Simplified silicon recovery from photovoltaic waste enables high performance, sustainable lithium-ion batteries

Conventional recycling methods to separate pure silicon from photovoltaic cells rely on complete dissolution of metals like silver and aluminium and the recovery of insoluble silicon by employing multiple leaching reagents. A common approach that eschews hydrofluoric acid (HF) treatment is the double reagent approach which utilizes nitric acid (HNO₃) and potassium hydroxide (KOH) to separate the metals from silicon cell. However, the double reagent approach is unable to remove the anti-reflective coating and use of KOH leads to formation of insoluble precipitates, in turn affecting the purity of recovered silicon. Herein, we report a single reagent approach for a streamlined process for recovery of high purity silicon with unmatched recovery yield. Phosphoric acid, (H₃PO₄) identified as a reagent for this approach, directly targets the anti-reflective coating and separates the Ag and Al present on the Si wafer surfaces. This approach led to an impressive recovery rate of 98.9% with a high purity of 99.2%, as determined by X-ray fluorescence and Inductively-coupled plasma optical emission spectroscopy. Such high-purity of recovered silicon enables upcycling into anodes for lithium-ion battery, with the battery performance comparable to as-purchased silicon. Such recovered silicon lithium-ion battery anodes demonstrated a high specific capacity of 1086.6 mAh g⁻¹ (62.3% of its initial specific capacity), even after 500 cycles at a high charging rate of 1.0C while maintaining high coulombic efficiency (>99%).