Catalytic carbonization of an uncarbonizable precursor by transition metals in olivine cathode materials of lithium ion batteries

Abstract

Herein, we report on catalytic effects of transition metals (Me) in phospho-olivines (LiMePO₄) on carbonization of cetyltrimethylammonium bromide (CTAB). Carbon coating is the required process to enhance electronic conductivity of phospho-olivines that are used as cathode materials for lithium ion batteries. Primary particles of phospho-olivines were in situ coated with CTAB and the adsorbed carbon precursor was carbonized to provide an electrically conductive pathway. CTAB was successfully carbonized in a significant amount with Fe in phospho-olivines (LiFe_xMn_1−xPO₄ with x = 1 and 0.5) even if CTAB is thermally decomposed around 300 °C without any residual mass in the absence of the phospho-olivines. LiMnPO₄ was the most inferior in terms of CTAB adsorption and thermal carbonization. LiNiPO₄ and LiCoPO₄ showed inefficient conversion of adsorbed CTAB to carbon even if their adsorption ability for CTAB is quite large. Also, the effect of the amount of carbon coating on LiFePO₄ was investigated, leading to a conclusion that the carbon thickness balanced between electronic and ionic conductances results in the best electrochemical performances of lithium ion batteries specifically at high discharge rates.