Abstract

Interfacial instabilities in electrodes control the performance and lifetime of Li-ion batteries. While the formation of solid-electrolyte interface (SEI) on anodes has received much attention, there is still lack of understanding about the formation of cathode-electrolyte interface (CEI) on the cathodes. To fill this gap, we report on dynamic deformations on lithium iron phosphate, LiFePO₄ cathodes during charge / discharge by utilizing in-operando digital image correlation, impedance spectroscopy and Cryo X-ray photoelectron spectroscopy. LiFePO4 cathodes were cycled in either LiPF₆, LiClO₄ or LiTFSI- containing organic liquid electrolytes. Beyond the first cycle, Li-ion intercalation results in a nearly linear correlation between electrochemical strains and the state of (dis)-charge, regardless of the electrolyte chemistry. However, during the first charge in LiPF₆ - containing electrolyte, there is a distinct irreversible positive strain evolution at the onset of anodic current rise as well as current decay at around 4.0V. Impedance studies show the increase in surface resistance in the same potential window, suggesting the formation of CEI layers on the cathode. The chemistry of the CEI layer was characterized by X-ray photoelectron spectroscopy. LiF is detected in CEI layer starting as early as 3.4 V and Li_$$x$$PO_$$y$$F_$$z$$ appeared at voltages higher than 4.0 V during the first charge. In conclusion, our approach offers new insights into the formation mechanism of CEI layers on the cathode electrodes, which is crucial for the development of robust cathode and electrolyte chemistries for higher performance batteries.

Authors:

Bal, Batuhan ^[1]; Ozdogru, Bertan ^[2]; Nguyen, Dan Thien ^[3]; Li, Zheng ^[4]; Murugesan, Vijayakumar  ^[3];

• Search DOE PAGES for author "Murugesan, Vijayakumar"
• Search DOE PAGES for ORCID "0000-0001-6149-1702"

Çapraz, Ömer Özgür  ^[5]

• Search DOE PAGES for author "Çapraz, Ömer Özgür"
• Search DOE PAGES for ORCID "0000-0002-2396-4748"

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+ Show Author Affiliations

1. Oklahoma State University, Stillwater, OK (United States)
2. Oklahoma State University, Stillwater, OK (United States); National Renewable Energy Laboratory (NREL), Golden, CO (United States)
3. Pacific Northwest National Laboratory (PNNL), Richland, WA (United States); Joint Center for Energy Storage Research (JCESR), Lemont, IL (United States)
4. Joint Center for Energy Storage Research (JCESR), Lemont, IL (United States); Purdue University, West Lafayette, IN (United States)
5. Oklahoma State University, Stillwater, OK (United States); The University of Maryland, Baltimore, MD (United States)

Publication Date:

Sat Sep 02 00:00:00 EDT 2023

Research Org.:

Pacific Northwest National Laboratory (PNNL), Richland, WA (United States); Univ. of Maryland Baltimore County (UMBC), Baltimore, MD (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

2222894

Alternate Identifier(s):

OSTI ID: 2281648

Report Number(s):

PNNL-SA-184392
Journal ID: ISSN 1944-8244

Grant/Contract Number:  

AC05-76RL01830; SC0021251

Resource Type:

Accepted Manuscript

Journal Name:

ACS Applied Materials and Interfaces

Additional Journal Information:

Journal Volume: 15; Journal Issue: 36; Journal ID: ISSN 1944-8244

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

25 ENERGY STORAGE; cathode−electrolyte interphase; strain; digital image correlation; X-ray photoelectron spectroscopy; Li-ion batteries; Cathode-electrolyte interphase