In-Situ Transmission Electron Microscopy Study On The Electrochemical Reaction Mechanism Of Sodium?lithium-air Batteries

Metal-air batteries use metals(Li,Na,K)as the negative electrode and air as the positive electrode.In principle,they can continuously supply energy.It has the characteristics of high capacity,high energy density,stable discharge and low cost,and has attracted great interest among scientific researchers in this field.It is expected to be widely used in the fields of new energy vehicles,portable equipment and power generation devices.However,the electrochemical reaction mechanism of metal-air batteries is still unclear,so this article analyzes the reaction mechanism of metal-air batteries from the perspective of in-situ ETEM.Co₃O₄ nano materials have attracted tremendous attention as effective catalysts for sodium oxygen(Na-O₂)batteries.However,their electrochemical processes and fundamental catalytic mechanism remain unclear till now.Herein,in situ environmental transmission electron microscopy(in situ ETEM)technique was used to study the catalysis mechanism of the Co₃O₄ nanoparticles in Na-O₂ nanobatteries during discharge and charge processes.It is found that during the 1^st discharge and charge processes,Na₂O₂ formed and decomposed,respectively,around the Co₃O₄ nanoparticles,but the following discharge and charge processes were very difficult.In order to promote the charge kinetics,we increased the charging temperature up to 500 ^oC,when the decomposition of Na₂O₂ became facile.Aberration corrected high-angle annular dark field(HAADF)imaging indicated that a thin layer of Co O grew epitaxially on the surface of Co₃O₄ nanoparticles after the first discharge.Density functional theory calculations(DFT)indicate that the Co O surface is energetically more favorable than Co₃O₄ for the nucleation of Na₂O₂.This study provides not only new fundamental understandings to the electrochemical reaction mechanisms of Na-O₂ batteries,but also strategies to improve the cycling performance of solid state Na-O₂ batteries.In addition,this chapter compares a variety of cathode materials commonly used in metal-air batteries,such as Mn O@C,Sn@CNT and CNT.Rechargeable lithium-carbon dioxide(Li-CO₂)batteries have attracted much attention due to their high theoretical energy densities and capture of CO₂.However,the electrochemical reaction mechanisms of rechargeable Li-CO₂ batteries,particularly the decomposition mechanisms of the discharge product Li₂CO₃ are still unclear,impeding their practical applications.Exploring electrochemistry of Li₂CO₃ is critical for improving the performance of Li-CO₂ batteries.Herein,in situ environmental transmission electron microscopy(ETEM)technique was used to study electrochemistry of Li₂CO₃ in Li-CO₂nanobatteries during discharge and charge processes.During discharge,Li₂CO₃ was nucleated and accumulated on the surface of the cathode media such as carbon nanotubes(CNTs)and Ag nanowires(Ag NWs),but it was hard to decompose during charging at room temperature.To promote the decomposition of Li₂CO₃,the charge reactions were conducted at high temperatures,during which Li₂CO₃ was decomposed to lithium with release of gases.Density functional theory(DFT)calculations revealed that the synergistic effect of temperature and biasing facilitates the decomposition of Li₂CO₃.This study not only provides a fundamental understanding to the high temperature Li-CO₂ nanobatteries,but also offers a valid technique,i.e.discharging/charging at high temperatures,to improve the cyclability of Li-CO₂ batteries for energy storage applications.