Inorganic film-forming electrolyte additives improving the cycling behaviour of metallic lithium electrodes and the self-discharge of carbon—lithium electrodes

Electrolyte solutions, containing the lithium sulfonyl methide salts lithium-tris(trifluoromethanesulfonyl)methide (LiTFSM) and lithium-[bis(trifluoromethylsulfonyl)-pentafluoroethylsulfonyl]methide (LiPFSM) dissolved in organic carbonate solvents, were electrochemically investigated in Li/graphite, Li/LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM) half-cells and compared to the LiPF 6 based electrolyte with regard to their ionic conductivity, electrochemical stability, thermal stability at 60 • C and the anodic dissolution behavior vs. Al. While the investigated salts show almost the same performance in Li/graphite half-cells compared to the LiPF 6 containing electrolyte, the methide salts show very promising results in Li/NCM half-cells, which depict superior capacity retention as well as higher Coulombic efficiencies compared to the LiPF 6 containing electrolyte. Taking the limited anodic stability as well as the occurring anodic dissolution into account, both salts but especially LiTFSM indicate the applicability in lithium ion battery electrolytes for cells with a cutoff potential up to 4. In the last 25 years the demand for lithium-ion batteries has grown tremendously. As a consequence, fundamental research has been carried out regarding the improvement and understanding of technological and safety related aspects. [1][2][3][4][5][6][7][8] Individual applications demand specifically tailored batteries in order to maximize the performance of the device which depicts a great challenge and opportunity for the scientific community to diversify the spectrum of compounds that can be utilized and to adapt the setup in a fast and efficient manner. 9,10 In this respect, the electrolyte, as a multifunctional battery component, can consist of a wide array of compounds such as different solvents, conductive salts and numerous additives. The combination of various electrolyte compounds opens up the possibility to tailor the electrolyte and thus, to a significant extent, the battery cell performance. 11-14The current state-of-the-art electrolyte composition is comprised of the conductive salt lithium hexafluorophosphate (LiPF 6 ) dissolved in a mixture of cyclic (e.g. ethylene carbonate and propylene carbonate [15][16][17][18][19] ) and linear carbonates (e.g. dimethyl-, diethyl-and ethyl-methyl carbonate). 11,[19][20][21][22][23][24][25] However, with increasing demands on the electrolyte regarding thermal and/or electrochemical stability, the limitations of such electrolyte mixtures are unraveled. 11,26,27 Alternative electrolyte compositions that depict certain improvements compared to the state-of-the-art electrolyte are still required to fulfil the following properties: a sufficient ionic conductivity to transport the lithium ions, the ability to form an effective solid electrolyte interphase (SEI) on the graphitic anode 28-37 which enables stable cycling in the low potential range as well as inertness toward aluminum to avoid anodic dissolution of the current collector on the cathode side. 38,39 In addition to performance, more...

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“…ethylene carbonate and propylene carbonate [15][16][17][18][19] ) and linear carbonates (e.g. dimethyl-, diethyl-and ethyl-methyl carbonate).…”

Section: -14mentioning

confidence: 99%

Electrochemical Performance and Thermal Stability Studies of Two Lithium Sulfonyl Methide Salts in Lithium-Ion Battery Electrolytes

Murmann

Schmitz

Nowak

et al. 2015

J. Electrochem. Soc.

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“…For example, it has been argued by some that the consumption of CO 2 is beneficial to cells, as it reacts to form a passivating film on the negative electrode. 3,4,6 However it has also been argued that the consumption of CO 2 is detrimental to cells, as it may reduce at the negative electrode to form Li 2 C 2 O 4 , which causes continual self-discharge at high voltage. 2 It is important for both scientists and manufacturers of lithium-ion cells to understand the causes and the effects of gas consumption.…”

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confidence: 99%

Quantifying, Understanding and Evaluating the Effects of Gas Consumption in Lithium-Ion Cells

Ellis

Allen

Thompson

et al. 2017

J. Electrochem. Soc.

114

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Lithium-ion cells produce a considerable amount of gas in their first cycle. If the gases are not removed in a degassing step, most are consumed by the cell over time. This phenomenon has never been investigated explicitly in the literature. In this paper, the evolution and subsequent consumption of gas in typical lithium-ion cells are measured by Archimedes' principle and gas chromatography. It is found that all evolved gases are subsequently consumed to some degree, except for saturated hydrocarbons. The consumption of gas occurs predominantly at the negative electrode, where the gases are reduced to form part of the solid-electrolyte interphase (SEI). Changes to the negative electrode SEI upon gas consumption are investigated using X-ray photoelectron spectroscopy. The effect of gas consumption on cell performance is studied with ultra-high precision charging and high voltage storage experiments. It is found that gas consumption does not result in measurable adverse effects to cell performance. Lithium-ion cells can produce a significant amount of gas during the first charge (in the formation cycle), as electrolyte and additives react at the surfaces of the charging electrodes to form passivating films. If lithium-ion cells are packaged in a flexible casing, these gases are normally removed by the manufacturer in a degassing step, to prevent deformation of the cell and to ensure uniform stack pressure on the electrodes. If the degassing step is omitted, a large portion of the gas evolved is consumed over time.1 The reactions that consume gas are presumably prevalent in hard-cased cylindrical cells, such as 18650 s, which are often hermetically sealed before the first charge, and therefore cannot be easily degassed. The reactions that consume gas are presumably less prevalent in pouch-type cells, which are degassed.Several authors have speculated about the fates of gases in lithiumion cells.2-5 There has been no work explicitly dedicated to understanding the phenomenon of gas consumption. There is no consensus as to whether the effects of gas consumption are beneficial or harmful to cell performance. For example, it has been argued by some that the consumption of CO 2 is beneficial to cells, as it reacts to form a passivating film on the negative electrode. 3,4,6 However it has also been argued that the consumption of CO 2 is detrimental to cells, as it may reduce at the negative electrode to form Li 2 C 2 O 4 , which causes continual self-discharge at high voltage. 2It is important for both scientists and manufacturers of lithium-ion cells to understand the causes and the effects of gas consumption. If gas consumption is quick, benign, or even beneficial to cell performance, then the time-consuming degassing step for lithium-ion pouch cells might be skipped. 7 The gases evolved in lithium-ion pouch cells could be left for consumption within the cell, perhaps leaving the pouch cell flat and rigid after several hours if all the gases were consumed. If gas consumption in a cell produces undesirable effects, such...

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“…Additionally, lithium oxalate releases only CO 2 during oxidation, which is considered to improve the interfacial stability of graphite as well as of lithium metal anodes. [11][12][13][14][15] Strehle et al 16 showed that the presence of CO 2 can suppress the formation of soluble lithium alkoxides and the follow-up electrolyte transesterification reactions. CO 2 can act further as a scavenger for detrimental trace water and protons.…”

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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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Inorganic film-forming electrolyte additives improving the cycling behaviour of metallic lithium electrodes and the self-discharge of carbon—lithium electrodes

Cited by 174 publications

References 8 publications

Electrochemical Performance and Thermal Stability Studies of Two Lithium Sulfonyl Methide Salts in Lithium-Ion Battery Electrolytes

Electrochemical Performance and Thermal Stability Studies of Two Lithium Sulfonyl Methide Salts in Lithium-Ion Battery Electrolytes

Quantifying, Understanding and Evaluating the Effects of Gas Consumption in Lithium-Ion Cells

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

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