IMPROVED CURRENT COLLECTOR FOR A BATTERY

Abstract

The present invention relates to a current collector for a negative electrode, coated with at least one electronically conducting and ionically insulating layer, to the method for producing such a collector, and to batteries containing same.

Claims

1. A negative electrode current collector comprising a material likely to be corroded in the presence of sulfides, wherein the collector is coated with at least one protective layer which is electronically conducting and insulates from Li.sup.+ ions, such that the protective layer is located at the interface of the collector with the active mass of the electrode.

2. The negative current collector according to claim 1, wherein said at least one protective layer contains at least one material selected from carbon, silicon, and mixtures thereof.

3. The negative current collector according to claim 1, wherein said protective layer contains at least one material selected from chromium, chromium oxide, or nickel oxide, or stainless steel.

4. The negative current collector according to claim 1, wherein said protective layer is devoid of at least one of fluorinated resin and oxalate.

5. The negative current collector according to claim 1, wherein the material that is likely to be corroded is copper.

6. A method of preparing a coated current collector according to claim 1, wherein said method comprises the deposition of said protective layer on the collector.

7. The method according to claim 5, wherein the deposition is carried out by physical or chemical vapor deposition (PVD or CVD).

8. The electrode comprising a coated current collector according to claim 1, wherein said active material of said electrode is graphite.

9. The electrochemical element comprising a coated current collector according to claim 1 and a solid sulfide electrolyte.

10. The electrochemical module comprising the stacking of at least two elements according to claim 8, each element being electrically connected to one or more other element(s).

11. The battery comprising one or more modules according to claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0071] FIGS. 1a and 1b show the structure of an electrochemical element according to the invention (FIG. 1a) and the detail of the current collector (FIG. 1b).

[0072] FIG. 2 shows the values of discharged capacity and coulombic efficiency obtained for a cell according to the invention (Cu—Si) and a comparative cell (Cu).

DETAILED DESCRIPTION

[0073] FIG. 1a schematically shows an electrochemical element comprising, at the negative electrode: a current collector (1) coated with a protective layer (2) according to the invention, and at the positive electrode, a current collector (7). The chemical element shown is solid-state, where the anode and cathode are composite, being made of a mixture of active material (3) and (6), respectively, and electrolyte (4).

[0074] The anode and the cathode are separated by the electrolyte.

[0075] As shown in FIG. 1b the protective layer (2) acts as an interface between the collector (1) and the particles of active material (3) and electrolyte (4) constituting the composite anode. In addition, conducting particles (5), such as carbon black, are inserted into the mixture comprising the active material (3) and the electrolyte (4). The active material is typically graphite. The electrolyte can in particular be a solid sulfide electrolyte.

[0076] According to an alternative configuration (not shown), the chemical element can also be of all-solid Li-metal, where the negative electrode can contain an alkali metal in the charged state, such as lithium metal.

[0077] Coulombic efficiency is the ratio of the capacity recovered in discharge divided by the capacity provided during the previous charge.

[0078] The following examples are given for illustrative and non-limiting purposes of the invention:

EXAMPLE

[0079] All the manipulations of the powders were carried out in a glove box under an argon atmosphere. The solid electrolyte used in this example is an argyrodite Li.sub.6PS.sub.5Cl (˜1 mS/cm at room temperature). The composite mixture of NCA and sulfide electrolyte (SE) used as a positive electrode was prepared manually with a mortar according to the NCA:SE mass quantities of 70:30. The mixture used as a negative electrode is prepared, according to the same protocol, from graphite and SE in graphite:SE mass proportions of 2:1. The complete graphite/SE/NCA cells were prepared in specific cells, similar to 7 mm diameter pellet molds of which the pistons are made of stainless steel and the body is made of electrically insulating material. First, 40 mg of electrolyte is introduced and then compressed under 250 MPa to form the separating electrolyte layer (SEL). The cell is then opened on one side to introduce 15 mg of the positive electrode mixture and an aluminum disc (acting as a current collector). The positive electrode is formed by compression at 250 MPa. 12 mg of the negative electrode mixture and a copper current collector are then introduced on the other side of the SEL. The entire cell is then compressed under 500 MPa for several minutes. A pressure of 250 MPa is maintained on the cell thereafter using screws. This first cell is referred to as “Comparative Example: Cu” in the graphical representations.

[0080] A second cell is assembled under the same conditions, but the copper collector of the negative electrode is replaced by a collector from the same copper strip, but on which a layer of 50 nm of silicon has previously been deposited by PECVD. This second cell is referred to as “Example 1: Cu—Si” in the graphical representations.

[0081] After a rest of 12 hours, the cells thus assembled are then characterized by galvanostatic cycling between 2.8 and 4.1 V at room temperature. The sequence [1 control cycle at C/20—20 cycles at C/10—1 control cycle at C/20] is repeated 7 times. FIG. 2 shows the discharged capacity and coulombic efficiency values obtained for these cells. Both cells have similar discharged capacity values during the first 100 cycles while the coulombic efficiency obtained for the cell containing the copper collector with silicon deposition is significantly improved compared to the comparative example. Indeed, the averages of the coulombic efficiency values between the 2nd and 22nd cycles (first sequence, excluding first cycle) are 97.6% for Example 1: Cu—Si and only 87.6% for the comparative example, respectively.

[0082] This discrepancy demonstrates the important reactions occurring within the negative electrode, especially between the sulfide electrolyte and the copper current collector. A protective layer of only 50 nm can significantly reduce these instabilities.