[sup 6]Li and [sup 7]Li Magic-Angle Spinning Nuclear Magnetic Resonance and In Situ X-Ray Diffraction Studies of the Charging and Discharging of Li[sub x]Mn[sub 2]O[sub 4] at 4 V

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...

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“…This is in direct contrast to observations showing spinel structural changes for LiMn 2 O 4 cycled on the 4 V plateau 9 (see also Ref. 10).…”

Section: Resultscontrasting

confidence: 95%

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

Tucker

Reimer

Cairns

1999

Electrochem. Solid-State Lett.

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“…Upon the cathodic sweep (from 8.3 to 13.0 h corresponding to a voltage sweep from 4.5 to 3.5 V), the cubic III → II → I transitions occur and the peaks shift back to lower 2θ values. The behavior during delithiation and lithiation seen for the bare LMO is consistent with previous reports . Other persistent peaks include a polytetrafluoroethylene (PTFE) peak at 8.49°, conductive carbon (graphite) peak at 12.38°, and the strong cubic Au peak at 17.78° .…”

Section: Resultssupporting

confidence: 90%

Operando Observations and First‐Principles Calculations of Reduced Lithium Insertion in Au‐Coated LiMn₂O₄

Bassett

Warburton

Deshpande

et al. 2019

Adv Materials Inter

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The deposition of protective coatings on the spinel LiMn2O4 (LMO) lithium‐ion battery cathode is effective in reducing Mn dissolution from the electrode surface. Although protective coatings positively affect LMO cycle life, much remains to be understood regarding the interface formed between these coatings and LMO. Using operando powder X‐ray diffraction with Rietveld refinement, it is shown that, in comparison to bare LMO, the lattice parameter of a model Au‐coated LMO cathode is significantly reduced upon relithiation. Less charge passes through Au‐coated LMO in comparison to bare LMO, suggesting that the reduced lattice parameter is associated with decreased Li+ solubility in the Au‐coated LMO. Density functional theory calculations show that a more Li+‐deficient near‐surface is thermodynamically favorable in the presence of the Au coating, which may further stabilize these cathodes through suppressing formation of the Jahn–Teller distorted Li2Mn2O4 phase at the surface. Electronic structure and chemical bonding analyses show enhanced hybridization between Au and LMO for delithiated surfaces leading to partial oxidation of Au upon delithiation. This study suggests that, in addition to transition metal dissolution from electrode surfaces, protective coating design must also balance potential energy effects induced by charge transfer at the electrode‐coating interface.

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“…Careful electrochemical, X-ray and neutron diffraction studies have shown that the charge/discharge process occurs in three steps, hence up to three phases coexist in the 0 B x B 1 range [7][8][9]. The structure of Li 0.5 Mn 2 O 4 has been determined as belonging to the modulated R 3m space group, Z = 6, with the O 2- …”

Section: Introductionmentioning

confidence: 99%

A new method of pretreatment of lithium manganese spinels and high-rate electrochemical performance of Li[Li0.033Mn1.967]O4

Potapenko

Chernukhin

Kirillov

2014

Mater Renew Sustain Energy

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Lithium manganese spinels tend to aggregate upon annealing and do not allow for attaining high discharge rates when used as cathodes in lithium-ion batteries. To obtain spinel samples of lower aggregation and better highrate properties, precursors synthesized by means of a citric acid-aided route are suggested to be pyrolyzed in an inert atmosphere, instead of pyrolysis in air. The synthesis of nanosized Li[Li 0.033 Mn 1.967 ]O 4 is described, and its characteristics including X-ray diffraction, scanning electron microscopy, and porosity, as well as electrochemical test results are presented. The particle size of the materials obtained is smaller, the degree of aggregation is lower, and high-rate properties are better than for analogues pyrolyzed in air. In particular, sample Li||Li[Li 0.033 Mn 1.967 ]O 4 cells deliver *60 mAh g -1 at the current loads of 4,000 mA g -1

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[sup 6]Li and [sup 7]Li Magic-Angle Spinning Nuclear Magnetic Resonance and In Situ X-Ray Diffraction Studies of the Charging and Discharging of Li[sub x]Mn[sub 2]O[sub 4] at 4 V

Cited by 76 publications

References 47 publications

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

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

Operando Observations and First‐Principles Calculations of Reduced Lithium Insertion in Au‐Coated LiMn₂O₄

A new method of pretreatment of lithium manganese spinels and high-rate electrochemical performance of Li[Li0.033Mn1.967]O4

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[sup 6]Li and [sup 7]Li Magic-Angle Spinning Nuclear Magnetic Resonance and In Situ X-Ray Diffraction Studies of the Charging and Discharging of Li[sub x]Mn[sub 2]O[sub 4] at 4 V

Cited by 76 publications

References 47 publications

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

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

Operando Observations and First‐Principles Calculations of Reduced Lithium Insertion in Au‐Coated LiMn2O4

A new method of pretreatment of lithium manganese spinels and high-rate electrochemical performance of Li[Li0.033Mn1.967]O4

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Operando Observations and First‐Principles Calculations of Reduced Lithium Insertion in Au‐Coated LiMn₂O₄