Revealing the structural roots of electrochemical differences in FePO4 under different physical states

Amorphous FePO4, due to its high theoretical specific capacity, simplicity of preparation, non-toxicity and low price, has been of wide interest to researchers. However, the electrochemical behavior of FePO4 in different physical states and its structural origin have so far lacked systematic studies. Herein, three different physical state, i.e., crystalline, glass-transition-free-amorphous and glassy, of FePO4/C were prepared and systematically tested as cathode materials for Na+-ion batteries. The results show that glass-transition-free-amorphous FePO4/C exhibits significantly better electrochemical properties than crystalline FePO4, while glassy FePO4 has almost no electrochemical activity. Combining the analytical results of the XPS and Raman test, it can be hypothesized that the root cause of the electrochemical differences should be attributed to the internal channel structure of the samples. In addition, this work revealed that ethylene glycol has the potential for low-temperature graphitization, which makes ethylene glycol promising as an excellent precursor for carbon-coated materials.