Lithium-Ion Intercalation by Calcium-Ion Addition in Propylene Carbonate-Trimethyl Phosphate Electrolyte Solution

Abstract

Electrochemical intercalation of lithium ions was investigated in propylene carbonate (PC)-trimethyl phosphate (TMP) electrolyte solution. Intercalation of lithium ions took place in 1 mol dm−3 lithium bis(trifluoromethanesulfonyl)amide (LiTFSA)/PC:TMP by adding a certain amount of calcium ions. When the molar ratio of PC:TMP:Li+ was 6:6:1, lithium-ion intercalation took place when the molar ratio of Ca2+/Li+ was 1.2. The criteria was Ca2+/Li+ = 0.8 when the molar ratio of the electrolyte was PC:TMP:Li+ = 2:10:1. It was suggested from Raman spectra that the solvation structure of lithium ions were altered from the four coordinated tetrahedral configuration in the case that intercalation reaction occurred. This change in the lithium-ion solvation structure was caused by adding calcium ions, which has stronger Lewis acidity than lithium ions. Different criteria of Ca2+/Li+ molar ratio for lithium-ion intercalation by the difference of PC:TMP:Li+ molar ratio shows that the lithium-ion solvation structure was also affected by the electrolyte composition.