Driss Mazouzi

A low-cost and high performance ball-milled Si-based negative electrode for high-energy Li-ion batteries

A Si-based anode with improved performance can be achieved using high-energy ball-milling as a cheap and easy process to produce Si powders prepared from a coarse-grained material. Ball-milled powders present all the advantages of nanometric Si powders, but not the drawbacks. Milled powders are nanostructured with micrometric agglomerates (median size ∼10 μm), made of submicrometric cold-welded particles with a crystallite size of ∼10 nm. The micrometric particle size provides handling and non-toxicity advantages compared to nanometric powders, as well as four times higher tap density. The nanostructuration is assumed to provide a shortened Li+ diffusion path, a fast Li+ diffusion path along grain boundaries and a smoother phase transition upon cycling. Compared to non-milled 1–5 μm powders, the improved performance of nanostructured milled Si powders is linked to a strong lowering of particle disconnection at each charge, while the irreversibility due to SEI formation remains unchanged. An electrode prepared in acidic conditions with the CMC binder achieves 600 cycles at more than 1170 mA h per gram of the milled Si-based electrode, in an electrolyte containing FEC/VC SEI-forming additives, with a coulombic efficiency above 99%, compared to less than 100 cycles at the same capacity for an electrode containing nanometric Si powder.

Surface modification of halogenated polymers. 4. Functionalisation of poly(tetrafluoroethylene) surfaces by diazonium salts

Reduced PTFE can be grafted by nitro and bromo-phenyl diazonium tetrafluoroborate salts in a manner similar to that used for carbon, except that no application of a reductive potential during grafting was required. Grafting was evidenced by cyclic voltammetry, X-ray fluorescence or ToF-SIMS. Nitro- and bromo-phenyl moieties were covalently linked to the PTFE material and could be eliminated only by abrasion.

Surface modification of halogenated polymers: 5. Localized electroless deposition of metals on poly(tetrafluoroethylene) surfaces

Localized metallization of polytetrafluoroethylene (PTFE) can be achieved by an electroless deposition procedure, once PTFE has been reduced locally at the contact or in the vicinity of an electrode by scanning electrochemical microscope (SECM). This process takes advantage of the n-doped character of polymeric carbon obtained when reducing PTFE. Metallization was evidenced with Au, Ag and Cu by cyclic voltammetry, SECM, MEB and X-ray fluorescence.

Nanostructured 3D porous hybrid network of N-doped carbon, graphene and Si nanoparticles as an anode material for Li-ion batteries

We report a facile and scalable process to prepare nanostructured 3D porous networks combining graphene, N-doped carbon and silicon nanoparticles (G@Si@C) as a promising anode material for batteries. It consists of preparing polymethylmethacrylate particles decorated by Si/graphene oxide and polypyrrole (PPy) in a one-pot process, followed by an appropriate thermal treatment that decomposes PMMA and converts graphene oxide into graphene and polypyrrole into N-doped carbon. The so-formed electrically conducting 3D porous network containing Si nanoparticles inside the cell walls accommodates the large volume changes of Si during charging/discharging and provides a fast electrolyte penetration/diffusion. Therefore, the designed G@Si@C material presents an excellent reversible capacity of 740 mA h g−1 at a current density of 0.14 A g−1 based on the total mass loading of the composite, with more than 99% coulombic efficiency, high rate capability and good cyclability, suggesting great potential for application as an anode material for lithium-ion batteries.