BORON-INCORPORATED PEO-BASED POLYMER ELECTROLYTES FOR ENHANCED LITHIUM-ION BATTERIES

Abstract

Advanced next-generation lithium-ion batteries (LIBs) necessitate the development of high-performance polymer electrolytes (PEs) that offer enhanced safety, thermal stability, and electrochemical performance. This study outlines a systematic approach for the design of novel polymer electrolyte systems based on three fundamental principles: (i) increased ion transport facilitated by polymers with low glass transition temperatures (Tg), (ii) enhanced lithium salt dissociation via acid–base interactions, and (iii) the simultaneous incorporation of acidic and basic functional groups into the polymer backbone to foster coordinated ion conduction. To achieve that, boron-containing polymers were synthesized. The modified polymers aim to enhance the performance of polyethylene oxide (PEO)-based polymer electrolytes (PEs) for lithium-ion batteries. The systems promise to reduce polyethylene oxide (PEO) crystallinity, increase salt dissociation, and selectively improve lithium-ion transport by immobilizing TFSI⁻ anions improving the overall lithium-ion battery performance. The modified polymers are named tripegylated boron (TPB), diglyme boron (DGB), and grafted polystyrene hairy nanoparticles (G-PS HNPs). TPB was synthesized by allylation and hydroboration of methoxypolyethylene glycol and blended with PEO and LiTFSI salt. The TPB-based PE (25 wt.% of TPB, EO/Li⁺ = 5:1) exhibited the highest ionic conductivity of 7.65 × 10⁻² S cm⁻¹ at 85 °C and a lithium transference number of 0.65, owing to enhanced segmental mobility and anion immobilization. DGB, a two-centered boron macromolecule synthesized from tetraethylene glycol, also showed similar benefits. When DGB was mixed with PEO and LiTFSI, DGB-based systems (25 wt.% of DGB, EO/Li⁺ = 5:1) possessed room temperature conductivities up to 3.43 × 10⁻³ S cm⁻¹ and lithium transference numbers above 0.5. Structural and morphological studies confirmed improved phase compatibility and reduced crystallinity of the polymer electrolytes, whereas electrochemical stability has been up to 3.7 V. Additionally, G-PS HNPs were synthesized by grafting allyl functionalized polystyrene nanoparticles with AMPEG and boron. When blended with 15 wt.% LiTFSI, the system exhibited enhanced amorphous structure, lower Tg (106 °C), and higher conductivity between 25-85 °C, with a transference number of 0.29. Collectively, these findings demonstrate boron-functionalized materials as being desirable components for future PEs, useful to enhance better conductivity, ion selectivity, and thermal-electrochemical stability in lithium battery applications.