Liu Chang, Wang Baowei, Xu Laiqiang, Zou Kangyu, Deng Wentao, Hou Hongshuai, Zou Guoqiang, Ji Xiaobo
School of Chemistry and Chemical Engineering, Hunan Institute of Engineering, Xiangtan411104, Hunan, China.
College of Chemistry and Chemical Engineering, Central South University, Changsha410083, China.
ACS Appl Mater Interfaces. 2023 Feb 1;15(4):5387-5398. doi: 10.1021/acsami.2c22206. Epub 2023 Jan 24.
Given the inherent features of open tunnel-like structures, moderate lithiation potential (1.0-3.0 V vs Li/Li), and reversible redox couples (Nb/Nb and Nb/Nb redox couples), niobium-based oxides with Wadsley-Roth crystallographic shear structure are promising anode materials. However, their practical rate capability and cycling stability are still hindered by low intrinsic electronic conductivity and structural stability. Herein, ultrathin carbon-confined NbO materials with rich oxygen vacancies (NbO@C) were designed and synthesized to address above-mentioned challenges. Computational simulations combined with experiments reveal that the oxygen vacancies can regulate the electronic structure to increase intrinsic electronic conductivity and reduce the Li diffusion barrier. Meanwhile, the carbon coating can enhance structural stability and further improve the electronic conductivity of the NbO material. As a result, the as-prepared NbO@C exhibits high reversible capacity (226 mAh g at 0.1 A g), excellent high-rate performance (83 mAh g at 5.0 A g), and durable cycling life (98.1% capacity retention at 1.0 A g after 3000 cycles). The lithium storage mechanism and structural stability of NbO@C were also revealed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. When applied as the anode of lithium-ion capacitors (LICs), the as-built LIC achieves high energy density (72.4 Wh kg) within the voltage window of 0.01-3.5 V, demonstrating the practical application potential of the NbO@C materials.
鉴于具有开放隧道状结构的固有特性、适中的锂化电位（相对于Li/Li为1.0 - 3.0 V）以及可逆的氧化还原对（Nb/Nb和Nb/Nb氧化还原对），具有瓦兹利 - 罗思晶体学剪切结构的铌基氧化物是很有前景的负极材料。然而，它们实际的倍率性能和循环稳定性仍然受到低本征电子电导率和结构稳定性的阻碍。在此，设计并合成了具有丰富氧空位的超薄碳包覆NbO材料（NbO@C）以应对上述挑战。计算模拟与实验相结合表明，氧空位可以调节电子结构以提高本征电子电导率并降低锂扩散势垒。同时，碳包覆可以增强结构稳定性并进一步提高NbO材料的电子电导率。结果，所制备的NbO@C表现出高可逆容量（在0.1 A g下为226 mAh g）、优异的高倍率性能（在5.0 A g下为83 mAh g）以及持久的循环寿命（在1.0 A g下循环3000次后容量保持率为98.1%）。还通过X射线衍射（XRD）、X射线光电子能谱（XPS）和拉曼光谱揭示了NbO@C的储锂机制和结构稳定性。当用作锂离子电容器（LIC）的负极时，所构建的LIC在0.01 - 3.5 V的电压窗口内实现了高能量密度（72.4 Wh kg），证明了NbO@C材料的实际应用潜力。
