Preparation of LiFePO4 composite based on dual carbon sources of phytic acid and glucose and its performance for lithium extraction from salt lake

In this study, biomass phytic acid (PhyA) was used as phosphorus source and internal carbon source, and glucose (GC) was used as external carbon source to prepare dual carbon source LiFePO4 (GC/IC/LFP) electrode material containing intercalated carbon (IC) and coated carbon (GC). Based on the working principle of rocking chair lithium ion battery, a new electrochemical system was constructed to efficiently extract Li+ from salt lake brine with high Mg/Li ratio (53) and Na/Li ratio (416). The effects of electrolytic voltage and coexisting ions on the capacity of lithium extraction/insertion at room temperature were investigated. It was found that when the electrolytic voltage was 1.0 V, the insertion capacity of lithium in pure lithium solution could reach 43.67 mg·LiFePO4 (1 g)−1, which was 99.25 % of the theoretical capacity (44 mg). The lithium extraction capacity can reach 43.20 mg·LiFePO4 (1 g)−1, which is 98.92 % of the insertion capacity. In the simulated salt lake brine with a large number of coexisting ions, when the electrolytic voltage is 0.8 V, the lithium insertion capacity can reach 38.09 mg·LiFePO4 (1 g)−1, which is 86.57 % of the theoretical capacity, and the lithium extraction capacity can reach 35.00 mg·LiFePO4 (1 g)−1, which is 91.89 % of the insertion capacity. The system maintains high selectivity for Li+ extraction. The concentration of coexisting ions of K+, Mg2+, Na+ and Ca2+ decreased by more than 8800, 4500, 25,000 and 1200 times, respectively. The Mg/Li ratio decreased from 53 to 0.09, and the Na/Li ratio decreased from 416 to 0.10. After ten times of extraction, the electrode still has high coexisting Men+/Li+ separation performance, although the extraction performance is decreased to a certain extent.