Method for producing a lithium-based electrolyte for a solid microbattery

Abstract

A method for producing a solid lithium-based electrolyte for a solid microbattery implements the cathode sputtering of a lithium-based target material on an object supported by a substrate holder. A grid made of lithium-free electrically conductive material is interposed between the object and the lithium-based target material, the grid being electrically connected to the substrate holder.

Claims

1. A method of forming a solid lithium-based electrolyte for a solid microbattery, by cathode sputtering of a target lithium-based material in a cathode sputtering device comprising a cathode supporting the lithium-based target material and an object supported by a substrate holder, wherein: the target lithium-based material is sputtered; a solid lithium-based electrolyte is formed on the object; and wherein prior to the sputtering of the target lithium-based material, a grid made of lithium-free electrically-conductive material, is interposed between the object and the lithium-based target material, and the grid and the substrate holder are electrically connected, wherein a distance between the grid and the object is shorter than a distance between the grid and the lithium-based target material, and wherein the grid is adapted to attenuate lithium depletion upon growth of the solid lithium-based electrolyte.

2. The solid electrolyte forming method of claim 1, wherein the grid of electrically-conductive material is made of a metal selected from the group consisting of titanium, stainless steel, tungsten, aluminum, platinum, copper, and alloys and mixtures thereof.

3. The solid electrolyte forming method of claim 1, wherein the grid is positioned at a distance in the range from 1 to 100 millimeters from the object.

4. The solid electrolyte forming method of claim 1, wherein the lithium-based target material is a solid lithium-based material selected from the group consisting of Li.sub.3PO.sub.4, LiSiPON, LiGePS, and LiSON.

5. The solid electrolyte forming method of claim 1, wherein the cathode sputtering is performed in the presence of nitrogen.

6. The solid electrolyte forming method of claim 1, wherein the grid has a thickness smaller than 10 millimeters.

7. The solid electrolyte forming method of claim 1, wherein the grid is made of a plurality of wires extending along at least two directions.

8. The solid electrolyte forming method of claim 7, wherein the wires along a same direction are spaced apart by a distance in the range from 0.5 millimeters to 2 centimeters.

9. The solid electrolyte forming method of claim 1, wherein the object successively comprises, towards the substrate holder, a lithiated electrode, a current collector, and a substrate.

10. The solid electrolyte forming method of claim 9, wherein the grid is also electrically connected to at least one of the substrate, the current collector and the lithiated electrode.

11. The solid electrolyte forming method of claim 1, wherein the electric connection between the grid and at least the substrate holder is provided by a metal ring.

12. The solid electrolyte forming method of claim 1, wherein the electrolyte material is selected from the group consisting of LiPON, LiSiPON, and LiSON.

13. The solid electrolyte forming method of claim 3, wherein the grid is positioned at a distance in the range of 5 to 50 millimeters from the object.

14. The solid electrolyte forming method of claim 6, wherein the grid has a thickness from 5 to 50 micrometers.

15. The solid electrolyte forming method of claim 8, wherein the wires along a same direction are spaced apart by a distance of 2 millimeters.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates the structure of a prior art microbattery.

(2) FIG. 2 shows a prior art reactor of vacuum cathode sputtering deposition implementing the cathode sputtering technique.

(3) FIGS. 3a-d illustrate the steps of lithium depletion during the deposition of the electrolyte on a lithiated electrode according to prior art methods implementing the cathode sputtering technique.

(4) FIGS. 4a-c concern examples of structures of the grid used in the method of the present invention.

(5) FIG. 5 illustrates a device having a specific embodiment of the method according to the present invention implemented therein.

DETAILED DESCRIPTION OF THE INVENTION

(6) The method according to the invention uses a grid having a plurality of examples of its possible structures illustrated in FIGS. 4a, 4b, and 4c. However, such examples do not limit the present invention whatsoever.

(7) All three examples show a grid comprising wires extending along two substantially perpendicular directions.

(8) The grid structure may be the consequence of constraints particularly due to the geometry of the cathode of the cathode sputtering device. Indeed, the density, as well as the energy of the generated species, may vary according to the cathode of the device. The position of the object to be covered may also impact the deposition of the solid electrolyte.

(9) Such constraints are also present in the case of a cathode sputtering deposition of “magnetron sputtering” type, for which the cathode comprises a magnet.

(10) The grid shown by FIG. 4a has only one distance between wires whatever the wire direction. It is adapted to a device or reactor where the electric field lines create a homogeneous electronic charge density at the surface of the object to be covered with electrolyte.

(11) The grid shown in FIG. 4b is better adapted to a reactor where the field lines promote the forming of a heterogeneous electron density, at the center of the surface to be covered. The wires forming the grid are thus concentrated at the center of the grid. Accordingly, according to this embodiment, the spacing between two consecutive wires is not regular. The distance between wires may vary from its center to its edge, according to the geometry of the reactor.

(12) However, in the case where the density of charged species is greater on the edges of the surface to be covered, a grid of the type shown in FIG. 4c is preferable.

(13) The grid patterns advantageously reflect the created electron density. The grid thus enables to modulate the potential at the surface of the growing electrolyte layer so that it is the same as that of the opposite surface (in contact with the object).

(14) Accordingly, the grid enables to limit the accumulation of negative charges at the surface and thus to attenuate the lithium depletion.

(15) FIG. 5 shows a device enabling to implement a specific embodiment of the method which is the object of the present invention. In this device, the metal grid is electrically connected to the substrate holder by means of an electrically-conductive ring.

(16) This drawing concerns the preparing of a solid LiPON electrolyte, in a vacuum chamber (5), the object to be covered with LiPON electrolyte being positioned on a substrate holder (4).

(17) The object comprises, towards the substrate holder, a lithiated electrode (3), a metal current collector (2), and a substrate (1).

(18) The substrate may advantageously be made of single-crystal silicon, of metal such as titanium, stainless steel, or of polymeric nature (polyimide, PEN).

(19) The metallic current collector may advantageously be made of a titanium, tungsten, platinum, or copper layer.

(20) The lithiated electrode (3) is made of a material comprising lithium (3).

(21) The substrate holder (4) and the object (electrode (3)) are electrically connected by means of a metal ring (6) in order to provide an electric continuity between the ring (6) and the metal current collector (2).

(22) A metal grid (7) is attached/connected to this ring (6) to provide an electric continuity between the two parts. The latter is made of 316L-type stainless steel. It has a 2-mm square mesh, that is, a distance between wires of 2 mm along two perpendicular directions. The thickness of the 316L stainless steel wire is 200 μm.

(23) The grid is positioned at a 1.5-cm distance from the object to be covered with LiPON electrolyte.

(24) Simultaneously, a layer of target material of chemical composition Li.sub.3PO.sub.4 (8) is bonded to the cathode (9) of the reactor (5).

(25) The cathode is submitted to the application of an electric radio frequency field due to the use of an electric generator (10).

(26) Further, a pumping system (11) is connected to the deposition chamber (5) to be able to create vacuum.

(27) A gas injection system (12) enables to inject a controlled nitrogen flow into the chamber (5).

(28) A solid LIPON electrolyte is thus deposited on the lithiated electrode (3) while limiting or canceling the depletion phenomenon.