WO2018090097A1 - Electrochemical cell - Google Patents

Abstract

The present invention provides an electrochemical cell comprising: an anode comprising an anode material including aluminium; a cathode comprising a cathode material including sulphur; and an electrolyte comprising lithium ions; wherein the anode material comprises at least 30 mol% aluminium. The present invention further provides a battery comprising one or more electrochemical cells of the present invention.

Description

ELECTROCHEMICAL CELL

The present application claims priority from Australian provisional patent application no. 2016904734 filed on 18 November 2016, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an electrochemical cell. More particularly, the invention relates to a lithium ion- based electrochemical cell. The invention also relates to a battery comprising the electrochemical cell.

BACKGROUND

Lithium ion based electrochemical cells and batteries are commercially popular due to their compact size and good capacitive properties . These are one of the most popular types of rechargeable batteries used in portable

electronics. Generally, a lithium ion (Li-ion)

electrochemical cell comprises an anode made of graphite or carbon material, a cathode made of lithium metal oxide compound, and an electrolyte comprising lithium ions.

These cells have been reported to provide good cell capacity of around 150-250 mAh/g.

Despite their compact size, convenient usage and good specific capacity, Li-ion batteries have some

disadvantages, including their high cost and safety risks especially when the cell/battery is damaged. There is therefore a need in the art to provide

alternative electrochemical cells and batteries. There is also a need in the art to provide alternative Li-ion electrochemical cells and batteries which can be prepared using less expensive anodes or cathodes than the anodes or cathodes used in some prior art Li-ion cells and

batteries .

SUMMARY OF THE INVENTION

In accordance with a first aspect, the present invention provides an electrochemical cell comprising:

an anode comprising an anode material including aluminium;

a cathode comprising a cathode material including sulphur; and

an electrolyte comprising lithium ions in contact with the anode and the cathode;

wherein the anode material comprises at least 30 mol % aluminium. In an embodiment, the cathode material comprises at least 5 % by weight sulphur. In an embodiment, the cathode material comprises at least 20 % by weight sulphur.

In accordance with a second aspect, the present invention provides an electrochemical cell comprising:

an anode comprising an anode material including aluminium;

a cathode comprising a cathode material including sulphur; and

an electrolyte comprising lithium ions in contact with the anode and the cathode;

wherein the anode material comprises at least 30 mole % aluminium and the cathode material comprises at least 20 % by weight sulphur. In an embodiment, the cathode material comprises 20% to 90% by weight sulphur.

In an embodiment, the cathode material comprises

sulphurised carbon.

In an embodiment, the anode material is aluminium metal or an alloy of aluminium with one or more other metals .

In an embodiment, the anode material comprises an alloy of aluminium and lithium. In an embodiment, the chemical formula of the alloy of aluminium and lithium metals is Al-Li , Al₂Li₃ or Al₄Li₉.

In an embodiment, the electrolyte comprises lithium hexafluorophosphate (LiPF₆) , lithium

Bis (trifluoromethylsulfonyl) amine (LiTFSI) or a mixture thereof dissolved in a solvent. In an embodiment, the electrolyte is lithium hexafluorophosphate (LiPF₆) in ethyl carbonate (EC; also known as ethylene carbonate) , ethyl methyl carbonate (EMC) or a mixture thereof. In an embodiment, the electrolyte is LiTFSI in dioxolane, 1,2- dimethoxyethane, triethylene glycol dimethyl ether or a mixture thereof. nt inven

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In accordance with a fourth aspect, the present invention provides an electrode for use as an anode in an

electrochemical cell, the electrode comprising an anode material including an alloy of aluminium and lithium;

wherein the amount of aluminium in the anode material is at least 30 mole %. In accordance with a fifth aspect, the present invention provides a method of forming a rechargeable

electrochemical cell comprising the steps of:

providing an anode comprising an anode material including aluminium, wherein the anode material comprises at least 30 mole % aluminium;

providing a cathode comprising a cathode material including sulphur;

providing an electrolyte comprising lithium ions; and arranging the electrolyte to be in contact with both the anode and the cathode.

In an embodiment, the cathode material comprises at least 20 % by weight sulphur.

In accordance with a sixth aspect, the present invention provides an Al/S lithium ion battery (an Al/S battery having an electrolyte comprising lithium ions) .

In accordance with a seventh aspect, the present invention provides an electrochemical cell comprising:

an anode comprising an anode material including aluminium;

a cathode comprising lithium polysulphide in contact with a carbon matrix; and

an electrolyte comprising lithium ions in contact with the anode and the cathode;

wherein the anode material comprises at least 30 mol% aluminium.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention are

described below, by way of example only, with reference to the accompanying drawings in which: Figure 1(a), 1(b) and 1(c) show schematics of three different configurations for rechargeable Aluminium- Lithium-Sulphur (Al-Li-S) electrochemical cells in accordance with embodiments of the present invention;

Figure 2(a), 2(b) and 2(c) show the configurations as shown in Figures 1(a), 1(b) and 1(c), respectively, where the sulphurised carbon is sulphurised polyacrylonitrile (SPAN) and the electrolyte comprises LiPF₆ in an organic solvent;

Figure 3(a) and 3(b) show schematics of two different configurations for rechargeable electrochemical cells in accordance with embodiments of the present invention.

Figure 3(a) depicts an embodiment having a lithiated SC cathode and an Al-Li alloy anode and Figure 3 (b) depicts an embodiment wherein the SC is carbon impregnated with lithium polysulfide (Li-PS-C) , and the electrolyte comprises LiTFSI in an organic solvent (a Li-ion

electrolyte) ; Figure 4(a), 4(b) and 4(c) show the galvanostatic charge and discharge curves for Al/SPAN cell, Li/SPAN half-cell and Al/Li-SPAN cell, respectively, as described in Example 1;

Figure 5 shows the galvanostatic charge and discharge curves for an Al-Li/Li-PS-C cell, as described in

Example 3;

Figure 6 shows a schematic of an Al-Li alloy/SPAN cell and illustrates a proposed mechanism for the discharging (upper) and charging (lower) process, as described in Example 1; Figure 7 (a) to 7 (d) show some characteristics of the alloying/de-alloying processes of aluminium in 1M LiPF₆ + EC/EMC electrolyte at 0.06 mA/cm², and Scanning Electron Microscopy (SEM) images of Al (c) and Al-Li alloy (d) , as described in Examples 1 and 2 ;

Figure 8 (a) shows cyclic voltammetry (CV) results of the Al-Li alloy/SPAN cell described in Example 2 ;

Figure 8 (b) shows galvanostatic charge and discharge curves of the Al-Li alloy/SPAN cell at different cycles at a current density of 200 mA/g, as described in Example 2;

Figure 8(c) shows cycling stability and Coulombic

efficiency of the Al-Li alloy/SPAN cell at 200 mA/g from the 2nd cycle to the 200th cycle, as described in Example 2; Figure 8(d) shows the trend of the discharge/charge voltages and the voltage efficiency of the Al-Li

alloy/SPAN cell during 200 cycles, as described in Example 2;

Figure 9 is a graph of specific capacity (mAh/g; y-axis) vs cycles (x-axis) and shows the cycling stability of the Al-Li/Li-PS-C cell over 100 cycles, as described in

Example 3.

