Solid-phase construction of high-performance sodium-ion battery cathode materials with three-dimensional porous structure: Na4MnCr(PO4)3/C

Na4MnCr(PO4)3 is a promising cathode material with high redox potential and high energy density, but the intrinsic poor electronic conductivity and substandard structural stability restrict its practical application. Herein, porous Na4MnCr(PO4)3/C with conductive networks and improved electrochemical properties is synthesized by a facile modified solid-state process using citric acid as a multifunctional additive. The results reveal that citric acid can be used as a grinding aid to make the raw materials mix more evenly and speed up the efficiency of ball milling. Besides, 3D conductive network and porous structure originated from polycondensation and carbonization of citric acid can promote the electrochemical properties of Na4MnCr(PO4)3/C by enhancing the electronic/ionic conductivity and (de)intercalation reaction kinetics. As expected, the optimal Na4MnCr(PO4)3/C delivers a high reversible capacity of 130.5 mAh g−1 at 0.1C rate, and exhibits a capacity retention of 82.62% at 10C rate after 500 cycles. In addition, the reversible biphasic reaction of the cathode is confirmed by the constant galvanostatic intermittent titration technique and ex-situ XRD, which shows great potential of the synthesized Na4MnCr(PO4)3/C for practical applications.