Facile Stabilization of the Sodium Metal Anode with Additives: Unexpected Key Role of Sodium Polysulfide and Adverse Effect of Sodium Nitrate

Abstract

Sodium metal is an attractive anode for next-generation energy storage systems owing to its high specific capacity, low cost, and high abundance. Nevertheless, uncontrolled Na dendrite growth caused by the formation of unstable solid electrolyte interphase (SEI) leads to poor cycling performance and severe safety concerns. Sodium polysulfide (Na S ) alone is revealed to serve as a positive additive or pre-passivation agent in ether electrolyte to improve the long-term stability and reversibility of the Na anode, while Na S -NaNO as co-additive has an adverse effect, contrary to the prior findings in the lithium anode system. A superior cycling behavior of Na anode is first demonstrated at a current density up to 10 mA cm and a capacity up to 5 mAh cm over 100 cycles. As a proof of concept, a high-capacity Na-S battery was prepared by pre-passivating the Na anode with Na S . This study gives insights into understanding the differences between Li and Na systems.

Electrolyte Additives for Room‐Temperature, Sodium‐Based, Rechargeable Batteries

“…Na 2 S 6 alone was found to improvet he electrochemical performance of the sodium-metal anode, even at ac urrent density as high as 10 mA cm À2 and ac apacity of 5mAh cm À2 over 100 cycles. [72] Unexpectedly,i nc ontrast to Li 2 S 6 ÀLiNO 3 ,w hich wasr eported to enhance the performance of the LiÀSb attery through as ynergistic effect, Na 2 S 6 ÀNaNO 3 was found to be detrimental on sodium metal. In an attempt to explain the startling effect, XPS analysisr evealed that the predominant SEI layer buildingm aterials,i fN a 2 S 6 alone was used, were of inorganic nature,e nlisting Na 2 O, Na 2 S 2 ,a nd Na 2 S. This, in turn, provided am echanicallys table SEI layer capable of suppressing sodium dendrite growth.…”

“…Inspired by the analogues use of Li 2 S n −LiNO 3 in the Li−S battery, Li and co‐workers evaluated sodium polysulfide (Na 2 S 6 ) alone and as a coadditive with sodium nitrate (NaNO 3 ) in ether‐based electrolyte. Na 2 S 6 alone was found to improve the electrochemical performance of the sodium‐metal anode, even at a current density as high as 10 mA cm −2 and a capacity of 5 mAh cm −2 over 100 cycles . Unexpectedly, in contrast to Li 2 S 6 −LiNO 3 , which was reported to enhance the performance of the Li−S battery through a synergistic effect, Na 2 S 6 −NaNO 3 was found to be detrimental on sodium metal.…”

Electrolytes and Interphases in Sodium‐Based Rechargeable Batteries: Recent Advances and Perspectives

“…Na 2 S 6 was found to boost the electrochemical performance of the Na electrode for over 100 cycles at high current density (10 mA cm −2 ) and cycled capacity (5 mAh cm −2 ). [ 290 ] However, while the combination of Li 2 S 6 and LiNO 3 is reported to enhance the performance of Li–S battery via a synergistic effect, the use of only Na 2 S 6 is preferred with Na. In fact, XPS analysis revealed that the SEI layer contains Na 2 O, Na 2 S 2 , and Na 2 O, which provide a mechanically stable SEI capable of suppressing (reducing) Na dendrite growth when only Na 2 S 6 is present ( Figure 18 a).…”

A Flexible Solid Electrolyte with Multilayer Structure for Sodium Metal Batteries

“…Similarly with lithium metal anode, Na metal batteries using conventional organic liquid electrolyte are facing some challenges, such as dendrite growth, volume changes, solid electrolyte interphase (SEI), suggesting an inferior cyclability and poor safety . Numerous efforts have been made to deal with abovementioned issues and obtain great achievements on the protection of sodium metal, such as artificial SEI, electrolyte additive, superconcentrated electrolyte, membrane modification, and 3D current collectors . Still, the inherent serious safety issues of the volatile and flammable of organic liquid electrolyte are like a sword hanging on the air.…”