Upgrading anode graphite from retired lithium ion batteries via solid-phase exfoliation by mechanochemical strategy

Vast quantities of anode graphite from waste lithium ion batteries (LIBs), as a type of underrated urban mine, has enormous potential to be exploited for resource recovery. Herein, we propose a benign process integrating low-temperature pyrolysis and mechanochemical techniques to upcycle spent graphite (SG) from end-of-life LIBs. Pyrolysis at 500 °C leads to about 82.2 % PVDF dissociation in thermal treated graphite (TG). Solid-phase exfoliation via ball milling assisted by urea successfully produces abundant graphite flakes and a small amount of monolayer graphene nanosheet at the edge of mechanochemically processed graphite (MG). Subsequent rinsing removes the residual LiF salts. High purity and unique edge structural features of the as-prepared MG offer more active sites and storage reservoir for intercalation and de-intercalation of lithium ions, resulting in enhanced lithium-ion diffusion kinetics, excellent reversible specific capacity and desirable rate capability. Inspiringly, MG exhibits a remarkably enhanced initial specific charge capacity of 521.3 mAh g-1 during the first charge-discharge, and only declines from 569.9 mAh g-1 to 538 mAh g-1 with slight attenuation after 50 consecutive cycles at 0.1 A/g, indicating satisfactory cycle stability. Additionally, the purification and reconstruction mechanism for MG have been illustrated in detail. This study offers a green strategy to reconstruct and upgrade anode graphite from LIBs, which can realize sustainable waste management.

Strengthened Fenton degradation of phenol catalyzed by core/shell Fe-Pd@C nanocomposites derived from mechanochemically synthesized Fe-Metal organic frameworks

We have prepared core/shell structured hollow Fe-Pd@C nanomaterials derived from Fe-metal organic frameworks which were synthesized via cheap, fast and simple mechanochemical technique. The obtained Fe-Pd@C can steadily and continuously release Fe²⁺ from the galvanic corrosion of Fe⁰ anode to trigger H₂O₂ decomposition into hydroxyl radicals and cause fast (10 min) and efficient (mineralization rate 95%) degradation of phenol. The presence of low level of Pd NPs in Fe-Pd@C (mass ratio of the raw material: Fe/Pd = 100:1) facilitated fast Fe³⁺/Fe²⁺ redox cycle and thus improved the catalytic performance and pH endurance of the Fe-Pd@C. After recycled four times, Fe-Pd@C remained high catalytic performance and released low level of iron ions (2.5 mg L^-1), which reduced the production of iron sludge after usage. In contrast to zero-valent iron (ZVI) and commercial physically mixed Fe/C materials, the core/shell structure of Fe-Pd@C ensured efficient electron transferring from Fe⁰ to carbon cathode and targets, and prevented the precipitation of iron ions on Fe⁰ surface, avoiding the deactivation of Fe⁰ and termination of Fe-C internal micro-electrolysis (IME) and extending their service life. The reactive species quenching experiments and ESR characterization proved the synergistic effect of electrons and hydroxyl free radicals on degradation of phenol. The carbon-centered DMPO radical detected in reaction solution can be regarded as a proof for the strengthened oxidation ability of the combined IME and Fenton reaction.