An easy way for preparing high performance porous silicon powder by acid etching Al-Si alloy powder for lithium ion battery

We developed a novel, simple method to prepare porous silicon powder by acid etching Al-Si alloy powder. .The morphology and structure of the as-obtained material were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM), and BET methods. It was found that the porous silicon powder (size about 15 μm) had a spongy structure, consisting of silicon nanobars with diameter about 50 nm and length of 1.5 μm. Its specific surface area was 102.8 m2 g−1. The electrochemical properties of porous silicon electrode were evaluated by measuring voltammograms and charge and discharge curves. The porous silicon electrode with ratio of porous Si powder:Super P:binder = 1:1:1 was tested in button style lithium/Si cell. It was found that due to its ability to promote the formation of primal SEI film on the surface of electrodes, additive fluoroethylene carbonate (FEC) had an effect to improve the charge and discharge cycle stability of porous silicon electrodes. In solution 1 M LiPF6, EC:DMC = 1:1 (V/V) containing 15% FEC, the first charge and discharge capacities of porous silicon electrode were 3450 mAh g−1 Si and 2072 mAh g−1 Si respectively, at current density 100 mA g−1. The discharge capacity retained 66% as 1368 mAh g−1 Si after 258 charge and discharge cycles. In 1 M LiPF6/EC:DEC = 1:1 (V/V) solution, the charge and discharge capacities of porous silicon electrode in first cycle were 3396 mAh g−1 Si and 2537 mAh g−1 Si respectively. At 69th cycle, the discharge capacity remained 59% as 1497 mAh g−1 Si. The high electrochemical performance of porous silicon powder could be attributed to its porous structure, which provides enough tiny space to buffer the huge volume change of Si anode during charging and discharging processes. The nano-size Si bars benefited the diffusion process of lithium in Li-Si alloy. Moreover, the firm connection between Si nanobars in spongy porous structure prevented the breakdown of porous Si particles. This new advanced method for preparing high performance porous Si material is simple and inexpensive, presenting a promising prospect for practical application.