Development of core-shell structured metal oxide powders to be used as lithium ion battery cathode materials

Abstract

Lithium Manganese Oxide (LiMn2O4, LMO) (4.1 V, 148 mAh/g) and Lithium Nickel Manganese Oxide (Li2NiMn3O8, LMNO) (4.7 V, 148 mAh/g) are high voltage cathode materials aiming at high energy density battery applications like electric vehicles [1]. However, their applicability in actual devices is limited due to their low electrochemical stability with most of the commercial electrolytes at high potentials. The purpose of this research is to introduce a core-shell structure for the battery cathode using LM(N)O as the core and TiO2 as the shell material to prevent the electrolyte decomposition on the surface of the LM(N)O particles. A kinetics controlled coating technique [2] mainly based on hydrolysis and condensation reactions of titanium butoxide (TBOT) was used to initiate heterogenous nucleation and growth of TiO2 on commercial LM(N)O particles in an ethanol based environment. The effect of different synthesis parameters; such as the LM(N)O amount, the TBOT amount and the reaction time on the shell formation was examined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). SEM images revealed changes in surface morphology when compared to the bare, commercial LMO powders. Titanium and oxygen signals revealed by EDS also pointed out possible formation of a thin TiO2 layer on LMO particles. However, powder agglomeration was observed via SEM after coating process. To avoid agglomeration, studies were focused on increasing the zeta-potential value of the core particles by surface functionalization. Citric acid functionalized [3] LMNO particles revealed stable dispersions at a pH of 10 with a zeta-potential value of about -54 mV in aqueous medium while the non-functionalized LMNO particles revealed about -16 mV at the same pH. Effect of using the citric acid functionalized starting powders in the ethanol based actual shell synthesis medium is further to be investigated.

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