Investigation of positive electrodes after cycle testing of high-power Li-ion battery cells IV: An approach to the power fading mechanism by depth profile analysis of electrodes using glow discharge optical emission spectroscopy

Depth profile of constituent elements of positive electrodes in lithium-ion batteries was analyzed by using glow discharge optical emission spectroscopy (GD-OES) from the surface to the interface with the current collector. Not only in pristine electrode but also in degraded electrode after 50,000 cycles of high rate charge and discharge, almost homogeneous concentration profile of lithium was observed, suggesting that particles of active electrode material in the deep region inside the electrode layer also concerned in the electrochemical reaction as well as the particles in the surface area. From observation of particles shape by scanning electron microscope (SEM), remarkable cracks were not observed in particles inside the electrode even in the degraded electrodes.