A Membrane-Free Rechargeable Seawater Battery Unlocked by Lattice Engineering

Seawater batteries that directly utilize natural seawater as electrolytes are ideal sustainable aqueous devices with high safety, exceedingly low cost, and environmental friendliness. However, the present seawater batteries are either primary batteries or rechargeable half-seawater/half-nonaqueous batteries because of the lack of suitable anode working in seawater. Here, a unique lattice engineering to unlock the electrochemically inert anatase TiO₂ anode to be highly active for the reversible uptake of multiple cations (Na⁺, Mg²⁺, and Ca²⁺) in aqueous electrolytes is demonstrated. Density functional theory calculations further reveal the origin of the unprecedented charge storage behaviors, which can be attributed to the significant reduction of the cations diffusion barrier within the lattice, i.e., from 1.5 to 0.4 eV. As a result, the capacities of anatase TiO₂ with 2.4% lattice expansion are ≈100 times higher than the routine one in natural seawater, and ≈200 times higher in aqueous Na⁺ electrolyte. The finding will significantly advance aqueous seawater energy storage devices closer to practical applications.