Figures 10(a) show the rate performance of the Al-Li alloy/SPAN cell at different current densities, as described in Example 2;

Figures 10(b) and 10(c) show cycling performance of the Al-Li alloy/SPAN cell charged at different current densities for 50 and 300 cycles, respectively, as

described in Example 2; Figure 10 (d) shows cycling performance of the Al-Li alloy/SPAN cell in terms of discharge/charge voltage and voltage efficiency of the full cell at different current densities, as described in Example 2 ; Figure 11 shows the galvanostatic charge and discharge curves for an Al-Li/Li-PS-C cell (the MPC-CC cell) at different charge and discharge rates, as described in Example 3.

Figure 12 shows the dependence of charge/discharge voltage difference on current density for the Al-Li alloy/SPAN cell, as described in Example 2 ;

Figure 13 (a) shows cyclic voltammetry (CV) curves of the Al-Li alloy/SPAN cell at different scan rates, as

described in Example 2; Figure 13 (b) shows the dependence of formal potential on different scan rates for the Al-Li alloy/SPAN cell, as described in Example 2;

Figure 13(c) shows dependence of the cathodic (negative) and anodic (positive) peak current densities on the square root of the scan rate for the Al-Li alloy/SPAN cell, as described in Example 2;

Figure 13(d) shows Nyquist plots of the Al-Li alloy/SPAN cell, as described in Example 2 ;

Figure 14 (a) shows voltage-capacity dependence of the SPAN vs Li°/Li⁺ cell, Al-Li alloy vs Li°/Li⁺ cell, and Al-Li alloy/SPAN cell, as described in Example 2 (105/106 = SPAN vs Li°/Li⁺; 107/108 = Al-Li alloy vs Li°/Li⁺; 109/104 = Al- Li alloy/SPAN) ; Figure 14(b) shows XRD spectra of Al-Li alloy anode:

original, after discharge in the 1st cycle, and after charge in the 1st cycle, as described in Example 2;

Figures 14(c) to 14(e) show XPS spectra of pristine, fully discharged, and fully charged SPAN cathodes respectively, as described in Example 2;

Figure 15 (a) shows XPS C Is spectra of pristine SPAN cathode; and Figure 15 (b) shows XPS C Is spectra of pristine SPAN cathode, fully discharged cathode and fully charged cathode, as described in Example 2;

Figure 16(a) and 16(b) are SEM images of the Al-Li alloy described in Example 2 after 50 cycles and 200 cycles, respectively, as described in Example 2 ;

Figure 16(c) is an XRD spectra of Al-Li alloy after 50 cycles and 200 cycles, as described in Example 2.

DETAILED DESCRIPTION OF EMBODIMENTS

In a first aspect, the present invention provides an electrochemical cell comprising:

an anode comprising an anode material including aluminium;

a cathode comprising a cathode material including sulphur; and

an electrolyte comprising lithium ions in contact with the anode and the cathode;

wherein the anode material comprises at least

30 mole % (30 mol%) aluminium.

In an embodiment, the cathode material comprises at least 20 % by weight (20 wt%) sulphur. The inventors have found that the combination of an anode having an anode material including at least 30 mole % aluminium, a cathode having a cathode material including sulphur (preferably at least 20 % by weight sulphur) , and a lithium-ion electrolyte, enables the preparation of Li- ion electrochemical cells, and rechargeable Li-ion batteries comprising the electrochemical cells, which have high capacity and good recharging properties . Aluminium and sulphur are abundant and relatively low cost

materials, and the use of these materials can provide cost savings in preparing the electrochemical cells of the present invention compared to electrochemical cells prepared using more expensive anode materials or cathode materials .

Certain batteries have previously been prepared comprising an aluminium anode and a sulphur cathode. For example, a primary Al/S battery was first reported with an aqueous alkaline electrolyte (Licht, S . ; Peramunage, D. Novel Aqueous Aluminum Sulfur Batteries. J. Electrochem. Soc. 1993, 140, L4-L6). However, in this battery, the overall cell reaction is irreversible at room temperature because Al(OH)₃ precipitates as the discharge product. The use of an ionic liquid-based (IL-based) electrolyte allows the Al plating/stripping at high Coulombic efficiency (up to 100%) . However, according to Cohn et al . (Cohn, G.; Ma, L.; Archer, L. A., A Novel Non-Aqueous Aluminium Sulphur Battery, J. Power Sources 2015, 283, 416-422) the sulphur cathode in this IL-based electrolyte displays low

reversibility, which may be due to the difficulty in oxidizing A1₂S₃ as well as the polysulfide shuttle. It has been reported that a rechargeable IL-based Al/S battery becomes viable with a confined sulphur/carbon cathode which facilitates the reversible oxidation of A1₂S₃ (Gao, T . ; Li, X.; Wang, X.; Hu, J.; Han, F . ; Fan, X.; Suo, L.; Pearse, A. J.; Lee, S. B . ; Rubloff, G. W. ; et al . A

Rechargeable Al/S Battery with an Ionic-Liquid Electrolyte. Angew. Chem. , Int. Ed. 2016, 128, 10052- 10055). Nevertheless, the practical discharge voltage of the rechargeable IL-based Al/S battery is only 0.5 V and is well below the thermodynamic voltage of Al/S battery (1.36V, 2A1³⁺ + 3S^2~ → A1₂S₃).

The present invention provides an Al/S battery with a lithium-ion electrolyte. Advantageously, the batteries o the present invention are rechargeable. Further, the low potential (0.28 V, vs. Li°/Li⁺) of the alloying reaction Al with Li ions (Li⁺) enables a relatively high cell voltage, e.g. 1.5 V.

Preferably, at least one of the anode material or the cathode material used to prepare the electrochemical cell of the present invention is pre-lithiated, that is, the anode material or cathode material is treated to comprise lithium (i.e. is lithiated) prior to incorporation of the anode material or cathode material into the

electrochemical cell. This is preferred because the lithium present in the pre-lithiated anode material or cathode material compensates for the deficiency of lithium ions in the electrolyte during the redox process. In some embodiments, the anode material comprises an alloy of aluminium and lithium. In some embodiments, the cathode material comprises lithium sulphide (Li₂S_x, x=l-8). In the electrochemical cells of the present invention, lithium ions play a dual role in terms of the formation of an alloy comprising aluminium and lithium at the anode and lithium sulphides at the cathode. The potential difference between the alloy and the sulphides enables the

preparation of electrochemical cells having high discharge voltages and specific capacity. Anode

The anode of the electrochemical cell of the present invention comprises an anode material where the anode material comprises at least 30 mole % aluminium.

The anode material is the material, forming part of the anode, that participates in the electrochemical reaction during charging and discharging of the electrochemical cell.

In some embodiments, the anode consists of the anode material. However, more typically, the anode comprises an electrically conductive substrate with the anode material on, or in electrical contact with, at least part of the surface of the substrate.

Typically, the anode material is selected from aluminium metal (i.e. aluminium metal with only trace amounts of impurities) or an alloy of aluminium with one or more other metals (sometimes referred to herein as an

"aluminium alloy") .

Without wishing to be bound by theory, it is believed that in such embodiments during charging of the cell, the lithium ions migrate towards the aluminium or aluminium alloy whereupon they contact/intercalate into the

aluminium or aluminium alloy. Once in contact/intercalated with the aluminium or aluminium alloy, the lithium ions can undergo reduction to lithium metal (i.e. the

electrochemical reaction) , to thereby generate an

electrical potential. The lithium may then alloy with the aluminium metal or aluminium alloy. In some embodiments, the anode material comprises at least 35 or at least 40 mole % aluminium. The anode material may, for example, comprise 30 to 100, 30 to 80, 35 to 80, or 40 to 80 mole % aluminium.

