Balancing the redox activity against structure stability in high-voltage manganese/iron-based layered oxide cathodes through copper doping for potassium-ion batteries

Earth-abundant manganese/iron-based layered oxide cathodes display high energy densities in cost-effective potassium-ion batteries, but still encounter severe structure distortions and irreversible phase transformations upon cycling. To ameliorate its structural stability , the highly electronegative but electrochemically inactive Cu 2+ is rationally introduced into Mn sites of P3-type K 0.5 Mn 0.8 Fe 0.2 O 2 cathode materials to regulate crystal structures and elemental valences toward a balance between redox activity and structure stability. Ranging from 4.2 to 1.5 V, the optimal K 0.5 Mn 0.7 Fe 0.2 Cu 0.1 O 2 cathode material with a lower formation energy and a narrower band gap could present a large initial discharging capacity of 91 mAh g −1 at 50 mA g −1 with an excellent capacity retention of 71.6 % over 50 cycles and a competitive capacity retention of 62.3 % at 100 mA g −1 after 100 cycles. Regardless of its compromised K + diffusion capabilities from a slightly contracted interlayer, a superior rate performance of 71 mAh g −1 can be achieved at 500 mA g −1 , implying a dominant function of structural stability in electrochemical depotassiation/potassiation. Additionally, the dynamic redox activities and high electrochemical reversibility of Mn 4+/3+ and Fe 4+/3+ couples are verified by ex-situ X-ray photoemission spectroscopies. This solid work would enlighten the novel structural manipulations of layered oxide cathodes for high-voltage potassium-ion batteries. • The highly electronegative but inactive Cu 2+ is doped into P3-type K 0.5 Mn 0.8 Fe 0.2 O 2 . • The structure stability and redox activity are simultaneously regulated in cathodes. • A superior rate capability of 71 mAh g −1 at 500 mA g −1 can be achieved. • The optimal material has a lower formation energy and a narrower band gap.