The dry process is a promising fabrication method for all‐solid‐state batteries (ASSBs) to eliminate energy‐intense drying and solvent recovery steps and to prevent degradation of solid‐state electrolytes (SSEs) in the wet process. While previous studies have utilized the dry process to enable thin SSE films, systematic studies on their fabrication, physical and electrochemical properties, and electrochemical performance are unprecedented. Here, different fabrication parameters are studied to understand polytetrafluoroethylene (PTFE) binder fibrillation and its impact on the physio‐electrochemical properties of SSE films, as well as the cycling stability of ASSBs resulting from such SSEs. A counter‐balancing relation between the physio‐electrochemical properties and cycling stability is observed, which is due to the propagating behavior of PTFE reduction (both chemically and electrochemically) through the fibrillation network, resulting in cell failure from current leakage and ion blockage. By controlling PTFE fibrillation, a bilayer configuration of SSE film to enable physio‐electrochemically durable SSE film for both good cycling stability and charge storage capability of ASSBs is demonstrated.
Metal−organic framework (MOF)-based membranes have received significant attention as separators for lithium−sulfur (Li−S) batteries because of their high porosities, well-defined and tailored structures, and other tunable features that are desirable for preventing the "shuttle effect" of soluble polysulfides. Because of the insulating nature of most MOFs, composite membranes are generally constructed by a combination of MOFs and electron-conductive materials. In this work, we examine the property−performance relation between MOF-based separators and Li−S batteries by systematically adjusting the electrical conductivity, thickness, and mass loading of the MOF-based composite. Beyond the commonly referenced trapping or blocking ability of MOFs toward polysulfides, we find that by fixing the thickness of the MOF-based composite coating layer (∼40 μm) on a Celgard membrane, the electrical conductivity of the MOF composite layer is of paramount importance compared with the physical/ chemical trapping ability of polysulfides. However, the trapping ability of MOFs becomes indispensable when the thickness of the composite layer is small (e.g., ∼20 μm), indicating the synergetic effects of the adsorption and conversion capabilities of the thin composite layer. This work suggests the importance of a holistic design consideration for a MOF-based membrane for long-life and high-energy-density Li−S batteries.
Nonaqueous fluidic transport and ion solvation properties under nanoscale confinement are poorly understood, especially in ion conduction for energy storage and conversion systems. Herein, metal−organic frameworks (MOFs) and aprotic electrolytes are studied as a robust platform for molecular-level insights into electrolyte behaviors in confined spaces. By employing computer simulations, along with spectroscopic and electrochemical measurements, we demonstrate several phenomena that deviate from the bulk, including modulated solvent molecular configurations, aggregated solvation structures, and tunable transport mechanisms from quasi-solid to quasi-liquid in functionalized MOFs. Technologically, taking advantage of confinement effects may prove useful for addressing stability concerns associated with volatile organic electrolytes while simultaneously endowing ultrafast transport of solvates, resulting in improved battery performance, even at extreme temperatures. The molecular-level insights presented here further our understanding of structure−property relationships of complex fluids at the nanoscale, information that can be exploited for the predictive design of more efficient electrochemical systems.
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