Preparation and High Temperature Electrochemical Performance of LiNi_0.08Mn_1.92O₄ Cathode Material of Submicron Truncated Octahedron

Abstract

The truncated octahedral LiNi0.08Mn1.92O4 (LNMO) cathode material with dominant {111}, truncated {110} and {100} crystal planes was prepared by a low temperature solid-state combustion method. The dominant {111} crystal plane of the unique truncated octahedron can form firm solid electrolyte interphase (SEI) layer and alleviate the manganese dissolution during the discharge-charge process, and a small part of {110} and {100} crystal planes can increase the rapid diffusion channels of Li ＋ ions. The field emission scanning electron microscope (SEM) and X-ray diffractometer (XRD) results show that LNMO has cubic spinel structure with submicron particle size. The electrochemical performances of LNMO are also outstanding at high temperature of 55 ℃, the initial discharge capacities are 109.9 and 98.0 mAh/g with capacity retentions of 75.8% and 80.5% after 300 cycles at 1 and 5 C, respectively. Even at high current rates of 10 and 15 C, the capacity retentions of 48.4% and 49.4% have been maintained after 1000 cycles, while the capacity loss of undoped LiMn2O4 is as high as 98% after 1000 cycles at 15 C. Moreover, the dynamic performance tests show that LNMO owns larger Li ＋ diffusion coefficient (D＝3.86×10 −15 cm 2 /s), smaller charge transfer resistances (before cycle and after cycles, the Rct＝158.0 and 279.8 Ω) and lower apparent activation energy (Ea＝17.63 kJ/mol) than LiMn2O4 (LMO), demostrate its enhanced Li ＋ transport dynamic. The XRD tests of two electrode slices after 1000 cycles at 10 C show that the crystal structure of LNMO electrode material is almost unchanged, which indicated that the Ni doping and the truncated octahedral structure of particles could improve the structural stability of material, effectively inhibit the Jahn-Teller effect and Mn dissolution, remarkably improve its high temperature electrochemical performance. Therefore, this work provides a reference for the application of spinel LiMn2O4 electrode material at high temperature.