Properties On Modification Of Polyvinyl Alcohol Polyelectrolyte For Flexible Zinc Air Battery

Facing serious environmental problems and increasing energy demand,sustainable development has become an important focus of current society.Zinc-air battery has the characteristics of high energy density,environmental friendliness,low cost,safety and portability,etc.It can play a good effect in a limited space and is widely used in various fields.As an important part of the zinc-air battery,the solid electrolyte not only isolates the positive and negative poles,promotes ion conduction,but also makes flexible batteries possible.Current research shows that the electrolyte of zinc-air batteries has problems such as easy water loss,low electrical conductivity,and poor battery cycle stability in an open environment.In this thesis,the molecular structure of polyvinyl alcohol was modified and designed.The hydroxyl group on the reaction site was used to introduce quaternized side chains and crosslinks.A series of polyvinyl alcohol polyelectrolyte membranes were prepared.Through the introduction of conductive groups,cross-linking,and gradual improvement of doped ionic liquids,the hydrophilic and water-retaining performance of the electrolyte can be improved,and the charge and discharge performance and cycle stability of the battery can be improved.To improve the cycle stability of flexible zinc-air batteries,In this paper,a long-chain multifunctional ionic liquid was prepared first,and a series of quaternized polyvinyl alcohol polyelectrolytes were prepared by side-linking.This method introduces chlorine atoms through the formalization reaction of polyvinyl alcohol and chloroacetaldehyde as a grafting site,and thus controls the grafting degree of the polymer to control the performance of the electrolyte.The uniform introduction of long-side-chain multifunctional group structure can increase the content of ionic groups in the membrane and improve the ion transport capacity of the electrolyte;the prepared membrane has good mechanical properties and can directly support the catalyst.The assembled battery is thin and flexible,with an overall thickness of less than 500 ?m.In order to control the swelling of the membrane material by water absorption,so that it can operate in a low-alkali environment and at the same time enhance the battery cycle stability,a hydrophilic quaternized chitosan material is introduced into the membrane and a semi-interpenetrating network is constructed to prepare a quaternary ammonium chitosan-polyvinyl alcohol cross-linked film.The conditions of this method are mild and controllable.By exploring different cross-linking conditions,a membrane material with high water absorption and low swelling is obtained.Among them,the conductivity of QCS-PVA-OH-52 is 8.43 m S cm-1 at room temperature under neutral conditions,and the highest conductivity is 24.68 m S cm-1 under heating conditions.The assembled battery can run for 120 min at 1M KOH.Under 6M KOH,the open circuit voltage of the battery is above 1.36 V,the maximum power density is 25.12 m W cm-2,and it can be cyclically charged and discharged for 450 min.In order to further improve the hydrophilicity and water retention capacity of the membrane material and extend the battery life,a silane coupling agent containing ammonium groups was introduced into the polyvinyl alcohol main chain to construct a hydrophilic crosslinking network while performing quaternization modification on the membrane,And on this basis,add an ionic liquid with good hygroscopic capacity to enhance the hydrogen bonding structure and hydrophilic capacity in the membrane.The silane-coupled polyvinyl alcohol-doped ionic liquid film prepared in this way reduces the amorphous region in the film due to its large ammonium side chain,and the addition of ionic liquid to it promotes ion transport in the film and reduces its electrochemical impedance.The open circuit voltage of DM-PVA-OH-20 can exceed 1.41 V.After adding 2 wt% BQA,the maximum power density of the battery can reach 50.1 m W cm-2.DM-PVA-20 / BQA is better at BQA content of 2 wt%,and the battery can be cycle charged and discharged for more than 1300 min.