POSITIVE ELECTRODES FOR LITHIUM-ION BATTERIES: PROGRESS OF RESEARCH AT BAR-ILAN UNIVERSITY

We report on novel studies of positive electrode materials for lithium-ion batteries with the main emphasis on their structural and surface modifications by coating and cation doping. For this investigation we have chosen Al³⁺ and Zr⁴⁺ as dopant cations and AlF₃, ZrO₂, Al₂O₃, LiAlO₂, and carbon as the coating materials. Sol-gel precipitation, atomic layer deposition, and sonochemical deposition techniques were used for coating of Li- and Mn-rich high-energy density and Ni-rich layered materials. We have demonstrated the impact of a minor level of Al-doping on the electrochemical characteristics of LiNi_0.5Co_0.2Mn_0.3O₂ electrodes and on the interfacial reactions. From electrochemical, thermodynamic and kinetic properties of this material studied by density functional theory (DFT) we confirmed the experimental finding that on complete delithiation, this material remains in an O3 phase.

It was shown by Rietveld refinement analysis of XRD patterns of Zr-doped material LiNi_0.6Co_0.2Mn_0.2O₂ that Zr⁴⁺ ions reside both in Li and in transition metals layers substituting partially Ni²⁺ and thus they act like pillars resulting in increasing the lattice c-parameter. Zr-doped electrodes demonstrated faster kinetics, much lower impedance measured upon Li⁺ extraction, and higher discharge capacities during cycling at 45⁰C. An important finding of our work is that Zr-doped material retained its structure upon electrochemical cycling, in contrast to the undoped one, which underwent partial structural layered-to-spinel transformation. For the first time, we proposed a mechanism of the above transformation that was elucidated by DFT calculations and is suggested to include Ni-ions migration to the Li-sites upon delithiation.

We will also demonstrate our recent results of in-situ measurements of the above surface modified and doped electrodes by X-ray diffraction, Raman and X-ray absorption spectroscopy.