Polybenzimidazoles (PBIs) are a series of super high performance polymers attracting researchers’ attention because of PBIs have a rigid structure of aromatic and hetero rings in their backbone to induce a good stability. Also, PBIs have active imidazole hydrogen (-NH) to receive chemical modification. However previously bio-based PBIs have ever been tried to prepare and base on such a background we have used renewable 3-amino-4-hydroxybenzoic acid (3, 4-AHBA) derived from Streptomyces sp. to produce bio-based PBI. Our bio-PBI showed high mechanical strength, Young’s moduli, and high thermal resistance considerable comparison with commercial PBIs, owing to strong π-π stadcking interaction among aromatics and imidazole rings and H-bonding between N-H and N of imidazole ring. Imidazole ring can be easily modified by substituting the imidazole proton. Here we report N-boronation of the PBI via lithiation to be ionically conductive (scheme 1). The PBI was modified by triethylborane substitution to imidazole proton (modification degree 46 % to NH) to create anionic PBI with Li counter ion. Ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMImTFSi) was added to the anionic PBI to prepare ion gels with different concentration. Li-ion shows ionic conductivity with 1.4x10-2 Scm-1 at maximum whereas Li-ion transference number was obtained (t+=0.623) at maximum. Ionic conductivity, Li-ion transference number, activation energy, and carrier ion number were changed with increasing ionic liquid concentration, to show maximums at a certain concentration. Further, charge-discharge measurement of the ion-gel was made by fabricating anodic half-cell composed of the ion gel as electrolyte, Si-electrode as anode, and Li-metal as cathode. The resulting value showed a good reversible capacity at discharge rates ranging 0.1 – 1.0 C. Thus, considerable electrochemical properties were confirmed which governs to use the N-boronated PBI as polymer electrolyte material in Lithium secondary batteries.

Novel biomolecular design of N-boronated polybenzimidazole with single ion conductivity

255th National Meeting (2018)

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