Etude du recyclage du graphite issu de black mass de batteries Li-ion (en ce compris une introduction à la méthodologie de la recherche)

Abstract

This work focuses on the valorization of recycled graphite obtained by froth flotation (gR-MF) from end- of-life LFP/Graphite lithium-ion batteries, in collaboration with Prayon. The objective is to assess whether this recycled graphite can be reused as a negative electrode material in new lithium-ion batteries. First, two commercial reference graphites were evaluated in half-cell configuration, yielding initial coulombic efficiencies (ICE) of 88 % for flake graphite and 91 % for spherical graphite, both meeting industrial requirements. Second, gR-MF was evaluated electrochemically for the first time. The graphitic structure is preserved after recycling; however, residual impurities and a high specific surface area (>40 m2 g–1), attributed to the presence of impurities and small particles, result in a low ICE of 39 %. Washing with 6 M HCl for at least 24 h improves the ICE to 59 %, as evidenced by the attenuation of the parasitic plateau at 0.8 V vs. Li+/Li and the partial reduction of secondary XRD peaks. Process reproducibility was also confirmed. Third, several improvement strategies were explored. Centrifugation, performed to remove small particles inducing a high specific surface area, showed no significant improvement (ICE 58 %), as this treatment failed to effectively separate these particles from the graphite. Thermal treatment at 900 °C increased the ICE to 69 %, likely through elimination of impurities and/or partial reconstruction of surface graphite planes. The deposition of a secondary carbon layer via chemical vapor deposition (CVD) through ethylene cracking proved the most promising strategy, raising the ICE to 80 % and reducing the specific surface area from 42 to 18 m2 g–1. Finally, the recycled graphites exhibit cycling profiles broadly similar to those of commercial graphites. These results demonstrate that the valorization of gR-MF is achievable, pending further optimization of the purification and post-treatment steps. Keywords : recycled graphite, froth flotation, LFP batteries, initial coulombic efficiency, post-treatments, electrochemical valorization.