Electrochemical energy storage is one of the main societal challenges of this century. The performances of classical lithium-ion technology based on liquid electrolytes have made great advances in the past two decades, but the intrinsic instability of liquid electrolytes results in safety issues. Solid polymer electrolytes would be a perfect solution to those safety issues, miniaturization and enhancement of energy density. However, as in liquids, the fraction of charge carried by lithium ions is small (<20%), limiting the power performances. Solid polymer electrolytes operate at 80 °C, resulting in poor mechanical properties and a limited electrochemical stability window. Here we describe a multifunctional single-ion polymer electrolyte based on polyanionic block copolymers comprising polystyrene segments. It overcomes most of the above limitations, with a lithium-ion transport number close to unity, excellent mechanical properties and an electrochemical stability window spanning 5 V versus Li(+)/Li. A prototype battery using this polyelectrolyte outperforms a conventional battery based on a polymer electrolyte.

To better understand the factors responsible for the poor electrochemical performances of the olivine-type LiMnPO 4 , various experiments such as chemical delithiation, galvanostatic charge and discharge, cyclic voltamperometry, and impedance conductivity, were carried out on both LiFePO 4 and LiMnPO 4 . Chemical delithiation experiments confirmed a topotactic two-phase electrochemical mechanism between LiMnPO 4 and the fully delithiated phase MnPO 4 ͑a = 5.909͑5͒ Å, b = 9.64͑1͒ Å, and c = 4.768͑6͒ Å͒. We conclude that the limiting factor in the MnPO 4 /LiMnPO 4 electrochemical reaction is nested mostly in the ionic and/or electronic transport within the LiMnPO 4 particles themselves rather than in charge transfer kinetics or structural instability of the MnPO 4 phase. For instance, the electrical conductivity of LiMnPO 4 ͑ ϳ 3.10 −9 S cm −1 at 573 K, ⌬E ϳ 1.1 eV͒ was found to be several orders of magnitude lower than that of LiFePO 4 ͑ ϳ 10 −9 S cm −1 at 298 K, ⌬E ϳ 0.6 eV͒.

No abstract

No abstract

No abstract

No abstract

Tortuosity is often used as an adjustable parameter in models of transfer properties through porous media. This parameter, not reducible to classical measured microstructural parameters like specific surface area, porosity, or pore size distribution, reflects the efficiency of percolation paths, which is linked to the topology of the material. The measurement of the effective conductivity of a bed of particles saturated with an electrolyte is a simple way to evaluate tortuosity. Nevertheless, it received only little attention because of the real difficulties in both getting reliable results and interpreting data. Notably, the discrimination between the contribution of interparticle and intraparticle porosities to the tortuosity is not resolved. To our knowledge, there is no model able to fit the experimental data of the tortuosity of a suspension, and a fortiori of a particle bed, in the whole porosity range. Only empirical expressions have been proposed, but they do not allow deriving intratortuosity of a porous particle. For a dilute system, Maxwell's equation predicts the effective conductivity of suspensions of spherical particles as a function of the bulk electrolyte conductivity and of particle conductivity. The intraparticle tortuosity can be derived from the particle conductivity obtained from the Maxwell equation applied to data at infinite dilution of particles. Then, by assuming that the Maxwell equation is a first-order approximation of the conductivity as a function of porosity, we propose an explicit relation of the tortuosity tau of a suspension of porous particles, obtained by conductivity measurement, as tau = tau(epsilon, epsilon(p), tau(p)), where epsilon is the total porosity of the suspension, tau(p) is the intraparticle tortuosity, and epsilon(p) is the particle porosity. This relationship fits the experimental data in the whole porosity range and can be used to determine tau(p) from an experiment at only one porosity. Finally, the obtained values of tau(p) for a set of porous particles used in chromatography are discussed and compared to the data available in the literature.

Li 2 S 2 species, sometimes considered as a solid product, [ 18,19 ] has never been experimentally detected by XRD, thus questioning its real existence as a solid. Sulfur reduction (complete [ 13,16 ] or incomplete [ 10,20 ] and recrystallization at the end of charge [ 11,12,16 ] was also an unresolved question. Until today, there have been few reports released on the study of Li/S cells, where in situ XRD was applied. [7][8][9]21 ] In the majority of these works, the formation of a solid sulfur at the end of charge was confi rmed. The appearance of crystalline Li 2 S was not evidenced by Nelson et al., [ 9 ] while other groups [ 8,21 ] reported on its formation at different states of discharge along the lower plateau. Both the reports offered only qualitative interpretation of the results. By applying in situ and operando XRD, information about the structural changes of sulfur positive electrode versus exchanged capacity upon cycling could be obtained. [7][8][9] This enables a deeper insight into the complex mechanism of the Li/S cell, which from the point of view of further improvements, is essential.Here we report, for the fi rst time, a quantitative evaluation of Li 2 S formation and consumption upon cycling and propose a mechanism of solid product(s) formation. Monitoring of further cycles, as well as C-rate infl uence (C/20 and C/8), is also taken into consideration. These results were obtained from a pouch cell using nonwoven carbon sheet as a current collector and relatively high sulfur loading, along with a controlled electrolyte amount. The effect of the electrolyte excess and electrode morphology on the solid phases formation was not the scope of this paper, therefore not investigated any further. Nevertheless, these important parameters may be studied in the future.The obtained electrochemistry displays an expected voltage profi le of a typical Li/S cell, where discharge and charge capacities of 980 and 976 mAh g −1 , respectively, were obtained. The corresponding XRD patterns evolution is shown on Figure S1a (Supporting Information). As the discharge proceeds, the peak intensities of the elemental orthorhombic α-sulfur (PDF-2; No. 00-008-0247) linearly decrease as a function of capacity ( Figure S2, Supporting Information). They vanish at the end of the fi rst discharge plateau, proving a complete reduction of sulfur. This linear evolution can be associated with a one-step electrochemical process, based on the reduction reaction of S 8 to S 8 2− . [ 22 ] The practical capacity of this fi rst region (so-called "solid/soluble"; 175 mAh g −1 ) is slightly lower than the theoretically expected one (209 mAh g −1 ), possibly because of a self-discharge associated with partial S 8 dissolution [ 23 ] (further details are provided in the Supporting Information). In the region Lithium/sulfur batteries are considered as a promising candidate for a next-generation energy storage system. This technology is based on the electrochemical reaction between elemental sulfur and metallic lithium (16Li + S 8