The use of these coal-derived carbons for energy storage, such as secondary batteries and supercapacitors, is also discussed in terms of their structural features. The review aims to provide valuable insight into the present challenges and inspire new ideas for the development of advanced coal-derived carbon materials.
CUEES concept and technical requirements Coal Underground space Electrochemical Energy Storage (CUEES) makes full use of the underground space of coal mining to store or release electrical energy (various types of batteries) through reversible chemical reactions, so as to achieve efficient use of electrical energy, as shown in Fig. 20 [ 94 ].
The use of coal mining space for electrochemical energy storage has not yet been commercialized [ 95 ], and four key problems still need to be broken through, namely, site safety evaluation of underground space for coal development, construction of electrochemical energy storage geological bodies.
In addition, the technology of using underground coal mine space for energy storage has become an effective means to promote the development of low-carbon clean energy due to its advantages of large space and low mining cost. However, there are still a few hazards and difficulties in its development and use procedures that need to be resolved.
While making full use of coal to develop underground space resources, it realizes power conversion and storage, stabilizes the power system's cycle and voltage, promotes the circulation of mine water, and guarantees flood storage and water transfer.
Various energy storage technologies and risks in coal mine are analyzed. A significant percentage of renewable energy is connected to the grid but of the time-space imbalance of renewable energy, that raises the need for energy storage technologies.