Practical 2-step milling process for sustainable lithium-ion battery anodes from photovoltaic module recycling

Abstract

Generally, economical recycling processes based on physical methods for recycling of photovoltaic (PV) modules include crushing or milling steps, accompanied by impurity contamination during the silicon (Si) recovery process of PV modules. Previous studies have deal with the contamination of metals, which can be treated relatively easily during further etching steps. However, the contamination of titanium dioxide (TiO2) from the backsheet during the separation of modules has not been considered. In particular, subsequent chemical treatments is hard to remove the TiO2 nanoparticles. This study presents a 2-step milling process including dry and wet sequences to control both the contamination and size of recovered Si (ReSi) powders directly recycled from PV modules. The proposed method achieved a tenfold reduction in TiO2 concentration in ReSi, attained through the different sedimentation rates exhibited by Si and TiO2 particles in the solvent during wet process. Moreover, the current methodology seamlessly establishes dry and wet milling conditions for minimizing the size of the ReSi powder by optimizing the ratio of milling media and milling time. The ReSi powders, of various particle sizes, were evaluated as anode materials for lithium-ion battery. In addition, the cycling performance and volume change of micro- and nano-sized ReSi were compared to validate the effect of 2-step milling. Nano-sized ReSi exhibited a 35.33% improvement in lithium-ion battery retention compared to micro-sized ReSi, along with a 57.67% decrease in volume expansion rate.