Défense de thèse de doctorat en sciences chimiques

Metal-Organic Frameworks and Their Derivatives Based Electrode Materials for Advanced Lithium-Selenium Batteries

Jury

Alexandru VLAD (UCLouvain), Yu LI (Wuhan University of Technology), Alain KRIEF (UNamur), Stéphane VINCENT (UNamur), Président, Olivier DEPARIS (UNamur), Bao-Lian SU (UNamur), promoteur

Résumé

The bursting market demands for mobile electronics, electric vehicles and large-scale energy storage, prompted the quick development of batteries with high energy density, long circles and low costs. Conventional cathode materials are intercalation compounds, such as olivine compounds LiFePO₄ and layered compounds LiMO₂ (M= Co, Mn, Ni), which are short of energy density and rate performance. Recently, Li-Se batteries attracted much attention due to its high theoretical capacity (678 mA h g^-1), however, undergo the dissolution of high-order polyselenides, giving rise to poorer cycle and lower coulombic efficiency. Porous materials are widely demonstrated to be efficient to solve the shuttle effect of selenium.

In this thesis, we will talk about the application of MOFs, a class of porous materials with tailorable pore shape, size and volume, and their derivatives to confine selenium that will lead to better Li-Se battery performances and exhaustive explanation of the mechanism.

1. The first example focus on the exact effect of meso and micro pores and the best pore composition to maximize the synergy effects. Three kinds of aluminium MOFs based hierarchically meso-microporous carbon materials have been successfully fabricated by facile carbonization. The micropores are efficient to suppress polyselenides dissolution while the mesopores typically good to electrolyte transportation, thus hierarchically meso-microporous carbon with more suitable mesopores obtain improved battery performance.

2. One of the above MOFs, MIL-68 (Al) was chosen to in situ synthesis on the surface of multi-walled carbon nanotubes (MWCNTs) to build a three dimensional conductive system. The better electrochemical performance benefits from uniform distribution of porous structure, polyselenide adsorption by micropores, thus effectively suppresses the shuttle effects. Besides, sufficient ion and electron transportation help to improve rate performance.

3. Another kind of MOFs, ZIF-8, was chosen to confine the selenium, because of the multi amounts of micropores and nitrogen doping after pyrolysis. The particle sizes of ZIF-8 have been detailed discussed to the final battery performance. 3D hollow microporous carbon materials ZIF-8-800 from 30 nm to 1.5 µm stringed by MWCNTs was obtained by in situ solvothermal reaction. This strategy provides the facile way to obtain the connection of MOFs to MWCNTs to alleviate the inefficient electron transportation. This unique structure can adsorb the soluble polyselenides and promote the conductivity of cathode materials for fast electron transportation. Besides, the interconnected MWCNTs can build the electron transport path, which will further improve the conductivity of the electrode.

 

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