Galvanic Replacement Synthesis of Graphene Coupled Amorphous Antimony Nanoparticles for High-Performance Sodium-Ion Capacitor

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.