Mohammad Rejaul Kaiser

Structure–Property Relationships of Organic Electrolytes and Their Effects on Li/S Battery Performance

Electrolytes, which are a key component in electrochemical devices, transport ions between the sulfur/carbon composite cathode and the lithium anode in lithium-sulfur batteries (LSBs). The performance of a LSB mostly depends on the electrolyte due to the dissolution of polysulfides into the electrolyte, along with the formation of a solid-electrolyte interphase. The selection of the electrolyte and its functionality during charging and discharging is intricate and involves multiple reactions and processes. The selection of the proper electrolyte, including solvents and salts, for LSBs strongly depends on its physical and chemical properties, which is heavily controlled by its molecular structure. In this review, the fundamental properties of organic electrolytes for LSBs are presented, and an attempt is made to determine the relationship between the molecular structure and the properties of common organic electrolytes, along with their effects on the LSB performance.

Reverse Microemulsion Synthesis of Sulfur/Graphene Composite for Lithium/Sulfur Batteries

Due to its high theoretical capacity, high energy density, and easy availability, the lithium-sulfur (Li-S) system is considered to be the most promising candidate for electric and hybrid electric vehicle applications. Sulfur/carbon cathode in Li-S batteries still suffers, however, from low Coulombic efficiency and poor cycle life when sulfur loading and the ratio of sulfur to carbon are high. Here, we address these challenges by fabricating a sulfur/carboxylated-graphene composite using a reverse (water-in-oil) microemulsion technique. The fabricated sulfur-graphene composite cathode, which contains only 6 wt % graphene, can dramatically improve the cycling stability as well as provide high capacity. The electrochemical performance of the sulfur-graphene composite is further enhanced after loading into a three-dimensional heteroatom-doped (boron and nitrogen) carbon-cloth current collector. Even at high sulfur loading (∼8 mg/cm2) on carbon cloth, this composite showed 1256 mAh/g discharge capacity with more than 99% capacity retention after 200 cycles.

A Facile Synthesis of High‐Surface‐Area Sulfur–Carbon Composites for Li/S Batteries

Small-grained elemental sulfur is precipitated from sodium thiosulfate (Na2 S2 O3 ) in a carbon-containing oxalic acid (HOOC-COOH) solution through a novel spray precipitation method. Surface area analysis, elemental mapping, and transmission electron micrographs revealed that the spray-precipitated sulfur particles feature 11 times higher surface area compared to conventional precipitated sulfur, with homogeneous distribution in the carbon. Moreover, the scanning electron micrographs show that these high-surface-area sulfur particles are firmly adhered to and covered by carbon. This precipitated S-C composite exhibits high discharge capacity with about 75 % capacity retention. The initial discharge capacity was further improved to 1444 mA h g(-1) by inserting a free-standing single-walled carbon nanotube layer in between the cathode and the separator. Moreover, with the help of the fixed capacity charging technique, 91.6 % capacity retention was achieved.

Ternary Porous Sulfur/Dual-Carbon Architectures for Lithium/Sulfur Batteries Obtained Continuously and on a Large Scale via an Industry-Oriented Spray-Pyrolysis/Sublimation Method

Ternary composites with porous sulfur/dual-carbon architectures have been synthesized by a single-step spray-pyrolysis/sublimation technique, which is an industry-oriented method that features continuous fabrication of products with highly developed porous structures without the need for any further treatments. A double suspension of commercial sulfur and carbon scaffolding particles was dispersed in ethanol/water solution and sprayed at 180 °C using a spray pyrolysis system. In the resultant composites, the sulfur particles were subjected to an ultrashort sublimation process, leading to the development of a highly porous surface, and were meanwhile coated with amorphous carbon, obtained through the pyrolysis of the ethanol, which acts as an adhesive interface to bind together the porous sulfur with the scaffolding carbon particles, to form a ternary composite architecture. This material has an effective conducting-carbon/sulfur-based matrix and interconnected open pores to reduce the diffusion paths of lithium ions, buffer the sulfur volumetric expansion, and absorb electrolyte and polysulfides. Because of the unique chemistry and the structure, the composites show stable cycling performance for 200 cycles and good rate capability of 520 mAh g(-1) at 2 C. This advanced spray-pyrolysis/sublimation method is easy to scale up and shows great potential for commercialization of lithium/sulfur batteries.

High performance pure sulfur honeycomb-like architectures synthesized by a cooperative self-assembly strategy for lithium-sulfur batteries

Honeycomb-like pure sulfur architectures were synthesized by a cooperative self-assembly strategy, in which a soft template is used to form the porous structure. Their electrochemical performance is significantly improved comparing with the commercial sulfur powder and the as-prepared sulfur without honeycomb morphology. There has been no report on using a soft template to prepare honeycomb-like sulfur particles.

Improvement in thermomechanical properties of injection molded nano-modified hybrid biocomposite

Biopolymers and their composites are one of the best alternatives for replacing petroleum-based plastic commodities. The main drawback of biopolymer is its high cost that restricts its applications; however, biopolymers filled with natural fibers are able to reduce cost but suffer lower impact strength and fracture toughness. Nanoclay which has a very high aspect ratio shows a significant effect on mechanical and thermal properties. This article concentrates on hybridization of nanoclay and natural fibers. Mechanical properties show that with the addition of nanoclay, impact strength increases more than 50%; however, other mechanical properties are also increased, which are proved by fractography analysis. Thermal analysis shows that hybrid biocomposite exhibits higher storage modulus, decomposition temperature and higher percentage of crystallinity. Fourier-transform infrared (FT-IR) analysis confirms formation of new bond between nanoclay and polymer matrix which is the main reason for improving thermal and mechanical properties of the hybrid biocomposite.

Dynamic Mechanical Behaviour of Poly Ethylene Glycol Plasticized Polylacticacid

Polylacticacid (PLA), produced from annually renewable, natural resources is a potential candidate for the partial replacement of petroleum based polymers and also for its biodegradability. PLA is well known for its better mechanical, thermal property but unfortunately the brittleness and rigidity limit its applicability. For a great number of applications such as packaging, fibers, films, etc., it is of high interest to formulate new PLA grades with improved flexibility and better impact properties. In order to develop PLA-based biodegradable packaging, the physico-mechanical properties of commercially available PLA should be modified using plasticizers. For this, PLA was melt-mixed with poly ethylene glycol (PEG) of 600 molecular weights by twin screw extruder. The thermal properties of plasticized PLA were characterized by utilization of dynamic mechanical analysis. The result shows that with addition of plasticizer glass transition temperature (Tg) is decreased sharply and the storage modulus was also decreased.