(Invited) Carbon Fiber-Paper–Supported Carbon Nanofoams As Free-Standing Electrode Architectures for Reversible Sodium-Ion Storage

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Hard (non-graphitizable) carbon has emerged as a prospective charge-storage material for negative electrodes in sodium-ion batteries, yet reported electrochemical performance across this broad category of carbons varies widely. Such discrepancies arise in part due to the multiple distinct sodiation reactions that are possible with disordered carbon electrodes, whereby sodium ions can be stored in defect sites, graphitic layers, and/or micropores depending on the pore–solid architecture, surface chemistry, and solid-state structure of a particular carbon. To address both fundamental questions and practical application in Na-ion batteries, we are investigating carbon nanofoam papers (CNFPs), synthesized by infiltrating the voids of carbon-fiber paper with resorcinol–formaldehyde (R–F) formulations to form porous polymer nanofoam that is subsequently converted to the conductive carbon analog via pyrolysis at 1000°C [1]. When tested as free-standing electrode architectures in Na-ion cells, CNFPs deliver specific capacity >300 mAh g–1 at a 1C rate and >250 mAh g–1 at 10C, with a first-cycle Coulombic efficiency near 85% under galvanostatic operation. The galvanostatic intermittent titration technique (GITT) confirms that Na-ion diffusion is facile in the defect-mediated charge-storage regime. We attribute these favorable properties to the high defect concentration in the disordered R–F-derived carbon domains, the 3D-interconnected porosity within the carbon nanofoam, and the absence of otherwise-necessary binder and conductive additives that are commonly used in conventional powder-composite electrodes. Our results demonstrate the utility of CNFPs as device-ready, self-supported electrodes and advance the design of related carbon materials for next-generation Na-ion batteries. [1] J.C. Lytle, J.M. Wallace, M.B. Sassin, A.J. Barrow, J.W. Long, J.L. Dysart, C.H. Renninger, M.P. Saunders, N.L. Brandell, and D.R. Rolison, Energy Environ. Sci., 4 (2011) 1913–1925.