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THE SEI REVISITED – WHAT DO WE KNOW ABOUT INTERFACES AND INTERPHASES?
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.ORCID iD: 0000-0003-4440-2952
2017 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Introduction

The Solid Electrolyte Interphase (SEI) and other interfaces in lithium- and sodium ion batteries are despite of many scientific studies still attracting a lot of interest. This presentation aims at reviewing why interfaces in batteries are so crucial for the function, thermal stability, lifetime and ageing of a battery.

     Characterizing interfaces in batteries is both simple and difficult. It is simple in the sense that it is easy to take a battery apart and then use different techniques to study the composition and morphology of interfaces of electrodes and separators post mortem. It is, however, difficult to study in situ how an interface forms and evolves during battery operation.

     The SEI on negative electrodes can be described as a mixture of inorganic and organic compounds where the inorganic compounds are formed closer to the electrode surface. The layer is a consequence of the low potential – close of that of lithium – where for lithium-ion batteries the reduction of the thermodynamically instable organic solvent (below 0.8V vs. Li+/Li) is taking place. There are even descriptions of the SEI consisting of an inner, more dense inorganic layer, where electrons can tunnel through until a certain thickness of the layer has been obtained where the SEI becomes electronically insulating but where ions can penetrate. How the different SEI-compounds interplay to form a well-functioning layer is not yet clear.

 

Experimental

The results shown are mainly based on electrochemical cycling combined with photoelectron spectroscopy (PES) results; both in house and synchrotron based. PES has been performed both at the Helmholtz Zentrum Bessy, Germany, and at Diamond UK. The advantage with synchrotron radiation is the possibility to tune the incoming photon energy to reach into a surface at different depths.

Results and discussion

The result and discussion will be based on a number of thesis produced at Uppsala University with the aim to answer the following questions:

    Will the electrolyte salt influence the interfaces formed in batteries? Yes. Examples will be given for both lithium and sodium batteries.

    Will the electrode material influence the SEI composition? Not very much but to some extent.

    Is particle size and morphology important for SEI formation?

    What is a good SEI former? Is it better to have an additive in the electrolyte forming the SEI or can the binder be just as good?

    How thick is the SEI? What does the buried interface between the SEI and the electrode look like?

     How is the conditions for a stable interface on a positive electrode? How can metal-ion dissolution be prevented?

 

There are results trying to answer all these questions which will be discussed in the presentation.

 

Conclusions

Interfaces in batteries are complex. They are formed electrochemically or chemically. A well-functioning interface protect from unwanted side reactions. New methods are needed to understand the true formation in situ and to better describe the function of interfaces.

 

Acknowledgments

To all colleagues and former post doc and PhD students that have contributed to this work. Funding agencies such as the Swedish Research Council, The Swedish Energy Agency, Horizon2020, FP7, Vinnova, and StandUp for Energy.

Place, publisher, year, edition, pages
2017.
Keywords [en]
Interface SEI Li-ion battery Na-ion battery
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-337512OAI: oai:DiVA.org:uu-337512DiVA, id: diva2:1169881
Conference
Nordbatt 3, Kokkola Finland
Funder
StandUpAvailable from: 2017-12-30 Created: 2017-12-30 Last updated: 2017-12-30

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