Browsing by Author "Ojha, Ved"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Fluorinated Multi-Walled Carbon Nanotubes Coated Separator Mitigates Polysulfide Shuttle in Lithium-Sulfur Batteries
    (MDPI, 2023) Salpekar, Devashish; Dong, Changxin; Oliveira, Eliezer F.; Khabashesku, Valery N.; Gao, Guanhui; Ojha, Ved; Vajtai, Robert; Galvao, Douglas S.; Babu, Ganguli; Ajayan, Pulickel M.
    Li-S batteries still suffer from two of the major challenges: polysulfide shuttle and low inherent conductivity of sulfur. Here, we report a facile way to develop a bifunctional separator coated with fluorinated multiwalled carbon nanotubes. Mild fluorination does not affect the inherent graphitic structure of carbon nanotubes as shown by transmission electron microscopy. Fluorinated carbon nanotubes show an improved capacity retention by trapping/repelling lithium polysulfides at the cathode, while simultaneously acting as the “second current collector”. Moreover, reduced charge-transfer resistance and enhanced electrochemical performance at the cathode-separator interface result in a high gravimetric capacity of around 670 mAh g−1 at 4C. Unique chemical interactions between fluorine and carbon at the separator and the polysulfides, studied using DFT calculations, establish a new direction of utilizing highly electronegative fluorine moieties and absorption-based porous carbons for mitigation of polysulfide shuttle in Li-S batteries.
  • Thumbnail Image
    ItemEmbargo
    Materials and Electromechanical Engineering of a Haptic System
    (2022-04-22) Ojha, Ved; Ajayan, Pulickel; O'Malley, Marcia
    Haptic technologies are set to play a key role in the design of next generation human-computer interfaces. While haptic feedback is being leveraged in areas such as consumer electronics, there is much to be done to create haptic systems that add value to our daily life. With the coming AR/VR revolution, wearables that add a sense of touch will enable truly immersive experiences. Haptic feedback is already augmenting professional training simulators used by astronauts, surgeons, soldiers to optimize learning routines. In other applications, haptic interfaces have already been shown to enable the deaf to "hear" again and the blind to navigate through environments with greater accuracy. Haptic feedback, therefore, is poised to redefine communications technology as a whole. I have explored actuation technologies, actuators with advanced polymers for generating crisp haptic feedback, data processing techniques and software design for triggering complex haptic patterns using sound signals, and low cost electronic design methodologies for driving arrays of electromagnetic actuators. I have demonstrated the above by designing a portable haptic vest using 112 eccentric rotating mass actuators, a haptic sleeve with 8 linear resonant actuators, and demonstrated a PVDF-TrFE polymer based piezoelectric actuator as a flexible and biocompatible alternative to traditional actuation technologies. A drawback that plagues most haptic systems is high power consumption, especially when operating at peak loads. When constructing energy efficient portable haptic systems, one must use an energy storage device capable of delivering high power while maintaining a stable energy density. Current lithium-ion batteries used in consumer electronics are energy dense but have low rate capability. I have explored a system known as a hybrid supercapacitor using a novel \ch{rGO/Nb2O5} nanocomposite anode, capable of delivering high energy at high current rates. As an intermediate energy storage device between batteries and supercapacitors it is ideal for analyzing the limitations of current energy storage systems and designing future energy solutions.