During discharging of the electrochemical cell, the proportion of the aluminium in the anode material will increase as lithium is stripped from the anode material. Similarly, during charging of the electrochemical cell, the proportion of aluminium in the anode material will decrease as the proportion of lithium in the anode material increases. In the electrochemical cell of the present invention, the anode material comprises at least 30 mole % aluminium at all states of charge of the electrochemical cell (when the electrochemical cell is in a fully charged state, a fully discharged state, or any state in between) .

In some embodiments, when the electrochemical cell is in a discharged state, the anode material may comprise 100% aluminium or close to 100% aluminium. In such embodiments, the anode may be composed of aluminium metal .

In some embodiments, the anode comprises the anode material on a substrate. Typically the substrate is electrically conductive. The substrate may be a

conventional electrode, such as an aluminium electrode, carbon electrode, or copper electrode. a metal from any may, for itals Pt, Ti, Al, W, Cu or Ni . The electrically conductive substrate may alternatively be formed from a non-metal substrate (e.g. carbon black, carbon nanotubes or graphene) .

In some embodiments, the anode material is an alloy of aluminium and lithium (Al-Li alloy) . The chemical formula of the Al-Li alloy may be AlLi (50 mole % aluminium) , Al₂Li₃ (approximately 40 mole % aluminium) , Al₄Lig

(approximately 30 mole % aluminium) or any combination of these forms (provided the anode material comprises at least 30 mole % aluminium) .

In some embodiments, the anode material is in powder form and is contained in a shell or matrix to provide

stability. For example, the anode may comprise Al-Li alloy in powder form which is contained in a carbon or graphene shell or matrix to provide mechanical stability to the electrode. The shell or matrix may also facilitate immobilisation of the powdered anode material on or proximal to the electrically conductive substrate to maintain the anode material in electrical contact with the electrically conductive substrate.

In some embodiments, an anode having an anode material consisting of aluminium (i.e. aluminium metal with only trace impurities) is used to construct the electrochemical cell, and an alloy of aluminium and lithium is formed during charging of the electrochemical cell. In other embodiments, the anode may first be prepared comprising an electrically conductive substrate and an anode material comprising an alloy of aluminium and lithium, and this anode used to construct the electrochemical cell. In the situation where an anode material is applied to an electrically conductive substrate prior to construction of the electrochemical cell, this may be performed by, for example, preparing a paste of the anode material (using typical additional paste components, such as binder, solvents and conductivity additives), and applying the paste to the substrate. A person skilled in the art will be able to determine suitable components and amounts for preparing a paste of the anode material.

In an embodiment, the anode comprises an anode material selected from aluminium or an alloy of aluminium with one or more other metals. The alloy of aluminium with one or more other metals comprises at least 30 mol% aluminium (for example, at least 35 or 40 mol% aluminium) . The alloy of aluminium with one or more other metals may, for example, comprise 30 to 100, 30 to 80, 35 to 80, or 40 to 80 mol% aluminium. The alloy of aluminium with one or more other metals may, for example, be an alloy of aluminium with one or more metals selected from lithium, copper, magnesium, manganese, silicon, tin, zinc, titanium, nickel, tungsten, boron, silicon, cobalt, iron, vanadium,

chromium, platinum and gold.

The anode of the electrochemical cell of the present invention is not limited to the above examples . The anode material can comprise of any compound/mixture containing at least 30 mole % aluminium. However, in a preferred embodiment the anode material is an Al-Li alloy.

Cathode

The cathode of the electrochemical cell of the first aspect of the present invention comprises a cathode material which includes sulphur. Preferably the cathode material comprises at least 20% sulphur by weight. The cathode of the electrochemical cell of the second aspect of the present invention comprises a cathode material which includes at least 20% sulphur by weight.

The cathode material is the material, forming part of the cathode, that participates in the electrochemical reaction during charging and discharging of the electrochemical cell.

In some embodiments, the cathode consists of the cathode material. In other embodiments, the cathode comprises an electrically conductive substrate with the cathode material on, or in electrical contact with, at least part of the surface of the substrate.

In some embodiments, the cathode material comprises 20% to 90% sulphur by weight. The cathode material may, for example, comprise 25% to 90%, 30% to 90%, 40% to 90%, 60% to 90% or 70% to 90% sulphur by weight.

In some embodiments, the cathode comprises the cathode material on, or in electrical contact with, a substrate. Typically the substrate is electrically conductive. The electrically conductive substrate may be a metal

substrate . The metal substrate may be formed from any suitable metal or alloy. The metal substrate may, for example, be formed from one or more of the metals Pt, Au, Ti, Al, W, or Ni . The electrically conductive substrate may alternatively be formed from a non-metal substrate (e.g. carbon black, carbon nanotubes or graphene) .

The cathode material may, for example, be applied to the substrate by preparing a paste of the cathode material (using typical additional paste components, such as binder, solvents and conductivity additives), and applying the paste to the substrate. A person skilled in the art will be able to determine suitable components and amounts for preparing a paste of the cathode material.

Sulphur has low conductivity. Accordingly, the cathode material typically comprises a composite of sulphur and a carbon material, where the carbon material provides conductivity to the cathode material.

In some embodiments, the cathode material comprises sulphurised carbon (SC) . Various types of sulphurised carbon, and the syntheses thereof, are known (see, for example, "Carbon materials for Li-S batteries: Functional evolution and performance improvement", Energy Storage Materials, Volume 2, January 2016, Pages 76-106).

Sulphurised carbon is a material comprising a sulphur species (e.g. elemental sulphur or a polysulphide such as -S i-g - ) in intimate contact with a carbon material. The sulphur species may be bound to, or in physical contact with, a carbon material. The sulphur species may be bound to the carbon material by covalent bonds, ionic bonds or dispersion forces. Alternatively, the sulphur species may be in physical contact with the carbon material. The carbon material (sometimes referred to as a carbon matrix) may be any compound or material predominantly formed of carbon. In some embodiments, the carbon material comprises at least 80%, at least 90%, or at least 95%, by weight carbon. The carbon material may, for example, be a carbonised organic compound, activated carbon, carbon nanotubes, carbon nanoparticles , graphene, graphene oxide, carbon fibre, carbon black or carbon cloth.

In some embodiments, the cathode material is a sulphurised polymer. A sulphurised polymer may be prepared by thermally annealing sulphur with a polymer. During the annealing process, the polymer is typically carbonised. Sulphurised polymers are described by reference to the polymer used to prepare the sulphurised polymer, for example, sulphurised polypyrrole is a sulphurised polymer formed from polypyrrole.

The SC may be, for example, sulphurised activated carbon, sulphurised mesoporous carbon, sulphurised carbon

molecular sieve, sulphurised carbon nanotubes, sulphurised graphene, sulphurised carbon nanoparticles or a

sulphurised conjugated conducting polymer.

In some embodiments, the cathode material is a sulphurised polymer containing 20-90% by weight sulphur. The

sulphurised polymer may be, for example, sulphurised polyacrylonitrile, sulphurised polyaniline, sulphurised polypyrrole, sulphurised polyvinylpyridone, sulphurised polydopamine , sulphurised polyethylene oxide, sulphurised polythiophene, or sulphurised PEDOT .

