A new method to compensate impedance artefacts for Li-ion batteries with integrated micro-reference electrodes

In order to measure the electrochemical characteristics of both electrodes inside Li-ion batteries, micro-reference electrodes (μREF) turned out to be very useful. However, measuring the electrochemical impedance with respect to μREF can lead to severe measurement artefacts, making a detailed analysis of the impedance spectra complicated. In the present work a new method is developed in which high-frequency measurement artefacts can be compensated. A theoretical analysis, using equivalent circuit models of the measurement setups, shows that if two different impedance measurements are averaged, the impedance contributions from the measurement leads can be completely eliminated. The theoretical analysis is validated using Li-ion batteries with seven integrated μREF, having all different impedances. The measurement results show that artefacts are dominating for high-impedance μREF in the high frequency range. However, these artefacts can be fully compensated by averaging two separate impedance measurements, as predicted by theory. This easily makes it possible to perform artefact-free impedance measurements, even at high frequencies

A Review of Degradation Mechanisms and Recent Achievements for Ni-Rich Cathode-Based Li-Ion Batteries

The growing demand for sustainable energy storage devices requires rechargeable lithium-ion batteries (LIBs) with higher specific capacity and stricter safety standards. Ni-rich layered transition metal oxides outperform other cathode materials and have attracted much attention in both academia and industry. Lithium-ion batteries composed of Ni-rich layered cathodes and graphite anodes (or Li-metal anodes) are suitable to meet the energy requirements of the next generation of rechargeable batteries. However, the instability of Ni-rich cathodes poses serious challenges to large-scale commercialization. This paper reviews various degradation processes occurring at the cathode, anode, and electrolyte in Ni-rich cathode-based LIBs. It highlights the recent achievements in developing new stabilization strategies for the various battery components in future Ni-rich cathode-based LIBs

Determination of state-of-charge dependent diffusion coefficients and kinetic rate constants of phase changing electrode materials using physics-based models

The simplified gravimetric intermittent titration technique (GITT) model, which was first proposed by Weppner and Huggins in 1977, remains a popular method to determine the solid-state diffusion coefficient (D1) and the electrochemical kinetic rate constant (k). This is despite the model having been developed on the premise of a single-slab electrode and other gross simplification which are not applicable to modern-day porous battery electrodes. Recently however, more realistic and conceptually descriptive models have emerged, which make use of the increased availability of computational power. Chief among them is the P2D model developed by Newman et al., which has been validated for various porous battery electrodes. Herein, a P2D GITT model is presented and coupled with grid search optimization to determine state-of-charge (SOC) dependent D1 and k parameters for a sodium-ion battery (SIB) cathode. Using this approach, experimental GITT steps could be well fitted and thus validated at different SOC points. This work demonstrates the first usage of the P2D GITT model coupled with optimization as an analytical method to derive and validate physically meaningful parameters. The accurate knowledge of D1 and k as a function of the SOC gives further insight into the SIB intercalation dynamics and rate capability

A comparison and accuracy analysis of impedance-based temperature estimation methods for Li-ion batteries

In order to guarantee safe and proper use of Lithium-ion batteries during operation, an accurate estimate of the battery temperature is of paramount importance. Electrochemical Impedance Spectroscopy (EIS) can be used to estimate the battery temperature and several EIS-based temperature estimation methods have been proposed in the literature. In this paper, we argue that all existing EIS-based methods implicitly distinguish two steps: experiment design and parameter estimation. The former step consists of choosing the excitation frequency and the latter step consists of estimating the battery temperature based on the measured impedance resulting from the chosen excitation. By distinguishing these steps and by performing Monte-Carlo simulations, all existing methods are compared in terms of accuracy (i.e., mean-square error) of the temperature estimate. The results of the comparison show that, due to different choices in the two steps, significant differences in accuracy of the estimate exist. More importantly, by jointly selecting the parameters of the experiment-design and parameter-estimation step, a more-accurate temperature estimate can be obtained. In case of an unknown State-of-Charge, this novel method estimates the temperature with an average absolute bias of 0.4. °C and an average standard deviation of 0.7. °C using a single impedance measurement for the battery under consideration

Fabrication and interfacial characterization of Ni-rich thin-film cathodes for stable Li-ion batteries

Ni-rich LiNi0.6Co0.2Mn0.2O2 (NCM) and LiNbO3-protected LiNi0.6Co0.2Mn0.2O2 (NCM) thin-film cathodes have been prepared by radio frequency (RF) magnetron sputtering. Electrochemical investigations show enhanced stability of LiNbO3-protected cathodes compared with bare LiNi0.6Co0.2Mn0.2O2. The interfacial interaction of LiNbO3 and LiNi0.6Co0.2Mn0.2O2 layers has been investigated by XPS depth profiling and demonstrated different cathode electrolyte interface (CEI) film formation processes at the electrodes. The results elaborate on the interaction between LiNbO3 and LiNi0.6Co0.2Mn0.2O2, emphasizing the role of the LiNbO3 layer in improving the cycling performance of Ni-rich cathodes

