Method for Producing an Electrochemical Cell Comprising a Lithium Electrode, and Electrochemical Cell

Abstract

A method produces an electrochemical cell for a solid-state battery having a negative electrode, a positive electrode and a lithium-ion-conducting solid electrolyte arranged between the negative electrode and the positive electrode. The negative electrode has a layer of metallic lithium which directly adjoins the solid electrolyte. In order to produce the electrochemical cell, the layer of metallic lithium is heated until it softens before being joined together with the solid electrolyte. An electrochemical cell includes the negative electrode with a layer of metallic lithium which directly adjoins the solid electrolyte, and a layer of a lithium-metal alloy on the layer of metallic lithium.

Claims

1. A method for producing an electrochemical cell for a solid-state battery comprising a negative electrode with at least one layer of metallic lithium, a positive electrode and a lithium-ion-conducting solid electrolyte arranged between the negative electrode and the positive electrode, the method comprising the steps of: providing the negative electrode; providing the positive electrode; providing a substrate composed of the solid electrolyte with a first surface and a second surface that that is opposite the first surface; joining together of the substrate with the positive electrode on the first surface and the negative electrode on the second surface, so that the solid electrolyte lies between the negative electrode and the positive electrode and the layer of metallic lithium is opposite the second surface, wherein the layer of metallic lithium, before being joined together with the substrate, is heated until it softens on at least one surface opposite the second surface of the substrate.

2. The method as claimed in claim 1, wherein heating of the layer of metallic lithium is carried out by induction heating, heating with a heating device, hot gas, or heated rollers.

3. The method as claimed in claim 1, wherein the layer of metallic lithium is heated to a temperature of at least 60 C.

4. The method as claimed in claim 1, wherein the layer of metallic lithium is heated to a temperature of at least 120 C.

5. The method as claimed in claim 1, wherein the layer of metallic lithium is heated until at least a part of the metallic lithium melts.

6. The method as claimed in claim 5, wherein the layer of metallic lithium is melted only over a part of the layer thickness.

7. The method as claimed in claim 1, wherein the negative electrode has a layer thickness of 0.001 mm to 1 mm.

8. The method as claimed in claim 1, wherein the negative electrode is composed of a layer stack with the layer of metallic lithium and a layer of a lithium-metal alloy.

9. The method as claimed in claim 8, wherein the layer of the metallic lithium in the layer stack has a thickness of 0.00001 to 0.9 mm.

10. The method as claimed in claim 9, wherein the layer of the metallic lithium in the layer stack has a thickness of 10 nm to 1 m.

11. An electrochemical cell for a solid-state battery, comprising: a negative electrode; a positive electrode; and a lithium-ion-conducting solid electrolyte arranged between the negative electrode and the positive electrode, wherein the negative electrode comprises a layer of metallic lithium that is directly adjacent to the solid electrolyte and a layer of a lithium-metal alloy on the layer of metallic lithium.

12. The electrochemical cell as claimed in claim 11, wherein the metal of the lithium-metal alloy is selected from the group consisting of: indium, aluminum, silicon, magnesium, germanium, gallium, and combinations thereof.

13. The electrochemical cell as claimed in claim 11, wherein the lithium-metal alloy is composed of the metal in an amount of 0.00001 to 30 wt %, with the remainder being lithium and unavoidable impurities.

14. The electrochemical cell as claimed in claim 11, wherein the lithium-metal alloy comprises the metal in an amount of 0.0001 to 10 wt %.

15. The electrochemical cell as claimed in claim 11, wherein the lithium-metal alloy comprises the metal in an amount of 0.001 to 2 wt %.

16. The electrochemical cell as claimed in claim 11, wherein no further metal layer is applied to the layer of the lithium-metal alloy.

17. The electrochemical cell as claimed in claim 11, wherein a further metal layer is applied to the layer of the lithium-metal alloy as a current conductor.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0033] FIG. 1 is a schematic structure of an electrochemical cell according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWING

[0034] The electrochemical cell 10 or solid-state battery shown in FIG. 1 comprises a negative electrode 12, a positive electrode 14, and a lithium-ion-conducting solid electrolyte 16 arranged between the negative electrode 12 and the positive electrode 14. The negative electrode 12 and the positive electrode 14 are arranged on opposite surfaces 18, 20 of the solid electrolyte 16.

[0035] The solid electrolyte 16 is preferably composed of oxide or sulfide lithium ion conductors. As an active material for the positive electrode 14, transition metal oxides such as Li(Ni.sub.1/3Co.sub.1/3Mn.sub.1/3)O.sub.2 or conversion materials such as FeF.sub.3 are preferably used. The current conductor 20 provided on the positive electrode 14 is preferably composed of aluminum.

[0036] The negative electrode 12 comprises a layer of metallic lithium 24 that directly adjoins the solid electrolyte 16. Preferably, high-purity metallic lithium with a degree of purity in the range of 99.8-99.9% is used. A layer of a lithium-metal alloy 26 is arranged on the layer of metallic lithium 24. The entire layer thickness of the negative electrode composed of the lithium layer 24 and the layer of the lithium-metal alloy 26 is preferably 0.001 mm to 1 mm.

[0037] The metal of the lithium-metal alloy can be selected from the group composed of indium, aluminum, silicon, germanium and gallium and combinations thereof, and may be present in an amount of 0.00001 to 30 wt %.

[0038] In the embodiment shown here, the layer of the lithium-metal alloy 26 serves simultaneously as a current conductor for the negative electrode 12 and as a lithium source.

[0039] In order to produce the electrochemical cell 10 comprising a negative electrode 12 containing metallic lithium, a film of high-purity lithium is provided. The lithium film is heated on one side, for example using an induction heater, heated rollers, or hot air. This causes the metallic lithium to be softened or locally melted over a portion of the film thickness.

[0040] In the next step, the heated lithium film is pressed onto the solid electrolyte 16 or a prefabricated stack composed of the solid electrolyte 16 and the positive electrode 14 and optionally a current conductor 22 for the positive electrode 14, wherein the heated or molten part of the lithium film is opposite the solid electrolyte 16. In this manner, the lithium film and the solid electrolyte 16 are firmly connected to each other. The high-purity lithium is softened by heating and conforms to the brittle and rough solid electrolyte so that the contact with the solid electrolyte is improved and the interface resistance is reduced.

[0041] Instead of the lithium film, one can also use a layer stack with a layer of a lithium-metal alloy 26 and a layer of high-purity lithium 24. The heat source is then arranged on the side of the layer stack on which the metallic lithium 24 is located. In this manner, one obtains an electrochemical cell as shown in FIG. 1 in which the layer of the lithium-metal alloy 26 can simultaneously serve as a current conductor. Optionally, a conventional current conductor, for example of copper or nickel, can be applied to the layer of the lithium-metal alloy (not shown).

[0042] Multiple electrochemical cells produced in this way are bundled by a conventional method into blocks, electrically connected to one another, and encapsulated in a housing to form a solid-state battery. The solid-state battery can be used as a primary or secondary (rechargeable) battery. Particularly preferred is use in motor vehicles with hybrid or electric drive or as a stationary energy storage unit.

[0043] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.