Tartaric acid-assisted sol–gel synthesis of LiNi0.5Co0.5−xTixO2 (0 ⩽ x ⩽ 0.5) as cathode materials for lithium-ion batteries

A series of LiNi0.5Co0.5−xTixO2 (0 ⩽ x ⩽ 0.5) are prepared by a tartaric acid-assisted sol–gel technique. The phase formation process is observed by TG–DTA. It is found that the target product appears at a temperature higher than 400 °C and completes to phase formation at 700 °C. The crystal structure and morphology are characterized by XRD, SEM and Raman spectroscopy. XRD patterns show that the as-prepared sample transforms from hexagonal structure into cubic structure with the increase of Ti content in LiNi0.5Co0.5−xTixO2. Raman spectra also demonstrate the successive substitution of Ti for Co in the structure with band blue-shift phenomenon. SEM images confirm that the as-prepared sample exhibits narrow and regular particles with the size between 0.5 and 1.5 μm. The apparent particle size of sample starts to decrease with x ⩽ 0.1, and the gradually increases by introducing Ti dopant with higher content (x ⩾ 0.15). The electrochemical behavior of the sample displays different characteristics after Ti substitution. It is found that the initial working potential increases with the increase of Ti doping content. As a result, the initial lithium storage capacity for trace Ti-doped sample is higher than that delivered by the pristine one. The decrease of reversible capacity for high degree Ti-doped sample is ascribed to the electrochemical inactivity of the cubic compound in the sample. Therefore, trace Ti doping is beneficial to achieve promising cathode material for lithium-ion batteries.