Stable cathode material enabled by Mg2+ intercalation layered potassium vanadate for high rate and long life potassium ion batteries

Potassium-ion batteries (PIBs) have become prominent as one kind of next generation electrochemical energy storage technologies recently considering the plentiful potassium resources available. However, the progress of PIBs continues to be impeded by several factors, particularly the large size of K+. As a class of layered oxides with large interlayer spacing, vanadium-based oxides are regarded as promising exploitable cathode materials. Herein, the significant performance improvement of layered potassium vanadate K0.5V2O5 is achieved by the intercalation of Mg2+. The obtained Mg-KVO provides reversible capacity above 60 mAh g−1 at 10 mA g−1, while 91.5% of capacity can be retained at 1000 mA g−1 over 1000 cycles. The full cell assembled with Mg-KVO and multi-porous hard carbon has a reversible capacity of 40.6 mAh g−1 after 100 cycles at 50 mA g−1 with 93% capacity retention, which verifies the superiority of this material in PIBs. Analytical techniques of electrochemical impedance spectroscopy and galvanostatic intermittent titration technique indicate that the slight amount of Mg2+ endows KVO with better electrochemical reaction kinetics and structural stability by coordinating with lattice oxygen during cycling. This study provides practicable insights into enhancing the electrochemical performance for PIBs.