Silicon Doping of High Voltage Spinel LiNi_0.5Mn_1.5O₄ towards Superior Electrochemical Performance of Lithium Ion Batteries

Si doping at high voltage spinel LiNi_0.5Mn_1.5O₄ are presented as an effective strategy to greatly increase the electrochemical performance. Well-crystallized LiNi_0.5Mn_1.5-xSi_xO₄ (x = 0.05, 0.10, 0.15, 0.20) with homogeneous Si distribution are successfully synthesized through solid-state reaction. Structural and electrochemical characteristics are investigated through FESEM, XRD, FTIR, Raman spectroscopy, cyclic voltammetry and galvanostatic charge/discharge testing. It can be demonstrated that Si doping significantly improves the electrochemical performance. LiNi_0.5Mn_1.35Si_0.15O₄ exhibits reversible capacities of 123 mAh/g after the 100th cycle at 0.5C and LiNi_0.5Mn_1.35Si_0.15O₄ as well as LiNi_0.5Mn_1.3Si_0.2O₄ show superior electrochemical stability over the pristine LiNi_0.5Mn_1.5O₄ material. Since the Si-O bond exhibits high dissociation energy of 798 kJ/mol (298 K), which is far beyond of the dissociation energies of the Mn-O or Ni-O bonds, the excellent electrochemical performance might be associated with an increased structural and chemical stability caused by incorporation of Si into the Oxygen-rich crystal lattice.