A kinetic study of electrochemical lithium insertion in nanosized rutile β-MnO2 by impedance spectroscopy

The kinetics of the electrochemical lithium insertion reaction in nano-sized rutile β-MnO2 has been investigated using ac impedance spectroscopy. The experimental kinetic data are obtained for a rutile compound synthesized by ball-milling the powder produced from the heat treatment of manganese nitrate salts. The results are discussed as a function of the Li content for 0 < x < 0.6 and the number of cycles in the 4.1-2 V window. From a comparison with data obtained on the micro-sized oxide, an improved kinetics is found with DLi values for the apparent chemical diffusion coefficient of lithium much higher by one order of magnitude than in microsized oxide. Impedance behaviour of the ball-milled rutile β-MnO2vs cycles demonstrates a new system takes place from the second cycle, characterized by a significant improvement of Li diffusion by a factor 5 and a cathode impedance which decreases by a factor 2, remaining thereafter unchanged during cycling.