Aim 2: Anodes

Understand the electrodeposition and stripping of metal anodes, and gain control of nucleation and growth, crystal structure, texture, and morphology across space and time.

Repeatedly depositing metal atoms onto an anode's substrate to form uniform crystal layers driven by an external electric current, and then stripping them from the substrate during discharge, presents multiple fundamental knowledge gaps and significant technical challenges to viable rechargeable aqueous battery technologies. Aim 2 is to understand these processes. The Aim 2 team also seeks to eliminate whisker-like growths on the anode surface, as they can short circuit the battery by contacting the cathode. The researchers also aim to control the texture and structure of the anode surface across space and time to ensure long life, as well as efficient depositing and stripping of the metal ions.

Rechargeable aqueous batteries based on metal anodes have been known for over a century. So far, no metal anodes that dissolve in the electrolyte have shown enough reversibility to merit commercial consideration. The fundamental challenge lies in the irreversible degradation of both structure and interfacial chemistry.

While advances in Aim 1 will widen the electrolyte stability window and minimize the thermodynamic driving force for parasitic side reactions, minimizing the surface area of the metal anodes, (e.g., iron, zinc, or manganese), is still necessary. Further, maintaining connectivity between different particles is crucial to prevent loss of active materials during dissolution. Finally, for metals with a tendency to form irregular shapes, such as zinc, random ion deposition leads to poor packing and a platelet growing vertically to the substrate also induces shorting due to punctuation of the separator.

By gaining control of the fundamental processes of metals dissolving into the electrolyte and subsequent reforming and growing as solid crystals on the anode's substrate, the Aqueous Battery Consortium researchers could lay the scientific foundation for making reversible metal anodes a reality.

Aim 2 will work closely with Aims 1 and 3 to ensure that optimization of the electrochemistry at the anode also benefits the cathode and the cell as a whole.