MULTI-FUNCTIONAL POLYPEPTIDES FOR APPLICATIONS IN LITHIUM ION BATTERIES
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Date
2019-01-01
Type of Work
Department
Chemistry & Biochemistry
Program
Chemistry
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Distribution Rights granted to UMBC by the author.
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Access limited to the UMBC community. Item may possibly be obtained via Interlibrary Loan thorugh a local library, pending author/copyright holder's permission.
This item is likely protected under Title 17 of the U.S. Copyright Law. Unless on a Creative Commons license, for uses protected by Copyright Law, contact the copyright holder or the author.
Abstract
Biological organisms have demonstrated the ability to synthesize complex inorganic structures through evolved polypeptides (nature's most diverse polymer). The investigation of these polypeptides has led to improved understanding of biomineralization processes and generated interest in biomimetic, non-natural materials, for applications in sensing or energy storage. Lithium ion (Li+) batteries represent one such material of interest due to their ubiquity as a portable energy device. While highly developed, current Li+ technology still faces limitations in cost, safety, cycle life, and power performance hindering its applications in future higher power systems. This research seeks to utilize a bio-inspired approach for addressing limitations in Li+ batteries by employing a bio-tethering polypeptide as a specific electrode binding agent. Initially, a versatile bacterial expression scheme was developed for generation of polypeptides identified through combinatorial display. A desired target peptide was expressed with an N-terminal 6xHis-SUMO tag and subsequently purified by ULP1 cleavage. Expression of 12mer and 24mer domains has resulted in yields of 8 – 13 mg/L of purified peptide which were then utilized for further study. M13 bacteriophage display was carried out against electrode materials utilized in Li+ batteries and mutant phage exhibiting binding for Li4Ti5O12 (LTO) and MWCNTs were identified. Phage affinity for LTO was assessed through binding assays and a peptide (THHSTKYWPPSQ) was selected for further characterization by isothermal titration calorimetry (ITC) where it demonstrated micromolar affinity for LTO. Alanine scanning and subsequent ITC experiments indicated three residues pertinent for the peptides' affinity. A bifunctional peptide composed of the characterized LTO peptide and an MWCNT peptide was expressed in bacteria and purified. The bifunctional peptide exhibited similar LTO affinity in ITC experiments. Incubation of the bifunctional peptide with MWCNTs in aqueous solution demonstrated its ability to interact with MWCNTs by enhancing their dispersion. This bifunctional peptide was utilized as a specific binding agent in LTO electrode slurries which were processed in aqueous rather than organic solvent. An optimized peptide electrode exhibited improved capacities at fast charge-discharge rates compared to a standard LTO electrode indicating the ability for a bifunctional peptide to be utilized as a specific binding agent in lithium ion battery electrodes.