Lithium-ion batteries (LIBs) containing silicon negative electrodes have been the subject of much recent investigation because of the extremely large gravimetric and volumetric capacity of silicon. The crystalline-to-amorphous phase transition that occurs on electrochemical Li insertion into crystalline Si, during the first discharge, hinders attempts to link structure in these systems with electrochemical performance. We apply a combination of static, in situ and magic angle sample spinning, ex situ (7)Li nuclear magnetic resonance (NMR) studies to investigate the changes in local structure that occur in an actual working LIB. The first discharge occurs via the formation of isolated Si atoms and smaller Si-Si clusters embedded in a Li matrix; the latter are broken apart at the end of the discharge, forming isolated Si atoms. A spontaneous reaction of the lithium silicide with the electrolyte is directly observed in the in situ NMR experiments; this mechanism results in self-discharge and potential capacity loss. The rate of this self-discharge process is much slower when CMC (carboxymethylcellulose) is used as the binder.

International audienceDue to its success in the domain of power electronics, the lithium ion battery technology is currently being considered for electric vehicle propulsion and even electric grid storage.1,2 However, the implementation of a lithium based technology on a large scale faces controversial debates on lithium availability and cost. Alternative lower cost and sustainable chemistries would be specially suited for large scale applications even if they involve a penalty in energy density. The most appealing alternative is to use sodium, instead of lithium. Indeed, it exhibits a rich intercalation chemistry3,4 and its resources are in principle unlimited (high concentrations in seawater) being very easy to recuperate. Sodium technology has already been successfully implemented in today's commercialized high-temperature Na/S cells for MW storage and for Na/NiCl2 ZEBRA-type systems for electric vehicles, both of which take advantage of the highly conducting solid beta-alumina ceramics at temperatures of ca. 300 C. Mindful of these considerations, and within the current knowledge gained in Li-ion technology, a room temperature analogous Na-ion cell is a realistic target. If achieved, it would bring about a radical decrease in cost with respect to lithium ion technology while ensuring sustainability

International audienceArgyrodite Li6PS5Cl is a good candidate for being a solid electrolyte for bulk all-solid-state Li-ion batteries because of its high ionic conductivity and its good processability. However, the interface stability of sulfide-based electrolytes toward active materials (negative or positive electrodes) is known to be lower than that of oxide-based electrolytes. In this work, we investigate the interface stability of argyrodite toward several positive electrode materials: LiCoO2, LiNi1/3Co1/3Mn1/3O2, and LiMn2O4. All-solid-state half-cells were cycled, and the interface mechanisms were characterized by Auger electron spectroscopy and X-ray photoelectron spectroscopy. We show that Li6PS5Cl is oxidized into elemental sulfur, lithium polysulfides, P2Sx (x ≥ 5), phosphates, and LiCl at the interface with the positive electrode active materials. In spite of this interface reactivity, good capacity retention was observed over 300 cycles. Li6PS5Cl shows some reversible electrochemical activity (redox processes) that might contribute to the reversible capacity of the battery

No abstract

Solid electrolytes that are chemically stable and have a high ionic conductivity would dramatically enhance the safety and operating lifespan of rechargeable lithium batteries. Here, we apply a multi-technique approach to the Li-ion conducting system (1-z)Li4SiO4-(z)Li3PO4 with the aim of developing a solid electrolyte with enhanced ionic conductivity. Previously unidentified superstructure and immiscibility features in high-purity samples are characterized by X-ray and neutron diffraction across a range of compositions (z = 0.0-1.0). Ionic conductivities from AC impedance measurements and large-scale molecular dynamics (MD) simulations are in good agreement, showing very low values in the parent phases (Li4SiO4 and Li3PO4) but orders of magnitude higher conductivities (10(-3) S/cm at 573 K) in the mixed compositions. The MD simulations reveal new mechanistic insights into the mixed Si/P compositions in which Li-ion conduction occurs through 3D pathways and a cooperative interstitial mechanism; such correlated motion is a key factor in promoting high ionic conductivity. Solid-state (6)Li, (7)Li, and (31)P NMR experiments reveal enhanced local Li-ion dynamics and atomic disorder in the solid solutions, which are correlated to the ionic diffusivity. These unique insights will be valuable in developing strategies to optimize the ionic conductivity in this system and to identify next-generation solid electrolytes.

No abstract

The crystal chemistry and the electrochemical properties upon Na + extraction/insertion of NASICON-type Na 3 Al y V 2Ày (PO 4 ) 3 compositions (y ¼ 0.1, 0.25 and 0.5) were investigated. It was found that this family of V/Al substituted NASICON materials undergoes multiple reversible phase transitions between À50 C and 250 C upon heating, from monoclinic to rhombohedral symmetry, related to progressive disordering of Na + ions within the framework. Na + insertion/extraction mechanisms were monitored by operando X-ray diffraction. It is shown for the first time that substitution of aluminum for vanadium in Na 3 Al 0.5 V 1.5 (PO 4 ) 3 increases significantly the theoretical energy density of these promising positive electrodes (425 W h kg À1 ) due to its lighter molecular weight and the possibility of reversible operation on the V 4+ /V 5+ redox couple at 3.95 V vs. Na + /Na.

Li-ion batteries based on liquid electrolytes have conquered the electronics marketplace, however, cost and safety are the overriding parameters limiting their widespread use in electric vehicles (EVs) or hybrid EVs (HEVs). [ 1 ] Ideally, Li-ion batteries should rely on the use of dry polymer or inorganic electrolytes, as they would then be free of solvent leakages. The former are still under development after many years of research and the latter currently fall short in terms of high impedance issues associated with poorly defi ned interfaces. [ 2,3 ] Here, we report the use of spark plasma sintering (SPS) as a novel assembly technique for preparing all-inorganic, monolithic Li-ion batteries; these batteries have cycling characteristics approaching their liquid Li-ion counterparts, while being safer and faster to make. This achievement is grounded in the structural quality of the electrode-electrolyte interfaces, as probed by impedance spectroscopy and electron microscopy, which enables both good charge transfer and mechanical integrity upon cycling. This work provides a new path worth pursuing for designing Li-ion batteries capable of operating safely over a wide temperature range.The all-solid-state battery consists of a stack of 3 components (composite positive electrode/electrolyte/composite negative electrode) ( Figure 1 a), which should be assembled in such a way that intimate interfaces can be generated both between grains of the materials in each of the three parts as well as between the components themselves. To achieve these objectives, the materials should be selected principally using electrochemical criteria to insure high performances, but also taking into account additional criteria such as chemical compatibility suitable for "high" temperature sintering process.The composite electrodes should possess a high content of electrochemically active material (AM) for the energy density and electronic and ionic conductor additives to ensure efficient and homogeneous transfer of electrons and ions through the electrode volume. The composite electrodes should also display good mechanical behavior to allow easy handling and to insure cell lifetime, but also, more importantly, to permit volume variation upon Li insertion/extraction. It has been shown that oxide materials such as LiCoO 2 or LiMn 0.5 Ni 0.5 O 2 react at temperatures between 300 ° C and 500 ° C in presence of a Nasicon-type solid electrolyte with the formation of an ionblocking interface. [ 2 ] Another approach is to use ductile glasses or glass ceramics, such as those based on sulfi des, to assemble batteries by cold compaction. [ 4 ] However, beyond the intrinsic instability of sulfi des under air and water, which increases the process cost, cold-compacted systems present strong interface limitations implying to apply pressure on the battery to insure its cycle life. Finally, the stored energy, which is linked to the thickness of the composite electrodes, is limited to less than a few hundred μ Ah.cm − 2 .Based on all the previously listed co...