Despite progress in solid-state battery engineering, our understanding of the chemo-mechanical phenomena that govern electrochemical behavior and stability at solid-solid interfaces remains limited compared to solid-liquid interfaces. Here, we use operando synchrotron X-ray computed microtomography to investigate the evolution of lithium/solid-state electrolyte interfaces during battery cycling, revealing how the complex interplay between void formation, interphase growth, and volumetric changes determines cell behavior. Void formation during lithium stripping is directly visualized in symmetric cells, and the loss of contact at the interface between lithium and the solid-state electrolyte (Li 10 SnP 2 S 12) is found to be the primary cause of cell failure. Reductive interphase formation within the solid-state electrolyte is simultaneously observed, and image segmentation reveals that the interphase is redox-active upon charge. At the cell level, we postulate that global volume changes and loss of stack pressure occur due to partial molar volume mismatches at either electrode. These results provide new insight into how chemo-mechanical phenomena can impact cell performance, which is necessary to understand for the development of solid-state batteries. File list (2) download file view on ChemRxiv Manuscript Updated.pdf (1.08 MiB) download file view on ChemRxiv Supplementary Information.pdf (1.02 MiB)

Operation of Li-ion batteries below −20 °C is hindered by low electrolyte conductivity and sluggish solid-state diffusion in electrodes. Li metal anodes show promise for low-temperature operation, but few electrolyte compositions exhibit high conductivity at reduced temperature while also allowing Li electrodeposition/stripping with high Coulombic efficiency. Here, we show that the Coulombic efficiency of Li metal anodes can be substantially improved at low temperatures (−60 °C) by tailoring the solid-electrolyte interphase (SEI) structure through the use of two classes of electrolyte solvents: cyclic carbonates and ethers. Cryogenic transmission electron microscopy and other methods show that fluoroethylene carbonate (FEC) induces temperature-dependent changes in the chemistry and structure of the SEI to be abundant with LiF and Li2CO3, while 17O nuclear magnetic resonance and molecular dynamics calculations show that FEC affects the solvation behavior and SEI formation process in this new electrolyte system. Our results demonstrate the promise of rechargeable Li-metal batteries to enable energy storage over a broad temperature range.

While Li-ion batteries are known to fail at temperatures below −20 °C, very little is known regarding the low-temperature behavior of next-generation high-capacity electrode materials. The lithium metal anode is of particular interest for high-energy battery chemistries, but improved understanding of and control over its electrochemical and nanoscale interfacial behavior in diverse conditions is necessary. Here, we investigate lithium deposition/ stripping, morphology evolution, and solid-electrolyte interphase (SEI) structure and properties down to −80 °C using an etherbased electrolyte (DOL/DME). As temperature is reduced, we find that the morphology of deposited lithium is significantly altered. Furthermore, cryogenic transmission electron microscopy coupled with vacuum-transfer X-ray photoelectron spectroscopy reveal that the SEI exhibits different structure, chemistry, thickness, and conductive properties at lower temperatures. These results show that Li is promising for batteries operating under extreme conditions, and the distinct nanoscale evolution of Li electrodes at different temperatures must be considered when designing high-energy batteries.

Nonaqueous sodium-based batteries are ideal candidates for the next generation of electrochemical energy storage devices. However, despite the promising performance at ambient temperature, their low-temperature (e.g., < 0 °C) operation is detrimentally affected by the increase in the electrolyte resistance and solid electrolyte interphase (SEI) instability. Here, to circumvent these issues, we propose specific electrolyte formulations comprising linear and cyclic ether-based solvents and sodium trifluoromethanesulfonate salt that are thermally stable down to −150 °C and enable the formation of a stable SEI at low temperatures. When tested in the Na||Na coin cell configuration, the low-temperature electrolytes enable long-term cycling down to −80 °C. Via ex situ physicochemical (e.g., X-ray photoelectron spectroscopy, cryogenic transmission electron microscopy and atomic force microscopy) electrode measurements and density functional theory calculations, we investigate the mechanisms responsible for efficient low-temperature electrochemical performance. We also report the assembly and testing between −20 °C and −60 °C of full Na||Na3V2(PO4)3 coin cells. The cell tested at −40 °C shows an initial discharge capacity of 68 mAh g−1 with a capacity retention of approximately 94% after 100 cycles at 22 mA g−1.

Water vapor condensation is a ubiquitous process in nature and industry. Over the past century, methods achieving dropwise condensation using a thin (<1 µm) hydrophobic 'promoter' layer have been developed, which increases the condensation heat transfer by 10 times compared to filmwise condensation. Unfortunately, implementations of dropwise condensation have been limited due to poor durability of the promoter coatings. Here, we develop thin film condensation which utilizes a promoter layer not as a condensation surface, but rather to confine the condensate within a porous biphilic nanostructure, nickel inverse opals (NIO) with a thin (<20 nm) hydrophobic top-layer of decomposed polyimide. We demonstrate filmwise condensation confined to thicknesses <10 µm. To test the stability of thin film condensation, we performed condensation experiments to show that at higher supersaturations (0.975 < S < 2.05), droplets coalescing on top of the hydrophobic layer are absorbed into the superhydrophilic layer through coalescence induced transitions. Through detailed This article is protected by copyright. All rights reserved.3 thermal-hydrodynamic modeling, we show that thin film condensation has the potential to achieve heat transfer coefficients approaching ≈100 kW m -2 while avoiding durability issues by significantly reducing nucleation on the hydrophobic surface. The work presented here develops an approach to potentially ensure durable and high performance condensation comparable to dropwise condensation.