NaCrO2 is a Fundamentally Safe Positive Electrode Material for Sodium-Ion Batteries with Liquid Electrolytes

Abstract

Layered structure NaCrO2 (R-3m) was successfully synthesized by solid state reaction. The electrochemical performance of NaCrO2 as a positive electrode material for sodium-ion batteries was tested at room temperature using two-electrode coin cells with NaClO4/PC electrolyte. NaCrO2 delivered a reversible capacity of 110 mAh/g during the first charge and had good cyclability. The reaction between deintercalated NaxCrO2 (~Na0.5CrO2) and ethylene carbonate/diethyl carbonate solvent was studied using Accelerating Rate Calorimetry (ARC). The results were compared to analogous results for Li0.5CoO2 and Li0FePO4 under the same conditions. Na0.5CrO2 showed an unexpected excellent thermal stability in solvent with no heat release in the ARC test temperature range. An X-ray diffraction study showed that Na0.5CrO2 decomposes to NaCrO2 and P3-type layered structure CrO2-δ with minimal oxygen release during the ARC tests, which explains the lack of exothermic behavior.