Undercooling-directed NaCl crystallization: an approach towards nanocavity-linked graphene networks for fast lithium and sodium storage

Despite the crystallization of inorganic salt is being technologically related to the fabrication of salt-templated materials, the two key steps, nucleation and crystal growth, still lack the kinetic control to enable precise design of salt scaffolds. Here, we study how the undercooling degree controls the construction of salt scaffolds by kinetically manipulating the nucleation and growth rates in a NaCl-F127-rhodanine system. An effective approach based on undercooling-directed NaCl crystallization is further proposed to tailor the morphology and structure of the carbon materials. Under different undercooling conditions (liquid nitrogen, -55 °C and -25 °C freezing), the salt scaffold can be tuned as spheroidal particles, ellipsoidal nanocrystal aggregates and cubic nanocrystals with round corners, respectively. Correspondingly, hollow carbon nanospheres, nanocavity-linked graphene networks (CGN) and graphene nanosheets (GNS) can be fabricated through a salt template method, respectively. The Li+ and Na+ storage mechanisms of 3D CGN and 2D GNS are discussed, focusing on the ion diffusion kinetics. The enhanced Li+ diffusion kinetics in the 3D interconnected network endows CGN with better rate performance than GNS as lithium-ion battery anode material, and Na+ adsorption dominates the Na+ storage in CGN as sodium-ion battery anode material. Our findings provide a general idea for the construction crystallization-induced architectures and offer valuable insights to achieve fast Li+/Na+ storage by boosting the ion diffusion kinetics.