GB2424511A

GB2424511A - Lithium sulphide battery and method of producing the same

Info

Publication number: GB2424511A
Application number: GB0505790A
Authority: GB
Inventors: Vladimir Kolosnitsyn; Elena Karaseva
Original assignee: Oxis Energy Ltd
Current assignee: Oxis Energy Ltd
Priority date: 2005-03-22
Filing date: 2005-03-22
Publication date: 2006-09-27
Anticipated expiration: 2025-03-22
Also published as: ATE527719T1; GB0505790D0; ES2374834T3; CN101128954B; CN101128954A; GB2424511B

Abstract

There is disclosed a chemical source of electrical energy comprising a positive electrode (cathode) made of an electrically conductive material, a mixture of lithium sulphide and sulphur, a permeable separator or membrane, and a negative electrode (anode) made of an electrically conductive material or a material that is able reversibly to intercalate lithium ions, wherein an aprotic electrolyte comprising at least one lithium salt in at least one solvent is provided between the electrodes.

Description

LITHIUM SULPHIDE BATTERY AND METHOD OF PRODUCING THE

SAME

TECHNICAl FIELD

The present invention relates to electrochemjcal power engineering, and in particular to chemical sources of electrical energy (batteries) comprising a negative electrode (anode) utilizing the oxidation-reduction pair Li/Li , a positive electrode (cathode) utilizing the oxidation-reduction pair S /S2, and a non-aqueous aprotic electrolyte.

Embodiments of the invention also relate to the composition of the depolarizer substance of the positive electrode.

BACKGROUND OF THE INVENTION

Throughout this application various patents and published patent applications are referred to by an identifring citation. The disclosures of the patents and published patent applications referred to in this application are hereby incorporated into the present disclosure by reference to more fully describe the state of the art to which this invention pertains.

An electroactive material that has been fabricated into a structure for use in a battery is referred to as an electrode. Of a pair of electrodes used in a battery, herein referred to as a chemical source of electrical energy, the electrode on the side having a higher electrochemical potential is referred to as the positive electrode, or the cathode, while the electrode on the side having a lower electrochemical potential is referred to as the: ** negative electrode, or the anode. * An electrochemically active material used in the cathode or positive electrode is * referred to hereinafter as a cathode active material. An electrochemically active: material used in the anode or negative electrode is hereinafter referred to as an anode * . S...

active material. A chemical source of electrical energy or battery comprising a *::: : cathode with the cathode active material in an oxidized state and an anode with the anode active material in a reduced state is referred to as being in a charged state.

Accordingly, a chemical source of electrical energy comprising a cathode with the cathode active material in a reduced state, and an anode with the anode active material in an oxidized state, is referred to as being in a discharged state.

There is a significant requirement for new types of rechargeable batteries, having high specific energy, long cycle life, safety for the user and the environment, as well as low cost. One of the most promising electrochemical systems is the lithium- sulphur system, which has high theoretical specific energy (2600 Whlkg), safety and low cost. Sulphur or sulphur-based organic and polymeric compounds are used in lithium-sulphur batteries as a positive electrode depolarizer substance. Lithium or lithium alloys are used as depolarizer substances in the negative electrode.

Elemental sulphur (US 5,789,108; US 5,814,420), sulphur-based organic compounds (US 6,090,504) or sulphur-containing polymers (US 6,201,100, US 6,174,621, US 6,117,590) usually serve as a depolarizer for the positive electrode in lithium-sulphur batteries. Metallic lithium is normally used as a material for the negative electrode (US 6,706,449). It has been suggested that it might be possible to make use of materials that can reversibly intercalate lithium for the negative electrode material.

These materials include graphite (D. Aurbach, B. Zinigrad, Y.Cohen, H. Teller; "A short review of failure mechanism of lithium metal and lithiated graphite anodes in liquid electrolyte solutions"; Solid State lonics; 2002; vol 148; pp 405-416), and oxides and sulphides of some metals (US 6,319,633). However, the present applicant has not been able to find specific examples of intercalation electrodes for lithium- :* sulphur batteries in the available literature. It must be stressed out that it is only * possible to use intercalation electrodes (negative or positive) when they are present in lithiated form. It is also necessary to take into account that intercalated compounds (where lithium is involved) are chemically active and have chemical properties close to the properties of metallic lithium. . *1S* S.,

S S I. S

One of the disadvantages of lithium-sulphur batteries (limiting their commercialization) is a moderate cycle life caused by a low cycling efficiency of the lithium electrode. Accordingly, twice to ten times the theoretically required amount of lithium is usually provided in lithiumsulphur batteries so as to provide a longer cycle life. In order to improve cycling of the lithium electrode, it has been proposed to add various compounds to the electrolyte (US 5,962,171, US 6,632,573) or to deposit protective layers of polymers (US 5,648,187, US 5,961,672) or nonorganic compounds (US 6,797,428, US 6,733,924) on the electrode surface. The use of protective coatings significantly improves the cycling of the lithium electrode but still does not provide a sufficiently long cycle life for many commercial applications.

