Electrochemical characterization of lithiated transition metal oxide cathode particles in the absence of carbon, binders and other additives

A novel method is herein described for the electrochemical characterization of lithiated transition metal oxides in powder form as cathode materials for lithium ion batteries. The procedure involves application of sufficiently high pressures to a layer of oxide powder evently dispersed on the surface of a Au foil so as to embed the particles into the soft metal substrate, thereby avoiding the use of carbon, binders and other additives. Implementation of this methodology for battery-grade LiMn₂O₄, LiCoO₂ and LiCo_0.15Ni_0.85O₂ particles supplied by various commercial sources yielded electrodes of excellent mechanical integrity displaying close to ideal cyclic voltammetric behavior in electrolytes of relevance to battery applications. The charge capacity of each of these compounds could be estimated quantitatively by dissolving the array of oxide particles in acid, once the electrochemical experiments were completed and then determining the amount of metal in the solutions by ICP-MS analysis. An analysis of voltammetric measurements as a function of scan rate yielded values of mean diffusion coefficients for Li in LiMn₂O₄ on the order of 5 × 10^-10 cm² s^-1.