"Carbon in Metal" Anode with High Processability for Sodium Metal Batteries

Sodium metal batteries are ideal candidates for next-generation grid-level energy storage systems. However, severe obstacles pertain with regard to the usage of metallic Na, including poor processability, dendrite growth, and violent side reactions. Herein, we design a "carbon in metal" anode (denoted as CiM) via a facile method by rolling a controllable amount of mesoporous carbon powder into the Na metal. The as-designed composite anode is endowed with dramatically lowered stickiness and increased hardness (3 times higher than that of pure Na metal) and strength along with improved processability, which can be fabricated into foils with varied patterns and limited thickness (down to 100 μm). Besides, nitrogen-doped mesoporous carbon, which can increase the sodiophilicity, is applied to fabricate N-doped carbon in the metal anode (denoted as N-CiM), which can effectively facilitate the diffusion of Na⁺ ions and decrease the depositing overpotential, consequently homogenizing the Na⁺-ion flow and rendering a dense and flat Na deposition. Therefore, the N-CiM anode offers enhanced cycling stability for 800 h at 1 mAh cm^-2 in symmetric cells and 1000 cycles with a high average Coulomb efficiency (CE) (99.8%) in full cells based on the conventional carbonate electrolyte.