Novel AlF3 surface modified spinel LiMn1.5Ni0.5O4 for lithium-ion batteries: performance characterization and mechanism exploration

• AlF3 is coated on the surface of LiMn1.5Ni0.5O4 via simple chemical deposition.
• AlF3 coating enhances the cycling and thermal stabilities of LiMn1.5Ni0.5O4.
• The optimum coating content of AlF3 is found to be 1 wt%.
• AlF3 coating can effectively suppress the undesirable growth of SEI layer.

Spinel LiMn1.5Ni0.5O4 (LMNO) cathode material synthesized by a sol-gel method is modified by different contents of AlF3 through simple chemical deposition. The effects of AlF3 coating on the structural and electrochemical properties of LMNO cathodes are investigated using X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). It is found that the AlF3 surface modification layers do not change the bulk structure of LMNO. Compared with the pristine sample, the AlF3-coated LMNO materials display enhanced cycling stabilities. Especially, the 1 wt% AlF3-coated LMNO demonstrates the best reversibility, with capacity retention of 93.6% after 50 cycles, much higher than that of the pristine material, 77.6%. EIS and FTIR data illustrate that the improvement of electrochemical performance can be attributed to the suppression of solid electrolyte interface (SEI) growth by AlF3 coating layer. DSC tests show that the AlF3 coating layer also helps in enhancing the thermal stability of LMNO cathode.