Optimization of photovoltaic waste recycling process for highly stable nano-silicon anodes in lithium-ion batteries

Recycling Si for use as an anode material in lithium-ion batteries (LIBs) from photovoltaic (PV) waste requires nanosized Si particles. However, highly ductile metallic impurities present in PV waste tend to form aggregates during the milling process. These aggregates inhibit chemical reactions by minimizing the contact between the etchant and metallic impurities, degrading the rate and efficiency of impurity removal. Herein, we modified the sequence of wet processes during recycling to maximize the removal of metallic impurities from Si while maintaining the nanoscale structure of the Si powder. Additionally, the increased brittleness of the Si powder, which is now free of metallic impurities, allowed for further comminution into finer Si particles, improving the particle size uniformity. By using HCl and HNO3, which do not react chemically with Si, we achieved a Si recovery rate of over 99.1 %. The etching reaction time was also optimized to remove Al and Ag impurities by 98.0 % and 99.8 %, respectively. Furthermore, we investigated the effects of retained Ag impurities and Si particle size on LIB performance. Electrochemical performance characterization revealed that a Si anode containing Ag impurities originally present in PV waste has an initial specific capacity of 1918 mAh/g. Without Ag impurities, the anode made from recycled Si has an initial specific capacity of 1687 mAh/g, thus confirming the effect of Ag impurities on battery capacity. As a final enhancement, extra milling further improved Si particle uniformity, and the resulting nano-Si anodes exhibited an excellent capacity retention of over 95.5 %.