Research On The Preparation And Property Of Polymer Ceramic Composite Separator For Lithium Ion Batteries

At present,lithium-ion batteries are widely used in mobile electronic devices and large-scale energy storage systems such as electric vehicles and state grid energy storage.The updating and iteration of various products in the market make the lithium-ion battery industry develop rapidly,at the same time,there are higher requirements for the safety,capacity,life and other aspects of lithium-ion batteries.The common polyolefin materials in commercial separators have poor stability,easy to curl and melt after being heated and be damaged by lithium dendrites,which will cause serious safety problems of batteries.Polyvinylidene fluoride hexafluoropropylene?PVDF-HFP?materials have the most potential in the new type of separator materials,showing excellent thermal stability,and PVDF-HFP materials are the research hotspot of lithium ion batteries.In this paper,the high-performance Li-MMT/PVDF-HFP composite separator was prepared by electrophoretic deposition technology for the first time,which effectively solved the problem of lithium dendrite at the interface between the separator and anode in lithium-ion battery.The mechanical strength,thermal stability and rate performance of four kinds of commercial separator and four polymer separators prepared by different molecular weight PVDF-HFP materials are compared.Compared with commercial polyolefin separators,PVDF-HFP separators show better thermal stability and electrochemical performance.The lithium montmorillonite ceramic materials were prepared by ion-exchange method,which is widely used in industry,and the separator with lithium channel was prepared by electrophoretic deposition technology through cross-linking layered silicate clay and PVDF-HFP polymer.By adjusting the proportion of Li-MMT particles,four kinds of separators with different contents were obtained and compared with pure PVDF-HFP separator in term of the rate performance.Li-MMT/PVDF-HFP polymer separators with the optimal addition of 10%was compared with pure PVDF-HFP and commercial separators by the tests of microstructure,mechanical strength,liquid absorption and electrochemical performance of the battery.It was found that the Li-MMT/PVDF-HFP polymer separator prepared by electrodeposition had excellent safety and electrochemical performance.This is mainly because the interlayer spacing?¹.31 nm?in the Li-MMT/PVDF-HFP composite separator provides more active sites for Li⁺,which makes the lithium ion transfer rapidly in the electrochemical reaction.At the same time,the parallel middle layer balances the flow direction of Li⁺and makes Li⁺deposit evenly on the anode,which effectively eliminates the problem of lithium dendrite in the Li⁺plating/stripping processes.After 300 cycles at 0.5 C,the reversible capacity of the battery is 152 mAh·g^-1 and the capacity retention rate is up to 98.5%.This is due to the fast ion transfer path with high ionic conductivity(>5.66×10^-4 S cm^-1)and the enhanced interaction between the polymer and phyllosilicate clay.In this paper,the composite separator made of ceramic materials in PVDF-HFP polymer can obtain better safety performance and electrochemical performance,which provides a useful reference for the application research of lithium battery separator.