Molecular‐Level Design of Pyrrhotite Electrocatalyst Decorated Hierarchical Porous Carbon Spheres as Nanoreactors for Lithium–Sulfur Batteries

Abstract

of 2600 Wh kg −1 and are recognized as one of high energy density storage devices for practical applications. In LSBs the cathode material is mainly sulfur, which is abundantly available, low cost, environmentally friendly and has high theoretical capacity of 1675 mAh g −1 . [1][2][3][4][5][6] However, the challenging issues associated with sulfur-based cathodes are: 1) the low electrical conductivity of sulfur, 2) the dissolution and shuttling effects of lithium polysulfides (LiPs), and 3) large volume variations during charge/discharge cycles. These bring about low efficiency, poor cycling stability, self-discharge phenomena, and ultimately degradation of the electrode material, all of which currently limit the potential commercialization of LSBs. These drawbacks, especially the difficulty to confine LiPs are the current research priorities in the field of LSBs. [1,7,8] To overcome these problems, a vast amount of research has been carried out in the last decade. The encapsulation of sulfur in a conductive carbon host can effectively improve the electrical conductivity of sulfur. Moreover, carbon offers a physical barrier that encapsulates the LiP intermediates. [9][10][11][12] Nevertheless, such weak physical confinement is not enough to suppress the eventual diffusion of LiPs over time. [13] Due to the polar nature of LiPs, the strategies involving functional polar substrates as Lithium-sulfur batteries (LSBs) are a class of new-generation rechargeable high-energy-density batteries. However, the persisting issue of lithium polysulfides (LiPs) dissolution and the shuttling effect that impedes the efficiency of LSBs are challenging to resolve. Herein a general synthesis of highly dispersed pyrrhotite Fe 1−x S nanoparticles embedded in hierarchically porous nitrogen-doped carbon spheres (Fe 1−x S-NC) is proposed.Fe 1−x S-NC has a high specific surface area (627 m 2 g −1 ), large pore volume (0.41 cm 3 g −1 ), and enhanced adsorption and electrocatalytic transition toward LiPs. Furthermore, in situ generated large mesoporous pores within carbon spheres can accommodate high sulfur loading of up to 75%, and sustain volume variations during charge/discharge cycles as well as improve ionic/mass transfer. The exceptional adsorption properties of Fe 1−x S-NC for LiPs are predicted theoretically and confirmed experimentally. Subsequently, the electrocatalytic activity of Fe 1−x S-NC is thoroughly verified. The results confirm Fe 1−x S-NC is a highly efficient nanoreactor for sulfur loading. Consequently, the Fe 1−x S-NC nano reactor performs extremely well as a cathodic material for LSBs, exhibiting a high initial capacity of 1070 mAh g −1 with nearly no capacity loss after 200 cycles at 0.5 C. Furthermore, the resulting LSBs display remarkably enhanced rate capability and cyclability even at a high sulfur loading of 8.14 mg cm −2 .

Confine sulfur in double-hollow carbon sphere integrated with carbon nanotubes for advanced lithium–sulfur batteries

“…Two prominent cathodic peaks at 2.30 and 2.02 V could be attributed to the reduction of sulfur to higher-order soluble lithium polysulfides (Li 2 S n , 4 ≤ n ≤ 8) and ultimately to insoluble Li 2 S/Li 2 S 2 , respectively. In the succeeding anodic scan, only one peak at about 2.46 V is observed, as a result of the oxidation of Li 2 S to lithium polysulfides [16,27,28]. During the first four cycles, there are no significant changes for both anodic and cathodic peaks, confirming the high reversibility and electrochemical stability of the cathode.…”

“…Besides, owing to their tendency to adsorb soluble polysulfides, polar metal oxide (MnO 2 ) [13], metal WS 2 -WO 3 heterostructure [14], and metal sulfide (MoS 2 ) [15] also have been developed as sulfur hosts. However, the polar inorganic metallic compounds possess poor electrical conductivity, leading to limit the electron transport and diminish the electrochemical performance of the batteries [16]. In these aspects, it is still very important to design carbon-based electrodes which can provide adequate space for the storage of the active materials and soluble polysulfides, leading to fast electron transport and oxidation-reduction reaction.…”

Low-temperature Liquid Exfoliation of Milligram-scale Single Crystalline Few-layer β12-Borophene Sheets as Efficient Electrocatalysts for Lithium–Sulfur Batteries

“…In addition, the simulated interfacial impedance of the Li-S cells sharply decreased from 41.2 Ω to 24.9 Ω when the electrodes changed from CNT to CNT/B (Fig. 3f), re ecting the β 12borophene was more favorable for the interface electrochemical reactions 8 .…”

“…The rapid development of electrochemical energy storage devices in the elds of electric vehicles, portable electronic devices and large-scale smart power grids continuously drive the researchers to explore lower cost, higher energy density, and better safety batteries than current lithium-ion batteries [1][2][3][4] . Among many candidates, lithium sulfur (Li-S) batteries have been gaining the global attention due to their overwhelming energy density (2600 Wh kg -1 ), natural abundance and environment-friendly of sulfur feedstock [5][6][7][8][9] . However, the existence of internal polysul de shuttling, large volume expansion of sulfur and sluggish redox kinetics inevitably lead to the sharp deterioration of the electrochemical performances of Li-S batteries [10][11][12] .…”

Polydopamine-Derived Carbon: What a Critical Role for Lithium Storage?

“…The Li-ion reaction behavior of the three electrodes was tested via cyclic voltammograms (CVs), as exhibited in Figure 3A and Supplementary Figure S7. The 0.9-V peaks can correspond to the decomposition of the electrolyte followed by the formation of a solid electrolyte interface (SEI) layer (Cui et al, 2019;Xu et al, 2019;Boyjoo et al, 2020). The 0.01-V cathodic peak is ascribed to the intercalation and deintercalation of Li ions into graphene-like planes Ould Ely et al, 2019;Rao et al, 2020).…”