The Science of Battery Degradation

Abstract

This report documents work that was performed under the Laboratory Directed Research and Development project, Science of Battery Degradation. The focus of this work was on the creation of new experimental and theoretical approaches to understand atomistic mechanisms of degradation in battery electrodes that result in loss of electrical energy storage capacity. Several unique approaches were developed during the course of the project, including the invention of a technique based on ultramicrotoming to cross-section commercial scale battery electrodes, the demonstration of scanning transmission x-ray microscopy (STXM) to probe lithium transport mechanisms within Li-ion battery electrodes, the creation of in-situ liquid cells to observe electrochemical reactions in real-time using both transmission electron microscopy (TEM) and STXM, the creation of an in-situ optical cell utilizing Raman spectroscopy and the application of the cell for analyzing redox flow batteries, the invention of an approach for performing ab initio simulation of electrochemical reactions under potential control and its application for the study of electrolyte degradation, and the development of an electrochemical entropy technique combined with x-ray based structural measurements for understanding origins of battery degradation. These approaches led to a number of scientific discoveries. Using STXM we learned that lithium iron phosphate battery cathodes display unexpected behavior during lithiation wherein lithium transport is controlled by nucleation of a lithiated phase, leading to high heterogeneity in lithium content at each particle and a surprising invariance of local current density with the overall electrode charging current. We discovered using in-situ transmission electron microscopy that there is a size limit to lithiation of silicon anode particles above which particle fracture controls electrode degradation. From electrochemical entropy measurements, we discovered that entropy changes little with degradation but the origin of degradation in cathodes is kinetic in nature, i.e. lower rate cycling recovers lost capacity. Finally, our modeling of electrode-electrolyte interfaces revealed that electrolyte degradation may occur by either a single or double electron transfer process depending on thickness of the solid-electrolyteinterphase layer, and this cross-over can be modeled and predicted.

Entropy profiling for the diagnosis of NCA/Gr-SiOx Li-ion battery health

“…We find that there is hysteresis in the entropy change at the start of cell life, and this hysteresis does not change significantly for calendar aged cells, but increases with cycle ageing. We hypothesise that these differences originate from microscopic material changes that reflect the unique ageing history [20,30]. Finally, as far as we know, no NCA-Gr|SiO x entropy ageing curves are available in the literature, so this work provides such data.…”

“…The measurement of entropy changes, known as entropy profiling, is another method that has been https://mc04.manuscriptcentral.com/jes-ecs proposed for understanding degradation [20,21,22,23]. Maher and Yazami [21] explored cycle ageing of a LCO/Gr cell, finding changes in the entropy profiles associated with loss of battery capacity, but there was no clear trend observed in the entropy profile changes.…”

“…Using Raman spectroscopy, changes in the entropy profiles were attributed to crystallographic changes in the cathode material with ageing. Sullivan et al [20] focused on LCO half-cell analysis. A clear trend was observed: with prolonged cycling, the characteristic LCO entropy profile features (maximum and minimum) became less pronounced.…”

Feasibility of Chemically Modified Cellulose Nanofiber Membranes as Lithium-Ion Battery Separators

“…30,31 The gas accumulated can delaminate the materials in the LIB, which can significantly affect the cycle life of the cell, and in the end, it is prone to lead to severe accidents. 31 Trace water has been blamed as a contributing factor triggering detrimental H 2 evolution reactions at the graphite surface (H 2 O + e − → OH − + 1/2H 2 ). 32−34 For example, Metzger et al 25 elucidated the origin of H 2 gas in LIBs and the effect of the vinylene carbonate (VC) additive on the gas evolution.…”

“…In practice, gas evolution in LIBs can jeopardize the electrochemical performance and the safety during storage and in use. , The gas accumulated can delaminate the materials in the LIB, which can significantly affect the cycle life of the cell, and in the end, it is prone to lead to severe accidents . Trace water has been blamed as a contributing factor triggering detrimental H 2 evolution reactions at the graphite surface (H 2 O + e – → OH – + 1/2H 2 ). − For example, Metzger et al elucidated the origin of H 2 gas in LIBs and the effect of the vinylene carbonate (VC) additive on the gas evolution.…”