Battery cell and method of operating the same

Abstract

A battery cell includes a negative electrode and a positive electrode. The battery cell also contains a thermally expandable graphite intercalation compound.

Claims

1. A battery cell, comprising: a negative electrode; a positive electrode; and a thermally expandable graphite intercalation compound configured to expand within the battery cell when exposed to a predefined temperature.

2. The battery cell according to claim 1, wherein the thermally expandable graphite intercalation compound does not comprise lithium intercalates.

3. The battery cell according to claim 1, wherein at least one of the positive electrode and the negative electrode contains the thermally expandable graphite intercalation compound.

4. The battery cell according to claim 1, wherein the thermally expandable graphite intercalation compound contains: an alkali metal or an alkaline earth metal; and at least one of ytterbium and europium.

5. The battery cell according to claim 1, wherein the thermally expandable graphite intercalation compound contains a halide.

6. The battery cell according to claim 1, wherein the thermally expandable graphite intercalation compound contains at least one of a hexafluorophosphate, a hexafluoroarsenate, a perchlorate, a hydrogensulfate, a nitrate and sulfur trioxide.

7. The battery cell according to claim 5, wherein the halide is at least one of iron chloride and copper chloride.

8. The battery cell according to claim 1, wherein the thermally expandable graphite intercalation compound comprises an organometallic compound having at least one of the chemical formulas Cs(C.sub.2H.sub.4)C.sub.24, Ba(NH.sub.3).sub.2.5C.sub.10.9, K(NH.sub.3).sub.4.3C.sub.24, RbN.sub.2—C.sub.24, KN.sub.2—C.sub.24, and K(C.sub.4H.sub.8O).sub.2C.sub.24.

9. The battery cell according to claim 1, wherein the thermally expandable graphite intercalation compound is converted into expanded graphite at a temperature that is greater than 150° C.

10. A method of operating a battery cell having a negative electrode and a positive electrode, the method comprising: producing expanded graphite from a thermally expandable graphite intercalation compound that is contained within at least one of the positive electrode and the negative electrode by heating the thermally expandable graphite intercalation.

11. A battery module, comprising: at least one battery cell, including: a negative electrode; a positive electrode; and a thermally expandable graphite intercalation compound configured to expand within the battery cell when exposed to a predefined temperature.

12. The battery cell according to claim 1, wherein the battery cell is configured for use in at least one of battery-operated vehicles and energy technology.

13. The battery cell according to claim 5, wherein the halide is a metal halide.

14. The battery cell according to claim 1, wherein the thermally expandable graphite is provided as a layer between the negative electrode and the positive electrode.

15. The battery module according to claim 11, wherein the thermally expandable graphite is provided as a layer between the negative electrode and the positive electrode.

16. The method according to claim 10, wherein producing expanded graphite from a thermally expandable graphite intercalation compound comprises: producing an expanded graphite layer on an area of an electrode facing away from a power outlet lead of the electrode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The figures show advantageous embodiments of the present disclosure and these are explained further in the following description of the figures. The figures show:

(2) FIG. 1: the schematic cross section of an electrode of a battery cell according to the disclosure as per a first embodiment of the present disclosure and

(3) FIG. 2: a schematic depiction of a plan view onto an electrode of a battery cell according to the disclosure as per a second embodiment of the present disclosure.

DETAILED DESCRIPTION

(4) FIG. 1 shows a battery cell 10 according to the disclosure as per a first embodiment of the present disclosure. This comprises, for example, a housing 12 which is shown in sections and is made, for example, of a polymer or a metal. The battery cell 10 comprises a first electrode 14 which represents, for example, an anode of the battery cell 10. The first electrode 14 is, for example, positioned on a copper foil as power outlet lead 16. A protective layer 18 containing a thermally expandable graphite intercalation compound has, for example, been applied to the large area of the first electrode 14 facing away from the power outlet lead 16. The general method of preparing thermally expandable graphite intercalation compounds is described, for example, in W. Zheng, S. C. Wong “Electrical conductivity and dielectric properties of PMMA/expanded graphite composites” Composites Science and Technology 63 (2003), pp. 225-235. As intercalates for thermally expandable graphite intercalation compounds, it is possible to use, in particular, cations such as alkali metal cations of sodium, potassium, cesium or barium and also cations of the alkaline earth metals strontium, barium and calcium and also cations of the rare earth metals ytterbium and europium. Graphite intercalates of lithium ions, which are usually formed in the region of the anodes of lithium ion cells and can also be additionally formed here are not encompassed by this definition.

(5) Further suitable intercalates for thermally expandable graphite intercalation compounds are halides, with metal halides such as iron chloride or copper chloride being particularly suitable. Further possible anions as intercalates are hexafluorophosphates, hexafluoroarsenates, perchlorates or hydrogensulfates. Sulfur trioxide as gas is also a suitable possible intercalate.

(6) In addition, organometallic compounds such as Cs(C.sub.2H.sub.4)—C.sub.24, Ba(NH.sub.3).sub.2.5, —C.sub.10.9, K(NH.sub.3).sub.4.3—C.sub.24, RbN.sub.2—C.sub.24, KN.sub.2—C.sub.24 and/or C.sub.xFeCl.sub.3—CH.sub.3NO.sub.2 are suitable as possible thermally expandable graphite intercalation compounds.

(7) The thermally expandable graphite intercalation compound used according to the disclosure displays decomposition of the corresponding intercalate at elevated temperature, whereupon an increase in volume of the thermally expandable graphite intercalation compound occurs so that this is present as thermally insulating and electrically insulating thermally expanded graphite. In this way, electric short circuits and a thermal runaway reaction of battery cells can be effectively prevented. The respective temperature at which thermal expansion of the thermally expandable graphite intercalation compound occurs can be controlled via the type of intercalate. Thus, for example, graphite oxidized by means of sulfuric acid in the form of a graphite hydrogensulfate decomposes above 150° C. and graphite oxidized by means of nitric acid in the form of graphite nitrate decomposes above 210° C.

(8) In an alternative embodiment, the protective layer 18 can, in addition or as an alternative, be applied to a second electrode (not shown in FIG. 1) of the battery cell 10.

(9) FIG. 2 shows a battery cell 10 as per a second embodiment of the present disclosure. This comprises, within the housing 12, a first electrode 14 in the form of an anode which has on its surface a protective layer 18a in the form of individual areal segments, for example areal segments which are not joined to one another, containing a thermally expandable graphite intercalation compound. The particular advantage of this embodiment is that a protective layer 18a consisting merely of areal segments results in a lower electrical resistance against charge transfer between the first electrode 14 and a further electrode (not shown) of the battery cell 10. If a heat-related expansion of the protective layer 18a made up of areal segments occurs, an essentially full-area covering of the large area of the electrode 14 with expanded graphite is nevertheless achieved purely because of the increasing volume of the expanded graphite.

(10) During operation of the battery cell 10, the thermally expandable graphite intercalation compound present in the protective layer 18 is initially present in an electrically conductive form. If a short circuit or excessive overheating occurs during operation of the battery cell 10, decomposition of the intercalates present in the thermally expandable graphite intercalation compound occurs as a result of thermal activation and the formation of expanded graphite on the surface of the first electrode 14 follows. Since expanded graphite is both thermally and electrically insulating, subsequent damage caused by the electric short circuit or a thermal runaway reaction in the battery cell 10 is avoided.

(11) The battery cell 10 according to the disclosure can be used, for example, in the form of battery modules in mobile and stationary applications such as hybrid or electric vehicles and for the storage of electric energy in stationary applications.