Electrodeposition of Cu-Based Nanofoams and Sodiophilic Metals for Highly Stable Anode-Free Sodium Batteries

Sodium-ion batteries (SIBs) represent a cost-effective and sustainable alternative to lithium-ion battery (LIBs).1 One of the main issues of SIB technology is the higher ionic radius of sodium, compared to lithium, which limits the cyclability due to unfavourable intercalation of Na+ ions into carbon-based anodes.2 Anode-free batteries represents a promising approach to improve the cyclability, changing the working principle at the anode from intercalation of Na+ ions to electrodeposition metallic sodium.3 Moreover, thanks to the anode-free configuration the energy density of the overall device can be drastically increased. To efficiently control the electrodeposition of the metallic layer of sodium, the current collector must be carefully designed. Copper nanofoams were produced by dynamic hydrogen-bubble template (DHBT) as high-surface area template for the sodium electrodeposition, as an innovative alternative to the traditionally flat electrodes. The electrodeposition of sodiophilic materials, i.e. tin and antimony, onto the nanofoam, was also investigated to control the nucleation of the metallic layer at the anode.4 Sn and Sb baths were optimized to guarantee an homogeneous distribution of the sodiophilic metal on the nanofoam. The morphology and the composition of the nanofoams was characterized and electrochemical characterization was performed in half-cell configuration, showing coulombic efficiency higher than 99% and good cyclability for 100 cycles, for both Sn and Sb compositions compared to the bare Cu. This demonstrates the feasibility of the usage of sodiophilic nanofoams as current collectors in anode-free sodium batteries. Vaalma, C., Buchholz, D., Weil, M. & Passerini, S. A cost and resource analysis of sodium-ion batteries. Nat. Rev. Mater. 2018 34 3, 1–11 (2018). Irisarri, E., Ponrouch, A. & Palacin, M. R. Review—Hard Carbon Negative Electrode Materials for Sodium-Ion Batteries. J. Electrochem. Soc. 162, A2476–A2482 (2015). Cohn, A. P. et al. Rethinking sodium-ion anodes as nucleation layers for anode-free batteries. J. Mater. Chem. A 6, 23875–23884 (2018). Seh, Z. W., Sun, J., Sun, Y. & Cui, Y. A highly reversible room-temperature sodium metal anode. ACS Cent. Sci. 1, 449–455 (2015).