Liquid-phase exfoliation of NH4Co0.4Ni0.6PO4·H2O for energy storage device

Liquid-phase exfoliation is an effective method to fabricate thin nanosheet materials with layered structure. In this paper, we successfully synthesized NH4Co0.4Ni0.6PO4·H2O nanosheets with the thickness of about tens of nanometers through liquid-phase exfoliation under ultrasonication. Specifically, the formamide solution was chosen as the exfoliation solvent due to it is capable of entering the interlayer of bulk materials and rapidly swelling between layers. Electrochemistry tests revealed that the optimized exfoliation time was 4 days. The asymmetric battery type energy storage device AC//NH4Co0.4Ni0.6PO4·H2O nanosheets showed an energy density of 10.8 Wh kg−1 at the power density of 703.1 W kg−1. More importantly, the long-term cycle stability measurements demonstrated that NH4Co0.4Ni0.6PO4·H2O nanosheets after exfoliation had an ultra-long cycling life that still retained 102.3% of specific capacitance even 10000 continuous charge/discharge cycles.