Rational Design and General Synthesis of S‐Doped Hard Carbon with Tunable Doping Sites toward Excellent Na‐Ion Storage Performance

Abstract

Heteroatom-doping is a promising strategy to tuning the microstructure of carbon material toward improved electrochemical storage performance. However, it is a big challenge to control the doping sites for heteroatom-doping and the rational design of doping is urgently needed. Herein, S doping sites and the influence of interlayer spacing for two kinds of hard carbon, perfect structure and vacancy defect structure, are explored by the first-principles method. S prefers doping in the interlayer for the former with interlayer distance of 3.997 Å, while S is doped on the carbon layer for the latter with interlayer distance of 3.695 Å. More importantly, one step molten salts method is developed as a universal synthetic strategy to fabricate hard carbon with tunable microstructure. It is demonstrated by the experimental results that S-doping hard carbon with fewer pores exhibits a larger interlayer spacing than that of porous carbon, agreeing well with the theoretical prediction. Furthermore, the S-doping carbon with larger interlayer distance and fewer pores exhibits remarkably large reversible capacity, excellent rate performance, and long-term cycling stability for Na-ion storage. A stable and reversible capacity of ≈200 mAh g is steadily kept even after 4000 cycles at 1 A g .

Self‐Polymerized Disordered Carbon Enabling High Sodium Storage Performance through Expanded Interlayer Spacing by Bound Sulfur Atoms

“…However, when S atom is introduced into intercalated sites in PS750 (Figure b), the interlayer bonded S atoms between two adjacent graphene layers can enlarge d 002 value to 3.65 Å, which matches with the TEM result in Figure g (3.7 Å) and calculated result (3.66 Å) in Table . Hence, it can be speculated that the enlarged d 002 value is mainly caused by the interlayer bonded S atoms rather than the substituted S atoms, which agrees well previous report ,. This result can be also deduced from the lower H/C molar ratio of PS750 than P750 (Table S1).…”

“…Secondly, the interlayer C−S−C bonds of PS750 effectively expand d 002 spacing, which promotes Na + ion adsorption and reduces Na + ion insertion/extraction barriers, increasing material utilization and Na + ion diffusion capability. Meanwhile, the C−S−C bonds between perylene rings can also act as alternative charge transfer routes,, leading to the conductivity improvement.…”

Nitrogen‐Doped Hard Carbon on Nickel Foam as Free‐Standing Anodes for High‐Performance Sodium‐Ion Batteries

“…The broad and low intensity peaks suggest a low degree of graphitization. Notably, the location of (002) peaks for NC/NF‐800 shifted to a lower degree compared with the NC/NF‐700, and NC/NF‐900, indicating the increased interlayer spacing of NC/NF‐800 materials . According to Bragg's equation, the (002) peak interlayer distance of the NC/NF‐800 can be calculated to be 0.48 nm, which is larger than that of the NC/NF‐700 (0.43 nm) and NC/NF‐900 (0.40 nm) sample.…”

A Mechanochemical‐Assisted Synthesis of Boron, Nitrogen Co‐Doped Porous Carbons as Metal‐Free Catalysts

“…Possibly owing to the interference from nearbys ignals, the characteristic vibrations of BÀNa t 1390 cm À1 and 780 cm À1 ,g enerated from GB-1-600~900, are not observed in the FTIR spectra.P eaks appearing at approximately 1170 cm À1 imply the formation of CÀBb onds in the samples. [19] Nitrogena dsorption/desorption experiments at 77.4 Kw ere carried out to elucidate the pore structure of GB-1-x and the results are summarized in Ta ble S2 (in the Supporting Information). From the X-ray diffraction (XRD)p atterns of the GB-1-x samples ( Figure S1 in the Supporting Information), two broad peaks of (0 02)a nd (1 00)d iffractions can be observed, which are typical of the disordered carbon.T he (0 02)p eaks shift to higher diffraction angles with carbonization temperature rising (Table S1 in the SupportingI nformation), revealing that the average interlayer d-spacing decreases owing to the increased relative ordering of the carbon structure.…”