Sodium ion batteries (SIBs), as an alternative and promising energy storage system, have attracted considerable attention due to the abundant reserves and low cost of sodium. However, it remains a great challenge to achieve high capacity and rate capability required for practical applications. Herein, hollow octahedral Co₃Se₄ particles encapsulated in reduced graphene oxide (Co₃Se₄@rGO) were designed and synthesized and exhibited excellent electrochemical performances as anodes of SIBs, especially rate capability. Sodiation/desodiation processes and involved mechanisms were investigated by using in situ TEM and in situ XRD. During sodiation, a crystalline Na₂Se layer with numerous amorphous fine Co nanoparticles dispersed on it was observed to appear on the surface of the original Co₃Se₄@rGO particles, and the movable Co–Na₂Se composites further migrated to the rGO network with high electron/ion dual conductivity, resulting in ultrafast sodium storage kinetics and remarkable rate performance of the Co₃Se₄@rGO anode evidenced by delivering a discharge capacity of 229.3 mAh g^–1 at a large current density of 50 A g^–1. Our findings reveal the fundamental mechanism behind the enhanced performance of the Co₃Se₄@rGO anode and offer valuable insights into the rational design of electrode materials for high-performance SIBs.

中文翻译：

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空心八面体 Co3Se4@rGO 用于高倍率钠离子存储的电化学过程研究

钠离子电池（SIBs）作为一种可替代且有前景的储能系统，由于钠的储量丰富且成本低廉而引起了人们的广泛关注。然而，实现实际应用所需的高容量和倍率能力仍然是一个巨大的挑战。在此，设计和合成了包裹在还原氧化石墨烯（Co ₃ Se ₄ @rGO）中的中空八面体Co ₃ Se ₄颗粒，并作为SIBs的负极表现出优异的电化学性能，尤其是倍率性能。使用原位TEM 和原位XRD研究了钠化/脱钠过程和相关机制。在钠化过程中，结晶 Na ₂在原来的Co ₃ Se ₄ @rGO 粒子的表面上出现了分散有大量无定形细Co纳米粒子的Se层，可移动的Co-Na ₂ Se复合材料进一步迁移到具有高电子/离子对偶的rGO网络中。 Co ₃ Se ₄ @rGO 阳极具有超快的钠储存动力学和卓越的倍率性能，这在 50 A g ^-1的大电流密度下提供 229.3 mAh g ^-1的放电容量证明了这一点。我们的研究结果揭示了 Co ₃ Se _{4性能增强背后的基本机制}@rGO 阳极，并为高性能 SIB 电极材料的合理设计提供有价值的见解。