Cross-linked PVDF-b-PAA composite binder enhanced LiMn2O4/C film based electrode for selective extraction of lithium from brine with a high Mg/Li ratio

A novel physically blended polyvinylidene fluoride (PVDF) and polyacrylic acid (PAA) composite binder enhanced LiMn2O4/C (carbon black) film based electrode was successfully fabricated, and applied in an electrochemically switched ion exchange (ESIX) process for selective extraction of Li+ from high Mg/Li ratio brine. The multifunctional composite binder system enabled the obtained LiMn2O4/C/PVDF-b-PAA film coated electrode to exhibit superior mechanical, hydrophilic and electrochemical properties compared with the LiMn2O4/C/ PVDF film coated electrode. Based on the density functional theory (DFT) calculations, the ion exchange interaction between H+ of -COOH groups in PAA and Li+ facilitated the transport of Li+ at the electrode interface, which enhanced lithium extraction performance of the film coated electrode. For treating the simulated brine (Mg/Li: -500), the intercalation capacity of Li+ was about 15.1 mg g+1, and the total extraction efficiency of lithium reached up to 62.8% after two electrochemical intercalation tests. Moreover, the film coated electrode displayed excellent selectivity towards Li+ ions even in pre-treated actual brine (Mg/Li: -292.2). The Mg/Li mass ratio in the recovery solution could decrease to 0.46, and the calculated Li+/Mg2+ separation coefficient reached as high as 631.08. In particular, the highly stable and scalable electroactive film could be prepared effectively, thus increasing its applicability. It is expected that such a LiMn2O4/C/PVDF-b-PAA film coated electrode could be a promising candidate for the selective extraction of Li+ from high Mg/Li mass ratio brines.

Automated summary

A novel composite binder based on physically blended PVDF and PAA was successfully fabricated to enhance LiMn2O4/C film coated electrodes. The resulting LiMn2O4/C/PVDF-b-PAA film exhibited better mechanical, hydrophilic, and electrochemical properties compared to the LiMn2O4/C/PVDF film. The ion exchange interaction between -COOH groups in PAA and Li+ facilitated the transport of Li+ at the electrode interface, leading to enhanced lithium extraction performance.