Preparation Of Polyimide/Titania Compasite Nano-Fibrous Membranes By Electrospinning

With rising interest in green electrode materials for lithium-ion batteries (LIBs), increasing attention has been paid to materials for lithium-ion batteries in recent years. The separator in battery plays an important role in electrically isolating cathode and anode to prevent electrical short circuits and at the same time allow rapid transport of ionic charge carriers. The polyolefin-microporous separators such as polyethylene (PE) and polypropylene (PP) separators are commercially available, because of their superior properties, such as the electrochemical stability, considerable mechanical strength and thermal shut-down property. Nevertheless, they have some disadvantages when they are used in future energy storage devices and electric or hybrid-electric vehicles. One of the most serious issues is their inferior thermal stability, due to their low softening or melting temperature. So it is difficult to perform the critical function of electronic isolation between cathode and anode in large-sized batteries at elevated temperature or under vigorous conditions. Tremendous efforts have been made to develop high performance separators with superior electrolyte wet-ability, improved thermal stability and enhanced rate capability. There are two strategies right now, One strategy is to improve polyolefin microporous membranes, inorganic nanoparticles with polyolefin microporous membranes or preparation polymer composite non-woven, although this method can improve the thermal stability, lead to reduce the strength of the membranes; The other one is to select other battery separator materials and new preparation methods, this method is a hotspot of current research.Electrospinning is one of the main preparation methods for nano-fibrous membranes, which has been applied to a variety of experimental researches and productions. As high-performance polymer, polyimide has widely application for its excellent mechanical、thermal、high and low temperature resistance and other properties, which has better dimensional stability, electrolyte uptake, cycle performance, lower mechanical property. So people want to improve the mechanical property of PI. The inorganic particles and polyimide composite nano-fibrous membranes can solve the defect of polyimide. Titanium dioxide as one of a rigid inorganic particles, can increase the mechanical strength of the polyimide, at the same time, has excellent electrolyte invasive, acid, alkaline, and thermal stability, which also has better electrolyte uptake、acid-base property、thermal stability and long cycle life, low cost, and minimum environmental impact.In this experiment, polyamide acid can be made as nano-fibrous membranes by electrospinning. Titanium dioxide sol can be made by sol-gel method. By impregnation and thermal imidization, the polyamide-acid/titania composite nano-fibrous membranes can be converted to polyimide/titania composite nano-fibrous membranes to research the battery performance as lithium-ion battery separator. In the composite, titania nano-layer can strongly attach onto polyimide nano-fibrous membranes surface, which can improve the storage modulus, tensile strength, thermal stability and desirable pore structure, higher electrolyte uptake and better dimensional stability. For composite nano-fibrous membranes, the highest thermal transmission temperature is 407.1 ℃, the highest storage modulus is 1571.7 Mpa, the highest tensile strength is 43.94 Mpa, the highest temperature of weightlessness 5% is 503.42 ℃, minimum water contact Angle is 101.7°, the highest electrolyte uptake is 152%, the highest porosity is 66%, the highest temperature deformation is 401℃;The polyimide/titania composite nano-fibrous membranes are used in lithium-ion battery as separator, which show the better electrochemical properties, that is,the highest ionic conductivity is 5.56 X 10’3S/cm; The highest discharge specific capacity is 168.0mAhg’’; under the current density of 5C, the highest discharge specific capacity is 140.1mAhg-1; after 100 times cycle, the composite nano-fibrous membranes still keep good electrochemical performance, which makes them more promising in application.