Unraveling the Mechanism of Very Initial Dendritic Growth Under Lithium Ion Transport Control in Lithium Metal Anodes

In situ formation of Li3N interlayer enhancing interfacial stability of solid-state lithium batteries

The uneven deposition of lithium ions has raised safety concerns related to the growth of lithium dendrites on the surface of lithium metal batteries. In this work, an in situ formed Li3N interlayer is introduced to regulate the deposition of lithium ions on the lithium metal surface effectively. The Li3N interlayer is formed on the lithium metal surface by the reaction of nitrogen gas (N2) released from the reaction layer at a specific temperature. The in situ Li3N interlayer enables the Li||Li symmetric cell exhibits cycling stability over 1200 h at 0.2 mA cm-2 due to the lower nucleation overpotential, demonstrating excellent Li plating/stripping performance. Furthermore, density function theory (DFT) calculations reveal that Li+ preferentially adsorb onto the Li3N (001) plane and diffuse along the surface during the Li+ migration process. This in situ Li3N interlayer effectively inhibits dendrite growth and the occurrence of side reactions, enabling stable cycling of Li||LiFePO4 cell for over 700 cycles at 0.5 C. Additionally, Li||LiCoO2 full cell also exhibits a capacity retention of 81.6 % after 500 cycles with a specific discharge capacity of 80.8 mAh/g and a coulombic efficiency (CE) of 99.4 %. This modification strategy is an effective approach for enhancing interfacial stability of solid-state lithium batteries.

Kinetic understanding of lithium metal electrodeposition for lithium anodes

Lithium, a representative alkali metal, holds the coveted status of the "holy grail" in the realm of next-generation rechargeable batteries, owing to its remarkable theoretical specific capacity and low electrode potential. However, the inherent reactivity of Li metal inevitably results in the formation of the solid-electrolyte interphase (SEI) on its surface, adding complexity to the Li electrodeposition process compared to conventional metal electrodeposition. Attaining uniform Li deposition is crucial for ensuring stable, long-cycle performance and high Coulombic efficiency in Li metal batteries, which requires a comprehensive understanding of the underlying factors governing the electrodeposition process. This review delves into the intricate kinetics of Li electrodeposition, elucidating the multifaceted factors that influence charge and mass transfer kinetics. The intrinsic relationship between charge transfer kinetics and Li deposition is scrutinized, exploring how parameters such as current density and electrode potential impact Li nucleation and growth, as well as dendrite formation. Additionally, the applicability of classical mass-transfer-controlled electrodeposition models to Li anode systems is evaluated, considering the influence of ionic concentration and solvation structure on Li+ transport, SEI formation, and subsequent deposition kinetics. The pivotal role of SEI compositional structure and physicochemical properties in governing charge and mass transfer processes is underscored, with an emphasis on strategies for regulating Li deposition kinetics from both electrolyte and SEI perspectives. Finally, future directions in Li electrodeposition research are outlined, emphasizing the importance of ongoing exploration from a kinetic standpoint to fully unlock the potential of Li metal batteries.

Highly Stable Lithium Metal Batteries Enabled by Tuning the Molecular Polarity of Diluents in Localized High-Concentration Electrolytes

Electrolyte plays a crucial role in ensuring stable operation of lithium metal batteries (LMBs). Localized high-concentration electrolytes (LHCEs) have the potential to form a robust solid-electrolyte interphase (SEI) and mitigate Li dendrite growth, making them a highly promising electrolyte option. However, the principles governing the selection of diluents, a crucial component in LHCE, have not been clearly determined, hampering the advancement of such a type of electrolyte systems. Herein, the diluents from the perspective of molecular polarity are rationally designed and developed. A moderately fluorinated solvent, 1-(1,1,2,2-tetrafluoroethoxy)propane (TNE), is employed as a diluent to create a novel LHCE. The unique molecular structure of TNE enhances the intrinsic dipole moment, thereby altering solvent interactions and the coordination environment of Li-ions in LHCE. The achieved solvation structure not only enhances the bulk properties of LHCE, but also facilitates the formation of more stable anion-derived SEIs featured with a higher proportion of inorganic species. Consequently, the corresponding full cells of both Li||LiFePO4 and Li||LiNi0.8Co0.1Mn0.1O2 cells utilizing Li thin-film anodes exhibit extended long-term stability with significantly improved average Coulombic efficiency. This work offers new insights into the functions of diluents in LHCEs and provides direction for further optimizing the LHCEs for LMBs.