Small but strong carbon nanotubes (CNTs) are fillers of choice for composite reinforcement owing to their extraordinary modulus and strength. However, the mechanical properties of the nanocomposites are still much below those for mechanical parameters of individual nanotubes. The gap between the expectation and experimental results arises not only from imperfect dispersion and poor load transfer but also from the unavailability of strong polymers that can be effectively utilized within the composites of nanotubes. Aramid nanofibers (ANFs) with analogous morphological features to nanotubes represent a potential choice to complement nanotubes given their intrinsic high mechanical performance and the dispersible nature, which enables solvent-based processing methods. In this work, we showed that composite films made from ANFs and multiwalled CNTs (MWCNTs) by vacuum-assisted flocculation and vacuum-assisted layer-by-layer assembly exhibited high ultimate strength of up to 383 MPa and Young's modulus (stiffness) of up to 35 GPa, which represent the highest values among all the reported random CNT nanocomposites. Detailed studies using different imaging and spectroscopic characterizations suggested that the multiple interfacial interactions between nanotubes and ANFs including hydrogen bonding and π-π stacking are likely the key parameters responsible for the observed mechanical improvement. Importantly, our studies further revealed the attractive thermomechanical characteristics of these nanocomposites with high thermal stability (up to 520 °C) and ultralow coefficients of thermal expansion (2-6 ppm·K(-1)). Our results indicated that ANFs are promising nanoscale building blocks for functional ultrastrong and stiff materials potentially extendable to nanocomposites based on other nanoscale fillers.

metric tons of carbon dioxide (CO 2 ) and other pollutants per year, which accelerate global warming and major climate changes. [2] In order to mitigate these serious issues caused by fossil fuels and to compete with the energy generating devices based on fossil fuels, renewable energy sources like solar energy, wind energy, bioenergy, and geothermal energy are potential alternative power resources. However, these renewable energy resources need highly efficient energy storage devices for integrating and well distribution of energy. Rechargeable battery technology with high energy, high power density, long life cycle capability, fast cycling rate, and reasonable cost is the possible solution to store energy obtained from these renewable sources. [3] Among many rechargeable energy storage devices, lithium-ion batteries (LIBs) are the promising energy sources for integrating renewable resources and high power applications, owing to high energy density, lightweight, high flexibility, slow self-discharge rate, high rate charging capability, long battery life, and environmental benignity. [4,5] The aforementioned attractive properties of rechargeable LIBs promote its utilization in the wide range of applications like laptops, cell phones, electric vehicle, hybrid electric vehicles, renewable power stations, stationary electric power, defense arsenal, subsurface exploration, thermal reactors, and space vehicles. [6][7][8][9] From the last 30 years, rapid development has been observed in LIBs technology. Presently, LIBs hold twofold energy density as compared to the first commercial LIBs developed by Sony in 1991, but still, there are some challenges associated with LIBs that need to be solved for achieving high power density and efficient performances at high and low temperatures. Safety, cost, and enhancement in energy and power densities are the major concerns in next generation LIBs. [10][11][12] Separator is one of the important components of LIBs that is not directly involved in the electrochemical reaction, however, its properties, structure, and composition greatly influence the performance of batteries with respect to internal resistance, long cycle performances, high capacity, and safety. [13] The basic functions of the separator are to prevent the contact between anode and cathode to avoid internal short circuits, store liquid electrolyte, and permit the migration of ions during the chargedischarge process. [14][15][16] The ideal separator should possess Lithium-ion batteries (LIBs) are promising energy storage devices for integrating renewable resources and high power applications, owing to their high energy density, light weight, high flexibility, slow self-discharge rate, high rate charging capability, and long battery life. LIBs work efficiently at ambient temperatures, however, at high-temperatures, they cause serious issues due to the thermal fluctuation inside batteries during operation. The separator is a key component of batteries and is crucial for the sustainability of LIBs at high-temperatures. Th...

No abstract

Lithium ion batteries (LIBs) are one of the most potential energy storage devices among various rechargeable batteries due to their high energy/power density, long cycle life, and low self‐discharge properties. However, current LIBs fail to meet the ever‐increasing safety and fast charge/discharge demands. As one of the main components in LIBs, separator is of paramount importance for safety and rate performance of LIBs. Among the various separators, composite separators have been widely investigated for improving their thermal stability, mechanical strength, electrolyte uptake, and ionic conductivity. Herein, the challenges and limitations of commercial separators for LIBs are reviewed, and a systematic overview of the state‐of‐the‐art research progress in composite separators is provided for safe and high rate LIBs. Various combination types of composite separators including blending, layer, core–shell, and grafting types are covered. In addition, models and simulations based on the various types of composite separators are discussed to comprehend the composite mechanism for robust performances. At the end, future directions and perspectives for further advances in composite separators are presented to boost safety and rate capacity of LIBs.

No abstract