Directional Oxygen Functionalization by Defect in Different Metamorphic‐Grade Coal‐Derived Carbon Materials for Sodium Storage

As the limiting factor for an energy storage technique from lab‐scale to industrial‐scale, cost means not only the price of raw materials but also the simplicity of processing technics. In this work, the oxygen functionalized carbon materials were obtained from three representative different metamorphic‐grade coals, that is, lignite, bitumite, anthracite. Oxygen functional groups like quinones, carboxylic anhydrides, and lactones are easier to form near defects according to the thermogravimetric‐mass spectrometry measurements and density functional theory calculation. Considering the highest amount of defects and C=O contained functional groups, the low metamorphic‐grade lignite derived carbon exhibits a reversible capacity of 259.7 mA h g−1 after 50 cycles at 0.03 A g−1, best among these micron sized coal‐based carbons. The surface active sites contribute highly stable and majority of sodium storage capacity evidenced by in situ Raman spectra and cyclic voltammetry curves at different scan rates. The coal‐based carbon materials in this work offer options for industrial applications of sodium‐ion battery anode materials. The coal‐based carbons match well with the sodium ion batteries, because of low cost and wide distribution of resources. Herein, three representative coal with different metamorphic grades are treated with simple process technic and shows different sodium storage behaviors when used as anodes. This work offers practical connections between the coals and large‐scale energy storage techniques.