| Lithium-ion batteries （LIBs） have been used widely in portable electronic devices, owing to their excellent energy-storage performance. However, lithium is not available in the amounts necessary for meeting the increasing market demand. Thus, rechargeable batteries based on alternative, abundantly available materials need to be developed. Sodium-ion batteries （NIBs） are a promising alternative to LIBs for large-scale energy storage applications, because of the high availability of sodium, its low cost, and the similarity in the intercalation chemistry of sodium and lithium. In this thesis studies, two kinds of cathode materials O3-Na（NixFe1-2xMnx）O2 and P2-Na2/3(Ni1/3Mn2/3)1-xMgxO2 were synthesized and the morphology, structure and electrochemical performances of the two samples were investigated by scanning electron microscope, X-ray diffraction （XRD）, and charge-discharge test.Firstly, the dissertation emphasized on optimization research of synthesis process conditions, and the effect of pH value of sol solution and the amount of citric acid on the physical and electrochemical performance were studied. Under the above optimized conditions, the effect of the different molar ration of the transition metal Ni, Fe and Mn on the electrochemical performance were studied. Faced with the problem of unsatisfactory cycle performance caused by slab-gliding in O3 phase materials, the dissertation attempted to dope aluminum, titanium and magnesium elements into transition metal layers respectively to improve the electrochemical performance on the base of the optimal compositon material Na(Ni0.4Fe0.2Mn0.4)O2. The results showed that the magnesium-substituted sample Na(Ni0.35Fe0.2Mn0.4Mg0.05)O2 display the best electrochemical performance. It exhibited improved capacity retention and rate performance at the price of the initial reversible capacity. The initial discharge capacity was 125.6 mAh/g and the capacity retention was 91.3% after 50 cycles at the current density of 10 mA/g. Even at a high discharge rate of 1 C, it still delivered a discharge capacity of 90.1 mAh/g.P2-type Na-2/3(Ni1/3Mn2/3)1-xMgxO2 （x= 0,0.05,0.1） have been synthesized by a sol-gel method and for the first time developed as promising cathode materials for sodium-ion batteries. X-ray diffraction （XRD） results revealed that the partial substitution of (Ni1/3Mn2/3) with Mg has no obvious effect on the main structure of P2-Na2/3Ni1/3Mn2/3O2. Drastic capacity fade occurred for P2-Na2/3Ni1/3Mn2/3 cathode, while Mg substituted cathode Na2/3(Ni1/3Mn2/3)0.95Mg0.05O2 still show high capacity retention over 89% after 25 cycles at the voltage range of 2.0-4.2 V with an satisfactory initial discharge capacity of 127.2 mAh/g at 10 mA/g. Furthermore, Mg substituted cathodes exhibit small voltage fade, reaching 3.25 V after 25 cycles. Furthermore, EIS measurements demonstrated that Mg substituted is an effective way to reduce the electrochemical reaction impedance.
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