Suppression of Phase Transition in LiTb0.01Mn1.99O₄ Cathodes with Fast Li⁺ Diffusion

The structural characteristics of terbium-doped spinel LiTb(x)Mn(2-x)O(4) 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(x)Mn(2-x)O(4) 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)O(4)). 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)O(4) 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)O(4), which was similar to that of LiMn(2)O(4) at 1C (476.1 W·kg(-1) for LiMn(2)O(4) vs 487.0 W·kg(-1) for LiTb(0.01)Mn(1.99)O(4)), was greatly improved at higher C rates. For example, the power density of LiTb(0.01)Mn(1.99)O(4) was improved to 4000 and 6000 W·kg(-1) at 10 and 20, respectively, compared with 3120 and 3320 W·kg(-1) for pristine LiMn(2)O(4).