Kim Seong Shik, See Kimberly A
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States.
ACS Appl Mater Interfaces. 2021 Jan 13;13(1):671-680. doi: 10.1021/acsami.0c19053. Epub 2020 Dec 24.
Mg batteries are attractive next-generation energy storage systems due to their high natural abundance, inexpensive cost, and high theoretical capacity compared to conventional Li-ion based systems. The high energy density is achieved by electrodeposition and stripping of a Mg metal anode and requires the development of effective electrolytes enabled by a mechanistic understanding of the charge-transfer mechanism. The magnesium aluminum chloride complex (MACC) electrolyte is a good model system to study the mechanism as the solution phase speciation is known. Previously, we reported that minor addition of Mg(HMDS) to the MACC electrolyte causes significant improvement in the Mg deposition and stripping voltammetry resulting in good Coulombic efficiency on cycle one and, therefore, negating the need for electrochemical conditioning. To determine the cause of the improved electrochemistry, here we probe the speciation of the electrolyte after Mg(HMDS) addition using Raman spectroscopy, Al nuclear magnetic resonance spectroscopy, and H-Si heteronuclear multiple bond correlation spectroscopy on MACC + Mg(HMDS) at various Mg(HMDS) concentrations. Mg(HMDS) scavenges trace HO, but it also reacts with MACC complexes, namely, AlCl, to form free Cl. We suggest that although both the removal of HO and the formation of free Cl improve electrochemistry by altering the speciation at the interface, the latter has a profound effect on electrodeposition and stripping of Mg.
镁电池因其天然丰度高、成本低廉以及与传统锂离子电池系统相比具有较高的理论容量，而成为极具吸引力的下一代储能系统。通过镁金属阳极的电沉积和剥离可实现高能量密度，这需要通过对电荷转移机制的机理理解来开发有效的电解质。氯化镁铝络合物（MACC）电解质是研究该机理的良好模型系统，因为其溶液相形态是已知的。此前，我们报道向MACC电解质中少量添加Mg(HMDS)会显著改善镁的沉积和剥离伏安法，从而在第一个循环中获得良好的库仑效率，因此无需进行电化学预处理。为了确定电化学性能改善的原因，我们在此使用拉曼光谱、铝核磁共振光谱以及在不同Mg(HMDS)浓度下对MACC + Mg(HMDS)进行H-Si异核多键相关光谱，来探究添加Mg(HMDS)后电解质的形态。Mg(HMDS)会清除痕量的HO，但它也会与MACC络合物（即AlCl）反应形成游离Cl。我们认为，虽然去除HO和形成游离Cl都通过改变界面处的形态来改善电化学性能，但后者对镁的电沉积和剥离有深远影响。
