An Optimized Approach Toward High Energy Density Cathode Material for K-Ion Batteries

Abstract Herein, we propose P’2-Kx[Ni0.05Mn0.95]O2 as a promising cathode material for high-energy-density potassium-ion batteries (KIBs). The P’2-K0.83[Ni0.05Mn0.95]O2 delivers a high discharge capacity of 155 mAh g−1 (52 mA g−1) as well as a high energy density of 420 Wh kg−1 in the voltage range of 1.5–4.3 V. Surprisingly, the fast K-ion migration in the P’2-K0.83[Ni0.05Mn0.95]O2 structure with a low activation barrier energy of ∼271 meV enables achievement of high capacity at high currents, 78 mAh g−1 at 2600 mA g−1, as well as long-term cycling stability with capacity retention of ∼77% after 500 cycles at 520 mA g−1. Operando synchrotron X-ray diffraction analysis reveals that P’2-K0.83[Ni0.05Mn0.95]O2 retains the P’2-phase without P’2-OP4 phase transition during charge/discharge in the voltage range of 1.5–4.3 V, which is abnormal compared to the other P’2-based layered cathode materials for sodium-ion batteries, being responsible for the long-term cycle stability of P’2-K0.83[Ni0.05Mn0.95]O2. First-principles calculation results indicate that the excellent electrochemical performance results from the structural stability associated with a single -phase reaction upon K+ extraction/insertion out of/into the host structure. The remarkable potassium storage capability of P’2-K0.83[Ni0.05Mn0.95]O2 makes it a promising cathode candidate for KIBs.