The study of chemo-mechanical stress taking place in the electrodes of a battery during cycling is of paramount importance to extend the lifetime of the device. This aspect is particularly relevant for all-solid-state batteries where the stress can be transmitted across the device due to the stiff nature of the solid electrolyte. However, stress monitoring generally relies on sensors located outside of the battery, therefore providing information only at device level and failing to detect local changes. Here, we report a method to investigate the chemo-mechanical stress occurring at both positive and negative electrodes and at the electrode/electrolyte interface during battery operation. To such effect, optical fiber Bragg grating sensors were embedded inside coin and Swagelok cells containing either liquid or solid-state electrolyte. The optical signal was monitored during battery cycling, further translated into stress and correlated with the voltage profile. This work proposes an operando technique for stress monitoring with potential use in cell diagnosis and battery design.
Research on batteries mostly focuses on electrodes and electrolytes while few activities regard separator membranes. However, they could be used as a toolbox for injecting chemical functionalities to capture unwanted species and enhance battery lifetime. Here, we report the use of biological membranes hosting a nanopore sensor for electrical single molecule detection and use aqueous sodium polysulfides encountered in sulfur-based batteries for proof of concept. By investigating the host-guest interaction between polysulfides of different chain-lengths and cyclodextrins, via combined chemical approaches and molecular docking simulations, and using a selective nanopore sensor inserted into a lipid membrane, we demonstrate that supramolecular polysulfide/cyclodextrin complexes only differing by one sulfur can be discriminated at the single molecule level. Our findings offer innovative perspectives to use nanopores as electrolyte sensors and chemically design membranes capable of selective speciation of parasitic molecules for battery applications and therefore pave the way towards smarter electrochemical storage systems.
Rechargeable Li-ion batteries with larger autonomy are needed to meet increasing market demands, hence the intensive research effort to switch from graphite to silicon (Si) anodes, despite their detrimental massive volume changes upon cycling. Many elegant polymer chemistries have addressed this issue by designing smart binders capable of buffering Si electrodes fracturing and maintaining their overall structure. In this sense, self-healing PR–PAA binders relying on the α-cyclodextrin (α-CD) supramolecular chemistry and prepared by cross-linking poly(acrylic acid) (PAA) with α-CD based polyrotaxanes (PR) have recently been proposed. We herein further explore this binder chemistry to understand the proper function of such mechanically interlocked networks. We successfully synthesized a wide range of PR–PAA binders by varying their structural parameters: the doping ratio of PR, the cross-linking density, as well as the polymer molecular weight and the PR ring coverage. Then, their electrochemical performances were tested in nano-sized Si composite electrodes, and a structure/property correlation was evidenced. By promoting the α-CD sliding motion through both an increase of the PR doping fraction and a decrease of the PR ring coverage, we succeeded in making a PR−PAA-based Si electrode having an initial capacity of >3000 mA h/g and showing 82% capacity retention after 100 cycles as opposed to only 42% for PAA-based Si electrodes. A resulting better stress dissipation was evidenced by ex situ scanning electron microscope analysis as well as operando internal stress monitoring experiments via optical sensors. Altogether, this work emphasizes the benefits that CD-based supramolecular architectures can offer to the battery community for designing self-healing binders.
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