It is known that graphite intercalate electrodes possess good cycling capabilities (D.

Aurbach, E. Zinigrad, Y.Cohen, H. Teller; "A short review of failure mechanism of lithium metal and lithiated graphite anodes in liquid electrolyte solutions"; Solid State lonics; 2002; vol 148; pp 405-416). However, in order to use such electrodes as a negative electrode, it is necessary to have a source of lithium ions. In traditional lithium-ion batteries, this may be lithiated oxides of transition metals, cobalt, nickel, manganese and others that are depolarizers for the positive electrode.

It is theoretically possible to use the end products of sulphur electrode discharge (lithium suiphide and disulphide) as the source of lithium ions. However, lithium suiphide and disulphide are poorly soluble in aprotic electrolyte systems, and are thus electrochemically non-active. Attempts to use lithium suiphide as a depolarizer for the positive electrode in lithium- sulphur batteries have hitherto been unsuccessful (Peled E., Gorenshtein A., Segal M., Sternberg Y.; "Rechargeable lithium- sulphur * battery (extended abstract)"; J. of Power Sources; 1989; vol 26; pp 269-271).

Lithium sulpbide is capable of reacting with elemental sulphur in aprotic media so as * S..

to produce lithium polysuiphides, these being compounds that have good solubility in.. : most known aprotic electrolyte systems (AES) (Shin-Ichi Tobishima, Hideo. .. *..S

Yamamoto, Minoru Matsuda, "Study on the reduction species of sulphur by alkali metals in nonaqueous solvents", Electrochjmjca Acta, 1997, vol 42, no 6, pp 1019- 1029; Rauh R.D., Shuker F.S., Marston J.M., Bruinmer S.B., "Formation of lithium polysuiphides in aprotic media", J. inorg. Nuci. Chem., 1977, vol 39, pp 1761-1766; J. Paris, V. Plichon, "Electrochemjcal reduction of sulphur in dimethylacetamide", Electrochjrnjca Acta, 1981, vol 26, no 12, pp 1823-1829; Rauh R.D., Abraham K.M., Pearson G.F., Surprenant J.K., Brummer S.B., "A lithium/dissolved sulphur battery with an organic electrolyte", J. Electrochem.Soc., 1979, vol 126, no 4, pp 523-527).

The solubility of lithium polysuiphides in an aprotic electrolyte system depends on the properties of the components (solvents and salts) thereof, as well as on the length of the polysuiphide chain. Lithium polysuiphides may undergo disproportionation in solutions according to the following schema: Li2S + Li2S11 2 1r 2Li2S + Li2S+1 It Li2S + Li2S..2 2Li2S.1 Accordingly, lithium polysulphides of various lengths may be found simultaneously in the electrolyte solution at the same time, being in thermodynamic equilibrium with each other. A molecular mass distribution of the polysuiphides is governed by the composition and physical/chemical properties of the electrolyte solution components. . : These solutions of lithium polysulphides possess high electroconductivity (Duck-Rye S Chang, Suck- Hyun Lee, Sun-Wook Kim, Hee-Tak Kim "Binary electrolyte based on * tetra(ethylene glycol) dimethyl ether and 1,3-dioxo lane for lithiumsulphur battery", * J. of Power Sources, 2002, vol 112, pp 452-460) and high electrochemical activity (Taitiro Fujnaga, Tooru Kuwamoto, Satoshi Okazaki, Masashi Horo, :: "Electrochemical reduction of elemental sulphur in acetonitrile", Bull. Chem. Soc. Jpn., 1980, vol 53, pp 285 1-2855; Levillain B., Gaillard F., Leghie P., Demortier A., Lelieur J.P., "On the understanding of the reduction of sulphur (S8) in dimethylfonnamide (DMF)", J. of Electroanalytical Chemistry, 1997, vol 420, pp 167-177; Yamin H., Penciner J., Gorenshtajn A., Elam M., Peled E., "The electrochemjcal behavior of polysuiphides in tetrahydrofliran", J. of Power Sources, 1985, vol 14, pp 129-134; Yamin H., Gorenshtein A., Penciner J., Stemberg Y., Peled E., "Lithium sulphur battery. Oxidationlreduction mechanisms of polysuiphides in THF solution", J. Electrochem. Soc., 1988, vol 135, no 5, pp 1045- 1048).

