Silicon has been regarded as one of the most promising anode materials for Li-ion batteries because of its higher specific capacity than carbon anodes. However, there is a fatal problem that Si undergoes massive volumetric change (about 400%) during lithiation/delithiation process. This large volume change results in the following sequential processes; pulverization, breakage of solid electrolyte interface (SEI), creation of new surface for SEI formation, continuous exhaustion of electrolyte, and finally sudden capacity fade. Among many attempts to solve these problems, the microstructure control with voids showed notable progress in improving the cycle performance. But the synthetic methods adopted so far were too complicate to apply to large scale commercial processes.

Here, we introduce a microstructure of Si-based anode materials with voids using water-soluble compounds. The role of water-soluble compounds is to create enough spaces within the anode agglomerate particles, so that they can expand without generating excessive crack on the surface during the electrochemical reaction. We synthesized active anode materials using ball-milled ferrosilicon alloy and fine water-soluble compound mixtures as starting materials. After coating with carbon precursor followed by carbonization heat treatment, they were washed with distilled water to remove the water-soluble compounds which create void structure in anode particles. The evidences of the removal of the water-soluble compounds were provided by X-ray diffraction, FIB cross-section/EDS analysis, and BET analysis. From the electrochemical cell test, significant improvement of battery performance including coulombic efficiency, irreversible capacity were observed, especially at the beginning of the cycles, compared to that of anode materials without void structure. The present study shows the simple and practical approach to realize an ideal microstructure of Si-based anode for rechargeable Li-ion batteries.