Sulphurised carbon can, for example, be synthesised by thermally annealing sulphur with a polymer or a carbon matrix (such as activated carbon, carbon nanotubes, carbon nanoparticles, graphene, graphene oxide, carbon fibre, carbon black or carbon cloth) at 150-300 °C for 1 to 12 hours. The mass ratio of sulphur to polymer or carbon matrix may, for example, be 3 to 1. Suitable polymers include, for example, polyacrylonitrile, polyaniline, polypyrrole, polyvinylpyridone, polydopamine, polyethylene oxide, polythiophene, and PEDOT.

In some embodiments, the sulphurised carbon is a carbon matrix impregnated with lithium polysulphide (LiSx, x=2- 8 or 3-8) . In such embodiments, the lithium polysulphide is part of the cathode material, and may also form part of the electrolyte in contact with the cathode.

Sulphurised carbon comprising a carbon matrix impregnated with lithium polysulphides may be prepared by mixing a carbon matrix (e.g. activated carbon, carbon nanotubes, graphene, carbon cloth, etc.) with a lithium sulphide (or a mixture of lithium sulphides) in an organic solvent, optionally with heating and optionally subsequently drying off the solvent.

In one embodiment, the cathode material comprises a lithiated sulphurised carbon.

The cathode material may be in the form of a solid or a suspension. For example, the cathode material may be a solid, e.g. SPAN; or fluidic (e.g. a suspension), e.g. an ink of carbon and lithium polysulfide.

As a person skilled in the art would appreciate, during charging and discharging of the electrochemical cell, the proportion of sulphur in the cathode material may change. In the electrochemical cell of the second aspect of the present invention, the cathode material comprises at least 20 % by weight sulphur at all states of charge of the electrochemical cell (when the electrochemical cell is in a fully charged state, a fully discharged state, or any state in between) .

The cathode of the electrochemical cell of the first or second aspects of the present invention is not limited to the above exemplary embodiments . The cathode material can comprise any compound/mixture containing sulphur. However, in a preferred embodiment the cathode material comprises sulphurised carbon.

In a further aspect, the present invention provides an electrochemical cell comprising:

an anode comprising an anode material including aluminium;

a cathode comprising lithium polysulphide in contact with a carbon matrix; and

an electrolyte comprising lithium ions in contact with the anode and the cathode;

wherein the anode material comprises at least 30 mol% aluminium.

Electrolyte The electrolyte may be any electrolyte comprising lithium ions .

Typically the electrolyte is non-aqueous, comprising less than 500 ppm water (e.g. less than 400 ppm, less than 300 ppm, less than 200 ppm, less than 100 ppm, less than 50 ppm, less than 20 ppm, less than 10 ppm or less than 5 ppm) .

The electrolyte may, for example, comprise a lithium salt dissolved in a suitable solvent (e.g. an organic solvent).

The lithium salt may be any lithium salt. The lithium salt may, for example, be LiPF₆, LiBF₆, LiC10₄, lithium

bis (trifluoromethane) sulfonimide (LiTFSI), LiCF₃S0₃, LiN0_3, or Li₂S_n where n is 1, 2, 3, 4, 5, 6, 7, or 8. The solvent may, for example, be ethyl carbonate (EC; also known as ethylene carbonate) , ethyl methyl carbonate (EMC) , dimethyl carbonate, diethyl carbonate, dioxlane (DOL) , 1 , 2-dimethoxyethane (DME), tetraethylene glycol dimethyl ether (TEGDME) , or a mixture thereof.

Examples of suitable electrolytes include 1M LiPF₆

dissolved in ethyl carbonate (EC) and ethyl methyl

carbonate (EMC); 1.0 M LiTFSI in dioxlane (DOL) and 1,2- dimethoxyethane (DME) (DOL: DME = 1:1 Vol%) with 1.0% LiN0₃; and 1.0 M LiTFSI in DOL and DME (DOL: DME = 1:1 Volt;. In the electrochemical cell of the present invention, an electrolyte comprising lithium ions is in contact with the cathode and the anode, thus allowing lithium ions to move from the cathode to the anode, and vice versa, through the electrolyte .

In some embodiments, the composition of the electrolyte in contact with the anode is the same as the composition of the electrolyte in contact with the cathode. In other embodiments, the composition of the electrolyte

(comprising lithium ions) in contact with the anode may differ from the composition of the electrolyte (comprising lithium ions) in contact with the cathode. For example, the composition of the electrolyte (comprising lithium ions) in one half cell may differ from the composition of the electrolyte (comprising lithium ions) in the other half cell. Electrochemical cell

As will be apparent to a person skilled in the art, the electrochemical cell of the present invention will further comprise a separator to separate the anode from the cathode. This separator plays a key role in separating ions and electrons produced near the anode and cathode during the redox reactions. For example, electrons generated near the anode are stopped by the separator from moving towards the cathode, and thus encouraged to flow through an external circuit to generate an electrical current .

The separator may be a conventional separator used in conventional Li-ion electrochemical cells and batteries . There are three common classes of separators used for conventional Li-ion based cells/batteries i.e. microporous polymer membranes, non-woven fabric mats and inorganic composite membranes . Any conventional separators such as polyethylene (PE) membrane, polypropylene (PP) membrane, PE-PP blend membrane, glass fibre membrane, or

carbon/polymer-coated separators can be used in the electrochemical cell of the present invention.

The electrochemical cell will also comprise a suitable housing/packaging .

Figures 1(a), 1(b) and 1(c) show three example

configurations of a rechargeable electrochemical cell in accordance with embodiments of the present invention.

These configurations describe an electrochemical cell which comprises an anode comprising an anode material including aluminium, a cathode comprising a cathode material including sulphur, and an electrolyte comprising lithium ions dissolved in a suitable solvent. The lithium ion electrolyte is in contact with the anode and the cathode. The anode material comprises at least 30 mole % aluminium, and the cathode material comprises at least 20 by weight sulphur.

Figure 1(a) shows a first configuration 10 that utilizes an aluminium metal anode material 13 (i.e. 100% aluminium and a sulfurized carbon (SC) cathode material 11 including 20% by weight sulphur.

Figure 1 (b) depicts a second configuration 101 that incorporates a pre-lithiated sulphurised carbon cathode material (Li-SC) 14, which is used to complement the low Li⁺ amount in the Li-ion electrolyte 15.

The third configuration 102 as shown in figure 1(c) deploys an Al-Li alloy anode material 19 in order to compromise the loss of lithium upon cycling.

Figure 2(a), 2(b) and 2(c) show the configurations as shown in Figures 1(a), 1(b) and 1(c), respectively, where the sulphurised carbon material is sulphurised

polyacrylonitrile (SPAN) and the electrolyte comprises LiPF₆ in an organic solvent.

Figure 3 shows further alternative configurations of rechargeable electrochemical cells in accordance with embodiments of the present invention. Figure 3(a) shows an embodiment that utilises Li-Al alloy as the anode material and a pre-lithiated SC cathode material. Figure 3(b) shows a similar embodiment in which the cathode material is a sulphurised carbon comprising lithium polysulphide. In both embodiments, the electrolyte comprises LiPF₆ in an organic solvent.

Figure 5 illustrates the proposed mechanism of the Al-Li alloy/SPAN cell shown in Figure 2(c) . When the cell is discharged, Li ions are removed from the alloy anode material and transferred through the electrolyte to the SPAN cathode material . The -S_x- chains on the SPAN cathode material are broken to form insoluble Li₂S, yet still tightly confined in the conjugated backbones. When the cell is charged, the Li ions leave the cathode and return/migrate to the anode forming the Al-Li alloy. In this system, the Al-Li alloy not only acts as the anode material but also as the current collector. Typically the Al-Li alloy is on an aluminium substrate. The intimate interface structure between the Al substrate and the Al-Li alloy layer allows fast electron transfer and stable electrode structure .

