Ab initio prediction of borophene as an extraordinary anode material exhibiting ultrafast directional sodium diffusion for sodium-based batteries

Abstract

Density functional theory calculations and ab initio molecular dynamics simulations are performed to study the feasibility of using borophene, a newly synthesized two-dimensional sheet of boron, as an anode material for sodium-ion and sodium–oxygen batteries. The theoretical capacity of borophene is found to be as high as 1,218 mAh g^–1 (Na_0.5B). More importantly, it is demonstrated that the sodium diffusion energy barrier along the valley direction is as low as 0.0019 eV, which corresponds to a diffusivity of more than a thousand times higher than that of conventional anode materials such as Na₂Ti₃O₇ and Na₃Sb. Hence, the use of borophene will revolutionize the rate capability of sodium-based batteries. Moreover, it is predicted that, during the sodiation process, the average open-circuit voltage is 0.53 V, which can effectively suppress the formation of dendrites while maximizing the energy density. The metallic feature and structural integrity of borophene can be well preserved at different sodium concentrations, demonstrating good electronic conductivity and stable cyclability.

摘要

本文通过密度泛函理论计算以及第一性分子动力学模拟研究了最新合成出的二维硼结构硼烯作为负极材料应用于钠离子电池和钠氧气电池中的可行性。理论预测硼烯作为钠负极材料的容量高达1,218 mA g^–1 (Na_0.5B). 更为重要的是,计算表明钠沿硼烯结构中谷方向扩散的能垒低至0.0019 eV,对应的扩散率比传统的负极材料(如Na₂Ti₃O₇ 和 Na₃Sb)高出一千多倍。因此,硼烯应用于钠负极会对钠电池的倍率性能带来革命性的提升。此外,根据预测,在钠离子嵌入过程中,平均开路电压为0.53 V。 该电压在保证抑制枝晶形成的同时可以将能量密度最大化。硼烯的金属特性和结构的完整性在不同的钠离子浓度下均可以保持,预示着良好的电子传导特性以及循环性能。