EFFECT OF DEPOLYMERIZATION ON ELECTROCHEMICAL PROPERTIES OF NANO-SILICON POWDERS

In order to limit the volume expansion of silicon in the process of lithiation/delithiation and achieve the ideal coating of silicon materials, the silicon needs to be depolymerized and dispersed. In this paper nano-silicon powders were depolymerized by ball milling and mechanical grinding, the effects of different depolymerization methods and different depolymerization time on nano-silicon powders were studied. The results showed that the particle size of nano-silicon powders decreased significantly after 30 min of ball milling and the D50 decreased from 4.9 μm to 0.041 μm. Meanwhile the morphology and specific surface area of the nano-silicon powders were greatly changed by ball milling. Both the initial charge capacity and the initial coulombic efficiency decreased obviously at 0.1 C rate. After mechanical grinded for 1 min, the particle size of D50 decreased from 4.9 μm to 1.77 μm, the morphology had no significantly changed and the specific surface area increased slightly.The initial coulombic efficiency at 0.1 C rate increased from 91.65% to 92.06%, and the capacity retention after 22 cycles with different rates increased from 75.02% to 81.3%. The results of XRD and Infrared spectrum showed that a small amount of nano-silicon powders were oxidized into SiOx in the process of depolymerization, and the degree of oxidation was increased with depolymerization time.