Preparation And Performance Study Of Polyimide Nanofiber Lithium Battery Separator

As an effective strategy to overcome the problem of energy storage,Lithium battery has received more and more attention.The separator,an important part of battery,mainly serves to separate the electrodes and avoid short circuit.At present,commercial separators are mainly made of polyolefin microporous membranes,which have poor electrolyte wettability,low porosity,poor thermal dimensional stability.Therefore,the research of new separators with high porosity,excellent electrolyte wettability and high temperature stability has become a hotspot in recent years.Electrospun polyimide nanofiber membrane have been researched widely for separator material due to its excellent high temperature resistance,high porosity and chemical stability.However,the low mechanical strength and serious self-discharge hindered its further development.Therefore,in order to solve such problems and improve electrochemical performance,the main contents of this paper are as follows:(1)A mixed solution was obtained by adding Octa(y-chloropropyl)polyhedral oligomeric silsesquioxane(OCP-POSS)nanoparticles to polyamic acid spinning solution.The polyimide/OCP-POSS composite separator was successfully prepared by electrospinning and imidization.The effects of different contents of OCP-POSS on the physicochemical properties of nanofiber membranes were analyzed by different characterization methods such as SEM,thermal stability test,mechanical properties and contact angle test.At the same time,the relevant electrochemical performance were tested to investigate the effect of different contents of OCP-POSS on the comprehensive performance of lithium-ion batteries.The results showed that when the OCP-POSS content was 3.5%,the fibers had a minimum diameter of 140.4 nm and the strength up to the maximum of 19.67 MPa.The battery with the composite membrane(3.5%OCP-POSS)exhibited the highest initial specific capacity of 168.4 mAh g-1 and good capacity retention rate of 91.96%.(2)A novel electrospun polyimide nanofiber separator for lithium-sulfur battery was successfully prepared by hot pressing process and imidization treatment in the polyamic acid membrane stage.The various tests showed that the separator had outstanding thermal stability,excellent mechanical properties and good ability to absorb and store electrolyte.Importantly,the interconnected tight microporous structure and the abundant polar functional groups of the polyimide macromolecule effectively inhibited the diffusion and loss of polysulfide intermediates in the electrolyte.In the cycle testing,the discharge specific capacity of the separator was 680 mAh g-1 after 200 cycles at 0.5 C rate and the capacity decay rate was only 0.08%,which indicated that the electrospun polyimide separator through special hot pressing treatment had excellent cycle stability.