NEGATIVE ELECTRODES FOR USE IN ACCUMULATORS OPERATING ACCORDING TO THE ION INSERTION AND DEINSERTION OR ALLOY FORMATION PRINCIPLE AND WITH SPIRAL CONFIGURATION

Abstract

A negative electrode for an accumulator functions based on the ion insertion and deinsertion principle and/or based on the alloy formation and dealloying principle. A first layer comprises an active material deposited on a first face of a current collector. A second layer comprises an active material deposited on a second face of a current collector, the first face being opposite the second face. The negative electrode extends lengthwise in an electrode longitudinal direction. Each of the first and second layers is partly coated with an assembly of strips of a metal, the cations of the metal are those involved in the ion insertion and deinsertion process and/or in the alloy formation and dealloying process in the active material of the first and second layers, the strips being separated along the electrode longitudinal direction and each extend lengthwise along a strip longitudinal direction substantially perpendicular to the electrode longitudinal direction.

Claims

1. Negative electrode for an accumulator functioning based on the ion insertion and deinsertion principle and/or based on the alloy formation and dealloying principle comprising: a first layer (1) comprising an active material deposited via one of its faces, on a first face of a current collector (13); a second layer (7) comprising an active material deposited via one of its faces, on a second face of a current collector (13), said first face being opposite said second face; said negative electrode extending in length along an electrode longitudinal direction, wherein each of the first layer and the second layer is partly coated with an assembly of strips (2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48) each composed of a metal, the corresponding cations of which are those involved in the ion insertion and deinsertion process and/or in the alloy formation and dealloying process in the active material of the first layer and the second layer, said strips being separated from each other along the electrode longitudinal direction and each extending in length along a strip longitudinal direction substantially perpendicular to said electrode longitudinal direction.

2. Negative electrode according to claim 1, wherein the active material, either for the first layer (1) and/or the second layer (7), is: a material that can intercalate or deintercalate alkali ions; or a material that can intercalate or deintercalate alkali earth ions.

3. Negative electrode according to claim 1, wherein the active material, either for the first layer (1) and/or the second layer (7), is chosen from among: silicon; a carbon material such as hard carbon, natural graphite or artificial graphite; and; mixtures thereof.

4. Negative electrode according to claim 1, wherein the strips composed of a metal among the set of strips (2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24) coating the first layer and the set of strips (26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48) coating the second layer are strips composed of an alkali metal or strips composed of an alkali earth metal.

5. Negative electrode according to claim 1, wherein each strip in the set of strips (2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24) coating the first layer and the set of strips (26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48) coating the second layer are in the form of a metal strip with a thickness greater than or equal to 50 m.

6. Negative electrode according to claim 1, wherein the current collector (13) is an unperforated collector in the form of metal foil.

7. Negative electrode according to claim 1, wherein the current collector (13) comprises one or several metals chosen from among copper, aluminium and alloys thereof.

8. Negative electrode according to claim 1, wherein each layer (namely the first layer and the second layer) has a first end (3, 9) without any strips extending along the electrode longitudinal direction, said first end (3, 9) having a length z.sub.1 along the electrode longitudinal direction.

9. Negative electrode according to claim 8, wherein the value of the length z.sub.1 along the electrode longitudinal direction is greater than the maximum separation y.sub.1 for each pair of two directly consecutive strips in the strip assembly.

10. Negative electrode according to claim 1, wherein each layer (namely the first layer and the second layer) has a second end (5, 11) that has no strips extending along the electrode longitudinal direction and opposite to the first end.

11. Negative electrode according to claim 10, wherein the length x.sub.1 of the second end (5, 11) along the electrode longitudinal direction is less than the length z.sub.1.

12. Negative electrode according to claim 9, wherein the length z.sub.1 satisfies the following relation:
z.sub.1=Lx.sub.1y.sub.1*(1n)l*n in which: L is the total length along the electrode longitudinal direction of the layer concerned (namely the first layer and/or the second layer); x.sub.1 is the length along the electrode longitudinal direction of the second end of the layer concerned (namely the first layer and/or the second layer); y.sub.1 is the separation along the electrode longitudinal direction, for each pair of two directly consecutive strips in the strip assembly in the layer concerned (namely the first layer and/or the second layer); n is the number of strips in the strip assembly in the layer concerned; l is the width (along the electrode longitudinal direction) of each strip in the set of strips.

13. Negative electrode according to claim 9, wherein the separation y.sub.1 satisfies the following relation:
y.sub.1=2x.sub.1 in which x.sub.1 is the length along the electrode longitudinal direction of the second end of the layer concerned (namely the first layer and/or the second layer).

14. Negative electrode according to claim 1, wherein the separation along the electrode longitudinal direction, for each pair of two directly consecutive strips in the strip assembly in the layer concerned is less than 2 cm.

15. Negative electrode according to claim 10, wherein the first end (3) of the first layer (1) is located opposite the first end (9) of the second layer (7) along the electrode longitudinal direction.

16. Negative electrode according to claim 1, wherein at least one strip in the strip assembly in the first layer is located along the electrode thickness direction, at least partly corresponding to a free zone defined between two directly consecutive strips coating the second layer, and vice versa.

17. Negative electrode according to claim 1, wherein each strip in at least part of the strip assembly in the first layer is located along the electrode thickness direction, at least partly corresponding to a free zone defined between two directly consecutive strips coating the second layer, and vice versa.

