1,720,961 research outputs found
Ionic liquids and their derivatives for lithium batteries: role, design strategy, and perspectives
Full text linkLithium-ion batteries (LIBs) are the predominant power source for portable electronic devices, and in recent years, their use has extended to higher-energy and larger devices. However, to satisfy the stringent requirements of safety and energy density, further material advancements are required. Due to the inherent flammability and incompatibility of organic solvent-based liquid electrolytes with materials utilized in high energy devices, it is necessary to transition to alternative conductive mediums. The focus is shifting from molecular materials to a class of materials based on ions, including ionic liquids (ILs) and their derivatives such as zwitterionic ILs, polymerized ILs, and solvated ILs, which possess high levels of safety, stability, compatibility, and the ability to rationally design ILs for specific applications. Ion design is crucial to achieve superior control of electrode/electrolyte interphases (EEIs) both on anode and cathode surfaces to realize safer and higher-energy lithium-metal batteries (LMBs). This review summarizes the different uses of ILs in electrolytes (both liquid and solids) for LMBs, reporting the most promising results obtained during the last years and highlighting their role in the formation of suitable EEIs. Furthermore, a discussion on the use of deep-eutectic solvents is also provided, which is a class of material with similar properties to ILs and an important alternative from the viewpoint of sustainability. Lastly, future prospects for the optimization of IL-based electrolytes are summarized, ranging from the functional design of ionic structures to the realization of nanophases with specific features
Insight into physico-chemical properties of oxalatoborate-based ionic liquids through combined experimental-theoretical characterization
Full text linkIonic liquids (ILs) including oxalatoborate anions, like bis(oxalato)borate (BOB) and difluoro(oxalato)borate (DFOB) are extensively used in the battery sector as additives to promote the formation of protective layers on the surface of high-voltage cathode materials. In this work four ILs have been synthesized: N-ethoxyethyl-N-methylpiperidinium bis(oxalato)borate (PIP1,2O2BOB), N-ethoxyethyl-N-methylpiperidinium difluoro(oxalato)borate (PIP1,2O2DFOB), N-propyl-N-methylpiperidinium bis(oxalato)borate (PIP1,3BOB) and N-propyl-N-methylpiperidinium difluoro(oxalato)borate (PIP1,3DFOB) and their thermal properties have been linked to their structure. The presence of an oxygen atom in the PIP1,2O2 lateral chain suppresses crystallization of the ILs. Furthermore, PIP1,2O2DFOB shows a lower glass transition temperature than PIP1,2O2BOB. These observations have been explained using a combined molecular dynamics and density functional theory approach and an increase in the degree of freedom of the lateral chain of the cation due to the ether oxygen has been found. Comparing PIP1,2O2DFOB and PIP1,2O2BOB, a notable interaction between different domains of the anions is observed and is stronger in the DFOB case due to the charge-delocalization induced by the fluorine atoms, which generates a relatively positive charge on the boron atom. This is correlated to the weaker cation-anion attraction which hinders the glass transition of PIP1,2O2DFOB
Effects of Difluoro(oxalato)borate-Based Ionic Liquid as Electrolyte Additive for Li-Ion Batteries
Full text linkIn this work, the use of N-methyl-N-propylpiperidinium difluoro(oxalato)borate Pip13DFOB ionic liquid (IL), originally synthesized in our laboratory, as an additive for liquid electrolytes in lithium-ion batteries (LIBs), is proposed. The synthesized IL exhibits glass and melting transitions at −70.9 °C and 17.1 °C, respectively, and a thermal decomposition temperature over 230 °C. A mixture based on 1.0 M LiPF6 in 1:1 v/v ethylene carbonate (EC): dimethyl carbonate (DMC) electrolyte solution (so called LP30) and the IL was prepared and tested in lithium metal cells versus two different commercially available carbonaceous electrodes, i.e., graphite (KS6) and graphene (GnP), and versus a high voltage LiNi0.5Mn1.5O4 (LNMO) cathode. A noticeable improvement was observed for Li|LNMO cells with an IL-added electrolyte, which exhibited a high specific capacity above 120 mAh g−1 with a Coulombic efficiency above 93% throughout 200 cycles, while the efficiency fell below 80% after 80 cycles with the absence of IL. The results confirm that the IL is promising additive for the electrolyte, especially for a longer cycle life of high-voltage cells
