Characterization of high-power lithium-ion cells during constant current cycling: Part I. Cycle performance and electrochemical diagnostics

Twelve cm2 pouch type lithium-ion cells were assembled with graphite anodes, LiNi0.8Co0.15Al0.05O2 cathodes and 1 M LiPF6/EC/DEC electrolyte. These pouch cells were cycled at different depths of discharge (100 and 70% DOD) at room temperature to investigate cycle performance and pulse power capability. The capacity loss and power fade of the cells cycled over 100% DOD was significantly faster than the cell cycled over 70% DOD. The overall cell impedance increased with cycling, although the ohmic resistance from the electrolyte was almost constant. From electrochemical analysis of each electrode after cycling, structural and/or impedance changes in the cathode are responsible for most of the capacity and power fade, not the consumption of cycleable Li from side-reactions.