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International audience; This paper is a contribution to fasten integration of battery pack innovation in commercial Electric Vehicles (EV) through massive digitalization: a seamless process detailed for battery design, battery safety, and battery management. Selected results of studies carried out on the EV value chain from design to recycling steps are presented, highlighting the importance of seamless integration and holistic state of mind when designing EV. Association between experimental and numerical approaches for efficient innovative EV production is crucial to achieve easy commercialisation. Successful forecasting of aging and thermal runaway evolution from single cell failure at module level using such methods illustrates their great potential. Hardware key counterparts under development are also introduced and give an idea of future architecture of EV battery packs and overall improvement of EV energy efficiency. Finally, a flexible and easily modifiable solution for battery electric vehicle (BEV) that allows rapid and cost-effective integration of future innovation is presented. This paper globally illustrates key breakthroughs gained in the context of the collaborative research project named ‘DEMOBASE’, for DEsign and MOdelling for improved BAttery Safety and Efficiency successfully submitted for funding by the European Commission in response to a 2017 call dedicated to ‘Green Vehicles’ under the EU Horizon 2020 work programme “Smart, green and integrated transport”.

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.

A three-dimensional (3D) printing method has been developed for preparing a lithium anode base on 3D-structured copper mesh current collectors. Through in situ observations and computer simulations, the deposition behavior and mechanism of lithium ions in the 3D copper mesh current collector are clarified. Benefiting from the characteristics that the large pores can transport electrolyte and provide space for dendrite growth, and the small holes guide the deposition of dendrites, the 3D Cu mesh anode exhibits excellent deposition and stripping capability (50 mAh cm-2), high-rate capability (50 mA cm-2), and a long-term stable cycle (1000 h). A full lithium battery with a LiFePO4 cathode based on this anode exhibits a good cycle life. Moreover, a 3D fully printed lithium-sulfur battery with a 3D printed high-load sulfur cathode can easily charge mobile phones and light up 51 LED indicators, which indicates the great potential for the practicability of lithium-metal batteries with the characteristic of high energy densities. Most importantly, this unique and simple strategy is also able to solve the dendrite problem of other secondary metal batteries. Furthermore, this method has great potential in the continuous mass production of electrodes.

We present optical in situ investigations of lithium-ion dynamics in lithium iron phosphate based positive electrodes. The change in reflectivity of these cathodes during charge and discharge is used to estimate apparent diffusion coefficients for the lithiation and delithiation process of the entire electrode. Thereby, a scaling analysis of the transport process is applied, which clearly reveals its diffusive character. Results are shown for cathodes, in which the common additive carbon as well as the conductive and electrochromic marker additives (indium tin oxide and antimony tin oxide) are used. The latter leads to a substantial increase of visibility of the optical effect in the cathodes while electric properties remain qualitatively unchanged. The procedure extends common characterization techniques of positive electrode materials via a novel and integral combination of electrical and optical measurements.

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.]

lithium-sulfur (Li-S) batteries have been regarded as one of the most promising systems for next-generation rechargeable batteries owing to their high energy density and low cost. However, the “Shuttle effect” of polysulfides and low sulfur utilization upon cycling are still hindering their practical applications. Herein, we report a series of marine organism-like hollow nanoarchitecture consisting of nitrogen (N) doped 1D carbon nanotubes (CNTs), which were derived from binary Fe/Ce Prussian blue analogs (PBAs) and melamine. This nitrogen-doped 3D hollow scaffold offers large inner space (ф ≈ 200 nm) and sufficient electric conducting for insulating sulfur and provides adsorption sites for immobilizing polysulphides. The introduced double metal species enable strong chemical adsorption toward polysulfides and could facilitate the redox reaction between sulfur and polysulphides. When applied in Li-S batteries, the as-prepared materials showed a high capacity of 1241 mAh g−1 and a stable cycling performance (1003 mAh g−1 after 100 cycles) at a current density of 0.2 C. The enhancement of electrochemical activity could be attributed to the 3D hollow architecture of the hybrid, in which the nitrogen-doping generates defects and active sites for improved interfacial adsorption. This work could inspire developing biomimetic architectures for high-performance Li-S batteries.

