Phase Evolutions of Sodium Layered Oxide Cathodes During Thermal Fluctuations

Abstract

Layered transition metal oxides (NaxTMO2) are considered to be highly appropriate for the practical applications of sodium ion batteries (SIBs) relying on their facile synthesis, high capacity, and low cost. Generally, the phase growth procedures of NaxTMO2 during solid-state reactions at high temperature closely related to their carbon footprint, prime cost, and the eventual electrochemical properties, while the thermal stability in various desodiated states associated with wide temperature fluctuations are extremely prominent to the electrochemical properties and safety of SIB devices. Therefore, in this review, the influences of sintering conditions such as pyrolyzation temperature, soaking time, and cooling rate on the phase growth patterns of NaxTMO2 are summarized. The thermodynamic and kinetics competitive driving behaviors at the highest temperature for the phase growths are deeply discussed. Furthermore, for the thermal stability of NaxTMO2 cathodes, the phase transition behaviors along with the alterations of battery system temperature under various electro-/chemical environments are concluded. The thermal stability enhancement strategies such as elemental composition modulations, surface reconstructions, and polyphase symbiosis using in the previous works are overviewed. Finally, we prospect the high-efficient preparation methods and the thermal devastation regulations of the NaxTMO2 layered oxides.