The impact of surface chemistry on the interfacial resistance between the Li 7 La 3 Zr 2 O 12 (LLZO) solid-state electrolyte and a metallic Li electrode is revealed. Control of surface chemistry allows the interfacial resistance to be reduced to 2 Ω cm 2 , lower than that of liquid electrolytes, without the need for interlayer coatings. A mechanistic understanding of the origins of ultra-low resistance is provided by quantitatively evaluating the linkages between interfacial chemistry, Li wettability, and electrochemical phenomena. A combination of Li contact angle measurements, X-ray photoelectron spectroscopy (XPS), first-principles calculations, and impedance spectroscopy demonstrates that the presence of common LLZO surface contaminants, Li 2 CO 3 and LiOH, result in poor wettability by Li and high interfacial resistance. On the basis of this mechanism, a simple procedure for removing these surface layers is demonstrated, which results in a dramatic increase in Li wetting and the elimination of nearly all interfacial resistance. The low interfacial resistance is maintained over one-hundred cycles and suggests a straightforward pathway to achieving high energy and power density solid-state batteries.

A mechanistic analysis of voltage shape changes in lithium metal anodes explains how dead lithium causes capacity fade and failure.

Solid-state electrolytes (SSEs) have attracted substantial attention for next-generation Li-metal batteries, but Li-filament propagation at high current densities remains a significant challenge. This study probes the coupled electrochemicalmorphological-mechanical evolution of Li-metal-Li 7 La 3 Zr 2 O 12 interfaces. Quantitative analysis of synchronized electrochemistry with operando video microscopy reveals new insights into the nature of Li propagation in SSEs. Several different filament morphologies are identified, demonstrating that a singular mechanism is insufficient to describe the complexity of Li propagation pathways. The dynamic evolution of the structures is characterized, which demonstrates the relationships between current density and propagation velocity, as well as reversibility of plated Li before short-circuit occurs. Under deep discharge, void formation and dewetting are directly observed, which are directly related to evolving overpotentials during stripping. Finally, similar Li penetration behavior is observed in glassy Li 3 PS 4 , demonstrating the relevance of the new insights to SSEs more generally.

rechargeable Li metal anodes are a key component required to enable next-generation battery systems including Li-S and Li-air batteries. [1] However, stability issues originating from undesirable electrode/ electrolyte interactions and Li dendrite formation have prevented long-term cycling of Li metal anodes. As a result, the performance of Li metal batteries suffer from low Coulombic efficiency (CE), instability against electrolyte decomposition, and formation of 3D topographies including mossy Li, dead Li, and dendrites. [2,3] Current collectors play a critical role in determining the performance of Li metal batteries because their geometry and surface chemistry both influence the uniformity of Li plating/stripping during cycling. Planar Cu foils have been widely used as a current collector/substrate for Li metal anodes owing to their relatively good stability against Li metal and compatibility with roll-to-roll manufacturing. However, cycling under practical current densities leads to nonuniform Li deposition due to an inhomogeneous Li-ion flux along the electrode surface, resulting in the onset of mossy or dendritic Li growth. [2] The formation of high-surface area Li causes a significant reduction in Coulombic efficiency and eventual cell failure due to undesirable side reactions with the electrolyte as well as "dead" Li formation that results from electrical and/or electrochemical isolation of active Li from the electrode surface. [4] One consequence of these issues has been the need to incorporate excess Li predeposited onto the anode current collector to compensate for losses that occur over the life of the cell. This compromises energy density and complicates manufacturing. In addition to decreasing the cell capacity, uncontrolled Li growth can also cause potential safety hazards as a result of gas evolution and formation of internal short circuits. Therefore, suppressing the formation of high-surface area Li structures during cycling is essential to improve the overall cycle life and efficiency of Li metal batteries.Recently, there has been a dramatic increase in the number of publications exploring the use of 3D current collectors to address these problems. [5][6][7][8][9][10][11][12][13] Several studies have shown that by using micro-or nanostructured current collectors, the effective current density can be reduced due to an increase in electroactive surface area, promoting more uniform Li plating/stripping during Improving the performance of Li metal anodes is a critical bottleneck to enable next-generation battery systems beyond Li-ion. However, stability issues originating from undesirable electrode/electrolyte interactions and Li dendrite formation have impaired long-term cycling of Li metal anodes. Herein, a bottom-up fabrication process is demonstrated for a current collector for Li metal electrodeposition and dissolution composed of highly uniform vertically aligned Cu pillars. By rationally controlling geometric parameters of the 3D current collector architecture, including pillar diameter, sp...

Lithium solid electrolytes are a promising platform for achieving high energy density, long-lasting, and safe rechargeable batteries, which could have widespread societal impact. In particular, the ceramic oxide garnet Li 7 La 3 Zr 2 O 12 (LLZO) has been shown to be a promising electrolyte due to its stability and high ionic conductivity. Two major challenges for commercialization are the manufacture of thin layers and the creation of stable, low-impedance interfaces with both anode and cathode materials. Atomic layer deposition (ALD) has recently been shown to be a powerful method for depositing both solid electrolytes and interfacial layers to improve the stability and performance at electrode− electrolyte interfaces in battery systems. Herein, we present a thermal ALD process for LLZO, demonstrating the ability to tune composition within the amorphous as-deposited film, which is studied using in situ quartz crystal microbalance measurements. Postannealing using a variety of substrates and gas environments was performed, and the formation of the cubic phase was observed at temperatures as low as 555 °C, significantly lower than what is required for bulk processing. Additionally, challenges associated with achieving a dense garnet phase due to substrate reactivity, morphology changes, and Li loss under the necessary high-temperature annealing are quantified via in situ synchrotron X-ray diffraction.