Sivakov Vyacheslav, Pavlov Sergey, Smirnov Vladimir, Kislenko Sergey
Joint Institute for High Temperatures of the Russian Academy of Sciences, Izhorskaya 13/2, 125412 Moscow, Russian Federation.
Center for Computational and Data-Intensive Science and Engineering, Skolkovo Institute of Science and Technology, Skolkovo Innovation Center, Nobel St. 3, Moscow, 143026, Russian Federation.
Phys Chem Chem Phys. 2021 Oct 13;23(39):22375-22383. doi: 10.1039/d1cp03429d.
An aprotic lithium-air battery is a promising candidate for next-generation energy storage systems, but its practical performance is still low. The addition of water to an electrolyte can substantially increase the capacity and round-trip efficiency of batteries. However, fundamental mechanisms of the water impact are still far from being fully understood. To contribute to this issue, we studied by molecular dynamics simulations the effect of water additives on the behaviour of discharge intermediates Li and O in two frequently used solvents: dimethoxyethane (DME) and dimethyl sulfoxide (DMSO). We have estimated the structures of the solvation shells around Li and O ions, and the residence times of various electrolyte components inside the solvation shells depending on the concentration of water additives. Furthermore, we have estimated the rate and the equilibrium of the Li and O association. Our results reveal that water additives in electrolytes shift the equilibrium of the association reaction toward soluble Li and O ions in both DME and DMSO. These data argue for the view that water promotes the solution discharge mechanism, thus increasing the capacity. Moreover, we show that water accelerates the kinetics of the association reaction due to the decrease of the stability of Li and O solvation shells. This may explain the reduced discharge overpotential when water is added.
非质子锂空气电池是下一代储能系统的一个有前途的候选者，但其实际性能仍然较低。向电解质中添加水可以大幅提高电池的容量和往返效率。然而，水的影响的基本机制仍远未被完全理解。为了解决这个问题，我们通过分子动力学模拟研究了水添加剂对两种常用溶剂：二甲氧基乙烷（DME）和二甲基亚砜（DMSO）中放电中间体Li和O行为的影响。我们估计了Li和O离子周围溶剂化壳层的结构，以及根据水添加剂浓度不同，各种电解质成分在溶剂化壳层内的停留时间。此外，我们还估计了Li和O缔合的速率和平衡。我们的结果表明，电解质中的水添加剂使DME和DMSO中缔合反应的平衡向可溶性Li和O离子方向移动。这些数据支持了水促进溶液放电机制从而增加容量的观点。此外，我们表明，由于Li和O溶剂化壳层稳定性的降低，水加速了缔合反应的动力学。这可能解释了添加水时放电过电位降低的原因。
