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Investigation of dimethyl carbonate and propylene carbonate mixtures for LiNi0.6Mn0.2Co0.2O2-Li4Ti5O12 cells
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.ORCID iD: 0000-0002-2736-9145
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.ORCID iD: 0000-0003-4440-2952
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.ORCID iD: 0000-0002-8019-2801
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2019 (English)In: Chemelectrochem, E-ISSN 2196-0216, Vol. 6, no 13, p. 3429-3436Article in journal (Refereed) Published
Abstract [en]

It has recently been shown that ethylene carbonate (EC) experience poor stability at high potentials in lithium-ion batteries, and development of electrolytes without EC, not least using ethyl methyl carbonate (EMC), has therefore been suggested in order to improve the capacity retention. In this context, we here explore another alternative electrolyte system consisting of propylene carbonate (PC) and dimethyl carbonate (DMC) mixtures in NMC-LTO (LiNi0.6Mn0.2Co0.2O2, Li4Ti5O12) cells cycled up to 2.95 V. While PC experience wettability problems and DMC has difficulties dissolving LiPF6 salt, blends between these could possess complementary properties. The electrolyte blend showed superior cycling performance at sub-zero temperatures compared to EC-containing counterparts. At 30 degrees C, however, the PC-DMC electrolyte did not show any major improvement in electrochemical properties for the NMC-LTO cell chemistry. Photoelectron spectroscopy measurements showed that thin surface layers were detected on both NMC (622) and LTO electrodes in all investigated electrolytes. The results suggest that both PC and EC will react on the electrodes, but with EC forming thinner layers comprising more carbonates. Moreover, the electrochemical stability at high electrochemical potentials is similar for the studied electrolytes, which is surprising considering that most are free from the reactive EC component.

Place, publisher, year, edition, pages
2019. Vol. 6, no 13, p. 3429-3436
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-381546DOI: 10.1002/celc.201900672ISI: 000475512500026OAI: oai:DiVA.org:uu-381546DiVA, id: diva2:1303900
Funder
Swedish Energy Agency, 37725-1StandUpAvailable from: 2019-04-11 Created: 2019-04-11 Last updated: 2019-08-19Bibliographically approved
In thesis
1. Avoiding ageing: Surface degradation of commercial electrode materials in lithium-ion batteries
Open this publication in new window or tab >>Avoiding ageing: Surface degradation of commercial electrode materials in lithium-ion batteries
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The battery market today expands rapidly, not least for electric vehicles. But to compete against the combustion engine, the cost of batteries must be reduced. After years of usage, the batteries degrade and need to be exchanged, increasing the cost over the vehicle lifecycle. This can be mitigated by tailoring the usage conditions and the battery materials. Understanding and avoiding ageing can be key to a more sustainable transport system. This thesis contains studies on degradation processes in Li-ion batteries utilizing the LiNixMnyCozO2 (NMC) cathode material, and suggests strategies for the improvement of battery life time.

When cycling different negative electrodes – including graphite, lithium foil and lithium titanium oxide (LTO) – against NMC electrodes, only minor capacity fading was observed in the NMC-LTO and NMC-graphite cells, in contrast to the NMC-Li-metal cells. The capacity fading for Li-metal cells was determined to be caused by degradation products formed at the lithium foil which thereafter diffused to the NMC electrode, leading to a higher resistance. Commercial NMC/LiMn2O4-graphite cells were also investigated after cycling in limited state of charge (SOC)-intervals. The cycle life was far longer in the low-SOC cell than in the high-SOC cell. Photoelectron spectroscopy revealed increased manganese dissolution in the high-SOC cell, likely causing a less stable solid electrolyte interphase layer on the negative electrode. This, in turn, limits the capacity. How temperature influence ageing in NMC-LTO was analysed in cells cycled at -10 °C, 30 °C and 55 °C. It was found that the initial side reactions at the LTO electrode limited the cell capacity, but that these also stabilized the NMC electrode. At 55 °C, excessive side reactions at LTO caused capacity fading due to loss of active lithium. At -10 °C, high cell resistance limited the capacity. Switching to a PC based electrolyte allowed stable low temperature cycling, although it was found that PC degraded and formed thick electrode surface layers. Also sulfolane-based electrolytes were investigated, showing thinner surface layers than the EC containing reference electrolyte at high potentials, thus indicating a more stable electrolyte system.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 72
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1802
Keywords
Li-ion battery, Ageing, Photoelectron spectroscopy, Nickel Manganese Cobalt Oxide
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-381548 (URN)978-91-513-0639-1 (ISBN)
Public defence
2019-06-05, Room 4001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2019-05-09 Created: 2019-04-11 Last updated: 2019-06-17

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Björklund, ErikEdström, KristinaBrandell, DanielYounesi, Reza

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