Rachid Yazami

Olivine-Type Nanosheets for Lithium Ion Battery Cathodes

Olivine-type LiMPO4 (M = Fe, Mn, Co, Ni) has become of great interest as cathodes for next-generation high-power lithium-ion batteries. Nevertheless, this family of compounds suffers from poor electronic conductivities and sluggish lithium diffusion in the [010] direction. Here, we develop a liquid-phase exfoliation approach combined with a solvothermal lithiation process in high-pressure high-temperature (HPHT) supercritical fluids for the fabrication of ultrathin LiMPO4 nanosheets (thickness: 3.7-4.6 nm) with exposed (010) surface facets. Importantly, the HPHT solvothermal lithiation could produce monodisperse nanosheets while the traditional high-temperature calcination, which is necessary for cathode materials based on high-quality crystals, leads the formation of large grains and aggregation of the nanosheets. The as-synthesized nanosheets have features of high contact area with the electrolyte and fast lithium transport (time diffusion constant in at the microsecond level). The estimated diffusion time for Li(+) to diffuse over a [010]-thickness of <5 nm (L) was calculated to be less than 25, 2.5, and 250 μs for LiFePO4, LiMnPO4, and LiCoPO4 nanosheets, respectively, via the equation of t = L(2)/D. These values are about 5 orders of magnitude lower than the corresponding bulk materials. This results in high energy densities and excellent rate capabilities (e.g., 18 kW kg(-1) and 90 Wh kg(-1) at a 80 C rate for LiFePO4 nanosheets).

Unravelling the Correlation between the Aspect Ratio of Nanotubular Structures and Their Electrochemical Performance To Achieve High-Rate and Long-Life Lithium-Ion Batteries†

The fundamental understanding of the relationship between the nanostructure of an electrode and its electrochemical performance is crucial for achieving high-performance lithium-ion batteries (LIBs). In this work, the relationship between the nanotubular aspect ratio and electrochemical performance of LIBs is elucidated for the first time. The stirring hydrothermal method was used to control the aspect ratio of viscous titanate nanotubes, which were used to fabricate additive-free TiO2 -based electrode materials. We found that the battery performance at high charging/discharging rates is dramatically boosted when the aspect ratio is increased, due to the optimization of electronic/ionic transport properties within the electrode materials. The proof-of-concept LIBs comprising nanotubes with an aspect ratio of 265 can retain more than 86 % of their initial capacity over 6000 cycles at a high rate of 30 C. Such devices with supercapacitor-like rate performance and battery-like capacity herald a new paradigm for energy storage systems.

Ultrahigh Rate Capabilities of Lithium‐Ion Batteries from 3D Ordered Hierarchically Porous Electrodes with Entrapped Active Nanoparticles Configuration

Three dimensional (3D) ordered hierarchically porous electrodes with an entrapped active nanoparticles configuration afford an extremely effective conductive 3D network from the micrometer to the nano meter scale for fast electron and Li-ion transport, and also allow the development of a stable solid electrolyte interphase over the electrode materials, therefore exhibiting extraordinary rate capabilities.

Direct growth of FeVO4 nanosheet arrays on stainless steel foil as high-performance binder-free Li ion battery anode

Amorphous FeVO4 nanosheet arrays have been grown directly from a flexible stainless steel (SS) substrate by a facile template-free and catalyst-free chemical vapour deposition (CVD) method. These FeVO4 nanosheets showed superior Li storage properties, especially at high current densities.

Fe2O3 nanocluster-decorated graphene as O2 electrode for high energy Li–O2 batteries

Fe2O3 nanocluster-decorated graphene (Fe2O3/graphene) hybrids with controlled contents of Fe2O3 were prepared by a facile electrochemical process. These Fe2O3/graphene hybrids were tested as O2 electrodes for Li–O2 batteries, which exhibited enhanced discharge capacities as compared to that of a pure graphene based O2 electrode, e.g. the Fe2O3/graphene electrode with 29.0 wt% of Fe2O3 delivered a discharge capacity of 8290 mA h g−1 and a round-trip efficiency of 65.9% as compared to 5100 mA h g−1 and 57.5% for a pure graphene electrode. The excellent electrochemical properties of Fe2O3/graphene as an O2 electrode is ascribed to the combination of the fast kinetics of electron transport provided by the graphene sheets and the high electrocatalytic activity for O2 reduction provided by the Fe2O3.

