UW-Madison researchers disclose a scalable and sustainable redox-mediated electrochemical direct recycling method. The reaction is performed in an electrochemical flow cell consisting of a carbon paper cathode, a nickel foam anode, a membrane, catholyte, and anolyte tanks. The electrolyte is a weakly basic aqueous lithium borate buffer solution (pH = 9.2). D-LFP is loaded in the catholyte tank, which contains a homogeneous redox mediator (RM) with a more negative redox potential than D-LFP. During the reactions, RM is electrochemically reduced to RM⁻ at the cathode, which is then pumped into the catholyte tank containing D-LFP. RM⁻ reduces Fe(III) in D-LFP to Fe(II) while inserting Li⁺ ions from the electrolyte, inducing relithiation. After the reaction, RM⁻ is oxidized to RM, which circulates to the catholyte for the next reaction cycle. Meanwhile, Li⁺ ions migrate from the anolyte to the catholyte for charge balance via a cation exchange membrane. At the anode, lithium hydroxide is electrolyzed to oxygen and water by oxygen evolution reaction, producing a Li+ ion.
Consequently, this relithiation approach requires only electricity and lithium hydroxide, generating environmentally clean oxygen and water as by-products. Furthermore, after the reaction, a regenerated LFP is easily collected by filtration, and the amount of lithium hydroxide used is precisely calculated based on the charge passed.