Sodium Deposition with a Controlled Location and Orientation for Dendrite‐Free Sodium Metal Batteries

Abstract

electrochemical reactivity of Na. [3] Meanwhile, Na ion (1.02 Å) has much larger radius than that of Li ion (0.76 Å), which results in the sluggish kinetics for Na transport and deposition. [1b,3d,4] With similar working principles to Li metal batteries, numerous strategies on Na metal anode stabilization emulated from the Li metal anode studies have been proposed to address the above issues, such as engineering 3D scaffold substrate, [3e,5] employing artificial solid electrolyte interphase, [3b,6] and choosing suitable electrolyte additives. [7] Recently, lithiophilic metals such as Au, that can form alloy with Li, have been introduced as heterogeneous seeds to control the Li deposition and lower Li deposition barrier. [8] Moreover, Au is coated on the bottom side of scaffold to guide Li deposition with the direction away from the separator, thus avoiding the dendrite-induced short circuits. [8a,c] Inspired by these works, herein we coat sodiophilic metals on the bottom sides (closing to battery case) of a series of 3D substrates, seeking for an optimal location and orientation of Na deposition. Similar to lithiophilic metals, the sodiophilic metals should has ability to alloy with Na, such as Sn and Au. [9] Meanwhile, according to our previous works, [4,10] the nucleation barrier of Na on Sn-based substrate is low, which benefits to guide the Na deposition and thus is selected as the source of coating layer. In this study, conductive matrix (i.e., carbon cloth and cupper foam) and insulative scaffold (i.e., polyacrylonitrile fiber (PAN) and filter paper) are investigated as a 3D substrate in order to suppress the dendrite growth by lowering the local current density. Surprisingly, we observed significantly different phenomena for Na compared to Li. When conductive matrix is used, unlike Li deposition on the Au bottom coated scaffold that takes place on the bottom Au guide layer and grows away from the separator, [8a,c] most of the Na deposits on the top side rather than the bottom side of the scaffold, let alone deposits along the direction away from the separator (Figure 1a). In contrast, when the substrate is insulative, Na deposits on the bottom Sn layer first and then tends to grow toward the separator (from bottom to top) instead of away from the separator (Figure 1b). This difference of the deposition behavior between Na and Li may be ascribed to the larger ion radius of Na that leads to sluggish kinetics for transport and deposition. [1b,3d] Na deposition with the direction from bottom to top in insulative substrate endows Na with being confined within the 3D

Interfacial Protection Engineering of Sodium Nanoparticles toward Dendrite‐Free and Long‐Life Sodium Metal Battery

“…[ 6,7 ] 2) More seriously, the formation and growth of Na dendrites during cycles easily induce the short circuit, overheating or even explosion of battery accompany with the penetration of dendrites through separator to reach the cathode. [ 8,9 ] Relative researches indicate that the emergence of Na dendrites is mainly induced by the uneven distribution of Na + ions, high local current density, and heterogeneous nucleation of Na. [ 10 − 12 ]…”

Homogeneous Na Deposition Enabling High‐Energy Na‐Metal Batteries

“…In this regard, Li et al systematically explored the difference of Na deposition behaviors between conductive and insulative scaffold with Sn coating at the bottom region. [ 149 ] The sodiophilic Sn layer can induce the Na preferential deposition on the bottom of these scaffolds. However, after the Sn layer was completely coated by Na, the following Na deposition was different in the conductive and insulative scaffold.…”

Guiding Uniform Sodium Deposition through Host Modification for Sodium Metal Batteries

“…Owing to the host‐less nature of Na, it is very difficult to confine the Na dendrite growth and volume change, and so elastic polymeric materials have been explored as hosts. Li and co‐workers [26] used an insulating scaffold i. e., polyacrylonitrile (PAN) as 3D host for Na metal. Due to the porous nature of the host, it is believed to regulate current density that may lead to curtailing dendrite growth.…”