Coaxial Fe3O4/CuO hybrid nanowires as ultra fast charge/discharge lithium-ion battery anodes

We report the facile, template free electrochemical fabrication of hierarchical Fe3O4/CuO hybrid wires, grown directly on a copper substrate. The electrodes are produced by the electrochemical deposition of Fe3O4 on CuO nanoneedle arrays, fabricated by anodization. The Fe3O4/CuO hybrid anodes displayed ultrafast charging/discharging properties and high rate capabilities, superior to those of their individual building blocks Fe3O4 and CuO. For example, at a current density of 820 mA g−1, the Fe3O4/CuO hybrid wires delivered high reversible specific capacity, good cycling stability (delivering 953 mA h g−1 discharge capacity with 98.7% Coulombic efficiency after 100 cycles) and excellent rate capability (319 mA h g−1 at 8200 mA g−1). The excellent performance of the Fe3O4/CuO hybrids comes from the intelligent integration of the two compatible components into unique hierarchical architectures with a high specific capacity, with one-dimensional CuO nanoneedle arrays electrochemically coated with mesoporous Fe3O4 nanocubes.

A gamma fluorinated ether as an additive for enhanced oxygen activity in Li–O2 batteries

Perfluorocarbons (PFCs) are known for their high O2 solubility and have been investigated as additives in Li–O2 cells to enhance the cathode performance. However, the immiscibility of PFCs with organic solvents remains the main issue to be addressed as it hinders PFC practical application in Li–O2 cells. Furthermore, the effect of PFC additives on the O2 mass transport properties in the catholyte and their stability has not been thoroughly investigated. In this study, we investigated the properties of 1,1,1,2,2,3,3,4,4-nonafluoro-6-propoxyhexane (TE4), a gamma fluorinated ether, and found it to be miscible with tetraglyme (TEGDME), a solvent commonly used in Li–O2 cells. The results show that with the TE4 additive up to 4 times higher O2 solubility and up to 2 times higher O2 diffusibility can be achieved. With 20 vol% TE4 addition, the discharge capacity increased about 10 times at a high discharge rate of 400 mA gC−1, corresponding to about 0.4 mA cm−2. The chemical stability of TE4 after Li–O2 cell discharge is investigated using 1H and 19F NMR, and the TE4 signal is retained after discharge. FTIR and XPS measurements indicate the presence of Li2O2 as a discharged product, together with side products from the parasitic reactions of LiTFSI salt and TEGDME.

Insertion compounds of graphite with improved performances and electrochemical applications of those compounds

The present invention relates to insertion compounds with improved performances for electrochemical applications. They are characterized in that they are obtained from a graphite with a specific surface area of at least 100 m2 /g, and a granulometry at most equal to 4 μm. The graphite oxide or the graphite-NiCl2 first stage obtained from such a graphite is used as constituting agent of the cathode of a lithium battery and it gives to same excellent characteristics. The graphite oxide performances may further be improved by preparing it by double oxidation of a graphite having any specific surface area and the granulometry is of the order of the μm, as shown by FIG. 2 which represents the intensiostatic discharge curves of the lithium batteries the cathode of which contains the graphite oxide.

Composes ioniques du graphite avec NiCl2, BF−4 et K+ pour le stockage electrochimique de l'energie

Abstract Ionic graphite intercalation compounds are used as positive and negative electrodes in primary or secondary high energy density batteries. This concerns first stage compounds as C 7 NiCl 2 (charge transfer complex), C + 24 BF − 4 (graphitic salt) for positive pole and Li +δ C −δ , K +δ C −δ 8 for negative one. Good values of energy densities are reached with Li/C 7 NiCl 2 and LiAl/C + 24 BF − 4 secondary systems. The negative electrodes are reversible under some conditions and they show very good cations diffusivity between the graphite layers.

A room-temperature refuelable lithium, iodine and air battery

We demonstrate a new refuelable lithium cell using lithium solvated electron solution (Li-SES) as anolyte and iodine solutions as catholyte. This cell shows a high OCV (~3 V). Unlike conventional rechargeable Li batteries, this kind of cell can be re-fueled in several minutes by replacing the spent liquids. We also show for the first time, that Li-SES/I2 cells which operate at room temperature, can be prepared in a fully discharged state (~0 V OCV) for safe handling, transportation and storage. Li-SES and iodine are then electrochemically generated during charge as is confirmed by UV-VIS and a qualitative test. We have also conducted proof-of-concept tests for an “indirect lithium-air” cell in which iodine is reduced at the cathode and subsequently is catalytically re-oxidized by oxygen dissolved in the catholyte.