Lithium–sulfur (Li–S) batteries are regarded as one of the most promising next-generation electrochemical cells. However, shuttling of lithium polysulfide intermediates and sluggish kinetics in random deposition of lithium sulfide (Li 2 S) have significantly degraded their capacity, rate and cycling performance. Herein, few-layered MoS 2 nanosheets enriched with sulfur vacancies are anchored inside hollow mesoporous carbon (MoS 2−x /HMC) via S–C bonding and proposed as a novel functional mediator for Li–S batteries. Ultrathin MoS 2 sheets with abundant sulfur vacancies have strong chemical affinity to polysulfides and in the meantime catalyze their fast redox conversion with enhanced reaction kinetics as proved by experimental observations and first-principles density functional theory (DFT) calculations. At a current density of 1C, the MoS 2−x /HMC-S composite cathode exhibits a high initial capacity of 945 mA h g −1 with a high retained capacity of 526 mA h g −1 and a coulombic efficiency of nearly 100% after 500 cycles. The present work sheds light on the design of novel functional electrodes for next-generation electrochemical cells based on a simple yet effective vacancy engineering strategy.
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Facile synthesis of hierarchical MoS 2 –carbon microspheres as a robust anode for lithium ion batteries
Molybdenum disulfide (MoS 2 ) may be a promising alternative for lithium ion batteries (LIBs) because it offers a unique layered crystal structure with a large and tunable distance between layers. This enables the anticipated excellent rate and cycling stability because they can promote the reversible lithium ion intercalation and de-intercalation without huge volume change which consequently prevents the pulverization of active materials during repeated charge and discharge processes. Herein, we prepared hierarchical MoS 2 –carbon (MoS 2 –C) microspheres via a continuous and scalable ultrasonic nebulization assisted route. The structure, composition, and electrochemical properties are investigated in detail. The MoS 2 –C microspheres consist of few-layer MoS 2 nanosheets bridged by carbon, which separates the exfoliated MoS 2 layers and prevents their aggregation and restacking, thus leading to improved kinetic, enhanced conductivity and structural integrity. The novel architecture offers additional merits such as overall large size and high packing density, which promotes their practical applications. The MoS 2 –C microspheres have been demonstrated with excellent electrochemical performances in terms of low resistance, high capacity even at large current density, stable cycling performance, etc. The electrodes exhibited 800 mA h g −1 at 1000 mA g −1 over 170 cycles. At a higher current density of 3200 mA g −1 , a capacity of 730 mA h g −1 can be also maintained. The MoS 2 –C microspheres are practically applicable not only because of the continuous and large scale synthesis via the current strategy, but also the possess a robust and integrated architecture which ensures the excellent electrochemical properties.
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- Award ID(s):
- 1301346
- NSF-PAR ID:
- 10081749
- Date Published:
- Journal Name:
- Journal of Materials Chemistry A
- Volume:
- 4
- Issue:
- 24
- ISSN:
- 2050-7488
- Page Range / eLocation ID:
- 9653 to 9660
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Transition metal dichalcogenides (TMDs) are a class of 2D materials demonstrating promising properties, such as high capacities and cycling stabilities, making them strong candidates to replace graphitic anodes in lithium-ion batteries. However, certain TMDs, for instance, MoS2, undergo a phase transformation from 2H to 1T during intercalation that can affect the mobility of the intercalating ions, the anode voltage, and the reversible capacity. In contrast, select TMDs, for instance, NbS2and VS2, resist this type of phase transformation during Li-ion intercalation. This manuscript uses density functional theory simulations to investigate the phase transformation of TMD heterostructures during Li-, Na-, and K-ion intercalation. The simulations suggest that while stacking MoS2layers with NbS2layers is unable to limit this 2H → 1T transformation in MoS2during Li-ion intercalation, the interfaces effectively stabilize the 2H phase of MoS2during Na- and K-ion intercalation. However, stacking MoS2layers with VS2is able to suppress the 2H → 1T transformation of MoS2during the intercalation of Li, Na, and K-ions. The creation of TMD heterostructures by stacking MoS2with layers of non-transforming TMDs also renders theoretical capacities and electrical conductivities that are higher than that of bulk MoS2.
