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This research elucidates novel insights into the electrochemical properties and degradation phenomena of propylene carbonate (PC)‐based supercapacitors at a large‐scale 18650 cylindrical jelly‐roll cell level. Central to our findings is the identification of 2‐ethyl‐4‐methyl‐1,3‐dioxolane (EMD) as a hitherto undocumented decomposition by‐product, highlighting the nuanced complexity of PC electrolyte stability. We further demonstrate that elevated operational voltages precipitate accelerated electrolyte degradation, underscoring the criticality of defining the operational voltage window for maximizing device longevity. Employing advanced analytical techniques, including gas chromatography‐mass spectrometry (GC‐MS), this study meticulously analyzes electrolyte decomposition mechanisms. The outcomes offer pivotal insights into the operational constraints and chemical resilience of PC‐based supercapacitors, contributing significantly to the optimization of supercapacitor design and application. By delineating a specific decomposition pathway, this investigation enriches the understanding of electrochemical dynamics in supercapacitor systems, providing a foundation for future research and technological advancement in energy storage devices. [ABSTRACT FROM AUTHOR]

Understanding gas evolution during battery operation is pivotal for elucidating the underlying mechanisms of battery behavior, a cornerstone for fostering innovation in energy storage technologies. Despite the wealth of quantitative analyses available, the realm of large-scale, practical, full-cell investigations remains relatively unexplored. This study bridges this gap by unveiling a novel, robust gas chromatography methodology designed to meticulously quantify gas generation within 18650 cylindrical cells Li-ion and anode-free Li-metal Ni-rich batteries across a spectrum of operational conditions. Our approach not only reaffirms the capability for precise, reliable quantitative measurements but also illuminates new findings on the dynamics of gas evolution. This includes the significant impact of temperature and cathode material composition on gas generation, alongside a pioneering exploration into the behavior of anode-free Li-metal batteries. These insights not only advance our understanding of battery performance and safety at a practical cell level but also pave the way for the development of more efficient, durable, and safer energy storage solutions. [Display omitted] • Developed precise gas chromatography for Li-ion and Li-metal batteries. • Higher temperatures, nickel content significantly boost gas production, degradation. • Revealed unique gas evolution in anode-free Li-metal batteries. • Identified key conditions influencing gas production, battery design optimization. • Data links gas evolution to battery degradation, boosts safety, efficiency. [ABSTRACT FROM AUTHOR]

We present a novel, non-flammable electrolyte for Ni-rich 18650 cylindrical lithium-ion batteries (LIBs) based on a blend of triethyl phosphate (TEP) and fluorinated ethylene carbonate (FEC). We conducted a comprehensive analysis of the electrolyte, including electrochemical tests, safety evaluations, electrode surface characterizations, and quantum calculations, to elucidate its property-function relationship. We found that combining TEP with a concentrated FEC as a co-solvent (1.2 M LiPF 6 in TEP/FEC, 30/70 %v) resulted in a robust solid electrolyte interface (SEI) predominantly composed of lithium fluoride (LiF). This innovation improved the SEI's stability and suppressed electrolyte decomposition during extended cycling, leading to consistent battery performance. Our findings introduce a promising non-flammable electrolyte solution for LIBs that offers both thermal runaway prevention and seamless integration into existing battery manufacturing processes. This positions it as a potential alternative to solid-state electrolytes in advanced battery technology, with the potential to revolutionize the field. • Novel Electrolyte : Non-flammable blend for 18650 LIBs using TEP and FEC. • Rigorous Analysis : Comprehensive tests and calculations for electrolyte understanding. • Enhanced SEI : TEP and FEC create a stable, lithium fluoride SEI. • Consistent Performance : Approach reduces decomposition, ensuring prolonged battery life. • Future Applications : Solution integrates with existing processes, challenging solid-state alternatives. [ABSTRACT FROM AUTHOR]

Electrolyte decomposition significantly impacts the long-term stability of Li-ion batteries, generating liquid and gaseous byproducts. This study focuses on formaldehyde formation, a critical byproduct from CO 2 reduction in Ni-rich Li-ion batteries. Through experimental and computational analyses, formaldehyde emerges from carbonate-based electrolyte decomposition. Examining overcharge, over-discharge, and fast charging conditions, formaldehyde concentration sharply increases under overcharge, indicating severe electrolyte breakdown, while over-discharge shows a gradual rise. Fast charging similarly elevates formaldehyde levels, underscoring the link between electrolyte decomposition and abusive conditions. Importantly, this research proposes utilizing formaldehyde concentration from the initial cycle as a predictive marker for assessing long-term Ni-rich Li-ion battery stability trends. Elevated initial formaldehyde indicates potential capacity fade and accelerated degradation, enabling proactive mitigation strategies. The study elucidates mechanisms governing formaldehyde formation, providing a foundation for developing electrolyte formulations and electrode materials with enhanced decomposition resistance and improved stability. This investigation contributes to the fundamental understanding of electrolyte decomposition in Ni-rich Li-ion batteries and presents a novel approach to predicting long-term performance based on initial formaldehyde measurements, advancing high-performance and reliable energy storage solutions. [Display omitted] • Formaldehyde predicts stability in Ni-rich Li-ion batteries under stress. • CO 2 reduction to formaldehyde marks electrolyte decomposition's critical pathway. • Overcharge significantly accelerates formaldehyde production, hinting at rapid degradation. • Precise formaldehyde measurement via NMR improves battery health evaluation. • Research inspires advanced battery designs limiting formaldehyde generation. [ABSTRACT FROM AUTHOR]

Although supercapcitors have been widely studied, large-scale 18650 cylindrical supercapacitor cells have been rarely investigated and reported. Here, we investigated the effects of polymer separators, electrode thickness, electrolyte additives, testing protocols, reproducibility, and stability of the supercapacitors at the large-scale pilot plant. The supercapacitor cells with polyethylene (PE) and Al 2 O 3 -coated PE separators are good at low and high specific currents, respectively. The Al 2 O 3 -coated PE exhibits better stability than the one with the PE separator. The supercapacitor with a thickness of 250 μm has a cell capacitance of over 120 F from 100 to 1000 mA, which is higher than that of the other cells studied in this work. Also, the cell capacitances of supercapacitors can be enhanced by having redox mediator additives. 25 mM hydroquinone and ferrocene methanol are the optimized concentrations. We also found that the cell capacitance and equivalent series resistance of the supercapacitors are sensitive to the testing protocol, for which the highest capacitance was observed using the IEC62391-1 standard method, followed by the Maxwell method and conventional galvanostatic charge discharge method without dwell time. High reproducibility and stability of the as-fabricated supercapacitors in this work may lead to the further development of practical large-scale supercapcitors in the future. [Display omitted] • Large-scale production of cylindrical supercapacitors. • Supercapacitors with Al 2 O 3 -coated PE separator are good at high specific currents. • Supercapacitors with a thickness of 250 μm has a cell capacitance of over 120 F. • 25 mM of hydroquinone and ferrocene methanol additives is the optimized concentration. • Cell capacitance and equivalent series resistance are sensitive to the testing protocal [ABSTRACT FROM AUTHOR]