Spray-drying synthesis of high-performance Na4MnCr(PO4)3 for sodium-ion batteries via a CNT-induced conductive network and optimized interface kinetics†

The high-voltage advantage enabled by activating the multi-electron reaction of manganese can effectively compensate for the low energy density caused by the large molecular weight of polyanionic cathode materials. However, such materials frequently demonstrate inadequate electrochemical response due to their inherently poor electrical conductivity. In this work, carbon nanotube (CNT)-modified Na₄MnCr(PO₄)₃/C (NMCP/C) cathode materials were produced through an efficient and scalable spray-drying method. The introduction of highly conductive CNTs constructs an efficient electron-conducting network, significantly reducing the charge transfer resistance (R_ct) and enhancing the Na⁺ transport kinetics at the electrode interface. In addition, the surface/near-surface dominated reaction mechanism compensates for sluggish bulk-phase diffusion limitations while promoting the generation of a robust SEI interphase throughout battery operation. Such multiscale synergistic effects impart superior rate capability and prolonged cycling performance to the NMCP/C/10CNT composite. Specifically, it delivers discharge capacities of 108.7, 102, 93.7, 82.7, 69.4, and 58.9 mA h g⁻¹ at 50, 100, 200, 500, 1000, and 1500 mA g⁻¹, respectively, and maintains ∼70% capacity retention over 1500 cycles at 1000 mA g⁻¹. This work not only advances fabrication strategies of Na₄MnCr(PO₄)₃-based electrodes but also elucidates fundamental principles for engineering composite electrodes through optimized conductive frameworks and regulated interfacial dynamics.