Sulfonate Functionalized Turbostratic Carbon Derived from Borassus flabellifer Flower: A Ultrathin Protective Layer to Mitigate the Dendrite Formation on the Metallic Lithium Anode

Development of Li-metal batteries (LMBs) is hampered due to Li-dendritic growth leading to serious safety issues and low Coulombic efficiency. Borassus flabellifer (Asian Palmyra Palm Male Tree) inflorescence flower (BoFIF) is the most earth-abundant agricultural biomass containing a substantial amount of carbon upon pyrolysis. Herein, we extracted turbostratic-activated-carbon (TAC) from BoFIF, followed by sulfonate functionalization of mono- and disulfonic acid groups with TAC using different sulfonating agents, such as p-aminobenzenesulfonic acid (S-TAC-ASA), 2-aminobenzene-1,4-disulfonic acid (S-TAC-ADSA), p-toluene sulfonic acid (S-TAC-PTSA), and H2SO4 (S-TAC-H2SO4). The obtained S-TACs coated on Li-metal anode enables the mitigation of dendrite growth upon charge–discharge process. The results attributed that the high surface area provided by porous structured carbon can reduce local current density and reducing the volume expansion. S-TAC coating leads to improve in mechanical properties with increase in the Li-plating capacity and thus inhibit the growth of Li-dendrites. The fabricated Li/Li symmetric cell with S-TAC coated on Li-metal anodes exhibits drastic decrease in cell polarization of 56 mV at 1200 h at 2 mAcm–2 (without short circuit) for S-TAC-ADSA-coated Li-metal anode compared to uncoated Li-metal anode of 198 mV at 300h at the end of cell-lifetime. We also evaluated full-cell performance of S-TACs-coated Li-metal anode coupled with LiNi1/3Mn1/3Co1/3O2 cathode. Among them S-TAC-ADSA-coated Li-metal anode exhibits enhanced discharge capacity of 248 mAhg–1 with ∼35% increase in cycle stability compared to uncoated Li-metal anode with 196 mAhg–1 at 0.1 C-rate. The proposed sulfonate functionalization of carbon coating on Li-metal anode strategy provides new avenue to LMBs energy storage research.