Thermal plasma synthesis and electrochemical properties of high-voltage LiNi0.5Mn1.5O4 nanoparticles

The synthesis of LiNi 0.5 Mn 1.5 O 4 has been reported to change the crystal structure with the oxygen partial pressure and affect the battery characteristics. LiNi 0.5 Mn 1.5 O 4 involves the formation of impurities, such as Li x Ni 1−x O, Li x Mn 3−x O 4 , and Li 2 CO 3 , at a high temperature range exceeding 700 °C because oxygen loss occurs during synthesis. LiNi 0.5 Mn 1.5 O 4 electrochemically contains Mn 4+ , however, Mn 3+ is formed because of oxygen deficiency. The Li–Ni–Mn-oxide causes a disproportionation of Mn 3+ in an oxygen-deficient state. The synthesized Li–Ni–Mn-oxide nanoparticles at 10,000 K by induction thermal plasma formed spinel-type LiNi 0.5 Mn 1.5 O 4 (space group Fd3m ) of Mn 4+ . The crystal structure of the cubic-spinel nanoparticles approached a LiNi 0.5 Mn 1.5 O 4 single phase as the flow rate of O 2 increased from 2.5 to 5 l min −1 . The formation of LiNi 0.5 Mn 1.5 O 4 was shown to be accelerated by increasing the O 2 gas flow rate. The measured current–voltage characteristics of LiNi 0.5 Mn 1.5 O 4 nanoparticles appeared at around 4.7–4.8 V as the reaction peak of Ni 2+ /Ni 3+ and Ni 3+ /Ni 4+ . In contrast, the Mn of the Li–Ni–Mn-oxide nanoparticles synthesized in the oxygen-deficient state was less than trivalent, which caused disproportionation of Mn. The measured current-voltage characteristics showed peak of an oxygen desorption at near 4.6 V. This study investigated the factors affecting the crystal structure formation and electrochemical properties of high-voltage LiNi 0.5 Mn 1.5 O 4 nanoparticles formed in thermal plasma.