Anode-free lithium metal batteries hold significant promise for high-energy-density storage applications. However, their practical deployment is hindered by limited cycle life, primarily due to heterogeneous lithium deposition and dendrite formation. These issues lead to rapid capacity fade as lithium inventory is consumed in side reactions, compounded by the lack of a lithium reservoir that conventional Li-metal anodes possess. To enhance anode-free battery stability, various strategies have been proposed, including innovative current collector designs, optimized electrolytes, tailored cycling protocols, and increased stack pressure, all of which have shown notable improvements in lithium plating/stripping behavior [1-3]. This talk elucidates the interaction between lithium and copper surfaces under varying charge conditions, utilizing classical molecular dynamics simulations of 1M LiPF6 in EC/DEC at the copper interface, complemented by XPS and SEM analyses [5]. Our findings indicate that as the voltage increases, PF6⁻ ions become more integrated into the lithium solvation shell near the interface. This is corroborated by XPS data, which reveal an increased presence of LiF at higher current densities. It is well established in the literature that an inorganic LiF-rich solid electrolyte interphase (SEI) is crucial for enhancing stability in subsequent cycles [5,6]. Our results suggest that a faster formation cycle promotes stronger interactions between Li and PF6⁻, leading to greater LiF incorporation into the SEI. Furthermore, SEM images at low current densities reveal that after stripping, several regions of the current collector remain exposed, which correlates with increased heterogeneity in lithium plating during subsequent cycles. These observations support the hypothesis that higher current densities facilitate SEI stabilization and improve lithium plating behavior, ultimately extending the cycle life of anode-free batteries. In conclusion, we demonstrate that the initial formation protocol plays a critical role in determining the long-term cycling stability of anode-free lithium metal batteries. Moreover, our results indicate that standard Li-ion formation protocols may not be suitable for metal-based systems. Therefore, optimizing operational conditions during the formation cycle is essential for enhancing the performance and durability of anode-free lithium metal batteries [4].
[1] Xie, Z.; Wu, Z.; An, X.; Yue, X.; Wang, J.; Abudula, A.; Guan, G. Anode-free rechargeable lithium metal batteries: Progress and prospects. Energy Storage Mater. 2020, 32, 386-401. DOI: https://doi.org/10.1016/j.ensm.2020.07.004.
[2] Weber, R.; Genovese, M.; Louli, A. J.; Hames, S.; Martin, C.; Hill, I. G.; Dahn, J. R. Long cycle life and dendrite-free lithium morphology in anode-free lithium pouch cells enabled by a dual-salt liquid electrolyte. Nat. Energy 2019, 4 (8), 683-689. DOI: https://doi.org/10.1038/s41560-019-0428-9.
[3] Tong, Z.; Bazri, B.; Hu, S.-F.; Liu, R.-S. Interfacial chemistry in anode-free batteries: challenges and strategies. J. Mater. Chem. A 2021, 9 (12), 7396-7406, DOI:https://doi.org/10.1039/D1TA00419K.
[4] Kim, S.; Didwal, P. N.; Fiates, J.; Dawson, J. A.; Weatherup, R. S.; De Volder, M. Effect of the Formation Rate on the Stability of Anode-Free Lithium Metal Batteries. ACS Energy Lett. 2024, 9, 10, 4753-4760.
[5] Chen, Z.; Wang, B.; Li, Y.; Bai, F.; Zhou, Y.; Li, C.; Li, T. Stable Solvent-Derived Inorganic-Rich Solid Electrolyte Interphase (SEI) for High-Voltage Lithium-Metal Batteries. ACS Appl. Mater. Interfaces 2022, 14, 28014-28020.
[6] Yang, G.; Frisco, S.; Tao, R.; Philip, N.; Bennett, T. H.; Stetson, C.; Zhang, J.-G.; Han, S.-D.; Teeter, G.; Harvey, S. P.; Zhang, Y.; Veith, G. M.; Nanda, J. Robust Solid/Electrolyte Interphase (SEI) Formation on Si Anodes Using Glyme-Based Electrolytes. ACS Energy Letters 2021, 6, 1684-1693.
