Temperature-controlled direct dry synthesis of Co-Ni free cathode materials 0.7Li2MnO3·0.3LiFeO2 for lithium-ion batteries

Cobalt-nickel (Co-Ni) free Lithium-rich cathode material (1 − x)Li2MnO3·xLiFeO2 is more environmental friendly and cheaper than other traditional cathode materials. However, the complex synthesis method limits its large-scale practical application. This work explores a simple dry synthesis route to directly obtain 0.7Li2MnO3·0.3LiFeO2 with good electrochemical performance. Calcination temperature is a key factor controlling the phase growth. With the calcination temperature increasing, the crystallization and ordered layered structure are improved, but the LiFe5O8 spinel phase appears in X-ray diffraction (XRD) patterns from 600 ℃. The results of selected area electron diffraction (SAED), element mapping (EDS) and vibrating sample magnetometer (VSM) demonstrate convincingly the growth progress of LiFe5O8 as the temperature rises. The spinel phase deteriorates the electrochemical performance. Furthermore, it is proved that the crystallization and activity of Li2MnO3 precursor are effective to retard the formation of LiFe5O8 and enhance the electrochemical performance. The sample calcined at 600 ℃ exhibits a high initial capacity above 200 mAh g−1, but capacity fades quickly to 120 mAh g−1 after 50 cycles at 0.2 C. The sample calcined at 650 ℃ with a little LiFe5O8 delivers a low initial capacity about 160 mAh g−1, but stabilizes at 160 mAh g−1 after 50 cycles. Therefore, how to control the formation of thermally stable phase LiFe5O8 is an important issue, and it needs further investigation to achieve Co-Ni free Li-rich cathode materials with excellent performance. Significantly, the simple synthesis and acceptable electrochemical properties make the practical application of Fe-Mn based Li-rich material possible.