Ultrashort and Vertically Aligned Channels: Boosted Lithium Selective Extraction via Hybrid Capacitive Deionization

Abstract

Hybrid capacitive deionization (HCDI) is energetically and operationally favorable for Li⁺ extraction from salt lake brines. The bottlenecks of current LiMn₂O₄ (LMO)-based electrodes are their limited Li⁺ adsorption rate and capacity, caused by disordered electron/ion transport channels and insufficient ion-accessible sites. Inspired by selective ion uptake processes in mangroves, we propose the strategy, fabricating ultrashort, vertically aligned channels for Li⁺ transport in the electrode to enhance the Li⁺ selective performance of HCDI. The self-supporting graphene/LMO/bacterial cellulose electrode featuring vertically aligned channels (VGLB) possesses sturdy framework, excellent electrical conductivity, fast electron/ion transport channels, and abundant available Li⁺ adsorption sites, enabling an ultrahigh Li⁺ adsorption rate of 2.6 mg g^-1 min^-1 and capacity up to 33.9 mg g^-1 with a high retention of 91.62% after 100 cycles. VGLB also manifests superior selectivity in various simulated salt lake brines with Li⁺ purity in recovered solution of over 85%. Most importantly, VGLB enables selective Li⁺ extraction in low-grade brine from Jingbian oil and gas-produced water. We conduct finite element simulations to study the Li⁺ distribution in the electrode and disclose how the electrode microstructure influences the Li⁺ extraction performance. This approach put forward an avenue for electrode structure design for efficient Li⁺ extraction from both salt lakes and low-grade brines with HCDI application.