Wang Beizhou, Zhao Ning, Wang Youwei, Zhang Wenqing, Lu Wencong, Guo Xiangxin, Liu Jianjun
State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050, P. R. China.
Department of Chemistry, College of Sciences, Shanghai University, 99 Shangda Road, Shanghai 200444, P. R. China.
Phys Chem Chem Phys. 2017 Jan 25;19(4):2940-2949. doi: 10.1039/c6cp07537a.
Tuning the composition of discharge products is an important strategy to reduce charge potential, suppress side reactions, and improve the reversibility of metal-oxygen batteries. In the present study, first-principles calculations and experimental confirmation were performed to unravel the influence of O pressure, particle size, and electrolyte on the composition of charge products in Na-O batteries. The electrolytes with medium and high donor numbers (>12.5) are favorable for the formation of sole NaO, while those with low donor numbers (<12.5) may permit the formation of NaO by disproportionation reactions. Our comparative experiments under different electrolytes confirmed the calculation prediction. Our calculations indicated that O pressure and particle size hardly affect discharge products. On the electrode, only one-electron-transfer electrochemical reaction to form NaO takes place, whereas two-electron-transfer electrochemical and chemical reactions to form NaO and NaO are prevented in thermodynamics. The present study explains why metastable NaO was identified as a sole discharge product in many experiments, while thermodynamically more stable NaO was not observed. Therefore, to achieve low overpotential, a high-donor-number electrolyte should be applied in the discharge processes of Na-O batteries.
调整放电产物的组成是降低充电电位、抑制副反应以及提高金属-氧电池可逆性的重要策略。在本研究中，进行了第一性原理计算和实验验证，以揭示氧压力、颗粒尺寸和电解质对钠-氧电池中充电产物组成的影响。具有中等和高给体数（>12.5）的电解质有利于形成单一的NaO，而具有低给体数（<12.5）的电解质可能通过歧化反应允许NaO的形成。我们在不同电解质下的对比实验证实了计算预测。我们的计算表明，氧压力和颗粒尺寸对放电产物几乎没有影响。在电极上，仅发生形成NaO的单电子转移电化学反应，而在热力学上阻止了形成NaO和NaO的双电子转移电化学反应和化学反应。本研究解释了为什么在许多实验中，亚稳的NaO被确定为唯一的放电产物，而热力学上更稳定的NaO却未被观察到。因此，为了实现低过电位，在钠-氧电池的放电过程中应使用高给体数的电解质。
