Mandai Toshihiko
Center for Green Research on Energy and Environmental Materials, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
ACS Appl Mater Interfaces. 2020 Sep 2;12(35):39135-39144. doi: 10.1021/acsami.0c09948. Epub 2020 Aug 21.
The development of noncorrosive but highly efficient electrolytes has been a long-standing challenge in magnesium rechargeable battery (MRB) research fields. As fluorinated alkoxyborate-based electrolytes have overcome serious problems associated with conventional electrolytes, they are regarded as promising for practical MRB applications. An electrolyte containing representative magnesium fluorinated alkoxyborate Mg[B(HFIP)] ([B(HFIP)]: tetrakis(hexafluoroisopropoxy) borate) was prepared through general synthetic routes using Mg(BH); however, it shows poor electrochemical magnesium deposition/dissolution behavior. Herein, we report an alternative synthetic route of highly reactive Mg[B(HFIP)] and several critical issues associated with the use of Mg[B(HFIP)]/glyme electrolytes in MRBs. The cycling performance of the electrolytes as well as the synthetic reproducibility of the salt was significantly improved upon adopting a transmetalation reaction between certain magnesium and boron compounds for the salt preparation. Despite the outstanding electrochemical activity of Mg[B(HFIP)]/glyme, the electrolytes were unstable with the magnesium metal. The remarkably high dissociativity of Mg[B(HFIP)] in glyme solutions and the resulting enhanced induction interaction of Mg with coordinated glymes make the solutions reductively unstable. Surface passivation by [TFSA]-based electrolytes (TFSA: bis(trifluoromethanesulfonyl)amide) effectively suppressed the decomposition of Mg[B(HFIP)]/glyme electrolytes. This passivation simultaneously caused a large overpotential for electrochemical cycling. The short-circuiting of the cells upon repeated deposition/dissolution cycling is rather problematic. Here, the findings disclose the issues of fluorinated alkoxyborate-based electrolyte solutions that should be resolved for practical MRB materialization. We also emphasize the importance of systematic strategies in manipulating the electrolytes and interfaces as well as base magnesium metal based on each appropriate approach.
在镁可充电电池（MRB）研究领域，开发无腐蚀性但高效的电解质一直是一项长期挑战。由于基于氟代烷氧基硼酸盐的电解质克服了与传统电解质相关的严重问题，它们被认为在实际的MRB应用中很有前景。通过使用Mg(BH)的常规合成路线制备了一种含有代表性的镁氟代烷氧基硼酸盐Mg[B(HFIP)]（[B(HFIP)]：四(六氟异丙氧基)硼酸盐）的电解质；然而，它表现出较差的电化学镁沉积/溶解行为。在此，我们报告了一种高反应性Mg[B(HFIP)]的替代合成路线以及与在MRB中使用Mg[B(HFIP)]/乙二醇二甲醚电解质相关的几个关键问题。在采用某些镁和硼化合物之间的金属转移反应来制备盐时，电解质的循环性能以及盐的合成重现性得到了显著改善。尽管Mg[B(HFIP)]/乙二醇二甲醚具有出色的电化学活性，但电解质与镁金属不稳定。Mg[B(HFIP)]在乙二醇二甲醚溶液中具有非常高的离解性，以及由此导致的Mg与配位的乙二醇二甲醚之间增强的诱导相互作用，使得溶液在还原时不稳定。基于[TFSA]的电解质（TFSA：双(三氟甲磺酰)酰胺）进行表面钝化有效地抑制了Mg[B(HFIP)]/乙二醇二甲醚电解质的分解。这种钝化同时导致了电化学循环的大过电位。在重复的沉积/溶解循环中电池短路是相当成问题的。在此，这些发现揭示了基于氟代烷氧基硼酸盐的电解质溶液在实际MRB实现中应解决的问题。我们还强调了基于每种适当方法来操控电解质和界面以及基础镁金属的系统策略的重要性。