Applicability of heat generation data in determining the degradation mechanisms of cylindrical li-ion batteries

The applicability of heat generation data obtained after cylindrical Li-ion cells discharging with a constant current was analyzed thoroughly to determine cell degradation mechanisms. Different commercial and noncommercial cylindrical Li-ion cells, wherein graphite was used for negative electrode creation, were considered in this study and the degradation mechanisms were analyzed during cycling and storage. The heat generation in the cylindrical cells was estimated using heat flux and temperature measurements of the cell surface. The results obtained using analysis of the heat generation data were compared with those obtained using differential voltage analysis. The use of the heat generation data was shown to improve the detection and separation of the degradation mechanisms in Li-ion batteries during cycling and storage. The differential curve, which is based on the heat generation data, was proposed to investigate the degradation mechanisms. Moreover, the effects of the C-rate current and temperature on the form of the proposed differential curve were evaluated

Wet-Chemical Synthesis of 3D Stacked Thin Film Metal-Oxides for All-Solid-State Li-Ion Batteries.

By ultrasonic spray deposition of precursors, conformal deposition on 3D surfaces of tungsten oxide (WO₃) negative electrode and amorphous lithium lanthanum titanium oxide (LLT) solid-electrolyte has been achieved as well as an all-solid-state half-cell. Electrochemical activity was achieved of the WO₃ layers, annealed at temperatures of 500 °C. Galvanostatic measurements show a volumetric capacity (415 mAh·cm-3) of the deposited electrode material. In addition, electrochemical activity was shown for half-cells, created by coating WO₃ with LLT as the solid-state electrolyte. The electron blocking properties of the LLT solid-electrolyte was shown by ferrocene reduction. 3D depositions were done on various micro-sized Si template structures, showing fully covering coatings of both WO₃ and LLT. Finally, the thermal budget required for WO₃ layer deposition was minimized, which enabled attaining active WO₃ on 3D TiN/Si micro-cylinders. A 2.6-fold capacity increase for the 3D-structured WO₃ was shown, with the same current density per coated area

Enhanced sulfur utilization in lithium-sulfur batteries by hybrid modified separators

The extraordinary energy density and low cost enable lithium-sulfur (Li-S) batteries to be a promising alternative to traditional energy storage systems. The principal hurdle facing Li-S batteries is the unsatisfactory utilization of sulfur cathodes. The detrimental shuttle issue of polysulfides and the sluggish charge transfer kinetics result in quick capacity degradation of Li-S batteries. An MFLC hybrid material composed of manganese-iron layered double hydroxides (Mn-Fe LDH) and carbon nanotubes (CNT) has been developed. Such heterostructure combines the advantages of effective chemical bonding of Mn-Fe LDH towards polysulfides with the high conductivity of CNT. When modified on a polypropylene (PP) separator, the hybrid material is proven to significantly inhibit the shuttle issue of polysulfides and accelerate their redox reaction kinetics. Li-S batteries with MFLC-modified separators revealed considerably improved electrochemical performance. A high initial capacity of 1138 mA h g−1 and 70 % capacity retention after 200 cycles were achieved at 0.2 C. The enhanced sulfur utilization can be directly evaluated from the discharge voltage plateaus. The results indicate a new solution for the practical application of Li-S batteries and provide a simple approach to determine the efficiency of sulfur utilization

Overpotential analysis of graphite-based Li-ion batteries seen from a porous electrode modeling perspective

The overpotential of Li-ion batteries is one of the most relevant characteristics influencing the power and energy densities of these battery systems. However, the intrinsic complexity and multi-influencing factors make it challenging to analyze the overpotential precisely. To decompose the total overpotential of a battery into various individual components, a pseudo-two-dimensional (P2D) model has been adopted and used for electrochemical simulations of a graphite-based porous electrode/Li battery. Analytical expressions for the total overpotential have been mathematically derived and split up into four terms, associated with the electrolyte concentration overpotential, the Li concentration overpotential in the solid, the kinetic overpotential, and the ohmic overpotential. All these four terms have been separately analyzed and are found to be strongly dependent on the physical/chemical battery parameters and the reaction-rate distribution inside the porous electrode. The reaction-rate distribution of the porous electrode is generally non-uniform and shows dynamic changes during (dis)charging, resulting in fluctuations in the four overpotential components. In addition, the disappearance of the phase-change information in the voltage curve of the graphite-based porous electrode/Li battery under moderate and high C-rates is ascribed to the Li concentration overpotential among solid particles, resulting from the non-uniform reaction-rate distribution