The present invention further provides a battery

comprising one or more electrochemical cells of the present invention. The cell or cells in the battery may be in plate or spiral form, or any other form. The cathode and anode of the cell or cells are in electrical

connection with the battery terminals. Advantageously, the batteries of the present invention are rechargeable. In addition, the batteries of the present invention may also be suitable, in some embodiments, for single use

applications

In a preferred embodiment, a rechargeable Al-Li-S battery with a high voltage of 1.5 V is constructed by using an Al-Li alloy anode material, a SPAN cathode material, and a lithium ion electrolyte. An advantage of this embodiment is that the lithium ions play dual roles in terms of the formation of the Al-Li alloy and the lithium sulphides. The potential difference between the alloy and the sulphides lead to an average discharge voltage of 1.5 V for the Al-Li/SPAN cell. The Al-Li/SPAN cell demonstrates a high reversible capacity of nearly 550 mAh/g at 200 mA/g, with an 83% capacity retention after 200 cycles. The specific energy of the Al-Li alloy/SPAN cell is estimated to be in the range of 589 Wh/kg to 762 Wh/kg, based on the total weight of active materials in both anode and cathode . Advantageously, the present invention enables the

construction of Al-Li-S based batteries which exhibit good reversibility and stability (e.g. a slow decaying rate of about 0.09% per cycle).

As referred to herem, except where the context requires otherwise due to ex;press language or necessary

implication, the word "cycle" or variations such as

"cycles" or "cycling" is used to refer to a charge and discharge cycle, i. e. to apply a voltage/current to a cell in order to "charge" the cell and then apply a load to the cell in order to "discharge" the eel1. As a person skilled in the art will appreciate, a "cycle" may also refer to applying a load to a charged cell, followed by applying a voltage/current to the cell in order to "re-charge" the cell (i.e. a "cycle" may refer to either a charge- discharge cycle or a discharge-charge cycle) . A cycle may refer to cycling between partially discharged and

partially charged states, but typically refers to cycling between a fully discharged and a fully charged state.

EXAMPLES

The present invention is further described below by reference to the following, non-limiting, examples.

Materials and Methods

Preparation of sulfurized polyacrylonitrile (SPAN) particles : SPAN was fabricated by heating a mixture of polyacrylonitrile and sulphur with a mass ratio of 1:3 in a tube furnace under a nitrogen atmosphere at 300 °C.

Preparation of SPAN cathodes:

The as-prepared SPAN material was mixed with binder

(polyvinylidene fluoride, Sigma Aldrich) and carbon black in a ratio of 70 wt% : 15 wt% : 15 wt% (SPAN : binder : carbon black) . The mixture was then ground in water to form a homogenous slurry. The slurry was then cast onto carbon-coated aluminium foil and dried in a vacuum oven at 80 °C for 24 h. Fabrication of Al-Li alloy and lithiated SPAN:

The Al-Li alloy was prepared via an electrochemical method. CR2032-type coin cells were assembled with lithium foil as the anode and aluminium foil as the cathode. 1M LiPF6 in ethylene carbonate/ethyl methyl carbonate

(EC/EMC, v/v=l:l) was used as electrolyte and Celgard 2500 polypropylene membrane was used as separator. After allowing the Al-Li alloy to form, the coin cell was disassembled and the cathode with Al-Li alloy was taken out, washed with dimethyl carbonate (DMC) to remove any residues. In a similar manner, a half-cell with a SPAN cathode and a Li anode was used to pre-lithiated SPAN.

Electrochemical measurement of full cell:

In Examples 1 and 2, 40 L of 1 M LiPF6 in EC/EMC was used as the electrolyte and Celgard 2500 polypropylene membrane was used as the separator. Galvanostatic charge-discharge was tested using Land battery tester (CT2001A) . Cyclic voltammetry and electrochemical impedance were conducted using a Biologic VSP potentiostat .

Materials characterization:

XRD pattern of Al-Li alloy was collected by PANalytical Empyrean II diffractometer with Cu Ka radiation (λ = 0.15406 nm) at 45 kV and 40 mA. The X-ray photoelectron spectroscopic (XPS) technique was performed on a Thermo Scientific, UK (model ESCALAB25 OXi ) using Mg Ka (hv = 1486.68 eV) as the excitation source with 150W power (13 kV x 12 mA) . The morphologies of alloy were obtained by scanning electron microscopy (SEM) via a FEI Nova NanoSEM 450 FE-SEM microscope at an accelerating voltage of 5 kV. EXAMPLE 1

Three configurations of electrochemical cells were prepared using the anode and cathode materials described above and 40 pL of 1 M LiPF₆ in EC/EMC as the electrolyte. Celgard 2500 polypropylene membrane was used as the separator. Galvanostatic charge-discharge was tested using Land battery tester (CT2001A) . Cyclic voltammetry and electrochemical impedance were conducted using a Biologic VSP potentiostat .

Figure 2 (a) shows a first configuration 20 that utilizes an aluminium metal anode material 23 (i.e. 100% aluminium) and a sulfurized polyacrylonitrile (SPAN) cathode material 21 including 20 wt% of sulphur. Figure 4(a) shows the galvanostatic charge and discharge curves (reference numerals 30 and 31 respectively) for the Al-Li-S cell as shown in configuration 20. It is evident from Figure 4(a) that although this configuration provides an open circuit voltage at 1.5 V, the cell capacity is negligible (~1 mAh/g) because the Li⁺ ion concentration in the electrolyte drops sharply upon battery discharging.

Figure 2 (b) depicts a second configuration 201 that incorporates a pre-lithiated SPAN cathode material (Li-

SPAN) 24, which is used to complement the Li⁺ removed from the electrolyte 25 during charging. Figure 4(b) shows the galvanostatic charge and discharge curve of the Al-Li-S cell of configuration 201. It is evident from Figure 4(b) that the cell capacity has improved significantly (~300 mAh/g), however, during the cycling process the cell capacity declines quickly (as shown by curves 32 and 33) indicating the exhaustion/depletion of Li⁺ ions in the system. Without wishing to be bound by theory, it is believed that the Al anode material, in both the first 20 and the second 201 configurations, undergoes irreversible reaction with Li⁺ ions upon cycling which leads to a sharp decline in the lithium concentration in the system, thereby adversely affecting its capacity.

The third configuration 202 as shown in Figure 2(c) deploys an Al-Li alloy anode material 29 in order to compromise the irreversible loss of lithium upon cycling. In this experiment, the Al-Li alloy is on an aluminium foil substrate (not depicted in Figure 2(c)) . Figure 4(c) shows the charge (reference numeral 34) and discharge (reference numeral 35) curves of the Al-Li-S cell of configuration 202. It is evident from these results that the third configuration 202 (referred to herein as the "Al-Li alloy/SPAN cell") provides better cell capacity during discharge and more stable charge-discharge cycling than configuration 20 and 201.

