Understanding the correlation between microstructure and electrochemical performance of hybridized pitch cokes for lithium-ion battery through tailoring their evolutional structures from ordered soft carbon to disordered hard carbon

Abstract

Pitch-derived cokes (PCs) with different optical textures and microstructures were produced by thermo-polymerization and subsequent heat treatment of a mixture of graphitizable and non-graphitizable precursors (i.e., naphthalene pitch and C9 resin). The effects of weight fractions of C9 resin and heat-treating temperatures on the evolutional microstructure and electrochemical performance of different hybridized PCs used as an anode material for lithium-ion batteries were investigated. The results show that the macro-texture, microstructure and structural evolution of PCs could be controlled by facilely tailoring the synthetic precursors through pitch-resin co-polymerizing reaction. The versatile and tunable structure of PCs closely dominates the inserting and extracting capability of lithium ions in the resultant PCs. With the introduction of C9 resin in the pitches from 0 to 100 wt%, the microstructure of resulting PCs changes from a highly oriented lamellar texture to a fine-grained mosaic texture (i.e., from anisotropic soft carbon to isotropic hard carbon). In addition, the electrochemical performance (e.g., in the range of 200–370 mA h g−1 for the specific capacity) of the PCs varies according to the textural orientation, microcrystallite sizes and graphitization degrees. The relationship between preliminary microstructure and electrochemical performance of PCs with controllable microstructure and crystalline orientation has been studied to understand the importance of structure control. Furthermore, this work provides a new strategy to adjust the electrochemical performance of hybridized PCs through tailoring the liquid crystal development of texture-tunable pitch precursor synthesis.