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.

The lack of a reliable rechargeable lithium metal (Li-metal) anode is a critical bottleneck for next-generation batteries. The unique mechanical properties of lithium influence the dynamic evolution of Li-metal anodes during cycling. While recent models have aimed at understanding the coupled electrochemical-mechanical behavior of Li-metal anodes, there is a lack of rigorous experimental data on the bulk mechanical properties of Li. This work provides comprehensive mechanical measurements of Li using a combination of digital-image correlation and tensile testing in inert gas environments. The deformation of Li was measured over a wide range of strain rates and temperatures, and it was fitted to a power-law creep model. Strain hardening was only observed at high strain rates and low temperatures, and creep was the dominant deformation mechanism over a wide range of battery-relevant conditions. To contextualize the role of creep on Li-metal anode behavior, examples are discussed for solid-state batteries, "dead" Li, and protective coatings on Li anodes. This work suggests new research directions and can be used to inform future electrochemical-mechanical models of Li-metal anodes.

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.

Improving the reversibility of lithium (Li) metal anodes is critical to enable next-generation batteries. However, a comprehensive understanding of the factors that influence the nucleation and dynamic evolution of Li morphology is lacking. In this study, a platform for plan-view operando video microscopy is presented. Using this platform, we quantitatively study (1) differences in the nucleation density of dendrites and pits as a function of current density, (2) the influence of the Li surface grain boundaries on nucleation location, (3) the role of pits formed in the first cycle on dendrite reversibility and extended cycling, (4) the temporal evolution of individual dendrite size, and (5) the impacts of individual dendrite size on “dead Li” formation. The results provide mechanistic insight into the influence of surface spatial heterogeneity on nucleation and growth behavior and suggest that dead Li formation is influenced more by nucleation than by growth.

Graphite felt modified with nanodispersed bismuth was studied as electrode in the positive half-cell of a vanadium redox flow battery (VRFB). The felt was easily modified by immersion in a Bi 2 O 3 solution followed by thermal reduction at 450°C in air. Despite the low metal content (1 at. %), the Bi-modified felt showed an excellent electrochemical performance (at 1 mVs -1 ) in terms of anodic and cathodic peak current densities (21 and 17 mA/cm 2 , respectively), reversibility (ΔE p = 0.050 V) and overpotential for the V(IV)/V(V) redox reactions. Furhtermore, repetitive cyclic voltammetry measurements, at various scan rates, evidenced the long term stability of this material. These results demonstrate that bismuth nanoparticles on the carbon surface act as stable active sites to promote these reactions, and represent a significant step forward towards the development of outstanding electrode materials for VRFB.

Glassy Li3BO3–Li2CO3 ALD films are deposited and shown to have excellent stability against Li metal and high ionic conductivity.