Three-dimensional carbon nanotube sponge supported LiMn2O4 hybrid for electrochemical lithium extraction with high capacity and stability

Abstract

LiMn₂O₄ (LMO) has been widely studied as a green and cost-effective electrochemical active material for lithium extraction from brine. Despite its potential, LMO faces inherent challenges such as poor conductivity and low stability, which lead to high energy consumption and rapid performance decay, thereby limiting its practical application. Here, a freestanding carbon nanotube sponge (CS) supported LMO (LMO@CS) hybrid is constructed through in-situ electrochemical anodic oxidation growth and hydrothermal lithiation. The three-dimensional (3D), conductive, and hydrophilic CS substrate can efficiently disperse the LMO nanoparticles and connect them, which endows the hybrid with reduced charge transfer resistance and shortened ion diffusion pathways, as well as high separation capability and enhanced structural stability. Consequently, when serving as a lithium extraction electrode, the optimal LMO@CS hybrid exhibits a lithium capacity of up to 4.12 mmol g⁻¹ and a high capacity retention of 87.8 % over 100 cycles. By employing the LMO@CS//Ag system in synthetic brine, the separation factors of Li⁺/Na⁺, Li⁺/K⁺, and Li⁺/Mg²⁺ reach 259, 73, and 76 after 10 cycles, respectively. Furthermore, the CS substrate can be recycled through an environmentally friendly process, extending its usability even after the LMO@CS electrode deteriorates over extended use. This study highlights the effectiveness of the 3D and binder-free LMO@CS hybrid design in maximizing the performance of pristine LMO and offers a promising route for developing high-performance electrodes in electrochemical lithium extraction.