Preparation And Properties Of Flexible And Stretchable Zinc-air Battery

Zn-air battery is considered as an ideal candidate for application in the field of wearable electronic devices,due to its theoretical energy density,low cost,safety and environmental protection.However,most of solid-state Zn-air batteries,reported in the current literatures,can be made into bending deformations but are difficult to withstand large tensile strains(>100%).To prepare stretchable Zn-air battery,parts of the catalyst,air cathode,zinc anode,and hydrogel electrolyte need to be redesigned and optimized to processes mechanical properties that can be bent or even stretched.An integrated cobalt oxide(Co3O4)/carbon cloth as flexible air cathode was prepared.Co3O4 nanosheets were in-situ grown on the flexible current collector(carbon cloth)by electrodeposition and thermal treatment.The Co3O4 nanosheets with micron and nanoscale porous structures possess large specific surface area,,as well as are rich in the catalytic active site of Co3+.Furthermore,a flexible and stretchable sandwich-structured Zn-air battery array(2 x 2 array)was assembled and displayed stable charging and discharging performance,and can withstand tensile strain higher than 100%,even under tensile strain higher than 100%.By adjusting the series and parallel mode of the internal electrodes of the flexible and stretchable Zn-air battery array,the output voltage(1-4 V)and current of the resultant battery array can be flexibly regulated to adapt to the needs of different environments.A novel sodium carboxymethyl cellulose(CMC)and polyacrylic acid(PAA)alkaline hydrogel developed with high water retention and large stretchability has been developed to replace the traditional polyvinyl alcohol-based hydrogel electrolyte which is easy to lose water.The physical introduction of CMC into polyacrylic acid hydrogel is conducive to increasing the connection of hydrogen bond and molecular chain network of the composite hydrogel.Compared with the common polyvinyl alcohol-based electrolyte,CMC/PAA composed hydrogel has higher ionic conductivity(141 mS cm-1),water retention(24 h in open environment,only 6.6%water loss)and fracture tensile rate(803%).After being placed in an open environment for a certain period of time,the ionic conductivity,water retention and deformation capacity are still stable.This article also studied the preparation of soft metal electrode with polyurethane sponge as substrate by an electroplating method,which breaks through the rigid limitation that traditional metal electrodes can only be simply bent and difficult to restore its original shape.By controlling the time of metal plating,the microstructure and the amount of metal deposition of the flexible sponge-based electrodes can be regulated.The flexible Zn-air battery with sandwich structure is assembled by in-situ crosslinking hydrogel.Because the preparation method of metal cloth electrode and electrolyte is simple and low cost,it is suitable for macro manufacturing.Inspired by the kirigami structure,a large-area flexible Zn-air battery was cut into stretchable structure to achieve tensile strain higher than 100%.Moreover,flexible and stretchable metal electrode was prepared by a novel method of pre-strain-load-recovery and dynamic stretching-electroplating with elastic spandex fabric as the substrate,which overcomes the problem that metal materials do not have intrinsic elasticity.Dynamic stretching-electroplated samples not only deposit sufficient amounts of metallic zinc or nickel,but also retain the textile and wavy structure of the original fabric,which gives the metal coated fabric excellent and stable conductivity and tensile property.A flexible and stretchable sandwich-shaped Zn-air battery was prepared by in-situ crosslinking CMC/PAA-based alkaline electrolyte on the metal-coated textile electrodes.The resultant battery can withstand a max tensile strain of 100%.It displayed stable discharge performance under dynamic stretching and bending deformation conditions.Because the preparation method of metal cloth electrode and electrolyte is simple and low cost,it is suitable for macro manufacturing.A battery with a large area(14 × 6.5 cm2)was prepared and presented a high output power of 1757 mW,which can expand the application range of flexible and stretchable zinc-air battery.In summary,a series of flexible and stretchable Zn-air batteries were prepared by redesigning electrode and electrolyte materials and adopting various strategies of tensile structure.This kind of battery can achieve stable battery performance under different bending and stretching conditions,which provides an important experimental and theoretical basis for the application of Zn-air battery into wearable devices.