Novel Ni and Al doped manganese oxide (NixAlyMnzO2) ternary catalyst materials synthesized by a homogeneous precipitation method for high performance air electrodes of lithium–oxygen batteries

Abstract

Lithium–oxygen batteries are high performance energy storage systems and air electrode catalysts directly determine their electrochemical properties. In this paper, a novel Ni and Al doped manganese oxide (Ni_xAl_yMn_zO₂) ternary catalyst is synthesized by a facile homogeneous precipitation method. Raman spectroscopy and X-ray diffraction tests show that Ni and Al atoms can be successfully introduced into the Mn–O structure owing to some obvious structural changes. Scanning electron microscopy shows that when the mole ratio of Ni, Al and Mn is 1 : 1 : 1.5, the micromorphology of the (Ni_xAl_yMn_zO₂) ternary catalyst displays a more uniform particle size and distribution. Most of all, Ni and Al ion doping can make the Ni_xAl_yMn_zO₂ ternary catalyst have the largest electrochemical specific surface area of 83.25 m² g⁻¹. This is the main reason for improved catalytic activity. In addition, cyclic voltammetry and electrochemical impedance spectroscopy show that the air electrodes with this ternary catalyst possess a lower polarization resistance and fast electron conduction and ion transfer. Charge and discharge test results illustrate that the specific discharge capacities of the air electrode using the ternary catalyst with a Ni : Al : Mn ratio of 1 : 1 : 1.5 are respectively 5693.78, 4501.70, and 4250.97 mA h g⁻¹ at 0.1, 0.2 and 0.5 mA cm⁻² current density and can carry out 19 charge and discharge cycles. This means that through a simple coprecipitation method, the performance of manganese based catalysts for air electrodes can be effectively improved owing to the change of the electrochemical specific surface area and structure.