Bronze-phase vanadium dioxide VO₂(B) is notable as a promising cathode material for high-capacity Li ion batteries. While various forms of VO₂(B) nanostructures have been experimentally investigated, a comprehensive theoretical understanding of the lithium storage mechanism is still lacking. In this research, we examine the redox mechanism, structural evolution, electronic characteristics, and the kinetics of Li ion diffusion in VO₂(B) by first-principles calculations. The impact of the surface environment on the Li ion insertion properties is also investigated. Our study demonstrates that, although VO₂(B) is capable of incorporating one Li per formula unit from a thermodynamic perspective, its actual capacity can be much less due to kinetic factors. Energy barrier calculations reveal a pronounced compositional dependence of Li diffusion in bulk VO₂(B): the b axis tunnels, which account for the excellent Li diffusivity at low Li content, become blocked when Li concentration goes up. The equilibrium surfaces are predicted to be oxygen-rich in an oxidizing atmosphere, which would lead to a steep gradient of Li concentration near the surfaces and further impede Li intercalation into the bulk. Yet, these limitations can be circumvented by facilitating the diffusion of Li in the c direction that is still feasible at high Li content and stabilizing the stoichiometric terminations of (0 0 1) and (1 1 0) facets, which can alleviate the load of excess Li near the surfaces. Our theoretical insights can provide a rationale for the different experimental values of specific capacity in the literature and inspire new strategies to optimize the electrochemical performance of VO₂(B).

中文翻译：

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VO ₂中Li嵌入的第一性原理分析（B）

青铜相二氧化钒VO ₂（B）作为高容量锂离子电池的有希望的正极材料而著称。尽管已通过实验研究了各种形式的VO ₂（B）纳米结构，但仍缺乏对锂存储机理的全面理论理解。在本研究中，我们通过第一性原理计算研究了氧化还原机理，结构演变，电子特性以及锂离子在VO ₂（B）中扩散的动力学。还研究了表面环境对锂离子插入性能的影响。我们的研究表明，尽管VO ₂（B）从热力学的角度来看，每个配方单元可以加入一个Li，由于动力学因素，其实际容量可能要少得多。能量垒计算表明，在大体积VO ₂（B）中，Li扩散具有明显的成分依赖性：当Li浓度升高时，b轴隧道（在低Li含量下具有出色的Li扩散性）被阻塞。预计平衡表面在氧化气氛中富含氧气，这将导致表面附近的Li浓度急剧下降，并进一步阻止Li嵌入主体中。但是，可以通过促进Li在C中的扩散来规避这些限制。在高Li含量和稳定（0 0 1）和（1 1 0）晶面的化学计量端接时仍然可行的方向，这可以减轻表面附近过量Li的负荷。我们的理论见解可以为文献中比容量的不同实验值提供理论依据，并激发出新的策略来优化VO ₂（B）的电化学性能。