(Battery Division Technology Award Address) Exploring Stable Manganese-Based Oxides As Cathodes for Na-Ion Batteries

Abstract

Sodium ion batteries (SIBs) promise the potential for large-scale grid storage, due to the high abundance and wide distribution of Na sources as compared to their lithium counterparts.1-3 Among various sodium storage cathodes, layered sodium transition metal oxides (NaxMnO2) have gained significant attention owing to their great variety of compositions, ease of scalable preparation and high reversible specific capacity. In the last several years, we have utilized different strategies such as alivovalent doping, ALD coating and controlled thermal treatments to synthesize several series of P2-type Mn-based cathodes materials and obtained promising results for future development[2-5]. For example, we propose an effective and synergetic strategy in combination of liquid N2 quenching and aliovalent doping to get new layered cathode materials [5]. As evidenced by X-ray diffraction, neutron diffraction and solid-state 23Na nuclear magnetic resonance techniques, the results reveal the significance of manipulating transition metal ions vacancies and valences to the electrochemical performance of P2-type Mn-based materials. Our results demonstrate that such a new structure significantly enhances the deliverable capacity, Na+ mobility and electronic conductivity of the materials. Furthermore, the effects of aliovalent doping elements and cooling approach on the long-range structure, local environment and electrochemical performance are comprehensively studied by comparing 15 sets of Na0.67MxMn1-xO2 materials (M = Al, Fe, Mg, Li ). The optimized Na0.67Al0.1Fe0.05Mn0.85O2 material exhibits a remarkably high initial capacity of 202 mAh g-1 among ever reported P2-type layered oxides within 2-4 V, a stable capacity retention of 81% after 600 cycles and outstanding rate capability of the specific capacity up to 122 mAh g-1 at 1200 mA g-1. In addition, some work about the air-stability of these oxides materials will be also presented.