π-Conjugated zinc phthalocyanine in polymer electrolyte induced stable interface for room-temperature solid-state lithium batteries.

Solid state lithium metal battery can effectively promote the energy density and mitigate safety hazards such as electrolyte leakage and explosion that are often associated with conventional liquid electrolytes. Solid polymer electrolytes (SPEs) have garnered significant attention in lithium metal batteries for their cost-effectiveness, good mechanical properties, and easy processing. However, low ionic conductivity and unstable interface accompanied with lithium dendrite growth are two major challenges. In this study, zinc phthalocyanine (ZnPc), featuring an extended π-conjugated structure, was introduced into a polyethylene oxide (PEO)-based composite electrolyte. By adjusting the redox state of the electrolyte, a LiF-enriched SEI layer was formed on the lithium metal surface. The ZnPc in polymer electrolyte exhibits excellent interfacial stability, achieving stable lithium deposition/stripping for over 2000 h. The Lewis acid sites of ZnPc can selectively adsorb TFSI- anions, facilitating the dissociation of LiTFSI and significantly enhancing the lithium-ion migration number (tLi+ = 0.62) and improved ion conductivity. The Li||LiFePO4 cell employing this electrolyte maintains ∼80 % capacity retention after 400 cycles at 0.5C under ∼25 °C, demonstrating superior cycling stability.