Na-ion storage performance of graphite and nanocarbons: Na-diglyme co-intercalation into graphene nanosheets

This study explores the sodium-ion (Na-ion) storage performance of various carbon materials, including commercially available carbon nanoparticles (C45), natural and artificial graphite, and few-layer graphene produced through a green and sustainable molten salt exfoliation method. Structural, microstructural, electrical and electrochemical characteristics of these materials are evaluated in both ester-based (carbonate) and ether-based (diglyme) electrolytes. While Na-ion intercalation into graphite and graphene remains limited in conventional ester electrolytes, co-intercalation with diglyme in ether-based systems is highly effective. Among the materials studied, the few-layer graphene exhibits the most promising electrochemical performance, delivering a rising capacity of 235 mAh/g after 220 cycles at 100 mA/g, with Na-ion diffusion reaching 8.4 × 10⁻¹¹ cm²/s after 150 cycles. This performance is attributed to graphene's exceptional electrical conductivity (1336 S/m at 6.2 MPa) and its nano-layered structure, which facilitates the formation of stable Na-diglyme intercalation compounds. In situ charge/discharge-Raman spectroscopy confirms this mechanism, revealing voltage plateaus at 0.58–0.63 V (discharge) and 0.66–0.80 V (charge), along with Raman features at 1456 and 1461 cm⁻¹. These findings demonstrate the high electrochemical potential of ether-compatible graphene-based anode for sustainable Na-ion storage.