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A three-step numerical procedure has been developed, which facilitatesthe conversion of NDP energy spectra into lithium concentrationdepth profiles for thin-film Li-ion batteries. The procedureis based on Monte Carlo modeling of the energy loss of chargedparticles (ions) in the solid media, using the publically availableSRIM/TRIM software. For the energy-to-depth conversion, the batterystack has been split into finite volume elements. Each finite volumeelement becomes a source of ions according to the employednuclear reaction. Ions loos energy when they move across the batterystack towards the detector. The as-obtained simulated spectrahave been compared with the experimentally measured spectra. Thethicknesses of the battery stack layers were estimated by minimizingthe deviation between the simulated and measured spectra. Subsequently,a relation between the average energy of detected ions andthe depth of the corresponding finite volume element, yielding a calibrationfunction, was used to relate that particular part of the spectrawith the depth of its source. At the final stage, a Bayesian estimatorwas used to find the distribution of lithium at a particular depth. Thedeveloped procedure was applied to a practically relevant case studyof Si immobilization in the LPO electrolyte of all-solid-state thin-filmbatteries. It is shown that the lithium immobilization process in theLPO electrolyte is responsible for the battery degradation process.

Electrolytes play an integral role in the successful operation of any battery chemistry. The reemergence of the sodium-ion battery (SIB) chemistry has therefore rejuvenated the search for optimized SIB salts and solvents. Recent experiments have found that 1 M NaPF 6 in ethylene carbonate (EC) and propylene carbonate (PC), EC 0.5 : PC 0.5 (w/w) is the best binary electrolyte for SIBs. However, mathematical models, to elucidate these experimental findings, have so far been lacking. Furthermore, no attempts to understand the effect of EC composition on the conductivity and electrolyte stability have been performed. Herein, the viscosity and conductivity profiles of NaPF 6 in EC 0.5 : PC 0.5 electrolyte are unraveled, using experimental and modeling approaches at different temperatures and salt concentrations. The viscosity is measured in a double-wall Couette cell and for the first time, the ionic conductivity is determined using two Pt blocking electrodes in a PAT-Cell electrochemical setup. Modeling is performed using the Advanced Electrolyte Model (AEM), a statistical mechanics software. It is shown that the conductivity and viscosity relationship follows a simple Stokes' law even at a low temperatures and high concentrations. In addition, the stability of binary and ternary electrolytes on hard carbon is shown to correlate with the preferential ion solvation of EC.

The solid-state spherical diffusion equation with flux boundary conditions is a standard problem in lithium-ion battery simulations. If finite difference schemes are applied, many nodes across a discretized battery electrode become necessary, in order to reach a good approximation of solution. Such a grid-based approach can be appropriately avoided by implementing analytical methods which reduce the computational load. The pseudo-steady-state (PSS) method is an exact analytical solution method, which provides accurate solid-state concentrations at all current densities. The popularization of the PSS method, in the existing form of expression, is however constrained by a solution convergence problem. In this short communication, a modified PSS (MPSS) expression is presented which provides uniformly convergent solutions at all times. To minimize computational runtime, a fast MPPS (FMPPS) expression is further developed, which is shown to be faster by approximately three orders of magnitude and has a constant time complexity. Using the FMPSS method, uniformly convergent exact solutions are obtained for the solid-state diffusion problem in spherical active particles.

Temperature measurements of Li-ion batteries are important for assisting Battery Management Systems in controlling highly relevant states, such as State-of-Charge and State-of-Health. In addition, temperature measurements are essential to prevent dangerous situations and to maximize the performance and cycle life of batteries. However, due to thermal gradients, which might quickly develop during operation, fast and accurate temperature measurements can be rather challenging. For a proper selection of the temperature measurement method, aspects such as measurement range, accuracy, resolution, and costs of the method are important. After providing a brief overview of the working principle of Li-ion batteries, including the heat generation principles and possible consequences, this review gives a comprehensive overview of various temperature measurement methods that can be used for temperature indication of Li-ion batteries. At present, traditional temperature measurement methods, such as thermistors and thermocouples, are extensively used. Several recently introduced methods, such as impedance-based temperature indication and fiber Bragg-grating techniques, are under investigation in order to determine if those are suitable for large-scale introduction in sophisticated battery-powered applications.

