The role of Li-ion battery electrolyte reactivity in performance decline and self-discharge

Sloop, Steven E; Kerr, John B.; Kinoshita, K.

doi:10.1016/s0378-7753(03)00149-6

Cited by 449 publications

(403 citation statements)

References 23 publications

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“…17 As protons are a possible product of electrolyte oxidation, 28 this effect would be especially relevant for high-voltage lithium ion cell chemistries like the LNMO/graphite system. Sloop et al 41 suggested that the reduction of CO 2 could lead to lithium oxalate formation at the anode, which could dissolve and be re-oxidized at the cathode, generating a shuttling current followed by self-discharge. To assess whether the presence of CO 2 indeed leads to enhanced side reactions, we calculated the charge end point slippage (the cumulative irreversible charge capacity, i.e., the charge capacity of each cycle subtracted by the previous discharge, summed up over all cycles), which is an indicator for oxidative or shuttling side reactions.…”

Section: Resultsmentioning

confidence: 99%

Lithium Oxalate as Capacity and Cycle-Life Enhancer in LNMO/Graphite and LNMO/SiG Full Cells

Solchenbach

Wetjen

Pritzl

et al. 2018

J. Electrochem. Soc.

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In the present study, we explore the use of lithium oxalate as a "sacrificial salt" in combination with lithium nickel manganese spinel (LNMO) cathodes. By online electrochemical mass spectrometry (OEMS), we demonstrate that the oxidation of lithium oxalate to CO 2 (corresponding to 525 mAh/g) occurs quantitatively around 4.7 V vs. Li/Li + . LNMO/graphite cells containing 2.5 or 5 wt% lithium oxalate show an up to ∼11% higher initial discharge capacity and less capacity fade over 300 cycles (12% and 8% vs. 19%) compared to cells without lithium oxalate. In LNMO/SiG full-cells with an FEC-containing electrolyte solution, lithium oxalate leads to a better capacity retention (45% vs 20% after 250 cycles) and a higher coulombic efficiency throughout cycling (∼1%) compared to cells without lithium oxalate. When CO 2 from lithium oxalate oxidation is removed after formation, a similar capacity fading as in LNMO/SiG cells without lithium oxalate is observed. Hence, we attribute the improved cycling performance to the presence of CO 2 in the cells. Further analysis (e.g., FEC consumption by 19 F-NMR) indicate that CO 2 is an effective SEI-forming additive for SiG anodes, and that a combination of FEC and CO 2 has a synergistic effect on the lifetime of full-cells with SiG anodes. Lithium nickel manganese spinel (LiNi 0.5 Mn 1.5 O 4 , LNMO) is a promising cathode material for high energy lithium ion batteries due to its high operating potential around 4.7 V vs. Li/Li + , its high rate capability, structural stability and the absence of cobalt. However, its lower specific capacity (146 mAh/g LNMO ) compared to layered oxide materials (e.g. lithium nickel manganese cobalt oxide (NMC), specific capacity 150-250 mAh/g NMC ) 1 is regarded as a major drawback. In full-cells, the practically achievable capacity of LNMO is even lower, as the formation of the solid-electrolyte interphase (SEI) on the graphite anode consumes active lithium. For many layered oxide cathodes, however, the first cycle irreversible capacity of the cathode is similar to the capacity needed for SEI formation (∼20 mAh/g NMC ), and hence the practical discharge capacity of the cathode and the remaining active lithium are more or less balanced again. 2,3 In contrast, the first cycle irreversible capacity of LNMO (∼6 mAh/g LNMO ) is much lower than the capacity needed for SEI formation. This leads to a mismatch between active lithium and practical cathode capacity, i.e., there is not enough active lithium available to fully discharge the LNMO cathode during subsequent cycling.In cells with silicon-based anodes, active lithium losses on the anode are even higher compared to graphite, as the expansion of the silicon particles during the first lithiation leads to a continuous exposure of fresh, unpassivated silicon surface. 4 On this new surface, electrolyte reduction occurs instantaneously, which reduces the total lithium reservoir in the cell. Therefore, different ideas to increase the amount of active lithium in lithium ion full-cells have been suggested, ...

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Section: Resultsmentioning

confidence: 99%

Lithium Oxalate as Capacity and Cycle-Life Enhancer in LNMO/Graphite and LNMO/SiG Full Cells

Solchenbach

Wetjen

Pritzl

et al. 2018

J. Electrochem. Soc.

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“…CO 2 is known to be reduced to lithium oxalate and/or lithium carbonate in the Li + -ions containing alkyl carbonate electrolyte at potentials below ≈0.7 V Li . 40,41 Moreover, CO 2 could react with lithium alkoxide species formed during formation, if the linear carbonate (in that case EMC) was reduced at the graphite electrode. Such a scavenging reaction could also lead to a decrease in CO 2 concentration.…”

Section: Discussionmentioning

confidence: 99%

Gas Evolution at Graphite Anodes Depending on Electrolyte Water Content and SEI Quality Studied by On-Line Electrochemical Mass Spectrometry

