Synthesis of LiNi 1/3Co 1/3Mn 1/3O 2 cathode materials by using a supercritical water method in a batch reactor

Abstract

LiNi 1/3Co 1/3Mn 1/3O 2 and LiCoO 2 cathode materials were synthesized by using a supercritical water (SCW) method with a metal salt solution in a batch reactor. Stoichiometric LiNi 1/3Co 1/3Mn 1/3O 2 was successfully synthesized in a 10-min reaction without calcination, while overlithiated LiCoO 2 (Li 1.15CoO 2) was synthesized using the batch SCW method. The physical properties and electrochemical performances of LiNi 1/3Co 1/3Mn 1/3O 2 were compared to those of Li 1.15CoO 2 by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and charge/discharge cycling tests. The XRD pattern of LiNi 1/3Co 1/3Mn 1/3O 2 was found to be similar to that of Li 1.15CoO 2, showing clear splitting of the (0 0 6)/(1 0 2) and (1 0 8)/(1 1 0) peak pairs as particular characteristics of the layered structure. In addition, both cathode powders showed good crystallinity and phase purity, even though a short reaction time without calcination was applied to the SCW method. The initial specific discharge capacities of the Li 1.15CoO 2 and LiNi 1/3Co 1/3Mn 1/3O 2 powders at a current density of 0.24 mA/cm 2 in 2.5–4.5 V were 149 and 180 mAh/g, and their irreversible capacity loss was 20 and 17 mAh/g, respectively. The discharge capacities of the Li 1.15CoO 2 and LiNi 1/3Co 1/3Mn 1/3O 2 powders decreased with cycling and remained at 108 and 154 mAh/g after 30 cycles, which are 79% and 89% of the initial capacities. Compared to the overlithiated LiCoO 2 cathode powders, the LiNi 1/3Co 1/3Mn 1/3O 2 cathode powders synthesized by SCW method had better electrochemical performances.