Structural Fatigue in Spinel Electrodes in High Voltage (4 V) Li/Li[sub x]Mn[sub 2]O[sub 4] Cells

Abstract

Evidence of structural fatigue has been detected at the surface of discharged Li x [Mn 2 ]O 4 spinel electrodes in (4 V) Li/Li x [Mn 2 ]O 4 cells. Under nonequilibrium conditions, domains of tetragonal Li 2 [Mn 2 ]O 4 coexist with cubic Li[Mn 2 ]O 4 , even at 500 mV above the thermodynamic voltage expected for the onset of the tetragonal phase. The presence of Li 2 [Mn 2 ]O 4 on the particle surface may contribute to some of the capacity fade observed during cycling of Li/Li x [Mn 2 ]O 4 cells.The exponential growth in the electronics industry has led to an increasing demand for lightweight power sources with high energy density and power capability. 1,2 This demand has been satisfied largely by the advent of rechargeable lithium-ion batteries. The bestknown system is Li x C/LiCoO 2 . Because of the relatively high cost of cobalt, a major international effort is underway to develop alternative positive electrodes, for example, those derived from the spinel Li[Mn 2 ]O 4 . 3-5 A disadvantage of Li[Mn 2 ]O 4 spinel electrodes is that they lose capacity during cycling, which limits the life of the cell. [5][6][7][8][9][10][11] The capacity loss is particularly noticeable at 50°C, a typical temperature that can be reached in devices such as laptop computers. Recent reports have attributed the capacity fade to an unstable electrode surface and to solubility effects at the top of charge. [6][7][8][9][10][11] It is well known that the cycle life of lithium-ion cells depends critically on the structural integrity of the host electrode structures during charge and discharge. 12 In the Li x [Mn 2 ]O 4 spinel system (0< x <2), the [Mn 2 ]O 4 spinel framework provides a three-dimensional interstitial space for lithium-ion transport. Lithium extraction from Li x [Mn 2 ]O 4 (i.e., for 0< x <1) occurs at 4 V vs. metallic lithium. The electrode cycles well over this range because the cubic structure (space group Fd3m) expands and contracts isotropically during lithium insertion and extraction. [3][4][5]12 For 1< x <2, lithium is inserted electrochemically into the spinel structure in a two-phase reaction process at a constant voltage; the open-circuit voltage for this reaction is 2.96 V. 13 This two-phase reaction is associated with the onset of an anisotropic (Jahn-Teller) distortion. As a result, the cubic symmetry of Li[Mn 2 ]O 4 , in which the lithium ions occupy tetrahedral sites, is reduced to tetragonal Li 2 [Mn 2 ]O 4 (space group F4 1 /ddm), in which the lithium ions occupy octahedral sites in an ordered rocksalt structure. [13][14][15] This crystallographic distortion, which results in a 16% increase in the c/a ratio of the unit cell parameters, is too severe for the electrode to maintain its structural integrity during cycling. Consequently, a Li x [Mn 2 ]O 4 spinel electrode cycles poorly over the range 1< x <2, and the cell suffers a capacity loss. It is, therefore, understandable from a structural viewpoint that for good cycle life, the composition of the Li x [Mn 2 ]O 4 spinel electrode must be kept within the limi...

Spinel LiNixMn2−xO4 as cathode material for aqueous rechargeable lithium batteries

“…The anodic and cathodic peaks correspond to lithium de-intercalation and intercalation. The splitting of the redox peaks into two couples shows, that the electrochemical reaction of the de-intercalation and intercalation of Li + ions consists of two processes, which is consistent with the results in both organic and aqueous electrolytes [2,5,6,12,19,24,33,34]. At the low scan rate, two separate couples of redox peaks can be observed for all electrodes.…”

“…At the relative high current densities of 1500 and 1 ISE Member * Correspondence, wuyp@fudan.edu.cn (Wu), jiazhao@uow.edu.au (Wang) 4 due the instability of the spinel structure and the dissolution of manganese into the electrolyte solution during cycling [11,12]. As a result, the urgent environmental and economic problems unceasingly promote the further development of safer, less expensive and greener battery materials and devices.…”

Electrode Property of Spinel-type LiNi_0.5Mn_1.5−<i>_x</i>Ti<i>_x</i>O₄ (0 ≤ <i>x</i> ≤ 1.5) Prepared by Electrostatic Spray Deposition

“…LiMn 2 O 4 is well known to exhibit three-dimensional diffusion paths of lithium ions and a high energy density. Its cyclic performance, however, is seriously degraded by Mn dissolution 2,3) and Jahn-Teller distortion 4,5) . As a workaround, oxides partly substituted with other transition metal ions have been prepared to improve the problem.…”

Electrochemical Performance of Carbon Coated LiMn2O4Nanoparticles using a New Carbon Source

“…Recently, manganese-based spinels (LiMn 2 O 4 ) received attention because of their low cost and safety advantages [13][14][15][16]. However, there are still several issues that need to overcome, such as an insufficient rate capability due to low electronic conductivity and an unstable cyclic performance attributed to surface and structural instabilities [17][18][19][20][21]. Carbon coating is a possible approach to improve the electrochemical performance of LiMn 2 O 4 .…”