Enhancement of the Electrochemical Performance of the Sodium Cathode Materials Via Zr Doping

Abstract

The last few decades in the world, the energy crisis become more severe, and the main reason is the high rise in energy demand. Therefore, the major current sources of electricity, which are fossil fuels and biomass, increase in demand, and 2016 covered 79.5% of the total energy consumption [1]. However, burning biomass and non-renewable resources could lead to another problem: the emission of carbon dioxide, the greenhouse effect, and global warming. This problem shifts the global electricity production trend towards green and renewable energy sources [2]. According to the [1] in 2016, rest electricity 18.2% after non-renewable resources covered by wind, solar and hydropower and 2.2% by nuclear energy. The energy produced from these sources is low cost but not stable, intermittent and low efficiency, requiring long permanent energy storage systems (ESS) or rechargeable batteries [3]. For example, during the night-time, the efficiency of solar panels is very low, and an off-grid application requires stable electricity, which can provide rechargeable batteries.Here we study one of the promising cathode materials for the sodium-ion battery NaMn0.5Ni0.5O2, and the effects of Zr doping on the layered positive electrode and the role in stabilizing the the crystal structure. This material has attracted attention because of its high reversible capacity, around 200 mAhg-1 in the voltage range of 2.0-4.5V. However, due to the depletion of oxygen charge density and subsequent oxygen instability upon a high state of charge lead to the oxygen gas release, electrolyte degradation, lattice contraction and finally, mechanical damage. All these mentioned problems lead to capacity fading and short cycle life. Among the proposed ways the doping with Zr, which substitutes inactive Mn in the structure, has enhanced the cathode cycle life by stabilizing the layered octahedral structure while carrying out electrochemical performance. It can proceed because of the larger ions of the Zr4+ (0.72 Å) compared with that of Mn4+ (0.53 Å) [4] and therefore lead to the larger interslab space in the structure, thereby demonstrates more continuous phase transition and easier Na+ transportation. Acknowledgments This work was supported by the Ministry of Education and Science of the Republic of Kazakhstan Grant (AP08856179), “Boosting the electrochemical performance of the cathode material for beyond lithium-ion batteries”.