Solvent‐Free Synthesis of Polymer Spheres and the Activation to Porous Carbon Spheres for Advanced Aluminum‐Ion Hybrid Capacitors

Porous carbon spheres (PCSs) characteristic of perfect symmetry and ideal rheological property have great potential in electrochemical energy storage (EES). However, conventional synthesis of PCSs heavily relies on solution-based methods that may lead to environmental issues. Herein, an environment-friendly solvent-free method toward the facile and mass production of m-phenylenediamine-formaldehyde (MPF) resin spheres, which can be converted into PCSs after carbonization and activation is reported. An ultrahigh productivity of 25.89 g in a 100-mL container and an impressive percent yield of 98.89% can be achieved for the MPF resin spheres, which are further converted into carbon spheres with a reasonable yield of 14.5% after carbonization. When employed as the cathode material for aluminum-ion hybrid capacitors, the obtained PCSs afford a double-layer capacity of ≈200 mAh g-1 , the highest value among reported porous carbon materials for Al-based EES devices. It is anticipated that the solvent-free synthesis method for PCSs developed here may play a significant role in other EES devices, such as magnesium-ion and calcium-ion hybrid capacitors.