The investigations of pyrophosphate CoNiP2O7 produced by hydrothermal process: a high-performance anode electrode material for Li-ion hybrid capacitor

The novel transition metal pyrophosphate shows high theoretical specific capacity and good chemical stability. In this work, the CoNiP2O7 is prepared by classical hydrothermal method, and this material is applied to lithium-ion hybrid capacitor (LIHC). The material's structure is composed of plate-like layers and fine particles. The half-cell exhibited a specific capacity of 253 mAh g(-1) after 300 cycles at a current density of 0.1 A g(-1). Then the LIHC device assembled with a capacitive material as the cathode and a battery-type material CoNiP2O7 as the anode exhibited a high energy density of 116.3 Wh kg(-1) at a power density of 200.02 W kg(-1)(current density is 0.1 A g(-1)); meanwhile, an ultra-high power density of 6486.5 W kg(-1) occurs at the energy density of 66.7 Wh kg(-1)(current density is 3.2 A g(-1)). Based on these results, we confirmed that CoNiP2O7 material will be a promising electrode material for LIHC.