Gradient Lithiophilic Composite Electrodes for Dendrite-Free Lithium Metal Batteries.

As the electric vehicle (EV) market grows, there is an increasing demand for high-energy-density lithium-ion batteries (LIBs) to gain a competitive edge over internal combustion engine vehicles. However, graphite-based anode materials have reached a limit in terms of the further enhancement of energy density. Recently, lithium-metal batteries (LMBs) have attracted considerable attention owing to their high theoretical capacity (3,860 mAh/g), low negative electrochemical potential (-3.04 V vs. the standard hydrogen electrode), and low density (0.534 g/cm3). However, developing LMBs poses challenges due to the growth of Li dendrites, potential short circuits, formation of dead Li, and significant volume changes. Various solutions are being considered to address this problem, including the use of solid electrolytes, surface coating techniques, electrolyte additives, and other methods. Nonetheless, fundamental problems persist, specifically an unstable solid-electrolyte interphase (SEI) and dendrite growth under high current density conditions1. In this study, we report the use of tin (IV) oxide/nanoporous graphene (SnO2/NPG) as a lithiophilic material in a three-dimensional (3D) network electrode for dendrite-free LMB anodes. Furthermore, we devise a 3D network structure with a lithiophilic/lithiophobic gradient using a straightforward vacuum filtration method with single-walled carbon nanotubes (SWCNTs) and SnO2/NPG. These electrode designs based on lithiophilicity gradients have been reported to suppress dendrite growth, even under high current densities. Furthermore, the design involves creating a 3D network structure using carbon nanotubes (CNTs), which accommodates volume expansion and reduces the localized current density by offering a high specific surface area. In the bottom layer of this structure, lithiophilic SnO2/NPG is uniformly distributed, forming a bottom-up deposition path and enabling uniform Li deposition. SnO2, an inexpensive and eco-friendly material, provides lipophilic sites with Sn4+ and O2-, reducing the Li nucleation energy and achieving dendrite-free performance2,3. Additionally, NPG reduces the local current density, contains functional groups, provides additional lithiophilic sites, and allows uniform Li-ion transport through its pores4,5. The top layer consists of lithiophobic SWCNTs acting as a protective layer and offering additional space for Li deposition. Furthermore, the lithophilicity gradient-based design capitalizes on the excellent electronic conductivity of CNTs present throughout the electrode, enabling electron transfer without the need for conductive additives. Additionally, owing to the highly reactive surface of the CNTs, they effectively adhere to SnO2/NPG, eliminating the need for binders and maximizing the energy density. As a result, a lithiophilic/lithiophobic gradient electrode is expected to provide a high dendrite-free capacity and long-term cycling stability. Further details regarding the analysis procedure, structure, and electrochemical properties will be presented in the meeting. References [1] Liu, Yucheng, et al. "Lamellar-structured anodes based on lithiophilic gradient enable dendrite-free lithium metal batteries with high capacity loading and fast-charging capability." Chemical Engineering Journal 451 (2023): 138570. [2] Guodong, Liang, et al. "Free-standing SnO2@ C/MWCNTs paper as anode for lithium-ion batteries." Materials Research Express 6.12 (2019): 125511. [3] Liu, Yucheng, et al. "Ultralow‐expansion lithium metal composite anode via gradient framework design." Advanced Functional Materials 32.35 (2022): 2202771. [4] Lee, Geon-Woo, et al. "Tortuosity modulation on microspherical assembly host of graphene via in-plane nano-perforations for stable Li metal anode." Carbon 198 (2022): 289-300. [5] Yu, Yikang, et al. "Thermally reduced graphene paper with fast Li ion diffusion for stable Li metal anode." Electrochimica Acta 294 (2019): 413.