Li＋在PC＋DMF混合溶剂中优先溶剂化的13C NMR研究

利用¹³C NMR光谱技术研究了Li^＋在碳酸丙烯酯(PC)＋N,N-二甲基甲酰胺(DMF)混合溶剂中的优先溶剂化现象. 根据溶剂分子中碳原子的化学位移随锂盐浓度的变化关系, 确定了与Li^＋发生配位的原子. 碳原子的配位位移值随混合溶剂组成的变化关系表明, 在LiClO₄＋PC＋DMF混合物中, DMF分子对Li^＋的溶剂化作用较PC分子强. 定量计算得到, 在n(PC)∶n(DMF)＝1∶1(摩尔比)的混合溶剂中, PC与DMF分子数在Li^＋第一溶剂化层中的比率为0.12, 说明Li^＋优先被DMF分子溶剂化.

13C NMR Studies on the Preferential Solvation of Li+ in PC+DMF Mixed Solvents

The preferential solvation of Li in propylene carbonate (PC) and N,N-dimethylformamide (DMF) mixed solvents has been studied by 13C NMR technique at various solvent and lithium salt concen- tration. The difference in the chemical shifts of the solvent with and without the electrolyte was attributed to the coordination of the solvent to Li . Based on the observed dependence of the 13C NMR chemical shift for the solvents on the composition of the electrolyte, the coordinated atoms of the solvents to Li have been determined. The solvation ability of DMF to Li was found to be stronger than PC from the variation of co- ordination shift with the molar fraction of PC. It was shown that the molar ratio of PC to DMF molecules in the first solvation shell of Li was 0.12 in the ternary solution with equal mole of PC and DMF. These re- sults indicated that Li was solvated preferentially by DMF molecules in the LiClO4 PC DMF mixtures.