The ageing mechanisms of C6/LiNi0.5Mn0.3Co0.2O2 batteries at various discharging currents and temperatures have systematically been investigated with electrochemical and post-mortem analyses. The irreversible capacity losses (ΔQir) at various ageing conditions are calculated on the basis of regularly determined electromotive force (EMF) curves. Two stages can be distinguished for the degradation of the storage capacity at 30 °C. The first stage includes SEI formation, cathode dissolution, etc. The second stage is related to battery polarization. The various degradation mechanisms of the individual electrodes have been distinguished by dVEMF/dQ vs Qout and dVEMF/dQ vs V plots. The Solid-Electrolyte-Interface (SEI) formation as well as the electrode degradation has been experimentally confirmed by XPS analyses. Both Ni and Mn elements are detected at the anode while Co is absent, indicating that the bonding of Co atoms is more robust in the cathode host structure. A Cathode-Electrolyte-Interface (CEI) layer is also detected at the cathode surface. The composition of the CEI layer includes Li salts, such as LiF, LiCOOR, as well as transition metal compounds like NiF2. Cathode dissolution is considered to be responsible for both the NiF2 detected at the cathode and Ni at the anode.

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 ( D 1 ) 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 D 1 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 D 1 and k as a function of the SOC gives further insight into the SIB intercalation dynamics and rate capability.

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.

Materials today / Communications 26, 102133 (2021). doi:10.1016/j.mtcomm.2021.102133, Published by Elsevier, Amsterdam [u.a.]

Among the existing energy storage technologies, lithium-ion batteries (LIBs) have unmatched energy density and versatility. From the time of their first commercialization in 1991, the growth in LIBs has been driven by portable devices. In recent years, however, large-scale electric vehicle and stationary applications have emerged. Because LIB raw material deposits are unevenly distributed and prone to price fluctuations, these large-scale applications have put unprecedented pressure on the LIB value chain, resulting in the need for alternative energy storage chemistries. The sodium-ion battery (SIB) chemistry is one of the most promising “beyond-lithium” energy storage technologies. Herein, the prospects and key challenges for the commercialization of SIBs are discussed. By comparing the technological evolutions of both LIBs and SIBs, key differences between the two battery chemistries are unraveled. Based on outstanding results in power, cyclability, and safety, the path toward SIB commercialization is seen imminent.

Electrochemistry communications 121, 106865 (2020). doi:10.1016/j.elecom.2020.106865, Published by Elsevier Science, Amsterdam [u.a.]

Lithium-ion batteries are indispensable in various applications owing to their high specific energy and long service life. Lithium-ion battery models are used for investigating the behavior of the battery and enabling power control in applications. The Doyle-Fuller-Newman (DFN) model is a popular electrochemistry-based model, which characterizes the dynamics in the battery through diffusions in solid and electrolyte and predicts current/voltage response. However, the DFN model contains a large number of parameters that need to be estimated to obtain an accurate battery model. In this paper, a computationally feasible two-step estimation approach is proposed that only uses voltage and current measurements of the battery under consideration. In the two-step procedure, the parameters are divided into 2 groups. The first group contains thermodynamic parameters, which are estimated using low-current discharges, while the second group contains kinetic parameters, which are estimated using a well-designed highly-dynamic pulse (dis-)charge current. A parameter sensitivity analysis is done to find a subset of parameters that can be reliably estimated using current and voltage measurements only. Experimental data are collected for 12 Ah nickel cobalt aluminum pouch lithium-ion cell. The voltage predictions of the identified model are compared with several experimental data sets to validate the model. A root mean square error between model predictions and experimental data smaller than 16 mV is achieved.