Bernhard

Metzger

Gasteiger

2015

J. Electrochem. Soc.

153

179

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The gas evolution during the formation of graphite electrodes is quantified by On-line Electrochemical Mass Spectrometry (OEMS) for dry electrolyte (< 20 ppm H 2 O) and 4000 ppm H 2 O containing electrolyte to mimic the effect of trace water during the formation process. While the formation in dry electrolyte mainly shows ethylene (C 2 H 4 ) from the reduction of ethylene carbonate (EC) and small amounts of hydrogen (H 2 ), the formation in water-containing electrolyte yields large amounts of H 2 and considerable amounts of CO 2 in addition to the expected C 2 H 4 evolution. We could show that a protective solid-electrolyte interphase (SEI) layer formed by pre-cycling the graphite electrode in 2% vinylene carbonate (VC) containing electrolyte can reduce the H 2 evolution in watercontaining electrolyte by a factor of 7.5 compared to a pristine graphite electrode. Consequently, the ability of graphite electrodes to form an SEI prevents excessive gassing from trace water, which, e.g., is observed for non-SEI forming lithium titanate ( Today's Li-ion batteries usually employ graphite or lithium titanate Li 4 Ti 5 O 12 (LTO) as anode material. Graphite electrodes are known to have an irreversible capacity loss upon the first charge, i.e., during the first Li + -ion intercalation into the layered graphite structure. 1 This effect is related to the formation of the so called solid-electrolyte interphase (SEI) and depends strongly on the electrolyte composition and the electrode potential.2 The capacity loss is explained by the reduction of electrolyte components on the graphite surface, which irreversibly consumes Li + -ions and forms the protective and passivating SEI layer on the negative electrode. On the one hand, the SEI inhibits further reduction reactions on the anode surface due to its electronically insulating nature, on the other hand it is still permeable for Li + -ions, allowing for Li + intercalation. [3][4][5][6][7][8][9][10][11] Recent work by the group of Brett Lucht showed that lithium ethylene dicarbonate (LEDC) and LiF are the main constituents of the SEI layer on graphite, when ethylene carbonate-based electrolytes are used, independent of the type of lithium salt. 12 The main gaseous components formed during electrolyte reduction on graphite anodes are ethylene (C 2 H 4 ), hydrogen (H 2 ) and other hydrocarbons like propylene (depending on the cyclic carbonate, which is used in the electrolyte mixture).13-15 When employing the common alkyl carbonate electrolytes containing ethylene carbonate (EC), dimethylcarbonate (DMC), diethylcarbonate (DEC) and/or ethyl methyl carbonate (EMC) with LiPF 6 , no carbon dioxide (CO 2 ) formation is observed during the SEI formation. 10In contrast to graphite, LTO is generally believed to possess no SEI protection, since its lithiation potential (1.55 V Li ) is too high to allow reduction of electrolyte components. Thus, LTO is more prone to gassing from trace water and other impurities in the alkyl carbonate electrolyte.16 Gassing studies with LTO as anode material...

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“…Spotnitz [45] and Ozawa et al [46] proposed that the oxidation of lithiated graphite negative electrode (low potential) and the reduction of delithiated positive electrode (high potential) by the electrolyte can lead to reversible and irreversible loss of cell capacity. A shuttle mechanism, in which the same species is reduced at one electrode (anode) and oxidized at another (cathode), can be at the origin of reversible capacity loss [47]. In this case, equal amount of cyclable lithium is exchanged between electrodes and electrolyte at both electrodes.…”

Section: °Cmentioning

confidence: 99%

Calendar aging of a graphite/LiFePO4 cell

Kassem

Bernard

Revel

et al. 2012

Journal of Power Sources

281

124

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Graphite/LFP commercial cells are stored under 3 different conditions of temperature (30°C, 45°C, and 60°C) and SOC (30, 65, and 100%) during up to 8 months. Several non-destructive electrochemical tests are performed at different storage times in order to understand calendar aging phenomena. After storage, all the cells except those stored at 30°C exhibited capacity fade. The extent of capacity fade strongly increases with storage temperature and to a lesser extent with the state of charge. From in-depth data analysis, cyclable lithium loss was identified as the main source of capacity fade. This loss arises from side reactions taking place at the anode, e.g. solvent decomposition leading to the growth of the solid electrolyte interphase. However, the existence of reversible capacity loss also suggests the presence of side reactions occurring at the cathode, which are less prominent than those at the anode. The analyses do not show any evidence about active-material loss in the electrodes. The cells do not suffer substantial change in internal resistance. According to EIS analysis, the overall impedance increase is 70% or less.

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The role of Li-ion battery electrolyte reactivity in performance decline and self-discharge

Cited by 449 publications

References 23 publications

Lithium Oxalate as Capacity and Cycle-Life Enhancer in LNMO/Graphite and LNMO/SiG Full Cells

Lithium Oxalate as Capacity and Cycle-Life Enhancer in LNMO/Graphite and LNMO/SiG Full Cells

Gas Evolution at Graphite Anodes Depending on Electrolyte Water Content and SEI Quality Studied by On-Line Electrochemical Mass Spectrometry

Calendar aging of a graphite/LiFePO4 cell

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