Improved electrochemical performance of 5 V spinel LiNi0.5Mn1.5O4 microspheres by F-doping and Li4SiO4 coating

Porous spinel LiNi0.5Mn1.5O4 microspheres were synthesized by a co-precipitation method. F-doping and Li4SiO4-coating were used as two effective ways to enhance the electrochemical performance of LiNi0.5Mn1.5O4 at both room temperature and elevated temperature. All the samples were characterized by thermogravimetric analysis/differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD), inductive coupled plasma-atomic emission spectroscopy (ICP-AES), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical tests, respectively. According to the SEM images, the LiNi0.5Mn1.5O4 microspheres are hollow with porous shell, and each microsphere is made up of nano-sized spinel grains. This hollow and porous structure favors the sufficient contact between electrolyte and the cathode material. It is indicated that 2 wt.% Li4SiO4-coated LiNi0.5Mn1.5O3.98F0.02 exhibits more superior performance than the pristine one. The doped fluorine ions that enhance the bonding can stabilize the structure of cathode material. The Li4SiO4 coating can suppress side reactions between electrolyte and cathode material as a protective material, and it is a superionic conductor with a three-dimensional lithium ion transfer network to decrease the charge-transfer resistance. The discharge capacity retention of 2 wt.% Li4SiO4-coated LiNi0.5Mn1.5O3.98F0.02 is 97.8% at 25 °C and 94.2% at 55 °C after 150 cycles, respectively.