Li-Doped Layered Na 1.0 Cu 0.22 Fe 0.30 Mn 0.48 O 2 Cathode with Enhanced Electrochemical Performance for Sodium-Ion Batteries

The introduction of copper (Cu) element to iron-manganese-based layered cathode materials can effectively enhance their cycling stability and air tolerance. However, the low redox reactivity of Cu 2+ decreases the capacity of the copper-iron-manganese layered oxide cathode material. Recently, lithium (Li) doping has been regarded as an efficient strategy to exploit high-capacity cathode materials by enabling high-covalency transition metals. Here, we report a Na 1.0 Li x Cu 0.22 Fe 0.30 Mn 0.48 O 2 ( x = 0.025, 0.05, 0.075) cathode material with increased capacity by adding Li into a Na 1.0 Cu 0.22 Fe 0.30 Mn 0.48 O 2 cathode via a simple solid-phase sintering method. The doped Li element can regulate the redox reactivities of the adjacent Fe and Mn elements, leading to the promotion of the Fe redox reactivity and the suppression of Mn redox reactivity, which prevents both the Jahn–Teller effect and the structure collapse during the charge/discharge process. In conclusion, Li doping can not only improve the capacity of the cathode material but also improve its stability. When x = 0.075, the capacity of Na 1 Li 0.075 Cu 0.22 Fe 0.30 Mn 0.48 O 2 cathode can reach 114.2 mAh g −1 with a high capacity retention of 90.2% after 300 cycles at 1 C. These results shed light on the role play of Li in the transition metal layer, and can guide the design and modification for high-performance SIBs of layered materials.