The Nanostructure of Water-in-Salt Electrolytes Revisited: Effect of the Anion Size.
The Nanostructure of Water-in-Salt Electrolytes Revisited: Effect of the Anion Size.
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DOI：
10.1021/acsnano.1c01737
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发表时间：
2021-07
期刊：
影响因子：
17.1
通讯作者：
Gabriela Horwitz;E. Härk;Paula Y. Steinberg;L. Cavalcanti;S. Risse;H. Corti
中科院分区：
文献类型：
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作者：
Gabriela Horwitz;E. Härk;Paula Y. Steinberg;L. Cavalcanti;S. Risse;H. Corti
对开发安全和可持续的储能系统的兴趣日益增加，导致人们对超浓缩电解质（通常称为盐包水（WiS））的关注迅速增加。一些工作表明，这些液体电解质的传输性质与纳米结构域的存在有关，但缺乏对这种结构的详细表征。在这里，锂WiS电解质的结构纳米异质性，包括锂三氟甲磺酸盐（LiTf）和双（三氟甲磺酰基）酰亚胺（LiTFSI）的解决方案作为浓度和温度的函数，进行了评估，通过小角中子散射（SANS）模式的分析。在3.5-5 nm-1左右的Q范围内，相关峰的浓度变化与温度无关，表明这些电解质由纳米级富水通道组成，该通道形成3D分散的富阴离子网络，Tf和TFSI阴离子之间的差异与其不同的体积和相互作用有关。此外，一个共同的趋势，发现这两个系统的形态以上的盐体积分数为0.05。这些结果表明，在形成的纳米结构的决定因素是盐的体积分数（相关的阴离子的大小），而不是其重量摩尔浓度。这些发现可能代表了设计WiS电解质的范式转变。
The increasing interest in developing safe and sustainable energy storage systems has led to the rapid rise in attention to superconcentrated electrolytes, commonly called water-in-salt (WiS). Several works indicate that the transport properties of these liquid electrolytes are related to the presence of nanodomains, but a detailed characterization of such structure is missing. Here, the structural nano-heterogeneity of lithium WiS electrolytes, comprising lithium trifluoromethanesulfonate (LiTf) and bis(trifluoromethanesulfonyl)imide (LiTFSI) solutions as a function of concentration and temperature, was assessed by resorting to the analysis of small-angle neutron scattering (SANS) patterns. Variations with the concentration of a correlation peak, rather temperature-independent, in a Q range around 3.5-5 nm-1 indicate that these electrolytes are composed of nanometric water-rich channels percolating a 3D dispersing anion-rich network, with differences between Tf and TFSI anions related to their distinct volumes and interactions. Furthermore, a common trend was found for both systems' morphology above a salt volume fraction of ∼0.5. These results imply that the determining factor in the formation of the nanostructure is the salt volume fraction (related to the anion size), rather than its molality. These findings may represent a paradigm shift for designing WiS electrolytes.