Synthesis And Application In Quasi-Solid-State Lithium Batteries Of Polyimide Nanofiber Film

With the rapid development of mobile electronic devices and electric vehicles,the development of high-performance lithium batteries and materials is particularly critical.Lithium（Li）metal anode is currently recognized as an ideal anode material due to the highest energy density in comparison with other electrode materials.However,the traditional liquid electrolyte（LE）has poor compatibility with Li metal,which leads to the uncontrollable formation of Li dendrites,severe volume expansion of anode,and unstable solid electrolyte interface,resulting in serious safety hazards and reduced service life of lithium metal batteries（LMBs）in practical applications.Compared with LE,solid-state electrolytes（SSEs）have obvious improvement in safety and energy density and promise to fundamentally solve the safety problems of LE.However,SSEs suffer from low ionic conductivity and poor interfacial contact,which limit their practical application.Quasi-solid electrolytes（QSEs）,characterized by liquid phase properties,can effectively combine the high ionic conductivity of LE and the safety performance of SSEs while mitigating the disadvantages of both.At present,studies have shown that in-situ polymerization technology is a convenient and effective method to prepare QSEs,and the electrolyte prepared by in-situ polymerization can minimize the problem of interfacial contact between electrolyte and electrode.Currently,commercial polyolefin separators are used as the supporting framework for in-situ gel QSEs,but the separators are prone to curling and shrinking when heated,and the mechanical properties in different directions are anisotropic,resulting in reduced thermal stability and mechanical properties of QSEs.When the battery is operating at an elevated temperature or subjected to external shock,it is easy to cause serious consequences such as fire and explosion.Based on the above problems,the polyimide（PI）nanofiber film was prepared by electrospinning technology to replace the traditional polyolefin separator and composite it with gel electrolyte precursor solution.An ultra-thin,high-strength,and thermally stable composite quasi-solid electrolyte（PIQSE）was formed by in-situ polymerization of gel electrolyte precursor solution at room temperature.As a special engineering material,PI has higher thermal dimensional stability and mechanical properties than polyolefin separators,the nanofiber film prepared by electrospinning technology has a 3D network structure,which can quickly absorb gel electrolyte precursor solution to form a uniform and stable QSE network.Here,we first explored the spinning solution concentration and spinning parameters to prepare pure PI nanofiber film that meets the requirements of battery separators,and then compounded it with the QSE precursor solution at room temperature,using lithium hexafluorophosphate（Li PF₆）to induce 1,3-dioxolane（DOL）ring-opening self-polymerization in the precursor solution to transform it into a gel state.As a result,the PIQSE film shows a high room-temperature ionic conductivity of 2.9×10^-3 S/cm,high mechanical strength of 31 MPa,and high heat resistance to160℃.The coin cell assembled with Li Fe PO₄ cathode also showed excellent electrochemical performance at a high rate of 0.5 C,its capacity retention rate was 91.8%after 200 cycles at25℃,showing an attractive prospect in industrial application.