Aluminum doping and Al2O3 coating for improving the electrochemical performance of layered Na2/3Ni1/2Mn1/2O2

In the present contribution the effects of doping and coating on the electrochemical performance of layered Na2/3Ni1/2Mn1/2O2 oxide are differentiated. As structural and surface modifiers, we used electrochemically inactive Al3+ ions. The structural modification consists in selective substitution for Ni3+ with Al3+ ion in the transition metal layer. The second approach aims to modify the oxide surface, therefore the pristine oxide as well as aluminium doped one was coated with Al2O3. The distribution of Al3+ ions into the layered crystal structure and Al2O3-coated oxides were monitored by X-ray powder diffraction and EPR spectroscopy. The electrochemical tests were carried out in model two- and three-electrode Swagelok type cells in presence of 1M NaPF6:PC as electrolyte solution and pure sodium metal as counter and reference electrode. Based on the experimental data, it was found that the electrochemical performance of layered Na2/3Ni1/2Mn1/2O2 depends critically on the kind of selected substituents and surface modifiers.