Microwave Assisted Ultra-Fast Method to Synthesize Carbonate-Phosphates, Na3MCO3PO4 (M = Mn, Fe, Co, Ni) - Relevant Materials Applied in Sodium-Ion Batteries

Although largely used in mobiles and electric vehicles applications, insertion batteries based on Li-ion technology are high-cost devices. These applications require high-performance energy storage systems with high-energy and high-power densities, which are better attained by Li-ion technology. However, stationary applications such as power plants and uninterruptible power supplies (UPS) mainly require low-cost energy storage devices. In this scenario Na-ion insertion batteries feature as a cheaper option for such applications. Among the several compounds for use as cathode in Na-batteries, a largely studied class of compounds are the sodium-carbonate-phosphates, Na3MCO3PO4 (M = Mn, Fe, Co or Ni), with structure analogue to the mineral sidorenkite. In this work, it was developed a new microwave-assisted hydrothermal method as an ultra-fast way to prepare sodium-carbonate-phosphate compounds. This methodology results in high-quality materials with general formula Na3MCO3PO4 (M = Mn, Fe, Co or Ni) upon only 5 min processing time. Characterization techniques indicate highly ordered materials with sidorenkite-like phase and different morphologies or crystal habits, including plates, rods, and a 'starfruit' shape. As a proof-of-application the Mn-based material was evaluated from electrochemical tests for Na+ insertion reactions. The obtained results evidence initial discharge capacity of 107 mA h g(-1) with good reversible capacity (65 mA h g(-1)) after several charge/discharge cycles.