Li metal anode is desirable for high energy density batteries because of its high theoretical specific capacity and lowest redox potential. However, its applications have been plagued for decades due to problems such as dendritic Li growth and low Li plating/stripping Coulombic efficiency (CE). The three-dimensional propagation of Li dendrites could penetrate the separator leading to safety concerns. In addition, Li dendrites could lead to dynamic breaking and forming of the solid-electrolyte interphase layer (SEI), causing fast electrolyte consumption and rapid capacity fading.

To address the above challenges, recently studies have demonstrated the effectiveness of 3D metal current collectors in suppressing Li dendrites and stabilizing the Li metal anode [1]. It has been suggested that the positive effect is mainly due to the high surface area of the 3D structure, which lowers the local current density and suppresses Li dendrites. Also the Li electrodeposits are accommodated inside the 3D current collector and this reduces the Li volume expansion. Although these reasons likely explain the benefits of using 3D current collectors, in-depth understanding of how 3D current collectors improve the SEI layer properties is not available. Gaining such knowledge is important for understanding the fundamental mechanism and designing effective 3D current collectors to stabilize Li metal anode.

In this study, we investigated the fundamental mechanism by which a 3D porous Ni current collector improves Li metal anode stability. Using a combination of galvanostatic intermittent titration technique and scanning electron microscopy, it was found that the 3D porous Ni current collector can effectively suppress the “dead” Li formation and forms a compact and robust surface layer. This surface layer protects Li metal and Li ion transport through this layer is unimpeded over cycling. However, without the 3D porous Ni current collector, significant amount of “dead” Li is accumulated on the Li metal over cycling, which leads to mass transport limitations. X-ray photoelectron spectroscopy results further revealed the differences in the SEI layer composition on the Li metal embedded in porous 3D Ni substrate and the 2D Li metal substrate.

1. S. S. Chi, Y. Liu, W. L. Song, L. Z. Fan and Q. Zhang, Adv. Func. Mater., 27, 1700348 (2017).