Improvement of cyclability of Si as anode for Li-ion batteries

Silicon working as anode for Li-ion batteries has attracted much attention due to its high capacity (∼4200 mAh g⁻¹). However, due to the large volume expansion during lithiation, the capacity of silicon fades very fast. In this systematic study, we focus on the issue to fight the capacity fading. Results show that Si with sodium carboxymethyl cellulose (Na-CMC) as a polymer binder exhibits a better cyclability than that with poly(vinylidene fluoride) (PVDF). Yet differing from the system used in PVDF, the addition of vinylene carbonate (VC) does not improve or even worsens the performance of the system using Na-CMC. In addition, the small particle size of Si, a large amount of carbon black (CB), the good choice of electrolyte/conducting salt and charge-discharge window also play important roles to enhance the cyclability of Si. It is found that electrode consisting of 40 wt.% nano-Si, 40 wt.% carbon black and 20 wt.% Na-CMC (pH 3.5) displays the best cyclability, and in the voltage range from 0 to 0.8 V, after 200 cycles, its capacity can still keep 738 mAh g⁻¹ (C/2, in 1 M LiPF₆ ethylene carbonate/diethyl carbonate electrolyte, with VC-free), almost twice as that of graphite.