7 mL of anhydrous tetrahydrofuran at -70°C.The mixture was then stirred for 1 hour between -70°C and -60°C, then allowed to warm to 0°C. A solution of hexafluoro-2-(2-hydroxyphenyl)propan-2-ol (1 g, 3 84 mmol) in 7 mL of anhydrous THF was added dropwise to the reaction mixture at room temperature. The mixture was stirred at 65°C for 4 hours and overnight at room temperature. Additional lithium borohydride (0.04 nth, 0.08 mmol) was added, and the reaction mixture was stirred at 65°C for 5 hours and overnight at room temperature. Propylene carbonate (0.96 mL, 11.5 mmol) was added. Further propylene carbonate was added to obtain a stable transparent liquid.

1H NMR (600 MHz) in deuterated THE: 6 (ppm), 1.38 (d, CH3, from propylene carbonate 15.4H), 1.61 (s, 5.3F1), 3.97 (m, CH, from propylene carbonate 5.3H), 4.52 (t, CH, from propylene carbonate, 5.3H), 4.80 (m, CH, from propylene carbonate 5.1H), 6.62 (m, 2H), 7.10 (td, J= 7.7 Hz, J=1.6 Hz, 1H), 7.27 (d, J=7.7 Hz, 1H).

From integration of NMR peaks, it was calculated that for one molecule of hexatluoro-2-(2-hydroxyphenyl)propan-2-ol corresponding to one molecule of lithium cation, there is 5.2 molecules of propylene carbonate.

Cell Example 1

A 2032-type coin cell was fabricated in a rigorously dry and oxygen-free Argon gas-filled MBraun glovebox using casings purchased from Cambridge Energy Solutions.

A stainless-steel spacer was inserted in a coin cell bottom, followed by a lithium disk and a fluoro-silicone stencil (purchased from Silex Silicones). The stencil was shaped as a disk of 15.5mm diameter, with a circular hole of 5mm diameter cut in its middle (the thickness of the stencil in the crimped cell was 360 pm). The hole was filled with 30p1 of an electrolyte solution containing Compound Example 1. Solvents are set out in Table 1 below.

On top of the stencil a lithium disk was placed, followed by a stainless-steel spacer, a wave spring and a coin cell top. Finally, the coin cell was crimped.

Cell Example 2

A cell was prepared as for Cell Example 1 except that Compound Example 3 was used in place of Compound Example 1.

Cell Example 3

A cell was prepared as for Cell Example 1 except that Compound Example 4 was used in place of Compound Example 1.

Comparative Cell 1 For the purpose of comparison, a cell was prepared as for Cell Example 1 except that Comparative Compound 1 was used in place of Compound Example 1.

Comparative Compound 1 Comparative Cell 2 For the purpose of comparison, a cell was prepared as for Cell Example 1 except that Comparative Compound 2 was used in place of Compound Example 1. e

B, CF3 I 0 0 CF3 Lie Comparative Compound 2 Measurements Electrochemical Impedance Spectroscopy (EIS) measurements were conducted at room temperature. Electrolyte impedances were taken over a frequency range of 1Hz to 1 MHz, with an amplitude of 5 mV.

Ionic conductivities were calculated from these data using the following formula: o-= A * R where: 1. 1 is the thickness of the material between the two lithium disks which corresponds to the thickness of the stencil in the crimped cell.

2. A is the area of the film which corresponds to the circular hole cut in the middle of the stencil.

3. R is the electrolyte impedance.

The impedance of the electrolyte is determined by estimating the intercept of the first semicircle of the Nyquist plot with the x-axis. This is the bottom left corner of the illustrative Nyquist plot of Figure 2 for Comparative Compound 1.

Lithium transference number (LTN) was measured according to Evans's method (J. Evans et al., POLYMER, 1987, Vol 28), using the 2032-type coin cell described above.

Devices were left resting overnight for about 19 hours before performing the LTN measurement, in order to ensure stabilisation of the interfaces between the electrolytes and the lithium disks.

After resting: 1. A first EIS spectrum was measured.

2. This was followed by a DC current measurement (the applied constant voltage is tuned individually for each cell in order to achieve an initial current of about 0.5uA. The measurement was terminated as soon as the current had decreased to a steady state.

3. The sequence was then finished with a second EIS measurement.

The EIS measurements were conducted at room temperature. The EIS measurements were taken over a frequency range of 1Hz to 1 MHz, with an amplitude of 5 mV.

The LTN values were calculated according to the following formula, based on the model developed by Evans et al.

