On the electrochemical behavior of Li insertion electrodes

This paper describes several general phenomena which relate to Li insertion electrodes. The theme of this work was to look for common denominators in the electrochemical behavior of a variety of Li insertion electrodes, both anodes and cathodes. Taking into account the fact that these are composite electrodes containing active mass in additives (binder, conducting powder), we studied the role of the electrodes' structure vs. the intrinsic properties of the active mass in determining their performance. We found common models which fit a wide variety of Li insertion electrodes. An important point that was explored was the importance of Li insertion via formation of solid solution or via phase transitions in terms of capacity, stability and rate. We also found common failure mechanisms for both anodes and cathodes. These involve the formation of inactive interphase at the boundary between the active mass and the solution, which considerably slows down the electrodes' kinetics. Hence, the electrodes cannot be fully utilized, due to kinetic limitations. The tools for this study included surface sensitive FTIR, EDAX, XPS, in situ XRD, BET (surface area determination), SEM, impedance spectroscopy, slow scan rate CV, chronopotentiometry and PITT (chemical diffusion coefficient vs. E, X).