Potassium-ion batteries (PIBs) have received much attention as next-generation energy storage systems because of their abundance, low cost, and slightly lower standard redox potential than lithium-ion batteries (LIBs). Nevertheless, they still face great challenges in the design of the best electrode materials for applications. Herein, we have successfully synthesized nano-sized CoSe₂ encapsulated by N-doped reduced graphene oxide (denoted as CoSe₂@N-rGO) by a direct one-step hydrothermal method, including both orthorhombic and cubic CoSe₂ phases. The CoSe₂@N-rGO anodes exhibit a high reversible capacity of 599.3 mA h g⁻¹ at 0.05 A g⁻¹ in the initial cycle, and in particular, they also exhibit a cycling stability of 421 mA h g⁻¹ after 100 cycles at 0.2 A g⁻¹. Density functional theory (DFT) calculations show that CoSe₂ with N-doped carbon can greatly accelerate electron transfer and enhance the rate performance. In addition, the intrinsic causes of the higher electrochemical performance of orthorhombic CoSe₂ than that of cubic CoSe₂ are also discussed.

中文翻译：

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N掺杂rGO修饰的混合相CoSe2在钾离子电池中的电化学性能

钾离子电池（PIBs）作为下一代储能系统受到了广泛关注，因为它比锂离子电池（LIBs）丰富、成本低、标准氧化还原电位略低。尽管如此，他们在设计最佳应用电极材料方面仍面临巨大挑战。在此，我们通过直接一步水热法成功合成了由 N 掺杂的还原氧化石墨烯封装的纳米尺寸 CoSe _{2 （表示为 CoSe 2 @N-rGO），包括正交和立方 CoSe 2}相。CoSe ₂ @N-rGO 阳极在 0.05 A g ^-1下表现出 599.3 mA hg ^{-1的高可逆容量}在初始循环中，特别是在 0.2 A g ^-1下 100 次循环后，它们还表现出 421 mA hg ^-1的循环稳定性。密度泛函理论（DFT）计算表明，掺氮碳的CoSe _{2可以极大地加速电子转移并提高倍率性能。}此外，还讨论了正交CoSe ₂电化学性能高于立方CoSe _{2的内在原因。}