Antimony (Sb) based materials, which have been proved to be promising anodes to fabricate high-performance sodium-ion batteries (SIBs), have attracted considerable interest owing to its large theoretical capacity (660 mAh g−1), appropriate inserting potential of sodium (0.5–0.8 V vs Na+/Na), and moderate electrode polarization (~0.35 V). Unfortunately, fast capacity decay and serious structure pulverization resulting from large volume variation upon cycling are often observed for Sb-based anodes, and further structure design is needed. In this work, a novel hybrid of amorphous Sb/N-doped layered carbon (a-Sb/NC) was fabricated through a facile bottom-up method, where ultrafine amorphous Sb nanoparticles are uniformly anchored on layered N-doped carbon (NC). When applied as anode material for SIBs, this hybrid exhibits a large reversible capacity (479.6 mAh g−1 at 0.1 A g−1 up to 100 cycles), robust rate capability (298.7 mAh g−1 at current density of 2 A g−1), and remarkable stability upon long-term cycling (280.5 mAh g−1 at 1.0 A g−1 up to 500 cycles), outperforming most of the reported amorphous anodes for SIBs. In principle, such impressive sodium storage properties of a-Sb/NC should be mainly ascribed to the amorphous feature of Sb nanoparticles as well as the synergistic effect between amorphous Sb and layered NC, thereby endowing the composite with improved electron/ion dynamics and efficient self-buffering ability.

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.]

Li10GeP2S12 (LGPS) is the fastest known Li-ion conductor to date due to the formation of one-dimensional channels with a very high Li mobility. A knowledge-based optimization of such materials for use, for example, as solid electrolyte in all-solid-state batteries requires, however, a more comprehensive understanding of Li ion conduction that considers mobility in all three dimensions, mobility between crystallites and different phases, as well as their distributions within the material. The spin alignment echo (SAE) nuclear magnetic resonance (NMR) technique is suitable to directly probe slow Li ion hops with correlation times down to about 10−5 s, but distinction between hopping time constants and relaxation processes may be ambiguous. This contribution presents the correlation of the 7Li spin lattice relaxation (SLR) time constants (T1) with the SAE decay time constant τc to distinguish between hopping time constants and signal decay limited by relaxation in the τc distribution. A pulse sequence was employed with two independently varied mixing times. The obtained multidimensional time domain data was processed with an algorithm for discrete Laplace inversion that does not use a non-negativity constraint to deliver 2D SLR–SAE correlation maps. Using the full echo transient, it was also possible to estimate the NMR spectrum of the Li ions responsible for each point in the correlation map. The signal components were assigned to different environments in the LGPS structure.

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.

For powering small-sized electronic devices, all-solid-state Li-ion batteries are the most promising candidates due to its safety and allowing miniaturization. Thin film deposition methods can be used for building new all-solid-state architectures. Well-known deposition methods are sputter deposition, pulsed laser deposition, sol-gel deposition, atomic layer deposition, etc. This review summarizes thin film storage materials deposited by metal-organic chemical vapor deposition (MOCVD) for all-solid-state Li-ion batteries. The deposition parameters strongly influence the quality of the films, such as surface morphology, composition, electrochemical stability and cycling performance. Some materials have been successfully deposited by MOCVD into 3D–structured substrates, revealing conformal, homogeneous and high performance battery properties.

