Advanced fluorinated gel polymer electrolyte enabling shunt current-free operation in quasi-solid-state bipolar stack batteries

Abstract

As demand grows for high-capacity batteries in electric vehicles, unmanned aerial vehicles, and energy-storage systems, cell sizes have increased accordingly. However, the conventional large-sized parallel configuration suffers from polarization due to the uneven potential distribution, particularly near tab and edge regions. To address this, bipolar stack designs with serial anode/cathode connections offer a promising solution for achieving uniform electrochemical reactions and high-power performance. In this study, a bipolar stack battery incorporating a quasi-solid-state gel polymer electrolyte (GPE) is successfully demonstrated, enabled by an effective edge-masking electrode sealing strategy to prevent shunt current between adjacent stacks. To enhance the oxidative stability of the GPE, we design a novel copolymer based on poly(ethylene glycol) diacrylate (PEGDA) and 2-(perfluorohexyl) ethyl acrylate (C6FA), and its molecular-level stability is investigated through density functional theory calculations. The quasi-solid-state 5-stack bipolar Li||NCM90 battery demonstrates 85.9 % capacity retention after 100 cycles and delivers an output voltage five times higher than that of a single cell, while maintaining non-flammability even under a nail penetration test. This novel design demonstrates the feasibility of bipolar stacking for Li-metal and Li-ion batteries using a quasi-solid-state GPE, enabling higher energy density, increased output voltage, and enhanced safety.