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Temperature dependence of electrochemical degradation in LiNi1/3Mn1/3Co1/3O2/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, Structural Chemistry.ORCID iD: 0000-0001-5641-7778
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.ORCID iD: 0000-0002-8658-8938
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: Energy Technology, ISSN 2194-4288, Vol. 7, no 9, article id 1900310Article in journal (Refereed) Published
Abstract [en]

Aging mechanisms in lithium‐ion batteries are dependent on the operational temperature, but the detailed mechanisms on what processes take place at what temperatures are still lacking. The electrochemical performance and capacity fading of the common cell chemistry LiNi1/3Mn1/3Co1/3O2 (NMC)/Li4Ti5O12 (LTO) pouch cells are studied at temperatures 10, 30, and 55 °C. The full cells are cycled with a moderate upper cutoff potential of 4.3 V versus Li+/Li. The electrode interfaces are characterized postmortem using photoelectron spectroscopy techniques (soft X‐ray photoelectron spectroscopy [SOXPES], hard X‐ray photoelectron spectroscopy [HAXPES], and X‐ray absorption near edge structure [XANES]). Stable cycling at 30 °C is explained by electrolyte reduction forming a stabilizing interphase, thereby preventing further degradation. This initial reaction, between LTO and the electrolyte, seems to be beneficial for the NMC–LTO full cell. At 55 °C, continuous electrolyte reduction and capacity fading are observed. It leads to the formation of a thicker surface layer of organic species on the LTO surface than at 30 °C, contributing to an increased voltage hysteresis. At 10 °C, large cell‐resistances are observed, caused by poor electrolyte conductivity in combination with a relatively thicker and LixPFy‐rich surface layer on LTO, which limit the capacity.

Place, publisher, year, edition, pages
2019. Vol. 7, no 9, article id 1900310
Keywords [en]
aging, lithium-ion batteries, photoelectron spectroscopy
National Category
Energy Engineering Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-381545DOI: 10.1002/ente.201900310ISI: 000483721900011OAI: oai:DiVA.org:uu-381545DiVA, id: diva2:1303899
Available from: 2019-04-11 Created: 2019-04-11 Last updated: 2019-12-09Bibliographically 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)
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Supervisors
Available from: 2019-05-09 Created: 2019-04-11 Last updated: 2019-06-17

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Björklund, ErikNaylor, Andrew J.Brant, WilliamBrandell, DanielYounesi, RezaEdström, Kristina

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