Interfacial Degradation Processes in Electrochemical Energy Storage and Conversion
Creators: name: Zhao, Dongni
Publisher: name: Lancaster University
Year: 2025
Subjects: Li-ion battery
Water electrolysis
Transition metal dissolution

description: The comprehensive usage of clean energy is the biggest challenge of
 society in the 21st century. Advanced energy storage and conversion
 systems play a critical role in this vision, and electrochemical energy
 storage and conversion are the most promising candidates. However, their
 premature ageing limits their wider application. One of the biggest issues
 is the active material dissolution under electrochemical conditions, but
 the limited availability of characterization methods hinders an in-depth
 understanding of the process as well as mitigation strategies. 
 
 
 In this thesis, we develop real-time/in-situ/operando electrochemical
 techniques to study the degradation processes and mechanisms happening at
 the electrode-electrolyte interfaces within the Li-ion battery and water
 electrolyzer. We first establish online inductively coupled plasma-optical
 emission spectrometry (online ICP-OES) for real-time electrolyte analysis,
 enabling the direct detection of transition metal dissolution from Li-ion
 cathodes, taking LiMn2O4 (LMO) as an example. 
 
 
 Then, we apply the rotating ring-disc electrode (RRDE) technique for
 real-time speciation of the dissolving transition metal ions, which is the
 basis of a comprehensive understanding of the dissolution mechanism, and
 supplements findings from online ICP-OES, which could provide
 extraordinary detection limits for multiple elements but is blind to the
 oxidation states of the dissolving species. We focus on Mn, and combine
 voltammetry on stationary and rotating electrodes with electrochemical
 impedance spectroscopy and Raman spectroscopy. With the understanding of
 Mn behaviour on the ring and disc electrodes, respectively, we then
 investigate LMO dissolution and speciation on the ring electrode in
 real-time. 
 
 
 One of the widely reported Mn dissolution mitigation strategies is to
 replace one-fourth of the Mn in LMO with Ni, which then forms
 LiNi0.5Mn1.5O4 (LNMO). We compared the chemical composition, morphology,
 crystal structure, and electrochemical properties including cycling
 capacity, stability, and rate capability of 2 commercial and 3
 lab-synthesized LNMO samples. Their dynamic phase transformation during
 (dis)charging was observed by operando Raman spectroscopy, aimed at
 studying the dynamic cathode-electrolyte interphase (CEI) changes under
 different electrochemical conditions and their impact on cycling and rate
 performances. 
 
 
 Water electrolysis is considered to be the most promising way to generate
 green hydrogen as the next-generation energy carrier. Such a process
 includes the hydrogen evolution reaction (HER) on the cathode and the
 oxygen evolution reaction (OER) on the anode. The complexity and sluggish
 kinetics of OER make it often the limit of the whole process and thus
 usually requires advanced electrocatalysts. Ideal OER electrocatalysts
 should have both excellent activity and stability. While the former can be
 directly observed electrochemically, the latter is usually hard to
 characterize due to the lack of available techniques. We here employed
 online ICP-OES for direct detection of active material dissolution of
 several promising candidates of OER electrocatalysis, which provide direct
 evidence of the stability of the electrocatalysts. 
 
 
 To summarize, we established several real-time/in-situ/operando
 electrochemical techniques for studying the electrode-electrolyte
 interface in electrochemical energy storage and conversion systems. These
 results will help to better understand and mitigate the premature ageing
 of those systems.