Solvionic (France)

Abstract This work presents an in‐depth chemical and morphological investigation of the solid electrolyte interphase (SEI) formed on binder‐free silicon electrodes, which include both nanowire (Si‐NW) and amorphous (a‐Si) configurations, for next‐generation lithium‐ion battery systems. The study focuses on the first five galvanostatic cycles to capture the critical early‐stage SEI consolidation process, essential for understanding the interfacial phenomena that dictate long‐term performance. By employing innovative electrode fabrication techniques such as plasma‐enhanced chemical vapor deposition and utilizing ionic liquid (IL)‐based electrolytes—specifically 1‐ethyl‐3‐methylimidazolium bis(fluorosulfonyl)imide (EMIFSI) formulations known for their low viscosity and high conductivity—this work addresses the challenges posed by the significant volume changes inherent to Si‐based materials. Advanced characterization methodologies, notably Optical‐Photothermal Infrared Spectroscopy (O‐PTIR) and Raman spectroscopy are utilized to probe the chemical and structural evolution of the SEI with high spatial resolution. This multifaceted approach reveals the interplay between electrode morphology and electrolyte composition on SEI formation and provides valuable insights into the fundamental processes governing irreversible capacity losses and electrode degradation. The findings demonstrate clear material‐ and electrolyte‐dependent differences in SEI characteristics, thereby establishing new avenues for optimizing interfacial stability and battery performance. Overall, the study contributes innovative perspectives on early SEI formation mechanisms critical for the design of safer and more durable high‐capacity battery electrodes.

The design of interfaces between nanostructured electrodes and advanced electrolytes is critical for realizing advanced electrochemical double-layer capacitors (EDLCs) that combine high charge-storage capacity, high-rate capability, and enhanced safety. Toward this goal, this work presents a novel and sustainable approach for fabricating ionogel-based electrodes using a renewed slurry casting method, in which the solvent is replaced by the ionic liquid (IL), namely 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI). This method avoids time-consuming and costly electrolyte-filling steps by integrating the IL directly into the electrode during slurry preparation, while improving the rate capability of EDLCs based on pure non-flammable ILs. The resulting ionogel electrodes demonstrate exceptional electrolyte accessibility and enable the production of symmetric EDLCs with high energy density (over 30 Wh kg-1 based on electrode material weight) and high-rate performance. These EDLCs could operate at temperatures up to 180 °C, far exceeding the limitations of traditional EDLCs based on organic electrolytes (e. g., 1 M TEABF4 in acetonitrile, up to 65 °C). Ionogel-type EDLCs exhibit remarkable long-term stability, retaining 88 % specific capacity after 10000 galvanostatic charge/discharge cycles at 10 A g-1 and demonstrating superior retention compared to conventional EDLCs (50 %), while also maintaining 92.4 % energy density during 100 h floating tests at 2.7 V. These electrochemical properties highlight their potential for robust performance under demanding conditions. This study highpoints the practical potential of ionogel-based electrodes to advance IL-based EDLC technology, paving the way for next-generation energy storage devices with high-temperature and high-voltage operational capabilities.

Polymer solid electrolytes for solid-state batteries typically suffer from low ionic conductivity and low oxidative stability. We report a polymer electrolyte based on a polymerized ionic liquid and an ionic liquid plasticizer offering simultaneously a high room-temperature ionic conductivity of 0.8 mS cm-1 and a high oxidative stability > 5.0 V vs Li+/Li. The electrolyte is compatible with lithium metal, exhibits high thermal stability up to 300 °C, is non-flammable upon direct flame exposure, shows decent lithium-ion transference number of 0.44, and possesses a low gravimetric density of only 1.6 g cm-3, important when targeting batteries with high gravimetric energy density. In symmetric lithium metal cells, the electrolyte enables stable lithium plating and stripping at 0.1 mA cm−2 with a capacity of 1 mAh cm−2 per half cycle for over 1700 h at 25 °C. Cells with a lithium metal anode cycled against a state-of-the-art high-energy uncoated layered LiNi0.8Mn0.1Co0.1O2cathode achieve an initial capacity of 162 mA h g-1 and a capacity retention of 72% after 600 cycles to an upper cut-off voltage of 4.4 V at 0.1 mA cm-2 and 25 °C. Cells with a high-voltage spinel LiMn1.5Ni0.5O4 cathode reach an initial capacity of 132 mAh g-1 and a capacity retention of 76% after 300 cycles to an upper cut-off voltage of 5 V at 0.1 mA cm-2 and 25 °C, confirming the high oxidative stability and technological potential of this electrolyte for high-voltage solid-state lithium metal batteries.

Two ethoxy containing ionic liquids (ILs) sharing the same anion, N-trimethyl-N (2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (N111(2O1)-TFSI) and N,N-diethyl-N-methyl-N (2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (N122(2O1)-TFSI), and their mixtures are studied by means of differential scanning calorimetry and infrared spectroscopy combined with DFT calculations. The two ILs, slightly differing only for the length of two short chains, diverge significantly in the thermal properties: N111(2O1)-TFSI undergoes to a crystallization upon cooling, whereas N122(2O1)-TFSI is likely to become a glass. Experimental results indicate that in N111(2O1)-TFSI the occurrence of hydrogen bonding is energetically favored, and become particularly evident in the solid phase. The comparison with computational results indicates that it could be ascribed to the CH bonds involving the C atoms directly linked to the central N atom. In N122(2O1)-TFSI, DFT calculations suggest that hydrogen bonding could take place; however, IR measurements suggest that hydrogen bonding is not energetically favored. Moreover, in N122(2O1)-TFSI there is a larger conformational disorder that prevents from the alignment of cation and anion that contributes to the detection of clear hydrogen bonding infrared active bands. The mixtures rich in N111(2O1)-TFSI crystallize at lower temperatures than the pure ionic liquid. Progressively, the energy gain due to the instauration of hydrogen bonding decreases as the concentration of N122(2O1)-TFSI increases.