Co doping in NASICON-structured Na3.5MnTi(PO4)3 enables superior structural stabilization and rate performance

NASICON-type Na3MnTi(PO4)3 has been regarded as one of the most ideal cathodes due to its high earth content elements and considerable cycling stability. However, poor electrical conductivity, low redox potential of Ti3+/4+ and undesirable rate performance remain restrict its practical application. Herein, a series of Co-doping Na3.5MnTi1-xCox(PO4)3 (x = 0, 0.05, 0.07 and 0.10) cathode materials are designed via the sol-gel method. By partial substitution with Co, the capacity contribution of the Mn2+/3+and Mn3+/4+ is increased and the rate performance is significantly enhanced. The Na3.5MnTi0.93Co0.07(PO4)3 (NMTP-0.07) delivers a high capacity (150.5 mA h g−1 at 0.1 C), superior rate performance (112.0 mA h g−1 at 10 C) and excellent cycling performance (94.7 % capacity retention after 100 cycles at 1 C). Benefiting from Co doping, the EIS and GITT affirm the superior sodium ion diffusion ability of NMTP-0.07 and the enhancement of its own conductivity. Moreover, in situ XRD measurement validates the highly reversible structural evolution and both solid-solution reaction and two-phase reaction are involved in the sodiation/desodiation process. This contribution provides a new perspective on the doping studies of NASICON materials. [Display omitted]