Dual-complexing agent dominated synthesis of carbon coated Na3V2(PO4)3 cathodes for high-performance sodium ion batteries

The currently prevailing single complexing agent-dominated sol-gel technologies for Na3V2(PO4)3 (NVP) cathodes in sodium-ion batteries (SIBs) always result in limited modification effects, especially in regards to the particle size of NVP and the quality of carbon coatings. Herein, we report a citric acid and glycine co-complexed strategy for fabricating carbon-coated NVP. It creates a favorable synergy for optimizing the microstructure and electrochemical performance of the NVP cathode. The introduction of glycine in citric acid not only decreases the solution viscosity for facilitated metal-ion diffusion, but also induces the self-construction of a 3D network through heteromolecular hydrogen bonds. The optimized carbon-coated NVP by co-complexing of citric acid and glycine (named as NVP/CG-5.0) presents distinctly decreased particle size, improved dispersity and moderate carbon coating thickness of ∼2 nm. It also features a large specific surface area of 44.4 m2 g−1 with rich mesopores. Impressively, the NVP/CG-5.0 electrode exhibits substantially improved electrochemical performance, such as the elevated specific capacity of 108.3 mAh g−1 with high initial Coulombic efficiency (95.2%), high capacity retention of 81.3% after 2000 cycles at 2 C and excellent rate performance (88.2 mAh g−1 at 20.0 C). Furthermore, the assembled NVP/CG-5.0║hard carbon full battery also exhibits superior electrochemical performance, suggesting the great potential of the co-complexed strategy for developing high-performance NVP cathodes in SIBs.