Oxygen-Plasma-Treated Fe–N–C Catalysts with Dual Binding Sites for Enhanced Electrocatalytic Polysulfide Conversion in Lithium–Sulfur Batteries

Abstract

Enhanced polysulfide conversion kinetics is essential for realizing lithium–sulfur batteries with high energy density and rate performance and promising cyclability. The modification of the local atomic structure of MN x active sites in single-atom M–N–C catalysts was proposed to improve their electrocatalytic activity for demanding reactions by fine-tuning the interaction with reaction intermediates. Here, we demonstrate that engineering the binding geometry of lithium polysulfides (LiPSs) by introducing dual binding sites improves the LiPS conversion kinetics. We use mild oxygen plasma treatment to introduce oxygen species into the Fe–N–C catalyst. The plasma-treated Fe–N–C (pFeNG) catalyst with dual sulfiphilic (mononuclear iron) and lithiophilic (oxygen) binding sites has a lower polysulfide decomposition energy, especially for Li2S redox, which is known to be the most sluggish process. The pFeNG cathode shows significant improvement, especially at high C rates (916.3 mA h g–1 at 5C), with promising cycling performance.

Atomically Dispersed Fe–N4 and Ni–N4 Independent Sites Enable Bidirectional Sulfur Redox Electrocatalysis

“…Ni–Fe–NC electrode presents the highest current density and the smallest peak separation, followed by Fe–NC and Ni–NC in order (Figure c). This indicates that the Fe–N 4 center tends to promote the conversion of soluble intermediates. , During the liquid–solid conversion process, the potentiostatic Li 2 S deposition capacity on Fe–NC (195.31 mAh g –1 ) is higher than that on Ni–NC (147.57 mAh g –1 ), while Ni–Fe–NC exhibits the highest capacity around 217.01 mAh g –1 and the earliest nucleation time (Figure d and Figure S17a–c). Based on Faraday’s law, the average precipitation rate of Li 2 S on Ni–Fe–NC (1.57 × 10 –7 mA cm –2 s –1 ) is higher than that on Fe–NC (1.04 × 10 –7 mA cm –2 s –1 ) and Ni–NC (8.24 × 10 –8 mA cm –2 s –1 ). , After the nucleation test, Ni–Fe–NC is uniformly covered by Li 2 S without apparent aggregation (Figure S18).…”

Proton‐Induced Defect‐Rich Vanadium Oxides as Reversible Polysulfide Conversion Sites for High‐Performance Lithium Sulfur Batteries

“…These defects could serve as active sites to anchor the soluble negative polysulfides. Besides, the introduction of chemical defect would improve the conductivity and enhance the kinetic reaction process [48] …”

“…Besides, the introduction of chemical defect would improve the conductivity and enhance the kinetic reaction process. [48] In order to evaluate the electrochemical performance of the Li-S battery, the functional G@HNVO separator was first fabricated and then was used to assemble coin-type batteries with pure sulfur electrode. Herein, the optimal graphene content (mass percentage) of G@HNVO is 10 % (Figure S3).…”

CoSe2anchored vertical graphene/macroporous carbon nanofibers used as multifunctional interlayers for high-performance lithium–sulfur batteries

“…4a shows the first five CV curves of the cells with VGMFs@CoSe 2 interlayer at a scan rate of 0.1 mV s −1 within the voltage range of 1.7–2.8 V. A pair of apparent negative peaks is located at about 2.31 and 2.0 V, representing the reduction of S 8 to long-chain polysulfides (Li 2 S n , 4 ≤ n ≤ 8) and further to insoluble Li 2 S 2 /Li 2 S. Correspondingly, two oxidation peaks located at about 2.36 and 2.44 are related to the translation of polysulfides to S 8 . 50,51 After activation at the first cycle, the reduction peaks shift to higher voltages, while the reversed situation happens on oxidation peaks. In addition, the CV curves show a nearly overlapped curvilinear path, indicating the excellent reversibility and stability of the batteries.…”