Sodium-ion batteries (SIBs) have received considerable attention as promising next-generation energy storage systems due to a large abundance of sodium and ion storage chemistry similar to that of lithium-ion batteries (LIBs). We report ultramicroporous hard carbon microspheres (HCMSs) derived from sucrose via a microwave-assisted solvothermal reaction as anode for SIBs. Because of the HCMSs with a larger interlayer spacing in graphitic domains and ultramicropores, it delivers excellent 3-RC features (reversible capacity, rate capability, and retention of capacity) reported to date for hard carbons derived from sugar-based carbon precursors through electrolyte optimization of carbonate esters (EC:PC, EC:DEC, EC:DMC). The HCMS-PC delivered the best reversible capacity of 265 mAh g −1 at a current density of 300 mA g −1 , showing 85.8% capacity retention after 100 cycles and 66.3% capacity retention after 500 cycles in a half-cell. A full-cell fabricated with an HCMS-PC anode and a Na 3 V 2 (PO 4 ) 3 cathode delivered reversible capacities of 81 and 48 mAh g −1 at current densities of 30 and 300 mA g −1 , respectively.
The sodium-ion storage mechanism of the hard carbon microspheres (HCMSs) synthesized using the microwave technique from the sucrose precursor and a 50% DEG/H 2 O solvent mixture carbonized at 1000 °C (50DEG-HCMS) is studied. The superior sodium-ion battery (SIB) anode, 50DEG-HCMS delivers the highest reversible capacities of 385 (ICE ∼75.5%) and 265 mAh g −1 (ICE ∼72%) at current densities of 30 and 300 mA g −1 , respectively. The plateau related capacity (PRC) solely determines the reversible capacity fade on cycling at all C-rates for the HCMS, validating the insertion/pore-filling mechanism for the low voltage (< ∼0.1 V) capacity. In this study, we substantiate that maximizing PRC may not be the best strategy in designing a high rate, a highly cyclable carbonbased anode for SIBs. HCMSs synthesized using a 20% DEG/H 2 O solvent mixture and at different carbonization temperatures are also studied to assert the defect/vacancy-assisted adsorption/insertion and insertion/micropore filling Na-ion storage mechanism in hard carbons.
The growing renewable energy sector worldwide and the depleting resources for the Li-ion battery (LIB) technology in a decade push the case of complementary storage technologies, especially for stationary energy...
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