1Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Korea
Correspondence: Professor B Kang, Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), 77 Cheongam-Ro, Nam-Gu, Pohang 790-784, Korea. E-mail: firstname.lastname@example.org
Received 19 March 2015; Revised 27 May 2015; Accepted 23 June 2015
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 ~1–2μm and can achieve 120mAhg−1 at 10C for 50 cycles and further deliver about 60mAhg−1 even at a rate of ~60C (1min 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.