Strain-modulated Mn-rich layered oxide enables highly stable potassium-ion batteries

Mn-rich layered oxides show great promise as cathode materials for potassium-ion batteries due to their high capacity and cost-effectiveness. However, internal structural strain and irreversible phase transitions caused by Jahn-Teller distortion affect their cycling stability. Here, we present an efficient strategy to concurrently modulate the internal strain and suppress the irreversible phase transition in Mn-rich cathodes by incorporating amounts of zinc (Zn) ions into the transition metal layers. The substituted Zn serves to regulate local chemistry, thereby mitigating octahedral distortion in Mn-O bonds, relieving the strain between layers, and reducing the occurrence of P3-O3 phase transition under high voltages. These findings are supported by EXAFS, in situ X-ray diffraction, advanced transmission electron microscopy, electron tomography, and DFT simulations. The lowstrain K0.5Mn0.8Co0.1Zn0.1O2 electrode exhibits a high reversible capacity retention about -90 % (105 mAh g-1 at 100 mA g-1), exceptional rate performance in the voltage of 1.5 - 3.9 V, and a substantial capacity retention after 500 cycles. This strain-relieved approach broadens the scope of lattice engineering by addressing internal strain concerns and mitigating the strain associated with potassium (de)intercalation, thereby having potential to advance the development of stable cathodes for PIBs.