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[en] The specific heat capacities of a polymer electrolyte and a polymer-containing composite cathode have been determined by differential scanning calorimetry in the range from 70 to 140 deg. C. This range well includes the operating temperature range of the devices incorporating these materials (lithium polymer batteries). The determination of the specific heat capacities of the battery polymeric components was driven by the need of designing high performance devices
[en] The chemical–physical properties of a ternary solid polymer electrolyte (SPE) system consisting of poly(ethylene oxide) and two salts, namely lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and the ionic liquid N-methyl-N-butyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI), are reported in this work. The ternary phase diagram shows the composition limits of the thermodynamically stabilized amorphous phase where the polymer electrolyte achieved the maximum conductivity. The important conductivity threshold of 10−3 S cm−1 at 40 °C is exceeded for these compositions. Two reasons for the high conductivity are identified; the decreased overall coordination to the Li+-ion and a Tg as low as −67 °C. Also presented is the thermal stability characterization of such polymer electrolytes. The amorphous phase seems to be thermodynamically unfavored; however, the recrystallization process is slow
[en] Herein, a new and facile synthesis of a tin-carbon nanocomposite and its electrochemical characterization is presented. Tin nanoparticles were embedded in micron-sized carbonaceous particles, thus successfully preventing the aggregation of tin nanoparticles and buffering the occurring volume strain, which accompanies the reversible (de-)alloying process. Such active material presents specific capacities of around 440 and 390 mAh g−1 for applied specific currents of 0.1 and 0.2 A g−1, respectively, as lithium-ion anode using environmentally friendly and cost-efficient carboxymethyl cellulose as binder. Even more remarkably, at very high specific currents of 2, 5, and 10 A g−1, electrodes based on this composite still offer specific capacities of about 280, 240, and 187 mAh g−1, respectively. In addition, this tin-carbon nanocomposite appears highly promising as anode material for sodium-ion batteries, showing very stable cycling performance in a suitable potential range, and specific capacities of more than 180, 150, 130, and 90 mAh g−1 for an applied specific current of 12.2, 122, 244, and 610 mA g−1, respectively, thus highlighting the high versatility of this composite active material for both Li-ion and Na-ion battery technologies
[en] X-ray absorption spectroscopy (XAS) is applied to study the local geometry of Co, Ni, and Mn sites in a new high voltage cathode for lithium batteries. The material is a solid solution between Li2MnO3 and Li(x)Mn0.4Ni0.4Co0.2O2. The XAS technique has permitted to check the local atomic structure and charge associated with the metals in a series of electrodes with different lithium concentration x, obtained during the first charge operation, and compared to the first discharge and a successive charge. The ex-situ XAS investigation on the initial activation of the cathode material (first charge) can be described by two separated reaction of LiMO2 (M = Ni and Co) and Li2MnO3. The strength and limitations of the ExAFS approach in these materials is underlined. (paper)
[en] Highlights: • Guar gum as aqueous binder for LIB electrodes. • Effect of guar gum on the SEI formed on graphite and NMC. • Mechanical properties of guar gum-based electrodes. - Abstract: Herein we report the investigation on the use of guar gum and two of its derivatives as LIB positive electrodes binders. These polymers are electrochemically stable within the operating voltage of LIBs (0.01–5 V vs Li/Li+) and do not show evidence of thermal decomposition up to 200 °C. The electrochemical performance of lithium nickel manganese cobalt oxide (NMC) electrodes made using guar gum is excellent as indicated, for instance, by the delivered capacity of 100 mAh g−1 upon 5C rate cycling. X-ray Photoelectron Spectroscopy (XPS) measurements of pristine electrodes reveal as the binder layer surrounding the active material particles is thin, resulting in the above-mentioned electrochemical performance. Full lithium-ion cells, utilizing guar gum on both positive and negative electrodes, display a stable discharge capacity of ∼110 mAh g−1 (based on cathode active material) with high coulombic efficiencies. Post-mortem investigation by XPS of cycled graphite electrodes from full lithium-ion cells revealed the formation of a thin solid electrolyte interface (SEI).
[en] This paper offers a comprehensive overview on the role of nanostructures in the development of advanced anode materials for application in both lithium and sodium-ion batteries. In particular, this review highlights the differences between the two chemistries, the critical effect of nanosize on the electrode performance, as well as the routes to exploit the inherent potential of nanostructures to achieve high specific energy at the anode, enhance the rate capability, and obtain a long cycle life. Furthermore, it gives an overview of nanostructured sodium- and lithium-based anode materials, and presents a critical analysis of the advantages and issues associated with the use of nanotechnology. .
[en] Highlights: ► Layered P2-Na0.45Ni0.22Co0.11Mn0.66O2 reversibly uptakes and releases Li and Na cations. ► Electrochemical performance of sodium intercalation is better than that of lithium. ► Na0.45Ni0.22Co0.11Mn0.66O2 shows good Na-ion intercalation capacity (125 mAh g−1). ► Na0.45Ni0.22Co0.11Mn0.66O2 shows high average discharge voltage (>3.3 V). ► Na-ion insertion in Na0.45Ni0.22Co0.11Mn0.66O2 offers high charge efficiency (≥99.5%). -- Abstract: Herein is reported the electrochemical performance of Na0.45Ni0.22Co0.11Mn0.66O2 as cathode material for lithium and sodium batteries. The material is able to reversibly accommodate both cation species but reveals a much better electrochemical performance towards Na-ion intercalation. Upon galvanostatic cycling for 100 cycles a much higher capacity retention (82% vs. Na, 61% vs. Li) and higher coulombic efficiency (99.5% vs. Na, 98.5% vs. Li) are shown by the sodium-based system. The worse electrochemical performance of the lithium-based system can be explained by the much higher irreversibility of the Mn3+/Mn4+ redox process
[en] Aqueous rechargeable batteries are becoming increasingly important to the development of renewable energy sources, because they promise to meet cost-efficiency, energy and power demands for stationary applications. Over the past decade, efforts have been devoted to the improvement of electrode materials and their use in combination with highly concentrated aqueous electrolytes. Here the latest ground-breaking advances in using such electrolytes to construct aqueous battery systems efficiently storing electrical energy, i.e., offering improved energy density, cyclability and safety, are highlighted. This Review aims to timely provide a summary of the strategies proposed so far to overcome the still existing hurdles limiting the present aqueous batteries technologies employing concentrated electrolytes. Emphasis is placed on aqueous batteries for lithium and post-lithium chemistries, with potentially improved energy density, resulting from the unique advantages of concentrated electrolytes. (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA)
[en] The stability vs. aging of Li2FeSiO4 (LFS) cathode material in fluorine-based electrolytes, especially at elevated temperature, was studied in this work. The LFS powder was initially synthesized using a hydrothermal route and then aged at 60 °C for 40 days in LiPF6 and LiBF4-based electrolytes. The residual powder and the electrolyte were investigated afterwards. In the case of LiPF6, a structural and compositional change of LFS to Li2SiF6 was observed by XRD. SEM images confirmed that this change led to a morphology change of the aged material. XPS, EDX and ICP-OES measurements showed a large increase of fluorine content inside the residual powder. NMR investigations indicated an accelerated decomposition of electrolyte in the presence of LFS compared to the electrolyte aged without LFS. Our results suggest a degradation of LFS to Li2SiF6 in the fluorine-based electrolyte at elevated temperatures while the electrolyte decomposition is accelerated.