Micro-nano structure hard carbon as a high performance anode material for sodium-ion batteries.

Superior first-cycle Coulomb efficiency (above 80%) is displayed by filter paper-derived micro-nano structure hard carbon, and it delivers a high reversible capacity of 286 mAh g after 100 cycles as the anode for Na-ion battery at 20 mA g. These advantageous performance characteristics are attributed to the unique micro-nano structure, which reduced the first irreversible capacity loss by limiting the contact between the electrode and electrolyte, and enhanced the capacity by accelerating electron and Na-ion transfer through inter-connected nano-particles and nano-pores, respectively. The good electrochemical performance indicates that this low-cost hard carbon could be a promising anode for Na-ion batteries.