Self‐Discharge of LiMn2 O 4/C Li‐Ion Cells in Their Discharged State: Understanding by Means of Three‐Electrode Measurements

The performance degradation of graphite/LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC) lithium ion cells, charged and discharged up to 300 cycles at different operating conditions of temperature and upper cutoff potential (4.2V/25 • C, 4.2V/60 • C, 4.6V/25 • C) was investigated. A combination of electrochemical methods with X-ray diffraction (XRD) both in situ and ex situ as well as neutron induced PromptGamma-Activation-Analysis (PGAA) allowed us to elucidate the main failure mechanisms of the investigated lithium ion cells. In situ XRD investigations of the NMC material revealed that the first cycle irreversible capacity is the cause of slow lithium diffusion kinetics. In full-cells, however, this "lost" lithium ions can be used to build up the SEI of the graphite electrode during the initial formation cycle. A new systematic approach to correlate the lithium content in NMC with its lattice parameters (c, a) allows a convenient quantification of the loss of active lithium in aged cells by determining the c/a ratio of harvested NMC cathodes in the discharged state using ex situ XRD. Besides loss of active lithium, transition metal dissolution/deposition on graphite and growth of cell impedance strongly effect cell aging, especially at elevated temperatures and high upper cutoff potentials. Besides their current use in portable power electronics, lithium ion batteries have recently been used for battery electric vehicles (BEV) and are envisioned for large-scale energy storage. For the latter applications, life times of >10 years are required so that it is essential to understand and quantify the mechanisms that contribute to battery failure. Among the commercially available lithium-ion battery chemistries, 1,2 the graphite/LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC) system is one of the materials currently envisioned for automotive applications. 3 This cathode material demonstrates high capacity, good structural stability due to its small volume changes (<2%) during Li insertion and extraction, and high thermal stability in the charged state. [4][5][6] In addition, this material could theoretically be operated with high charge cutoff potentials up to 5.0 V, as its bulk structure is claimed to be stabilized by the presence of Mn 4+ , 7 even though other authors suggest that irreversible structural changes occur at these very high potentials and at high temperature.8 Due to its sloped potential profile, the capacity and also the average cell voltage increase with increasing charging potential. 7,9 Despite the improved safety and cycling performance of NMC material, operating NMC based cells (full-cells or half-cells) at elevated temperatures or at high charge potential leads to poor cycle life. [10][11][12][13] During cycling of graphite/NMC full-cells, transition metal dissolution from the NMC material is found to be a crucial factor controlling capacity fade. 11,12 In one of these studies, Zheng et al. demonstrated that upper cutoff potentials of >4.3 V lead to transition metal dissolution from NMC and thus compromise cycling performa...

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“…accelerate the loss of transition metal ions from the NMC electrode and their deposition on the graphite anode. 52 At 25…”

Section: Ex Situ Xrd Analysis Of Aged Nmc Electrodes-mentioning

confidence: 99%

Aging Analysis of Graphite/LiNi_1/3Mn_1/3Co_1/3O₂Cells Using XRD, PGAA, and AC Impedance

Buchberger

Seidlmayer

Pokharel

et al. 2015

J. Electrochem. Soc.

227

238

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“…Li-ion batteries are presently being considered for this application but performance needs to be improved, and the expensive LiCoO 2 positive electrode currently in use must be replaced with something cheaper. Manganese oxides are potential candidates, but the most common variant based on a spinel structure suffers from a rapid capacity fade at elevated temperatures due to manganese dissolution [1]. Others phases of manganese oxides have also been considered, such as those with tunnel [2] or layered structures [3], [4].…”