Predicting the Thermal Behavior in the Design of Type V Deep Eutectic Solvents: The Combined Role of Polarity and Steric Asymmetry
No full textThe thermal behavior of the hydrophobic eutectic mixtures formed by l-menthol (MEN) with 4-methoxyphenol (4-Met), 2-tert-butyl-4-methoxyphenol (BHA), 2-tert-butyl-4-ethylphenol (TBEP), and tert-butylhydroquinone (TBHQ) has been investigated to elucidate the different factors governing the solid–liquid equilibrium (SLE) at the molecular level. Our comparative study highlights the contribution of hydrogen-bonding (H-bonding) asymmetry of deep eutectic solvent (DES) precursors, i.e., their ability to act as strong H-bond donors and weak H-bond acceptors or vice versa. When deriving from resonance effects, this concept was previously presented as “polarity asymmetry” and introduced to explain the thermal behavior of type V DES. Here, we expand this concept to demonstrate that steric factors led by the insertion of ad hoc functional groups in the precursor molecules also have a dominant role in the deviation from thermodynamic ideality. In this way, an increasing temperature depression is observed starting from the 4-Met/MEN mixtures up to the BHA/MEN, TBHQ/MEN, and TBEP/MEN ones. The SLE prediction has been carried out through an innovative approach combining the COSMO-RS solvation model and density functional tight-binding molecular dynamics simulations, benchmarked against experimental data, and presented here for the first time. The impact of this work is that of providing new tools for a more conscious understanding and design of hydrophobic type V DES as new sustainable media for applicative purposes
Structural degradation of O3-NaMnO2 positive electrodes in sodium-Ion batteries
Full text linkIn this manuscript, we report an extensive study of the physico-chemical properties of different samples of O3-NaMnO2, synthesized by sol–gel and solid state methods. In order to successfully synthesize the materials by sol–gel methods a rigorous control of the synthesis condition has been optimized. The electrochemical performances of the materials as positive electrodes in aprotic sodium-ion batteries have been demonstrated. The effects of different synthesis methods on both structural and electrochemical features of O3-NaMnO2 have been studied to shed light on the interplay between structure and performance. Noticeably, we obtained a material capable of attaining a reversible capacity exceeding 180 mAhg−1 at 10 mAg−1 with a capacity retention >70% after 20 cycles. The capacity fading mechanism and the structural evolution of O3-NaMnO2 upon cycling have been extensively studied by performing post-mortem analysis using XRD and Raman spectroscopy. Apparently, the loss of reversible capacity upon cycling originates from irreversible structural degradations
Different impact of menthol chirality on ideal and deep eutectic solvents: Thermal and structural insights
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Ionic Liquids as Cathode Additives for High Voltage Lithium Batteries
No full textTwo oxalatoborate ionic liquids (ILs), which are commonly utilized as electrolyte additives that form a protective layer on the cathode surface, are investigated for the first time as electrode additives. Cathodes based on LiNi0.5Mn1.5O4 (LNMO) containing 3 wt % ILs, i. e., “IL-enriched cathodes”, exhibit capacity values above 120 mAh/g with high Coulombic efficiencies throughout cycling over 200 times. A cathode without ILs also exhibits a capacity of 119 mAh/g but its Coulombic efficiency becomes low and unstable after 109 cycles. In addition, when 0.3 M ILs are added to conventional carbonate-based electrolytes, the battery cycle life improves but there is a reduction in the capacity probably due to low ionic conductivity of the electrolyte mixtures. Post-mortem analyses of electrodes retrieved from cycled cells highlight less electrolyte decomposition and less cathode corrosion, enabled by using the IL as the additive in LNMO, which are confirmed by a particle shape with smooth surface identical to the fresh cathode. The study demonstrates that oxalatoborate ILs can be used as the electrode additive, and this provides a new concept for cathode formulations for high performance batteries with a small amount of ILs
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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