Electrochemical Oscillation during Galvanostatic Charging and Discharging of LiCrTiO4 in Li-Ion Batteries

As a well-known two-phase material, spinel Li4Ti5O12 has been widely studied and commercially applied in lithium-ion batteries, and its zero-strain phase transition derives some unique electrochemical phenomena such as memory effect and electrochemical oscillation. Due to the same spinel structure and redox element, the spinel LiCrTiO4 presents similar electrochemical properties including memory effect and electrochemical oscillation. However, electrochemical oscillation has not yet been observed during the discharge process of LiCrTiO4. In this study, spinel LiCrTiO4 was prepared by spray-drying in a vertical tube furnace and then sintered at a high temperature, which exhibits electrochemical oscillation during both charging and discharging. According to XPS, TEM, NMR, and in-situ XRD results, the nonstoichiometric Li1–xCr1–yTiO4 (x, y = 0.2, 0.1, and 0) samples possess a good spinel structure with partial Li ions at 16d sites and take a reversible two-phase transition between the spinel and rock-salt structures. In addition, a schematic diagram is proposed to interpret the electrochemical oscillation of LiCrTiO4, in which the nucleation and phase transition processes play the rate-determining step alternatively. Therefore, it is the first time the electrochemical oscillation is achieved during both charge and discharge of LiCrTiO4, and an alternative rate-determining step is proposed to elucidate the electrochemical oscillation, which offers an original perspective for understanding two-phase reactions and their derivative phenomena in lithium-ion batteries.