PROCESS FOR MANUFACTURING A STRUCTURE ACTING AS A POSITIVE ELECTRODE AND AS A CURRENT COLLECTOR FOR A LITHIUM-SULFUR ELECTROCHEMICAL ACCUMULATOR

Abstract

A process for preparing a structure acting both as a positive electrode for a lithium-sulfur battery and as a current collector, comprising the following operations: depositing one or more liquid compositions comprising the constituent ingredients of this structure on a removable substrate; drying the one or more deposited compositions; separating the removable substrate from the structure thus obtained, which forms the structure acting both as a positive electrode for a lithium-sulfur battery and as a current collector.

Claims

1-16. (canceled)

17. A process for preparing a structure both acting as a positive electrode for a lithium-sulphur battery and a current collector comprising the following operations of: depositing one or more liquid compositions comprising the components of this structure onto a removable substrate; drying the composition(s) deposited; separating the removable substrate from the structure thus obtained, which is the structure both acting as a positive electrode for a lithium-sulphur battery and a current collector, wherein: when the structure is for being part of the composition of a lithium-sulphur accumulator operating in a catholyte type configuration, the depositing consists in depositing onto the removable substrate a single liquid composition comprising the components of said structure; or when the structure contains a sulphur active material therein, the depositing consists in depositing onto the removable substrate a single composition comprising the components of said structure, including, in this case, a sulphur active material; or when the structure contains a sulphur active material therein, the depositing consists in depositing onto the removable substrate a first composition comprising the components of said structure except for the sulphur active material and a second composition comprising the sulphur active material, wherein a drying can be interposed between both compositions deposited; or when the structure contains a sulphur active material therein, the depositing consists in depositing onto the removable substrate a composition comprising the components of said structure except for the sulphur active material, the sulphur active material being introduced into the structure after separating the removable substrate.

18. The process according to claim 17, wherein the components of said structure are the following ones: at least one inorganic carbon additive; at least one polymeric binder; optionally, a sulphur active material.

19. The process according to claim 18, wherein the inorganic carbon additive is chosen from carbon fibres, carbon powders and mixtures thereof.

20. The process according to claim 19, wherein the carbon fibres are milled carbon fibres, carbon fibres obtained in vapour phase and mixtures thereof.

21. The process according to claim 19, wherein the carbon powders are carbon black.

22. The process according to claim 18, wherein the polymeric binder is chosen from: polymeric binders belonging to the cellulosic polymer category; binders belonging to the fluorinated ethylenic polymer category; binders belonging to the vinylic polymer category; or mixtures thereof.

23. The process according to claim 18, wherein the sulphur active material is elemental sulphur (S.sub.8) or lithium disulfide (Li.sub.2S).

24. The process according to claim 17, wherein the composition(s) mentioned in step a) comprise(s) at least one surfactant and, optionally, a pore forming material.

25. The process according to claim 17 further comprising, after drying, a step of air sintering the structure obtained and/or a step of impregnating the structure obtained with a resin followed by a step of carbonising the structure thus impregnated under a reducing atmosphere.

26. The process according to claim 17, wherein the removable substrate is of glass or of polymeric material.

27. A structure both acting as a positive electrode for a lithium-sulphur battery and a current collector likely to be obtained by the process as defined in claim 17.

28. The structure according to claim 27, which comprises at least one inorganic carbon additive belonging to the carbon fibre category and at least one polymeric binder.

29. The structure according to claim 28, wherein the carbon fibres are carbon fibres obtained in vapour phase, milled carbon fibres and mixtures thereof.

30. The structure according to claim 28, wherein the polymeric binder belongs to the cellulosic polymer family, the fluorinated ethylenic polymer family and mixtures thereof.

31. The structure according to claim 17, further comprising a carbon powder, such as carbon black.

32. A lithium-sulphur accumulator comprising at least one cell comprising: a structure acting as a positive electrode and a current collector as defined in claim 27; a negative electrode; and a lithium-ion conducting electrolyte disposed between said structure and said negative electrode.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0131] FIG. 1 is a graph illustrating the potential E (in V) as a function of the capacity C (in a.u).

[0132] FIGS. 2-3 are photographs taken from above of the structures described in the experimental example 1.

[0133] FIG. 4 is a graph illustrating the potential E (in V) as a function of the specific capacity C (in mAh/g.sub.s) of the accumulators described in the experimental example 3.

DETAILED DISCLOSURE OF PARTICULAR EMBODIMENTS

EXAMPLE 1

[0134] The present example illustrates the preparation of a structure obtained according to a process in accordance with the invention.

[0135] The composition used comprises the following ingredients: [0136] 39.72 g of methylcellulose as a 1.15 mass % water dispersion (10.60 mass % in the final structure); [0137] 3.4 g of carbon fibres obtained in vapour phase VGCF (78.30 mass % in the final structure); and [0138] 0.8 g of a surfactant Triton (11.10 mass % in the final structure).

