Variation of Li Diffusion Coefficient during Delithiation of Spinel LiNi0.5Mn1.5O4

Abstract

For this study, the sol gel method was used to synthesize the spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) electrode material. Structural, morphological, electrochemical, and kinetic aspects of the LNMO have been characterized. The synthesized LNMO was indexed with the Fd3m 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 (D Li ) changes non-monotonically across three orders of magnitude, from 10 -9 to 10 -12 cm 2 s -1 determined from GITT method. The variation of D Li seemed to be related to three oxidation reactions that happened throughout the charging process. A small dip in D Li at the beginning stage of Li deintercalation is correlated with the oxidation of Mn 3+ to Mn 4+ . While two pronounced D Li minima at 4.7 V and 4.75 V are due to the oxidation of Ni 2+ /Ni 3+ and Ni 3+ /Ni 4+ respectively. The depletion of D Li at the high voltage region is attributed to the occurrence of two successive phase transformation phenomena.