Ni₂P₂O₇ micro-sheets supported ultra-thin MnO₂ nanoflakes: A promising positive electrode for stable solid-state hybrid supercapacitor

A new core-shell structured MnO₂@Ni₂P₂O₇ (NPO) nanohybrid with unique nano-design is engineered by simple solution process and utilized as promising positive electrode for solid-state hybrid supercapacitors (HSCs). Firstly, two-dimensional (2D) NPO micro-sheets are grown on the Ni foam where the ultrathin MnO₂ nanoflakes are decorated on NPO micro-sheets to realise MnO₂@NPO core-shell nanohybrid. The as-synthesized MnO₂@NPO electrode delivers impressive electrochemical performances with specific capacity of 309 mA h/g with long-term cycling stability over the 12,000 charge-discharge cycles. A solid-state hybrid supercapacitor (HSC) is fabricated using MnO₂@NPO and activated carbon (AC) as positive and negative electrodes with polymer-gel electrolyte. The assembled HSC offers an upgraded cell potential of 1.6 V with high specific energy of 66 Wh/kg at specific power of 640 W/kg. More importantly, the HSC delivers excellent cycling stability over the 10,000 cycles (∼93% of capacity retention) with good energy efficiency at all current densities.