It has been proposed to use polysuiphide solutions in ABS as liquid depolarizers for lithium-sulphur batteries (Rauh R.D., Abraham K.M., Pearson G.F., Surprenant J.K., Brummer S.B., "A lithium/dissolved sulphur battery with an organic electrolyte", J. Electrochem.Soc., 1979, vol 126, no 4, pp 523-527; Yamin H., Peled E., "Electrochemistry of a nonaqueous lithium/sulphur cell", J. of Power Sources, 1983, vol 9, pp 28 1-287). Such batteries are generally known as "lithium-sulphur batteries with liquid cathodes". The degree of sulphur utilization in such batteries with liquid suiphide cathodes depends on the nature and polarization conditions of the ABS. In many cases it is close to 100% if counting full sulphur reduction and lithium suiphide formation (Rauh R.D., Abraham K.M., Pearson G.F., Surprenant J.K., Brummer S.B., "A lithium/dissolved sulphur battery with an organic electrolyte", J. Electrochem.Soc., 1979, vol 126, no 4, pp 523-527). An energy output of liquid cathodes based on lithium polysulphides is determined by their solubility. Tn some solvents (tetrahydrofliran, for example) sulphur solubility in the form of lithium polysulphides can reach 20M (Yamin H., Peled E., "Electrochemistry of a: * ** nonaqueous lithium/sulphur cell", J. of Power Sources, 1983, vol 9, pp 28 1-287). *. * : The energy output of such liquid cathodes is more than 1000 Ah/1. The cycle life of lithium-sulphur batteries is also determined by the metal lithium electrode behaviour and is limited by the cycling efficiency of this electrode, which is about 80-90% in:.: : sulphide systems (Peled E., Stemberg Y., Gorenshtein A., Lavi Y., "Lithium-sulphur **** **** * * * ** * battery: evaluation of dioxolane-based electrolytes", J. Electrochem. Soc., 1989, vol 136, no 6, pp 1621-1625).

Investigations made by the present applicant have shown that the cycle life of lithium-sulphur batteries with liquid cathodes could be improved by using graphite as the negative electrode. But in this case a source of lithium ions is needed.

Solutions of long-chain polysuiphides (Li2S where n =8) are normally used as liquid sulphur cathodes. In such molecules, eight or more atoms of sulphur are due to one ion of lithium. Accordingly the cycling depth of lithium-sulphur batteries with liquid cathodes will be low and is determined by the length of the polysuiphide chain.

Reducing the length of the lithium polysulphide chains will increase the cycling depth of lithium-sulphur batteries with a liquid cathode based on lithium suiphides.

However, the shorter the chain lengths of the lithium polysulpbides, the lower their solubility in an aprotic electrolyte system, and hence the energy output of the liquid sulphide cathode is decreased.

The present applicant has found that a solution of lithium polysulphides will be formed during contact of an aprotic electrolyte system with a mixture of lithium suiphide with sulphur. The concentration of the polysuiphides in the solution and the length of the polysuiphide chains will be determined on the one hand by the molar ratio between lithium sulphide and sulphur, and on the other hand by the nature of the aprotic electrolyte system. Generally, complete dilution of sulphide will not occur in the presence of a small quantity of sulphur. However, during charging of the cell accompanied by oxidation of soluble polysulphides to elemental sulphur, further dilution of lithium suiphide will occur as a result of the reaction with the generated:. . sulphur until complete dilution of the lithium sulphide. :** ::

SUMMARYOFTHEINYENTION

According to a first aspect of the present invention, there is provided a chemical * source of electrical energy comprising a positive electrode (cathode) made of an * : : :.

electrically conductive material, a permeable separator or membrane, a negative electrode (anode) made of an electrically conductive material or a material that is able reversibly to intercalate lithium ions, and a mixture of lithium suiphide and sulphur, wherein an aprotic electrolyte comprising at least one lithium salt in at least one solvent is provided between the electrodes.

