Filtern
Dokumenttyp
- Vortrag (4)
- Zeitschriftenartikel (2)
- Posterpräsentation (1)
Sprache
- Englisch (7)
Schlagworte
- Ageing (2)
- Differential voltage analysis (2)
- Lithium-Ion Battery (2)
- Overdischarge (2)
- Safety (2)
- Accelerated ageing (1)
- Batteries (1)
- Battery degradation (1)
- Cyclic Voltammetry (1)
- Degradation processes (1)
Organisationseinheit der BAM
Eingeladener Vortrag (wissenschaftliche Konferenzen)
- nein (4)
Differential voltage analysis (DVA) and cyclic voltammetry (CV) are powerful
electroanalytical techniques. While CV can be used to study the kinetics of electron transfer reactions [1], DVA can visualise phase transitions by correlating the opencircuit voltage and exchanged charge [2]. Recently, DVA receives an increasing attention in the battery community for characterising full-cell setups. In contrast, CV is less prominent for batteries, yet the prevalently used technique for ex-situ characterisations of novel electrode materials in half-cell configuration.
In this study, we have investigated the overdischarge process of LiFePO4 pouch cells – which is usually presumed to result in a decomposition of the solid electrolyte interphase (SEI) and a corrosion of the copper current collector – in a complementary electrochemical analysis which uses both, CV and DVA in full-cell mode. For this purpose, CV consisting of three low sweep-rate scans and DVA of three low current rate cycles was performed. Degradation was traced by successive CV/DVA sequences during, pre- and post-overdischarge which allowed to pinpoint the features, the limitations, and similarities of both techniques.
In this manner, we demonstrate that CV can successfully identify the dynamics of degradation processes, indicating that an irreversible side reaction starts at cell voltages below 0.55 V. For this reason, this study underlines that CV can be effectively used for spotting dynamic degradation mechanisms which are hardy seen in DVA. This may pave the way for further analysis which can be used for fingerprinting characteristic degradation.
Lithium-iron-phosphate (LFP) and sodium-ion batteries (SIBs) offer safe and cost-effective options for energy storage. In this study, the effects of continuous electrical stress, including high current loads and overdischarge, during cyclic ageing are investigated by tracing capacity loss and Coulombic efficiency during cycling of both cell types. Additionally, differential voltage analysis of pseudo open-circuit voltage discharges is utilised for degradation mode analysis. The results show that electrical stress accelerates degradation in both LFPs and SIBs, with high current rates potentially triggering plating or even cell failure in SIBs. Overdischarging primarily intensifies ageing by promoting accelerated solid electrolyte interphase growth.
Lithium-iron-phosphate (LFP) and sodium-ion batteries (SIBs) are promising technologies for energy storage systems due to their safe handling and cost-effectiveness. SIBs can be discharged to 0V without the safety concerns associated with lithium-ion batteries' copper current collector oxidation. However, overdischarging both types of batteries may decompose and subsequently rebuild the solid electrolyte interphase (SEI), leading to irreversible capacity loss and degradation.
This study performs an in-situ analysis of the overdischarge process of LiFePO4 pouch and Na-ion cylindrical cells. Therefore, the cells are characterised for three low C-rate constant current or three slow-scan voltage cycles. While the voltage range of the manufacturer’s specifications is chosen for the first and third cycle, for the second cycle the minimum voltage is modified to 0.5V (LFP) and 0V (SIB), respectively. This enables tracing the degradation during the overdischarge, as well as through a comparison of the results pre- and post-overdischarging. For this purpose, the study employs two electrochemical characterisation techniques: differential voltage analysis (DVA) and cyclic voltammetry (CV). While cyclic voltammetry allows for the study of the kinetics of electron transfers [1], DVA enables the assessment of lithium distribution homogeneity and capacity degradation [2].
In both cells, the characterisation shows significant differences before and after overdischarging, indicating lasting changes through the decomposition and rebuilding of the SEI. This comparative study elucidates the overdischarge-induced degradation in sodium- and lithium-ion batteries, highlighting the utility of CV and DVA in analysing degradation mechanisms.
This study presents a test protocol that greatly accelerates the ageing process of lithium-ion battery cells comprising a positive electrode of nickel manganese cobalt oxide while preserving their characteristic degradation upon cyclic ageing. Applying a repetitive restricted overdischarge, resulting in a depth of discharge larger than 100%, a capacity loss of 20% is achieved over five times faster compared to conventional cycling. The well-known overdischarge degradation phenomenon of copper current collector dissolution is deliberately prevented by setting a discharge cutoff voltage above the theoretical threshold of copper oxidation. Hence, the accelerated degradation can be primarily connected to solid electrolyte interphase growth.
A comparative assessment of the ageing dynamics using electrochemical impedance spectroscopy and differential voltage analysis hints towards similar, characteristic degradation processes during accelerated and conventional ageing. A post-ageing examination of the electrical behaviour (i.e., coulombic and energy efficiency, capacity fade) under reference conditions reveals very little to no lasting damages caused by
overdischarging. Additionally, post-mortem analysis discloses no increased copper dissolution when comparing cells subjected to accelerated and conventional ageing. Generally, the developed ageing method appears suitable for providing cells with a defined state of health at a reasonable timescale without altering the main degradation mechanisms significantly.
