A research team led by Prof. Cao from Central South University has developed an innovative dual-modification strategy that significantly boosts the performance of hard carbon anodes in sodium-ion batteries (SIBs)—a promising low-cost alternative to lithium-ion batteries for large-scale energy storage. The new approach combines atomic-level cobalt (Co) doping with an innovative high-current formation cycling (FC) technique, targeting the key challenge of sluggish sodium-ion transport and unstable interfacial films.
Hard carbon is widely regarded as the most commercially viable anode material for sodium-ion batteries. However, its disordered structure and unstable electrolyte interface limit fast-charging performance and long-term cycling stability. To address this, the team introduced single cobalt atoms into the carbon structure. Theoretical simulations confirmed that Co atoms embedded in a nitrogen-coordinated configuration (Co-N₄) significantly lower the energy barrier for electrolyte decomposition, catalyzing the formation of an inorganic-rich solid electrolyte interphase (SEI) — a protective layer critical to battery function.
X-ray photoelectron spectroscopy (XPS) and high-resolution electron microscopy revealed that introducing atomically dispersed cobalt atoms in a Co–N₄ configuration not only promoted partial graphitization of the carbon matrix—enhancing sodium-ion diffusion—but also catalyzed the decomposition of electrolyte salts to form a uniform, inorganic-rich solid electrolyte interphase (SEI) layer. DFT calculations similarly verified that doping of single atoms reduces the dissociation energy of electrolyte salts and promotes crystalline SEI films rich in sodium fluoride (NaF)，in contrast to the uneven and organic-rich layers on undoped carbon. This SEI not only improves interface stability but also facilitates faster Na⁺ ion transport.
The innovation doesn't stop there. The researchers applied a rapid high-current pre-cycling process, which further promoted the growth of high-quality SEI films. This step enabled the formation of a compact, inorganic-dominated interfacial layer within minutes, ensuring robust electrochemical stability. Depth-profiled XPS showed that this process led to a more homogeneous distribution of inorganic species throughout the SEI, unlike conventional cycling, which tends to form layered structures with poor ionic conductivity.
Thanks to this dual approach, the optimized Co-GC electrode delivered exceptional performance — maintaining a high reversible capacity of 229.63 mAh g⁻¹ even after 3000 cycles at 1.5 A g⁻¹, and demonstrating outstanding rate capability in full battery configurations.
This study demonstrates the power of combining atomic-level material design with interface engineering, offering a scalable pathway to accelerate the commercialization of high-performance sodium-ion batteries — a critical step toward affordable and sustainable energy storage.