Study Of Poly(vinyl Alcohol)-based Gel Polymer Electrolytes For Flexible Zinc-Air Batteries

Recent advances in flexible electronics such as roll-up displays,skin-like sensors,and implantable devices require the development of high-energy-density and low-cost power sources featured by light-weight,ultrathin,bendable,twistable,stretchable or wearable properties.As a promising energy supply,in the last few decades,flexible zinc–air batteries?ZABs?have received significant interest due to their high theoretical energy density(1086 Wh kg^–1),low cost and environmental friendliness.Usually a flexible ZAB consists of a zinc anode,a semi-solid/solid-state electrolyte,a separator,an air cathode,current collectors and package materials.The semi-solid/solid-state electrolyte is the medium to ionically connect the cathode and anode which is a key component for the performance of ZABs including cycle life,rate characteristics and power output.In an intermediate state between liquid and solid,gel polymer electrolytes?GPEs?are composed of polymer hosts and liquid electrolytes,which have been widely used for flexible ZABs because of their relatively high ionic conductivity,flexibility and good interfacial contact with electrodes.Poly?vinyl alcohol??PVA?is one of the commonly used polymer matrices due to its excellent chemical stability,electrochemical inertness,durability,nontoxicity and easy fabrication process.Considering the advantages of PVA and high hydroxide-ion conductivity of KOH,PVA–KOH GPEs have been widely utilized in ZABs.With such GPEs,researchers have developed flexible ZABs with different structures including sandwich-like and cable-type.However,rarely reports have been focused on the properties of such PVA–KOH GPEs.Moreover,this conventional PVA–KOH GPE system suffers from:?1?low concentration of KOH in the GPE results in a low ionic conductivity,?2?unsatisfied electrolyte uptake due to the closeness of the cross-linked structure of PVA matrix,?3?poor electrolyte retaining property because of the half-opened system of ZABs with evaporation from the exposed air electrode side.In this study,on the one hand,the detailed investigation of conventional PVA–KOH GPE as well as the effect of GPE membrane under ambient condition with different time on the size,weight,ionic conductivity of the GPE and the performance of the fabricated ZAB was first discussed.On the other hand,considering the relatively poor water uptake of PVA matrix and hydroxyl groups on the surface of SiO₂ which were reported to be beneficial for the water retention,an optimized porous PVA-based nanocomposite GPE containing SiO₂ with high ionic conductivity and electrolyte retention was first prepared and applied in flexible ZABs.At the end of the thesis,the development direction and application prospects of PVA-based GPEs for the application of flexible ZABs are prospected.To the best of our knowledge,there are few thesis of PVA-based GPEs in the application of flexible ZABs.And this work provides an avenue for future research and development.