Boosted cycling stability of CoP nano-needles based hybrid supercapacitor with high energy density upon surface phosphorization

The supercapacitors with high energy density and long cycle life are of great need as alternative energy storages beside lithium-ion batteries. Herein, CoP nano-needles are prepared by hydrothermal synthesis which is post-treated by surface phosphorization (CoP/P). The CoP/P sample manifests excellent electrochemical performance of 422.4 C g^-1 at 1 A g^-1 with 81.7% pseudocapacitive contribution. Besides, an asymmetrical supercapacitor device has been assembled, which delivers a high energy density of ~59.2 Wh kg^-1 at power density of 942.7 W kg^-1 and a capacity retention rate of 99% after 10,000 cycles. The high electrochemical performance is mainly attributed to the healing of the surface atomic defects and intimate integration of active species, which provide new strategy to improve supercapacitor performance of transition metal compounds.