Low-Temperature Carbonized Nitrogen-Doped Hard Carbon Nanofiber Toward High-Performance Sodium-Ion Capacitors

Carbon nanofiber(CNF)was widely utilized in the field of electrochemical energy storage due to its superiority of conductivity and mechanics.However,CNF was generally prepared at relatively high temperature.Herein,nitrogen-doped hard carbon nanofibers(NHCNFs)were prepared by a lowtemperature carbonization treatment assisted with electrospinning technology.Density functional theory analysis elucidates the incorporation of nitrogen heteroatoms with various chemical states into carbon matrix would significantly alter the total electronic configurations,leading to the robust adsorption and efficient diffusion of Na atoms on electrode interface.The obtained material carbonized at 600°C(NHCNF-600)presented a reversible specific capacity of 191.0 mAh g^(−1)and no capacity decay after 200 cycles at 1 A g^(−1).It was found that the sodium-intercalated degree had a correlation with the electrochemical impedance.A sodium-intercalated potential of 0.2 V was adopted to lower the electrochemical impedance.The constructed sodium-ion capacitor with activated carbon cathode and presodiated NHCNF-600 anode can present an energy power density of 82.1 Wh kg^(−1)and a power density of 7.0 kW kg^(−1).

A safe,low-cost and high-efficiency presodiation strategy for pouch-type sodium-ion capacitors with high energy density

Sodium-ion capacitors(SICs)have attracted appreciable attention in virtue of the higher energy and power densities compared with their rivals,supercapacitors and sodium-ion batteries.Due to the lack of sodium resources in cathode,presodiation is critical for SICs to further augment performances.However,current presodiation strategy utilizes metallic sodium as the presodiation material.In this strategy,assembling/disassembling of half-cells is required,which is dangerous and in creases the time and cost of SIC leading to the restriction of their industrialization and commercialization.Herein we present a safe,low-cost and high-efficiency presodiation strategy by first employing Na_(2)C_(2)O_(4) as the sacrificial salt applied in SICs.Na_(2)C_(2)O_(4) is environmentally friendly and possesses considerably low expenditure.No additional residues remain after sodium extraction ascribed to its"zero dead mass"property.When paired with commercial activated carb on as the cathode and commercial hard carbon as the ano de,the constructed pouch-type SICs exhibit high energy and power densities of 91.7 Wh/kg and 13.1 kW/kg,respectively.This work shows a prospect of realizing the safe and low-cost manufacturing for high-performance SICs commercially.