[0139] The dry solid content (that is, the mass percentage of the dry product in the composition) is 9.89%.

[0140] The composition is mixed using a Dispermat (VMA) at 6000 rotations per minute for 30 minutes, is coated on a glass plate using a doctor blade (coating technology) and then dried at 80 C. in open air for 30 minutes.

[0141] The resulting structure is manually peeled off from the glass plate and dried at 95 C. under the air overnight.

EXAMPLE 2

[0142] The present example illustrates the preparation of a structure obtained according to a process in accordance with the invention.

[0143] The composition used comprises the following ingredients: [0144] 39.72 g of methylcellulose as a 1.15 mass % water dispersion (8.80 mass % in the final structure); [0145] 2 g of carbon fibres obtained in vapour phase VGCF (38.20 mass % in the final structure); and [0146] 1.4 g of carbon particles Vulcan (27.80 mass % in the final structure); [0147] 1.23 g of a 60 mass % water PTFE dispersion (15 mass % in the final structure); [0148] 0.8 g of a surfactant Triton (11.10 mass % in the final structure).

[0149] The dry solid content is 11.45%.

[0150] The composition is mixed using a Dispermat (VMA) at 6000 rotations per minute for 30 minutes, is coated on a glass plate using a doctor blade (coating technology) and then dried at 80 C. in open air for 30 minutes.

[0151] The resulting structure is manually peeled off from the glass plate and dried at 95 C. under the air overnight.

[0152] Finally, the resulting structure is sintered at 350 C. for 30 minutes under the air.

COMPARATIVE EXAMPLE 1

[0153] A carbon non-woven felt (H2315V1, Freudenberg) has been bought to the manufacturer. It is rinsed with water and dried under the air at 95 C.

EXPERIMENTAL EXAMPLE 1

[0154] A scanning electron microscope (LEO 1530 FEG-SEM) has been used to obtain images of the structures obtained in the example 1 and comparative example 1. FIGS. 2 and 3 clearly show that the morphology and size of the pores of the structures obtained are influenced by the formulation and are differentiated from the commercial product (respectively FIG. 2 for the material obtained in the example 1 and FIG. 3 for the material obtained in the comparative example 1).

EXPERIMENTAL EXAMPLE 2

[0155] The density value of the structures obtained in the examples 1, 2 and comparative example 1 has been determined, said density corresponding to the mass of the structure considered (obtained by weighing discs with a 14 mm diameter cut out in the structures obtained in said abovementioned examples) and its volume (obtained by measuring the dimensions of the disc using a micrometric gauge). The measurement has been repeated 10 times and its results are reported in Table 1 below.

[0156] The active area value has been obtained through a gas adsorption/desorption measurement at 77 K. The BET areas obtained are also reported in Table 1.

TABLE-US-00001 Structure Density (g .Math. cm.sup.3) Active area (m.sup.2 .Math. g.sup.1) Example 1 0.25 0.05 7.12 0.43 Example 2 0.26 0.01 (before sintering) Not measured 0.19 0.02 (after sintering) Comparative 0.46 0.01 <Detection limit example 1

EXPERIMENTAL EXAMPLE 3

[0157] Discs with a 14 mm diameter have been cut out in the structures obtained in the examples 1, 2 and comparative example 1, and dried under vacuum (20 torr) at 80 C. for 48 hours. Then, they have been integrated, as a positive electrode, in a button cell type accumulator (CR2032) thus constructed: [0158] a negative electrode of lithium with a 130 m thickness, cut out at a diameter 16 mm and deposited onto a stainless steel disc acting as a current collector; [0159] a positive electrode; [0160] a Celgard 2400 separator and a Viledon separator, soaked with a liquid electrolyte based on the salt LiTFSI (1 mol.L.sup.1), LiNO.sub.3(0.1 mol.L.sup.1) and Li.sub.2S.sub.6 (0.25 mol.L.sup.1) in solution in a 50/50 volume mixture of TEGDME (tetraethylene glycol dimethylether)DIOX (Dioxolane).

[0161] The sulphur amount and the nominal capacity of the accumulator are respectively 7.20 mg (4.68 mg.sub.s.cm.sup.1) and 12.06 mAh.

[0162] After assembly, the accumulator thus made is sealed under an inert atmosphere and tested during a C/20 galvanostatic cycling.

[0163] The cycling curves of the accumulators made with the materials of the examples 1, 2 and comparative example 1 are presented in FIG. 4 (respectively curves a), b), c) for the accumulators made with the structures of the examples 1, 2 and comparative example 1) and in Table 2. The mass storage capacity is clearly influenced by the formulation used and the active area of the final structure, and is visibly improved by the use of the structures obtained in accordance with the process of the invention (600 versus400 mAh.g.sup.1 during the first cycle).

TABLE-US-00002 Comparative Structure Example 1 Example 2 example 1 Mass 560 530 200 capacity (mAh .Math. g.sub.s) at cycle 30