Shang Chaoqun, Hu Le, Luo Dan, Kempa Krzysztof, Zhang Yongguang, Zhou Guofu, Wang Xin, Chen Zhongwei
National Center for International Research on Green Optoelectronics South China Academy of Advanced Optoelectronics South China Normal University Guangzhou 510006 China.
Department of Chemical Engineering University of Waterloo Waterloo Ontario N2L 3G1 Canada.
Adv Sci (Weinh). 2020 Oct 8;7(22):2002358. doi: 10.1002/advs.202002358. eCollection 2020 Nov.
Germanium (Ge)-based materials have been considered as potential anode materials for sodium-ion batteries owing to their high theoretical specific capacity. However, the poor conductivity and Na diffusivity of Ge-based materials result in retardant ion/electron transportation and insufficient sodium storage efficiency, leading to sluggish reaction kinetics. To intrinsically maximize the sodium storage capability of Ge, the nitrogen doped carbon-coated CuGe/Ge heterostructure material (CuGe/Ge@N-C) is developed for enhanced sodium storage. The pod-like structure of CuGe/Ge@N-C exposes numerous active surface to shorten ion transportation pathway while the uniform encapsulation of carbon shell improves the electron transportation, leading to enhanced reaction kinetics. Theoretical calculation reveals that CuGe/Ge heterostructure can offer decent electron conduction and lower the Na diffusion barrier, which further promotes Ge alloying reaction and improves its sodium storage capability close to its theoretical value. In addition, the uniform encapsulation of nitrogen-doped carbon on CuGe/Ge heterostructure material efficiently alleviates its volume expansion and prevents its decomposition, further ensuring its structural integrity upon cycling. Attributed to these unique superiorities, the as-prepared CuGe/Ge@N-C electrode demonstrates admirable discharge capacity, outstanding rate capability and prolonged cycle lifespan (178 mAh g at 4.0 A g after 4000 cycles).
锗（Ge）基材料因其高理论比容量而被认为是钠离子电池的潜在负极材料。然而，锗基材料的导电性和钠扩散率较差，导致离子/电子传输受阻，储钠效率不足，反应动力学迟缓。为了从本质上最大化锗的储钠能力，开发了氮掺杂碳包覆的CuGe/Ge异质结构材料（CuGe/Ge@N-C）以增强储钠性能。CuGe/Ge@N-C的豆荚状结构暴露出大量活性表面，从而缩短离子传输路径，而碳壳的均匀包覆则改善了电子传输，导致反应动力学增强。理论计算表明，CuGe/Ge异质结构可以提供良好的电子传导并降低钠扩散势垒，这进一步促进了锗合金化反应，并将其储钠能力提高到接近其理论值。此外，氮掺杂碳在CuGe/Ge异质结构材料上的均匀包覆有效地减轻了其体积膨胀并防止其分解，进一步确保了其在循环过程中的结构完整性。由于这些独特的优势，所制备的CuGe/Ge@N-C电极表现出令人钦佩的放电容量、出色的倍率性能和延长的循环寿命（在4.0 A g下循环4000次后为178 mAh g）。
