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Abstract
The shuttle effect hinders the practical application of lithium-sulfur (Li-S) batteries due to the poor affinity between a substrate and Li polysulfides (LiPSs) and the sluggish transition of soluble LiPSs to insoluble Li2S or elemental S. Here, we report that Ni hexatomic clusters embedded in a nitrogen-doped three-dimensional (3D) graphene framework (Ni-N/G) possess stronger interaction with soluble polysulfides than that with insoluble polysulfides. The synthetic electrocatalyst deployed in the sulfur cathode plays a multifunctional role: (i) selectively adsorbing the polysulfides dissolved in the electrolyte, (ii) expediting the sluggish liquid-solid phase transformations at the active sites as electrocatalysts, and (iii) accelerating the kinetics of the electrochemical reaction of multielectron sulfur, thereby inhibiting the dissolution of LiPSs. The constructed S@Ni-N/G cathode delivers an areal capacity of 9.43 mAh cm−2 at 0.1 C at S loading of 6.8 mg cm−2, and it exhibits a gravimetric capacity of 1104 mAh g−1 with a capacity fading rate of 0.045% per cycle over 50 cycles at 0.2 C at S loading of 2.0 mg cm−2. This work opens a rational approach to achieve the selective adsorption and expediting of polysulfide transition for the performance enhancement of Li-S batteries.
Highlights
In imminent pursuit of next-generation electrical energy storage (EES) technologies, lithium-sulfur (Li-S) batteries have attracted enormous research interests due to the high sulfurspecific capacity of 1675 mAh g-1 and the earth-abundant sulfur sources [1,2,3,4]
The synthesis procedure of nitrogen-doped three-dimensional (3D) graphene framework (Ni-N/G) is schematically illustrated in Figure 1(a) [18,19,20]
Since the Ni-N/G and N/G cells have identical test conditions, their overpotential difference is mainly attributed to the existence of Ni6 catalytic sites. These results demonstrate that the Ni-N/G structure can significantly improve the utilization of sulfur species, accelerate electrocatalytic effect, and enhance Li polysulfides (LiPSs) redox kinetics
Summary
In imminent pursuit of next-generation electrical energy storage (EES) technologies, lithium-sulfur (Li-S) batteries have attracted enormous research interests due to the high sulfurspecific capacity of 1675 mAh g-1 and the earth-abundant sulfur sources [1,2,3,4]. One common countermeasure to address the shuttling effects is to adsorb Li polysulfides (LiPSs) through the porous carbon hosts [6], binder [7], and membrane [8, 9]. Another recently emerging alternative is the use of electrocatalysts in the cathode to accelerate the conversion of soluble LiPSs to insoluble end products (sulfur in the charge reaction and Li2S in the discharge reaction), thereby reducing the polysulfide presence in the electrolyte [10,11,12]. An excellent electrocatalyst in the sulfur cathode must have strong interaction with LiPSs, together with good electronic conductivity and electrochemical stability simultaneously.
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