Study On The Preparation And Performance Of Hybrid Polyacrylonitrile Gel Polymer Electrolyte

The widespread application and rapid development of lithium-ion batteries have put forward higher requirements for the development of electrolyte.Polyacrylonitrile(PAN)based gel polymer electrolyte(GPE),as one of the earliest polymer electrolyte,has higher ionic conductivity than GPEs based on other traditional polymer matrix.However,the higher crystallinity of PAN causes a certain degree of impediments to the lithium ion transference in the GPE,and the poor compatibility between GPE and electrode can not be ignored,all of these defects affect the electrochemical performance of GPE.The addition of inorganic nano-filler to the polymer matrix is an effective measure to improve electrolyte performance.Nevertheless,the poor compatibility and dispersibility between the inorganic filler and organic polymer matrix need to be addressed.This paper prepared a kind of cage-type nanoparticles polyhedral oligomeric silsesquioxane(POSS),which has intramolecular organic-inorganic hybrid three-dimensional structure.Based on the better matrix compatibility of organic terminal groups in POSS and the good solubility of POSS,the POSS was introduced into the PAN matrix by physical doping and chemical polymerization to prepare modified hybrid PAN-based GPE.The effects of POSS on the system performance and the reasons for these effects were studied by different characterization methods.The main results obtained are as follows:(1)The POSS(MA-POSS)with a long-chain was firstly synthesized by hydrolysis and dehydration condensation,then the MA-POSS and PAN were physically doped to prepare PAN/MA-POSS based composite polymer film and GPE.The products were characterized by fourier transform infrared spectroscopy(FTIR),nuclear magnetic resonance(H-NMR),differential scanning calorimetry(DSC),thermogravimetric analysis(TGA),X-ray diffraction(XRD),scanning electron microscopy(SEM),electrolyte uptake,porosity and different electrochemical tests,the results exhibited that MA-POSS with good thermal stability had been successfully synthesized.The pore structure of PAN/MA-POSS composite film with 8 wt.%MA-POSS was remarkable,and the highest porosity and electrolyte uptake reached 79.7%and 540.4 wt.%,respectively.The crystallinity of PAN/MA-POSS film was effectively reduced by doping MA-POSS.The composite GPE with 8 wt.%MA-POSS achieved the best electrochemical performance:ion conductivity reached 2.62×10-3 S cm-1 at room temperature;The ion conduction mode accords with the typical Arrhenius model;The lithium ion transference number was 0.38;The electrochemical stability window reached 5.7 V(vs.Li/Li+).The compatibility between GPE and electrode was satisfactory.At 0.2 C,the discharge capacity of LiFePO4 battery equipped with PAN/MA-POSS GPE was 140 mAh g-1 and the coulomb efficiency was 95%after 80 cycles.(2)P(AN-MAH),PAN based copolymer with good film formability,was synthesized by solution polymerization using acrylonitrile(AN)and maleic anhydride(MAH)as monomers.Then,the MA-POSS and P(AN-MAH)were physically doped to prepare P(AN-MAH)/MA-POSS composite film and corresponding GPE.The products were tested by FTIR,TGA,XRD,SEM and a series of electrochemical tests.The results presented that the P(AN-MAH)copolymer was successfully synthesized and the composite film containing 5 wt.%MA-POSS had good pore structure.At the same time,the best porosity(69.9%),electrolyte uptake(340.4 wt.%)and significantly reduced crystallinity were demonstrated,and the corresponding GPE achieved the highest electrochemical performance:The ionic conductivity at room temperature was 2.51×10-3 S cm-1;The ion conduction model followed Arrhenius's behavior;The lithium ion transference number and the electrochemical stability window were 0.53 and 5.6 V(vs.Li/Li+),respectively.The GPE had relatively small interfacial impedance with the electrode;The discharge capacity of LiFePO4 battery at 0.2 C was 147 mAh g-1.(3)Octavinyl POSS(OV-POSS)was synthesized by dehydration condensation with vinyltrimethoxysilane(VTMS)as monomer.Then PAN based copolymer P(AN-POSS)was synthesized by solution copolymerization using OV-POSS and AN as monomer,and P(AN-POSS)based copolymer film and GPE were further prepared.The prepared products were characterized.The results exhibited that OV-POSS and P(AN-POSS)with excellent thermal stability were successfully synthesized.The copolymerization of POSS significantly reduced the crystallinity of the matrix.The copolymer film with 8 wt.%OV-POSS polymerization had the highest porosity and liquid uptake of 83.1%and 471.7 wt.%,respectively.The ion conductivity of the corresponding GPE was 6.02 × 10-3 S cm-1 at room temperature,and the ion conduction mode was consistent with the Arrhenius model;The lithium ion transference number was 0.59;The potential of electrochemical stability was 5.7 V(vs.Li/Li+);The electrolyte and electrode had good interfacial compatibility;The discharge capacity of LiFePO4 battery was 148 mAh g-1 at 0.2 C,and after 80 cycles,the initial capacity of 93.7%was retained.