Sanghoon Kim

Conception de matériaux poreux silicatés stimuli-responsive en utilisant des nanoparticules lipidiques solides (SLN) et tensioactifs magnétiques pour la vectorisation de la curcumine: Ce travail a consisté à préparer des matériaux silicatés poreux à caractère stimuli-sensible à base de nanoparticules lipidiques solides (SLN) et de tensioactifs magnétiques. Plusieurs systèmes à base de tensioactifs ont été utilisés afin de synthétiser des matériaux silicatés à porosité contrôlée en utilisant des méthodes décrites dans la littérature ou mises au point au laboratoire. De différents caractères stimuli-sensible ont été introduits dans les matériaux silicatés poreux en fonction de système utilisé: les nanoparticules lipidiques solides (SLN) pour les matériaux sensible au pH et les tensioactifs magnétiques pour les matériaux sensible au champ magnétique. Premièrement, les matériaux à base de nanoparticules lipidiques solides (SLN) ont été utilisés pour la vectorisation d’un principe actif, la curcumine. La libération de la curcumine a été contrôlée en fonction de pH. Un revêtement sur la surface silice a été également employé pour mieux contrôler la libération de la curcumine. D’autre part, la sensibilité au champ magnétique a été introduite dans des silices mésoporeuses en utilisant des tensioactifs magnétiques. Leurs propriétés d’auto-assemblage (i.e. micelles, vésicules) ont été mise en évidence. Ainsi, la synthèse de matériaux silicatés poreux à caractère magnétique-sensible a été effectuées en utilisant ces tensioactifs. Enfin, les SLN magnétiques ont été préparés en combinant les SLN avec un tensioactif magnétique, qui ont été servi pour la synthèse de catalyseur à base de la silice méso-macroporeuse dopée en nanoparticules d’oxyde de fer

In this work, we investigated the influence of gas impurity in oxygen as calcination gas on the electrochemical properties of high Ni LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode materials. Among investigated gas compositions, the oxygen mixed with a small amount of argon (96% O2, 4% Ar) shows the same level of Li/Ni cation mixing as 100% O2 sample, with not only a very stable discharge capacity retention (89% at 200 cycles) but also higher C-rate capability (67% at 20C) compared to other samples. Despite well suppressed Li/Ni cation mixing, 100% O2 sample suffers from an over-oxidation of Ni and Co of the surface, leading to an increase of surface resistance, as a consequence, a fast capacity fade over cycling with lower C-rate capability compared to the material calcined under 96% O2/4% Ar. This result demonstrates that calcination gas composition plays a key role in determining the electrochemical properties of high Ni cathode materials, not only in terms of Li/Ni cation mixing in the bulk structure, but also the oxidation properties of Ni, Co at the surface.

The surface fluorination of lithium cobalt phosphate (LiCoPO₄, LCP) using a one‐step, room temperature processable, easily up‐scalable and dry surface modification method with XeF₂ as fluorine source was developed. After fluorination, fluorine‐rich nanoparticles were observed mainly on the particle surface, which facilitates the improvement of surface stability and electrochemical performance such as cycling stability and rate capability, as the fluorinated LCP can be protected against side reactions with electrolyte or by‐products of electrolyte decomposition at high voltage (5 V). More importantly, the direct surface fluorination proved more efficient than adding a fluorinated electrolyte additive (i. e., FEC). These results suggest that surface fluorination using XeF₂ is of great promise for practical applications of high voltage positive materials for lithium‐ion batteries.

A new strategy for the synthesis of mesoporous TiO₂@C nanocomposites through the direct mineralization of seaweed‐derived alginic acid cryogel by TiCl₄ through a solid/vapor reaction pathway is presented. In this synthesis, alginic acid cryogel can have multiple roles; i) mesoporous template, ii) carbon source, and iii) oxygen source for the TiO₂ precursor, TiCl₄. The resulting TiO₂@alginic acid composite was transformed either into pure mesoporous TiO₂ by calcination or into mesoporous TiO₂@C nanocomposites by pyrolysis. By comparing with a nonporous TiO₂@C composite, the importance of the mesopores on the performance of electrodes for lithium‐ion batteries based on mesoporous TiO₂@C composite was clearly evidenced. In addition, the carbon matrix in the mesoporous TiO₂@C nanocomposite also showed electrochemical activity versus lithium ions, providing twice the capacity of pure mesoporous TiO₂ or alginic acid‐derived mesoporous carbon (A600). Given the simplicity and environmental friendliness of the process, the mesoporous TiO₂@C nanocomposite could satisfy the main prerequisites of green and sustainable chemistry while showing improved electrochemical performance as a negative electrode for lithium‐ion batteries.

An original, halide‐free non‐hydrolytic sol–gel route to mesoporous anatase TiO₂ with hierarchical porosity and high specific surface area is reported. This route is based on the reaction at 200 °C of titanium(IV) isopropoxide with acetic anhydride, in the absence of a catalyst or solvent. NMR spectroscopic studies indicate that this method provides an efficient, truly non‐hydrolytic and aprotic route to TiO₂. Formation of the oxide involves successive acetoxylation and condensation reactions, both with ester elimination. The resulting TiO₂ materials were nanocrystalline, even before calcination. Small (about 10 nm) anatase nanocrystals spontaneously aggregated to form mesoporous micron‐sized particles with high specific surface area (240 m² g⁻¹ before calcination). Evaluation of the lithium storage performances shows a high reversible specific capacity, particularly for the non‐calcined sample with the highest specific surface area favouring pseudo‐capacitive storage: 253 mAh g⁻¹ at 0.1 C and 218 mAh g⁻¹ at 1 C (C=336 mA g⁻¹). This sample also shows good cyclability (92 % retention after 200 cycles at 336 mA g⁻¹) with a high coulombic efficiency (99.8 %). Synthesis in the presence of a solvent (toluene or squalane) offers the possibility to tune the morphology and texture of the TiO₂ nanomaterials.

Eco-friendly and cheap lithium ion battery electrode processing using a seaweed-derived mesoporous carbon additive (Starbon® A800) and binder (sodium alginate) was elaborated for LiMn₂O₄ (LMO) and LiNi_1/3Mn_1/3Co_1/3O₂ (NMC) lithium ion batteries. Compared to electrodes made using conventional formulations (i.e. Super P/PVDF) the ‘green’ electrodes can provide significantly ‘upgraded’ reversible capacity, almost reaching their theoretical capacity at low C-rate, likely due to good accessibility of lithium ions via the mesopores of the carbon additive. In addition, a synergistic effect was observed for a binary carbon additive system composed of Starbon® A800 with conventional carbon black (Super P), improving both the initial capacity and the rate capability of LMO and NMC electrodes.

We report here a simple process for the synthesis of Li ₄ Ti ₅ O ₁₂ (LTO)/carbon nanocomposites by a one-pot method using an alginic acid aquagel as a template and carbon source, and lithium acetate and TiO ₂ nanoparticles as precursors to the LTO phase.

A mesoporous LiMn₂O₄ grafted with carbonaceous species was synthesized using a mesoporous carbon Starbon®.