Superior electrochemical performance of Li-rich layered cathode material with Li-rich spinel Li4Mn5O12 and MgF2 double surface modifications

Although the Li-rich layered material is one of the most potential cathode materials owing to its high capacity (>250 mAh g−1), low cost and less pollution, it still faces some problems to be solved, including low initial coulombic efficiency, poor cycling performance, and bad rate capability. In this work, Li-rich spinel Li4Mn5O12 and MgF2 are constructed on the surface of Li-rich layered material by simple liquid phase erosion and liquid phase deposition methods, respectively. The Li-rich spinel Li4Mn5O12 layer provides 3D Li-ion channels and it restrains the growth of the SEI film and oxygen release. The outermost amorphous MgF2 coating layer is also in favor of Li-ion migration and further protects Li4Mn5O12 from HF corrosion. It is found that double surface modifications induce phase transformation from the layered structure to the Li4Mn5O12-type spinel during cycling, which is different from the traditional structural transformation from the layered structure to the LiMn2O4 spinel-like and exhibits slower structural transformation. Benefiting from these collaborative contributions of Li4Mn5O12 and MgF2, the material shows superior electrochemical properties, including the high initial coulombic efficiency of 96.4%, excellent capacity retention of 80% after 300 cycles, the small voltage decay rate of 1.5 mV/cycle and remarkable rate capability.