Abstract:

Silicon/carbon anodes have received extensive attention in the development of high-energy Li-ion batteries. However, Si's rapid capacity fading impedes their commercial application because of the huge volume change in Si upon lithiation-delithiation. In this study, multilayer graphite materials with flexible structures and nanosilicon particles were modified separately by the COOH groups in carboxymethyl cellulose (CMC) and the NH₂-groups in ethyl silicate (TEOS) to fabricate the nanosilicon/multilayer graphite composite (S/MG). In the silicon carbon anode materials prepared by traditional mechanical mixing processes, nanosilicon particles and carbon materials fail to form homogeneous composites. However, in this study, the modified nanosilicon particles were homogeneously deposited on the surface of graphite layers through electrostatic interaction. Through ball milling, a novel carbon-coated granule with a hollow structure was formed by the S/MG layers. Such micron hollow structures were confirmed via scanning electron microscopy, elemental mapping, and high-resolution tunneling electron microscopy measurements. The structural uniqueness not only includes an inner buffer space for silicon volume expansion but also an excellent conductive three-dimensional network for silicon particles. Compared to the silicon carbon material prepared from the graphite material and nanosilicon particles under the same conditions, S/MG showed a high reversible capacity of 958 mAh/g, and good cycling stability (88% of capacity retention) was achieved after 500 cycles at a 0.5 C rate through the coin half-cell test. We also evaluated S/MG from a practical perspective through the characterization of pouch full cells prepared with NCM811 as the cathode. The cells exhibited a stable cycling performance with a capacity retention of 86% over 1,000 cycles at a 1 C rate. Thus, this study provides a potential anode material for the research and development of high-energy-density LIBs.

Key words: nano silicon particles, multi-layers graphite, silicon/carbon composites, hollow structure