Preparation Of Self-Standing Electrodes And The Performance Studies In Neutral Aqueous Batteries

With the rapid development of wearable/portable electronics,research on flexible energy storage devices has attracted widespread attention.Among various new energy storage devices,neutral aqueous batteries have become an ideal choice for powering wearable electronics due to their high safety,low cost,and excellent ion conductivity.Flexible self-standing electrodes are the key to realize wearable energy storage devices,which can avoid the use of binders,thereby improving the contact area between the active materials and the electrolytes and the overall conductivity of the electrodes.However,due to the lack of electrode materials for aqueous batteries,preparation of self-standing electrodes is still a challenge.In addition,low volumetric/areal energy density is also a key issue to limit the development of wearable aqueous batteries.Therefore,this paper designs and prepares flexible self-standing electrodes with hierarchical structures by template conversion,direct growth,and the introduction of three-dimensional(3D)conductive skeletons to increase the volumetric/areal capacities of the electrodes,accordingly constructing high-performance wearable aqueous batteries.The main research content is divided into the following parts:(1)The preparation of self-standing electrodes has always been a challenge in constructing flexible ASIBs.In this paper,KNiFe(CN)6 and NaTi2(PO4)3 are grown on carbon nanotube fibers(CNTFs)by chemical etching and solvothermal methods as self-standing cathode and anode respectively,and a quasi-solid-state fiber-shaped ASIB based on all self-standing electrodes is successfully assembled.The device achieves high volumetric capacity(34.21 mAh cm-3)and excellent volumetric energy density(39.32 mWh cm-3)as well as mechanical flexibility.(2)In addition,low voltage platforms of self-standing cathodes limit energy densities of flexible ASIBs.In this paper,K2Zn3(Fe(CN)6)2·942O with cubic structure is synthesized on the surface of carbon cloth by water bath method using metal zinc nanosheet array as zinc source and reducing agent,providing a new strategy for the preparation of prussium blue analogues-based self-standing electrodes.The obtained flexible self-standing cathode achieves an output voltage of-0.8 V and an area capacity of 0.76 mAh cm-2.By combining NaTi2(PO4)3 as a self-standing anode,we successfully assemble a flexible ASIB with a high output voltage(1.6 V),achieving high area energy density(0.92 mWh cm-2)and power density(14.3 mW cm-2).(3)The low active material load of the self-standing cathode limits the development of flexible aqueous zinc ion batteries(AZIBs).In this paper,MnO2 nanosheets are deposited on the surface of a three-dimensional porous metal nickel skeleton by electrochemical deposition to prepare a flexible self-standing cathode(Ni@MnO2)with high mass loading and conductivity.Zn-MnO2 microbattery assembled with Ni@MnO2 as the cathode achieves a high areal energy density.The microbattery is integrated with a flexible pressure sensor,which can be attached to the human skin to monitor the human health signal in real time,achieving multi-function integrated device.(4)In addition to the design of the metal nickel skeleton in the previous chapter,a high-conductivity 3D carbon skeleton is derived from Co-MOF(ZIF-67)nanowall array grown on CNTFs by high-temperature carbonization reduction and etching.Then,V2O5 nanosheets are grown on the skeleton by a solvothermal method,forming a self-standing cathode with core-shell structure.In addition,the assembled fiber-shaped quasi-solid-state AZIB achieves high volumetric energy density(40.8 mWh cm-3)and power density(5.6 W cm-3),and exhibits ultra-fast charge-discharge character.(5)The application conditions of MOFs in the previous chapter were complex and harsh,and high-temperature carbonization destroyed the intrinsic active sites and pore structure.In this paper,3D V-MOFs(MIL-47)nanowire bundle arrays are grown on CNTFs by a self-sacrifice template method,directly as a self-standing cathode(CNTF@V-MOF)for AZIBs.The design of CNTF@V-MOF makes up for the lack of poor electronic conductivity of MOF,and makes full use of its advantages of rich active sites and high ion diffusivity.Therefore,the assembled quasi-solid-state fiber-shaped AZIB delivers excellent energy density(17.4 mWh cm-3),power density(1.46 W cm-3),and excellent rate performance.