Hierarchical Co3O4 anode for high-performance Na-ion battery

In this work, we aimed to address the challenges of using Co₃O₄ as an anode material for sodium-ion batteries (SIBs), particularly its poor electrical conductivity, severe volume expansion during cycling, and significant irreversible capacity loss.To overcome the above challenges, we developed a hierarchical Co₃O₄ nanostructure using a two-step heating process (low-temperature preheating followed by high-temperature calcination) which resulted in an interconnected, porous network that significantly improved charge transport and buffered volume fluctuations and optimized the crystallinity of the material via enhancing the Co³⁺ states to improvise the electrochemical activity.The engineered electrode demonstrated a high reversible capacity (70% of the theoretical limit at 25 mA/g), excellent rate performance (123 mAh/g at 1 A/g), and stable cycling with 82% capacity retention after 250 cycles at 1 A/g. Further, the electrochemical impedance spectroscopy (EIS) has been performed, confirmed a significant reduction in charge transfer resistance (Rct), which facilitated better Na-ion kinetics.Further to understand the storage mechanism, in-situ Raman spectroscopy has employed, revealed a conversion-type Na-ion storage process. The ex-situ ToF-SIMS and TEM analysis has also performed that confirmed homogeneous Na-ion storage and structural integrity of the electrode after extensive cycling.In summary, by combining morphology engineering, crystallinity optimization, and detailed mechanistic studies, we have successfully developed a scalable and cost-effective Co₃O₄ anode with significantly improved electrochemical performance, making it a promising candidate for next-generation sodium-ion batteries.

本研究旨在解决四氧化三钴（Co₃O₄）作为钠离子电池（sodium-ion batteries, SIBs）负极材料面临的挑战，尤其是其导电性差、循环过程中体积膨胀严重以及不可逆容量损失显著等问题。
为克服上述挑战，我们通过两步加热工艺（低温预热后高温煅烧）制备了分级结构的Co₃O₄纳米材料，形成了相互连接的多孔网络，显著改善了电荷传输并缓冲了体积波动；同时通过增强Co³⁺态优化了材料的结晶度，从而提升其电化学活性。
该工程化电极表现出高可逆容量（25 mA/g下达到理论容量的70%）、优异的倍率性能（1 A/g下为123 mAh/g）以及稳定的循环性能（1 A/g下250次循环后容量保持率为82%）。此外，通过电化学阻抗谱（electrochemical impedance spectroscopy, EIS）测试证实，电荷转移电阻（charge transfer resistance, Rct）显著降低，这有利于改善钠离子动力学。
为进一步理解存储机制，我们采用原位拉曼光谱（in-situ Raman spectroscopy）分析，揭示了转化型钠离子存储过程。此外，通过异位飞行时间二次离子质谱（ex-situ ToF-SIMS）和透射电子显微镜（TEM）分析，证实了电极在长期循环后仍具有均匀的钠离子存储能力和结构完整性。
综上，通过结合形貌工程、结晶度优化和详细的机理研究，我们成功制备了一种可规模化且成本效益高的Co₃O₄负极，其电化学性能显著提升，有望成为下一代钠离子电池的候选材料。