Figure 6 illustrates the proposed working mechanism of the Al-Li alloy/SPAN cell. When the cell is discharged, Li ions are removed from the alloy anode material and transferred through the electrolyte to the SPAN cathode material. The -S_x- chains on the SPAN cathode material are broken to form insoluble Li₂S, yet still tightly confined in the conjugated backbones of the SC. When the cell is charged, the Li ions leave the cathode and return to the anode forming the Al-Li alloy. In this system, the Al foil with the Al-Li alloy provides the anode material as well as acting as the current collector. The intimate interface structure between the Al substrate and the Al-Li alloy layer (as shown in Figure 7 (d) ) ensures fast electron transfer and stable electrode structure. Note that the alloy phase of Al-Li alloy as anode material includes three types, namely Al-Li, AI₂L1₃ , and AI₄L1₉ , with high theoretical specific capacity of 993 mAh/g, 1490 mAh/g and 2235 mAh/g, respectively. These values are 3-6 times higher than that of graphite (372 mAh/g) . Given a specific capacity of 680 mAh/g for the SPAN cathode material at 100 mA/g, the specific energy of a Al₄Lig/SPAN cell can reach 762 Wh/kg (based on the total mass of active phases);

while for a AlLi/SPAN cell, the value is about 589 Wh/kg. Excluding the weight of electrolyte, separator, cell case as well as current collectors, the specific energy of the Li-ion Al/S cell will be between 589 Wh/kg and 762 Wh/kg, depending on the relative ratio of different Al-Li alloy phases. Another merit of the Al alloy anode material lies in the moderate potential versus Li°/Li⁺. The measured potential of Al alloy vs Li°/Li⁺ is around 0.2 - 0.3 V, and it could disadvantage the lithium dendrite growth that occurs with silicon or graphite anodes (<0.05 V vs

Li°/Li⁺) , which is crucial for battery safety. In addition, Al has the smallest volume change (~96 %), compared with other metal anodes, such as Si (320%), Sn (260%) and Sb (200%). The electrode expansion/shrinkage is a main challenge for the alloy anode due to the cracking and pulverization during charge and discharge that leads to capacity decay and low Coulombic efficiency. The SEM characterisation from Figure 16 (a) and 16 (b) with the cycled Al anode after 50 cycles and after 200 cycles, respectively, showed the stable interface connection with negligible cracks, despite the coarse alloy crystallites. The XRD spectra shown in Figure 16(c) demonstrates the stable and reversible phase evolution of the Al-Li alloy after long cycles (after 50 cycles is the top line, and after 200 cycles is the bottom line, in Figure 16(c)) . EXAMPLE 2

The following discussion provides experimental results and analysis for the Al-Li alloy/SPA cell.

Figure 7 (a) shows the alloying (bottom) and de-alloying (top) curves of aluminium in 1M LiPF₆ + EC/EMC electrolyte at 0.06 mA/cm². A flat plateau at 0.28 V vs . Li°/Li⁺ was observed during the discharge process, which indicates the alloying process of Al with lithium ions. The alloying was maintained for 12 hours. The de-alloying potential was determined to be around 0.42 V vs. Li°/Li⁺.

Figure 7 (b) shows Coulombic efficiency of alloying and de- alloying processes of aluminium in 1M LiPF₆ + EC/EMC electrolyte at 0.06 mA/cm². The high Coulombic efficiency of 94-98% indicates that most of the Li⁺ ions are

reversibly stored and released. Despite this, there is a 2-6% loss of lithium ions per cycle which explains the capacity decay in the second configuration 201 as shown in Figure 2 (b) . The lithium-enriched Al-Li alloy should contain an excessive amount of lithium ions to accommodate the little portion of Li⁺ loss, and could improve the cycling stability of the Al-Li alloy/SPAN with the high Coulombic efficiency.

The cross-sectional microstructure of the Al-Li alloy was compared with that of the Al foil by using scanning electron microscopy (SEM) images as shown in Figures 7(c) and 7 (d) . The top-surface greyish layer is a 9 \im thick layer with a different contrast to the Al substrate. The intimate interface shows the strong binding between the greyish alloy layer and the bottom Al metal layer, which is good for electrode stabilization during cycling. The electrochemical behaviour of the Al-Li alloy/SPA cell, which is manufactured in accordance with the third configuration 202 of Figure 2 (c) , was characterised by using cyclic voltammetry. Figure 8 (a) shows cyclic voltammetry (CV) results which were obtained for a voltage range between 0.3 V and 2.6 V at a scan rate of 0.1 mV/s . The first cathodic peak 62 at around 0.8 V is relevant to the activation of the SPAN cathode material. The cathodic peak shifts to 1.25 V in the following cycles (represented by reference numeral 63), corresponding to the solid-to- solid transition (S_n to Li₂S/Li₂S₂) in cathode material. The typical cyclic voltammetry of sulphur crystals contain two reduction peaks at 2.3 V and 2.0 V. The 2.3 V peak

(reference numeral 61) describes a solid-to-liquid transition from S₈ to Li₂S₈/Li₂S₆; and the 2.0 V peak

(reference numeral 64) is attributed to the liquid-to- solid transition from Li₂S₆ to Li₂S/Li₂S₂. With the SPAN cathode material, the direct solid-to-solid phase

transition from elemental sulphur to sulphides could effectively mitigate the polysulphide shuttling and hence enhance the cycling stability. Figure 8 (b) displays the galvanostatic charge/discharge profile of the Al-Li alloy/SPAN cell (the third configuration 202 of Figure 2(c)) at different cycles at a current density of 200 mA/g. The first discharge plateau corresponds with the cathodic peak 62 in the first cycle of CV. For the first cycle the discharge capacity is higher than the charge capacity, which reveals the irreversible storage of lithium ions during the activation of SPAN cathode material. For the following cycles, the discharge and charge capacity is gradually stabilized. The discharge plateau also shifts upwards showing the enhanced electron transfer kinetics. Figure 8(c) illustrates the cycling performance of the Al-Li alloy/SPAN cell determined at 200 mA/g. The capacity decay rate is about 0.09% per cycle. The average capacity is about 480 mAh/g with a high

Coulombic efficiency close to 100%. The capacity loss might be due to the volume variation of the electrodes during lithiation/de-lithiation . Figure 8(d) shows the voltage values for the discharge and charge plateaus during the 200 cycles. The voltage efficiency hits the highest point at 70% during the 20th-30th cycles, and ends at 65%, which suggests the slightly increased cell resistance .

Figure 10(a) shows Galvanostatic charge/discharge curves for the Al-Li alloy/SPAN cell at different current densities from 100 mA/g to 1000 mA/g. The voltage

difference between the charge and discharge plateaus at different current densities is compared in Figure 12. The voltage difference increases from 0.35 V to 1.05 V with the current density increases. The minimal polarization of 0.35 V at 100 mA/g (reference numeral 81) shows the good reaction kinetics of the electrodes at low current. Figure 10 (b) exhibits various specific capacities at a range of current densities. The initial capacity at 100 mA/g is 680 mAh/g, which stabilizes at 580 mAh/g after 10 cycles. With the current density increasing to 200 mA/g, 500 mA/g and 1000 mA/g, the corresponding specific capacity drops to

