Lithium-ion batteries pitch-based carbon anode materials: The role of molecular structures of pitches

Abstract

To understand the effect of molecular configurations of coal tar pitch (CTP) on the reaction mechanism of carbonization and Li storage performance of subsequent carbonized products, four CTPs with different molecular structures are treated by liquid and solid phase carbonization and then tested the electrochemical performance of their carbonized products as anode materials for Lithium-ion batteries (LIBs). The results reveal that CTP-1 with hexagon rings, zigzag edges, and long alkyl side chains provides a large number of free radicals during pyrolysis, promoting the parallel arrangement of aromatic molecules. Special addition patterns (linear and nonlinear simultaneous) of aromatic molecular in CTP-3 generate a large number of edge carbons and surface defects in the carbonized products. The high viscosity and arm-chair edge reduce the reactivity of CTP-4 molecules, and the presence of loops and oxygenated aromatics in CTP-4 also reduces the orientation of carbon stacks and the flatness of the microstructure. The electrochemical performance of the final products shows a significant difference. Among them, CTP-1-M-1400 with a specific capacity of 349 mAh g⁻¹ at 0.1 A g⁻¹ displays an excellent cycling performance. Large amounts of Li-ions (about 39.2 %) are stored at the edge and surface of CTP-3-M-1400. While large number of Li-ions (about 23.5 %) are stored in the microspaces of CTP-4-M-1400. In addition, excessive structure defects and oxygen-containing groups in CTP-4-M-1400 lead to decreased capacity retention.