Modification Of Polyvinylidene Fluoride-based Composite Electrolyte And Its Application In High-voltage Lithium Metal Batteries

Solid polymer electrolytes with good mechanical properties,wide electrochemical window,and excellent safety performances are considered as the key materials to solve the safety hazards and poor electrolyte/electrodes interface compatibility of traditional liquid electrolytes.However,solid polymer electrolytes still have the problems of low room temperature ionic conductivity and big electrolyte/electrodes interface contact impedance.Gel polymer electrolytes with amounts of organic liquid electrolytes can have high room temperature ionic conductivity and achieve good electrolyte/electrodes interface wettability.However,this premise is at the expense of the mechanical properties and safety performances of the polymer electrolytes.In order to prepare polymer electrolytes with high room temperature ionic conductivity,good mechanical properties,superior safety performance and excellent electrode interface compatibility and stability to satisfy the application and development of high-performance polymer lithium battery,a selective wetting design strategy for polymer electrolytes is presented in this paper.The details are as follows.Polyvinylidene fluoride/polyvinyl acetate-based composite polymer electrolytes?PVDF/PVAC-based CPE?selectively wetted by tetramethylene sulfone?TMS?with low flammability,high thermal stability,and excellent anodic stability is first fabricated as a rigid-flexible coupling polymer electrolyte for 4.5 V high performance LiCoO₂-based high-voltage lithium metal batteries.More importantly,due to the distinct intermolecular interaction difference of PVDF and PVAC with TMS,TMS can only selectively wet and interact with PVAC in PVDF/PVAC-based CPE,which is helpful to enhance lithium ion conductivity and interfacial contact.The rigid PVDF framework maintains sufficient high mechanical strength and the flexible PVAC/TMS components possesses high ionic conductivity and electrochemical stability window.In addition,the as-prepared polymer electrolyte has excellent interfacial compatibility and electrochemical stability with the lithium metal anode.And the reason behind the excellent interface stability between the polymer electrolyte and lithium metal anode was analyzed by scanning electron microscopy,atomic force microscopy,X-ray photoelectron spectroscopy?XPS?,and time of flight secondary ion mass spectrometry.LiCoO₂/Li battery with the as prepared polymer electrolyte was assembled to test its long-term cycle performance and rate capability at room temperature.As a result,the as-assembled LiCoO₂/Li batteries present excellent cyclability with 85%capacity retention after 200 cycles between 3.0 and 4.5 V at room temperature.The cathode interface was characterized by energy dispersive spectrometer?EDS?and XPS to further explain the reasons behind the long-term cycle stability of the batteries.Furthermore,the as-obtained PVDF/PVAC-based CPE membranes endow the high-voltage solid-state lithium metal batteries with the ability to withstand the tough tortures of large external forces and high temperature under harsh conditions,which demonstrates the outstanding safety characteristic of the PVDF/PVAC-based CPE.This study offers a promising and general selectively wetted design strategy to handle the compatibility and safety issues in high-voltage lithium metal batteries.