520 mAh/g, 480 mAh/g and 390 mAh/g, respectively. When the current density is re-set to 100 mA/g after 40 cycles of fast charge/discharge, the specific capacity returns to 540 mAh/g, showing the good cell stability despite the cycling tests at varied current densities. The specific energy of the SPAN cathode at 1.5 V for each current density varies from 990 Wh/kg @ 100 mA/g, 812 Wh/kg @ 200 mA/g, 631 Wh/kg @ 500 mA/g and 528 Wh/kg at 1000 mA/g. Figure 10 (c) displays the cell stability evaluated by discharging the cell at 200 mA/g, and charging at 200 mA/g, 500 mA/g and 1000 mA/g, respectively. The low discharge current density is used in order to fully extract all the charges stored in the cell. The discharge capacity corresponding with the 200 mA/g charging drops from 530 mAh/g to 410 mAh/g over the first 100 cycles with 77% capacity retained. At the 500 mA/g charging current density, the discharge capacity drops from 400 mAh/g to 295 mAh/g within the second 100 cycles with a retention ratio of 74%. For the stability at 1000 mA/g charging, the capacity stepwise declines from 310 mA/g to 220 mA/g with a retention ratio of 71%. Capacity decay rate at 500 mA/g and 1000 mA/g is larger than that at 200 mA/g. Without wishing to be bound by theory, the inventors postulate that the transition of a variety of charging rates might induce structural changes in the electrodes, especially the Al-Li alloy anode material, which are correlated with the inferior stability at high rate. The charge/discharge voltage difference is plotted in Figure 10 (d) . The charge voltage is higher for the larger charging current density. The discharge voltage gets lower for the second and the third 100 cycles, in spite of the same discharge rate as that of the first 100 cycles (200 mA/g) . The lower discharge voltage suggests the accumulated internal resistance upon cycling that is likely induced by internal structural rearrangement of the electrode material. As a result, the voltage efficiency decreases at high charging current densities. Quick-charging technologies are becoming popular for portable devices. The above tests indicate the feasible quick-charging function of the present Li-ion Al/S batteries for consumer electronics. Figure 13 (a) shows the reaction kinetics of the Al-Li alloy/SPAN cell using cyclic voltammetry (CV) measurement at different scan rates. It is evident from this plot that the cathodic peak shifts negatively and anodic peak shifts positively with the increment of the scan rates. The incremental peak separation is attributed to the

overpotential associated with mass transfer and electric resistance. At high scan rate, the diffusion of Li ions is limited to the exterior surface. Figure 13(b) shows the dependence of the formal potential of the cathodic and anodic peak voltages (Eo' = (E_PfC + E_p,_a)/2) at different scan rates. The formal potential keeps nearly constant at 1.67 V despite the different scan rates, which is

characteristic of the quasi-reversible feature of the overall reaction. The dependence of the anodic and cathodic peak current (i_p) on the square root of scan rates

(v^{1 2}) is shown in Figure 13(c) . Both curves are linear, and are in good agreement with the Randles-Sevcik equation

(Eq. 1) for reversible redox systems: i_p = (2.69 x 10⁵ ) n^{3 2} A D^{1 2} C_± v^{1 2} (1) where D is the transfer coefficient (cm²/s), n represents the number of electrons transfer, A is the electrode area (cm²), Ci is the concentration of lithium ions (mol/cm³) . This result indicates that the reaction is diffusion controlled. The linear relationship given by i_p/v^{1 2} also shows the reversible electron transfer through which the cell equilibrium could be obtained between reduced and oxidized forms. Figure 13(d) is the electrochemical impedance spectroscopy (EIS) measurement of the fresh cell, the used cells after 50 cycles and after 200 cycles. A single semi-circle could be found at the high frequency, together with an inclined line at the low frequency region. These two parts are ascribed to the charge transfer resistance R_ct and the mass transfer resistance. The R_ct of the cell after 50 cycles is slightly smaller than 200 cycles, which means the charge transfer kinetics of the former is superior to the latter. The fresh cell shows the largest radius of the semi-circle, indicating the cell was not activated and had very large charge transfer resistance with the original structure. The value of the intersection with the X axis of the cell after 50 cycles (8 Ω) is smaller than that after 200 cycles (18 Ω) , which demonstrates the large resistance for the cell after long cycles and agrees with the declining voltage

efficiency as shown in Figure 8 (d) .

The mechanism of the Al-Li alloy/SPAN cell was studied by probing the potential changes of both the anode and cathode with a Li°/Li⁺ reference electrode. Figure 14(a) demonstrates the voltage-capacity dependence of three different cells. The first cell comprises of SPAN as cathode material and Li°/Li⁺ reference electrode as anode. The second cell comprises of Li°/Li⁺ reference electrode as cathode and Al-Li alloy as anode material. The third cell is the full cell (i.e. Al-Li alloy/SPAN cell) comprising Al-Li alloy as anode material and SPAN as cathode

material. The voltage-capacity profile of the full cell envelopes the respective charge and discharge curves of the two half reactions. The Al-Li alloy vs Li°/Li⁺ cell exhibits a discharge plateau at 0.28 V for the alloying reaction (see curve 107) and a charge plateau at 0.42 V for the de-alloying reaction (curve 108), which is consistent with the results given in Figure 7 (a) . The alloying/de-alloying processes in the Al-Li alloy/SPA cell upon charging/discharging was verified by using X-ray diffraction (XRD) . Figure 14(b) illustrates the XRD results of the original Al-Li alloy anode (spectrum 110), and the anodes after the charge (spectrum 112) and discharge (spectrum 111) of full cells. Apart from the peaks of the Al substrate found in the alloy anode, there are two peaks assigned to AlLi and AI₄L1₉ phases (spectrum 110) . The AlLi phase is more prominent. When the full cell is discharged, the peak intensity of the AlLi and Al₄Lig phases reduces sharply (spectrum 111), indicating the de- alloying process . When the full cell is charged, the

AlLi (0) and Al₄Lig (V) phases are recovered, with the formation of a new Al₂Li₃ phase (#) , indicating the alloying process (spectrum 112) . The XRD characterisation supports the electrochemical analysis of the phase evolution of the Al anode during full cell charging and discharging .

The SPAN cathode has the same voltage-capacity trend as reported with Li-S batteries, characterised with the ~2.25 V charge potential and the ~1.8 V discharge potential. The single discharge plateau agrees with the solid-state reaction of SPAN with lithium. As shown in Figure 14(c) to 14 (e) , the X-ray photoelectron spectroscopy (XPS) S 2p spectra of the SPAN cathodes at different states

(pristine, discharged and charged) provide further insights. When the full cell is discharged, the peak at 160 eV could be observed, which can be attributed to Li₂S. When the full cell is charged, this Li-S bond disappears; whereas the peak at 163.0 eV recovers and is assigned to the -S_y- chains that mimic the original SPAN structure. The sulphate/thiosulphate species detected at 167 to 168 eV are due to the oxidation of Li₂S.

Figure 15 (a) shows the X-ray photoelectron spectroscopy (XPS) for the pristine SPAN cathode material. Figure 15(b) shows the XPS C Is spectra for the SPAN cathode material at pristine (top spectrum) , discharged (middle spectrum) and charged (bottom spectrum) states. This data shows the change of n-n conjugation during charge and discharge. The delocalized electrons increased in the lithiated state (discharged) , compared with the delithiated state

(charged) .

Figure 16(a) and 16(b) show the SEM images of Al-Li alloy after 50 and 200 cycles respectively. Figure 16(c) shows the XRD spectra of Al-Li alloy after 50 and 200 cycles. Example 3

The following describes an electrochemical cell using an Al-Li alloy anode and a lithiated sulphurised carbon.

