First-principles study of the impact of grain boundary formation in the cathode material LiFePO4

Motivated by the need to understand the role of internal interfaces in
Li migration occurring in lithium-ion batteries, a first-principles
study of a coincident site lattice grain boundary in LiFePO₄ cathode material and in its delithiated counterpart FPO₄
is performed. The structure of the investigated grain boundary is
obtained, and the corresponding interface energy is calculated. Other
properties, such as ionic charges, magnetic moments, excess free volume,
and the lifetime of positrons trapped at the interfaces are determined
and discussed. The results show that while the grain boundary in LiFePO₄ has desired structural and bonding characteristics, the analogous boundary in FePO₄ needs to be yet optimized to allow for an efficient Li diffusion study.