Component Design And Optimization Of Rechargeable And Flexible Zinc-air Batteries And Studies Of The Performance

The development of flexible and wearable technology requires flexible energy storage devices with rechargeability and high energy density.The rechargeable and flexible zinc-air battery can meet these requirements,making it promissing to be the next generation of flexible energy storage devices.However,it still faces many challenges,such as poor charge and discharge performance,short life and low capacity.Therefore,how to improve the charge and discharge performance,prolong the life and increase the capacity,etc.has become the key to the rechargeable and flexible zinc-air battery.The rechargeable and flexible zinc-air battery is a whole system and needs to be systematically studied.In order to improve the battery performance,we designed and optimized the key components such as catalyst,air electrode,gel electrolyte and zinc electrode.Ultrathin Co₃O₄ nanosheets were prepared by combining solvothermal method and fast heat treatment.The specific surface area was increased and the surface structure was adjusted,which accelerated the charge transfer and improved the performance.Combined with electrodeposition and heat treatment,an ultrathin Co₃O₄/CC integrated electrode was prepared to optimize the interface between the catalyst and the substrate,thus reduce the interface resistance,enhance the interfacial adhesion,and improve the catalytic performance and bending performance.The introduction of tetraethylammonium hydroxide?TEAOH?in the PVA-KOH alkaline gel electrolyte system enhanced the interaction between the molecules inside the gel,improved the water retention capacity,reduced the deformation caused by dehydration,maintained the contact interface with the electrode,and prolonged the battery life.The 3D Zn electrode was prepared by using the copper foam as template to increase the contact interface with the gel electrolyte,improve the charge and discharge performance at a large current density,and increase the area specific capacity.The main work includes:1.Ultrathin Co₃O₄ nanosheets were prepared by solvothermal method and fast heat treatment.H₂O₂ could partially oxidize ethylene glycol to form?-glycolic acid,which could selectively adsorb on the surface of the precursor,facilitating the horizontal growth of the precursor,and at the same time acted as an oxidative exfoliation.H₂O₂played a critical role in the formation of ultrathin precursors.Ultrathin Co₃O₄ nanosheets could increase the specific surface area and increase the contact area with the reactants.At the same time,the surface had a special atomic arrangement and electronic structure,and an unsaturated coordination Co which was favorable for catalytic reaction.The ORR and OER performance were improved by 25%and 50%compared to commercial Co₃O₄ nanoparticles,respectively.Using ultrathin Co₃O₄ nanosheets as a bifunctional catalyst,at a current density of 1.6 mA cm^–3,the volumetric capacity and energy density of the assembled fiber-type rechargeable and flexible Zn-air battery reached 7.7 Ah L^–1 and 7.3 Wh L^–1,and the battery could stably cycle for 8 h.The discharge voltage of the fiber-type rechargeable and flexible Zn-air battery was almost unaffected by the bending,which maintained at about 1.10 V at 1.6mA cm^–3.Moreover,the battery could be woven into the clothes and drived electronic devices.2.The adsorption of ethylene glycol?EG?could inhibit the vertical growth of Co?OH?₂,so that Co?OH?₂ horizontally growed on the carbon cloth?CC?to form an ultrathin structure,and transformed into ultrathin mesoporous Co₃O₄/CC integrated air electrode by heat treatment.In-situ growth of ultrathin mesoporous Co₃O₄/CC could increase the contact interface between the catalyst and the substrate,reduce the interface resistance,accelerate charge transfer,and the ultrathin structure was beneficial to improve the catalytic performance.The ORR and OER performance could reach 14.34 mA g^–1 and298.3 mA g^–1,approximately 28 and 12 times of commercial Co₃O₄/CC.Using ultrathin mesoporous Co₃O₄/CC as air electrode,when the assembled Zn-air battery cycled at a current density of 2 mA cm^–2,the average discharge voltage was?1.03 V,the average charge voltage was?1.95 V,and the charge-discharge voltage gap was?0.92 V,energy utilization efficiency was?52.8%.The battery could stably cycle for more than 10 h.At the discharge current density of 2,5,10 mA cm^–2,the area specific capacities were5.42,5.00,4.95 Ah cm^–2,and the energy densities were 5.42,4.62,and 4.02 Wh cm^–2,respectively.The ultrathin mesoporous Co₃O₄/CC had stronger bonding force between the catalyst and the substrate,so that it had good mechanical stability and bending stability.After 300 bending cycles,the discharge platform and discharge duration only decreased by 0.01 V and 0.04 h,respectively.Furthermore,the charge and discharge cycle performance was almost unchanged under various bending conditions.3.PVA-TEAOH-KOH-H₂O alkaline gel electrolyte was prepared by introducing TEAOH into PVA-KOH-H₂O system.The introduction of TEAOH enhanced hydrogen bonding in the gel electrolyte,improved water retention,and increased resistance to electrolyte carbonation.At the same time,the PVA-TEAOH-KOH-H₂O alkaline gel electrolyte maintained the initial ionic conductivity of the PVA-KOH-H₂O alkaline gel electrolyte,and slowed down the decline of ionic conductivity.The PVA-TEAOH-KOH-H₂O alkaline gel electrolyte had good water retention performance and high ionic conductivity.The deformation caused by water loss was small,which could maintain the contact area with the electrode.The assembled Zn-air battery had a cycle life of more than 66.6 h at a current density of 2 mA cm^–2,which was higher than that of the PVA-KOH-H₂O alkaline gel electrolyte for 37 h.4.3D Zn electrode was successfully prepared by electroplating metallic zinc on the copper foam.In an alkaline plating environment,the solution was more diffusible and zinc was more likely to deposit on the skeleton of copper foam.The prepared 3D Zn electrode had a higher specific surface area and increased the contact interface with the alkaline gel electrolyte,thereby increasing the discharge voltage,lowering the charging voltage,and increasing the area specific capacity.At a discharge current density of 5 mA cm^–2,the initial discharge voltage could reach 1.11 V,and the discharge area specific capacity could be 10.55 mAh cm^–2.And the battery with good charge and discharge cycle performance,could cycle for 30 h?90 cycles?at a current density of 5mA cm^–2,and the average discharge voltage droped from 1.08 V to 0.87 V,and the average charging voltage rose from 2.08 V to 2.19 V.