Polyethylene Glycol Based Solid Polymer Electrolyte with Disordered Structure Design for All-Solid-State Lithium-Ion Batteries

In this work, a novel solid polymer electrolyte with analogous block copolymer structure has been designed, combining polyethylene glycol (PEG) as the rigid segments and hexamethylene diisocyanate (HDI) as the flexible segments. The synthesis was realized by alternating flexible PEG with rigid HDI through -NH-CO- groups, which are destroying the ordered structures of PEG and generating electron-deficient Lewis acid groups. The pathbreaking introduction of HDI blocks not only bridge links between the PEG molecules, but also generate electron-deficient Lewis acid groups. Therefore, the originally ordered structures of PEG are destroyed by both the alternated chains between PEG and HDI as well as the Lewis acid groups. As a result, the PEGH/L4000 electrolytes (PEG molecular weight of 4000) behave a strong anion-capture ability to decrease the crystallinity of polymers, which further achieve a high ionic conductivity close to 10-3 S·cm-1 with the lithium-ion transfer numbers up to 0.88 and the electrochemical stability window of 5.8 V (vs.Li+/Li). The symmetric Li|PEGH/L4000|Li cells maintain the low and stable voltage polarization for more than 800 hours at 0.1 mA·cm-2. Furthermore, the LiFePO4|PEGH/L4000|Li all-solid-state cells perform well both in cycling and rate performances. The design of polymer disordered structures for polymer electrolytes provides a new thought for manufacturing all-solid-state lithium-ion batteries with high safety as well as long life.