UC Berkeley

Lithium (Li) batteries comprising multivalent positive active materials such as copper vanadium oxide have high theoretical capacity. These batteries with a conventional liquid electrolyte exhibit limited cycle life because of copper dissolution into the electrolyte. We report here on the characterization of solid-state Li metal batteries with a positive electrode based on α-Cu6.9V6O18.9 (α-CuVO3). We replaced the liquid electrolyte by a nanostructured solid block copolymer electrolyte comprising of a mixture of polystyrene-b-poly(ethylene oxide) (SEO) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt. In situ X-ray diffraction was used to follow the Li insertion/de-insertion mechanism into the α-CuVO3 host material and its reversibility. In situ X-ray scattering revealed that the multistep electrochemical reactions involved are similar in the presence of liquid or solid electrolyte. The capacity fade of the solid-state batteries is less rapid than that of α-CuVO3-Li metal batteries with a conventional liquid electrolyte. Hard X-ray microtomography revealed that upon cycling, voids and Cu-rich agglomerates were formed at the interface between the Li metal and the SEO electrolyte. The void volume and the volume occupied by the Cu-rich agglomerates were independent of C-rate and cycle number.