High‐Performance Sodium‐Ion Battery Anode via Rapid Microwave Carbonization of Natural Cellulose Nanofibers with Graphene Initiator

Cellulose is a promising natural bio-macromolecule due to its abundance, renewability and low cost. Here, a new method is developed to prepare pre-sodiated carbonaceous anodes for sodium-ion batteries (SIBs) from cellulose nanofibers (CNFs) under microwave irradiation for potential ultrafast and large-scale manufacturing. While direct carbonization of CNFs through microwave treatment is usually impossible due to the weak microwave absorption of CNFs, it is found that a small amount of reduced graphene oxide (rGO) can act as an effective initiator. Microwaving rGO releases extremely high energy, giving rise to local ultrahigh temperature as well as ultrahigh heating rate, which then induces the fast carbonization of CNFs and the production of pre-sodiated carbonaceous materials within seconds. The sodium in the carbonaceous materials, introduced from the carbonization of CNFs containing sodium-ion carboxyl, offer favorable spaces for sodiation/desodiation, which improves the electrochemical performance of the sodium-inserted carbonaceous anode. When the microwaved rGO-CNF (MrGO-CNF) is used as an anode for SIBs, a high initial capacity of 558 mAh g^-1 is delivered and the capacity of 340 mAh g^-1 remains after 200 cycles. The excellent reversible capacity and cycling stability indicate MrGO-CNF a promising anode for sodium-ion batteries.