Biomass carbon-reinforced zinc-based composite oxide as an anode for superior sodium storage

The pursuit of high-abundance, cost-effective sodium-ion batteries represents a longstanding and valuable objective in the field. However, significant challenges remain in the quest for breakthroughs, particularly in the discovery of high-performance anode materials and a deeper understanding of the sodium storage mechanism. In this study, we present novel insights into the sodium storage properties of biomass carbon-reinforced Zn2P2O7 (Zn2P2O7/C-c) synthesized via a hydrothermal method followed by annealing, marking the first report of its kind. The unique loose porous structure of the Zn2P2O7/C-c composite offers multiple advantages. It facilitates efficient electrolyte infiltration, enhances the diffusion pathways for sodium ions, expedites electron transfer, and crucially, promotes the retention of Zn2P2O7 on the carbon substrate, even under conditions of mechanical stress or pulverization. Consequently, the Zn2P2O7/C-c composite demonstrates significantly improved rate capability, exhibiting specific capacities of 276.11, 234.41, 195.28, and 149.56mAh g-1 at current densities of 0.2, 0.5, 1, and 2Ag-1, respectively. Furthermore, it exhibits exceptional cyclic stability with a capacity retention rate of 71% after 1000 charge-discharge cycles at 1Ag-1. In-depth in-situ/ex-situ characterization techniques confirm that the sodium storage mechanism involves a conversion reaction between Zn2P2O7 and Zn, as well as an alloying reaction between Zn and ZnNa13. Kinetic analysis underscores the predominant role of pseudocapacitance in facilitating sodium storage, particularly at high charge-discharge rates. These findings offer valuable insights and inspiration for the exploration of high-performance Zn2P2O7-based anode materials for sodium-ion batteries, representing a significant step toward the realization of cost-effective and efficient sodium-ion battery technology in the future.