Explaining the role and mechanism of carbon matrices in enhancing reaction reversibility of metal oxide anodes for high performance Li ion batteries

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Using NiO as a representative oxide, it is shown that the inter-particle electronic conductivity in lithium battery anodes can be drastically enhanced by additive carbon. Two types of carbon, Vulcan XC-72R and reduced graphene oxide (rGO), were added in various amounts ranging from 2.5 to 40 wt %. The conductivity boost is highly dependent on the carbon type, where rGO requires much less addition to realize the same effect due to its higher charge carrier concentration and charge carrier utilization efficiency. Half-cell charge discharge experiments were performed at various rates between C/5 and 5C, from which direct quantitative links are made between the active layer electronic conductivity and: i) reaction reversibility (achievable capacity); and ii) conversion kinetics (mechanism and rate capability). Through Tafel analysis and electrochemical impedance spectroscopy it is shown that enhanced conductivity does not affect the underlying reaction mechanism, but allows for more complete utilization of the active layer. These findings provide new insight into the design of high performing metal oxide-advanced carbon nanocomposite Li-ion battery anodes – and allowed us to achieve long-term stable capacity retention for NiO with 10% rGO (925 mAh/g after 250 charge/discharge cycles at 1C) and stable performance at high rates (600 mAh/g at 5C).