Nickel and nickel oxide nanoparticle-embedded functional carbon nanofibers for lithium sulfur batteries.

Lithium-sulfur (Li-S) batteries are attracting tremendous attention owing to their critical advantages, such as high theoretical capacity of sulfur, cost-effectiveness, and environment-friendliness. Nevertheless, the vast commercialisation of Li-S batteries is severely hindered by sharp capacity decay upon operation and shortened cycle life because of the insulating nature of sulfur along with the solubility of intermediate redox products, lithium polysulfides (LiPSs), in electrolytes. This work proposes the use of multifunctional Ni/NiO-embedded carbon nanofibers (Ni/NiO@CNFs) synthesized by an electrospinning technique with the corresponding heat treatment as promising free-standing current collectors to enhance the kinetics of LiPS redox reactions and to provide prolonged cyclability by utilizing more efficient active materials. The electrochemical performance of the Li-S batteries with Ni/NiO@CNFs with ∼2.0 mg cm-2 sulfur loading at 0.5 and 1.0C current densities delivered initial specific capacities of 1335.1 mA h g-1 and 1190.4 mA h g-1, retrieving high-capacity retention of 77% and 70% after 100 and 200 cycles, respectively. The outcomes of this work disclose the beneficial auxiliary effect of metal and metal oxide nanoparticle embedment onto carbon nanofiber mats as being attractively suited up to achieve high-performance Li-S batteries.

Catalytic effects of Ni nanoparticles encapsulated in few-layer N-doped graphene and supported by N-doped graphitic carbon in Li-S batteries.

Although lithium-sulfur batteries possess the highest theoretical capacity and lowest cost among all known rechargeable batteries, their commercialization is still hampered by the intrinsic disadvantages of low conductivity of sulfur and polysulfide shuttle effect, which is most critical. Considerable research efforts have been dedicated to solving these difficulties for every part of Li-S batteries. Separator modification with metal electrocatalysts is a promising approach to overcome the major part of these disadvantages. This work focuses on the development of Ni nanoparticles encapsulated in a few-layer nitrogen-doped graphene supported by nitrogen-doped graphitic carbon (Ni@NGC) with different metal loadings as separator modifications. The effect of metal loading on the Li-S electrochemical reaction kinetics and performance of Li-S batteries was investigated. Controlling the Ni loading allowed for the modulation of the surface area-to-metal content ratio, which influenced the reaction kinetics and cycling performance of Li-S cells. Among the separators with different Ni loadings, the one with 9 wt% Ni exhibited the most efficient acceleration of the polysulfide redox reaction and minimized the polysulfide shuttling effect. Batteries with this separator retained 77.2% capacity after 200 cycles at 0.5C, with a high sulfur loading of ∼4.0 mg cm-2, while a bare separator showed 51.3% capacity retention after 200 cycles under the same conditions. This work reveals that there is a vast utility space for carbon-encapsulated Ni nanoparticles in electrochemical energy storage devices with optimal selection and rational design.