Enhancing the Rate Capability and Cycling Stability of Na4MnV(PO4)3/C Composite Cathodes via in Situ Carbon Dots Formation for Sodium-Ion Batteries

Abstract

NASICON-structured Na4MnV(PO4)(3) (NMVP) has attracted considerable interest due to its notable characteristics, including a high theoretical capacity of 110 mAh/g, good ionic conductivity, and structural stability. NMVP, achieved through suitable manganese (Mn) substitution for vanadium(V), not only exhibits reduced toxicity but also minimizes the use of expensive V. However, NMVP suffers from low electronic conductivity, leading to unsatisfactory rate and cycle performance. In this work, we address a critical limitation by employing two key strategies: carbon coating and morphology control. NMVP/C-Carbon dots (NMVP/C-CDs) were prepared via a scalable spray-drying method to control morphology, utilizing citric acid (C) and activated carbon derived from coconut shell chars (AC) as carbon sources. Notably, our process enables the in situ formation of CDs from AC, significantly enhancing the material's conductivity. Compared to NMVP/C, NMVP/C-CDs exhibited outstanding rate performance, especially at high C-rates. It also demonstrated excellent cycling stability, retaining 81.1% of its capacity at a 1 C rate over 1000 cycles. CDs serve as a conductive carbon source, improving electron transport and strengthening the structural integrity of the carbon matrix. These findings highlight NMVP/C-CDs as a promising cathode material for sodium-ion batteries (SIBs), effectively addressing the challenge of poor electronic conductivity through the incorporation of CDs and providing a practical and scalable solution with a strong potential for large-scale commercialization.