Preparation of carbon cloth fibre (CC) and modified porous carbon on carbon cloth (MPC-CC) Unless otherwise stated, all of the materials were used as received. Carbon cloth (1cm diameter) was first washed with 2M HC1 under sonication conditions (5 times) and deionized water (2 times) in order to remove impurities. Then the carbon cloth was heated at 80 °C to remove water for 12 h. 2.5 g D-glucose (Sigma Aldrich) and 12.5 mg sodium dodecyl sulfate (SDS, Sigma Aldrich) was dispersed into 50 mL water together with carbon cloth by

ultrasonication to get a homogenous solution. Then the solution was transferred to a 100 mL autoclave Teflon and heated at 190 °C for 15 h (hydrothermal method) . The dark brown sample was taken out after hydrothermal reaction and washed with deionized water (5 times) and dried at 80 °C overnight. Later the as-prepared sample was calcined at 800 °C under N₂ atmosphere for 4 h to afford the MPC-CC product. The pure carbon cloth was washed and calcined under the same conditions without the hydrothermal method Then both carbon cloth and MPC-CC were punched into small disks with the diameter of 8 mm (0.5 cm²) and mass of <5mg. Preparation of Al-Li alloy

The Al-Li alloy was prepared via an electrochemical method as stated above.

Preparation of electrolyte and catholyte

"Blank electrolyte" was prepared by dissolving an

appropriate amount of bis ( trifluoromethane ) sulfonimide lithium salt (LiTFSI, 99.95%, Sigma Aldrich) in

triethylene glycol dimethyl ether (TEGDME, 99%, Sigma Aldrich) to form "blank electrolyte" solutions having a molarity of 0.5 to 5 M LiTFSI. To prepare a lithium polysulfides solution, an amount of lithium sulphide (Li₂S, 99.98%, Sigma Aldrich) and sublimed sulfur (Sigma Aldrich) were mixed in TEGDME and stirred at 60 °C overnight to form a 1M Li₂S₄ in TEGDME solution. The stated molarities were based on the amount of sulphur. All of these procedures were performed inside a glove box.

Electrochemical measurement of cell

The Al-Li/Li polysulfides cell was assembled in a glove box. First of all, 12 pL of 1 M Li₂S₄ was loaded onto the MPC-CC, resulting in 0.768 mg/cm² of sulphur (if desired, a greater volume of the L1₂S₄ solution, and/or a more concentrated Li₂S₄ solution, could have been used) . Then a Celgard 2500 polypropylene membrane was used as the separator, followed by a drop of 20 blank electrolyte on the separator. At last, Al-Li alloy was placed on the separator. A control test with carbon cloth was assembled using an analogous procedure. Galvanostatic charge- discharge was then tested using a Land battery tester (CT2001A) . Cyclic voltammetry and electrochemical

impedance were conducted using a Biologic VSP

potentiostat .

Characterization

The morphology of the Al-Li alloy was assessed by scanning electron microscopy (SEM) via a FEI Nova NanoSEM 450 FE- SEM microscope at an accelerating voltage of 5 kV. The elemental mapping results were examined through an energy dispersive spectrometer (EDS) attached to the FEI Nova NanoSEM 450 FE-SEM. XRD pattern of Al-Li alloy was collected by PANalytical Empyrean II diffractometer with Cu Ka radiation (λ = 0.15406 nm) at 45 kV and 40 mA.

Before test, the sample was covered by a sample holder in an Ar-filled glove box. The X-ray photoelectron

spectroscopic (XPS) technique was performed on a Thermo Scientific, UK (model ESCALAB25 OXi ) using Mg Ka (hv = 1486.68 eV) as the excitation source with 150W power (13 kV x 12 mA) . For all of the cycled samples, including Al- Li alloy, MPC-CC and CC current collector, were first disassembled in the glove box, and washed by TEGDME solvent three times then dried under vacuum overnight. The samples were then sealed and taken out for tests (XRD, XPS, SEM) . Results

Figure 5 shows the difference of voltage hysteresis for two types of carbon matrix, namely, carbon cloth fibre (CC) and modified porous carbon on carbon cloth (MPC-CC) , each impregnated with lithium polysulphides .

Electrochemical reversibility of both cells can be determined from Figure 5. It is noted that higher charge overpotential for CC at about 0.57 V can be observed when compared with MPC-CC (0.45 V), which shows there is an influence of carbon matrix on the cell performance. As exhibited in Figure 9, the specific capacity at 0.2 C is maintained in the range of from 680 to 500 mAh/g from the 10th to 100th cycles, corresponding to a retention of 74% of the specific capacity. There is a sharp decrease of capacity within the beginning 10 cycles. It is speculated that the reason could be the activation process. Figure 11 demonstrates the good rate performance of the MPC-CC cell with lithium polysulphide and Al-Li alloy.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive .

In the claims which follow and in the preceding

description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Claims

CLAIMS :

1. An electrochemical cell comprising:

an anode comprising an anode material including aluminium;

a cathode comprising a cathode material including sulphur; and

an electrolyte comprising lithium ions in contact with the anode and the cathode;

wherein the anode material comprises at least 30 mol% aluminium.

An electrochemical cell comprising:

an anode comprising an anode material including aluminium;

a cathode comprising a cathode material including sulphur; and

an electrolyte comprising lithium ions in contact with the anode and the cathode;

wherein the anode material comprises at least 30 mol% aluminium and the cathode material comprises at least 20 wt % sulphur.

The electrochemical cell of claim 1 or 2 wherein th cathode material comprises 20 wt% to 90 wt% sulphur.

The electrochemical cell of any one of claims 1 to wherein the cathode materi .1 is sulphurised carbon.

The electrochemical cell of any one of claims 1 to wherein the cathode materi .1 is a sulphurised polymer

The electrochemical cell of claim 5 wherein the sulphurised polymer is selected from sulphurised polyacrylonitrile, sulphurised polyaniline, sulphurise polypyrrole, sulphurised polyvinylpyridone, sulphurise polydopamine, sulphurised polyethylene oxide,

sulphurised polythiophene and sulphurised PEDO .

The electrochemical cell of any one of claims 1 to 3 wherein the cathode material is lithiated sulphurised carbon .

8. The electrochemical cell of any one of the preceding claims wherein the anode material is aluminium metal or an alloy of aluminium and one or more other metals .

9. The electrochemical cell of any one of the claims 1 to 8 wherein the anode material is an alloy of

aluminium and lithium.

The electrochemical cell of any one of the preceding claims wherein the electrolyte comprises a non-aqueous fluid of Lithium hexafluorophosphate (LiPF₆) in ethyl carbonate or ethyl methyl carbonate .

A battery comprising one or more electrochemical cells in accordance with any one of claims 1 to 10.

An electrode for use as an anode in an

electrochemical cell, the electrode comprising an ano material including an alloy of aluminium and lithium; wherein the amount of aluminium in the anode material is at least 30 mol%.

13 A method of formin a rechargeable electrochemical ill comprising the teps of: providing an anode comprising an anode material including aluminium, wherein the anode material

comprises at least 30 mol% aluminium;

providing a cathode comprising a cathode material including sulphur;

providing an electrolyte comprising lithium ions; arranging the electrolyte to be in contact with both the anode and the cathode . . The method of claim 13 wherein the cathode material comprises at least 20 wt % sulphur.

An Al/S lithium-ion battery.

An electrochemical cell comprising:

an anode comprising an anode material including aluminium;

a cathode comprising lithium polysulphide in contact with a carbon matrix; and

an electrolyte comprising lithium ions in contact with the anode and the cathode;

wherein the anode material comprises at least 30 mol% aluminium.