The mixture of lithium suiphide with elemental sulphur serves as a positive electrode depolariser substance (electroactive substance) and addresses the problems (cycle life and manufacturing costs) inherent in using a material that can reversibly intercalate lithium ions as the negative electrode.

The lithium sulphide/sulphur mixture may be incorporated directly in the positive electrode during its manufacture, or may be provided as a colloid solution or suspension added to the electrolyte.

The positive electrode is preferably porous, highly electricallyconductive and advantageously has a developed surface.

The positive electrode may be made of carbon or graphite, or of a metallic material with high porosity that is resistant to corrosion in suiphide media.

The permeable separator or membrane may be made of a porous film or nonwoven material, for example microporous polypropylene (Celgard separator) or non- ** * . . Where the lithium sulphide/suiphur mixture is provided in the form of a suspension or colloid, the solids content of the suspension or colloid is preferably from 5 to 50%.

The content of lithium sulphide in the colloid or suspension is preferably from 10 to * 90% by weight of the content of sulphur. *:. : a... S.. a. .

According to a second aspect of the present invention, there is provided a method of manufacturing a chemical source of electrical energy, the method comprising the steps of: i) providing a porous cathode having a developed surface; ii) providing a suspension of lithium sulphide and sulphur in an aprotic electrolyte comprising at least one lithium salt in at least one solvent; iii) applying a coating of the suspension to the porous cathode; iv) applying a permeable separator or membrane over the coated cathode; v) applying a coating of an aprotic electrolyte comprising at least one lithium salt in at least one solvent over the permeable separator or membrane; vi) providing an anode on the coating of aprotic electrolyte, the anode being made of an electrically conductive material or a material that is able reversibly to intercalate lithium ions; vii) providing terminal connections for the anode and cathode and hermetically sealing the structure obtained by the steps of the method.

In step v), the aprotic electrolyte may optionally also contain a suspension of lithium sulphide and sulphur as in step ii), or it may be free of lithium suiphide and sulphur: ** in suspension.

The structure may be folded or shaped as desired prior to sealing.

DETAILED DESCRIPTION OF THE INVENTION S...

S S S S. *

It is known that lithium suiphide, in the presence of aprotic solvents, reacts with sulphur to produce lithium polysuiphides of various lengths: Aprotic solvent L12S solid + nS solid * Li2S solution Lithium polysulphides are well soluble in most known aprotic electrolyte systems and possess high electrochemical activity. In solution, they undergo multi-step dissociation: Li2S -3 LI + LiSa LiSa 3 LI + S2 During charging of a cell comprising a mixture of lithium suiphide with sulphur constructed according to the scheme: Inert electrode I LiS + nS+ salt solution I Inert electrode there will take place a reaction of lithium reduction on the negative electrode: LI+e-+Lj and a reaction of sulphur oxidation at the positive electrode: S2-2e--*nS * * * * * * ** During discharging of the cell, the reverse reactions will take place on the electrodes. ***

At the negative electrode: * . : *..S * S * .5* Li -e--+Li.. : At the positive electrode: nS- 2ne -+ nS2 The power intensity and cycling efficiency of such a cell will be strongly affected by the molar ratio of lithium sulphide and sulphur. On the one hand this ratio has to provide a high energy density, and on the other hand it has to provide a long cycle life.

EXAMPLE I

A porous electrode made up of 50% electroconductjve carbon black (Ketjenblack EC-600JD, available from Akzo Nobel Polymer Chemicals By, Netherlands) and 50% polyethylene oxide (PEO, 4,000,000 molecular weight, available from Sigma- Aldrich, UK) as a binder was prepared according to the following procedure.

A mixture of dry components was milled in a high speed grinder (Microtron MB550) for 15 to 20 minutes. Acetonitryl was then added to the mixture as a solvent for the binder. The resulting suspension was then mixed for 15 to 20 hours in a DLII laboratory stirrer. The solids content of the suspension was 5%. The suspension thus produced was deposited by an automatic film applicator (Elcometer SPRL) to one side of an 1 8im thick aluminum foil with an electroconductive carbon coating (Product No. 60303 available from Rexam Graphics, South Hadley, Mass.) as a current collector. *

I S S * *S

The carbon coating was dried in ambient conditions for 20 hours. After drying, the S..

electrode was pressed at a pressure of 1 000kg/cm2. The resulting dry cathode layer * : :: had a thickness of 8j.m after pressing and contained 0.47mg/cm2 of carbon - PEO *...

