Synthesis and Electrochemical Characterization of N-Doped Graphene-like Graphite Material for Lithium-Ion Battery Applications

Abstract

Graphite is the most commercialized electrode active compound for lithium-ion batteries (LIB). However, its limited theoretical capacity (372 mAh/g) and relatively poor rate performance make it unsuitable for LIB with higher energy density and fast charge ability. Therefore, alternative carbon-based materials, like graphene, have also been explored due to their attractive electrochemical properties.1 Despite having these properties, the low density and the high specific surface area of graphenic materials result in a low coulombic efficiency when it is used in LIB. To solve this, the physical and electrochemical properties of graphenic materials can be modified during the process of obtention of this material. This work presents a methodology with unique advantages in terms of low cost, stability, scalability, and non-use of hazardous conditions for obtaining an N-doped graphene-like graphite material. This procedure consists of the electrochemical oxidation of graphite rods and a subsequent hydrothermal reduction of the oxidated graphene. First, the electrochemical exfoliation of graphite rods was carried out under constant potential in a basic solution. Due to the exfoliation process, this graphenic material was characterized by having oxygenated functional groups and a graphite-like structure. The structural properties of this material were investigated at room temperature using X-ray diffraction (XRD), infrared spectroscopy (FTIR), and Raman spectroscopy. To reduce the oxygenated functional groups on the graphenic material, a hydrothermal method was used. Simultaneously to the reduction, heteroatom doping was carried out to enhance the electrochemical properties of the obtained reduced graphenic material. To further control the doping process of the rGO and the final properties of the material, a pre-reduction treatment was also introduced. This low-cost, pre-reduction process allowed the controlled introduction of defects in the material to enhance the doping percentage of the N-rGO. Besides the structural characterization techniques previously indicated, electrochemical impedance spectroscopy (EIS) and voltammetric methods were used to characterize the final N-doped electrochemical properties fully. The observed features of the samples indicate that the graphenic material possesses a graphite-like graphene structure, which allows the material to act like independent graphene layers that maintain a highly regulated orientation between the sheets, which can increase the charge/discharge capacity if used in LIB.2 Furthermore, it was shown that the pre-reduction treatment allowed an increase in the doping percentage of the graphenic material. This increased doping led to an increased charge-transfer conductivity, as indicated by the electrochemical characterization methods. Overall, this low-cost, scalable procedure allows the obtention of graphenic materials with properties suitable for their applications in LIB. Al Hassan, M. R., Sen, A., Zaman, T. & Mostari, M. S. Emergence of graphene as a promising anode material for rechargeable batteries: a review. Mater. Today Chem. 11, 225–243 (2019).Matsuo, Y. et al. Electrochemical Intercalation Behaviors of Lithium Ions into Graphene-Like Graphite. J. Electrochem. Soc. 165, A2409 (2018).