Increasing the interlayer spacing and generating closed pores to produce petroleum coke-based carbon materials for sodium ion storage

Abstract

Petroleum coke (PC) is a valuable precursor for sodium-ion battery (SIB) anodes due to its high carbon content and low cost. The regulation of the microcrystalline state and pore structure of the easily-graphitized PC-based carbon is crucial for creating abundant Na+ storage sites. Here we used a precursor transformation strategy to increase the carbon interlayer spacing and generate abundant closed pores in PC-based carbon, significantly increasing its Na+ storage capacity in the plateau region. This was achieved by introducing a large number of oxygen functional groups through mixed acid treatment and then using high-temperature carbonization to decompose the oxygen functional groups and rearrange the carbon microcrystallites, resulting in a transition from open to closed pores. The optimized samples provide a large reversible capacity of 356.0 mAh g−1 at 0.02 A g−1, of which approximately 93% is below 1.0 V. Galvanostatic intermittent titration (GITT) and in-situ X-ray diffraction (XRD) analysis indicate that the sodium storage capacity in the low voltage plateau region involves a joint contribution of interlayer insertion and closed pore filling processes. This study presents a comprehensive method for the development of high-performance carbon anodes using low-cost and highly aromatic precursors.

1. Introduction

The production of petroleum coke (PC), a by-product of oil refining, has been steadily increasing in tandem with advancements in crude oil refining technology[1–5]. However, the PC, especially with high sulfur content (S ≥ 3%), is directly burned as fuel in the cement industry and power plants, which lead to low-level utilization of PC and environmentally unfriendly[6–9]. Therefore, the investigation of novel sustainable pathways facilitating the value-added utilization of PC is imperative.

Several methods have been employed to transform PC into high value-added materials, such as carbon electrode materials, taking the advantages of its high carbon content, low ash content and volatile, and low economic cost[1,10–12]. Moreover, the heteroatoms, such as S in the PC can be removed after calcination at high temperatures, which optimizes the electronic structure of the carbon electrode materials[13–15]. Fan et al. prepared artificial graphite as anode materials for Li-ion batteries from PC by carbonization at 2400–3000 °C[16]. Similarly, Qiu et al. successfully synthesized porous carbon cathode materials by a KOH activation for Li-ion capacitor, which shows a high energy density (231 Wh kg−1) and ultralong cycling life[17]. These results indicate that PC is a promising precursor for preparing carbon electrodes material. However, high temperature treatment requires high energy consumption and the KOH activation process causes corrosion of the facilities. Thus, the imperative objective is to research and develop cutting-edge carbon electrode materials for batteries in an efficient and environmentally friendly way.

Carbon materials have attracted considerable attention as anodes for alkali metal-ion batteries, such as sodium-ion batteries (SIBs), lithium-ion batteries (LIBs), and potassium-ion batteries (PIBs), because of their low-cost, nontoxicity, and controllable structures[18,19]. SIBs are promising rechargeable batteries for large-scale electrical energy storage due to the natural abundance and low cost of sodium resources[20–24]. Alcántara et al. reported the use of PC as raw materials to prepare carbon electrode materials at temperatures below 1 000 °C for SIBs with a discharge capacity of about 100 mAh g−1, which is much low for practical application[8]. As one kind of soft carbon, PC is easily converted to graphitic carbon with narrow layer spacing during the carbonization, which is detrimental to sodium storage[25–27]. Thus, it is necessary to enhance Na+ storage capacity for PC-based carbon.