Nanoparticle Assembled Mesoporous MoO₂ Microrods Derived from Metal Organic Framework and Wrapped with Graphene as the Sulfur Host for Long‐Life Lithium–Sulfur Batteries

Abstract

several key challenges, such as 1) the poor electrical conductivity of elemental sulfur, 2) shuttle effects due to the dissolution of intermediate lithium polysulfides (LiPSs) into the electrolyte, and 3) sluggish conversion kinetics for LiPSs. [2] Several approaches, including physical confinement, [3] chemical confinement, [4] integrating sulfur into conductive matrix, [5] interlayers, [6] modified separators, [7] and functional binders, [8] have been developed. In particular, the incorporation of sulfur into conductive porous carbon materials can well ameliorate the matter of low electrical conductivity to a great extent. [9] Considering of the weak interaction between routine nonpolar carbon materials and polar polysulfides, heteroatom doping has been adopted to bind polar sulfur based on guest-host interactions. [10] Nonetheless, the contents of doping atoms are not enough to control the flood of LiPSs. In light of this, a small dosage of polar materials such as metal oxides, [11,12] sulfides, [13,14] nitrides, [15] and carbides [16] into sulfur cathodes are extensively investigated.Several polar metal oxides based sulfur hosts were investigated and found to be promising due to strong adsorption of polysulfides on polar surfaces. [12,[17][18][19][20] Nazar and co-workers, reported nonconductive mesoporous SiO 2 and TiO 2 as efficient polysulfide reservoir. [18] Nonetheless, insulating oxides impede electron transport, leading to lower sulfur utilization and rate capability. Recently Ti 4 O 7 [19,21] and GC-TiO@CHF [22] were reported with both good conductivity and polar nature. Metal-organic frameworks (MOFs) also attracts increasing research interest. [23,24] However, the conductivity of the pristine MOF materials are not good enough, [23,25] or the porosity and polarity are compromised in case of mixing with polymer and carbon materials. [26] Therefore, exploration of novel metal oxides derived from MOFs acting as sulfur hosts with conductivity, porosity, and polarity are highly desirable.Inspired by the morphology of "crispy rice" (Figure 1a), we employed nanoparticle assembled mesoporous MoO 2 microrods derived from MOFs and wrapped with rGO as the sulfur host. Different from previous nanoparticle-type cathode materials, i) the microsized rods require less polymer binder Lithium-sulfur (Li-S) batteries are highly potential for next-generation electrochemical energy storage due to their high energy density. However, low conductivity of the sulfur cathode, dissolution, and poor conversion kinetics of lithium polysulfides (LiPSs) are the key challenges. Herein crispy rice-like nanoparticle assembled mesoporous MoO 2 microrods derived from metal organic frameworks and wrapped with graphene (MoO 2 /rGO) are fabricated, exhibiting high electron and lithium ion conductivity from the inherent metallic conductivity for MoO 2 and mesoporous-structural microrod morphology, physical confinement for LiPSs through mesopores, chemical adsorption, and catalytic conversion of LiPSs by formation of thiosulfates (polyt...

Dense MoS2 Micro‐Flowers Planting on Biomass‐Derived Carbon Fiber Network for Multifunctional Sulfur Cathodes

“…The FESEM images show that the S-MoS 2 /CFs composite well maintains the original morphology (Figure 3a, b), suggesting that no extra sulfur exists outside the MoS 2 /CFs structure. However, the composites after sulfur loading by both melt diffusion method [19] ( Figure S4a) and in situ oxidation method [26] ( Figure S4b) present sever aggregates of sulfur. EDX mappings of S-MoS 2 /CFs show that sulfur is homogeneously distributed on the MoS 2 /CFs host (Figure 3c-f), indicating that sulfur has been successfully accommodated and immobilized on the surface and within the voids of MoS 2 /CFs.…”

“…To further enhance the binding with LPSs, the third category, namely, polar and conductive transition metal compounds collaborated with carbon materials, such as transitional metal oxides, [18,19] carbides, [20] nitrides, [21][22][23] sulfides [24][25][26][27] and porphyrin, [28] have emerged to chemically adsorb LPSs. Generally, most of the previously reported transition metal composites are either micro-sized or bulk materials, restricting available anchoring sites towards LPSs.…”

Recent Advances in Molybdenum-Based Materials for Lithium-Sulfur Batteries

“…At 0.5 C, the MoO 2 /C-NC/S electrode delivered 801 mAh g −1 after 200 cycles, corresponding to 73.4% retention of the initial capacity. Following this direction, Razaq et al prepared the MoO 2 /rGO host by annealing Mo-based MOF (Mo-MOF) wrapped with graphene oxide (GO) in Ar [ 62 ]. The obtained MoO 2 microrods featured crispy rice-like mesoporous structure and exhibited high electron and Li + conductivity, good confinement for LiPSs, and catalytic conversion of LiPSs to thiosulfates (polythionates).…”

Bio‐Derived Materials Achieving High Performance in Alkali Metal–Chalcogen Batteries

“…Extensive research on the hosts of chalcogen materials for ACBs has been conducted, according to which hosts could efficiently suppress PSs/PSes shuttle effects by physically trapping and accommodating volume changes of chalcogens during cycling, thus enhancing electrical conductivity. [ 18,19 ] Unlike conventional porous carbon (Super‐P, Ketjen black, and CMK‐3), porous carbon from bio‐derived materials possesses unique chemical properties that can improve the suppression of PSs/PSes shuttle effects. Various materials have been introduced as hosts for chalcogenides; these have been derived from the natural structural characteristics and chemical compositions of bio‐derived materials (detailed in Table 2 ).…”