A fundamental electrochemical model is developed, describing the capacity fade of C6/LiFePO4 batteries as a function of calendar time and cycling conditions. At moderate temperatures the capacity losses are mainly attributed to Li immobilization in Solid-Electrolyte-Interface (SEI) layers at the anode surface. The SEI formation model presumes the availability of an outer and inner SEI layers. Electron tunneling through the inner SEI layer is regarded as the rate-determining step. The model also includes high temperature degradation. At elevated temperatures, iron dissolution from the positive electrode and the subsequent metal sedimentation on the negative electrode influence the capacity loss. The SEI formation on the metal-covered graphite surface is faster than the conventional SEI formation. The model predicts that capacity fade during storage is lower than during cycling due to the generation of SEI cracks induced by the volumetric changes during (dis)charging. The model has been validated by cycling and calendar aging experiments and shows that the capacity loss during storage depends on the storage time, the State-of-Charge (SoC), and temperature. The capacity losses during cycling depend on the cycling current, cycling time, temperature and cycle number. All these dependencies can be explained by the single model presented in this paper.

Mg-based hydrogen storage alloys are promising candidates for many hydrogen storage applications because of the high gravimetric hydrogen storage capacity and favourable (de)hydrogenation kinetics. In the present study we have investigated the synthesis and electrochemical hydrogen storage properties of metastable binary Mg yTi 1−y (y = 0.80–0.60) and ternary Mg 0.63Ti 0.27X 0.10 (X = Ni and Si) alloys. The preparation of crystalline, single-phase, materials has been accomplished by means of mechanical alloying under controlled atmospheric conditions. Electrodes made of ball-milled Mg 0.80Ti 0.20 powders show a reduced hydrogen storage capacity in comparison to thin films with the same composition. Interestingly, for a Ti content lower than 30 at.% the reversible storage capacity increases with increasing Ti content to reach a maximum at Mg 0.70Ti 0.30. The charge transfer coefficients (α) and the rate constants (K 1 and K 2) of the electrochemical (de)hydrogenation reaction have been obtained, using a theoretical model relating the equilibrium hydrogen pressure, electrochemically determined by Galvanostatic Intermittent Titration Technique (GITT), and the exchange current. The simulation results reveal improved values for Mg 0.65Ti 0.35 compared to those of Mg 0.80Ti 0.20. The addition of Ni even more positively affects the hydrogenation kinetics as is evident from the increase in exchange current and, consequently, the significant overpotential decrease.

© 2019 Elsevier Ltd A silicon-based anode in lithium-ion battery exhibits several times higher gravimetric energy storage capacity compared to an established carbon-based anode. However, the cycling performance of the silicon anode is poor due to the extremely large volume variation during the intercalation of lithium ions. The micro-structuring of silicon facilitates cycling performance. In particular, patterned microstructures are discussed as a possible solution. The large volumetric change can be adopted in such structures by bending walls and rotation around fixed vertexes. Nevertheless, the cycling performance of known patterned anodes remains poor due to plastic deformations. In this paper, a new square-based-patterned silicon anode is proposed and analyzed using the finite element method. The maximal stress in the topologically optimized structure is below the yield strength of lithiated silicon. In contrast to known structures, the deformed pattern of the new structure is explicitly defined by its initial geometry. A similar modification of the honeycomb-based-patterned anode leads to a slightly larger bending stress, but still below the yield stress of lithiated silicon. The related pure elastic deformation behavior is favorable to a prolonged cycling life of the micro-structured silicon anode. The developed approach can be applied for analysis of other severely swelling metamaterials.

