Hierarchically nitrogen-doped carbon wrapped Ni0.6Fe0.4Se2 binary-metal selenide nanocubes with extraordinary rate performance and high pseudocapacitive contribution for sodium-ion anodes

Abstract

Because of their considerable theoretical capacity and intrinsic conductivity, transition metal selenides have been considered as advanced electrode materials for sodium-ion batteries (SIBs). However, fast capacity fade and inferior rate performance still impede their large-scale application. Herein, a hierarchically nitrogen-doped carbon (NC) wrapped binary transition metal selenide (Ni_0.6Fe_0.4Se₂@NC, termed NFS@NC) nanomaterial derived from polydopamine coated Prussian blue analogs (Ni₃[Fe(CN)₆]₂, Ni–Fe–PBA) was synthesized through a low-energy selenization and carbonization process. The excellent morphology, large surface area, intimate contact of nanoparticles with the carbon matrix and better combination of binary metal selenides can achieve outstanding sodium storage performance through their synergy. Notably, nitrogen-containing compound are efficiently converted to nitrogen-doped carbon with functional Fe–N–C bonds, facilitating the faster transfer of Na⁺. As a result, the as-obtained NFS@NC showed superior rate performance (449.3 mA h g⁻¹ at 0.2 A g⁻¹ and 289.5 mA h g⁻¹ at 10 A g⁻¹) and stable long-term cyclability (372.4 mA h g⁻¹ after 2000 cycles at 5 A g⁻¹) as an anode material for SIBs. Kinetic analysis showed that the excellent Na-storage performance of the NFS@NC anode was mainly due to the large pseudocapacitive contribution resulting from the unique nano-multilevel composite structure.