Carbon-coated Co2VO4 with high pseudo-capacitance to enhance Na+ storage performance for advanced sodium-ion capacitors

Abstract

Developing high-performance anode materials is crucial for the advancement of sodium-ion capacitors with high-energy density and large power density. Bimetallic oxides exhibit a high specific capacity due to their synergistic effects in electrochemical processes. However, challenges such as poor electrical conductivity, slow ion transport, and volume expansion severely limit their development. In this study, Co₂VO₄@C-1.5 was synthesized through a straightforward method involving solvent-heating and carbonization via calcination. The synergistic effect of Co and V, mitigation of volume expansion by the carbon-coated layer, enhancement of pseudocapacitive behavior and improved electrical conductivity of Co₂VO₄@C-1.5 contribute to its superior electrochemical performance. The specific capacity of Co₂VO₄@C-1.5 remained steady at 288.8 and 171.7 mAh g⁻¹ after 100 and 500 cycles at 100 and 1000 mA g⁻¹, respectively. Density functional theory (DFT) calculations show a notable reduction in the energy barrier of Co₂VO₄@C-1.5. Furthermore, the assembled sodium-ion capacitor Co₂VO₄@C-1.5//AC demonstrates high-energy density (108.5 Wh kg⁻¹ at 99.8 W kg⁻¹), remarkable power density (38.2 Wh kg⁻¹ at 12,000 W kg⁻¹), and long-cycle stability (capacity retention of 80.6% after 6000 cycles). The design and optimization of the carbon-coated structure provide valuable insights for the development of bimetallic oxide materials in sodium-ion capacitors (SICs).

Graphical abstract