Lianqi Zhang

Synthesis and electrochemical properties of layered Li–Ni–Mn–O compounds

Abstract An attempt to prepare solid solutions in the system of LiNiO 2 , LiMnO 2 and Li 2 MnO 3 was performed by heating metal acetates. The solid solutions between end members LiNiO 2 and Li 2 MnO 3 can be successfully prepared in the overall compositional ranges. Both the structure and capacity were compared based on Rietveld analysis and electrochemical investigation on solid solutions between LiNiO 2 and Li 2 MnO 3 . The result showed that the cationic disorder as well as capacity was closely related to the ratio of Li, Mn and Ni in formula. The investigation of chronopotentiogram and ex situ XRD on the solid solutions indicated that the complex phase transitions in LiNiO 2 during delithiation were strongly suppressed with low Mn content (Mn/(Mn+Ni) ratio was 0.1 or 0.2) and completely suppressed with the ratio more than 0.5.

Novel Layered Li ­ Cr ­ Ti ­ O Cathode Materials Related to the LiCrO2 ­ Li2TiO3 Solid Solution

The electrochemical properties of novel layered Li-Cr-Ti-O cathode materials related to the LiCrO 2 -Li 2 TiO 3 solid solution were described. These materials demonstrated that Cr 3+ /Cr 6+ is capable of reversibly cycling in a Li 2 TiO 3 -like framework. The sample with y = 0.5 (the content of Ti/(Ti + Cr) at starting compositions) was found to be the most promising cathode material in light of the high capacity and excellent cycling performance. It can deliver the discharge capacities of 202 and 173 mAh/g at 60°C and 30°C, respectively. Further characterizations on the sample, including chemical analysis, scanning electron microscopy, rate charge/discharge, quasi-open-circuit voltage, cyclic voltammetry, and ex situ X-ray diffraction and constant-capacity charge/ discharge tests were performed. The results showed that this material has a relatively slow kinetics of Li + diffusion and the original layered structure gradually changes to a disorder structure during cycling; furthermore, during the process two distinct phases with similar structure were observed.

Peculiar electrochemical behaviors of (1 − x)LiNiO2·xLi2TiO3 cathode materials prepared by spray drying

Abstract The cathode materials, (1−x)LiNiO2·xLi2TiO3 with 0.05≤x≤0.5, were first prepared by a spray drying route. The XRD results indicated that co-substituting Li and Ti for Ni in LiNiO2 contributes to increasing cations disorder in the materials. Charge–discharge tests in the voltage range of 3.0–4.4xa0V exhibited expected results: the more simple charge–discharge curves, the deceased capacity and the increased Columbic irreversibility with increasing x. However, when charged up to 4.8xa0V, the materials with x≥0.075 surprisingly presented unusual electrochemical properties, an excess charge capacity beyond the oxidization of Ni3+ to Ni4+ in materials with the presence of a charge plateau at about 4.5–4.7xa0V during the initial cycle. These phenomena are very similar to those reported in (1−y)LiNi0.5Mn0.5O2·yLi2MnO3 [J. Electrochem. Soc. 149 (2002) A815]. The sample with x=0.05 indicated promising electrochemical properties in term of capacity and cyclability even charged to 4.8xa0V.

Novel layered Li-Cr-Ti-O cathode materials for lithium rechargeable batteries

Abstract New cathode materials of Li–Cr–Ti–O compounds were synthesized using conventional solid-state reaction at different conditions in air. XRD patterns for these materials indicated that they are isostructure with Li 2 MnO 3 or Li 2 TiO 3 , which have a layered structure with a monoclinic symmetry (space group C2/m). The sample with the best electrochemical properties can deliver initial discharge capacities of 152 and 202 mAh/g for cycling between 2.0 and 4.8 V at a constant current density of 0.44 mA / cm 2 (32 mA/g) at room temperature (about 30 °C) and 60 °C, respectively. The excellent cycling performance was also observed, even at the elevated temperature. These materials demonstrated that Cr 3+ /Cr 6+ could reversibly cycle with a considerably high capacity in a Li 2 TiO 3 -like framework after a significant irreversible capacity loss during the initial cycle.