3D Graphene Network Encapsulating Mesoporous ZnS Nanospheres as High‐Performance Anode Material in Sodium‐Ion Batteries

Self-supporting network-structured MoS2/heteroatom-doped graphene as superior anode materials for sodium storage

Layered graphene and molybdenum disulfide have outstanding sodium ion storage properties that make them suitable for sodium-ion batteries (SIBs). However, the easy and large-scale preparation of graphene and molybdenum disulfide composites with structural stability and excellent performance face enormous challenges. In this study, a self-supporting network-structured MoS₂/heteroatom-doped graphene (MoS₂/NSGs-G) composite is prepared by a simple and exercisable electrochemical exfoliation followed by a hydrothermal route. In the composite, layered MoS₂ nanosheets and heteroatom-doped graphene nanosheets are intertwined with each other into self-supporting network architecture, which could hold back the aggregation of MoS₂ and graphene effectively. Moreover, the composite possesses enlarged interlayer spacing of graphene and MoS₂, which could contribute to an increase in the reaction sites and ion transport of the composite. Owing to these advantageous structural characteristics and the heteroatomic co-doping of nitrogen and sulfur, MoS₂/NSGs-G demonstrates greatly reversible sodium storage capacity. The measurements revealed that the reversible cycle capacity was 443.9 mA h g^-1 after 250 cycles at 0.5 A g^-1, and the rate capacity was 491.5, 490.5, 453.9, 418.1, 383.8, 333.1, and 294.4 mA h g^-1 at 0.1, 0.2, 0.5, 1, 2, 5 and 10 A g^-1, respectively. Furthermore, the MoS₂/NSGs-G sample displayed lower resistance, dominant pseudocapacitive contribution, and faster sodium ion interface kinetics characteristic. Therefore, this study provides an operable strategy to obtain high-performance anode materials, and MoS₂/NSGs-G with favorable structure and excellent cycle stability has great application potential for SIBs.

Revealing the Simultaneous Effects of Conductivity and Amorphous Nature of Atomic-Layer-Deposited Double-Anion-Based Zinc Oxysulfide as Superior Anodes in Na-Ion Batteries

Although sodium-ion batteries (SIBs) are considered promising alternatives to their Li counterparts, they still suffer from challenges like slow kinetics of the sodiation process, large volume change, and inferior cycling stability. On the other hand, the presence of additional reversible conversion reactions makes the metal compounds the preferred anode materials over carbon. However, conductivity and crystallinity of such materials often play the pivotal role in this regard. To address these issues, atomic layer deposited double-anion-based ternary zinc oxysulfide (ZnOS) thin films as an anode material in SIBs are reported. Electrochemical studies are carried out with different O/(O+S) ratios, including O-rich and S-rich crystalline ZnOS along with the amorphous phase. Amorphous ZnOS with the O/(O+S) ratio of ≈0.4 delivers the most stable and considerably high specific (and volumetric) capacities of 271.9 (≈1315.6 mAh cm^-3 ) and 173.1 mAh g^-1 (≈837.7 mAh cm^-3 ) at the current densities of 500 and 1000 mA g^-1 , respectively. A dominant capacitive-controlled contribution of the amorphous ZnOS anode indicates faster electrochemical reaction kinetics. An electrochemical reaction mechanism is also proposed via X-ray photoelectron spectroscopy analyses. A comparison of the cycling stability further establishes the advantage of this double-anion-based material over pristine ZnO and ZnS anodes.