Shuzhang Niu

A carbon sandwich electrode with graphene filling coated by N-doped porous carbon layers for lithium–sulfur batteries

A sheet-like carbon sandwich, which contains a graphene layer as the conductive filling with N-doped porous carbon layers uniformly coated on both sides, is designed as a novel sulfur reservoir for lithium–sulfur batteries and experimentally obtained by a hydrothermal process of a mixture of graphene oxide, glucose and pyrrole, followed by KOH activation. In the hydrothermal process, graphene oxide is both employed as the precursor for the central graphene filling and a sheet-like template for both-side formation of N-doped porous carbon layers, resulting in an N-doped carbon sandwich structure (N-CS). This carbon sandwich is about 50–70 nm in thickness and has a high specific surface area (∼2677 m2 g−1) and a large pore volume (∼1.8 cm3 g−1), making it a promising high capacity reservoir for sulfur and polysulfide in a lithium–sulfur cell. The sheet-like morphology and the interconnected pore structure of the N-CS, together with a nitrogen content of 2.2%, are transformed to the assembled N-CS/sulfur cell with a high rate performance and excellent cycling stability because of fast ion diffusion and electron transfer. At a 2C rate, the reversible capacity is up to 625 mA h g−1 and remains at 461 mA h g−1 after 200 cycles with only 0.13% capacity fading per cycle. More interestingly, the sheet-like structure helps the N-CS materials form a tightly stacked coating on an electrode sheet, guaranteeing a volumetric capacity as high as 350 mA h cm−3.

Dual-functional hard template directed one-step formation of a hierarchical porous carbon–carbon nanotube hybrid for lithium–sulfur batteries

A novel hierarchical porous carbon-carbon nanotube hybrid (HPCC) is prepared using a one-step strategy that uses nickel nanoparticles as the template for pore formation and at the same time, as the catalyst for carbon nanotube (CNT) growth. Such a structure can not only store sulfur in the micro- and mesopores, which restrict the shuttling of polysulfides, but also ensure good electrical conductivity of the whole system due to the incorporation of CNTs. The hierarchical porous structure also ensures fast mass transportation. These factors effectively guarantee the high electrochemical performance of sulfur stored in this carbon in lithium-sulfur batteries.

A Carbon-Sulfur Hybrid with Pomegranate-like Structure for Lithium-Sulfur Batteries.

A carbon-sulfur hybrid with pomegranate-like core-shell structure, which demonstrates a high rate performance and relatively high cyclic stability, is obtained through carbonization of a carbon precursor in the presence of a sulfur precursor (FeS2 ) and a following oxidation of FeS2 to sulfur by HNO3 . Such a structure effectively protects the sulfur and leaves enough buffer space after Fe(3+) removal and, at the same time, has an interconnected conductive network. The capacity of the obtained hybrid is 450 mA h g(-1) under the current density of 5 C. This work provides a simple strategy to design and prepare various high-performance carbon-sulfur hybrids for lithium-sulfur batteries.

Preparation and electrochemical performance of a graphene-wrapped carbon/sulphur composite cathode

Abstract Graphene is used as a barrier film to suppress the “shuttle effect” and to improve the performance of activated carbon-sulphur hybrid cathode materials in a lithium-sulphur battery by forming a core-shell structure. Graphene wraps around the activated carbon-sulphur hybrid to form a core-shell structure, in which the porous carbon framework stores most of the sulphur and the graphene layer suppresses the movement of the soluble polysulfide in the electrolyte during charge-discharge, resulting in an improvement of capacity and cyclic stability during long-term cycling. Such a core-shell structure is formed by changing the hydrophilicity of graphene oxide during reduction, in which the hydrophobic graphene closely wraps around the hydrophobic carbon surface.

A Dual-Function Na2SO4 Template Directed Formation of Cathode Materials with a High Content of Sulfur Nanodots for Lithium–Sulfur Batteries

The sulfur content in carbon-sulfur hybrid using the melt-diffusion method is normally lower than 70 wt%, which greatly decreases the energy density of the cathode in lithium-sulfur (Li-S) batteries. Here, a scalable method inspired by the commercialized production of Na2 S is used to prepare a hierarchical porous carbon-sulfur hybrid (denoted HPC-S) with high sulfur content (≈85 wt%). The HPC-S is characterized by the structure of sulfur nanodots naturally embedded in a 3D carbon network. The strategy uses Na2 SO4 as the starting material, which serves not only as the sulfur precursor but also as a salt template for the formation of the 3D carbon network. The HPC-S cathode with such a high sulfur content shows excellent rate performance and cycling stability in Li-S batteries because of the sulfur nanoparticles, the unique carbon framework, and the strong interaction between them. The production method can also be readily scaled up and used in practical Li-S battery applications.

A one-step hard-templating method for the preparation of a hierarchical microporous-mesoporous carbon for lithium-sulfur batteries

Abstract Porous carbon materials can increase the conductivity of sulfur and restrain the shuttling of polysulfides in the electrolyte. A hierarchical microporous-mesoporous carbon (HMMC) with a large surface area and pore volume was prepared by the simple one-step carbonization of a mixture of magnesium gluconate (MG) and phenolic resin. The MG was transformed into nanosize magnesium oxide that acted as a hard template during carbonization to create mesopores. The HMMC has a high surface area (∼1 560 m2 g−1) and large pore volume (∼2.6 cm3 g−1), which provides abundant space for sulfur loading and accommodates volume changes during charge/discharge. The interconnected pore structure and carbon framework ensure fast electron and Li ion transfer. As the cathode of a Li-S battery the sulfur-loaded HMMC has a high discharge capacity of 939 mAh g−1 at 0.3 C and a reversible capacity of 731 mAh g−1 after 150 cycles with only a 0.15% capacity fade per cycle. Even at a high rate of 2 C, it still delivers a high discharge capacity of 626 mAh g−1, showing an excellent rate performance.

A Nacre-Like Carbon Nanotube Sheet for High Performance Li-Polysulfide Batteries with High Sulfur Loading

Abstract Lithium‐sulfur (Li‐S) batteries are considered as one of the most promising energy storage systems for next‐generation electric vehicles because of their high‐energy density. However, the poor cyclic stability, especially at a high sulfur loading, is the major obstacles retarding their practical use. Inspired by the nacre structure of an abalone, a similar configuration consisting of layered carbon nanotube (CNT) matrix and compactly embedded sulfur is designed as the cathode for Li‐S batteries, which are realized by a well‐designed unidirectional freeze‐drying approach. The compact and lamellar configuration with closely contacted neighboring CNT layers and the strong interaction between the highly conductive network and polysulfides have realized a high sulfur loading with significantly restrained polysulfide shuttling, resulting in a superior cyclic stability and an excellent rate performance for the produced Li‐S batteries. Typically, with a sulfur loading of 5 mg cm−2, the assembled batteries demonstrate discharge capacities of 1236 mAh g−1 at 0.1 C, 498 mAh g−1 at 2 C and moreover, when the sulfur loading is further increased to 10 mg cm−2 coupling with a carbon‐coated separator, a superhigh areal capacity of 11.0 mAh cm−2 is achieved.