Simple introduction of anion trapping site to polymer electrolytes through dehydrocoupling or hydroboration reaction using 9-borabicyclo[3.3.1]nonane

Abstract

Organoboron-based anion trapping polymer electrolytes were synthesized through hydroboration or dehydrocoupling reaction between poly(propylene oxide) (PPO) oligomer ( M n = 400, 1200, 2000 and 4000) and 9-borabicyclo[3.3.1]nonane (9-BBN). Obtained oligomers were added various lithium salts (LiN(CF 3SO 2) 2, LiSO 3CF 3, LiCO 2CF 3 or LiBr) to analyze the ionic conductivity and lithium ion transference number ( t L i + ). The ionic conductivity of the oligomer in the presence of LiN(CF 3SO 2) 2 showed higher ionic conductivity than other systems, however, the t L i + was less than 0.3. When LiSO 3CF 3 or LiCO 2CF 3, was added high t L i + over 0.6 was obtained. Such difference in t L i + can be explained by HSAB principle. Since boron is a hard acid, soft (CF 3SO 2) 2N − anion can not be trapped effectively. High ionic conductivity of 1.3 × 10 −6 S cm −1 and high t L i + of 0.73 was obtained when PPO chain length was 2000. These values of facilely prepared polymer electrolytes are comparable to those of the PPOs having covalently bonded salt moieties on the chain ends.