Journal of Power Sources Advances最新文献

Precise explanation and prediction of the aging behavior of lithium-ion batteries (LIBs) is essential for improving battery management systems. It is quickly becoming a hotspot in battery research. Solid electrolyte interphase (SEI) growth is regarded as the dominant factor of capacity losses in LIBs. However, the growth of SEI is yet to be understood in more detail due to its complexity. In the present paper, an advanced voltage-based aging model using an electron tunneling mechanism is proposed and validated by experiments. This model employs the electrode voltage as an input parameter for the first time with a tunneling mechanism, which is more flexible than existing energy-based approaches and can be used to predict the electron tunneling (dis)charge cycles. The proposed model is used to simulate tunneling current profiles during (dis)charging of graphite, LTO, and blend Si/C negative electrodes. The simulation results prove and explain that lower states-of-charge of LIBs mitigate electron tunneling and SEI growth, further reducing calendar aging. That work can be used to describe battery capacity losses better and it is crucial for predicting the state-of-health of LIBs.

The comprehensive understanding of the local structural changes surrounding lithium in lithium silicate (Li_xSiO_y) and silicide (Li_xSi) within Li/SiO_x batteries during the reversible structural transformations has been hindered by the limitations of current methodologies. In this work, the evolution of electronic structure at various lithiation stages has been addressed well by examining the Li K-edge spectra through X-ray Raman spectroscopy (XRS). The features observed in the Li K-edge XRS spectra provide insights into the development and alteration of Li_xSiO_y, which emerges in the initial phases and may be accompanied by a reduction in the ionicity of Li–O bonding during lithiation. These features also agree well with the accompanying FDMNES code simulation. The correlation between electrochemical mechanisms and spectral characteristics is further explored by applying pseudo-Voigt peaks and cumulative pseudo-Voigt functions for fitting purposes. The absence of a significant edge shift indicates a similarity in the electronic structure of Li_xSi throughout lithiation, and no evidence of Li₂O formation has also been observed. The Li K-edge XRS spectra exhibit strong agreement with the electrochemical behavior, establishing it as a valuable tool for investigating the evolution of electronic structure in Li/SiO_x batteries.

Imide-based ionic liquids (ILs) are intriguing candidates for constructing safer electrolytes and better rechargeable batteries. In this work, a sulfinyl-functionalized imide anion, (trifluoromethanesulfinyl) (trifluoromethanesulfonyl)imide anion ([(CF₃SO) (CF₃SO₂)N]⁻, [qTFSI]⁻), is proposed as negative charge for building low-melting ILs and high-performing electrolytes. The physicochemical properties of [qTFSI]-based ILs and their electrolytes are extensively characterized, and the reference systems with the classic sulfonimide anion, bis(trifluoromethanesulfonyl)imide anion ([(CF₃SO₂)₂N]⁻, [TFSI]⁻) are also comparatively investigated. It has been revealed that the [qTFSI]⁻ anion shows lesser extent of negative charge delocalization as compared to the reference [TFSI]⁻ anion, which is responsible for slightly stronger interactions between IL cations and the sulfinyl-functionalized anion. The asymmetric feature of the [qTFSI]⁻ anion contributes to lower glass and melting transitions of the corresponding ILs vs. [TFSI]-based ones, which effectively expands the operational temperature of the rechargeable batteries. Furthermore, the co-utilization of [qTFSI]⁻ with [TFSI]⁻ is found to improve the electrochemical compatibility of Li metal anode with the IL-based electrolytes, sustaining better cycling stability of the Li symmetric cells. The current work offers an elegant approach for the design of new anions for interface-favorable ILs and their electrolytes.

