Enhanced Polysulfide Conversion with Highly Conductive and Electrocatalytic Iodine‐Doped Bismuth Selenide Nanosheets in Lithium–Sulfur Batteries

Abstract

The shuttling behavior and sluggish conversion kinetics of intermediate lithium polysulfides (LiPS) represent the main obstacles to the practical application of lithium–sulfur batteries (LSBs). Herein, an innovative sulfur host is proposed, based on an iodine‐doped bismuth selenide (I‐Bi2Se3), able to solve these limitations by immobilizing the LiPS and catalytically activating the redox conversion at the cathode. The synthesis of I‐Bi2Se3 nanosheets is detailed here and their morphology, crystal structure, and composition are thoroughly. Density‐functional theory and experimental tools are used to demonstrate that I‐Bi2Se3 nanosheets are characterized by a proper composition and micro‐ and nano‐structure to facilitate Li+ diffusion and fast electron transportation, and to provide numerous surface sites with strong LiPS adsorbability and extraordinary catalytic activity. Overall, I‐Bi2Se3/S electrodes exhibit outstanding initial capacities up to 1500 mAh g−1 at 0.1 C and cycling stability over 1000 cycles, with an average capacity decay rate of only 0.012% per cycle at 1 C. Besides, at a sulfur loading of 5.2 mg cm−2, a high areal capacity of 5.70 mAh cm−2 at 0.1 C is obtained with an electrolyte/sulfur ratio of 12 µL mg−1. This work demonstrated that doping is an effective way to optimize the metal selenide catalysts in LSBs.

Mo2N Quantum Dots Decorated N‐Doped Graphene Nanosheets as Dual‐Functional Interlayer for Dendrite‐Free and Shuttle‐Free Lithium‐Sulfur Batteries

“…[ 67–69 ] Mo 2 N@NG electrode shows a much higher precipitation capacity (265.1 mA h g –1 ) and earlier current response time (449 s) than that of the pure NG cathode (95.3 mA h g –1 , 1146 s), which manifests that the Mo 2 N@NG can significantly facilitate Li 2 S nucleation and promote the rapid kinetics of LiPSs redox reaction of Li–S batteries. [ 10 ] Besides, the dissolution capacity of Mo 2 N@NG (284.2 mA h g –1 ) is much higher compared to NG (107.2 mA h g –1 ), further confirming the rapid LiPSs transformation process. The SEM images after deposition and dissolution of Li 2 S likewise substantiate the superior regulation of LiPSs by Mo 2 N@NG (Figure S28a–d, Supporting Information).…”

“…Figure S13 (Supporting Information) presents the values of diffusion coefficient for all cells, where Mo 2 N@NG/PP separator has a significantly larger diffusion rate of Li + compared to those of the other cells, manifesting the boosted LiPSs kinetics conversion during the discharge/charge processes. [10,63] The galvanostatic discharge-charge curves at 0.2 C for Li-S cells with different separators show the corresponding overpotentials denoted as ΔE, representing the voltage gap between the anodic and cathodic plateaus (Figure 4b). [59] Furthermore, the cell with Mo 2 N@NG/PP delivers the lowest polarization potential (145 mV) and the highest initial discharge capacity (1309.2 mA h g -1 ) compared to PP (870.2 mA h g -1 ) and NG (1088.9 mA h g -1 ).…”

“…As shown in Figure 4c, the phase conversion coefficient (denoted Q2/Q1) of Mo 2 N@NG (2.35) is higher than that of PP (2.06) and NG (2.02), where Q1 denotes the solid‐liquid conversion process of S 8 to Li 2 S 4 and Q2 corresponds to the liquid‐solid‐solid conversion process of Li 2 S 4 to Li 2 S 2 /Li 2 S, implying the high sulfur utilization ability and effective LiPSs conversion during the redox process. [ 10 ] Besides, the cell with Mo 2 N@NG/PP has excellent performances of 1309.2, 1175.1, 1048.2, 967.4, and 860.2 mA h g –1 for rates ranging from 0.2 to 4 C, respectively (Figure 4d). Beyond that, when the current is switched back to 0.2 C, the reversible capacity of 1284.9 mA h g –1 can still be maintained, confirming good reversibility and high stability.…”

“…Figure S13 (Supporting Information) presents the values of diffusion coefficient for all cells, where Mo 2 N@NG/PP separator has a significantly larger diffusion rate of Li + compared to those of the other cells, manifesting the boosted LiPSs kinetics conversion during the discharge/charge processes. [ 10,63 ]…”

“…Furthermore, the intractable "shuttling effect" derived from the intermediate lithium polysulfides (LiPSs) dissolved in the electrolyte also gives rise to grievous capacity degradation and low coulombic efficiency (CE). [9][10][11][12] Simultaneously, uncontrollable lithium-ion (Li + ) stripping-deposition and uneven distribution of Li + flux will lead to lithium dendrites growth and potential safety hazard, while the solid-electrolyte interface (SEI) film is formed and destructed repeatedly by the corrosion side effects of soluble LiPSs to lithium anode, which is about to cause the continuous consumption of electrolyte and lithium metal with the rapid decay of capacity. [13][14][15][16] Thus, it is highly desirable to design an advanced Li-S battery with a shuttling-inhibition cathode and dendrite-free anode configuration.…”