Nitrogen-doped porous carbon skeleton derived from glycine boosting superior rate capability and long lifespan for Na3V2(PO4)3 with high thermal safety

Abstract

Currently, the both low electronic and ionic conductivity have seriously hindered the further application of Na₃V₂(PO₄)₃ (NVP). Nevertheless, traditional carbon materials modification only improves the electronic conductive property, rather than modifying the ionic conductivity. Herein, N-rich carbon resources of glycine (GLY) is introduced to synthesize NVP, which can act as reducing agent and morphology inducer to optimize NVP sample. Notably, GLY supplies favorable N-doped carbon skeleton, and this defective carbon structure benefits for the accelerated electronic conductivity. Besides, porous construction is established after introducing GLY. This unique morphology significantly improves the infiltration effects of electrolyte, thus providing more electrochemical active sites for Na⁺ de-intercalation to improve the ionic conductivity. Meanwhile, porous framework supplies enough space for the shrinkage of crystal cells, so the stress-strain effect is highly restrained, which is demonstrated by Ex-situ XRD. The stabilized crystal and morphological structure of NVP@GLY-2 has been verified by after-cycled XRD/SEM/XPS. Highly improved kinetic characteristics are also investigated by In-situ EIS. Moreover, Accelerating Rate Calorimeter (ARC) measurements indicate that NVP@GLY-2-based half and full cells also have excellent thermal safety properties. Comprehensively, NVP@GLY-2 reveals a high capacity of 119 mAh g⁻¹ at 0.1 C. It reveals 84.5 and 71.2 mAh g⁻¹ at 10 and 50 C, with capacity retention rates of 88.9 % and 85.8 % after 1000 cycles.