3D microbatteries are indispensable to cope with the increasing energy demand of autonomous smart devices. To synthesize 3D microbatteries, step-conformal deposition of thin films into 3D-substrates is vital, and low pressure chemical vapor deposition (LPCVD) is a technique that is capable of achieving this goal. In the present work, the 3D-deposition of TiO2 is investigated. It is shown that the growth of anatase TiO2 can be characterized by two rate-determining processes. In the diffusion-controlled temperature region, the TiO2 films deposited into 3D-substrates lack step-conformity. In contrast, in the kinetically controlled temperature region, uniform films were deposited inside these microstructures. To understand and improve the LPCVD deposition process, the experimental results were simulated using a Monte Carlo chemical kinetics (MCCK) model. Good agreement between the model and experiments was achieved in all cases. It was found that the deposition probability is low in the kinetically controlled deposition region, while this probability was found to be high in the diffusion-controlled region. It is also shown that the reflections of precursor molecules inside the trenches play an important role in achieving homogeneous 3D deposition. To show the strength of the MCCK model, the optimized deposition parameters are applied to predict the film thickness profiles in narrower microstructures.

Electromotive force (EMF) voltage curves are regularly determined to facilitate in-depth understanding of aging mechanisms of C6/LiFePO4 batteries during cycling. The irreversible capacity losses under various cycling conditions and temperatures are accurately obtained from the extrapolated EMF curves and are found to increase with cycle number and time. A new mathematical extrapolation method is proposed to distinguish between calendar ageing and cycling-induced ageing. The capacity losses due to calendar aging are obtained by extrapolating the total irreversible capacity losses to zero cycle number. It is found that calendar ageing increases logarithmically in time. On the other hand, cycling-induced ageing is accurately determined by extrapolating the capacity losses to zero time. In this case the capacity losses are found to increase linearly with cycle number. It is furthermore found that iron dissolution from the cathode at 60 °C and the subsequent deposition onto the anode enhances significantly the SEI formation on the graphite electrode and, consequently, battery ageing. Interestingly, the graphite electrode decay has been quantified in much more detail, by analyzing the d V E M F / d Q curves. The analyses show that the electrode decay can be related to both the structural deterioration and the inter-layer surface blockage of the graphite electrode, as has also been experimentally confirmed by Raman and XPS spectroscopy.

A new mathematical model has been developed describing the thermodynamics of the hydrogen absorption and desorption process in Metal Hydrides via the gas phase. This model is based on first principles chemical and statistical thermodynamics and takes into account structural changes occurring inside hydrogen storage materials. A general state equation has been derived considering the chemical potentials of reacting species and volume expansion, from which the equilibrium hydrogen pressure dependence on the absorbed hydrogen content can be calculated. The model is able to predict the classical Van ’t Hoff equation from first-principle analytical expressions and gives more insight into the various hydrogen storage characteristics. Pressure-Composition Isotherms have been simulated for various hydride-forming materials. Excellent agreement between simulation results and experimental data has been found in all cases.

A new advanced mathematical model is proposed to accurately simulate the behavior of all-solid-state Li-ion batteries. The model includes charge-transfer kinetics at both electrode/electrolyte interfaces, diffusion and migration of mobile lithium ions in the electrolyte and positive electrode. In addition, electrical double layers are considered, representing the space-charge separation phenomena at both electrode/electrolyte interfaces. The model can be used to simultaneously study the individual overpotential and impedance contributions together with concentration gradients and electric fields across the entire battery stack. Both galvanostatic discharge and impedance simulations have been experimentally validated with respect to 0.7 mAh Li / LiPON / LiCoO 2 thin film, all-solid-state, batteries. The model shows good agreement with galvanostatic discharging, voltage relaxation upon current interruption, and impedance measurements. From the performed AC and DC simulations it can be concluded that the overpotential across the LiPON electrolyte is most dominant and is therefore an important rate-limiting factor. In addition, it is found that both ionic and electronic diffusion coefficients in the LiCoO 2 electrode seriously influence the battery performance. The present model is generally applicable to all-solid-state batteries where combined ionic and electronic transport takes place and allows for optimizing the battery components to increase the effective energy density, which leads to a decreasing demand for materials and costs.

