Lithium extraction from high Mg/Li ratio brine is a key technical problem in the world. Based on the principle of rocking‐chair lithium‐ion batteries, cathode material LiFePO₄ is applied to extract lithium from brine, and a novel lithium‐ion battery system of LiFePO₄ | NaCl solution | anion‐exchange membrane | brine | FePO₄ is constructed. In this method, Li⁺ is selectively absorbed from the brine by FePO₄ (Li⁺ + e + FePO₄ = LiFePO₄); meanwhile, Li⁺ is desorbed from LiFePO₄ (LiFePO₄ − e = Li⁺ + FePO₄) and enriched efficiently. To treat a raw brine solution, the Mg/Li ratio decreases from the initial 134.4 in the brine to 1.2 in the obtained anolyte and 83% lithium is extracted. For the treatment of an old brine solution, the Mg/Li ratio decreases from the initial 48.4 in the brine to 0.5 and the concentration of lithium in the anolyte is accumulated about six times (from the initial 0.51 g L⁻¹ in the brine to 3.2 g L⁻¹ in the anolyte), with the absorption capacity of about 25 mg (Li) g (LiFePO₄)⁻¹. Additionally, it displays a great perspective on the application in light of its high selectively, good cycling performance, effective lithium enrichment, environmental friendliness, low cost, and avoidance of poisonous organic reagents and harmful acid or oxidant.

The preparation of Li₂CO₃ from brine with a high mass ratio of Mg/Li is a worldwide technology problem. Membrane separation is considered as a green and efficient method. In this paper, a comprehensive Li₂CO₃ preparation process, which involves electrochemical intercalation-deintercalation, nanofiltration, reverse osmosis, evaporation, and precipitation, was constructed. Concretely, the electrochemical intercalation-deintercalation method shows excellent separation performance of lithium and magnesium, and the mass ratio of Mg/Li decreased from the initial 58.5 in the brine to 0.93 in the obtained lithium-containing anolyte. Subsequently, the purification and concentration are performed based on nanofiltration and reverse osmosis technologies, which remove mass magnesium and enrich lithium, respectively. After further evaporation and purification, industrial-grade Li₂CO₃ can be prepared directly. The direct recovery of lithium from the high Mg/Li brine to the production of Li₂CO₃ can reach 68.7%, considering that most of the solutions are cycled in the system, the total recovery of lithium will be greater than 85%. In general, this new integrated lithium extraction system provides a new perspective for preparing lithium carbonate from high Mg/Li brine.