Synthesis of LiNi_0.5Mn_0.5-xTi_xO₂ by an Emulsion Drying Method and Effect of Ti on Structure and Electrochemical Properties

Abstract

Layered LiNi 0.5 Mn 0.5-x Ti x O 2 was prepared by an emulsion drying method. Solid solution of LiNi 0.5 Mn 0.5-x Ti x O 2 (R3 hm, space group) was formed to x e 0.3, and when x > 0.3, the layered structure transformed to the simple cubic structure. Rietveld refinement of X-ray diffraction data clearly showed that a small amount of Ti doping into LiNi 0.5 Mn 0.5 O 2 structure resulted in reduced cation mixing in the Li layer, and the stronger Ti-O bond relative to the Mn-O one would stabilize the crystal structure. Consequently, charge-discharge capacity and Li + chemical diffusion of Li/LiNi 0.5 Mn 0.5-x Ti x O 2 cells were enhanced by the improvement of physical properties in the oxide matrix. For a higher level of Ti doping, the obtained capacity decreased because a large amount of electro-inactive Ti 4+ (d 0 ) depressed the conduction of electrons in the oxide. The cyclability of Li/LiNi 0.5 Mn 0.5-x Ti x O 2 (x ) 0-0.3) cells was also dependent on the amount of Ti because of a different degree of cation mixing. In situ XRD observation confirmed that the variation in c-axis was different by increasing the Ti doping amount. That is, the Ti doping resulted in a smaller variation in the c-axis, which would be ascribed to the improvement of structural integrity by the stronger bond of Ti-O in the oxide matrix, compared to the Ti-free one. The Ti-doped LiNi 0.5 Mn 0.5-x Ti x O 2 materials also have good thermal safety characteristics at a highly oxidized state, as confirmed by differential scanning calorimetry.

Effect of Metal (Mn, Ti) Doping on NCA Cathode Materials for Lithium Ion Batteries

“…In particular, the (003) peak of NCAMn and NCA-Ti shifted slightly toward the lower-angle region (inset of Figure 2) because Mn 4+ and Ti 4+ ions were introduced into the octahedral lattice space occupied by the Li-ions to expand the Li layer spacing and, thereby, improve the lithium diffusion kinetics [22]. The variations in the lattice parameters were calculated by the Rietveld refinement method; the results are provided in Table 1 Table 1, the I (003) /I (104) diffraction peaks are higher for NCA-Ti, which could be greatly affected by the presence of Ti-metal ions in the lithium layer, thus leading to better electrochemical properties.…”

Particle size effect of Li[Ni0.5Mn0.5]O2 prepared by co-precipitation

“…For the Li[Ni 0.5 Mn 0.5 ]O 2 particle size of 3 m, it showed a good crystallinity with 8.3% of cation mixing confirmed by the Rietveld. The larger particles also showed the similar content of Ni 2+ in Li layer around 8.5% [14][15][16]. From those results, it is found that the difference in the particle size does not significantly change crystal structure.…”

Tartaric acid-assisted sol–gel synthesis of LiNi0.5Co0.5−Ti O2 (0 ⩽x⩽ 0.5) as cathode materials for lithium-ion batteries

“…As shown in Fig. 3b, the lattice constants, a and c, increase linearly with Ti replacement, suggesting that Ti was substituted for the Co obeyed the Vegard's law [38]. Usually, the ionic radius of Ti is larger than that of Ni and Co in the octahedral coordination structure.…”