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

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.