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In this work we analyzed the phenomenon of quasi solid state (QSS) lithiation of sulfur-carbon (S/C) composite electrodes with sulfur confined in the micropores of carbon matrices based on our recent studies and data published in literature. We demonstrated that the existence of sulfur in the form of small molecules is not a necessary condition for the realization of QSS mechanism. QSS operation behavior was demonstrated both for carbons with small up to 1nm micropores and for carbons with larger pore size up to 2-3 nm. A key role in the operation of S/C electrodes via a QSS mechanism plays surface electrolyte interphase (SEI) which is formed on the surface of S/C composite during the initial discharge. The formation of SEI was supported by X-ray photoelectron spectroscopy and by scanning electron microscopy. Small pore size (up to 1 nm) of the carbon matrices has a positive effect on the cycling of S/C electrodes. A superior cycling performance for more than 3500 charge-discharge cycles was demonstrated for S/C composite electrodes based on carbons synthesized by carbonization of polyvinylidene dichloride (PVDC) resin. In recent years lithium-sulfur batteries have been the subject of very intensive research due to the high theoretical specific capacity of sulfur cathodes (1672 mA h g −1 ) which is an order of magnitude higher than that of lithiated transition-metal oxides and phosphates cathode materials used in commercial Li-ion batteries (140-200 mA h g −1 ). [1][2][3][4][5][6] This high capacity relates to the ability of sulfur atoms to accept two electrons resulting in the conversion of elemental sulfur to lithium sulfide (Li 2 S). Furthermore, sulfur is naturally abundant, environmentally friendly and relatively cheap.Due to the low electrical conductivity of elementary sulfur the addition of conductive additives or the use of conductive host materials it is necessary to ensure good performance of sulfur electrodes. Besides, during the discharge process elemental sulfur S 8 accepts electrons to give a chain of electroactive Li-polysulfides (Fig. 1a). The long-chain polysulfides Li 2 S n (4 ≤ n ≤ 8) are soluble in commonly used ethereal solvents and diffuse freely throughout the cell to the anode side where they are chemically reduced. This phenomenon known as the shuttle effect presents one of the main problems of Li-S cells. 7 The shuttle reactions prevent the possibility of extracting the full capacity of sulfur cathodes and lead to low Coulombic efficiency. Encapsulation of sulfur within activated carbons with high pores volume is one of the most effective approaches to mitigate the detrimental shuttle mechanism and stabilize composite sulfur cathodes during prolong cycling. 8-10The typical cyclic voltammetry and galvanostatic charge-discharge curves of the Li-S cell with C/S encapsulated cathode are shown in Fig. 1a. Two peaks observed in the cathodic voltammetric response of sulfur electrodes correspond to two plateaus observed in the voltage profiles of the discharge processes of these cathodes upon ...

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We report on a rigorous comparative study of nano-and microparticles of LiMn 1.5 Ni 0.5 O 4 spinel as cathode materials for Li-ion batteries. The stability of these materials in LiPF 6 /alkyl carbonate solutions in temperatures up to 70°C was explored. Capacity, cycling, rate capabilities, and impedance behavior were also studied. The methods included X-ray diffraction, Raman, X-ray photelectron, Fourier transform infrared, and electron paramagnetic resonance spectroscopies, and electron microscopy, in conjunction with standard electrochemical techniques: voltammetry, chronopotentiometry, and impedance spectroscopy. These materials show an impressive stability in solutions at elevated temperature. The use of nanomaterials was advantageous for obtaining a better rate capability of LiMn 1.5 Ni 0.5 O 4 electrodes. LiMn 1.5 Ni 0.5 O 4 particles develop a unique surface chemistry in solutions that passivates and protects them from detrimental interactions with solution species at elevated temperatures.

a Composite sulfur-carbon electrodes were prepared by encapsulating sulfur into the micropores of highly disordered microporous carbon with micrometer-sized particles. The galvanostatic cycling performance of the obtained electrodes was studied in 0.5M Li bis(fluorosulfonyl)imide (FSI) in methylpropyl pyrrolidinium (MPP) FSI ionic-liquid (IL) electrolyte solution. We demonstrated that the performance of Li-S cells is governed by the formation of solid electrolyte interphase (SEI) during the initial discharge at potentials lower than 1.5V vs. Li/Li + . Subsequent galvanostatic cycling is characterized by one plateau voltage profile specific to quasi-solid-state reaction of Li ions with sulfur encapsulated in the micropores in solvent deficient conditions. The stability of the SEI thus formed, is critically important for the effective desolvation of Li ions participating in quasi-solid-state reactions. We proved that realization of the quasi-solid-state mechanism is controlled not by the porous structure of the carbon host but rather by the nature of the electrolyte solution composition and the discharge cut off voltage value. The cycling behavior of these cathodes is highly dependent on sulfur loading. The best performance can be achieved with electrodes in which the sulfur loading was 60% by weight, when sulfur filled micropores are not accessible for N2 molecules according to gas adsorption isotherm data. A limited contact of the confined sulfur with the electrolyte solution results in the highest reversible capacity and initial Coulombic efficiency. This insight into the mechanism provides a new approach in the development of new electrolyte solutions and additives for Li-S cells.