Aluminum-doped lithium nickel cobalt oxide electrodes for high-power lithium-ion batteries

Non-doped and aluminum-doped LiNi0.8Co0.2O2 cathodes from three industrial developers coupled with graphite anodes were made into lithium-ion cells for high-power applications. The powder morphology of the active cathode materials was examined by a scanning electron microscope. The electrochemical performance of these cells was investigated by hybrid pulse power characterization (HPPC) testing, accelerated aging, and AC impedance measurement of symmetric cells. Although all of the fresh cells are found to meet and exceed the power requirements set by PNGV, the power capability of those cells with non-doped LiNi 0.8Co0.2O2 cathodes fades rapidly due to the rise of the cell impedance. Al-doping is found very effective to suppress the cell impedance rise by stabilizing the charge-transfer impedance on the cathode side. The stabilization mechanism may be related to the low average oxidation state of nickel ions in the cathode. The powder morphology also plays a secondary role in determining the impedance stabilization.