Nitrogen doped holey carbon nano-sheets as anodes in sodium ion battery

Abstract

Though the insertion mechanism of lithium and sodium ions in carbon nano-structures is similar, anodes used in sodium ion batteries face many practical difficulties due to the fact that the sodium ion is 55% larger than its lithium counterpart. One way of accommodating the spatial requirements of the large sodium ion is by increasing the ‘active surface area’ of anodes in sodium-ion batteries. In this manuscript, we developed a microwave based solvothermal technique for synthesis of nitrogen doped, holey-carbon nano sheets (hCNS) by using eco-friendly ionic liquids and potassium ethoxide. Morphological studies by SEM and TEM showed ‘in-plane’ spherical nano-pores well distributed through hCNS, whereas XPS studies showed that the nitrogen doping exists predominantly as pyridinic groups. When applied as electrodes in sodium-ion batteries, our 3D holey carbon nano-sheets show high specific capacitance of 268 mA h g⁻¹, good rate capability and 93% of initial capacitance retention even after 200 cycles. The presence of chemically active nano-holes on the carbon nano-sheet surface increases the surface area, acts as anchoring points for sodium ions, and favours fast diffusion of the electrolyte.