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Like all rechargeable battery systems, conventional Li-ion batteries (LIB) inevitably suffer from capacity losses during operation. This also holds for all-solid-state LIB. In this contribution an in operando neutron depth profiling method is developed to investigate the degradation mechanism of all-solid-state, thin film Si–Li3PO4–LiCoO2 batteries. Important aspects of the long-term degradation mechanisms are elucidated. It is found that the capacity losses in these thin film batteries are mainly related to lithium immobilization in the solid-state electrolyte, starting to grow at the anode/electrolyte interface during initial charging. The Li-immobilization layer in the electrolyte is induced by silicon penetration from the anode into the solid-state electrolyte and continues to grow at a lower rate during subsequent cycling. X-ray photoelectron spectroscopy depth profiling and transmission electron microscopy analyses confirm the formation of such immobilization layer, which favorably functions as an ionic conductor for lithium ions. As a result of the immobilization process, the amount of free moveable lithium ions is reduced, leading to the pronounced storage capacity decay. Insights gained from this research shed interesting light on the degradation mechanisms of thin film, all-solid-state LIB and facilitate potential interfacial modifications which finally will lead to substantially improved battery performance.

Ageing mechanisms of NMC-based Li-ion (C6/LiNi1/3Mn1/3Co1/3O2) batteries have been investigated under various cycling conditions. The electromotive force (EMF) curves are regularly determined by mathematical extrapolation of voltage discharge curves. The irreversible capacity losses determined from the EMF curves have been investigated as a function of time and cycle number. Parasitic side reactions, occurring at the cathode and anode, determine the charge-discharge efficiency (CDE) and discharge-charge efficiency (DCE), respectively. The recently developed non-destructive voltage analysis method is also applied to the present battery chemistry. The decline of the second plateau of the dVEMF/dQ curves upon cycling is considered to be an indicator of graphite degradation whereas the development of the third peak in these derivative curves is considered to be an indicator for electrode voltage slippage. X-ray Photoelectron Spectroscopy (XPS) measurements confirm the deposition of transition-metal elements at the graphite electrode, indicating dissolution of these metals from the cathode. Furthermore, XPS analyses confirm the existence of a Cathode-Electrolyte-Interface (CEI) layer. The outer CEI layer is composed of various compounds, such as carbonate-related Li salts, LiF and NiF2, etc., while the inner CEI layer is dominantly composed of fluoride-related compounds, such as NiF2. Finally, a cathode degradation model including transition-metal dissolution and electrolyte decomposition is proposed.

The demand for electrochemical energy storage technologies is rapidly increasing due to the proliferation of renewable energy sources and the emerging markets of grid- scale battery applications. The properties of batteries and electrochemical energy storage (EES) technologies ideal for most of these applications, yet, faced with resource constraints, the ability of current lithium-ion batteries (LIB) to match this overwhelming demand is uncertain. Sodium-ion batteries (SIB) are a novel class of batteries with similar performance characteristics to LIB. Since they are composed of earth abundant elements, cheaper and utility scale battery modules can be assembled. As a result of the learning curve in LIB technology, a phenomenal progression in material development has been realised in the SIB concept. In this SIB review, various innovative strategies used in material development, as well as the electrochemical properties of possible anode, cathode and electrolyte combinations are unravelled. Attractive performance characteristics are herein evidenced, based on comparative gravimetric and volumetric energy densities to state-of-the-art LIB. Furthermore, opportunities and challenges towards commercialization are herein discussed. Combined with more industrial adaptations, the commercial prospects of SIB look promising and this challenging new technology is set to play a major role in grid-scale EES applications.

A novel approach in modeling the ionic transport in the electrolyte of Li-ion batteries is here presented. Diffusion and migration processes govern the transport of ions in solution in the absence of convection. In the porous electrode theory [1] it is common to model these processes via mass balance equations and electroneutrality. A parabolic set of equations arises, in terms of a non constant electric field which is afflicted by the paradox of being generated without electrical charges. To remedy this contradiction, Maxwell's equations have been used here, coupled to Faraday's law of electrochemical charge transfer. The set of continuity equations for mass and Maxwell's equations lead to a consistent model, with distinctive energy characteristics. Numerical examples show the robustness of the approach, which is well suited for multi-scale analyses [2,3].

