Direct ink writing of conductive materials for emerging energy storage systems

Direct ink writing (DIW) has recently emerged as an appealing method for designing and fabricating three-dimensional (3D) objects. Complex 3D structures can be built layer-by-layer via digitally controlled extrusion and deposition of aqueous-based colloidal pastes. The formulation of well-dispersed suspensions with specific rheological behaviors is a prerequisite for the use of this route. In this review article, the fundamental concepts of DIW are presented, including the operation principles and basic features. Typical strategies used for ink formulation are discussed with a focus on the most widely used electrode materials, including graphene, Mxenes, and carbon nanotubes. The recent progress in printing design of emerging energy storage systems, encompassing rechargeable batteries, supercapacitors, and hybrid capacitors, is summarized. Challenges and future perspectives are also covered to provide guidance for the future development of DIW.