Strategies for Dendrite-free Lithium and Sodium Metal Anodes

Abstract

As the public demand for electric vehicles and consumer electronics grows at an exponential rate, traditional energy storage systems like lithium-ion batteries are proving to be insufficient. A potential candidate to replace these conventional systems is the lithium metal battery. However, replacing the anode of lithium-ion batteries with lithium (Li) metal comes with its own challenges. Safety concerns and capacity loss during cycling (discharge-charge) are caused by internal dendrite formation and infinite volume change of the Li metal. In this work, two different strategies have been explored to counter these issues:

1. 3-dimensional metallic host for Li metal
2. Surface layer deposition

As the 3D metal host, a 3D porous nickel (3DPNi) substrate was used. It was fabricated in-house through a facile template-free electrodeposition process. Detailed electrochemical Li cycling tests were performed using a symmetric cell to investigate the performance of the substrate. Different aspects of the Li cycling like substrate structure and morphology, electrolyte modification (with LiNO3), kinetics of Li+ diffusion and the electrochemical impedance performance of the substrate were investigated. The 3DPNi substrate was also tested for its compatibility with sodium metal. To investigate the effect of surface layer deposits, atomic layer depositions (ALD) of Al2O3 and TiO2 were done on planar nickel substrates. Each of these were subjected to electrochemical Li cycling tests.

Our results show that the 3DPNi substrate can be effectively cycled with Li for up to 300 cycles at a capacity of 0.5 mAh⋅cm-2 and a current rate of 1 mA⋅cm-2. Increasing the capacity to 3 mAh⋅cm-2 (6 times) at the same current rate resulted in up to 60 cycles. It was also found out that this substrate could be used for sodium metal cycling. ALD on planar substrates have enabled the Li metal to be cycled for more than 300 cycles without failure, albeit at a capacity of 0.25 mAh⋅cm-2 and a current rate of 0.125 mA⋅cm-2. Hence, our study confirms that both the methods significantly improve the performance of the lithium (and sodium) metal anodes.