Lithium-sulfur (Li–S) batteries have emerged as a next-generation battery technology owing to their prospects of high capacity and energy density. They, however, suffer from rapid capacity decay due to the shuttling of reaction intermediate species: Li polysulfides (LiPSs). One of the more important and intriguing PSs is the tri-sulfur radical ($S_3^{•-}$), observed mainly in high-donor number (DN) solvent-based electrolytes. Although this radical has been proposed to be crucial to full active material (AM) utilization, there is currently no direct evidence of the impact of $S_3^{•-}$ on cycling stability. To gain more insight into the role of the $S_3^{•-}$, we studied the use of radical traps in low and high DN solvent-based electrolytes by operando Raman spectroscopy. The traps were based on nitrone and iminium cation, and $S_3^{•-}$ was indeed successfully trapped in ex situ analysis. However, it was the ionic liquid-based trap, specifically pyridinium, that effectively suppressed $S_3^{•-}$ during battery operation. Overall, the PS formation was altered in the presence of the traps and we confirmed the impact of $S_3^{•-}$ formation on the Li–S battery redox reactions and show how the trapping correlates with Li–S battery performance. Therefore, stabilization of the $S_3^{•-}$ might be a path to improved Li–S batteries.

Previously, lithium-acetylide (Li₂C₂) had been identified as electrolyte degradation product on lithium-metal based electrodes using Raman spectroscopy. This raised the question, if Li₂C₂ is also be formed on graphitic electrodes in lithium-ion batteries without lithium metal present. In order to shed light on this research question, we performed a series of in situ Raman experiments with graphitic electrodes in half- and full-cell configuration. The recorded cell potential dependent spectra clearly prove the presence of Li₂C₂ in the lithiated state of the electrodes, but the according peak vanishes when delithiating. This observation indicates a somewhat reversible process involving Li₂C₂. Several chemical/electrochemical reactions are in question to contribute to this effect. With respect to its properties and potential role in the solid-electrolyte interphase (SEI) DFT calculations of Li₂C₂-nanoclusters were performed, which revealed an exceptionally low energy band gap, hence a remarkable electric conductivity. In conjunction with a relatively high ionic conductivity, Li₂C₂ appears to play a key role in the degradation of lithium-ion batteries, which had not yet been revealed nor taken into account in simulations of the interphase.

State-of-the-art lithium-ion cell chemistries with pronounced open-circuit voltage hysteresis (OCV), characterised by asymmetry and directional dependence, present a challenge for estimating the state of charge (SOC). Without understanding the hysteresis behaviour, OCV measurement points that lie within the hysteresis window cannot be used for SOC correction. After obtaining the data efficiency of the trajectory correction hysteresis (TCH) model with the introduction of the transfer fit (TF) method, this work applies the TF TCH for OCV-based SOC correction. The TF method plays a key role as it enables the cell-specific adaptation of an existing TCH model - ageing update is achieved with solely 12 (SOC/OCV) measurement points. With the precise hysteresis model, the developed framework successfully corrects the faulty SOC history, which could originate from a vehicle data logger. Given that two OCV measurement points are available that arbitrarily lie within the SOC history, the SOC correction is achieved by minimising the voltage deviation between the measurement points and the TCH model’s simulation. Identifying the two SOC parameters shift and scale enables subsequent SOC estimation until an additional OCV measurement is available for a further update. The functionality of the presented SOC correction framework is demonstrated using two validation profiles.

A quasi-steady, CFD-based modeling approach is employed to investigate the heat loading within a small package of twenty-five 18650 Li-ion cells. The quasi-steady approach allows for computationally efficient simulations to capture the compressible and turbulent flow field through the safety vent structure and out into the space surrounding a failing cell. Combustion of vent gases leads to high heat loading on neighboring cells and nearby surfaces. Heat transfer mechanisms within the enclosure include convection from hot gases, radiation from the participating medium, and radiation exchange between surfaces. Simulations provide insight into the magnitude of each heat transfer mechanism, and the spatial distribution of heat flux on nearby cells and surfaces within the pack. The complex geometry of the safety vent geometry resulted in an asymmetric jet flow pattern, which induces highly localized impingement heat transfer on specific cells within the enclosure. Radiation from hot surfaces was more significant than radiation from hot gases and soot to neighboring cells. The quasi-steady simulations may be used in the future to develop reduced-order heat transfer models that include the effects of venting and combustion on propagating failure.