Popcorn-Inspired Expanded Graphite Microspheres with Controlled Morphology and Considerable Conductivity

The structured processing of graphite is complex and challenging, in which expanded graphite plays a crucial role. Given its superior physical and chemical properties, expanded graphite finds extensive application in diverse domains such as electrochemistry and thermal management. However, the traditional preparation process is inconvenient in effectively meeting the design requirements on the macro and micro scales, which presents a challenge for the structured processing of expanded graphite materials. Here, an innovative method is first proposed for the controllable preparation of expanded graphite microspheres. Inspired by the explosion process of popcorn, the controlled gas release inside the natural flake graphite during chemical expansion is regulated by fuming sulfuric acid, realizing the controllable preparation of expanded graphite microspheres. Subsequently, sulfur trioxide can also intensify the degree of oxidation on the surface of the microspheres. The controllable microsphere morphology endows the composite with good isotropic network bonding, with considerable thermal conductivity of 1.703 W m^-1 K^-1 at low loading of 10 wt.% and reliable cyclic stability. This work opens up a new way for the morphology control of expanded graphite and provides a novel design thought for the physical and chemical structure control of carbon materials in the future.