Bismuth phosphate: A novel cathode material based on conversion reaction for lithium-ion batteries

Highlights: •BiPO4 is initially reported as a cathode material for lithium-ion batteries. •We have explored that BiPO4 is a cathode material based on conversion reactions. •Its theoretical specific capacity and output voltage are 264.5 mA h g−1 and 3.14 V. •Its theoretical volumetric energy density is close to twice higher than LiCoO2. •Effects of the phase transformation on electrochemistry of BiPO4 are discussed. -- Abstract: Here, we provide a new scientific insight in the field of lithium-ion batteries, in which BiPO4 is initially reported as a cathode material based on conversion reaction. BiPO4 exists in three polymorphic phases, which have been synthesized using a room-temperature liquid precipitation route followed by heating treatment. The effects of phase transformation on electrochemical performances of BiPO4 have been investigated. Herein the hexagonal BiPO4 exhibits the best reversibility, rate capability and cycling stability. A conversion reaction has also been proved to occur in BiPO4 with reduction of BiPO4 into a metallic Bi0 phase and a Li3PO4 phase upon lithiation, and the reformation of BiPO4 phase during next charge process. Its theoretical specific capacity and theoretical output voltage are 264.5 mA h g−1 and ∼3.14 V, respectively. Especially, its theoretical volumetric energy density is as high as 5253.1 Wh L−1, close to twice higher than LiCoO2. Therefore, it is still worthy of further study for lithium-ion batteries