Study On The Performance And Mechanism Of Bifunctional Mn-Based Electrodes For Aqueous Zn-Based Energy Storage

The development of new generation aqueous batteries with wearable characteristics,environmental friendliness as well as safety is a current research hotspot.Among which,aqueous zinc-based energy storage devices（including zinc-ion batteries and zinc-air batteries）are highly expected.The performance of zinc-ion batteries significantly depends on its cathode.Mn-based compounds have been widely studied as the earliest materials utilized in zinc-ion batteries.Nevertheless,the three key problems of them including their structure collapses during continuous charge-discharge processes,cathode dissolution and poor conductivity have not been effectively resolved yet.Zinc-air batteries are considered to be the preferred battery system for driving wearable electronic devices due to their long service life,low standby capacity loss,and large theoretical capacity.They can be used as emergency backup batteries to become a good supplement to zinc-ion batteries.However,traditional flexible electrode preparation methods will reduce the electrode conductivity,and the sluggish kinetic mechanism of ORR clamps down on its development.Therefore,for the above two systems,the design of high-performance cathode is particularly important.However,these two Zn-based energy storage systems have been discussed separately for a long time,and few researchers have found a suitable entry point to integrate them,let alone conduct normalization research.Hence,this study improved the synthesis method of Mn-based materials,and prepared a low-cost bifunctional Mn-based electrode with higher zinc ion storage performance/ORR catalytic activity.The specific results are as follows:（1）Micron-sized spherical manganese trioxide（H-Mn₂O₃）with secondary structure was obtained via a hydrothermal synthesis method followed by heat treatment.The modable electrode MH-Mn₂O₃ was prepared via hot-press method,and the ductility as well as surface hydrophobicity of the material are studied via a series of physical/mechanical tests.As a cathode of zinc-ion battery,the capacity of MH-Mn₂O₃ can reach remarkable 433.1 m Ah g^-1,and the well-assembled Zn//MH-Mn₂O₃ solid-state zinc-ion battery exhibits a long cycle life of more than 1100 times.Reaction process and kinetic mechanism of the electrode were both well-revealed via series of in situ tests.As the cathode of Zinc-air battery,the open circuit potential of MH-Mn₂O₃ reaches 1.35 V.The discharge capacity of the battery is as high as 160 m Ah cm^-2,and it maintains a stable discharge voltage platform under different current densities.Finally,the practical application potential of the battery is demonstrated through physical tests.（2）Micron-sized cubic manganese carbonate（H-Mn CO₃）with secondary structure was prepared by a simple hydrothermal synthesis method,and the modable electrode MH-Mn CO₃ was prepared via hot-press method.As the cathode of zinc-ion battery,MH-Mn CO₃exhibits a capacity of 220 m Ah g^-1 at a current density of 0.1 A g^-1.The assembled single solid-state Zn//MH-Mn CO₃ battery also maintains excellent cycle stability in the life test.Subsequently,the reaction kinetic mechanism of the material was preliminarily explored by in situ EIS.In addition,the solid-state Zn-air battery assembled with MH-Mn CO₃ as the catalytic cathode displays an ORR overpotential of 198 m V at 10 m A cm^-2,and a discharge capacity of 100 m Ah cm^-2.It reflects the application potential as a bifunctional electrode.