Vinylene carbonate (VC) is a widely used electrolyte additive in lithium-ion batteries for enhanced solid electrolyte interphase formation on the anode side. However, the cathode electrolyte interphase (CEI) formation with VC has received a lot less attention. This study presents a comprehensive investigation employing advanced in situ/operando-based Raman and X-ray absorption spectroscopy (XAS) to explore the effect of electrolyte composition on the CEI formation and suppression of surface reconstruction of Li_xNi_yMn_zCo_1-y-zO₂ (NMC) cathodes. A novel chemical pathway via VC polymerization is proposed based on experimental results. In situ Raman spectra revealed a new peak at 995 cm^-1, indicating the presence of C-O semi-carbonates resulting from the radical polymerization of VC. Operando Raman analysis unveiled the formation of NiO at 490 cm^-1 in the baseline system under ultrahigh voltage (up to 5.2 V). However, this peak was conspicuously absent in the VC electrolyte, signifying the effectiveness of VC in suppressing surface reconstruction. Further investigation was carried out utilizing in situ XAS compared X-ray absorption near edge structure spectra from cells of 3 and 20 cycles in both electrolytes at different operating voltages. The observed shift at the Ni K-edge confirmed a more substantial reduction of Ni in the baseline electrolyte compared to that in the VC electrolyte, thus indicating less CEI protection in the former. A sophisticated extended X-ray absorption fine structure analysis quantitatively confirmed the effective suppression of rock-salt formation with the VC electrolyte during the charging process, consistent with the operando Raman results. The in situ XAS results thus provided additional support for the key findings of this study, establishing the crucial role of VC polymerization in enhancing CEI stability and mitigating surface reconstruction on NMC cathodes. This work clarifies the relationship between the enhanced CEI layer and NMC degradation and inspires rational electrolyte design for long-cycling NMC cathodes.

Li-sulfur (Li-S) batteries are promising as the next-generation energy storage technology but face challenges due to sluggish sulfur redox reaction (SRR) kinetics and a sulfur shuttling effect. While many studies have explored polycaprolactone (PCL)-based gel polymer electrolytes (GPEs) to address these issues, the influence of solvent properties, including dielectric constant (ϵ) and donor and acceptor numbers (DN and AN), remain unexplored despite their critical impact on performance and full-scale implementation. This study systematically compares three distinct electrolytes, dimethoxyethane (DME), dimethyl sulfoxide (DMSO), and tetraethylene glycol dimethyl ether (TEGDME)-paired with PCL, to correlate the varied solvent properties and their effects on the physical properties of the GPE, in terms of Li⁺ transport and solvation, and polysulfide's confinement. Among them, the DME-based GPE, with an intermediate DN, exhibited the lowest crystallinity (2.31%), highest ionic conductivity (7.49 mS/cm), and high Li⁺ transference number (0.77). As a result, it achieved a specific capacity of 795 mAh/g sulfur and an average Coulombic efficiency of 97.5% after 120 cycles at C/5, outperforming its competitors. Operando Raman and UV-vis spectroscopy confirmed that PCL effectively confines long-chain polysulfides within its network, mitigating the shuttle effect and facilitating reversible polysulfide conversion. These findings demonstrate that GPEs with moderate DN values and balanced ϵ significantly enhance stability, extend cycle life, and improve rate performance for Li-S batteries. This work provides valuable insights into the design of advanced electrolyte systems for practical energy storage applications.

Lithium-sulfur (Li-S) batteries stand promising for next-generation energy storage systems due to their high specific capacity and cost-effectiveness. However, their commercialization is hindered by sluggish sulfur reduction reaction (SRR) kinetics and polysulfide migration. To address these challenges, we introduce bis(4-nitrophenyl) carbonate (BNC) as a bifunctional electrolyte additive. At an optimal concentration, BNC leverages its polar nature to anchor soluble polysulfides while simultaneously modifying the Li⁺ solvation structure at the molecular level, enhancing SRR kinetics. This dual functionality is confirmed through molecular dynamics simulations and electrochemical analyses. In situ electrochemical impedance spectroscopy (EIS) further shows that optimal BNC concentration reduces activation energy for polysulfides formation by 40.6%. Operando spectroscopic techniques, including Raman and X-ray absorption spectroscopy (XAS), demonstrate BNC’s dual effect, with a focus on the middle-chain polysulfides conversion, supported by detailed polysulfide quantification. X-ray fluorescence (XRF) mapping reveals decreased sulfur deposition on lithium, indicating the effectiveness of shuttle suppression. These effects contribute to outstanding cycling performance under practical conditions, achieving 650.93 mAh gsulfur−1 and coulombic efficiency of 93% over 200 cycles at a C-rate of C/2. This work not only offers valuable insights into the use of unconventional carbonate-based additives but also provides a blueprint for advancing Li-S battery designs through targeted solvation structure modifications.

Solid electrolytes are critical to enabling safe and high-energy-density batteries; yet, their practical deployment is impeded by poor electrochemical stability, inadequate interfacial contact, and challenging manufacturing processes. Here, we introduce a novel "solid-in-solid" electrolyte architecture comprising a porous Li zeolite electrolyte (LiX) infiltrated with a melt-processable plastic crystal electrolyte (PCE). This LiX-PCE electrolyte achieves an ionic conductivity of 0.55 mS/cm at 20 °C, alongside improved electrochemical stability over pure PCE. Solid-state nuclear magnetic resonance reveals three Li⁺ transport pathways: through LiX, through PCE, and via ion exchange at phase boundaries. Leveraging the melt-processability of the PCE, we proposed a roll-to-roll-compatible melt infiltration strategy for scalable solid-state battery (SSB) fabrication with the LiX-PCE electrolyte. The SSBs demonstrate excellent rate performance (up to 10 C), 93% capacity retention after 200 cycles at 2C, and 4.5 V compatibility. This work elucidates critical design principles for high-performance solid-state electrolytes and presents a viable path toward practical, fast-charging, high-power SSBs.