LITHIUM ION BATTERY

Abstract

A lithium ion battery includes a plurality of cells, each comprising a positive electrode, a negative electrode and an electrolyte. The electrolyte includes a lithium salt and contacts the positive and the negative electrode. The lithium ion battery includes a heating layer made of a PTC polymer. In another embodiment, a lithium ion cell includes an electrolyte comprising a lithium salt, a positive electrode in contact with the electrolyte, a negative electrode in contact with the electrolyte, and a heating layer made of a PTC polymer.

Claims

1. A lithium ion battery, comprising: a plurality of cells, each cell comprising a positive electrode, a negative electrode and an electrolyte; wherein the electrolyte comprises a lithium salt and contacts the positive and the negative electrode; and a heating layer made of a PTC polymer.

2. The lithium ion battery according to claim 1, wherein the PTC polymer is a mixture comprising carbon black particles and a polymer.

3. The lithium ion battery according to claim 2, wherein the polymer is a thermoplastic polymer.

4. The lithium ion battery according to claim 2, wherein the polymer is polyethylene or polyvinylidene flouride.

5. The lithium ion battery according to claim 1, wherein the heating layer is provided on each cell.

6. The lithium ion battery according to claim 5, wherein a first side of each cell is covered by the heating layer and a second side of each cell is free of the heating layer.

7. The lithium ion battery according to claim 5, wherein each cell comprises a container in which the electrolyte is arranged, the heating layer being arranged on a surface of the container.

8. The lithium ion battery according to claim 5, wherein the PTC polymer is arranged on at least one of the electrodes of each cell.

9. The lithium ion battery according to claim 1, wherein a plurality of cells is arranged in a casing and the heating layer is arranged on a surface of the casing.

10. The lithium ion battery according to claim 1, wherein the PTC polymer has a low temperature crystalline state and a high temperature amorphous state, and wherein the PTC polymer changes from the low temperature state to the high temperature state in a temperature range between 40° C. and 130° C.

11. The lithium ion battery according to claim 1, wherein terminals for applying a voltage to the PTC polymer are buried in the PTC polymer.

12. A lithium ion cell, comprising: an electrolyte comprising a lithium salt; a positive electrode in contact with the electrolyte; a negative electrode in contact with the electrolyte; and a heating layer made of a PTC polymer.

13. The lithium ion cell according to claim 12, wherein the cell is a pouch cell.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings illustrate the invention. In such drawings:

[0016] FIG. 1 shows schematically an embodiment of a lithium ion battery with a heating layer made of a polymer PTC;

[0017] FIG. 2 shows schematically an embodiment of a lithium ion cell with a heating layer made of a polymer PTC; and

[0018] FIG. 3 shows schematically another embodiment of a lithium ion cell with a heating layer made of a polymer PTC.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] FIG. 1 shows a lithium ion battery comprising a positive electrode 1, a negative electrode 2, a casing 3 containing an electrolyte, e.g. a lithium salt in an organic solvent, and a heating layer 4 provided as PTC polymer. The lithium salt may be lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate monohydrate (LiAsF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), or lithium triflate (LiCF3SO3), for example.

[0020] In the embodiment shown, the PTC polymer heating layer 4 is provided on an outer surface of the casing 3. Another possibility is to provide the PTC polymer heating layer 4 on an inside surface of the casing 3. A PTC polymer heating layer on an inner surface of the casing may offer the advantage of improved thermal coupling. A PTC polymer heating layer on an outer surface of the casing may offer the advantage of an easy electrical connection of the PTC polymer heating layer.

[0021] The terminals for applying a voltage to the PTC polymer heating layer 4 may be made of sheet metal on top and below the PTC polymer heating layer 4. Heating current will then flow in a direction perpendicular to the PTC polymer heating layer 4. Another possibility is to bury one or several conductors in the PTC polymer heating layer 4 to provide a terminal. Heating current will then flow lengthwise within the plane of the PTC polymer heating layer 4.

[0022] It is possible to apply the PTC polymer heating layer 4 on opposing sides of the casing 3. Thereby heating power can be increased. There may be separate PTC polymer heating layers on different sides of the casing 3 or a single layer that may circumvent the lithium ion battery or cell. In the embodiment shown, the PTC polymer heating layer 4 is applied only on one of the sides of the casing 3 so that the opposite side of the casing is available for cooling the battery or cell.

[0023] In FIG. 1, the casing 3 is a cuboid or more generally a prism. However, the casing may also have any other shape.

[0024] FIG. 2 shows a lithium ion cell comprising a cylindrical body. Electrodes 1, 2 are sheets. A lithium salt comprising electrolyte is present inside the body. The electrolyte may be a liquid that is enclosed a container or a polymer. The PTC polymer heating layer 4 is applied on the outside of the cell, but may also be applied on the inside. In the embodiment shown, the PTC polymer heating layer 4 covers about half of the lateral surface of the cell.

[0025] FIG. 3 shows a pouch cell comprising a pouch, e.g. container made of flexible film or foil, wherein an electrolyte and electrodes are arranged. The electrolyte may be a lithium salt in a solvent or in a polymer. Foil tabs are connected, e.g. by soldering or welding, to the electrodes and brought to the outside in a fully sealed way.

[0026] A plurality of cells can be connected to form a battery or lithium ion accumulator.

[0027] Although several embodiments have been described in detail for purposes of illustration, various modifications may be made to each without departing from the scope and spirit of the invention. Accordingly, the invention is not to be limited, except as by the appended claims.