High Areal Capacity Si/LiCoO2 Batteries from Electrospun Composite Fiber Mats.

Freestanding nanofiber mat Li-ion battery anodes containing Si nanoparticles, carbon black, and poly(acrylic acid) (Si/C/PAA) are prepared using electrospinning. The mats are compacted to a high fiber volume fraction (≈0.85), and interfiber contacts are welded by exposing the mat to methanol vapor. A compacted+welded fiber mat anode containing 40 wt % Si exhibits high capacities of 1484 mA h g-1 (3500 mA h g-1Si ) at 0.1 C and 489 mA h g-1 at 1 C and good cycling stability (e.g., 73 % capacity retention over 50 cycles). Post-mortem analysis of the fiber mats shows that the overall electrode structure is preserved during cycling. Whereas many nanostructured Si anodes are hindered by their low active material loadings and densities, thick, densely packed Si/C/PAA fiber mat anodes reported here have high areal and volumetric capacities (e.g., 4.5 mA h cm-2 and 750 mA h cm-3 , respectively). A full cell containing an electrospun Si/C/PAA anode and electrospun LiCoO2 -based cathode has a high specific energy density of 270 Wh kg-1 . The excellent performance of the electrospun Si/C/PAA fiber mat anodes is attributed to the: i) PAA binder, which interacts with the SiOx surface of Si nanoparticles and ii) high material loading, high fiber volume fraction, and welded interfiber contacts of the electrospun mats.

High Performance Particle/Polymer Nanofiber Anodes for Li-ion Batteries using Electrospinning.

Electrospun nanofiber mats containing carbon nanoparticles in a poly(vinylidene fluoride) binder were prepared and characterized as Li-ion battery anodes. The mats exhibited an initial capacity of 161 mAh g(-1) with 91.7% capacity retention after 510 cycles at 0.1 C (1 C=372 mA gcarbon (-1)). Whereas many nanoscale electrodes are limited to low areal and/or volumetric capacities, the particle/polymer nanofiber anodes can be made thick with a high fiber volume fraction while maintaining good rate capabilities. Thus, a nanofiber anode with a fiber volume fraction of 0.79 exhibits a volumetric capacity of 55 mAh cm(-3) at 2 C, which is twice that of a typical graphite anode. Similarly, thick nanofiber mats with a high areal capacity of 4.3 mAh cm(-2) were prepared and characterized. The excellent performance of electrospun anodes is attributed to electrolyte intrusion throughout the interfiber void space and efficient Li(+) transport between the electrolyte and carbon nanoparticles in the radial fiber direction.