High Li-ion diffusion coefficient in LiMn_1.5Ni_0.5O₄ thin films for all-solid Li-ion battery applications

Among various choices of high-performance cathode materials, Ni substituted LiMn2O4 spinel LiMn1.5Ni0.5O4 (LMNO) has proved to be one of the solutions to yield a high-performance and high-energy density material, which can operate at a higher potential window. This study explores the high diffusion coefficient and electrochemical performance at wide current rates of LMNO thin films with less than 50 nm thickness, fabricated on SrTiO3 and SS substrates by the pulsed laser deposition method. The LMNO film with less thickness and the performance without binder and conducting carbon widen the Li-ion path and decrease diffusion length, resulting a higher diffusion coefficient on the order of 10(-5) to 10(-6) cm(2)/s, which is several orders higher than the previously obtained reports for bulk counterpart. The cycling stability and rate capability at different current densities of LMNO thin film electrodes are further investigated. Charge-discharge profile at varying current rates of 5, 10, 15, 20, 25, 50, 75, 100, and 125 mA/cm(2) is obtained for 500 cycles. The as fabricated film shows a stable profile for 500 cycles with 1.3 and 2.3 mu A h/cm(2) areal discharge capacity at 25 and 5 mA current rates, respectively. Electrode interfacial properties of LMNO film (before and after cycles) are analyzed using impedance technique. This study indicates that the LMNO thin films can be employed as a cathode layer for fabricating the all-solid thin film batteries for energy applications.