18. Method of preparing a negative electrode as defined in claim 1, comprising the following steps: a) a step to deposit a first layer on a current collector, comprising an active material on a first face of the current collector and a second layer comprising an active material on a second face of the current collector, said first face and said second face being opposite each other; b) a step to deposit a strip assembly each composed of a metal on each of the layers (namely the first layer and the second layer), the corresponding cations of the metal are those involved in the ion insertion and deinsertion process or the alloy formation or dealloying process in the active material of the first layer and the second layer, said strips being separated from each other along the electrode longitudinal direction and each extending in length along a strip longitudinal direction substantially perpendicular to said electrode longitudinal direction.

19. Method of activating a negative electrode as defined according to claim 1, comprising a step to bring the negative electrode into contact with an electrolyte for a fixed duration and at a fixed temperature to cause corrosion of the metal in the layer composed of a metal into metal cations.

20. Accumulator functioning based on the principle of ion insertion-deinsertion and/or the alloy formation and dealloying process comprising a negative electrode as defined according to claim 1.

21. Accumulator according to claim 20, that is a spiral architecture accumulator, wherein the negative electrode is wound around an axis parallel to the electrode width direction.

22. Accumulator functioning based on the principle of ion insertion-deinsertion and/or the alloy formation and dealloying process comprising a negative electrode obtained after the activation method defined in claim 19.

23. Accumulator according to claim 22, that is a spiral architecture accumulator, wherein the negative electrode is wound around an axis parallel to the electrode width direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0151] FIG. 1, already commented upon, illustrates a specific negative electrode conforming with the invention and shown in an exploded view.

[0152] FIG. 2 is a graph representing the variation of the discharged capacity C (in mAh) as a function of the number of cycles N.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

Example

[0153] This example illustrates the preparation of an accumulator with a spiral architecture, in which the negative electrode corresponds that shown on [FIG. 1] attached in the appendix.

[0154] More specifically, the accumulator comprises: [0155] a positive electrode composed of a composite material comprising 92% by mass of an NMC type active material, 4% by mass of a Super P65 (Imerys) type carbon black electron conducting additive and 4% by mass of a PVDF (Solvay) type binder, the positive electrode being 65 m thick and being associated with an aluminium foil type current collector with a thickness of 20 m, the capacity per unit area of the positive electrode being fixed at 2 mAh/cm.sup.2/face; [0156] a 20 m thick Celgard 2320 type polymeric separator with a porosity of 40%; [0157] for the negative electrode, the first layer and the second layer composed of a composite material comprising an active material consisting of a graphite silicon composite (92% by mass), 2% by mass of a Super P65 type carbon black electron conducting additive and 6% by mass of an acrylic polymer type binder, said electrode being associated with a 10 m copper foil type current collector.

[0158] The capacity per unit area of the negative electrode is fixed at 6 mAh/cm.sup.2/face. It then remains to prelithiate 4 mAh/cm.sup.2, and thus conserve 2 mAh/cm.sup.2 cyclable with the capacity of the positive electrode.

[0159] The 65 m thick positive electrode is 239 mm long over a width of 63 mm. The collector is exposed over a strip 6 mm wide at one of the ends of the strip so as to be able to solder an aluminium current transfer tab.

[0160] The 100 m thick negative electrode is 310 mm long and 66 mm wide. The collector is exposed over a 6 mm strip at one of the ends of the strip so as to solder a nickel current transfer tab.

[0161] It is calculated that 24 5010 mm (50 m thick) lithium strips correspond to 120 cm.sup.2, namely the 1200 mAh necessary to prelithiate 4 mAh/cm of negative electrode.

[0162] The 50 m thick lithium strips are arranged on the negative electrode in the manner illustrated on [FIG. 1], with the following dimensions: x.sub.1 corresponding to 5 mm and y.sub.1 corresponding to 10 mm.

[0163] They are also distributed assuring that they are not arranged on at the beginning and the end of the electrodes that are inactive in the chosen prismatic spiral design (winding on a 34 mm wide flat mandrel), the length z.sub.1 of 69 mm corresponding to the first and last turns on the spool, in which the negative electrode is not facing a positive electrode.

[0164] The accumulator is fabricated by simultaneously winding the 4 components (positive electrode/separator/negative electrode/separator) so as to form a prismatic coil with dimensions 40705 mm.

[0165] The accumulator thus obtained is placed in an aluminised flexible bag (multilayer packaging comprising a polypropylene type hot melt polymer rolled on an aluminium foil acting as a vapour barrier and a third polyamide type polymer, the melting temperature of which is higher than the melting temperature of the internal layer) and then filled with electrolyte comprising LiPF.sub.6 (1M) and a mixture of ethylmethyl carbonate (EMC) and fluoroethylene carbonate (in the proportion 70/30) and 2% by mass of vinylene carbonate (VC). The bag is then heat sealed at low pressure.

[0166] The accumulator is then placed in a drying oven for 4 days, at a temperature fixed at 40 C. under a mechanical stress applied by means of support plates placed so as to apply a pressure on each side of the accumulator contained in the bag, this treatment making it possible to obtain corrosion of the layer composed of lithium and diffusion of lithium ions through the entire thickness of the negative electrode.

[0167] After these 4 days, the accumulator conforming with the invention is subjected to a formation cycle at C/10 between 2.5 and 4.2V then a cycling test at C/20 for more than 200 cycles, the result of this test being shown on [FIG. 2] attached in the Appendix, this figure illustrates the variation in the discharged capacity C (in mAh) as a function of the number of cycles N.

[0168] The capacity obtained remains at a high level even after more than 200 cycles.