Lewis Acid–Base Interactions between Polysulfides and Boehmite Enables Stable Room‐Temperature Sodium–Sulfur Batteries

Abstract

Room‐temperature sodium–sulfur (RT Na–S) batteries are among the ideal candidates for grid‐scale energy storage due to their high theoretical energy density. However, rapid dissolution of polysulfides along with extremely slow redox kinetics lead to a low practical cell capacity and inferior cycling stability, inhibiting their practical applications. Herein, an innovative design strategy is introduced for a chemical and structural synergistic immobilization of sodium‐polysulfides in the cathode structure. An aluminum oxyhydroxide (AlOOH) nanosheets decorated sulfur/carbon black nanocomposite (S@CB@AlOOH) is used as an efficient cathode material for stable RT Na–S batteries. The cathode material exhibits extremely stable cycling performance, delivering an initial specific capacity of 392 mA h g–1 and retains 378 mA h g–1 after 500 cycles at 1C. The excellent performance is attributed to the synergistic effect of the structural encapsulation as well as chemical immobilization of polysulfides, significantly suppressing their gradual dissolution into liquid electrolyte. Density functional theory (DFT) calculations reveal that through favorable Lewis acid–base interactions, AlOOH catalyzes the redox conversion of the higher‐order polysulfides (Na2Sn, 6 ≤ n ≤ 8) to the lower‐order polysulfides (Na2Sx, 1 ≤ x ≤ 2). The importance of Lewis acid–base catalysis to enhance the overall performance of these batteries is demonstrated.

Recent Advances in Emerging Non‐Lithium Metal–Sulfur Batteries: A Review

“…[88][89][90] Therefore, a more reasonable approach is to design hybrid hosts that combine highly conductive carbonaceous materials with highly polar compounds such as metals, [91][92][93][94][95] metal oxides, [96,97] metal sulfides, [98][99][100][101][102] metal carbides, [103,104] metal phosphides, [105] and metal oxyhydroxides. [106] Taking molybdenum disulfide (MoS 2 ) as a typical example; Xu et al prepared a sulfur carrier of hollow carbon spheres decorated with MoS 2 nanosheets (Figure 7a). [98] The hollow carbon spheres can serve as a reservoir for sulfur species and electrolytes, whereas the outer MoS 2 nanosheets chemically absorb the soluble sodium polysulfides.…”

Crystalline Multi‐Metallic Compounds as Host Materials in Cathode for Lithium–Sulfur Batteries

“…[114] Lewis acid-base interaction could be an alternative strategy which is introduced for a chemical and structural synergistic immobilization of polysulfides. [115][116][117] One approach that leads to an occupied lower energy level, accounts covalent interaction between the highest occupied molecular orbital of a Lewis base and lowest occupied molecular orbital of a Lewis acid. [115] This level is considered to be a combination of the highest occupied molecular orbital of the Lewis base and the lowest occupied molecular orbital of the Lewis acid which lead to an effective charge transfer from Lewis base to Lewis acid (Figure 9a).…”

“…[115][116][117] One approach that leads to an occupied lower energy level, accounts covalent interaction between the highest occupied molecular orbital of a Lewis base and lowest occupied molecular orbital of a Lewis acid. [115] This level is considered to be a combination of the highest occupied molecular orbital of the Lewis base and the lowest occupied molecular orbital of the Lewis acid which lead to an effective charge transfer from Lewis base to Lewis acid (Figure 9a). [118] Another strategy to suppress the higher order dissolution polysulfides is polar-polar interactions.…”

Generating Short‐Chain Sulfur Suitable for Efficient Sodium–Sulfur Batteries via Atomic Copper Sites on a N,O‐Codoped Carbon Composite

“…fading and low Coulombic efficiency of the batteries. [18][19][20] Different methods have been reported to overcome these issues, such as the confinement of sulfur physically by carbon hosts or chemically by covalent CS bonds. [21][22][23] Among them, one promising method is to prevent generation of sodium polysulfides by reducing the size of sulfur molecules (S 8 ring) to short-chain sulfur (S 2-4 ), which was first reported in 2012 for Li-S batteries.…”

“…[ 14–17 ] There are still a number of challenges for those Na–S batteries, such as i) insulating nature of S, which results in a low reactivity of S with Na, and ii) ease of formation of polysulfides (Na 2 S n , 4 ≤ n ≤ 8) which could dissolve into and shuttle through liquid electrolyte (“shuttle effect”), resulting in fast capacity fading and low Coulombic efficiency of the batteries. [ 18–20 ] Different methods have been reported to overcome these issues, such as the confinement of sulfur physically by carbon hosts or chemically by covalent CS bonds. [ 21–23 ] Among them, one promising method is to prevent generation of sodium polysulfides by reducing the size of sulfur molecules (S 8 ring) to short‐chain sulfur (S 2‐4 ), which was first reported in 2012 for Li–S batteries.…”