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: bwkang@postech.ac.kr

Received 19 March 2015; Revised 27 May 2015; Accepted 23 June 2015

Abstract

Electrochemical activity in high-voltage spinel LiNi_0.5Mn_1.5O₄ (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.