Hard carbon nanoparticles as high-capacity, high-stability anodic materials for Na-ion batteries

Hard carbon nanoparticles (HCNP) were synthesized by the pyrolysis of a polyaniline precursor. The measured Na+ cation diffusion coefficient (10(-13)-10(-15) cm(2) s(-1)) in the HCNP obtained at 1150 degrees C is two orders of magnitude lower than that of Li+ in graphite (10(-10)-10(-13) cm(2) s(-1)), indicating that reducing the carbon particle size is very important for improving electrochemical performance. These measurements also enable a clear visualization of the stepwise reaction phases and rate changes which occur throughout the insertion/extraction processes in HCNP, The electrochemical measurements also show that the nano -sized HCNP obtained at 1150 degrees C exhibited higher practical capacity at voltages lower than 1.2 V (vs. Na/Na+), as well as a prolonged cycling stability, which is attributed to an optimum spacing of 0.366 nm between the graphitic layers and the nano particular size resulting in a low -barrier Na+ cation insertion. These results suggest that HCNP is a very promising high-capacity/stability anode for low cost sodium-ion batteries (SIBS). (C) 2015 Elsevier Ltd. All rights reserved.