Section: Introductionmentioning

confidence: 99%

Investigation of layered intergrowth LixMyMn1?yO2+z (M=Ni, Co, Al) compounds as positive electrodes for Li-ion batteries

et al. 2004

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TitleInvestigation of layered intergrowth LixMyMn1-yO2+z (M=Ni,Co,Al) compounds as positive electrodes for Li-ion batteries electrodes may be prepared from the corresponding sodium manganese metal oxide compounds by ion-exchange. Stacking arrangements (O2, O3, or O2/O3 intergrowths) in the lithiated materials are dependent upon the Na/transition metal ratio in the sodium-containing precursors, the degree of substitution, and the identity of the substituting metal. O3 layered materials deliver up to 200 mAh/g at moderate current densities in lithium cell configurations, but convert rapidly to spinels upon cell cycling, while O2 compounds are more stable but deliver less capacity.Intergrowths show intermediate behavior, with higher capacities than pure O2 materials and better phase stability than O3 compounds. Some intergrowth structures do not appear to convert to spinel during normal cycling, suggesting it may be possible to tailor high energy density, phase stable layered manganese oxide electrodes for lithium batteries.

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“…For example, it is well known that adsorbed and absorbed H 2 O will react with fluorinated electrolyte salts to produce HF, which then degrades the positive electrode. 32,34 Furthermore, the reactions between HF and the positive electrode are autocatalytic, leading to significant destruction of the electrode's surface. 32,36 While the formation of Li 2 CO 3 and other impurity species on the surface of layered oxide materials is frequently documented, the exact growth mechanisms are not well understood.…”

mentioning

confidence: 99%

Editors' Choice—Growth of Ambient Induced Surface Impurity Species on Layered Positive Electrode Materials and Impact on Electrochemical Performance

Faenza

Bruce

Lebens-Higgins

et al. 2017

J. Electrochem. Soc.

169

233

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Surface impurity species, most notably Li 2 CO 3 , that develop on layered oxide positive electrode materials with atmospheric aging have been reported to be highly detrimental to the subsequent electrochemical performance. LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) was used as a model layered oxide compound to evaluate the growth and subsequent electrochemical impact of H 2 O, LiHCO 3 , LiOH and Li 2 CO 3 . Methodical high temperature annealing enabled the systematic removal of each impurity specie, thus permitting the determination of each specie's individual effect on the host material's electrochemical performance. Extensive cycling of exposed and annealed materials emphasized the cycle life degradation and capacity loss induced by each impurity, while rate capability measurements correlated the electrode impedance to the impurity species present. Based on these characterization results, this work attempts to clarify decades of ambiguity over the growth mechanisms and the electrochemical impact of the specific surface impurity species formed during powder storage in various environments.

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Self‐Discharge of LiMn2 O 4/C Li‐Ion Cells in Their Discharged State: Understanding by Means of Three‐Electrode Measurements

Cited by 455 publications

References 4 publications

Aging Analysis of Graphite/LiNi_1/3Mn_1/3Co_1/3O₂Cells Using XRD, PGAA, and AC Impedance

Aging Analysis of Graphite/LiNi_1/3Mn_1/3Co_1/3O₂Cells Using XRD, PGAA, and AC Impedance

Investigation of layered intergrowth LixMyMn1?yO2+z (M=Ni, Co, Al) compounds as positive electrodes for Li-ion batteries

Editors' Choice—Growth of Ambient Induced Surface Impurity Species on Layered Positive Electrode Materials and Impact on Electrochemical Performance

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Self‐Discharge of LiMn2 O 4/C Li‐Ion Cells in Their Discharged State: Understanding by Means of Three‐Electrode Measurements

Cited by 455 publications

References 4 publications

Aging Analysis of Graphite/LiNi1/3Mn1/3Co1/3O2Cells Using XRD, PGAA, and AC Impedance

Aging Analysis of Graphite/LiNi1/3Mn1/3Co1/3O2Cells Using XRD, PGAA, and AC Impedance

Investigation of layered intergrowth LixMyMn1?yO2+z (M=Ni, Co, Al) compounds as positive electrodes for Li-ion batteries

Editors' Choice—Growth of Ambient Induced Surface Impurity Species on Layered Positive Electrode Materials and Impact on Electrochemical Performance

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Product

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Aging Analysis of Graphite/LiNi_1/3Mn_1/3Co_1/3O₂Cells Using XRD, PGAA, and AC Impedance

Aging Analysis of Graphite/LiNi_1/3Mn_1/3Co_1/3O₂Cells Using XRD, PGAA, and AC Impedance