Lamellar intercalated spherical Na3V2(PO4)3 with enlarged surface area induced by phenol-formaldehyde boosting high capacity and long lifespan for sodium ion batteries

To improve the inherent conductivity and extend the cycling durability of Na 3 V 2 (PO 4 ) 3 (NVP), this study suggests a technique for synthesis of phenol-formaldehyde (PF) resin-derived lamellar intercalated spherical NVP (PF-NVP/C) structures via solvothermal method. The unique lamellar intercalated sphere structure typically possesses good mechanical toughness, enabling better tolerance to the current impact. Moreover, spherical morphology features a significantly enlarged specific area of 144.32 m 2 g -1 , facilitating full contact between electrolyte and electrode, and providing additional active sites for Na + storage. Coupled with protective effect of carbon coating layers, the cycling stability is significantly improved. Meanwhile, highly conductive graphitized carbon skeleton from the pyrolysis of PF bonding with the uniform amorphous carbon layers constructs favourable networks for electronic transportation. Notably, the modified PF-NVP/C delivers a capacity of 115.5 mAh g -1 at 0.1 C. Remarkably, it can maintain a high capacity of 71.1 mAh g -1 and keeps 50.8 mAh g -1 even after 16000 cycles at 50 C, exhibiting outstanding cycling stability. Ex-situ XRD indicates the redox reaction of V 3+ /V 4+ is highly reversible. Furthermore, by comparing morphological and electrochemical kinetic characteristics of the PF-NVP/C before and after cycling, further evidence is provided to demonstrate its unique lamellar intercalated spherical morphology and excellent structural stability.