Anion Coordination Interactions in Solvates with the Lithium Salts LiDCTA and LiTDI

Lithium 4,5-dicyano-1,2,3-triazolate (LiDCTA) and lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI) are two salts proposed for lithium battery electrolyte applications, but little is known about the manner in which the DCTA– and TDI– anions coordinate Li+ cations. To explore this in depth, crystal structures are reported here for two solvates with LiDCTA(G2)1:LiDCTA and (G1)1:LiDCTAwith diglyme and monoglyme, respectively; and seven solvates with LiTDI(G1)2:LiTDI, (G2)2:LiTDI, (G3)1:LiTDI, (THF)1:LiTDI, (EC)1:LiTDI, (PC)1:LiTDI, and (DMC)1/2:LiTDIwith monoglyme, diglyme, triglyme, tetrahydrofuran, ethylene carbonate, propylene carbonate, and dimethyl carbonate, respectively. These latter solvate structures are compared with the previously reported acetonitrile (AN)2:LiTDI structure. The solvates indicate that the LiTDI salt is much less associated than the LiDCTA salt and that the ions in LiTDI, when aggregated in solvates, have a very similar TDI–···Li+ cation mode of coordination through both the anion ring and cyano nitrogen atoms. Such coordination facilitates the formation of polymeric ion aggregates, instead of dimers. Insight into such ion speciation is instrumental for understanding the electrolyte properties of aprotic solvent mixtures with these salts.二氰基-1,2,3-三唑锂（Lithium 4,5-dicyano-1,2,3-triazolate，LiDCTA）与2-三氟甲基-4,5-二氰基咪唑锂（lithium 2-trifluoromethyl-4,5-dicyanoimidazole，LiTDI）是两类拟应用于锂电池电解液的锂盐，但目前人们对DCTA⁻与TDI⁻阴离子配位锂离子（Li⁺）的具体方式仍了解有限。为深入阐明该问题，本文报道了两种LiDCTA溶剂化物的晶体结构：分别与二甘醇二甲醚（diglyme）形成的(G2)₁:LiDCTA，以及与单甘醇二甲醚（monoglyme）形成的(G1)₁:LiDCTA；同时报道了七种LiTDI溶剂化物的晶体结构，分别为与单甘醇二甲醚形成的(G1)₂:LiTDI、与二甘醇二甲醚（diglyme）形成的(G2)₂:LiTDI、与三甘醇二甲醚（triglyme）形成的(G3)₁:LiTDI、与四氢呋喃（tetrahydrofuran，THF）形成的(THF)₁:LiTDI、与碳酸乙烯酯（ethylene carbonate，EC）形成的(EC)₁:LiTDI、与碳酸丙烯酯（propylene carbonate，PC）形成的(PC)₁:LiTDI，以及与碳酸二甲酯（dimethyl carbonate，DMC）形成的(DMC)₁/₂:LiTDI。本文将上述LiTDI溶剂化物结构与此前已报道的乙腈（acetonitrile，AN）₂:LiTDI结构进行了对比分析。结构研究结果表明，LiTDI盐的离子缔合程度远低于LiDCTA盐；且在溶剂化物中聚集时，LiTDI中的离子可通过阴离子环与氰基氮原子共同配位，TDI⁻与Li⁺的配位模式高度相似。该类配位方式有利于形成聚合型离子聚集体，而非二聚体。对这类离子物种分布的深入认知，可为理解含此类锂盐的非质子溶剂混合体系的电解液性能提供关键理论支撑。