Synthesis of mixed ionic and electronic conducting garnet with doping of transition elements (Fe, Co, Ni)

Garnet structure electrolyte Li7La3Zr2O12 (LLZO) exhibits high ionic conductivity, high fracture toughness, and low strain during cycling. The mechanical stability of cathodes could be improved by an LLZO coating. Nevertheless, the electronic conductivity of LLZO is in the order of 10−9 S cm−1, and therefore the electron conduction of cathodes is blocked by the LLZO coating layer. The electronic conductivity is raised by doping variable valence elements (Fe, Co, Ni) into garnets. The doping has only a weak effect on the ionic conductivity, while the electronic conductivity is increased to 10−6 S cm−1. Co-doped sample exhibits the highest electronic conductivity of 2.75 × 10−6 S cm−1. The mixed conducting garnets could be used as the coating material of cathodes, and besides could reduce the interfacial resistance between cathodes and solid electrolyte in all-solid-state batteries.