Less energy-intensive synthesis of mesoporous multi-oriented graphite microspheres with low defect concentration for advanced potassium-ion battery anodes

Potassium-ion batteries (KIBs) have emerged as prospective alternatives to lithium-ion batteries (LIBs) given the wide availability of K resources and the similar operating voltage. As in the case of LIBs, graphite is regarded as the most promising anode material for KIBs due to high energy density attributed to its low potential plateau and resource abundance. However, the practical use of graphite in KIBs is hindered by poor stability due to huge volume changes during K+ ion insertion-deinsertion. Here, a facile and scalable synthesis method of mesoporous multi-oriented graphite microspheres via pilot-scale spray drying process and less energy-intensive graphitization step is introduced. A high degree of graphitization is achieved even at 1100 °C by virtue of in situ formed Fe nanocrystals within the microsphere that serve as graphitization catalyst. The degree of graphitization can be further improved by selective removal of amorphous carbon by oxidation at 450 °C, which greatly increases the initial Coulombic efficiency and reversible capacity of the graphite microspheres. The synthesized microspheres with the multi-oriented graphite grains and the mesoporous network enable rapid K+ ion insertion-deinsertion, and alleviate stress from volume changes during cycling, thereby exhibiting markedly improved cyclability (247 mA h g−1 after 400 cycles at 0.5C) and rate performance (58 mA h g−1 at 3C) that outperform those of commercial artificial graphite. This study provides a new perspective for designing reliable nanostructured graphite materials for advanced KIB anodes.