The poor cycling stability and inferior rate capability of the cathodes critically restrict the application of sodium ion batteries (SIBs). Herein, we propose a strategy to optimize the electrochemical performances of P2- Na0.7Mn0.75Fe0.25-x- yNixCOyO2 cathode materials for SIBs through modulating the crystal structure with a synergistic substitution of Fe by Ni and Co. The structure-performance relationship and the synergistic improvement mechanism have been unraveled by means of x-ray diffraction, neutron diffraction and electrochemical techniques. The synergistic substitution of Fe by Ni and Co leads to the enlargement of the interlayer spacing and the Na-O bond length, and shrinks the TM-O and O-O bonds, which enhances the sodium ion diffusion coefficient, the rate capability and the cycling stability. In addition, JahneTeller effect is also alleviated owing to the reduction of Mn3+, which can further enhance the stability of the layered structure. Ni and Co co-doped Na0.7Mn0.75Fe0.15Ni0.05Co0.05O2 (FNC) cathode shows a relatively smooth charge- discharge curve in 1.5e4.2 V and demonstrates a much better rate performance in compared to Na0.7Mn0.75Fe0.25O2 (MF), Na0.7Mn0.75Fe0.15Ni0.1O2 (FN) and Na0.7Mn0.75Fe0.15Co0.1O2 (FC). At a high current density of 1C, 2C, 5C and 10C, FNC can still deliver a reversible capacity of 127, 109, 83 and 58 mAh g(-1), respectively. FNC also provides a higher reversible capacity of 181mAh g(-1) at 0.1C with a high cycling stability. This study offers some new insights into designing high performance cathode materials for SIBs through cooperatively modulating the crystal structure with multi-elements doping. (C) 2018 Elsevier Ltd. All rights reserved.