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Series Li1.2Ni0.2Mn0.6O2 (LNMO) cathode materials have been synthesized by an improved one-step solvothermal method. Structural characterization reveals that all samples are composed of layered and spinel phases and the spinel phase content can be easily tuned by Na-doping or reducing lithium in the LNMO materials. The spinel phase content increases from 2.6% for the x = 0.02 Na-doped sample to 9.2% for the deficient lithium sample. Electrochemical performance measurement shows that the electrochemical performance of the series samples is closely related to the spinel phase content. The deficient lithium sample with the largest spinel phase content has the most excellent cyclic and rate performance. The deficient lithium sample displays a high discharge capacity of 118.9 mAh g−1 at 5 C rate and much more stable capacity retention of 89.4% after 50 cycles at 0.1 C rate, whereas the corresponding values are 66.7, 27.4, and 2.7 mAh g−1 at 5 C rate and 69.4, 58.7, and 37.8% at 0.1 C rate for the Na-doped samples with x = 0, 0.01, and 0.02. The excellent cyclic and rate performance of the electrodes with higher spinel phase content originated from more 3D Li-ion diffusion channels in spinel framework and the relatively stable layered structure improved by an appropriate spinel phase integration. [ABSTRACT FROM AUTHOR]