Reliable seawater battery anode: controlled sodium nucleation via deactivation of the current collector surface

Abstract

Seawater battery, which consists of a Na metal anode and a seawater cathode, has highly attractive features because of its eco-friendliness in use of seawater and cost-effectiveness in the use of Na, the 6(th) most abundant element of the Earth's crust. Herein, we demonstrate a reliable Na metal anode for the seawater battery by covering the Cu current collector with a graphene monolayer. The surface of the chemically uniform graphene-coated current collector facilitates control of the nucleation rate of surficial Na metal at the initial stage and enhances the coulombic efficiency in current collector|separator|Na metal cells by lowering the nucleation and plating potentials. Further deliberate modification of the graphene surface by using O-2 plasma and thermal treatments supports the significance of the homogeneity of the interface of the current collector. Problematically, heterogeneous Cu surfaces covered with islands of oxide layers significantly altered the surface morphology of plated Na metal and consequently resulted in the decrease in electrochemical performance due to the impeding effect on Na ion diffusion near the current collector surface. Through successful implantation of the graphene-coated Cu current collector as an anode in the seawater battery, the battery performance drastically improved, which was confirmed by monitoring the discharge/charge performance and durability of LED lighting.