The application of silicon (Si) as potential anode material in Li-ion batteries provides a more than nine-fold increase in gravimetric storage capacity compared to conventional graphite anodes. However, full lithiation of Si induces the volume to increase by approximately 300%. Such enormous volume expansion causes large mechanical stress, resulting in non-elastic deformation and crack formation. This ultimately leads to anode failure and strong decrease in cycle life. This problem can be resolved by making use of structured anodes with small dimensions. Particularly honeycomb-shaped microstructures turned out to be beneficial in this respect. In the present paper, finite element modeling was applied to describe the experimentally observed mechanical deformation of honeycomb-structured Si anodes upon lithiation. A close agreement between simulated and experimentally observed shape changes is observed in all cases. The predictive ability of the model was further exploited by investigating alternative geometries, such as square-based microstructure. Strikingly, dimension and pattern optimization shows that the stress levels can be reduced even below the yield strength, while maintaining the footprint-area-specific storage capacity of the microstructures. The pure elastic deformation is highly beneficial for the fatigue resistance of optimized silicon structures. The obtained results are directly applicable for other (de)lithiating materials, such as mixed ionic–electronic conductors (MIEC) widely applied in Li-ion and future Na-ion batteries.

C6/LiFePO4 (LFP) batteries have been cycled at various temperatures (20 and 60◦C) and State-of-Charge (SoC) ranges (0–30, 35–65, 70–100% and 0–100%). Electromotive force (emf) curves have regularly been determined by regression extrapolation of the measured voltage discharge curves. A non-destructive approach to quantitatively determine the graphite electrode decay has been proposed on the basis of dVEMF/dQ curves. It is concluded that the graphite inaccessibility is more pronounced at lower SoC (0–30%) than at higher SoC. The graphite electrode decay at 35–65%, 70–100% and 0–100% is identified to be negligible at moderated temperatures but becomes significant at elevated temperatures. The graphite electrode degradation has been confirmed by XPS and Raman spectroscopy, supporting the conclusions drawn from the dVEMF/dQ results. A model is proposed to explain the various graphite degradation mechanisms.

A new impedance-based approach is introducedin which the integral battery temperature is related to otherfrequencies than the recently developed zero-intercept frequency(ZIF). The advantage of the proposed non-zero-intercept frequency(NZIF) method is that measurement interferences,resulting from the current flowing through the battery (pack),can be avoided at these frequencies. This gives higher signal-to-noiseratios (SNR) and, consequently, more accurate temperaturemeasurements. A theoretical analysis, using an equivalent circuitmodel of a Li-ion battery, shows that NZIFs are temperaturedependent in a way similar to the ZIF and can therefore alsobe used as a battery temperature indicator. To validate theproposed method impedance measurements have been performedwith individual LiFePO4 batteries and with large LiFePO4battery packs tested in a full electric vehicle under drivingconditions. The measurement results show that the NZIF isclearly dependent on the integral battery temperature and revealsa similar behavior to that of the ZIF method. This makes itpossible to optimally adjust the NZIF method to frequencies withthe highest SNR.

Thin-film Solid-State Batteries (TFSSB) is one of most promising and quickly developing fields in modern electrochemical energy storage. Modeling these devices is interesting from theoretical and practical point of view. This paper represents a simulation approach for TFSSB which overcome a major drawback of available mathematical models, i.e. decline in accuracy of the models at high current rates. A one-dimensional electrochemical model, including charge transfer kinetics on the electrolyte-electrode interface, diffusion and migration in electrolyte as well as diffusion in intercalation electrode has been developed and the simulation results are compared to experimental voltage-capacity measurements. A new definition of diffusion coefficient as a function of concentration, based on the experimental measurements, is used to improve the performance of the model. The simulation results fit the available experimental data at low and high discharge currents up to 5 mA cm−2. The models show that the cathode diffusion constant is a prime factor limiting the rate capability for TFSSB in particular for ultrafast charging applications.