The mechanisms for Li diffusion in LixCo0.5Ni0.5O2 were investigated by using the galvanostatic intermittent titration technique. Membrane electrodes prepared with polyvinylidene fluoride and carbon black were used. The measured Brunauer–Emmett–Teller area of the LixCo0.5Ni0.5O2 powder was combined with the galvanostatic intermittent titration technique data to obtain the Li chemical diffusion coefficient, the Li self-diffusion coefficient (DLi+) and the thermodynamic factor as a function of Li concentration, x. All 3 parameters varied non-monotonically with x. A minimum in the chemical diffusion coefficient and DLi+ at x = 0.5, together with structural changes, suggested the formation of a Li superlattice at that concentration. The behavior of the chemical diffusion coefficient was complex but, for x < 0.34, it eventually underwent a continuous decrease due to the metallic character of LixCo0.5Ni0.5O2. The limitation of the specific reversible capacity of LixCo0.5Ni0.5O2 was attributed to this decrease in chemical diffusion coefficient, and to elevated electrode voltages. The Li transport in LixCo0.5Ni0.5O2 was analyzed taking account of variations in the cell parameters and the oxidation states of the Ni, Co and O ions.

The Role of Structural and Electronic Alterations on Lithium Diffusion in LixCo0.5Ni0.5O2. L.A.Montoro, J.M.Rosolen: Electrochimica Acta, 2004, 49[19], 3243-9