Facile synthesis and characterization of a SnO-modified LiNiMnO high-voltage cathode material with superior electrochemical performance for lithium ion batteries.

A thin-layer-SnO modified LiNiMnO@SnO material is synthesized via a facile synthetic approach. It is physically and electrochemically characterized as a high-voltage lithium ion battery cathode and compared to the pristine LiNiMnO material prepared under similar conditions. The two materials are proved to be crystals of a well-defined disordered spinel phase with the morphology of aggregates of micron/submicron polyhedral particles. The Mn ions and the inactive NiLiO phase in the LiNiMnO@SnO is less than those in the LiNiMnO due to incorporation of a very small amount of Sn into the spinel structure upon high-temperature calcination of the precursor. Besides, the mean particle size of the LiNiMnO@SnO is obviously smaller than that of the LiNiMnO. The LiNiMnO@SnO demonstrates much superior electrochemical performance over the LiNiMnO in terms of specific capacity, rate capability and cyclability. For example, the discharge capacities at current rates of 0.2C, 2C and 20C are 145.4, 139.9 and 112.2 mA h g, respectively. A capacity retention rate of ca. 75% is obtained after 500 cycles at 2C rate. The improved electrochemical performance is attributed to the positive effect of the surface protective SnO coating layer as well as the structural and morphological modifications of the spinel.