Intern in “upgrading vivianite recovered from sewage sludge as precursor of lifepo4 li-ion battery cathode material”

Background:

Vivianite (Fe₃(PO₄)₂∙8H₂O), a blue mineral, is the main FeP form in digested sludge when enough Fe is dosed. Vivimag™, a magnetic separation technology to selectively recover vivianite from sewage sludge, has been proven in multiple pilots. The key remaining challenge is to identify outlet for the recovered vivianite. LiFePO₄ (LFP), Li-ion battery cathode material, represent a high-value outlets for recovered vivianite, providing an early economic incentive and a practical market destination that can help ViviMag™ technology to enter the market and stimulate more waterboards to recover this mineral. Vivianite is considered as a potential precursor for LFP because it contains both iron and phosphate, with an Fe : P molar ratio of 1.5. By adding an appropriate Li source, the overall stoichiometry can be adjusted to the required Li : Fe : P=1:1:1 for LFP synthesis. Compared to other cathodes, LFP is promising material because of its high theoretical capacity (170 mAh g^-1), absence of critical metals, and the phosphate’s capacity to stabilize the structure, providing a higher tolerance to heat. Importantly, this pathway is motivated not only by the sustainability of LFP, but also by the opportunity to valorize recovered P and reduce the dependance on mined phosphate rock.

Project description:

Recovered vivianite from sewage sludge often contains impurities, including residual organic matter and divalent cation substitutions at Fe sites. Whether such impurities are beneficial or not for LFP synthesis remains unknown. Hence, these impurities may influence the way we can directly valorize vivianite.

Organic matter: In LiFePO4/C synthesis, carbon is typically added intentionally to improve electronic conductivity and enable carbon coating formation. Organic matter residues in vivianite concentrate may play such a role as a carbon source.

Heavy metal impurities: divalent ion substitution is a widely used strategy to improve the electrochemical performance of LiFePO4. Thus, such metal impurities may play a beneficial role.

This project aims to:

• Investigate the effects of organic matter on LFP synthesis, structure and electrochemical performance
• Investigate the effects of heavy metal impurity on LFP structure and electrochemical performance.