Controlling Electrodeposition in Nonplanar High Areal Capacity Battery Anodes via Charge Transport and Chemical Modulation.

Controlling the morphological evolution of electrochemical crystal growth in battery anodes is of fundamental and practical importance, particularly towards realizing practical, high-energy batteries based on metal electrodes. Such batteries require highly reversible plating/stripping reactions at the anode to achieve a long cycle life. While conformal electrodeposition and electrode reversibility have been demonstrated in numerous proof-of-concept experiments featuring moderate to low areal capacity (≤3 mA h/cm 2 ) electrodes, achieving high levels of reversibility is progressively challenging at the higher capacities (e.g., 10 mA h/cm 2 ), required in applications. Nonplanar, "3D" electrodes composed of electrically conductive, porous substrates are conventionally thought to overcome trade-offs between reversibility and capacity because they hypothetically "host" the electrodeposits in an electronically conducting framework, providing redundant pathways for electron flow. Here, we challenge this hypothesis and instead show that a nonplanar substrate with moderate electrical conductivity (ideally, with an electrical conductance similar to the ionic conductance of the electrolyte) and composed of a passivated cathode-facing surface efficiently regulates electro-crystallization. In contrast, an architecture with a high intrinsic electrical conductivity or with a high electrical conductivity coating on the front surface results in dominantly out-of-plane growth, making the 3D architecture in effect function as a 2D substrate. Using Zn as an example, we demonstrate that interconnected carbon fiber substrates coated by SiO 2 on the front and Cu on the back successfully ushers electroplated Zn metal into the 3D framework at a macroscopic length scale, maximizing use of the interior space of the framework. The effective integration of electrodeposits into the 3D framework also enables unprecedented plating/stripping reversibility >99.5% at high current density (e.g., 10 mA/cm 2 ) and high areal capacities (e.g., 10 mA h/cm 2 ). Used in full-cell Zn||NaV 3 O 8 batteries with stringent N/P ratios of 3:1, the substrates are also shown to enhance cycle life.