Assessing the degradation of battery cathodes in real time via spatially resolved electrochemical methods

My doctoral research focuses on key degradation mechanisms of cathode materials that lead to capacity decay in Li-ion batteries (LiBs), with a particular emphasis on a) kinetics and b) chemical nature of lattice oxygen loss. To elucidate this phenomenon, I have developed a highly sensitive and selective in situ scanning electrochemical microscopy (SECM) based method to quantitatively investigate lattice oxygen loss in real-time. This method also helps in capturing spatial heterogeneity in oxygen release across the sample, which is not possible through alternate, state-of-the-art methods such as differential electrochemical mass spectrometry. Moreover, the SECM method is versatile and does not require any specialized sample preparation. This characteristic enabled me to quantitatively study lattice oxygen loss from three commercial cathodes: LiCoO2, LiNi0.33Mn0.33Co0.33O2, and LiNi0.8Mn0.1Co0.1O2. Additionally, it helped in correlating crystal facet orientation with lattice oxygen evolution, using preferentially faceted LiCoO2 synthesized via electrodeposition. Furthermore, the sensitivity and temporal resolution of the SECM approach provides unprecedented insights by capturing previously unreported, sub-monolayer quantities of oxygen loss at low potentials (~3 V vs Li+/Li). Combing the experimental results with COMSOL Multiphysics simulations helped in quantifying the flux of oxygen release from the cathodes as a function of potential. With regards to the chemical nature of lattice oxygen loss, recent computational studies have reported that a part of the released oxygen is in the form of the highly reactive singlet oxygen species (1O2, instead of ground state 3O2). However, the short lifetime of 1O2 (~3 µs) makes its experimental investigation a challenge. The formation energy of 1O2 is 95 kJ/mol higher than the ground state (3O2), translating to a significant E0 difference of 1 V between them. This significant difference underscored the urgent need for its experimental characterization to better understand the reactivity of 1O2. I addressed this knowledge gap by developing a high temporal resolution SECM method to characterize the reduction potential of 1O2. My investigation helped in characterizing the reduction potential of 1O2 to -1.0 V (vs Fc+/Fc). Notably, this value is approximately 1 V more positive than the reduction potential of 3O2, consistent with the thermodynamic estimates. In summary, my research has led to the development of new SECM methods that facilitate real time investigation of cathode degradation processes via lattice oxygen loss. These findings have the potential to develop mitigation approaches to degradation processes and enhance the efficiency and lifetime of LiBs.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Materials Science & Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Mishra, Abhiroop

Contributors dc:contributor

• Rodríguez-López, Joaquín
• Braun, Paul V.
• Shoemaker, Daniel P.
• Zhang, Yingjie

• Li-ion Battery
• Scanning Electrochemical Microscopy

Statement dc:rights

• © 2024 Abhiroop Mishra

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/125747

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F125747