High electrochemical performance of high-voltage LiNi0.5Mn1.5O4 by decoupling the Ni/Mn disordering from the presence of Mn3+ ions

Abstract

Electrochemical activity in high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is strongly affected by the disordering of Ni/Mn and the presence of Mn3+ ions. However, understanding the effect of the Ni/Mn disordering or the presence of Mn3+ ions on electrochemical properties is not trivial because disordering is typically coupled with the presence of Mn3+ ions. Here, we demonstrate for the first time that the doping of Li instead of Ni increases Ni/Mn disordering, which is decoupled from the presence of Mn3+ ions. The resultant material has a particle size of ~1–2 μm and can achieve 120 mAh g−1 at 10 C for 50 cycles and further deliver about 60 mAh g−1 even at a rate of ~60 C (1 min discharge). Superior electrochemical performance is achieved by increased solid-solution phase transition behavior, which is caused by increased Ni/Mn disordering during delithiation. By decoupling, we find that the electrochemical properties in LNMO strongly depend on the phase transformation behavior and that the Ni/Mn disordering, rather than Mn3+ ions, affects the phase transformation by increasing the solid-solution reaction. The fundamental understanding gained from this work could be applied to the development of other phase-separating compounds to improve their electrochemical performance. Doping LiNi0.5Mn1.5O4 (LNMO) with Li instead of Ni significantly improves its electrochemical performance, find scientists in Korea. Cathode materials with high redox potentials are needed to realize lithium-ion batteries with high energy densities. The high-voltage spinel LNMO is a promising cathode material, but its electrochemical performance is strongly affected by the disordering of Ni/Mn in the presence of Mn3+ ions. Now, Junghwa Lee, Chaeah Kim and Byoungwoo Kang at Pohang University of Science and Technology in Korea have found that doping LNMO with Li decouples Ni/Mn disordering from the presence of Mn3+ ions. This significantly improves its electrochemical performance through enhanced solid-solution phase transition. The researchers anticipate that the results of the current study can be used to improve the electrochemical performance of other phase-separating compounds. We at the first time demonstrate that the Ni/Mn disordering in LNMO spinel is decoupled from the presence of Mn3+ ions by doping Li and strongly affects phase transformation resulting in the increase of solid-solution phase transformation. The resulting material with 1–2 μm achieves superior rate capability, 120 mAh g−1 at ~38 C and 60 mAh g−1 at 60 C.