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Abstract Ni‐rich LiNi0.8Co0.1Mn0.1O2(NCM811) has been considered as a promising cathode material for high energy density lithium‐ion batteries. However, it experiences undesirable interfacial side‐reactions with the electrolyte, which lead to a rapid capacity decay. In this work, a homogeneous precipitation method is proposed for forming a uniform silicon dioxide (SiO2) coating on the NCM811 surface. The strong Si−O network provided a stable protective layer between the NCM811 active material and electrolyte to improve the electrochemical stability. As a result, the NCM811@SiO2cathode showed superior cycling stability (84.9 % after 100 cycles at 0.2 C) and rate capability (142.7 mA h g−1at 5 C) compared to the pristine NCM811 cathode (56.6 % after 100 cycles, 127.9 mA h g−1at 5 C). Moreover, the SiO2coating effectively suppressed voltage decay and pulverization of the NCM811 particles during long term cycling. This uniform coating technique offers a viable approach for stabilizing Ni‐rich cathode materials for high‐energy density lithium‐ion batteries.
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This study reports the preparation of a set of hybrid materials consisting of molybdenum disulfide (MoS 2 ) nanopatches on reduced graphene oxide (rGO) nanosheets by microwave specific heating of graphene oxide and molecular molybdenum precursors followed by thermal annealing in 3% H 2 and 97% Ar. The microwave process converts graphene oxide to ordered rGO nanosheets that are sandwiched between uniform thin layers of amorphous molybdenum trisulfide (MoS 3 ). The subsequent thermal annealing converts the intermediate layers into MoS 2 nanopatches with two-dimensional layered structures whose defect density is tunable by controlling the annealing temperature at 250, 325 and 600 °C, respectively. All three MoS 2 /rGO samples and the MoS 3 /rGO intermediate after the microwave step show a high Li-ion intercalation capacity in the initial 10 cycles (over 519 mA h g MoSx −1 , ∼3.1 Li + ions per MoS 2 ) which is attributed to the small MoS 2 nanopatches in the MoS 2 /rGO hybrids while the effect of further S-rich defects is insignificant. In contrast, the Zn-ion storage properties strongly depend on the defects in the MoS 2 nanopatches. The highly defective MoS 2 /rGO hybrid prepared by annealing at 250 °C shows the highest initial Zn-ion storage capacity (∼300 mA h g MoSx −1 ) and close to 100% coulombic efficiency, which is dominated by pseudocapacitive surface reactions at the edges or defects in the MoS 2 nanopatches. The fast fading in the initial cycles can be mitigated by applying higher charge/discharge currents or extended cycles. This study validates that defect engineering is critical for improving Zn-ion storage.more » « less
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Rechargeable lithium–sulfur batteries have emerged as a viable technology for next generation electrochemical energy storage, and the sulfur cathode plays a critical role in determining the device performance. In this study, we prepared functional composites based on polypyrrole-coated MnO 2 nanotubes as a highly efficient sulfur host (sulfur mass loading 63.5%). The hollow interior of the MnO 2 nanotubes not only allowed for accommodation of volumetric changes of sulfur particles during the cycling process, but also confined the diffusion of lithium polysulfides by physical restriction and chemical adsorption, which minimized the loss of polysulfide species. In addition, the polypyrrole outer layer effectively enhanced the electrical conductivity of the cathode to facilitate ion and electron transport. The as-prepared MnO 2 -PPy-S composite delivered an initial specific capacity of 1469 mA h g −1 and maintained an extremely stable cycling performance, with a small capacity decay of merely 0.07% per cycle at 0.2C within 500 cycles, a high average coulombic efficiency of 95.7% and an excellent rate capability at 470 mA h g −1 at the current density of 3C.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C6TA03310E
