Key Takeaways & Executive Findings
- •• Bi@NC composite anode delivers high specific capacity (300 mAh g−1 at 0.5 A g−1) and exceptional rate capability up to 75 A g−1. • The anode exhibits outstanding cycling stability over 12,000 cycles, addressing kinetic imbalance in sodium-ion capacitors. • Three-electrode tests confirm reduced kinetic gap with activated carbon cathode, enabling high energy/power densities. • The fabricated SIC achieves maximum energy density of 115 Wh kg−1, peak power density of 45,535 W kg−1, and cycle life exceeding 8,000 cycles.
Abstract
Sodium-ion capacitors (SICs) typically feature a hybrid design, incorporating a battery-type anode that operates by faradaic redox reactions and an activated carbon cathode that functions through electrical double-layer (EDL) adsorption/desorption. However, the kinetics of faradaic processes are inherently slower than those of EDL processes, leading to a fundamental problem known as kinetic imbalance between the electrodes, which hinders the development of high-performance SICs. To address this, we synthesized composites of bismuth nanoparticles in N-doped carbon (Bi@NC) by a high-temperature sintering method. The resulting Bi@NC anode has a specific capacity of 300 mAh g−1 at 0.5 A g−1, an exceptional rate capability (maintaining performance at currents exceeding 75 A g−1), and outstanding cycling stability over 12,000 cycles. Three-electrode Swagelok cell tests revealed that this high-rate Bi@NC composite effectively decreases the kinetic gap with the activated carbon cathode, as shown by an analysis of their respective potential swing windows (vs. Na/Na+). This enables the fabricated SIC to achieve a maximum energy density of 115 Wh kg−1, a peak power density of 45,535 W kg−1, and a long cycle life exceeding 8,000 cycles.
1. Introduction
Since Sony's commercialization of lithium-ion batteries, the fields of portable electronics and electric vehicles (EVs) have entered a period of significant advancement and growth. Nevertheless, the elevated extraction costs associated with lithium ore, coupled with its adverse environmental impact, are incongruent with the principles of sustainable development. Owing to the extensive crustal abundance and economy, sodium-ion capacitors (SICs) have become the attractive choice for the next-generation of energy storage technology.
As a category of metal ion capacitors, SICs comprise a battery-type anode and a capacitive cathode, thereby possessing the multiple characteristics of high energy and power densities. Activated carbon (AC) is presently widely utilized as a cathode material of a capacitor with highly porous structure, economic viability, and excellent physicochemical properties. Furthermore, the abundance of micropores and mesopores on the AC surface facilitates rapid mass transfer, thereby exhibiting superior kinetic performance. Among the diverse range of anode materials, carbon-based materials are the most extensively utilized. However, the large ionic radius of Na+ contributes to the sluggish reaction rate observed at the anode, which leads to poor rate capability. Sluggish reaction kinetics of the anode may further reduce the capacity utilization of a capacitive cathode, which in turn affects the overall capacitor energy density. Exploring and designing anodes with high-rate performance to accommodate the kinetic mismatch in SICs is of great importance.
Recently, alloy-based anode materials have been widely investigated due to the high reversible sodium storage capacity and high conductivity. Among them, bismuth has excellent properties such as low and suitable sodium storage potential and high theoretical specific capacity. Moreover, it has been confirmed that the bismuth-sodium system has the highest conductivity and sodium diffusivity of all metal-sodium systems, showing kinetics that can be matched with the cathode material. This is because in the ether-based electrolyte, the bismuth metal can gradually undergo nanostructure evolution during the cycle.
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Man Xiaoge, Huang Xinli, Min Xinyue, Yan Yijie, Shi Yuanchang, Li Tao, Wang Chengxiang, Zhang Zhiwei, Yin Longwei, Wang Rutao (2025). A fast bismuth-carbon composite anode for achieving kinetic matching between the anode and cathode of sodium-ion capacitors. SinoTechIntel Verified Research. https://doi.org/10.1016/S1872-5805(NCM2026-41-02-08)
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
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Frequently Asked Questions
What is the main challenge in sodium-ion capacitors addressed by this research?
The main challenge is the kinetic imbalance between the slow faradaic anode and the fast capacitive cathode, which limits the overall performance of sodium-ion capacitors.
How does the Bi@NC composite anode improve performance?
The Bi@NC composite anode provides high specific capacity, exceptional rate capability, and long cycling stability, effectively reducing the kinetic gap with the cathode.
What are the key performance metrics of the fabricated sodium-ion capacitor?
The SIC achieves a maximum energy density of 115 Wh kg−1, a peak power density of 45,535 W kg−1, and a cycle life exceeding 8,000 cycles.
What method was used to synthesize the Bi@NC composite?
The Bi@NC composite was synthesized by a high-temperature sintering method.
Why is bismuth chosen as the anode material?
Bismuth offers low and suitable sodium storage potential, high theoretical capacity, and the highest conductivity and sodium diffusivity among metal-sodium systems, enabling fast kinetics.
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