A [sup 7]Li NMR Study of Lithium Insertion into Lithium Manganese Oxide Spinel

Abstract

7 Li magic angle spinning nuclear magnetic resonance was used to observe coexisting cubic and tetragonal phases in Li 1+x Mn 2 O 4 . Cubic phase peaks are observed at 500-580 ppm vs. 1 M LiCl(aq); tetragonal phase peaks are observed around 100 ppm. Cycling Li 1+x Mn 2 O 4 on the 3 V plateau does not result in significant changes in the cubic phase. A small amount of residual tetragonal phase accounting for ~3% of the 7 Li NMR intensity, however, is observed in spinel deep discharged to x = 1 then returned to x = 0.Lithium manganese oxide spinel has been studied extensively for use as a positive electrode material in lithium rechargeable batteries. LiMn 2 O 4 is an inexpensive and environmentally benign alternative to positive electrode materials based on nickel and cobalt oxides. Starting at LiMn 2 O 4 composition, lithium ions can be extracted at 4 V or inserted at 3 V vs. lithium metal. Insertion of lithium ions on the 3 V plateau (up to Li 2 Mn 2 O 4 ) is accompanied by a cubic-totetragonal (c/a = 1.16) distortion resulting from the dynamic JahnTeller effect. This effect originates at the Mn 3+ ion when the average Mn oxidation state is below 3.5. 1,2 The volume expansion accompanying the distortion is partly responsible for the rapid capacity fade observed upon repeated 3 V cycling. 3 Limiting electrochemical cycling to the 4 V plateau is generally believed to avoid bulk JahnTeller transformation, but fast discharge rates can lead to surface overlithiation and tetragonal distortion at the end-of-discharge on the 4 V plateau. 4 Understanding the effect of the Jahn-Teller distortion on spinel electrochemistry is therefore required for informed discussion of cycling behavior in any potential range. The present work attempts to observe directly lithium in the cubic and tetragonal phases in unsubstituted Li 1+x Mn 2 O 4 (0 < x < 1) utilizing 7 Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. For clarity of interpretation, the present work is limited to unsubstituted LiMn 2 O 4 , because interpretation of the 7 Li NMR spectrum is considerably more complicated when other metals, including lithium, are substituted for manganese. Experimental LiMn 2 O 4 was prepared from a stoichiometric mixture of Li 2 CO 3 (J.T. Baker) and MnO 2 (Japan Metals). The mixture was fired at 850°C in flowing oxygen for 20 h with one intermediate grinding, and then cooled at 50°C/h. The spinel was characterized by X-ray diffraction (XRD) on a Siemens D5000 diffractometer using Cu Kα 1 radiation (Fig. 1). Particle size distribution was measured with a Coulter LS230 laser diffraction particle size analyzer. Electrodes were prepared by dispersing spinel, acetylene black (Shawinigan), graphite (Timcal), and poly(vinylidene fluoride) (PVDF, Elf Atochem) (90:2:4:4) in n-methyl pyrrolidinone (NMP, Aldrich). The dispersion was cast onto stainless steel foil and dried at 150°C for 40 min, resulting in a final electrode thickness of ~250 µm. This yields sufficient material for the NMR experiment. Electrodes were punched o...

Numerical Simulation of Stress Evolution in Lithium Manganese Dioxide Particles due to Coupled Phase Transition and Intercalation

“…Many materials undergo large volume changes during intercalation and deintercalation of lithium ions into electrode materials, [1][2][3] and fractures on electrode material have been reported in several compounds, including graphite, 4,5 LiCoO 2 , 6 LiMn 2 O 4 , [7][8][9][10][11][12] and LiFePO 4 . 13,14 Fragmentation of LiMn 2 O 4 particles during lithium insertion/deinsertion has been observed via various experimental techniques, including X-ray diffraction ͑XRD͒, 9 scanning electron microscopy ͑SEM͒, 7 tunneling electron microscopy ͑TEM͒, 9 NMR spectroscopy, 8,12 and acoustic emission spectroscopy ͑AES͒. 10,11 In Li x Mn 2 O 4 spinel systems, lithium is inserted into and extracted from the interstitial sites in the host Mn 2 O 4 framework when 0 Ͻ x Ͻ 1.…”

Multi-Scale Characterization Studies of Aged Li-Ion Large Format Cells for Improved Performance: An Overview

“…An isotropic 7 Li peak is observed in C0 while similar speak is absent in C6. 69 ides such as LiCoO 2 and LiNiO 2 have been studied by Dahn et al, 215 Marichal et al, 216 Levasseur et al, 217 and Carlier et al 218,219 The spinel structured materials, such as LiMn 2 O 4 , have been studied by Morgan et al, 220 Gee et al, 221 Lee et al, 222,223 Lee and Gray, 224 Tucker et al, 225 and Verhoeven et al 226 The spinel structured materials, such as LiFePO 4 , have also been studied by Gaubicher et al, 227 Tucker et al, 213,225,228 and Arrabito et al 229 The goal in these studies has been to understand and predict the effect of local and electronic structure on lithium NMR shift in these battery materials. In situ NMR studies using a toroid detector with limited resolution have also been conducted by Gerald et al 230 Chevallier et al 231 have also shown that NMR signals from plastic bag batteries can be successfully obtained for analysis.…”

Modeling and Simulation of Lithium-Ion Batteries from a Systems Engineering Perspective

“…27,56,57 Since lithium diffuses within the particle, the expansion and contraction of the material will not happen uniformly across the particle (i.e., the outer regions of the particle will expand first due to lithium intercalating there first). This spatial nonuniformity causes stress to be induced in the particle and may lead to fracture and loss of active material, 58,59 which is one of the mechanisms for capacity fade. Various models have been developed to examine the volume change and stress induced by lithium-ion intercalation for single particles.…”