Hollandite cathodes for lithium ion batteries. 2. Thermodynamic and kinetics studies of lithium insertion into BaMMn7O16 (M = Mg, Mn, Fe, Ni)

The thermodynamics and kinetics of the lithium insertion reaction into holl andite oxides BaMMn7O16 (M = Mg, Mn, Fe, Ni) have been studied. The electro chemical lithium insertion was achieved using the oxide as the cathode at c urrent densities from 0.025 to 0.1 mA cm(-2), using 1 M LiClO4 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 en tropy as a function of the degree of insertion (x) were estimated from emf- temperature measurements in the range from 298 to 360 K. These thermodynami c parameters varied with the oxide composition and with the Li concentratio n in the oxide structure. The chemical diffusion coefficient for lithium D* in the hollandite and the electrical conductivity of the oxides were measu red as a function of the lithium composition. Both parameters decrease with x, the largest variation being observed around x = 1. The values of D*, me asured at 298 K, followed the order: Ni > Fe > Mg = Mn. The hollandite oxid es were characterized by X-ray diffraction analysis and magnetic susceptibi lity measurements as a function of temperature in the range 298-550 K which in turn allows postulation of each cationic distribution. BaNiMn7O16 inser ts almost 6 mol of lithium ions per mole of the oxide. (C) 2001 Elsevier Sc ience Ltd. All rights reserved.