Enhanced cycling stability and thermal stability of YPO4-coated LiMn2O4 cathode materials for lithium ion batteries

LiMn2O4 cathode materials synthesized by a sol-gel method are coated by YPO4 via wet coating strategy. The phase structures, components and morphologies of as-synthesized LiMn2O4 and YPO4-coated LiMn2O4 are characterized by X-ray diffraction, Raman spectroscopy and field emission scanning electron microscopy. The cycling performances are thoroughly investigated and compared at room temperature and 55 °C. The YPO4-coated LiMn2O4 displays much enhanced cycling properties than pristine LiMn2O4. The optimal coating amount is determined to be 3 wt.%. The 3 wt.% YPO4-coated LiMn2O4 exhibits capacity losses of only 15.9% after 200 cycles at room temperature and 19.7% after 100 cycles at 55 °C, much better than those of the pristine electrodes, 60% and 59.8%. Cyclic voltammetry confirms that YPO4 coating effectively improves the structure stability of spinel LiMn2O4. Electrochemical impedance spectroscopy data further demonstrates that YPO4 surface coating suppresses the undesirable growth of thick SEI (solid electrolyte interfacial) layer. Differential scanning calorimetry tests show that the existence of YPO4 helps to enhance the thermal stability of LiMn2O4 cathode.