Hollandite cathodes for lithium ion batteries. 2. Thermodynamic and kinetics studies of lithium insertion into BaMMn 7O 16 (M=Mg, Mn, Fe, Ni)

Abstract

The thermodynamics and kinetics of the lithium insertion reaction into hollandite oxides BaMMn 7O 16 (M=Mg, Mn, Fe, Ni) have been studied. The electrochemical lithium insertion was achieved using the oxide as the cathode at current densities from 0.025 to 0.1 mA cm −2, using 1 M LiClO 4 solution of PC and EC. The Ni compound inserts about three times more efficiently than the Mn compound. The changes of the partial molar enthalpy and the molar entropy as a function of the degree of insertion ( x) were estimated from emf–temperature measurements in the range from 298 to 360 K. These thermodynamic parameters varied with the oxide composition and with the Li concentration in the oxide structure. The chemical diffusion coefficient for lithium D* in the hollandite and the electrical conductivity of the oxides were measured as a function of the lithium composition. Both parameters decrease with x, the largest variation being observed around x=1. The values of D*, measured at 298 K, followed the order: Ni>Fe>Mg=Mn. The hollandite oxides were characterized by X-ray diffraction analysis and magnetic susceptibility measurements as a function of temperature in the range 298–550 K which in turn allows postulation of each cationic distribution. BaNiMn 7O 16 inserts almost 6 mol of lithium ions per mole of the oxide.