A highly nitrogen-doped porous graphene – an anode material for lithium ion batteries

Abstract

A novel nitrogen-doped porous graphene material (NPGM) was prepared by freeze-drying a graphene/melamine-formaldehyde hydrogel and subsequent thermal treatment. The use of melamine-formaldehyde resin as a cross-linking agent and nitrogen source enhances the nitrogen content. NPGM possesses a hierarchical porous structure, a large Brunauer-Emmett-Teller surface area (up to 1170 m 2 g -1 ), and a considerable nitrogen content (5.8 at%). NPGM displays a discharge capacity of 672 mA h g -1 at a current density of 100 mA g -1 when used as an anode material for lithium ion batteries, much higher than that observed for a nitrogen-free graphene porous material (450 mA h g -1 ). The NPGM electrode also possesses superior cycle stability.No capacity loss was observed even after 200 charge/discharge cycles at a current density of 400 mA g -1 . The enhanced electrochemical performance is attributed to nitrogen doping, high specific surface area, and the three-dimensional porous network structure.Melamine-formaldehyde resin (MF) was synthesized by adding formaldehyde (1.01 g, 37 wt%) and 0.63 g melamine into ultrapure water (7.86 g), followed by the addition of aqueous sodium hydroxide solution (0.5 mL, 0.1 M). This mixture was heated at 80 °C for 15 min till it turned clear. The resultant soluble MF (1.0 g) was 13 of graphene material. In addition, a great amount of crumpled sheets can be observed in the TEM images of NPGM and PGM, and these sheets are entangled with each other (Figs. 4c and d). Both NPGM and PGM possess a 3D interconnected network structure as expected, which may deliver superior electrochemical properties. Fig. 4 SEM images of NPGM (a) and PGM (b), TEM images of NPGM (c) and PGM (d).A nitrogen adsorption-desorption measurement was applied to further investigate porous properties. Both NPGM and PGM exhibit type IV isotherms, and their nitrogen adsorption-desorption isotherms show high uptake at a low relative pressure of 0-0.1, suggesting the microporous nature. Compared with PGM, NPGM displays a larger hysteresis at the relative pressure range of 0.45-1.0 (Fig. 5a), indicating the presence of 21 graphene sheets, which is helpful to the adsorption and infiltration of lithium ions into electrode. 23 The reduced charge-transfer resistance is beneficial to the electron transfer and lithium ion transport between the electrode and electrolyte. Fig. 9 (a) Electrochemical impedance spectra of NPGM and PGM electrodes (Inset is the corresponding simulation results for NGPM and PGM electrodes), (b) the simulated Randles equivalent circuit for NPGM and PGM electrodes. (CPE and R stand for the constant phase element and resistance, respectively.) ConclusionsIn this work, we prepared a graphene-based hydrogel by using melamine-formaldehyde resin as a cross-linking agent. NPGM was fabricated through freeze-drying of GMF hydrogel and subsequent thermal treatment. The as-prepared NPGM possessed a hierarchical porous structure, large specific surface area, and

Ultrasmall SnS2nanoparticles anchored on well-distributed nitrogen-doped graphene sheets for Li-ion and Na-ion batteries

“…15,32,33 In the following test up to 120 cycles, the discharge capacity maintains at about 1407 mA h g -1 . 10 Without NGS, the reversible capacity of pure SnS 2 declines quickly( Figure S5). For comparative analysis, the SnS 2 -GN electrode is also conducted under similar conditions.…”

“…[6][7][8][9][10] Although the Na-storage capacities of these carbon anode materials have ascended up to some extent, the reversible capacities below 200 mA h g -1 still can not satisfy the long-term requirement of emerging fields, such as electric vehicles. [6][7][8][9][10] Although the Na-storage capacities of these carbon anode materials have ascended up to some extent, the reversible capacities below 200 mA h g -1 still can not satisfy the long-term requirement of emerging fields, such as electric vehicles.…”

Poly(ionic liquid)‐Derived N‐Doped Carbons with Hierarchical Porosity for Lithium‐ and Sodium‐Ion Batteries

“…It clearly shows that NCP2 delivers comparable or higher electrochemical performance than the best reported N‐doped carbons in the literature . This work shows that the nature of the polymer precursor for NPC and the pyrolysis temperature affect the structure characteristics of NPCs, such as specific surface area, the structured porosity, and N‐doping level, and are effective ways to improve cycling performance of electrode for LIBs …”

Nitrogen‐Doped Defective Graphene Aerogel as Anode for all Graphene‐Based Lithium Ion Capacitor

“…The semicircle at high frequency represents the charge transfer resistance (R ct ) between the electrode and electrolyte, R e and R f are the pure Ohmic resistance and the SEI formed on the surface of the electrode, respectively. The constant phase element (CPE1) and non‐constant phase element (CPE2) represent the double layer capacitance and the dielectric relaxation capacitance, Z w is the Warburg diffusion impedance ,. The fitted parameters are shown in Table .…”