Abstract:

Sodium-ion energy storage devices are considered as an ideal substitute for popular lithium-ion counterparts because of its resource richness and environmental friendliness. Among the various sodium-ion energy storage devices, sodium-ion capacitors (SICs) have the combined advantages in high energy and power densities as well as long-term cycling stability in theory. Antimony (Sb) is considered as an attractive anode material for SICs due to its high theoretical capacity of 660 mAh∙g⁻¹, low operating potential (0.5–0.8 V vs. Na/Na⁺), and high density of 6.68 g∙cm⁻³. However, the large volume change of Sb during the Na⁺ insertion leads to fast decay in capacity and poor rate capability, which becomes a fundamental issue greatly hindering the practical application. Herein, a facile galvanic replacement approach is proposed for the synthesis of an ultrafine amorphous Sb nanoparticles anchoring on carbon coated two-dimensional (2D) reduced graphene oxides (RGO). Half-cell test (vs. metal Na) shows that as-prepared Sb-C@RGO anode delivers a high specific capacity of 521.5 mAh∙g⁻¹ at 0.1 A∙g⁻¹. As the current density increases to 10 A∙g⁻¹, Sb-C@RGO anode still maintains a specific capacity of 83.5 mAh∙g⁻¹, suggesting its high-rate properties. The excellent Na⁺ charge storage property of Sb-C@RGO anode is primarily due to its unique 2D hybrid architecture, which largely increases the atomic interface contact with Na⁺ and shortens ion diffusion path, thus facilitating ion/electron transfer. To demonstrate the feasibility of Sb-C@RGO as the high-performance electrode for emerging energy-storage devices, a hybrid cell configuration (e.g., SIC) was fabricated by employing the Sb-C@RGO as the negative electrode (battery type) and home-made activated carbon (PDPC) as the positive electrode (capacitive type) in a Na⁺ based organic electrolyte. This SIC is capable of operating at a high voltage of 4.0 V and exhibiting a high energy density of 140.75 Wh∙kg⁻¹ at a power density of 250.84 W∙kg⁻¹. Even the power density is magnified ~50 times to 12.43 kW∙kg⁻¹, this SIC still delivers a high energy density of 55 Wh∙kg⁻¹. Within a short charge/discharge of ~3.2 min, this SIC can store/release quite a high energy density of 108.5 Wh∙kg⁻¹, which represents the remarkable performance among the reported Sb-based capacitors. In addition, this SIC shows the good cycling stability with an acceptable capacity retention value of 66.27% after 1000 cycles at a current density of 2 A∙g⁻¹. Our results may provide insight into the rational design and construction of high-capacity Sb-based anode materials for advanced sodium-ion based energy storage devices.

Key words: Graphene, Sb anode, Galvanic replacement reaction, 2D composite, Sodium-ion capacitor