Electrochemical Performance Of Li-Organic Batteries With Heat-resistance PVA/HNTs Nanofiber Separator

Organic electroactive materials have recently captured intensive attentions owing to their flexible structure designability,high theoretical capacity,and environmental benignity.However,most of them exhibit inferior cycling performance because of the severe solubility of raw materials and their discharge products in organic electrolytes.Especially in large batteries applications,the internal temperature of the battery systems will rise steeply,and the dissolution phenomenon of organic electrode will also proceed rapidly.In this dissertation,a new-type composite fiber membranes（PVA/HNTs）with biodegradability,high thermal stability and good wettability were prepared through electrostatic spinning technology,which were composed of PVA and HNTs.When applied as separator in Li-organic batteries,they demonstrate long cycling life and good capacity retention rate.The outer layer of the HNT nanotube,which contains silica,has an opposite electrical charge.Poly（vinyl alcohol）is a polymer with excellent heat-resistance,water solubility and film-forming properties.The main contents and research results are listed as below:In this work,the morphology and structure characterization of composite membranes proved that the HNTs were uniformly coated in the PVA nanofibers to form an oriented arrangement.Furthermore,the strongly intermolecular hydrogen bonding between PVA and HNTs was enhanced with the increase of HNTs content.As a result,the mechanical strength,thermal stability and wettability of the PVA/HNTs composite membrane have been significantly improved by introducing more HNTs.In order to explore the application potential of PVA/HNTs for electrochemical energy storage,the PVA/HNTs composite membrane was used as a separator to assemble the Li-anthraquinone（AQ）battery.The linear sweep voltammetry（LSV）and electrochemical impedance spectroscopy（EIS）tests proved that the PVA/HNTs composite separator has better electrochemical stability（0-5.49 V）and higher ionic conductivity(4.92×10^-3 S cm^-1),respectively.The Li-AQ battery with PVA/HNTs-10separator（HNTs:PVA=0.1）exhibits an initial discharge capacity of 221.7 m Ah g^-1 at a charge-discharge rate of 0.2 C,and maintain 74%of the initial capacity after 200cycles.Even under extreme conditions with a temperature of 80°C,the Li-AQ battery can maintain 46%of initial capacity after 50 electrochemical cycles.In the self-discharge test,the fully charged Li-AQ battery has a self-discharge rate of only～1.5%during the 48-hour storage period.The results show that,benefit from the three-dimensional porous structure of PVA/HNTs and electrostatic repulsion,the PVA/HNTs composite separator can slow down the shuttle of anthraquinone discharge products to the anode Li,thereby slowing down the degradation of capacity.In addition,the PVA/HNTs composite separator has also been applied to Li-Li Fe PO₄battery.It also showed good electrochemical stability in the cyclic voltammetry test,and showed satisfactory separator properties in the charge-discharge tests.This proves that the PVA/HNTs composite separator has good universality in a variety of Li-ion battery systems.