Relaxation Effects in Self-Discharge Measurements of Lithium-Ion Batteries

Self-discharge is an important indicator in evaluating the quality of lithium-ion cells. This paper proposes a novel method to quickly measure the self-discharge of lithium-ion cells. A self-discharge equivalent model is developed for analyzing self-discharge measurement requirements. The load capacitance in the model is obtained by using the characteristic curve of open circuit voltage and state of charge. Based on the relationship between the weak current and time of the cell in the charging state, the self-discharge resistance is quickly determined. The corresponding measurement process is introduced. The first experiment preliminarily verifies the plausibility of the load capacitance measurement method proposed in this paper. The second experiment uses this new method to investigate the self-discharge dependence of state-of-charge and further analyzes the influence of load capacitance accuracy on measurement. In order to verify the efficiency and accuracy of the new method, a comparison experiment is conducted by three typical methods and the new method. The results show that this new method is useful; the difference between the results is acceptable while the required measurement time is shortened to less than 6 hours.

“…K value can be can be further converted to the average self-discharge current through the load capacitance. 35…”

Section: Resultsmentioning

confidence: 99%

A Novel Measurement Method for the Self-Discharge of Lithium-Ion Cells Employing an Equivalent Resistance Model

Xu¹,

Tu²,

Li³

et al. 2023

“…The stability of the REs can thus be analyzed in the real cell with all influences of any by-products the electrode materials or impurities may form. Unfortunately, a state where the local lithiation degrees are identical at all locations in the active electrode area and the anode overhang region cannot be reached due to very slow long-term equalization processes, 53 as will be described in detail in the results section. To minimize the influence of inhomogeneous potential distributions within the cell, a GWRE was placed next to the LTO-RE for the stability study in 3f), so none of these special discharge steps are included in the data during this period.…”

Section: Methodsmentioning

confidence: 99%

“…They show a stronger response compared to the LTO-RE in cell ③, which could also be due to the increased separator thickness, as already speculated in the literature. 56 The overhang close to the active area may still have a reduced current density, 53 which causes the ohmic potential drop to be lower. Again, a further dropping potential is observed at 0% SoC after the end of the pulse, which can be interpreted as an indicator of the equalization process between the active electrode region and the overhang.…”

Section: External Reference Electrode Measurements During Hppc-mentioning

confidence: 99%

Multi-Reference Electrode Lithium-Ion Pouch Cell Design for Spatially Resolved Half-Cell Potential and Impedance Measurements

Oehler,

Graule,

Kücher

et al. 2023

Self Cite

Reliable experimental methods for measuring local potentials in lithium-ion battery cells are challenging but vital for a deep understanding of internal processes at the individual electrode level, and to parameterize and validate electrochemical models. Different three-electrode setups and reference electrodes (REs) have been developed in recent years. Some are based on custom laboratory setups or are small, e.g., coin cell sized. This work addresses internal potentials and half-cell impedances in the widely used single-layer pouch cell format and proposes a novel multi-reference electrode cell design, enabling spatially resolved measurements. For the first time, it is shown how multiple 25 and 50 μm thin gold wire REs, together with a larger LTO-RE, can be used to study occurring inhomogeneities, considering the geometrical anode overhang. Special attention is given to the subtleties of the measurements and their interpretation. Multiple REs allow plausibility checks and confirm stability for both types during a continuous measurement period of more than 7,500 h (>10 months), demonstrating suitability, e.g., for long-term cycling measurements. Results from electrochemical impedance spectroscopy and half-cell potential measurements at low currents of C/100 and during fast charging at up to 3C highlight the versatility of the easily reproducible cell design.

“…Such a phenomenon can come from the anode overhang, where charges flow from the inactive to the active anode areas. 41 A positive shift of the DEP means a capacity loss and is mainly attributed to SEI growth and electrolyte reduction. 40,42 Therefore, the cells with more SiOx content are expected to show more SEI growth related to the volume work of the electrode.…”

Section: ιιmentioning

confidence: 99%

Cycle Characterization of SiO-Based Lithium-Ion-Batteries Using Real Load Profiles

Moyassari,

Li,

Tepe

et al. 2023

Self Cite

Understanding the cyclic behavior of Lithium-Ion Batteries (LIBs) is crucial for optimizing their performance and extending their operational lifespan. This work presents a study on the cycle characterization of silicon-oxide-based (SiOx) cells, focusing on the impact of real load profiles and state-of-charge (SoC) ranges while varying the SiOx content in the cells. Various load profiles representing real usage patterns obtained from an industrial partner were applied to SiO-based pouch cells. These load profiles are represented over different SoC ranges to explore the effect of varying levels of charge/discharge on battery aging. The aging characteristics of the batteries are evaluated by monitoring capacity fade, state-of-health (SoH), and capacity end-point-slippage. The experimental results demonstrate that the different SiOx content of the investigated cells and the SoC range significantly influence the cycle behavior of the cells. The resulting capacity loss was affected especially by the anode overhang effect. Cycling under high SoC conditions accelerates capacity fade and leads to higher SoH loss. The findings also indicate that SiO-based cells exhibited higher aging than traditional graphite-based cells. The capacity fade rate increased at higher SiOx content.