Electrode Performance of P3-type Na_0.6[Mn_0.9Me_0.1]O₂ (Me = Mn, Mg, Ti, Zn) as Lithium Intercalation Host (Supporting Information)

Designing positive electrode materials for Li-ion and Na-ion batteries without using expensive metals is of critical importance for sustainable energy storage systems. One of the most promising candidates, P3-type layered sodium manganese oxide (P3-Na_xMnO₂) can be obtained via solid-state reaction. While there is no report on P3-Li_xMnO₂ synthesis and electrochemistry because of its instability, lithium ion exchange with Na in P3-Na_xMnO₂ is a plausible strategy to test its Li insertion/extraction. In this study, we investigate the electrochemical activity of P3-Na_xMnO₂ electrode in both Li and Na cells. We found that high capacity of ca. 200 mAh/g is achieved in both cells, and P3-Na_xMnO₂ electrodes undergo spontaneous Na/Li ion exchange in the Li⁺-containing electrolyte, which can thereafter be reversibly cycled. To improve electrochemical performance, we demonstrated two approaches: partial Ti or other metal substitution for Mn in P3-Na_xMnO₂ and using a highly concentrated electrolyte of 5.5 mol dm⁻³ Li(N(SO₂F)₂) dimethyl carbonate solution. Particularly, the highly concentrated Li-electrolyte provides a significant enhancement on the cycle stability in the Li cell, demonstrating no apparent capacity loss up to 100 cycles.