mixture. The volume density of the carbon layer was 590mg/cm and the porosity. . * * S...

was 72%. .. :

EXAMPLE 2

A suspension comprising a mixture of lithium suiphide with sulphur in an electrolyte was produced. Lithium suiphide, 98% (Sigma-Aldrich, UK) and sublimated sulphur, 99.5 % (Fisher Scientific, UK) were ground at a mass ratio of 90:10 in a high speed mill (Microtron MB550) for 15 to 20 minutes in an atmosphere of dry argon (moisture content 20-25ppm). The ground mixture of lithium sulphide and sulphur was placed into a ball mill, and an electrolyte was added to the mill. A solution of trifluoromethanesulphonate of lithium (available from 3M Corporation, St. Paul, Minn.) in sulfolane (99.8 %, standard for GC available from Sigma-Aldrich, UK) was used as the electrolyte. The liquid to solid ratio was 10:1.

EXAMPLE 3

The hard composite cathode from Example 1 was used in a small cell producing electric current with an electrode surface area of about 5 cm2. The electrode was dried in a vacuum at 50 C for 5 hours before being installed in the cell. Celgard 2500 (a trade mark of Tonen Chemical Corporation, Tokyo, Japan, and also available from Mobil Chemical Company, Films Division, Pittsford, N.Y.) was used as a porous separator. A copper foil was used as a current collector for the negative electrode.

The cell was assembled in the following way: A thin even layer of the lithium sulphide and sulphur suspension in the electrolyte * from Example 2 was deposited onto the porous carbon cathode from Example 1 in a: quantity of about 7.5mg/cm2 of the cathode surface. Then one layer of Celgard 2500 was placed onto the the electrode over the deposited suspension. An electrolyte S comprising a solution of trifluoromethanesuiphonate of lithium (available from 3M: Corporation, St. Paul, Minn.) in sulfolane (99.8 %, standard for GC available from * Sigma-Aldrich, UK), but without any lithium sulpbide-sulphur suspension, was deposited onto the separator in a quantity of 1/LlIcm2. A copper current collector was placed on top of the,,sandwich" structure thus produced. Finally, the cell was hermetically sealed.

The cell was kept at ambient room conditions for 24 hours and then charged at a current dencity of 0.O5mA]cm2 to a voltage of 2.8V.

Thereafter, the cell was cycled. Charge and discharge was conducted at a current density of 0. lmA/cm2 with discharge termination at 1.5V and charge termination at 2.8V. The charge-discharge plots are shown in Figure 1. The charge- discharge plots are similar to those obtained for lithium-sulphur cells using elemental sulphur as a cathode depolariser (electroactive substance) . The efficiency of lithium-sulphur utilisation is 55 to 65%.

The preferred features of the invention are applicable to all aspects of the invention and may be used in any possible combination.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", mean "including but not limited to", and are not intended to (and do not) exclude other components, integers, moieties, additives or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well ***. :* as singularity, unless the context requires otherwise. a.. * .*. * . a s S S... * S S... *SS. S a. S. S

Claims

CLAIMS: I. A chemical source of electrical energy comprising a positive

electrode (cathode) made of an electrically conductive material, a mixture of lithium suiphide and sulphur, a permeable separator or membrane, and a negative electrode (anode) made of an electrically conductive material or a material that is able reversibly to intercalate lithium ions, wherein an aprotic electrolyte comprising at least one lithium salt in at least one solvent is provided between the electrodes.
2. A chemical source of electrical energy as claimed in claim 1, wherein the positive electrode is porous.
3. A chemical source of electrical energy as claimed in claim 1 or 2, wherein the positive electrode has a developed or roughened surface.
4. A chemical source of electrical energy as claimed in any preceding claim, wherein the positive electrode is made of carbon or graphite, or a metallic material that is resistant to corrosion in sulphide media.
5. A chemical source of electrical energy as claimed in any previous claim, wherein the permeable separator or membrane is made of a porous woven or non-
6. A chemical source of electrical energy as claimed in any previous claim, wherein the mixture of lithium suiphide and sulphur is provided as a suspension or ***. : colloid.
7. A chemical source of electrical energy as claimed in claim 6, wherein the suspension or colloid has a solids content of 5 to 50%. * :. : S...

