Impact of Degree of Graphitization, Surface Properties and Particle Size Distribution on Electrochemical Performance of Carbon Anodes for Potassium-Ion Batteries

Carbons are considered as anode active materials in potassium-ion batteries (PIBs). Here, the correlation between material properties of disordered (non-graphitic) and ordered graphitic carbons and their electrochemical performance in carbon||K metal cells is evaluated. First, carbons obtained from heat treatment of petroleum coke at temperatures from 800 to 2800 degrees C are analyzed regarding their microstructure and surface properties. Electrochemical performance metrics for K+ ion storage like specific capacity and Coulombic efficiency (C-Eff) are correlated with surface area, non-basal planes and microstructure properties, and compared to Li+ ion storage. For disordered carbons, the specific capacity can be clearly correlated with the defect surface area. For highly ordered graphitic carbons, the degree of graphitization strongly determines the specific capacity. The initial C-Eff of graphitic carbons shows a strong correlation with basal and non-basal planes. Second, kinetic limitations of ordered graphitic carbons are re-evaluated by analyzing commercial graphites regarding particle size and surface properties. A clear correlation between particle size, surface area and well-known challenges of graphitic carbons in terms of low-rate capability and voltage hysteresis is observed. This work emphasizes the importance of bulk and surface material properties for K+ ion storage and gives important insights for future particle design of promising carbon anodes for PIB cells.