(491a) Graphene Nanoribbons As Conductive Pathways in Directly Deposited Silicon Nanofiber Anodes for High Performance Lithium-Ion Batteries

Silicon is the best candidate for the next generation of Li-ion battery anodes due to its high specific capacity of 4200 mAh/g .However, it expands to 300% of its original size upon insertion of lithium ions^[1], which results in crack formation and pulverization of active material with cycling and thus capacity fading. Crack formation also results in constant solid electrolyte interface formation on the surface of the newly exposed silicon, which brings about unstable performance. Several strategies such as use of nanoparticles^[2] and composites^[3] have been employed by research groups to overcome aforementioned issues. However, all the modifications to silicon has to be done in an economical manner for the product to become an industrial realization.

In the present work we are engineering the nanostructure of a silicon composite with graphene nanoribbons (GNRs) and polyvinyl alcohol (PVA) to create a reliable anode for lithium ion batteries. Silicon nanoparticles and GNRs are dispersed along PVA nanofibers via a water-based electrospinning process to directly form functional fiber mats on top of the copper current collector. This method is compatible with a role to role production, and bypasses several long-winded steps in the conventional paste-based electrode making. Physical and chemical properties of the nanoparticles and their dispersion affect the fiber morphology and ultimately electrochemical performance of the composite material. Graphene nanoribbons, made by unzipping carbon nanotubes, offer unique electrochemical and structural properties when inside the composite fibers. It was observed that GNRs outperform their precursor CNTs in terms of overall capacity and retention. The Silicon-GNR-PVA fiber anode exhibited an outstanding 2000 mAh/g at a rate of C/15 and 1200 at C/5 over 200 cycles. Inclusion of GNRs improved the structural stability and conductivity of the fibers, while protection of nanoparticles from the electrolyte offered by the polymer resulted in stable cycling of the directly deposited electrodes.

[1] C.-M. Wang, X. Li, Z. Wang, W. Xu, J. Liu, F. Gao, L. Kovarik, J.-G. Zhang, J. Howe, D. J. Burton, Z. Liu, X. Xiao, S. Thevuthasan, D. R. Baer, Nano Lett. 2012, 12, 1624.

[2] M. M., Ryu I, Wu H, Liu N, Hu L, Nix WD, Cui Y Yao Y, Nano Lett. 2011, 11, 2949.

[3] Y.-S. Hu, R. Demir-Cakan, M.-M. Titirici, J.-O. Müller, R. Schlögl, M. Antonietti, J. Maier, Angew. Chem. Int. Ed. 2008, 47, 1645.