Operando Stem Study Of Lithium Microbattery

Recently,for satisfying the global energy demand for storing renewable power sources,developing high-density electrical energy storage devices became more and more crucial.Among various kinds of electrochemical energy storage systems,rechargeable lithium battery has attracted extensive attention,owing to its high theoretical energy density,low cost,environmentally friendly and design flexibility.Among the lithium battery,lithium-ion battery and lithium-oxygen battery with lithium metal as an anode are very important.However,based on the previous research achieved in several decades,lithium metal as anode still cannot be commercially applied in the highly efficient and stable lithium battery,because of its unstable surface.Fortunately,solid electrolyte interphase(SEI)film as an interface film between lithium anode and electrolyte spontaneously grows on the lithium anode surface to protect the anode and improve the efficiency and stability of the anode.But there still exist several key puzzles of SEI film,including how to develop strong and robust SEI film to avoid battery failed,how to improve the catalytic effect of cathode catalyst to enhance the performance of the lithium-oxygen battery and so on,which are difficult to be solved by traditional nonintuitive characterizations.Moreover,the cathodic processes also play a key role in determining the efficiency and stability of the lithium battery,especially the lithium-oxygen battery.Even though the cathodic catalysts on cathode can improve the efficiency and stability of lithium-oxygen battery,the underlying catalytic mechanisms of different catalysts are still elusive.In this backdrop,a state-of-the-art in-situ Cs-corrected scanning transmission electron microscopy(STEM)liquid microcell technology was performed in this study to provide an opportunity for investigating the puzzling issues of anode and cathode in rechargeable lithium battery system at a sub-nano-scale level.In this study,there are mainly three scientific issues of lithium battery,which are researched and discussed below.Firstly,the surface instability of anode in a lithium battery is one of the most crucial problems that seriously limits the further development of highly efficient and stable lithium battery.While the SEI film exhibits an obviously crucial role to stable the anode,control lithium ions diffusion,avoid lithium consummation during cyclings,and inhibit lithium dendrite and dead lithium formation.Although SEI film is very crucial,the non-intuitive traditional characterizations are difficult to characterize its evolution process.Thus,the liquid rechargeable lithium ions micro-cells were assembled to mimic the real working condition of lithium-ion battery for operando high angle annular dark-field(HAADF)and an annual bright-field(ABF)STEM observations of SEI formation,growth and failure at a high current density directly during charging and discharging.According to the operando observations,it reveals a bi-layer hybrid structure of SEI films and demonstrates the radical assisted SEI growth after the SEI thickness beyond the electron tunneling regime.The failure of SEI films is associated with the rapid dissolution of inorganic layers when they directly contact with the electrolyte in broken SEI films.The initiation of cracks in SEI films is caused by heterogeneous volume changes of the electrodes during delithiation.These results can provide the experimental supports for designing robust and stable SEI film.Secondly,the cathodic catalysts on the air cathode play a key role in improving energy efficiency,cycling lifetime and battery stability of the lithium-oxygen battery.Ru O₂ as a classical solid catalyst possesses excellently bi-functional catalysis.While the underlying catalytic mechanism of Ru O₂ is still a puzzle.For example,how the Ru O₂unceasingly catalyzes the Li₂O₂ formation to maintain a low ORR overpotential after being passivated via a mass of preexisted Li₂O₂ products during the ORR process.And how Ru O₂ catalyzes the floating Li₂O₂products without directly contact Ru O₂/Li₂O₂ interface to maintain a low OER overpotential during the OER process.For intuitive observing the catalyzed redox reaction of Ru O₂,a liquid rechargeable lithium-oxygen micro-cell was assembled to mimic the real working environment of rechargeable lithium-oxygen battery for operando HAADF-STEM observations of Ru O₂ catalyzed oxygen reduction and evolution reactions of Li₂O₂.Through the in-situ STEM technique,the observation unveils how Ru O₂ catalyzes the formation and decomposition of Li₂O₂ during discharging and charging and provides nanoscale insights into cathodic reactions of Li-O₂ batteries with solid catalysts,which provides experimental supports for developing the advanced catalysts.Thirdly,according to the properties of solid and liquid catalysts,each single-phase catalyst possesses drawbacks.In addition,the solid and liquid catalysts are cooperated with each other to be a new synergetic catalyst.However,the cooperating mechanism is still unclearly.For developing advanced synergetic RM and solid catalysts to improve the commercial application of rechargeable lithium-oxygen battery,a liquid in-situ rechargeable lithium-oxygen battery was assembled,cooperating with ex-situ electrochemical characterization,to directly investigate the combination of solid catalyst(Ru O₂)and liquid RM(tetrathiafulvalene,TTF)during cycling.It indicates that Ru O₂ and TTF exhibits a synergetic effect in cathodic kinetics and energy efficiency.it also revealed the cooperating catalytic mechanism of TTF and Ru O₂ catalyst during the charging and discharging process,which provides the experimental supports for developing the advanced catalysts.In summary,for solving these three crucial issues of anode and cathode in lithium battery,a liquid in-situ rechargeable lithium-oxygen battery was assembled,cooperating with ex-situ electrochemical characterization to investigate the underlying dynamic mechanism of redox reactions occurred on anode and cathode in the rechargeable lithium battery.This study can supply the experimental supports for further commercial development of highly efficient and stable lithium batteries.