Electrochemical properties of tetravalent Ti-doped spinel LiMn ₂O ₄

Ti-doped spinel LiMn ₂O ₄ is synthesized by solid-state reaction. The X-ray photoelectron spectroscopy and X-ray diffraction analysis indicate that the structure of the doped sample is Li(Mn ³⁺ Mn _1-x ⁴⁺ Ti _x ⁴⁺)O ₄. The first principle-based calculation shows that the lattice energy increases as Ti doping content increases, which indicates that Ti doping reinforces the stability of the spinel structure. The galvanostatic charge-discharge results show that the doped sample LiMn _1.97Ti _0.03O ₄ exhibits maximum discharge capacity of 135.7 mAhg ^-1 (C/2 rate). Moreover, after 70 cycles, the capacity retention of LiMn _1.97Ti _0.03O ₄ is 95.0% while the undoped sample LiMn ₂O ₄ shows only 84.6% retention under the same condition. Additionally, as charge-discharge rate increases to 12C, the doped sample delivers the capacity of 107 mAhg ^-1, which is much higher than that of the undoped sample of only 82 mAhg ^-1. The significantly enhanced capacity retention and rate capability are attributed to the more stable spinel structure, higher ion diffusion coefficient, and lower charge transfer resistance of the Ti-doped spinel.