Recycled crystalline micro-sized silicon particles modified by pyrolytic coatings using poly(ether ether ketone) precursor for stable lithium ion battery anodes

Highlights: • Crystallized micron Si particles recycled from wafer cutting waste are modified. • Si particles are coated by pyrolysis of PEEK precursors at designated temperatures. • The pyrolysis temperatures are keys in coating the Si with suitable carbon layers. • The Si particles with designated carbon coatings show enhanced cycling stability. • The originally unusable Si particles become potentially practical anode materials. - Abstract: Crystalline micro-sized Si wafer sawing chips recycled from the waste slurry are modified to be practical anode materials by designated pyrolytic coatings using Poly(ether ether ketone) (PEEK) as the precursor. Si-C composite particles are obtained at different pyrolysis temperatures (500–800 °C), covering different stages of polymer degradation in PEEK. The Si-C anodes obtained at a suitable pyrolysis temperature exhibit an initial capacity greater than 2000 mAhg⁻¹ and less than 10% of initial irreversible capacity at 0.1 C. The Si-C anode exhibits a reversible capacity of 960 mAhg⁻¹ with capacity retention of ∼90% over 50 cycles at 1 C. The designated pyrolytic coating provides a buffer layer, which serves as a conductive pathway as well as a durable surface cap to accommodate the huge volume change during lithiation and de-lithiation of Si. These originally unusable Si particles are modified into practical Si-C composites with enhanced capacity and cycling stability.