A low-cost non-conjugated dicarboxylate coupled with reduced graphene oxide for stable sodium-organic batteries

Eco-efficient and renewable organic electrodes are considered to be a promising alternative for upcoming large-scale applications of low-cost energy storage systems. Here we report that cost-effective and green sodium humate (Na2HA) with non-conjugated carboxylate groups, can serve as a highly reversible anode material for sodium-organic batteries. Functionalized by reduced graphene oxide (rGO), the hybrid electrode delivers a highly reversible discharge capacity of 133 mAh g−1 at a current density of 500 mA g−1, achieving a capacity retention of 91.6% over 2000 cycles. The Na-cycling mechanism in Na2HA is proposed. Density functional theory calculations demonstrate that the low energy barriers for Na-ion insertion/extraction in Na2HA facilitate the charge transfer. Such findings may offer new possibilities for designing and enlarging eco-efficient and renewable organic compounds for sodium-organic batteries.