Poly(Ethylene Terphthalate)Separators Were Modified By Dip-blade Coating Method

Separator is one of the important parts in lithium-ion batteries, its properties have effects on the electrochemical performance and safety performance of lithium-ion batteries.Commercial polyolefin separators have some disadvantages, such as poor thermal stability,poor electrolyte wettability and low porosity. Thus lithium-ion batteries could not meet these requirements for high power and energy density, high safety. Poly（ethylene terephthalate）（PET） nonwoven separator has been considered to use in LIBs because of its high porosity, high electrolyte wettability, and high melt point. In this paper, the poly（ethylene terephthalate）（PET） nonwoven separator is Poly（ethylene terephthalate）（PET）nonwoven separator to solve its large pore size and uneven pore size distribution, and PP separator severed as a comparison.Firstly, Al₂O₃/PVDF-HFP was coated on PET nonwoven separator surface by dipblade coating method. Different ratios of Al₂O₃/PVDF-HFP（namely, 70/30, 50/50, 30/70,0/100; composite separators are named as P-7, P-5, P-3, P-0） were researched. The SEM photographs, permeability, porosity, electrolyte wettability, ionic conductivity, thermal stability, and electrochemical performance were tested. The results show that P-3 and P-0separators have excellent physicochemical properties and electrochemical performance.The ionic conductivity of P-3 and P-0 separators are 1.098mS/cm and 1.071mS/cm at room temperature respectively. The batteries assembled with P-3 and P-0 separators have excellent cycle and rate performance.Secondly, according to the results of above-mentioned experiments, we optimized experimental parameters. Different drying temperature was researched based on the preparation of P-0 composite separator. Composite separators were dried at 50℃, 80℃,110℃ respectively, named as P-0, P-1, P-2. The physicochemical properties and electrochemical performance of composite separators were tested, results showed that when the drying temperature become higher the pore size of composite separator smaller.But the temperature could not indefinitely increase, the porous structure become collapse when the drying temperature was 110℃. Composite separator P-1（namely drying temperature was 80℃） has excellent physicochemical properties and electrochemicalperformance.Finally, different ratios of SiO₂/Al₂O₃ coated on the PET nonwoven surface, and PVDF-HFP severed as binder based on the results of above-mentioned experiments. The ratio of SiO₂/Al₂O₃ was respectively 0/1, 3/7, 1/1, 7/3, 1/0, and composite separator named as S-0, S-1, S-2, S-3, S-4. The results showed that S-1 separator owned good interstitial voids, higher thermal stability, and better electrolyte wettability. These batteries assembled with S-1 separators showed superior cycle and rate performance.