Variation of Li Diffusion Coefficient during Delithiation of Spinel LiNi0.5Mn1.5O4
Ahmad Syahmi Rahim, M. Z. Kufian, A.K. Arof, Z. Osman
Abstract
For this study, the sol gel method was used to synthesize the spinel LiNi0.5Mn1.5O4 (LNMO) electrode material. Structural, morphological, electrochemical, and kinetic aspects of the LNMO have been characterized. The synthesized LNMO was indexed with the Fd3̄m cubic space group. The excellent capacity retention indicates that the spinel framework of LNMO has the ability to withstand high rate charge-discharge throughout long cycle tests. The Li diffusion coefficient (DLi) changes non-monotonically across three orders of magnitude, from 10−9 to 10−12 cm2 s−1 determined from GITT method. The variation of DLi seemed to be related to three oxidation reactions that happened throughout the charging process. A small dip in DLi at the beginning stage of Li deintercalation is correlated with the oxidation of Mn3+ to Mn4+. While two pronounced DLi minima at 4.7 V and 4.75 V are due to the oxidation of Ni2+/Ni3+ and Ni3+/Ni4+ respectively. The depletion of DLi at the high voltage region is attributed to the occurrence of two successive phase transformation phenomena.