Xiaofei Yang

1-D oriented cross-linking hierarchical porous carbon fibers as a sulfur immobilizer for high performance lithium–sulfur batteries

One-dimensional (1D) oriented cross-linking hierarchical porous carbon fibers (CHPCF) were designed and proposed as the sulfur immobilizer for application in lithium–sulfur (Li–S) batteries. The CHPCFs exhibit a large length/diameter (L/D) ratio, a cross-linked structure and a reasonable hierarchical porous distribution, which provides “green channels” for both e− and Li+ transport. Besides, the CHPCFs possess large micro-porous surfaces to confine the polysulfide (PS) diffusion. As a result, the S/CHPCF cathodes simultaneously achieve excellent C-rate performance and cycling stability of 535 mA h g−1 at 15C (1C = 1672 mA g−1), and 0.076% capacity attenuation per cycle at 5C during 500 cycles. The structure–performance relationship of the carbon materials and Li–S batteries was studied in detail. This research work sheds light on material design for Li–S batteries with excellent C-rate performance.

Sulfur embedded in one-dimensional French fries-like hierarchical porous carbon derived from a metal–organic framework for high performance lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries suffer from poor cycling stability mainly caused by one of their own drawbacks, namely, the shuttle effect, which makes them far from conquering the marketplace. To tackle this problem, a novel French fries-like hierarchical porous carbon (FLHPC) with a one-dimensional (1D) structure was constructed by carbonizing an aluminum metal–organic framework (Al-MOF). In FLHPC, sulfur was infiltrated mainly into the micro- and mesopores, while macro-pores were used to facilitate the transportation of Li ions (Li+). On the basis of this concept, even without LiNO3 as additive, Li–S batteries not only delivered a high initial discharge capacity of nearly 1200 mA h g−1 at 0.1 C (1 C = 1672 mA h g−1) but also showed good cycling stability with a capacity retention of 68% at 0.5 C after 200 cycles. In addition, when the capacity rate (C-rate) was increased to 2 C, a high discharge capacity of 763 mA h g−1 was obtained after 20 cycles, proving their excellent C-rate performance.

Rational design of a nested pore structure sulfur host for fast Li/S batteries with a long cycle life

A nested pore structure carbon with spherical quad-modal pores was designed and used as a sulfur host material in Li/S batteries. The carbon pores were interconnected and there was an orderly distribution of 2.5, 15, 24 and 100 nm pores, giving a high pore volume of 4.15 cm3 g−1. The delicate nested pore structure allowed a uniform distribution of sulfur and rapid access of the electrolyte across the carbon, leading to an excellent C-rate performance and cycle stability. Even at 3C, the C/S composite containing 78 wt% S still delivered a maximum discharge capacity of 1228 mA h g−1 and maintained a reversible capacity of 914 mA h g−1 after 200 cycles.

Layer-by-Layer Assembled C/S Cathode with Trace Binder for Li–S Battery Application

The C/S cathode with only 0.5 wt % binder, composed with Nafion and PVP, was assembled layer-by-layer for lithium-sulfur battery (Li-S) application. It achieved excellent binding strength and battery performance compared to the cathode with 10 wt % PVDF, which is promising to further increase the practical energy density of Li-S batteries.

Sulfur impregnated in a mesoporous covalent organic framework for high performance lithium–sulfur batteries

Undesirable cycling performance has been considered as the main bottleneck that has hindered the practical application of lithium–sulfur (Li–S) batteries, which mainly results from soluble polysulfides shuttling between the anode and the cathode (so-called shuttle effect). To solve this problem effectively, a covalent organic framework (COF), Azo-COF, with a regular pore distribution of 2.6 nm was prepared as the host for sulfur. Such small mesopores can not only confine the sulfur well in the nanopores but also supply Li+ with one-dimension (1D) transmission channels. Benefiting from this concept, even without a LiNO3 additive, the Li–S battery assembly with a S/Azo-COF cathode presented a high stable capacity of 741 mA h g−1 after 100 cycles while delivering a high initial discharge capacity of nearly 1536 mA h g−1 at 0.1C (1C = 1672 mA g−1). Additionally, when the capacity rate (C-rate) was increased to 2C, a high discharge capacity of 770 mA h g−1 can be still achieved after 20 cycles, proving excellent C-rate performance.

Fabrication of a nano-Li+-channel interlayer for high performance Li–S battery application

A nano-Li+-channel interlayer was first proposed and successfully prepared for Li-S batteries, based on a totally new concept of separating the polysulfide particles via a size exclusion effect. The Li-S battery assembled with the interlayer exhibited much lower polysulfide permeability and better battery performance than that without the interlayer. This concept could help overcome the polysulfide permeating problems and shed light on the development of Li-S batteries.

Iridium incorporated into deoxygenated hierarchical graphene as a high-performance cathode for rechargeable Li–O2 batteries

A novel Li-O-2 cathode was designed with a nanocrystal iridium catalyst functionalized on the purposely deoxygenated surfaces of hierarchical graphene. Due to the synergistic effect between the ORR/OER activity and deoxygenated porous supporter, this cathode exhibited excellent battery performance, cycling 150 times with a limited capacity of 1000 mA h g(-1) at a current density of 2000 mA g(-1).

A novel facile and fast hydrothermal-assisted method to synthesize sulfur/carbon composites for high-performance lithium–sulfur batteries

Hydrothermal-assisted sulfur impregnation method was first proposed to prepare sulfur/carbon (S/C) composites for lithium–sulfur (Li–S) battery applications. Comparing with the currently existing sulfur impregnation method, this facile one-pot method is proved to be energy-saving and time-saving, to have a sulfur content that is exactly controllable and to be environment-friendly. In the hydrothermal environment, sulfur would selectively diffuse into the pores of carbon hosts due to its high mobility, homogeneous dispersibility, hydrophobicity and carbon affinity. As a result, the S/C composite obtained from hydrothermal-assisted method under a low temperature of 120 °C and a short time of 2 hours exhibits a comparable battery performance to that obtained from the traditional melting method under 155 °C for 20 hours, which reached 1239 mA h g−1 at 0.2C and 796 mA h g−1 at even 1C between 1.85–2.8 V, being rather suitable for large-scale manufacture and commercial development.

Multi-functional nanowall arrays with unrestricted Li+ transport channels and integrated conductive network for high-areal-capacity Li-S batteries

The rational design of cathode hosts with superior polysulfide (PS) confinement properties, excellent Li+/e− transport and improved cyclability is of the utmost importance for high-areal-capacity lithium–sulfur (Li–S) batteries. Herein, multi-functional nanowall arrays (MNWAs) combining the aforementioned properties are fabricated to improve the electrochemical performance of Li–S batteries with high areal sulfur loadings. The integrated conductive networks and top-down vertically aligned Li+ transport channels are beneficial to Li+/e− transport, resulting in high rate performance with a discharge capacity of 620 mA h g−1 at a high current density of 9.6 mA cm−2 for 4 mg cm−2 sulfur-loaded S/MNWA electrodes. Additionally, the strong PS shuttling suppression via the synergetic effects of physical confinement and chemical adsorption leads to Li–S batteries with a sulfur loading of 10 mg cm−2 capable of delivering a high areal capacity of 12.4 mA h cm−2 with a high capacity retention of nearly 85% for over 100 cycles. Whats more, the Li–S batteries assembled with 4 mg cm−2 sulfur-loaded S/MNWA electrodes show an ultra-low capacity decay of 0.07% per cycle over 400 cycles at 3.2 mA cm−2.