Fully Reversible Homogeneous and Heterogeneous Li Storage in RuO 2 with High Capacity

In this paper, we report that Li can be stored in RuO 2 with an unusually high coulombic efficiency. The process involves three electrochemical steps: i) formation of a Ru/Li 2 O nanocomposite, ii) formation of a Li‐containing surface film, and iii) interfacial deposition of Li within the Ru/Li 2 O matrix. Corresponding to the storage of 5.6 mole of Li ions per mole of RuO 2 , a high capacity of 1130 mAh g –1 is achieved. Furthermore, virtually all inserted Li ions can be extracted, corresponding to a nearly 100 % coulombic efficiency at the first cycle. Achieving a complete reversibility for such a Li storage system through complex heterogeneous solid‐state electrochemical reactions is possible because of the formation of nanoscale Ru/Li 2 O during Li insertion and nano‐RuO 2 during Li extraction, in addition to the favorable transport properties of RuO 2 itself. A completely reversible Li storage in RuO 2 with a high capacity of 1130 mA h g –1 (see Figure) and a nearly 100 % coulombic efficiency at the first cycle is achieved through heterogeneous solid‐state electrochemical reactions. Such an unusually good performance is due to the nanostructures formed in situ and favorable transport properties of RuO 2 .