ALD Protection of Li‐Metal Anode Surfaces – Quantifying and Preventing Chemical and Electrochemical Corrosion in Organic Solvent

Abstract

batteries (e.g., Li-S battery and Li-air battery) due to the low electrochemical potential and high theoretical specific capacity of Li metal (3861 mAh g −1 ). The battery industry expended considerable effort to commercialize Li metal anodes via electrolyte additive engineering in the late 1980s. [4][5][6] However due to the instability of the Li-metal/electrolyte interface, and the formation of dangerous dendrites on Li metal surface, the use of lithium anodes decreased in popularity.The low electrochemical potential of Li metal makes it highly reactive, readily forming thin native surface layers during manufacturing. In principle, the insulating native surface layer could suppress or block electron transfer to the electrolyte, serving as a self-limiting protection layer on the Li surface to prevent solvent decomposition. However, the chemical/electrochemical instability of the interface leads to significant battery degradation through Li metal corrosion, solvent/electrolyte consumption, and flammable gas generation, largely associated with formation of a solid electrolyte interphase (SEI) layer by chargetransfer-initiated decomposition of the organic solvent. [7,8] The technology potential of Li anodes provides strong incentive to understand and prevent these Li surface degradation mechanisms at the surface of Li foils that would be employed in high energy Li anode storage systems. [9][10][11][12][13][14][15][16][17] Solvent Decomposition on Li Metal FoilsFoils of Li-metal are commonly used as negative electrode in pursuit of Li-metal batteries. Because of Li's exceptionally high reactivity, the surface is always covered with an oxide layer. We characterize the as-prepared Li foil surface by the in situ X-ray Photoelectron Spectroscopy (XPS) results in Figure 1a, where a Li metal foil was directly transferred from a purified Arfilled glovebox through ultrahigh vacuum to the XPS system, thus avoiding air exposure ( Figure S1, Supporting Information). The Li (1s) XPS spectrum indicates a mixture of Li 2 O, Li 2 CO 3 , and LiOH on the Li surface. Since prior investigations using our in situ XPS capabilities revealed no measurable carbon or carbonate following growth of Li 2 O by atomic layer deposition (ALD), [18] the presence of a carbonate feature Chemical and electrochemical instability of the Li metal interface with organic solvent has been a major impediment to use of Li-metal anodes for next-generation batteries. Here the character of Li surface degradation and the application of atomic layer deposition (ALD) as a protection layer to suppress the degradation are addressed. Using standard Li foil samples in organic solvent with and without in situ deposited ALD Al 2 O 3 protective layers, results from in situ atomic force microscopy, mass spectrometry (including differential electrochemical mass spectrometry), X-ray Photoelectron Spectroscopy (XPS), and ex situ scanning electron microscopy/energy dispersive X-ray spectroscopy are reported. Despite the presence of a thin oxide/hydroxide/carbonate layer on th...

Atomic and Molecular Layer Deposition for Superior Lithium‐Sulfur Batteries: Strategies, Performance, and Mechanisms

“…The protective roles of the ALD‐Al 2 O 3 coatings recently further prompted another insightful study conducted by Lin et al . Using SEM and EDX mapping, Lin et al.…”

“…In 1 : 1 DME/DOL solution, the H 2 gas was released and detected only with the bare Li metal sample, which indicated that the ALD coatings were effective in suppressing the unwanted parasitic reactions. For symmetric cells using the electrolyte of 1 M LiPF 6 in 1 : 1 ethylene carbonate (EC)/dimethyl carbonate (DEC), Lin et al . found that the Li−S cell with the bare Li electrodes produced much higher H 2 partial pressure, whereas the Li−S cell with the ALD‐coated Li anode was electrochemically stable without releasing noticeable H 2 .…”

“…(b) 3D cross‐sectional EC‐AFM images show the evolution of the height morphology at various duration time of Li surface solvent reaction. (c) Average RMS roughness of a 20 μm×20 μm scanned area on an ALD coated Li (blue) and a bare Li (red) . Reprinted (adapted) with permission from ref.…”

XPS on Li-Battery-Related Compounds: Analysis of Inorganic SEI Phases and a Methodology for Charge Correction

“…One common method for probing the chemical composition of the SEI in liquid-electrolyte based systems is gas chromatography. [7][8][9] In these studies, GC measurements detect gases that evolve during the formation and cycling of a battery, providing clues about interfacial reactions. Complementary approaches such as optical microscopy, scanning electron microscopy and X-ray diffraction provide direct information about the morphology and crystallinity of SEI phases present in cycled electrode materials, but provide no direct information on chemical bonding environments.…”

Low‐Weight 3D Al2O3 Network as an Artificial Layer to Stabilize Lithium Deposition

“…[6] The Li dendrite formation is due to the cracks formed in the insoluble solid-electrolyte interphase (SEI) layer between Li metal and electrolyte, as a result of drastic volume changes during continuous Li stripping/plating. [9,10] Various routes have thus been developed to restraint he growth of dendrites, including stabilizing the SEI layer by optimizingt he solvents, [11] lithiums alts, [4,12,13] and/ore lectrolyte additives; [14,15] introducing high-modulus solid electrolytes (such as lithium garnets [16][17][18] and composite electrolyte [19] )t op hysically impede dendrite infiltration;a nd building an interface layer on the lithium metal as an artificial protective SEI layer [20] (such as SiO 2 , [21] Al 2 O 3 , [22][23][24] LiF, [25,26] and polymer [27] ). [3] These decompositionr eactions lead to increasingi nternal resistance, low Coulombic efficiency (CE), and bad cycling performance of LIBs.…”