Enabling High Performance Calcium-Ion Batteries from Prussian Blue and Metal–Organic Compound Materials

Full cell calcium-ion batteries (CIBs) were fabricated from Prussian blue and metal–organic compound (MOC) materials and characterized. The anode materials were prepared via the simple precipitation of a nickel salt and various organic sodium salts (C6H6-x-y(COONa)x(NH2)y). The OH vibration in FTIR results indicated the partial hydrolysis of Ni-based MOCs during the synthesis. Particularly, the addition of NH2 groups in the ligand increased the steric hindrance; thus, the partial hydrolysis of the Ni-based MOC was inhibited. When the anode material was a partially hydrolyzed MOC (Ni(OH)[C6H4(COOH)(COO)]), the full cell gave an initial discharging capacity of 82 mAh g–1 and a capacity retention of 62% at 0.1 A g–1 after 100 cycles, while the Coulombic efficiency was maintained at approximately 95.4%. The cell obtained from an NH2-functionalized MOC (Ni[C6H4(NH2)(COO)2]) delivered an initial discharging capacity of 86 mAh g–1 and a capacity retention of 77% at 0.1 A g–1 after 100 cycles, while the Coulombic efficiency was maintained at approximately 97%. The impedance tests suggested that Ni-based MOCs had typically low resistance, which is essential to achieve stable full cell CIBs.