Stabilizing NASICON-type Na4MnCr(PO4)3 by Ti-substitution toward a high-voltage cathode material for sodium ion batteries.

[Display omitted] • Na 3.4 Mn 0.7 Ti 0.3 Cr(PO 4) 3 /C cathode material is prepared by a simple sol–gel method. • Ti substitution shortens the average bond length of TM-O. • Ti substitution can suppress the Jahn-Teller effect of Na 4 MnCrPO 4 cathode material. • Ti substitution reduces the R ct of cathode and suppress interface side reactions. The sodium superionic conductor Na 4 MnCr(PO 4) 3 gains increasing attention owing to its three-dimensional structure and the three-electron reaction. However, rapid structure degradation during cycling is the major challenge for its practical application. Herein, Ti4+ is utilized to replace a portion of Mn2+ in Na 4 MnCr(PO 4) 3. The low redox voltage and d 0 electronic configuration of the Ti4+ ions are helpful to suppress the structure alteration and improve electronic conduction. Consequently, the as-prepared Na 3.4 Mn 0.7 Ti 0.3 Cr(PO 4) 3 /C cathode exhibits a remarkable good 91.0% capacity retention after 500 cycles at 10C rate, with exceptional rate capacities of 99.5 mAh g−1 and 81.0 mAh g−1 at 5C and 10C rate, respectively. Furthermore, based on ≈2.86-electron reactions involving Mn2+/Mn3+ (3.5 V), Mn3+/Mn4+ (4.1 V), Cr3+/Cr4+ (4.3 V), and Ti3+/Ti4+ (2.1 V), the material can provide an energy density of approximately 541.6 Wh kg−1, slightly surpassing that of Na 4 MnCr(PO 4) 3. Ex-situ XRD investigation further elucidates that throughout the entire charge–discharge process, the Ti-substituted material experiences highly reversible solid-solution and two-phase reactions. Additionally, Ti substitution can greatly promote the interfacial charge transfer of the material and suppress the decomposition of the electrolyte during cycling. This work might open a new insight for designing sodium-ion battery cathode materials with good cycling stability and high energy density. [ABSTRACT FROM AUTHOR]