Investigation of Process Conditions for PVDF Recovery from Spent Li-ion Batteries via Supercritical CO2 and Co-solvent

Licentiate thesis, 2025

The exponential growth in lithium-ion battery (LiB) demand for electric vehicles and portable electronics has escalated the need for efficient and sustainable recycling processes. Current industrial recycling strategies focus predominantly on the recovery of valuable transition metals such as Li, Co, Ni, and Mn, while neglecting the polymeric binder, poly(vinylidene fluoride) (PVDF), which constitutes a fraction of the electrode mass and represents a potential source of fluorine emissions when incinerated. This work investigates the separation and recovery of PVDF from the black mass of spent LiBs using supercritical carbon dioxide (scCO₂) with polar co-solvents such as dimethyl sulfoxide and acetone.

The study explores the effect of pressure (60 - 120 bar), temperature (30 - 90 ℃), and solvent composition on PVDF solubility and extraction efficiency. The influence of process conditions identified for PVDF extraction from a complex battery waste, so-called black mass. The results demonstrated that at X_CO2≈ 0.34 (at 80 bar, 70 ℃) a balance between CO₂ density/diffusivity and co-solvent polarity yields favorable PVDF separation. Morphological analyses (SEM/EDS) reveal increased liberation of cathode active materials from graphite at lower pressures, corroborating the thermal and compositional evidence from TGA and FTIR.

The findings highlight the potential of scCO₂-based processes as a green and tunable alternative to conventional solvent- or heat-based PVDF removal methods. By enabling controlled binder recovery without toxic emissions, this approach supports the development of a closed-loop and fluorine-responsible recycling strategy for Li-ion batteries in line with the EU Battery Regulation 2023/1542.