Structural and electrochemical properties of natural spheronized graphite

Spheronized particles of natural graphite with various diameters were obtained using a centrifugal impact method. The evolution of particle shape during spheronization was examined, with particular attention to the influence of electrochemically active surface area and substructural modifications on the efficiency of lithium-ion intercalation. Reducing the average particle size to 20 μm (roundness 0.9) was found to provide for a sufficiently high discharge capacity of 330–340 mAh/g with a coulombic efficiency above 90%, driven by factors such as better particle contact, a larger intercalation area and lower diffusion limitations. Further fragmentation of graphite to sizes under 5 μm leads to a loss of the mechanical integrity of the particles, alters intercalation kinetics, destabilizes charge-discharge cycling and results in lower capacity. A step-by-step scheme describing the transformation of natural graphite flakes into rounded particles during spheronization is proposed. A model has been developed to predict the specific discharge capacity of spheronized graphite based on its structural properties, such as the specific surface area of particles and the nanocrystallites size.