Fig. 1

Models of structural units for coals with varying degrees of coalification"

Table 1

Basic properties of coals with varying degrees of coalification"

Table 2

Physical properties of different micropetrological constituents"

Fig. 2

The mechanism of free radical reactions in coal pyrolysis[12]"

Fig. 3

Schematic diagram of types of structural control strategies for coal-based carbon materials"

Fig. 4

Schematic diagram of the preparation of anthracite-based hard carbon by flash Joule heating method; (b) rate performance, (c) discharge curves of the resulting hard carbon at current densities of 0.05—1 A/g[19]"

Fig. 5

(a) Structural evolution of coal during pre-oxidation and carbonization; (b) Relationship between plateau capacity and BET surface area and closed pore volume; (c) In situ Raman spectroscopy during charging and discharging[23]"

Fig. 6

(a) Schematic diagram of the preparation process and microcrystalline structure of lignite/sucrose composites[29]; (b) Raman spectra and (c) constant-current charge-discharge curves at 0.03 A/g of hard carbon obtained by carbonization of coal coupled with different ratios of glucose molecules[30]"

Fig. 7

(a) Schematic diagram of the preparation process of N-doping coal-based hard carbon; theoretical simulations of sodium adsorption based on various N-doping structures: (b) N-Q, (c) N-5, and (d) N-6, where the brown spheres are C, the silver spheres are N, and the green spheres are Na[33]"

Fig. 8

Interaction diagram of oxygen-containing functional groups and Na+ during sodium insertion/extraction process[39]"

Fig. 9

Schematic diagram of the preparation process of coal-based hard carbon optimized by mechanical ball milling[46]"

Fig. 10

Schematic diagram of preparation of pitch-coated coal-based carbon[43]; (b) Synthesis method and electrochemical performance of coal-based amorphous carbon with “core-shell structure”[44]"

Fig. 11

(a) Schematic diagram of thermal transformation pathways for activated coal-based hard carbon; (b) BET surface area and closed pore surface area of AC700, CAC1100, CAC1300, CAC1500, and DC1300; (c) Schematic illustration of the pore structure evolution during various thermal treatment processes; (d) The first discharge-charge curves of AC700, CAC1300, and DC1300 at the current density of 0.1 C[48]"

Fig. 12

Schematic diagram of (a) the process of preparing porous carbon rods using MgO as a template[51]; (b) the preparation of nitrogen-doped porous charcoal via the salt template method[52]"