Host For Lithium-sulfur Batteries Research Articles

Lightweight, free-standing 3D interconnected carbon nanotube foam as a flexible sulfur host for high performance lithium-sulfur battery cathodes

The still hindered practical application of lithium-sulfur (Li-S) batteries with a high theoretical energy density of 2.6 kWh kg−1 can only be feasible by a simple and scaling-up fabrication of highly stable sulfur-based cathodes. Herein, a free-standing, mechanically flexible, binder-free 3D interconnected carbon nanotube ‘foam’ (CNTF) is prepared by a single-step facile method and used as a sulfur host in Li-S batteries. For the first time, such a simple method has been adopted for the preparation of free-standing CNT scaffolds for use in Li-S cells, as our method is free from the widely reported solvent-based techniques such as vacuum infiltration of CNTs to obtain free-standing forms but requires further purification and/or drying. A high-areal sulfur loading of 7.1mgScm−2, accounting to a total electrode mass of 10.9mgelectrodecm−2, with yet high electrochemical sulfur utilization of 72% is achievable by the foam-like CNT structure. Reversible areal capacities of up to 9mAhcm−2 at extremely low electrode weight (800mAhgelectrode−1) and specific capacities up to 1378mAhgS−1 are demonstrated. The interconnected porous network acts as a reservoir for trapping soluble lithium polysulfide compounds and greatly improves the sulfur reutilization. The lightweight CNT scaffold further provides enduring electrical contact with the sulfur species, resulting in excellent cycling stability and a potentially high gravimetric energy density desirable for automobiles and aerospace applications. The CNTF/sulfur composite cathode exhibits better rate performance and cycling stability than most of the recently reported CNT-based cathode materials for Li-S batteries.

A nitrogen-doped 3D hierarchical carbon/sulfur composite for advanced lithium sulfur batteries

Abstract Hybrid nanostructures containing one-dimensional (1D) carbon nanotubes (CNTs) and three-dimensional (3D) mesoporous carbon sphere have many promising applications due to their unique physical chemical properties. In this study, a novel 3D hierarchical carbon material (MCCNT) composed of mesoporous carbon sphere core and nitrogen rich CNTs shell is successfully prepared via an aerosol spray and subsequent chemical vapor deposition (CVD) processes. Owning to its well defined porous structure and favorable conductive framework, MCCNT is used as a potential sulfur host in lithium sulfur batteries through a classic melt-diffusion method. When cycled at a current density of 0.2 C (1 C = 1675 mA h g −1 ), it delivers an initial capacity as high as 1438.7 mAh g −1 . Even if the current density increase to 1 C, the specific capacity still remain up to 534.6 mAh g −1 after 300 cycles. The enhanced electrochemical performance can be attributed to the hybrid structure of MCCNT, in which, the porous core works as a host to confine sulfur and accommodate volume expansion and the external CNTs provide excellent electron and ion conductive frame work. Furthermore, the in-situ doped nitrogen on the surface of CNTs enables effective trapping of lithium polysulfides, leading to a much-improved cycling performance.

Polypyrrole/TiO2 nanotube arrays with coaxial heterogeneous structure as sulfur hosts for lithium sulfur batteries

The lithium-sulfur cell has shown great prospects for future energy conversion and storage systems due to the high theoretical specific capacity of sulfur, 1675 mAh g−1. However, it has been hindered by rapid capacity decay and low energy efficiency. In this work, polypyrrole (PPy)/TiO2 nanotubes with coaxial heterogeneous structure as the substrate of the cathode is prepared and used to improve the electrochemical performance of sulfur electrodes. TiO2 nanotubes decorated with PPy provide a highly ordered conductive framework for Li+ ion diffusion and reaction with sulfur. This architecture also is helpful for trapping the produced polysulfides, and as a result attenuates the capacity decay. Furthermore, the heat treatment temperature used in the sulfur loading process has been confirmed to have an important impact on the overall performance of the resultant cell. The as-designed S/PPy/TiO2 nanotube cathode using an elevated heating temperature shows excellent cycling stability with a high discharge capacity of 1150 mAh g−1 and average coulombic efficiency of 96% after 100 cycles.

Lotus Root-like Structured Carbon Fibers as Encapsulated Sulfur Host for Lithium Sulfur Batteries

Novel lotus root-like carbon fibers with hierarchical pores are synthesized using alginate fibers as precursor. The as-prepared carbon fibers are of high specific surface area (∼1354 m2 g− 1) and large pore volume (∼1.27 m2 g− 1). The unique structure could effectively anchor sulfur, confine polysulfides and provide sufficient space to buff sulfur volumetric expansion, which plays an important role during the electrochemical reaction of lithium sulfur batteries. Thus the lotus root-like carbon fibers/sulfur composite demonstrates a high initial capacity of 1477 mAh g− 1 at 0.1 C, excellent cycling stability (a reversible capacity of 1040.7 mAh g−1 after 100 cycles), and good rate performance.