Mussel-inspired surface engineering for LiMn1.9Cr0.1O4@carbon cloth electrodes for high-selectivity membrane capacitive Li-extraction from old brine

Membrane capacitive Li-extraction technology (MCLiE) emerges as a highly promising technology for extracting lithium from saline brines, catering to the surging demand for lithium resources. In this study, a positively charged polymeric membrane consisting of dopamine-polyethyleneimine is adhered to the surface of LiMn_1.9Cr_0.1O₄@carbon cloth (LMC@CC/DA-PEI) via surface engineering strategy, which is then employed as a flexible electrode for Li-extraction assembled in the membrane capacitive deionization (MCDI) system. Experimental results confirm that the old brine from West Taijinar with high Li content and low Mg/Li ratio is proper for practical Li-extraction, and the initial discharge/absorption capacities of LMC@CC/DA-PEI-0.5 electrode are 105.9 mAh·g⁻¹/27.4 mg·g⁻¹. Following 200 cycles, capacity retentions of bare LMC@CC and LMC@CC/DA-PEI-0.5 are 43.40 % (13.5 mg·g⁻¹) and 59.77 % (16.4 mg·g⁻¹), respectively. Therefore, surface incorporation of DA-PEI mitigates structural degradation of LMC and stabilizes long-cycle (de)lithiation of Mn-based electrodes. Moreover, the high Li⁺ selectivity (α_Li/Mg = 156.7) is due to the spinel lattice of the LMC in combination with the electrostatic repulsion of the positively charged DA-PEI layer. Considering the strict environmental protection requirements and abundant new energy power supply in salt-lake areas, the assembled MCDI system with the DA-PEI-assisted LMC@CC electrode holds great potential for yielding enhanced Li⁺ selectivity in the lithium recovery from old brine.