Na-stabilized Ru-based lithium rich layered oxides with enhanced electrochemical performance for lithium ion batteries

Lithium-rich layered oxides have being regarded as one of the most promising cathodes for next generation high energy density lithium ion batteries due to their extremely high capacity beyond 250 mAh g−1. Among which, Ru-based lithium-rich layered oxides attract special research interests recently for their relatively low irreversible capacity loss during initial cycle and good rate performance. However, as a typical Ru-based lithium-rich layered oxides, Li2RuO3 suffers severely from poor cycling stability and huge voltage decay upon prolonged cycling. Here, we propose a mono-valence cationic substitution strategy of Na+ ions into Li2RuO3 lattice to form Li2-xNaxRuO3 (x = 0, 0.02, 0.06, 0.1) series and systematically investigate their electrochemical properties. The results show that Na+ substitution significantly enhance electrochemical performance of Li2RuO3. Specifically, Li1.94Na0.06RuO3 exhibits the best cycling stability, possessing capacity of over 220 mAh g−1 after 50 cycles at 1C rate and retaining energy density of 673 Wh kg−1 after 50 cycles at 0.2C rate. Li1.9Na0.1RuO3 displays the least voltage decay with only 61 mV after 50 cycles compared with 228 mV for Li2RuO3. The Na-doped Li2RuO3 samples in this work are leading the electrochemical performance of all ever reported Ru-based lithium-rich layered oxides previously, providing a new scope for the strategy to rationally design high-performance lithium-rich layered oxides with balanced cycling stability and voltage maintainance.