Suppression of Phase Transition in LiTb_(0.01)Mn_(1.99)O4 Cathodes with Fast Li~+ Diffusion

摘要

The structural characteristics of terbium-doped spinel LiTb_xMn_(2-x)O4 related to the electrochemical performance were studied as the cathode in lithium-ion batteries. We chose terbium as the dopant, which is a well-known mixed-valent cation (~(3+)/4+), expecting that it would provide structural stabilization and improve the power density. LiTb_xMn_(2-x)O4 revealed that terbium doping significantly affected the lattice structure and lithium-ion diffusion during charge-discharge cycles, resulting in an enhanced capacity retention and rate capability at an extremely small amount of terbium doping (LiTb_(0.01)Mn_(1.99)O4). The absence of two-cubic phase formation in the delithiated state and a tetragonal phase in the overlithiated state, along with a reduced dimensional change of the main cubic phase during charge—discharge, provided LiTb_(0.01)Mn_(1.99)O4 with structural stability at both room temperature and 60 °C. The fast lithium-ion diffusion resulted in reduced polarization, which became more conspicuous as the C rates increased. As a result, the power density of LiTb_(0.01)Mn_(1.99)O4, which was similar to that of LiMn2O4 at 1C (476.1 W·kg~(-1) for LiMn2O4 vs 487.0 W·kg~(-1) for LiTb_(0.01)Mn_(1.99)O4), was greatly improved at higher C rates. For example, the power density of LiTb_(0.01)Mn_(1.99)O4 was improved to 4000 and 6000 W·kg~(-1) at 10 and 20, respectively, compared with 3120 and 3320 W·kg~(-1) for pristine LiMn2O4.