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

Organoboron-based anion trapping polymer electrolytes were synthesized through hydroboration or dehydrocoupling reaction between poly(propylene oxide) (PPO) oligomer (Mn=400, 1200, 2000 and 4000) and 9-borabicyclo[3.3.1]nonane (9-BBN). Obtained oligomers were added various lithium salts (LiN(CF3SO2)2, LiSO3CF3, LiCO2CF3 or LiBr) to analyze the ionic conductivity and lithium ion transference number (tLi+). The ionic conductivity of the oligomer in the presence of LiN(CF3SO2)2 showed higher ionic conductivity than other systems, however, the tLi+ was less than 0.3. When LiSO3CF3 or LiCO2CF3, was added high tLi+ over 0.6 was obtained. Such difference in tLi+ can be explained by HSAB principle. Since boron is a hard acid, soft (CF3SO2)2N- anion can not be trapped effectively. High ionic conductivity of 1.3x10-6Scm-1 and high tLi+ 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