In-situ Quantification of the Ageing Dynamics in Lithium-Ion Cells up to Failure-Near Conditions
(2023)
Implementing end-of-life (EOL) lithium-ion batteries from automotive applications in stationary energy storages is of utmost relevance for a sustainable handling of scarce resources. Beneficial from an economic and ecological perspective, such second-life applications urgently require a guarantee for safe operation. Unlike the state of health (SOH), defined by classical performance indicators such as capacity and voltage, the state of safety (SOS) of an aged battery cannot be assessed straightforward. Its determination requires a plethora of cells to be tested which is a particular challenge for new technologies with limited access to EOL batteries.
For providing cells with a defined SOH at a reasonable timescale, we herein propose a novel method of greatly accelerating the ageing process of lithium-ion batteries. In a preliminary test series, lithium-ion NMC pouch cells are exposed to incrementally increasing temperatures, current rates and/or states of charge (SOC), until thermal runaway is induced. In this manner, the critical state in proximity to cell failure is spotted for individual and combined stress parameters. Based on this knowledge, cell-specific test parameters for heavily accelerated ageing are developed. In this protocol, electrical abuse conditions are defined by over/under charging and high current rates. Typically, the cells are cycled utilizing a depth of discharge above 100 %.
The accelerated aging dynamics under these critical conditions are monitored by systematic capacity, open circuit voltage and electrochemical impedance spectroscopy (EIS) measurements. This enables a comparative assessment of the electrical behaviour, following conventional vs. heavily accelerated ageing. Such knowledge will in turn help to define the threshold to which cyclic ageing can be accelerated without changing the characteristic degradation mechanisms of lithium-ion batteries.
Repurposing end-of-life (EOL) lithium-ion batteries from mobile applications, such as electric vehicles, is of utmost importance for a sustainable handling of scarce resources. For an economically and ecologically desirable reuse of aged batteries in second-life applications, a guarantee for safe and reliable operation is urgently required. However, the assessment of the state of safety (SOS) is not straightforward, as multiple abuse cases, variables and interactions need to be considered [1]. Therefore, defining safety parameters and test procedures, as well as determining the SOS requires a plethora of aged cells to be tested.
In this study, a novel method of greatly accelerating the ageing process of lithium-ion batteries is proposed. Overcharging and overdischarging are embedded in cyclic ageing, continuously employing a depth of discharge larger than 100 %. Different electrical abuse conditions (overcharge, overdischarge, high current rates) are applied on lithium-ion NMC and LFP pouch cells in a preliminary test series. In this manner, the cells are stressed until a cell failure or a thermal runaway is induced. Thus, the critical state in proximity to a cell failure is spotted for individual and combined stress parameters. Based on this knowledge, a test protocol for strongly accelerated ageing with cell-specific, abusive electrical parameters is developed. The aging dynamics under these critical conditions are monitored by systematic capacity, open circuit voltage and electrochemical impedance spectroscopy (EIS) measurements. This enables an assessment of the degradation mechanisms induced by overdischarge and overcharge cycling. A special focus is set on the comparative assessment of the electrical behaviour, following conventional vs. greatly accelerated ageing.
This novel method is suitable for providing cells with a defined SOH at a reasonable timescale. Furthermore, the results are of high relevance for the evaluation to which degree cyclic ageing can be accelerated without changing the characteristic degradation mechanisms of lithium-ion batteries.
This study presents a systematic, characterization of electrolytes from commercial lithium-ion batteries (LIB), encompassing 90 batteries from leading global manufacturers across diverse formats and application sectors. An integrated, complementary mass spectrometric workflow combining LC–MS/MS, GC–MS, and high-resolution MS was employed. To ensure robust structural annotation, molecular identifications were assigned confidence levels following Schymanski et al. (2014).
Across all formats, PF6− was confirmed as the dominant Li+ counterion, frequently coexisting with BF4−, PO2F2−, and bis(fluorosulfonyl)imide (FSI−), forming binary and ternary salt systems optimized for both conductivity and safety. Solvent systems revealed the widespread use of propylene carbonate (PC) combined with diverse carbonate mixtures, demonstrating trends in performance optimization specific to cell format. A variety of additives were identified, reflecting a clear shift towards multifunctional, synergistic additive packages and the gradual replacement of fluorinated species with environmentally safer alternatives. Cycling studies demonstrated that electrolyte degradation mechanisms are strongly influenced by electrode composition and additive chemistry, with oxidative degradation pathways dominating.
Together, these findings provide rare empirical insight into the evolving formulation strategies of electrolytes in commercial LIB, still employing classic carbonates and LiPF6, but highlighting a trend toward safer, more robust, and sustainable electrolyte architectures by using synergistic multifunctional systems.
