Cost-effective and efficient lithium extraction technology is vital to foster the growth of lithium industry. This paper proposed a novel approach for the high value utilization of spent LiFePO₄ (S-LiFePO₄) in the field of lithium extraction from salt lakes was proposed using spent LiFePO₄ (S-LiFePO₄) as raw material. The anode, made from spent LiFePO₄, is prepared via a sintering process, while FePO₄, obtained through chemical oxidation, is used as the cathode. Compared with commercial LiFePO₄, this system not only reduces the cost but also greatly shortens the preparation time of FePO₄ (only about 10min is required). And the electrochemical extraction system had a favorable lithium extraction capacity (29.25 mg/g) from actual brine, reducing the Mg/Li ratio from 61.4 to 0.8. This study not only achieved the low-cost preparation of electrode materials and facilitated the large-scale implementation of this process, but also proposed a high-value comprehensive utilization strategy for lithium-ion batteries recycling.

Thick electrodes greatly enhance lithium extraction capacity. However, with the increase of active substances loading, the traditional thick electrodes are more hydrophobic, severely limiting the utilization of active substances. Hence, a sulfonation process to functionalize thick electrodes was applied to enhance their wettability (~45 mg·cm⁻¹) in brine. Experimental and theoretical results show that the lithium extraction capacity of thick electrodes can be significantly improved by enhancing the electrodes hydrophilicity. At 0.8 V, the S-PVDF electrode's capacity for lithium extraction in simulated brine (41.72 mg·g⁻¹) significantly surpassed the PVDF electrode (35.72 mg·g⁻¹), and it also performed well in actual brine (28.8 mg·g⁻¹). The Mg²⁺/Li⁺ ratio in actual brine dropped from 65 to 0.37, achieving effective magnesia‑lithium separation. This method offers a novel approach to developing high-efficiency lithium extraction thick electrodes.

In response to the problems of large interfacial diffusion resistance and low lithium extraction efficiency in traditional high-loading film electrodes during lithium extraction from salt lakes by the electrochemical de-intercalation method, this paper presents an interfacial engineering strategy based on the carboxymethyl cellulose lithium (CMC[sbnd]Li) binder. By modulating the structure of the inner Helmholtz plane (IHP) of the electrical double layer and enlarging the effective specific surface area, the migration rate of Li⁺ and the lithium extraction efficiency are remarkably enhanced. In this study, a CMC-Li composite electrode sheet was prepared using Spent LiFePO₄ as the raw material. It was demonstrated that the carboxyl (-COOH) and hydroxyl (-OH) functional groups of CMC-Li can be directionally adsorbed on the electrode surface. This adsorption event reconstructs the IHP-layer structure, reduces the solvation energy barrier of Li⁺, and increases the effective specific surface area of the film electrode. As a result, the contact angle decreased from 130.01° to 55.17°. Furthermore, in the CMC-Li system, the lithium extraction rate in simulated brine increased from 0.33 mg·g⁻¹·min⁻¹ to 0.69 mg·g⁻¹·min⁻¹, while the energy consumption decreased by a factor of 3. In the West Taijinar brine, the lithium extraction capacity reached 23.01 mg·g⁻¹ with a concurrent dramatic reduction in the Mg/Li ratio from 141 to 0.42. These results indicate that the CMC-Li system exhibits excellent lithium extraction performance and high selectivity. Overall, this study proposes a groundbreaking interfacial design concept that achieves both high efficiency and sustainability for lithium extraction from salt lake brines.