Long-Term Study on the Impact of Depth of Discharge, C-Rate, Voltage, and Temperature on the Lifetime of Single-Crystal NMC811/Artificial Graphite Pouch Cells

Abstract

This work examined the impact of depth of discharge (DOD), C-rate, upper cut-off voltage (UCV), and temperature on the lifetime of single-crystal NMC811/Artificial Graphite (AG) cells. Cells were cycled at C/50, C/10, C/5, or C/3, and 25, 50, 75, or 100% DOD at room temperature (RT, 20. ± 2°C) or 40.0 ± 0.1°C. The UCVs were 4.06 or 4.20 V. After 12000 hours of cycling, experiments such as electrochemical impedance spectroscopy, Li-ion differential thermal analysis (DTA), ultrasonic mapping, X-ray fluorescence, differential capacity analysis, synchrotron computed tomography (CT) scans, and cross-section scanning electron microscopy (SEM) were carried out. We showed that capacity loss increased slightly with DOD and C-rate, and that cells with 4.06 V UCV have superior capacity retention and impedance control compared to 4.20 V. SEM, CT scans, and differential capacity analysis show that microcracking and positive electrode mass loss did not occur regardless of DOD, C-rate, or UCV. DTA and ultrasonic mapping showed no C-rate or DOD dependency for electrolyte changes or “unwetting.” A simple square-root time model was used to model SEI growth in 4.06 V UCV cells, and a cell design with impressive performance is demonstrated.

Interpretable Data-Driven Modeling Reveals Complexity of Battery Aging

“…Optimizing new battery designs is challenging due to the need to simultaneously meet many performance targets and design constraints. Improving battery lifetime is especially difficult due to the slow, nonlinear, and coupled physics of the aging process [9][10][11][12][13][14][15][16][17][18]. It is time and resource consuming to observe the impact that design choices have on battery life and understand why one battery degrades more rapidly than another.…”

A method for battery fault diagnosis and early warning combining isolated forest algorithm and sliding window

“…The intuitive symptoms of inconsistency fault are mainly manifested in the following three aspects, the inconsistency of the performance parameters of the single power battery, the inconsistency of the working state of the battery and the inconsistency of temperature 10–19 . Karden et al 12 analyzed the impedance spectrum of the battery.…”

Synergistic Degradation Mechanism in Single Crystal Ni-Rich NMC//Graphite Cells

“…The slight difference has been attributed to faster SEI growth with a 3.6 V DoD. 4,22 In addition, C/20 diagnostic cycling, in Table 1, recovers almost all the capacity loss, i.e, kinetically limited.…”

“…The study of degradation mechanisms for Li(Ni,Mn,Co)O 2 or NMC cathodes at high voltages and state of delithiation is an active area of research, − which is important for assisting the electrification of the transport sector . The degradation rate varies with the Ni content in NMC, − operational voltage windows, , and particle morphology, i.e., polycrystalline (PC) vs single crystal (SC) . In principle, an optimal choice of these three features (SC, Ni ≈ 50%, 3.0–4.3 V) can lead to long-term cell stability to power an electric vehicle for over 1.6 million kilometers …”

“…Most studies to date focus on understanding oxygen loss induced degradation at high voltage, often in half coin cell configurations. , However, increasing evidence suggests considering both low and high voltage cutoffs for degradation studies when focusing on full cells. For example, Dahn et al show a steady performance of SC Ni-rich systems (Ni ≈ 80%) with adjustments to the (3.0–4.2 V) voltage window, i.e., avoiding degradation at both voltages limits. Meanwhile, Dose et al studied degradation in PC NMC811//graphite cells in a wider voltage window (2.5–4.3 V), observing faster degradation when cycling in the full voltage window (with less time spent at high voltages) compared to high voltage holds or cycling.…”