Lithium electrochemical generator of the lithium-oxygen or lithium-air type comprising a specific negative electrode material

Abstract

A lithium-air or lithium-oxygen electrochemical generator comprising at least one electrochemical cell comprising a positive electrode, a negative electrode and an electrolyte conducting lithium ions disposed between the negative electrode and the positive electrode wherein the negative electrode comprises, as active material, a lithium and calcium alloy.

Claims

1. Lithium-air or lithium-oxygen electrochemical generator comprising at least one electrochemical cell comprising a positive electrode, a negative electrode and an electrolyte conducting lithium ions disposed between said negative electrode and said positive electrode, characterised in that the negative electrode comprises, as active material, a lithium and calcium alloy, the lithium and calcium alloy being a lithium alloy comprising calcium to the extent of 2% to 34% atomic.

2. Lithium-air or lithium-oxygen electrochemical generator according to claim 1, wherein the negative electrode consists solely of the active material, which is the lithium and calcium alloy.

3. Lithium-air or lithium-oxygen electrochemical generator according to claim 1, wherein the negative electrode is in the form of a sheet or plate having a thickness ranging from 5 to 200 μm.

4. Lithium-air or lithium-oxygen electrochemical generator according to claim 1, wherein the lithium and calcium alloy comprises solely lithium and calcium.

5. Lithium-air or lithium-oxygen electrochemical generator according to claim 1, wherein the lithium and calcium alloy is a lithium alloy comprising calcium to the extent of 2% to 15% atomic.

6. Lithium-air or lithium-oxygen electrochemical generator according to claim 1, wherein the calcium in the lithium and calcium alloy is wholly or partly in the form of CaLi.sub.2.

7. Lithium-air or lithium-oxygen electrochemical generator according to claim 1, wherein the negative electrode is self-supporting.

8. Lithium-air or lithium-oxygen electrochemical generator according to claim 1, wherein the positive electrode is an air or oxygen electrode.

9. Lithium-air or lithium-oxygen electrochemical generator according to claim 1, wherein the positive electrode comprises: at least one electron-conducting material; optionally at least one catalyst; and optionally at least one binder.

10. Lithium-air or lithium-oxygen electrochemical generator according to claim 9, wherein the electron conducting material is a carbon material chosen from graphite, mesocarbon beads, carbon fibres, carbon black, graphene, carbon nanotubes and mixtures thereof.

11. Lithium-air or lithium-oxygen electrochemical generator according to claim 9, wherein the at least one catalyst is: a catalyst consisting of a transition metal with a degree of oxidation 0, such as cobalt, and more specifically a noble metal with a degree of oxidation 0 such as platinum, gold, palladium, ruthenium or alloys thereof, such as a Pt—Au alloy; a catalyst comprising a simple ruthenium oxide such as RuO.sub.2, a simple manganese oxide such as MnO.sub.2 or Mn.sub.2O.sub.3, a simple iron oxide such as Fe.sub.3O.sub.4 or Fe.sub.2O.sub.3, a simple cobalt oxide such as Co.sub.3O.sub.4 or a simple copper oxide such as CuO; a catalyst comprising a mixed cobalt oxide such as CoFe.sub.2O.sub.4, a mixed manganese oxide such as LaMnO.sub.3 or a mixed nickel oxide such as LaNiO.sub.3; or mixtures thereof.

12. Lithium-air or lithium-oxygen electrochemical generator according to claim 1, wherein the at least one binder is a polymeric binder.

13. Lithium-air or lithium-oxygen electrochemical generator according to claim 1, wherein the electrolyte is an aqueous or non-aqueous liquid electrolyte, an ionic liquid, a solid electrolyte or a polymer electrolyte.

14. Lithium-air or lithium-oxygen electrochemical generator according to claim 1, wherein the electrolyte is a non-aqueous liquid electrolyte.

15. Lithium-air or lithium-oxygen electrochemical generator according to claim 1, wherein the electrolyte is a non-aqueous liquid electrolyte, which comprises: as solvent(s), one or more organic solvents chosen from carbonate solvents, ether solvents, sulfone solvents, sulfoxide solvents, lactone solvents, lactam solvents, nitrile solvents, fluorinated solvents and mixtures thereof; at least one lithium salt; optionally an additive other than a lithium salt.

Description

BRIEF DESCRIPTION OF THE SINGLE FIGURE

(1) The single FIGURE is a graph illustrating the change in the discharge voltage U (in V) at 30 μA as a function of the surface capacity C (in mAh par cm.sup.2 of positive electrode) for the electrochemical generator according to the invention (curve a) and for the electrochemical generator not in accordance with the invention (curve b) of the example disclosed below.

DETAILED DISCLOSURE OF A PARTICULAR EMBODIMENT

Example

(2) The following example illustrates a lithium-air electrochemical generator in the form of a button battery comprising: a negative electrode consisting of a disc with a diameter of 16 mm and a thickness of 100 μm and composed of a lithium and calcium alloy with calcium to the extent of 2% atomic; a positive electrode consisting of a disc 14 mm in diameter and 200 μm thickness composed of a fabric of carbon fibres of the Freudenberg H2315 type; between the negative electrode and the positive electrode, a Celgard 2400° separator in the form of a 16 mm diameter disc, said separator being impregnated with an electrolyte (300 μL) consisting of a mixture of perfluorodecaline/perfluorooctanol/propylene carbonate solvents in respective proportions by mass of 2.55/2.4/0.45 and a lithium salt 1 M LiTFSI.

(3) By way of comparison, another lithium-air electrochemical generator not in accordance with the invention was produced in this example, this electrochemical generator meeting the same specificities as that of the invention except that the negative electrode is made from pure lithium.

(4) These two electrochemical generators are supplied with a flow of oxygen of 0.6 ml/min at a pressure of 1 bar.

(5) For these two electrochemical generators, the change in the discharge voltage U (in V) at 30 μA is determined as a function of the surface capacity C (in mAh per cm.sup.2 of positive electrode), the results being set out in the accompanying single FIGURE (curve a) for the electrochemical generator according to the invention and curve b) for the electrochemical generator not in accordance with the invention).

(6) For the electrochemical generator according to the invention, the discharge potential is similar to that of the electrochemical generator using a negative electrode made solely from lithium, which demonstrates that the electrode comprising calcium is as functional as a lithium electrode in such a system.

(7) Furthermore, the presence of calcium in the lithium alloy constituting the negative electrode helps to make the alloy easier to roll than pure lithium, which makes it possible to envisage the use of such an alloy for forming thinner negative electrodes and thus larger developed surfaces, which may prove a major asset in electrochemical generators intended for power applications.