Onset Mechanism of Jahn-Teller Distortion in 4 V LiMn[sub 2]O[sub 4] and Its Suppression by LiM[sub 0.05]Mn[sub 1.95]O[sub 4] (M = Co, Ni) Coating

Abstract

There have been several causes for the capacity fading of LiMn 2 O 4 reported by many authors, which include Mn dissolution into the electrolyte, and the onset of a Jahn-Teller distortion. One of the main remedies suggested to combat those causes has been doping with other transition-metal ions. However, most of the deterioration reactions take place on the LiMn 2 O 4 surface. In this study, LiMn 2 O 4 was coated with a doped-spinel oxide to combat the causes of capacity fading in LiMn 2 O 4 , which modifies only the surface of the electrodes, and its effect was diagnosed using the bending beam method ͑BBM͒. The doped-spinel coated LiMn 2 O 4 showed an excellent cycle performance. From the BBM data, it was confirmed that this excellent performance was largely due to the suppression of the Jahn-Teller distortion, which takes place at the end of the cathodic sweep in the 4 V range. Furthermore, the mechanism for the onset and suppression of Jahn-Teller distortion in 4 V LiMn 2 O 4 is proposed based on the strain variations of the stoichiometric, doped, and doped-spinel coated spinel electrodes.

Synthesis of a Co–Ni doped LiMn2O4 spinel cathode material for high-power Li-ion batteries by a sol–gel mediated solid-state route

“…Various mechanisms have been proposed to explain the capacity fading, including dissolution of Mn cations into electrolyte, Jahn-Teller distortion, and changes in crystallinity [5][6][7]. It was found that doping of metal ions, such as Al [8], Ni [9], Co [10], Cr [11] and Ti [12] ions, into LiMn 2 O 4 spinel can enhance its structural stability, consequently its cyclability can be apparently improved.…”

Suppression of Jahn–Teller distortion of spinel LiMn2O4 cathode

“…lattice would undoubtedly affect the three-dimensional Li + diffusion pathway, which results in the capacity fade of active materials [6]. Therefore, Jahn-Teller distortion is one of the most important causes of capacity fade of spinel LiMn 2 O 4 [7]. And this phase transition should be suppressed to obtain the excellent cycling performance of active materials.…”

Spectroscopic studies of the structural properties of Ni substituted spinel LiMn2O4

“…Many works have been done to study the relationships between the structural properties and electrochemical properties of LiNi x Mn 2 À x O 4 . Our recent work using in situ bending beam method has found that the Ni substitution suppressed the JahnTeller distortion of the [MnO 6 ] octahedron [14]. Wakihara et al [15], have studied the electrochemical and structural properties of Ni substituted LiMn 2 O 4 , and found the Ni substitution gave rise to a more stabled crystal structure than the non-substituted one.…”