Electrochemical graphitization in the molten salts: Progress and prospects

In 2020, the Chinese government proposed the goals of “peaking carbon dioxide emissions” in 2030 and reaching “carbon neutrality” in 2060, with the expectation of enhancing the optimization of industrial structure and energy structures as well as promoting the development of control technologies and new energy technologies for pollution prevention. Carbon emissions lead to global warming, glacier melting, sea level rising, and other unexpected climate changes. It is highly significant to develop sustainable technologies for treating or converting carbon dioxide and low value-added solid carbon wastes and other carbon pollutants to achieve solid-state valuable carbon products. Carbon pollutants are also regarded as secondary carbon resources, which provide sufficient raw materials for developing carbon materials. Graphitization alters the chemical structure of carbonaceous materials. However, there are still some critical issues in the traditional graphitization processes, such as high processing temperature, insufficient graphitization, and emission of greenhouse gas. In recent years, an efficient and environmentally friendly method for electrochemical graphitization in molten salts has been established, which can be used to directly convert carbon pollutants into high graphitized products. In this review, there are three main topics: (1) process flow, (2) structure characteristics, (3) conversion mechanism of electrochemical graphitization. The use of carbon nanomaterials in secondary batteries such as lithium-ion batteries and aluminum-ion batteries has been discussed for a potential application. As a result, the efficient strategies of transforming and utilizing abundant secondary carbon resources to achieve the applications have also been analyzed. Finally, the ultimate goals for bridging the gap between molten salt electrochemical graphitization and engineering of graphitized products have been identified. Further efforts should be made to develop large-scale electrolytic technology with low energy consumption, build advanced in-situ characterization technology and quantitative analysis method for high-temperature molten salt electrochemistry, and understand the mechanism of electrochemical graphitization at the microscale.