Preparation And Electrochemical Properties Of Alumina Nanofiber Composite Separators

The separator is one of the key materials in the battery component,and its structure and material properties determine the electrochemical performance and cycle life of the battery.Microporous polyolefin commercial separators have been widely used in batteries due to their excellent mechanical properties and stable electrochemical properties.However,their poor thermal stability,low porosity,and poor wettability properties have severely limited their development.Therefore,it is important to develop a high-performance separator material for batteries.In this paper,alumina(Al₂O₃)nanofibers were prepared by using efficient and low-cost electro-blown spinning technology,and they were successfully mixed with organic nanofibers(PAN or PI)by wet-laid method to prepare composite separator for batteries.As a widely used inorganic fiber,Al₂O₃ nanofibers have outstanding high temperature resistance and wettablity properties.Both PAN and PI nanofibers have high mechanical properties and heat resistance,which can improve the overall mechanical properties of the separator.Therefore,the composite separator combines the characteristics of inorganic fibers and organic fibers,and exhibits excellent physical and electrochemical properties.The specific research contents are as follows:(1)Al₂O₃ nanofibers and PAN nanofibers were prepared based on electro-blown spinning technology,and they were successfully mixed to prepare composite separator for batteries(Al₂O₃&PAN-NFCM)by wet-laid method.The physical and electrochemical properties of Al₂O₃&PAN-NFCM were analyzed by means of SEM,mechanical property test,thermal stability test,AC impedance spectroscopy and constant current charge-discharge method.Experiments show that when the composite separator is doped with 30 wt%Al₂O₃ nanofibers(30 wt%Al₂O₃&PAN-NFCM),the comprehensive performance of the separator is the best.It is comparable to pure PAN and commercial separators(Al₂O₃/PP,PP/PE/PP).In comparison,the composite membrane has the best heat resistance,the highest porosity,and the best wettability.The ionic conductivity is as high as 1.7×10^-3 S/cm.It is used as a separator in lithium ion batteries with a current density of 0.5 C,the initial specific capacity is as high as 152.9 m Ah/g,and it still has a specific discharge capacity of 83.1%after 200 cycles.(2)Al₂O₃ nanofibers were prepared based on electro-blown spinning technology,ultrafine PAA nanofibers were prepared by electrospinning technology,and thermal amidation process was performed after wet-laid to obtain composite membrane of Al₂O₃ nanofiber and PI nanofiber(Al₂O₃&PI-NFCM).Similarly,the physical and electrochemical properties of Al₂O₃&PI-NFCM were analyzed by the relevant characterization methods in(1).The experiments show that when 50 wt%Al₂O₃nanofibers(50 wt%Al₂O₃&PI-NFCM)are doped in the composite separator,the separator has the best comprehensive performance.Compared with Al₂O₃/PP and PP/PE/PP,the separator shows outstanding flame retardancy,high porosity,good wettability.The ionic conductivity is as high as 2.71×10^-3 S/cm,used as a separator in lithium ion capacitors,its energy density can reach 12.5 Wh/kg even at the high power density of 15 k W/kg.At the current density of 0.5 A/g,its initial energy density is as high as 57.3 Wh/kg and it can maintain a high cycle stability even after 10000cycles.