Optimized NiHCF/MnO2 Composite Electrodes for Selective Extraction of Lithium from Low-grade Salar Brine via Capacitive Deionization

The rapid growth of lithium (Li)-ion batteries particularly in electric vehicles (EVs) and large-scale energy storage facilities has catalyzed an ever-increasing demand for Li. Current Li mining from brines based on evaporation-precipitation is time-consuming and water-intensive. Here, we report three NiHCF/MnO2 composite electrodes based on core-shell construction strategies for Li+ extraction from brine on a rocking-chair capacitive deionization (RCDI) platform. We find that the MnO2 components varied with the composing condition from α-, δ- to λ-MnO2 and that the core-shell structured NiHCF@λ-MnO2 electrode showed the optimal ion migration rate, highest specific capacity, and the best cycling stability. Notably, we reveal that the NiHCF@λ-MnO2 electrode presented the optimum Li+ extraction performance with respect to adsorption capacity, adsorption rate, and energy consumption (e.g., achieving the highest Li+ capacity of 40.51 mg Li+ g−1 with a rate of 8.1 mg g−1 min−1, and at an energy cost of 0.86 Wh g−1 in 20 mM LiCl solution at 1.2 V). In addition, we demonstrate that the NiHCF@λ-MnO2 electrode maintained high cycling stability over 40 consecutive cycles of Li+ intercalation/deintercalation, with 78.4% capacity retention in 10 mM of LiCl solution. Importantly, the NiHCF@λ-MnO2 electrode also provided excellent Li+ selectivity in both the synthetic brine and the actual brine from the East Taijinaier salt lake, with exceptional separation factors as high as 68.7 and 21.0 for Li+ against Na+ and Mg2+ ions, respectively. Such unparalleled selectivity is believed to be attributed to the combination of structural and charge synergy of the NiHCF@λ-MnO2 composite. Our study highlights that a rational core-shell construction strategy can boost the optimal integration of NiHCF and MnO2, thus leveraging their potential to preferentially extract Li+ from brines.