Qu Zilin, Zhou Bo, Li Bo, Song Qi, Cao Yong Hua, Jiang Zhenyi
Institute of Modern Physics, Shanxi Key Laboratory for Theoretical Physics Frontiers, Northwest University, Xi'an 710127, People's Republic of China.
School of Mechanical and Electrical Engineering, Henan Institute of Science and Technology, Xinxiang 453003, People's Republic of China.
Phys Chem Chem Phys. 2021 Feb 25;23(7):4187-4194. doi: 10.1039/d0cp05717g.
Double-layered V2O5 and its analogues have received increasing attention as a proper cathode for Mg2+, Na+, Li+ ion batteries, even for ammonium ion batteries. Our theoretical research focuses on the effects of NH4+ ions on the structural stability and the ion diffusion properties of double-layered V2O5. The elastic constant calculations indicate the NH4+ and water contents have a dramatic influence on the stability of the electrode. When the ratio of H2O and ammonia ions decreases to (NH4)0.125V2O5·0.125H2O, double-layered bronze will transform into other phases. The predicted specific capacity for the redox process from (NH4)0.5V2O5·0.5H2O to (NH4)0.125V2O5·0.125H2O is 54.6 mA h g-1, which agrees with the experimental value of 55.6 mA h g-1. From the diffusion barrier calculations, it is found that the H2O molecules can shield the polarization of NH4+ and lower the diffusion barrier of NH4+ ions. Furthermore, the migrations of common charge carriers in NH4+ pre-intercalated V2O5 have also been studied, which implies that Li+, Zn2+, Na+, Mg2+ ions may move easily in the electrode with energy barriers lower than 525 meV. Our findings match well with the reported experimental results. A special structure of Mg6NH4V8O20 with a much higher Mg ion concentration has been reported. Our findings show that the theoretical specific density of Mg batteries based on NH4+ pre-intercalated V2O5 can be improved to 431 mA h g-1, which is 2.5 times larger than the reported values. This work highlights the effects of the ratio of NH4+ and H2O on double-layered V2O5 and provides insights into designing vanadium oxide based fast-diffusion multivalent ion conductors, which are suitable for battery applications.
双层V2O5及其类似物作为镁离子、钠离子、锂离子电池甚至铵离子电池的合适正极受到了越来越多的关注。我们的理论研究聚焦于铵根离子对双层V2O5结构稳定性和离子扩散特性的影响。弹性常数计算表明铵根离子和水的含量对电极稳定性有显著影响。当水与铵离子的比例降至(NH4)0.125V2O5·0.125H2O时，双层青铜会转变为其他相。从(NH4)0.5V2O5·0.5H2O到(NH4)0.125V2O5·0.125H2O的氧化还原过程预测比容量为54.6 mA h g-1，与55.6 mA h g-1的实验值相符。通过扩散势垒计算发现，水分子可以屏蔽铵根离子的极化并降低铵根离子的扩散势垒。此外，还研究了铵根预嵌入V2O5中常见电荷载流子的迁移情况，这表明锂离子、锌离子、钠离子、镁离子在电极中可能以低于525 meV的能垒轻松移动。我们的研究结果与报道的实验结果非常吻合。已报道了一种具有更高镁离子浓度的特殊结构Mg6NH4V8O20。我们的研究结果表明，基于铵根预嵌入V2O5的镁电池理论比能量可提高到431 mA h g-1，比报道值大2.5倍。这项工作突出了铵根离子与水的比例对双层V2O5的影响，并为设计适用于电池应用的基于氧化钒的快速扩散多价离子导体提供了见解。
