A solid composite electrolyte poly(PEGDA-co-AN)/LiTFSI/nano-SiO2 with high conductivity and high entropy structure and its Li+ transport behavior

Abstract

Using solid electrolytes instead of traditional liquid electrolytes to assemble all-solid-state batteries can effectively solve the problem of electrolyte leakage and reduce risks caused by lithium dendrite growth during charging and discharging processes, which is capable to improving the safety of lithium battery. Solid polymer electrolytes have been widely studied in consideration of the factors, such as flexible structural design, convenient preparation, low cost, good interface contact with electrodes, and ease of large-scale production. Polyethylene oxide (PEO) polymers have a good solvation for most lithium salts, but PEO segments in polymers have high crystallinity at room temperature and a narrow electrochemical stability window (ESW), which will limit some advanced electrode materials with high potential used in batteries and restricts the improvement of battery performance as well. Polyacrylonitrile (PAN) with high dielectric constant has high electrochemical and thermal stability, good mechanical processing properties, and excellent fire retardancy. In this manuscript, a cross-linked copolymer, poly(PEGDA-co-AN), is prepared using polyethylene glycol diacrylate (PEGDA) and acrylonitrile (AN) as monomers and 2,2-azobisisobutyronitrile (AIBN) as a thermal initiator; the influence of Lewis acid–base interaction between nano-SiO₂ additive and –C≡N or C–O–C on Li⁺ transport has been investigated, and a new idea was proposed to improve the lithium ion transport in poly(PEGDA-co-AN)-based polymer composite electrolytes by adjusting the local charge environment of polymer electrolytes. Finally, a composite polymer electrolyte poly(PEGDA-co-AN)/LiTFSI/nano-SiO₂ with high entropy structure and high conductivity has been designed and fabricated, and it exhibits a room temperature ionic conductivity of 3.5 × 10⁻³ S cm⁻¹, Li⁺ transference number of 0.58, and the electrochemical stability window greater than 5 V.