Influence of Li diffusion distance on the negative electrode properties of Si thin flakes for Li secondary batteries

Pure Si thin flakes (Si Leaf Powder® (Si-LP)) of different thicknesses (50, 100, 200, 300 and 400nm) were prepared, and their charge/discharge properties were investigated as negative electrode materials for lithium ion batteries (LIBs). High reversible capacity (2200–2500mAhg−1) and good capacity retention were obtained for thinner Si-LPs (50–200nm), while thicker samples (300 and 400nm) exhibited rapid capacity fade upon cycling at C/6. For the thinner flakes, agglomeration and large cracks were confirmed on the composite electrodes, but no pulverization of the flakes was observed. These data suggested that Li atoms diffused easily within the thinner Si-LPs and the uniformity of Li distribution suppressed the localized physical stress that caused by alloying and de-alloying. In addition, the addition of vinylene carbonate (VC) in the electrolyte was found to be quite effective for improving not only the cycleability, but also the rate-capability. The best performance was obtained for Si-LP (100nm), which exhibited a superior cycleability (ca. 2300mAhg−1 at C/6 after 50 cycles) and a high rate capability (ca. 1400mAhg−1 at 12C rate). ► Si thin flakes of different thicknesses as anodes for lithium ion batteries. ► Thin Si flakes (≤200nm) showed high reversible capacity (2200–2500mAh g–1). ► The thin Si flakes showed good capacity retention as well. ► Vinylene carbonate addition improved both cycleability and rate-capability.