Effects of conductive agent type on lithium extraction from salt lake brine with LiFePO₄ electrodes

Abstract

Electrochemical lithium extraction from salt lakes is an effective strategy for obtaining lithium at a low cost. Nevertheless, the elevated Mg : Li ratio and the presence of numerous coexisting ions in salt lake brines give rise to challenges, such as prolonged lithium extraction periods, diminished lithium extraction efficiency, and considerable environmental pollution. In this work, LiFePO₄ (LFP) served as the electrode material for electrochemical lithium extraction. The conductive network in the LFP electrode was optimized by adjusting the type of conductive agent. This approach resulted in high lithium extraction efficiency and extended cycle life. When the single conductive agent of acetylene black (AB) or multiwalled carbon nanotubes (MWCNTs) was replaced with the mixed conductive agent of AB/MWCNTs, the average diffusion coefficient of Li⁺ in the electrode increased from 2.35 × 10⁻⁹ or 1.77 × 10⁻⁹ to 4.21 × 10⁻⁹ cm²·s⁻¹. At the current density of 20 mA·g⁻¹, the average lithium extraction capacity per gram of LFP electrode increased from 30.36 mg with the single conductive agent (AB) to 35.62 mg with the mixed conductive agent (AB/MWCNTs). When the mixed conductive agent was used, the capacity retention of the electrode after 30 cycles reached 82.9%, which was considerably higher than the capacity retention of 65.8% obtained when the single AB was utilized. Meanwhile, the electrode with mixed conductive agent of AB/MWCNTs provided good cycling performance. When the conductive agent content decreased or the loading capacity increased, the electrode containing the mixed conductive agent continued to show excellent electrochemical performance. Furthermore, a self-designed, highly efficient, continuous lithium extraction device was constructed. The electrode utilizing the AB/MWCNT mixed conductive agent maintained excellent adsorption capacity and cycling performance in this device. This work provides a new perspective for the electrochemical extraction of lithium using LFP electrodes.

Keywords

salt lake brine lithium extraction / electrochemical lithium extraction / conductive agent / extraction efficiency / adsorption capacity

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