LiMn₂O₄ (LMO) has emerged as a promising electrode material for the electrochemical extraction of lithium from salt lakes due to its excellent lithium-ion selectivity and structural stability. However, the cyclic use of LMO in Salt Lake brines is often hindered by manganese dissolution and crystal structure collapse, primarily caused by the Jahn-Teller effect. These issues significantly reduce the cycling stability and lithium extraction efficiency of LMO, limiting its practical application. To address this challenge, we developed a molten salt-assisted gradient doping-coating synergistic modification technique aimed at effectively suppressing the Jahn-Teller effect. This approach facilitates the formation of chemically bonded MgO nanolayers on the LMO surface and incorporates Mg²⁺ into the bulk structure, thereby significantly enhancing the material's structural stability. Through a combination of density functional theory (DFT) calculations and experimental validation, the modified composite electrode exhibited superior kinetic performance, high capacity, and remarkable cycling stability. In simulated brine, it maintained a lithium adsorption capacity of 26.21 mg·g⁻¹ after 20 consecutive extraction cycles. Furthermore, in the West Taijinar old brine with a high Mg²⁺/Li⁺ ratio of 65.6, the modified electrode demonstrated a capacity retention rate of 81.8 %, approximately 34 % higher than pristine LMO, and reduced the Mg²⁺/Li⁺ ratio from 65.6 to 0.24. Furthermore, the modified electrode exhibited a manganese dissolution rate of only 0.34 %. These findings indicate that the proposed modification strategy significantly improves the cycling stability and lithium extraction performance of LMO, offering a viable pathway for its large-scale application in Salt Lake environments.