(569d) Tailoring the Assembly of Electrode Materials Via Scalable Processes for High Capacity Li-Ion, Li-Sulfur, and Li-Air Batteries
Controlling the assembly of electrochemically active materials at nanoscale has a significant effect on the performance of energy storage systems. Employing circumferentially uniform air flow through the sheath layer of the concentric coaxial nozzles, gas-assisted electrospinning and air-controlled electrospray utilize both high electric field and controlled air flow which can offer i) enhanced stretching of fluid jet and drops, and thus much higher throughput, and ii) better control of dispersion and configuration of nanofillers in a jet or droplet even at high loadings. The ability to tailor the distribution of various nanofillers (Si nanoparticles (NP) and rod/tubeâlike carbon nanotubes (CNTs), and carbon nanoribbons (GNRs)) in a polyvinyl alcohol (PVA) jet was demonstrated by varying air flow rates in gas-assisted electrospinning. Our results reveal that two to three fold improvement in NP distribution can be obtained with the application of high, but controlled air flow. The substantial improvement in the orientation of CNTs and GNRs by additional controlled air flow was also observed. These results are validated by the coarse-grained Molecular Dynamics (CGMD) study of nanofillers in a polymer matrix under elongational flow. The enhanced electrochemical performance by controlling dispersion and configuration of nanofillers in nanofibers has been demonstrated in the directly deposited, Li-ion battery anode application, exhibiting over 2,000 mAh/g of capacity which is about 1,000 mAh/g higher than the anode obtained by conventional electrospinning. The direct deposit approach has been extended to the air-controlled electrospray process to create a compact deposition of Si particles wrapped by graphene sheets, and the resulting anode of directly deposited Si/graphene exhibits about 1,500 mAh/g of capacity with above 90% capacity retention after 300 cycles. Finally, we demonstrate that the direct deposit approach based on air-controlled electrospray enables high sulfur loading in mesoporous carbon and sandwich-stacking of different graphene materials for high performance Li-sulfur batteries with areal capacity of 7 mAh/cm2 for 100 cycles, and Li-air batteries with areal capacity up to 18 mAh/cm2, respectively.