Zr‑doped HMO lithium-ion sieves: structural stability, cycling performance, and Li+ adsorption mechanism

With the increasing popularity of electric vehicles, the demand for lithium batteries is growing. Extracting lithium from salt-lake brine is an important method for lithium separation. This study successfully synthesized high-valence Zr 4+ -doped spinel manganese oxides using a hydrothermal-calcination approach to enhance adsorption capacity and address capacity degradation issues during the cycling of manganese-based lithium-ion sieves (Mn-based LIS). The results indicate that Zr 4+ -doping reduces the particle size and increases specific surface area from 24.22 to 32.70 m 2  g −1 . The adsorption isotherm was well fitted by the Langmuir model for 2% ZrCl 4 -doped H 1.6 Mn 1.6-x Zr x O 4 (2-HMZO) indicating a monolayer chemisorption mechanism, and the theoretical maximum adsorption capacities ( q m ) of 2-HMZO at 298, 308, and 318 K were 55.13, 58.24, and 65.92 mg g −1 , respectively. The adsorption capacity of the 2-HMZO achieved 88% of its theoretical adsorption capacity. After ten cycles of adsorption and desorption, the material maintained the Mn dissolution loss of 3.77%. Meanwhile, theoretical calculations confirmed that Zr 4+ doping enhances structural stability and facilitates easier Li + transport. Combined characterization results further confirmed that the primary Li + adsorption mechanism of 2-HMZO involves ion exchange. This research provides experimental evidence for advancing the practical application of Mn-based LIS and achieving efficient lithium extraction from salt-lake brines. Graphical abstract A spinel-type Zr-doped H 1.6 Mn 1.6 O 4 adsorbent was synthesized via hydrothermal, solid-state and ion-exchange methods, using high-valence Zr 4+ as the dopant ion. The introduction of Zr 4+ significantly enhanced the Li + adsorption capacity of HMO, and it also exhibited excellent ion selectivity in real brine samples. The primary adsorption mechanisms are ion exchange and surface electrostatic interactions. Furthermore, the adsorbent well retains its intact spinel structure even after ten consecutive adsorption-desorption cycles.