In-situ ETEM Investigations Of Anode Materials Produce,Growth Mechanisms And Mechanical Properties Of Li Dendrites In Lithium-metal Batteries

Lithium(Li)metal is the ultimate anode material for Li batteries because of its highest capacity and lowest electrode potential(versus the standard hydrogen electrode)among all candidates.Recent years,secondary lithium-sulfur and lithium-air batteries have become a research hotspot and an important development direction.Metal Li as the anode for Li metal batteries(LMBs)have received extensive attention.It is now widely recognized that Li-metal anodes suffer from severe drawbacks.For instance,due to the chemical reactivity of Li metal,it is not easy to store and transport.Metal Li is easy to react with electrolyte,resulting in the increase of interface impedance and relative infinite volume changes during plating and stripping,thus continuously causing low Coulombic efficiency(CE),fast capacity fading,increased voltage hysteresis.In addition,undesired dendrite growth and"dead lithium"formation in the cycling process will also reduce of the CE of batteries and even cause a series of safety problems such as short circuit or explosion of the battery.In order to solve the above problems,in situ transmission electron microscopy(TEM)was used to study the systhesis and modification of Li-metal anodes in LMBs;the growth mechanism and electrochemical behavior of lithium dendrites during charging and discharging process;and the deposition and mechanical properties metal Li in electrode materials.In the environmental transmission electron microscope,carbon nanotubes(CNTs)are used as the gas cathode material to construct a lithium carbon dioxide nano-battery.We herein demonstrate the production of air-stable Li spheres using electrochemical plating under applied voltage.The air-stable Li spheres exhibit a core-shell structure with a Li core and a Li₂CO₃ shell.Furthermore,the air-stable Li spheres can be used as anodes in lithium-ion batteries,and they exhibit similar electrochemical behavior to metallic Li,which can realize the safe storage and utilization of metal Li.In the environmental transmission electron microscope,CNTs are used as the gas cathode material to construct a lithium-carbon dioxide nanobattery and Li dendrites were produced by in-situ electrochemical plating.The growth process of dendrites and the cracking/self-healing of solid electrolyte interphase were observed successfully by adjusting the experimental conditions,enabling studies of the the growth mechanism of Li whiskers.Our results highlight the importance of overpotential and solid electrolyte interface(SEI)in controlling the lithium deposition morphology.As such it is possible to tailor the lithium deposition morphology and mitigate lithium whisker growth by SEI engineering such as artificial SEI,electrolyte additives,and appropriate controlling the overpotential.By using an environmental transmission electron microscopy-atomic force microscopy(ETEM-AFM)platform,we observed real-time growth of individual Li whiskers of different growth directions under applied voltage and mechanical confinement,and measured stress generation and yield strength during the growth process concurrently.The whisker growth map in solid electrolyte was developed by finite element analysis based on the measured mechanical properties of Li whiskers.The results provide quantitative benchmarks for the design of Li dendrite growth suppression strategies in all-solid-state batteries.A lithium-oxygen and lithium-carbon dioxide nano-battery are constructed by using?-MnO₂ nanowires with channel structure as the positive electrode material.The deposition of lithium in electrode material during charge and discharge process was observed in situ lithium deposition induced degradation of the electrode material was observed.The channel structure of the original MnO₂ nanowires was characterized in a probe-corrected FEI Themis Z electron microscope.We found not only the 1×1,2×2 tunnels,but also the intergrowth of 2×3,2×4 tunnels structures.Moreover,the fracture stress of the original(1.3 GPa?2.2 GPa)and the lithiated MnO₂ nanowires(100 MPa?200 MPa)were measured by using an environmental transmission electron microscopy-atomic force microscopy(ETEM-AFM)platform.The results provide important guidace for the design of electrode materials in LMBs.