Phase field modelling of LLZO/LCO cathode-electrolyte interfaces in solid state batteries

This work describes two phase field models for the simulation of the interface evolution between a LiCoO2 cathode (LCO) and a Li7La3Zr2O12 solid electrolyte (LLZO) in a Li-metal/LLZO/LCO battery during high temperature sintering. In these conditions atomic species tend to diffuse into the opposing material, creating an intermediate layer of mixed composition which resists the movement of lithium ions. This undesired effect prevents the resulting solid-state battery to achieve its theoretical performances and needs to be avoided. The first model is an adaptation of the work of J. M. Hu et alii [1] for a similar interface problem encountered between yttria-stabilized zirconia electrolytes (YSZ) and lanthanum-strontium-manganite cathodes (LSM) in solid oxide fuelcells (SOFC), while the second is based on the work of D. A. Cogswell [2][3] for phase separation in metal alloys, extended to include electrostatic effects due to internal charge unbalances and externally applied electric fields. Animplementation of the latter is however lacking, and the interested reader is encouraged to build one up on the theoretical framework presented in this paper. In the conclusion section it is possible to find insights on how to prevent the interfacial diffusion between LCO and LLZO with reference to experimental attempts and simulations, as well as future directions for the development of the models