Layered P3-Type K_0.4Fe_0.1Mn_0.8Ti_0.1O₂ as a Low-Cost and Zero-Strain Electrode Material for both Potassium and Sodium...

Layered transition metal oxides are ideal Na⁺/K⁺ host materials due to their high theoretical capacities and appropriate working potentials, and the pursuit of cost-effective and environmentally friendly alternatives with high energy density and structural stability has remained a hot topic. Herein, we design and synthesize a low-cost and zero-strain cathode material, P3-type K_0.4Fe_0.1Mn_0.8Ti_0.1O₂, which demonstrates superior properties for both potassium and sodium storage. The cathode delivers a reversible potassium storage capacity of 117 mA h g^-1 at 20 mA g^-1 and a fast rate capability of 71 mA h g^-1 at 1000 mA g^-1. In situ X-ray diffraction reveals a solid-solution transition with a negligible volume change of 0.5% upon K⁺ insertion/deinsertion that ensures long cycling stability over 300 cycles. When the material is employed for sodium storage, a spontaneous ion-exchange process with Na⁺-containing electrolytes occurs. Thanks to the positive effects of the remaining K⁺ ions that protect the layered structure from collapse as well as expand the interlayer structure, and the resulting K_0.12Na_0.28Fe_0.1Mn_0.8Ti_0.1O₂ demonstrates a high sodium storage capacity of 160 mA h g^-1 and superior cycling stability with capacity retention of 81% after 300 cycles as well as fast kinetics.