S SS S. *
8. A chemical source of electrical energy as claimed in claim 6 or 7, wherein the content of lithium suiphide in the colloid or suspension is from 10 to 90% by weight of the content of sulphur.
9. A chemical source of electrical energy as claimed in any preceding claim, wherein the aprotic electrolyte comprises a solution of lithium trifluoromethanesuiphonate in sulfolane.
10. A method of manufacturing a chemical source of electrical energy, the method comprising the steps of: i) providing a porous cathode having a developed or roughened surface; ii) providing a suspension of lithium sulphide and sulphur in an aprotic electrolyte comprising at least one lithium salt in at least one solvent; iii) applying a coating of the suspension to the porous cathode; iv) applying a permeable separator or membrane over the coated cathode; v) applying a coating of an aprotic electrolyte comprising at least one lithium salt in at least one solvent over the permeable separator or membrane; vi) providing an anode on the coating of aprotic electrolyte, the anode being made of an electrically conductive material or a material that is able reversibly to: ** intercalate lithium ions; . vii) providing terminal connections for the anode and cathode and hermetically sealing the structure obtained by the steps of the method. * : a., S..' S * S.
11. A method according to claim 10, wherein in step v), the aprotic electrolyte contains a suspension of lithium suiphide and sulphur.
12. A method according to claim 10, wherein in step v), the aprotic electrolyte does not contain a suspension of lithium suiphide and sulphur.
13. A method according to any one of claims 10 to 12, wherein the structure is folded or otherwise shaped prior to sealing.
14. A method of manufacturing a chemical source of electrical energy, substantially as hereinbefore described.

14. A chemical source of electrical energy, substantially as hereinbefore described.

15. A method of manufacturing a chemical source of electrical energy, substantially as hereinbefore described. *b S e a * , * S 4 p * 4. 4. p * *, * a p S. a * 4 papa a... a *4 *

Amendments to the claims have been filed as follows CLAIMS: 1. A chemical source of electrical energy comprising a positive electrode (cathode) made of an electrically conductive material, a colloid solution or a suspension of lithium suiphide and sulphur in an aprotic electryte comprising at least one lithium salt in at least one solvent applied to the positive electrode, a permeable separator or membrane, and a negative electrode (anode) made of an electrically conductive material or a material that is able reversibly to intercalate lithium ions, wherein an aprotic electrolyte comprising at least one lithium salt in at least one solvent is provided between the permeable separator and the negative electrode.

2. A chemical source of electrical energy as claimed in claim 1, wherein the positive electrode is porous.

3. A chemical source of electrical energy as claimed in claim 1 01 2, wherein the positive electrode has a developed or roughened surface.

4. A chemical source of electrical energy as claimed in any preceding claim, wherein the positive electrode is made of carbon or graphite, or a metallic material that is resistant to corrosion in sulphide media.

5. A chemical source of electrical energy as claimed in any previous claim, wherein the permeable separator or membrane is made of a porous woven or non- woven material.

6. A chemical source of electrical energy as claimed in any preceding claim, wherein the suspension or colloid has a solids content of 5 to 50%.

7. A chemical source of electrical energy as claimed in any preceding claim, wherein the content of lithium sulphide in the colloid or suspension is from 10 to 90% by weight of the content of sulphur.

8. A chemical source of electrical energy as claimed in any preceding claim, wherein the aprotic electrolyte comprises a solution of lithium trifluoromethanesulphonate in sulfolane.

9. A method of manufacturing a chemical source of electrical energy, the method comprising the steps of: i) providing a porous cathode having a developed or roughened surface; ii) providing a suspension of lithium suiphide and sulphur in an aprotic electrolyte comprising at least one lithium salt in at least one solvent; iii) applying a coating of the suspension to the porous cathode; iv) applying a permeable separator or membrane over the coated cathode; v) applying a coating of an aprotic electrolyte comprising at least one lithium salt in at least one solvent over the permeable separator or membrane; vi) providing an anode on the coating of aprotic electrolyte, the anode being made of an electrically conductive material or a material that is able reversibly to intercalate lithium ions; vii) providing terminal connections for the anode and cathode and hermetically sealing the structure obtained by the steps of the method.

10. A method according to claim 9, wherein in step v), the aprotic electrolyte contains a suspension of lithium suiphide and sulphur.

11. A method according to claim 9, wherein in step v), the aprotic electrolyte does not contain a suspension of lithium suiphide and sulphur.

12. A method according to any one of claims 9 to 11, wherein the structure is folded or otherwise shaped prior to sealing.

13. A chemical source of electrical energy, substantially as hereinbefore described.