In Situ Characterization and Phase‐Filed Modeling of the Interaction between Dendrites and Gas Bubbles during an Electrochemical Process

External Pressure Affecting Dendrite Growth and Dissolution in Lithium Metal Batteries During Cycles

Lithium (Li) metal has garnered significant attention as the preferred anode for high-energy lithium metal batteries. However, safety concerns arising from the growth of Li dendrites have hindered the advancement of Li metal batteries. In this study, we first elucidate the impact of external pressure and internal stress on dendrite growth and dissolution behavior of Li metal batteries during continuous charging-discharging cycles, employing a developed electrochemomechanical phase-field model. A typical parameter is defined to calculate the amount of dead Li that affects the electrochemical performance of Li metal batteries during multiple cycles. The underlying mechanisms of dendrites observed from in situ experiments are explained through the developed phase-field model. After charging/discharging, dendrites with a treelike structure yield a greater amount of dead Li compared to those with a needlelike configuration. Increasing the pressure appropriately can effectively reduce the growth points of dendrites and suppress the Li dendrite growth. Excessive pressure not only induces dendritic fractures that lead to the formation of dead Li but also undermines the battery performance. The accumulated internal stress might threaten the structural stability of the Li metal, thereby influencing the evolution of the Li dendrite morphology. A reasonable strategy is proposed to strike a balance between external pressure and the growth and dissolution of Li dendrites. These findings offer valuable insights into the judicious application of pressure to mitigate the advancement of electroplating reactions.

Gas induced formation of inactive Li in rechargeable lithium metal batteries

The formation of inactive lithium by side reactions with liquid electrolyte contributes to cell failure of lithium metal batteries. To inhibit the formation and growth of inactive lithium, further understanding of the formation mechanisms and composition of inactive lithium are needed. Here we study the impact of gas producing reactions on the formation of inactive lithium using ethylene carbonate as a case study. Ethylene carbonate is a common electrolyte component used with graphite-based anodes but is incompatible with Li metal anodes. Using mass spectrometry titrations combined with ¹³C and ²H isotopic labeling, we reveal that ethylene carbonate decomposition continuously releases ethylene gas, which further reacts with lithium metal to form the electrochemically inactive species LiH and Li₂C₂. In addition, phase-field simulations suggest the non-ionically conducting gaseous species could result in an uneven distribution of lithium ions, detrimentally enhancing the formation of dendrites and dead Li. By optimizing the electrolyte composition, we selectively suppress the formation of ethylene gas to limit the formation of LiH and Li₂C₂ for both Li metal and graphite-based anodes.

Elucidating the Role of Rational Separator Microstructures in Guiding Dendrite Growth and Reviving Dead Li

Li metal has attracted considerable attention as the preferred anode material for high-energy batteries. However, Li dendrites have limited the development of Li-metal batteries. Herein, the effects of tuning the porous separator microstructure (SM) for guiding Li dendrite growth and reviving dead Li are revealed using a mechano-electrochemical phase-field model. A strategy of guiding, instead of suppression, was applied to avoid disordered Li dendrite growth. By analyzing the effects of the number of layers, thickness, degree of staggered overlap in the separator, interlayer spacing, and porosity of SM on Li dendrite behavior, we discovered that applying a rationally designed SM can finely guide the Li nucleation and growth direction toward dense deposition. The revival of dead Li was also observed via an in situ experiment on Li dendrites. The reactivation of dead Li after it recontacts Li metal was verified. These findings not only provide fundamental information for the tuning of the SM but can also help better understand the dendrite growth of other alkali metal-ion batteries.