Dispersive NiCoP/LDO heterostructure nanosheets scattered by CNTs enabling high-performance electrochemical energy storage

Abstract The bimetallic phosphide NiCoP has been reported with promising electrochemical performance for batteries and supercapacitors. In this work, the lithiation reaction of NiCoP is theoretically proved to be spontaneous, and the metallicity of NiCoP is revealed both before and after lithiation. This provides advantageous features for NiCoP to be applied as potential electrode materials, especially for lithium ion batteries. Then, a NiCo-phosphide/NiCo-layered double oxide–carbon nanotube (NCP/LDO-CNT) composite is synthesized via low-temperature phosphorization of NiCo-LDO-CNT that is derived from nickel-cobalt glycolates-CNT (NiCo-EG-CNT). The small amount of CNTs successfully prevents the self-assembly of NiCo-LDO nanosheets into nanoflowers, leading to dispersed NCP/LDO sheets in the CNT framework with high electron conduction effect. At the same time, the pre-calcination of NiCo-EG before phosphorization is also proved necessary to create a large amount of nanopores in the resultant NCP/LDO sheets, which endures high electrochemical reactions activities, rapid lithium ion diffusion and gradually increased capacities during long cycling. The NCP/LDO-CNT composite shows promising potential as a bifunctional material, which delivers a specific capacitance of 1888F g−1 as the positive electrode material for supercapacitors, and a reversible specific capacity of 901.2 mAh g−1 as the anode material for lithium-ion batteries, both higher than that of NCP (NiCo-phosphide), NCP/LDO (NiCo-phosphide/LDO) and commercial electrodes. An asymmetric supercapacitors assembled with NCP/LDO-CNT and activated carbon can reach a high energy density of 21.3 Wh kg−1 at the power density of 748.5 W kg−1 and unexceptionable electrochemical cycling stability with a high capacitance retention of 117.4% after 4500 cycles. As a bifunctional material, NCP/LDO-CNT has a potential application prospect in lithium ion batteries, supercapacitors, as well as catalysis and fuel cells.