Hugues Duncan

High capacity anode materials for Li-ion batteries based on spinel metal oxides AMn2O4 (A = Co, Ni, and Zn)

Manganites of transition and/or post-transition metals, AMn2O4 (where A was Co, Ni or Zn), were synthesized by a simple and easily scalable co-precipitation route and were evaluated as anode materials for Li-ion batteries. The obtained powders were characterized by SEM, TEM, and XRD techniques. Battery cycling showed that ZnMn2O4 exhibited the best performance (discharge capacity, cycling, and rate capability) compared to the two other manganites and their corresponding simple oxides. Further studies on the effect of different sintering temperatures (from 400 to 1000 °C) on particle size were performed, and it is found that the size of the particles had a significant effect on the performance of the batteries. The optimum particle size for ZnMn2O4 is found to be 75–150 nm. In addition, the use of water-soluble and environmentally friendly binders, such as lithium and sodium salts of carboxymethlycellulose, greatly improved the performance of the batteries compared to the conventional binder, PVDF. Finally, ZnMn2O4 powder sintered at 800 °C (<150 nm) and the use of the in-house synthesized lithium salt of carboxymethlycellulose (LiCMC) binder gave the best battery performance: a capacity of 690 mA h g−1 (3450 mA h mL−1) at C/10, along with good rate capability and excellent capacity retention (88%).

Study of the Cathode–Electrolyte Interface of LiMn1.5Ni0.5O4 Synthesized by a Sol–Gel Method for Li-Ion Batteries

High voltage spinel LiMn 1.5 Ni 0.5 O 4 has been synthesized by a modified Pechini sol-gel method and has been characterized by transmission electron microscopy, X-ray diffraction (XRD), and electrochemical methods. The synthesized materials are porous structures of nanosized crystallites ranging in size from 21 to over 400 nm depending on the sintering temperature used. The XRD patterns of the materials were assigned to the disordered spinel structure of the space group Fd3m. The Li-ion batteries assembled using the synthesized cathode materials showed significant capacity fade for samples sintered at 500°C, while for those sintered at 800°C the capacity fade was low. Impedance spectroscopy, Fourier transform IR spectroscopy, and X-ray photoelectron spectroscopy were used to determine the compositions of the cathode electrolyte interphase (CEI). Impedance spectroscopy confirmed the spontaneous formation of the CEI on LiMn 1.5 Ni 0.5 O 4 and that its thickness grows on cycling. After more than 100 cycles, it is found that the CEI film is composed of polycarbonates, polyether, LiF, and Li x PO y F z salts. The composition of the organic layer was the same regardless of the capacity fade.

Study of the LiMn1.5Ni0.5O4/Electrolyte Interface at Room Temperature and 60°C

The surface layer (Cathode-Electrolyte Interface; CEI) on LiMn 1.5 Ni 0.5 O 4 , a promising, high voltage positive electrode for Li-ion batteries, was studied by XPS, AC impedance spectroscopy and FTIR spectroscopy. Half cells and full cells with LiMn 1.5 Ni 0.5 O 4 as positive electrode material and Li 4 Ti 5 O 12 as a negative electrode material were assembled in conventional carbonate-based electrolytes with LiPF 6 or LiBF 4 as the salt, and the effect of cycling at different operating conditions (short and long storage time, state of charge and temperature) on the surface layer composition was assessed. Capacities reaching near the theoretical value of 140 mAh g -1 were obtained in half cells cycled at C/2 and room temperature, with 85% of the capacity being retained after 100 cycles. Cycling at 60°C leads to a decrease in capacity and coulombic efficiency. The surface analysis by XPS revealed that the CEI is composed of inorganic species such as LiF and Li x PFyO z or Li x BF y O z as well as organic species such as polyethers and carbonates. Generally, it was found that cycling or storing the material at 60°C with an electrolyte using LiPF 6 as a salt yield more organic species and less LiF at the surface than the one with LiBF 4 .