Metal-N/P coordination assisted construction of robust heterointerface for stable and superior-rate electrodes in battery-type supercapacitors

Abstract

Holding ultralong cycle life and superior rate capability with high specific capacity is an inevitable requirement for the practical applications of transition metal compounds battery-type supercapacitor electrode materials. In this paper, a novel class of transition metal phosphide (TMP) nanostructures evenly bonded on N/P co-doped graphene nanotubes (N/P-GNTs@b-TMP) is firstly built via one-step in-situ growth procedure. The N, P elements as substitutions of C in GNTs skeleton introduce rich electronic centers, further change the surface electronic structures of the skeleton, inducing the TMPs to anchor the surface of N/P-GNTs through metal-N and metal-P bonds, which is demonstrated by the characterizations and Density functional theory (DFT) calculation. The unique chemical bonding can not only reinforce the integration of the hybrid electrode materials during durable cycling, but also generate the typical internal electric field and greatly reduce the free energy of the reaction system, endowing a superior rate capacity and easy redox process relating to high specific capacity. Moreover, ex-situ impedance and capacitive/diffusion control analysis suggest the fast ions diffusion behavior and reaction kinetics. Benefiting from the unique architecture, the achieved N/P-GNTs@b-NiCoP positive electrode possesses high specific capacity of 250 mAh g−1 (1800 F g−1) at 2 A g−1 and 166 mAh g−1 (1200 F g−1) at 50 A g−1. Meanwhile, the N/P-GNTs@b-Fe2NiP and N/P-GNTs@b-FeCoP negative electrodes constructed by the same approach can also own a high specific capacity of 151.9, 159.7 mAh g−1 (547, 575 F g−1) at 1A g−1 and 63.6, 73.6 mAh g−1 (229, 265 F g−1) at 50 A g−1, respectively. More significantly, they all can present ∼90% capacity retention after 75000 cycles, which can be comparable to all of the reported transition metal compound electrodes even commercial carbonaceous materials. In addition, an asymmetric supercapacitor (ASC) using the achieved N/P-GNTs@b-NiCoP as electrode expresses a remarkable energy density of 77.8 Wh kg−1 and cycling stability. This work provides an innovative structural design strategy for obtaining battery-type supercapacitor electrode materials with commercial application prospects.