The structure and works of separation of LiFePO4/FePO4 interfaces, interfacial energies, and relevant surface energies are evaluated using ab initio calculations based on the density functional theory (DFT). The calculations concern various modes of separation of (100) and (010) interfaces which result in stoichiometric and non-stoichiometric surfaces. Corresponding interfacial fracture toughnesses are calculated based on the works of separation. The analysis reveals the most stable separation configurations and quantifies the cleavage energies. The findings can be used to explain the fracture behavior observed in experiments.