Molecular-Level Engineering of Protected Li Metal Anodes for High Performance Next-Generation Batteries

Li metal is a promising anode material for next-generation Li-metal battery systems due to its ultra high theoretical capacity (3860 mAh g-1) and low electrochemical potential (-3.04 V vs. standard hydrogen electrode). However, the instability of Li metal towards liquids electrolytes, unstable solid electrolyte interphase (SEI) formation, and dendritic lithium have caused significant safety concerns that have inhibited its commercialization [1]. It is believed that artificial SEI layers formed through various techniques can stabilize the Li metal interface and enable stable electrochemical cycling with higher Coulombic efficiency. Atomic layer deposition (ALD) and molecular layer deposition (MLD) are nanoscale coating techniques that are capable of controlling the interfacial chemistry down to the atomic level [2]. Herein, we demonstrate the effectiveness of these techniques in enabling high performance Li metal anodes for next-generation battery systems. Various polymeric protective coatings are synthesized on Li metal by MLD to enable prolonged lifetime and cycling stability. Metalcones including Alucone and Zircone are explored and shown to greatly enhance the performance of Li-S and Li-O2 systems [3]. Moreover, the ability to fine tune the composition of artificial SEI layers is exemplified by combining ALD/MLD techniques to form hybrid organic/inorganic protection layers to further improve the stability of the Li metal anode. The performance of the protected Li metal anodes are optimized in various electrolyte systems to achieve long life times at relatively high current densities in symmetrical cells and full cells. Furthermore, a better understanding of the role of these organic/inorganic polymeric films are gained through advanced ex-situ and in-situ characterization techniques, providing insight into the mechanism of improved performance. These works display the advantages of ALD/MLD for precise interfacial engineering at the atomic/molecular level towards achieving high performance next-generation batteries. [1] Cheng, X.B.; Zhang, R.; Zhao, C.Z.; Zhang Q. Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review. Chem. Rev., 2017, 117(15), 10403-10473. [2] Meng, X.; Yang, X.Q.; Sun, X. Emerging applications of atomic layer deposition for lithium-ion battery studies. Adv. Mater., 2012, 24(27), 3589-3615. [3] Zhao, Y.; Goncharova, L.V.; Sun, Q.; Li, X.; Lushington, A.; Wang, B.; Li, R.; Dai, F.; Cai, M.; Sun, X. Robust Metallic Lithium Anode Protection by the Molecular Layer Deposition Technique. Small Methods, 2018, 2(5), 1700417.