Cathode of LiMg y Mn2 − y  O 4 and LiMg y Mn2 − y  O 4 − δ Spinel Phases for Lithium Secondary Batteries

Abstract

To improve the cycle performance of LiMn2O4 false(normalFdtrue3¯mfalse) as the cathode of 4 V class lithium secondary batteries, the cathode properties of the quaternary cubic spinel phases LiMgyMn2−yO4 synthesized at 750°C were examined. Although the cycle performance of the LiMgyMn2−yO4 was improved by the substitution of Mg2+ for Mn3+ in the octahedral sites, the first discharge capacity was reduced considerably compared with that of the parent LiMn2O4 . In order to compensate for the theoretical capacity reduction in LiMg1/6Mn11/6O4 , nonstoichiometric spinel oxides LiMg1/6Mn11/6O4−δ were prepared under controlled oxygen partial pressures at 750°C. The single‐phase region of δ in LiMg1/6Mn11/6O4−δ was 0 ≤ δ < 0.04, which was larger than that of parent LiMn2O4 (0 ≤ δ < 0.018) in our previous work. From density data, a metal excess model false(normalLi)8afalse[Liδ/false(4−δfalse)Mgδ/6false(4−δfalse)Mn11δ/6false(4−δfalse)]16cfalse[Mg1/6Mn11/6]16dO4 was proposed as the defect structure in the LiMg1/6Mn11/6O4−δ . The chemical diffusion coefficient of lithium ion for nonstoichiometric LiMg1/6Mn11/6O4−δ was smaller than that for the stoichiometric LiMg1/6Mn11/6O4 . This also supported the metal excess model, because excess metals in 16c sites prevented an easier diffusion of lithium in the 8a-16c-8a diffusion path. © 1999 The Electrochemical Society. All rights reserved.

Suppression of Jahn–Teller distortion by chromium and magnesium doping in spinel LiMn2O4: A first-principles study using GGA and GGA+U

“…It is therefore very important to stabilize the cubic spinel structure. Various divalent and trivalent ions, which make the structure more stable, have been tried as dopants by different groups [8][9][10]. Experimentally, among the various possible dopants chromium and magnesium have been studied extensively [9,10].…”

Graphene assisted template based LiMn2O4flexible cathode electrodes

“…Therefore, the amount of substituent ions within the spinel structure should be carefully adjusted in order to obtain higher specific capacities around the 4 V potential window. Several reports have also confirmed that substituting metal ions such as Cr, Co or Ni less than 0.2% will significantly improve the cyclability . Wu et al have reported that the substitution of Cr ions in LiMn 2‐x Cr x O 4 results in a conversion of Cr 3+ to Cr 6+ for x > 0.2.…”

“…Several reports have also confirmed that substituting metal ions such as Cr, Co or Ni less than 0.2% will significantly improve the cyclability. 16 Electron paramagnetic resonance and X-ray diffraction studies have shown that x Cr = 0.06 samples have significantly suppressed the Jahn-Teller distortion. The results clearly indicates that the increment above x Cr = 0.06 will decrease the first discharge capacity gradually since Cr ions will not oxidize around 4 V. 21 Moreover, surface coatings have been widely employed to prevent micro-strain during cycling and reduce capacity fading in LMO.…”

Er-Doped LiMn2O4

“…In addition, the Er ion has a larger bonding energy (615 kJ/mol) in ErO 6 octahedra compared to the Mn ion in MnO 6 octahedra (402 kJ/mol), which is another reason for the improved capacity retention of LiMn 2 − x Er x O 4 electrodes. Hayashi et al thought that the larger the bonding energy in the octahedral MO 6 sites, the smaller the lattice parameter of the spinel oxide [20]. Accordingly, the increase of the bonding energy for the Er-substituted spinel would cause a shrinkage of the lattice, which could stabilize the spinel LiMn 2 O 4 structure.…”