One-step self-embedding of CoP nanoparticles in N, P-codoped hard carbon for high-performance lithium ion capacitors

Abstract

The inherently low electrical conductivity of transition metal phosphides and most synthetic strategies rely on a multi-step post-processing process from an external phosphorus source, limiting their widespread application. Herein, we explore an in-situ activation and phosphating strategies to prepare CoP nanoparticles self-embedded in N, P-codoped hard carbon (CoP@NPHC) by using chitosan as nitrogen-rich carbon sources and phytic acid (PA) as trifunctional role of crosslinking/chelating agent, phosphorus source and activation reagent. Relying on the unique coordination ability of amino groups of chitosan with metal ions and the cooperative hydrogen bonding of chitosan with long chain structure and PA to form a 3D superstructure. Thanks to the highly dispersed CoP nanoparticles self-embedded in porous and highly conductive carbon skeleton, the CoP@NPHC exhibits high specific capacity of 694 mAh g−1 at 0.1 A g−1 and excellent rate performance. More importantly, a novel lithium ion capacitor is assembled using pre-lithiated CoP@NPHC as anode material and acid etched N, P-codoped porous carbon (NPAC) as the cathode material, which can provide a stable operating voltage of 4.2 V and high energy density of 139.2 Wh kg−1 at a power density of 394 W kg−1, as well as excellent capacity retention of 89.3% after 4000 cycles.