Carbon Coating of Si Thin Flakes and Negative Electrode Properties in Lithium-Ion Batteries

Abstract

To reduce the high irreversible capacity (Qirr) of Si thin flake (Si-LP) negative electrode, carbon-coated Si-LPs were prepared using citric acid as a precursor and their charge/discharge properties were investigated as negative electrodes in lithium-ion batteries. The carbon-coated powder was homogeneously coated with a thin carbon layer (8–10 and 6–8 nm in thickness for Si-LPs heat-treated at 600 and 700°C, respectively, 14 wt% for each). The irreversible capacity Qirr was successfully reduced to about a half (ca. 1100 mAh g−1) of that of the pristine Si-LP (2336 mAh g−1), though the cycleability was slightly deteriorated. The cycleability of Si-LP@Cs was significantly improved by the addition of 10 wt% VC in the electrolyte solution. Si-LP@C(700°C) kept high discharge capacities over 2000 mAh g−1 even after 50 cycles with a reduced Qirr of ca. 1300 mAh g−1 compared with the pristine Si-LP (ca. 2450 mAh g−1).