LTN-

I°(AV -Is Rs) where (referring to the illustrative Nyquist plots for Comparative Compound 1 shown in Figure 2): Is (AV -R°) 1. R° is the initial impedance taken from the first EIS spectrum (determined by estimating the intercept on the x-axis of the Nyquist plot of the second semicircle (right hand side)).

2. Rs is the steady state impedance taken from the second EIS after a DC bias was applied (determined by estimating the intercept on the x-axis of the Nyquist plot of the second semicircle (right hand side)).

3. I° is the initial current taken when the voltage is stepped to set value.

4. I' is the steady state current taken at the end of the DC measurement.

The ionic conductivities and LTN were calculated for different solvate ionic liquids, and representative values arc reported in Table 1 in which -PC" is propylene carbonate and -DME" is dimethoxyethane

Table I

Material Mol of solvent / Ionic LTN mol of Li* conductivity (S/cm) Compound 6.0 PC 1.8x104 0.58

Example 1

Compound 8.5PC -F 3.6 DME 1.3x1e 0.80

Example 1

Compound 7.4 PC 6.8x104 0.34

Example 3

Compound 6.2 PC 1.9x104 0.54

Example 4

Comparative 6.0 PC 1.1x10-4 0.31 Compound 1 Comparative 6.2 PC 2.4x104 0.74 Compound 2 Linear Sweep Voltmnmetry The oxidative stability of Compound Example 1 and Comparative Compounds 1 and 2 were measured using linear sweep voltammetry of an asymmetrical coin cell. The cells were assembled as described for Cell Example 1 and Comparative Cells 1 and 2, respectively, but without the top lithium disk.

Measurements were carried out for Compound Example 1 with 0.1 moles of THF and 4.0 moles of propylene carbonate per mole of lithium; Comparative Compound 1 with 0.05 moles of THE and 1.9 moles of propylene carbonate per mole of lithium; and Comparative Compound 2 with 6.0 moles of propylene carbonate per mole of lithium.

A linear sweep voltammomum was taken for each cell using a Gamry potentiostat. The sweep rate was 1 mV per second and the cell was swept from the open circuit potential to 5 V vs Li/Lit, except for the cell containing Comparative Compound 1 which was swept to 6V due to its high electrochemical stability.

Oxidative stability was calculated by fitting a line to the region below 4V and a line to the region above 5 RA and calculating the voltage value for the intersection between the two lines.

CH -CA Eo -x

CA -S B

where: 1) E, is the oxidative stability value in volts 2) CA is the y-intercept of the line fitted between two points -one with a current at 12 RA and one with a current at 6 RA.

3) SA is the slope of that same line.

4) CB is the y-intercept of the line fitted between two points with a voltage at 4V and a voltage at 3.3 V. 5) SE is the slope of that same line.

Figure 3 shows the linear sweep voltammograms of the asymmetric cells containing Compound Example 1 and Comparative Compounds 1 and 2. Calculated oxidative stabilities are set out in Table 2.

Table 2

Material Oxidative StabilityN Compound 4.6

Example 1

Comparative 4.8 Compound 1 Comparative 4.3 Compound 2 As set out in Tables 1 and 2, Compound Example 1 has higher ionic conductivity and LTN than Comparative Compound 1, and higher oxidative stability than Comparative Compound 2, thus providing a combination of good stability, ionic conductivity and LTN.

Claims

CLAIMS1. A compound of formula (I): /0 /OR1 R2 x \ / \ 0 OR1 (I) wherein X is Al or B; R1 in each occurrence is independently a monovalent substituent; R2 is a divalent organic group; and WI is a cation.
2. The compound according to claim I wherein R2 is a group of formula (II): (R3)2C Arl (11) wherein R3 in each occurrence is independently H or a substituent and Arl is a Con° arylene group or heteroarylene group.
3. The compound according to claim 2 wherein Ar I is unsubstituted or substituted 1,2-phenylene.
4. The compound according to any one of the preceding claims wherein each R1 is independently selected from Ci-20 alkyl wherein one or more C atoms other than the C atom bound to 0 of ORI or a terminal C atom may be replaced with 0, and one or more H atoms may be replaced by F.
5. The compound according to any one of the preceding claims wherein X is B.
6. The compound according to any one of the preceding claims wherein M is a lithium ion. M+
7. An electrolyte comprising a compound according to any one of the preceding claims and at least one of a solvent and a polymer.
8. An electrolyte according to claim 7 wherein the electrolyte comprises a solvent selected from Cmo alkylene carbonates; di(C140 alkyl) carbonates; linear, branched or cyclic compounds containing two or more ether groups; and mixtures thereof.
9. A metal battery or a metal ion battery comprising an anode, a cathode and an electrolyte according to claim 7 or 8 disposed between the anode and the cathode.