Three dimensionally (3D) structured indium tin oxide (ITO) thin films are synthesized and characterized as a 3D electrode material for current collection applications. Using metal citrate chemistry in combination with ultrasonic spray deposition, a low cost wet-chemical method has been developed to achieve conformal ITO coatings on non-planar scaffolds. Although there is room for improvement with respect to the resistivity (9.9.10-3 Omega. cm, 220 nm thick planar films), high quality 3D structured coatings were shown to exhibit conductive properties based on ferrocene reactivity. In view of applications in Li-ion batteries, the electrochemical stability of the current collector was investigated, indicating that stability is guaranteed for voltages of 1.5 V and up (vs. Li+/Li). In addition, subsequent 3D coating of the ITO with WO3 as a negative electrode (battery) material confirmed the 3D ITO layer functions as a proper current collector. Using this approach, an over 4-fold capacity increase was booked for 3D structured WO3 in comparison to planar samples, confirming the current collecting capabilities of the 3D ITO coating. Therefore, the 3D ITO presented is considered as a highly interesting material for 3D battery applications and beyond. (C) 2017 Elsevier B.V. All rights reserved. This study was partly supported by the IWT SBO SOS Lion project.

© 2019 IEEE. A modification of the differential voltage analysis method is developed. It allows determination of the degradation mechanisms during charging of Li-ion batteries. A constant current (CC) with relatively high C-rate can be used in the analysis method. The modification of the differential voltage analysis method is based on measuring the heat generated during CC charging of Li-ion batteries. The advantages and the applicability of the presented modified differential voltage analysis (MDVA) method are verified by a comparison with currently existing and proven methods used in determining the Li-ion battery degradation mechanisms.

High capacity sodium (Na) metal anodes open up new opportunities for developing next-generation rechargeable batteries with both high power and high energy densities. However, many challenges still plagued their practical application, including low plating/stripping Coulombic efficiency (CE) and dendrite growth after repeated cycle inducing safety issue. Especially, the sodium metal is less stable in organic (i.e. carbonate-based) electrolytes than lithium metal, due to the more unstable organic solid–electrolyte interface (SEI). Herein, we report a facile technology to stabilize sodium metal anode and inhibit the growth of sodium dendrites. The in-situ ultrathin NaI SEI layer successfully endows best-performance Na/I2 metal batteries (>2200 cycles) with high capacity (210 mA h g−1 at 0.5 C) based on the conversion reaction chemistry with higher discharge voltage plateau (> 2.7 V) and lower overpotential (134 mV) due to the fast charge transfer dynamics and interfacial stability compared with pristine Na anode. The detailed theoretical calculations and experimental results elucidate that NaI layer has a much lower diffusion barrier compared to that of NaF (NaF as one the most commonly found inorganic components in Na-based SEI layer), and actually facilitates more uniform sodium deposition. This work provides a new avenue for designing low-cost, high-performance and high-safety sodium metal-iodine batteries and other metal-iodine batteries.

© 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.

Li4Ti5O12 is well known to be a safe and efficient anode material for Li-ion batteries. A metal-organic chemical vapor deposition process has been developed for the synthesis of Li4Ti5O12 thin film anodes on planar and 3D substrates. The influences of various deposition parameters, including precursor flow rates and post-annealing temperatures, have been investigated by material and electrochemical analyses. Li4Ti5O12 thin films deposited at the optimized process parameters showed a high crystallinity and high electrochemical activity. A reversible storage capacity of 151 mAh/g was achieved at a current of 0.5 C, corresponding to 86.3% of the theoretical specific capacity of Li4Ti5O12. Up to almost 600 cycles, the electrodes showed no significant capacity loss. Furthermore, the deposited thin film anodes also showed excellent rate performance. Compared to the storage capacity at 0.5 C, 93% of the capacity was maintained at 10 C. Thin films were also deposited on highly structured substrates to investigate the uniformity and electrochemical performance. With the same footprint area, the 3D Li4Ti5O12 film anode showed a 2.5 times higher storage capacity than planar electrode.

Journal of the Electrochemical Society 163(10), A2385-A2389 (2016). doi:10.1149/2.1141610jes, Published by Electrochemical Society, Pennington, NJ

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.

© 2018, Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature. Recently, Prussian blue and its analogues (PBAs) have attracted tremendous attention as cathode materials for sodium-ion batteries because of their good cycling performance, low cost, and environmental friendliness. However, they still suffer from kinetic problems associated with the solid-state diffusion of sodium ions during charge and discharge processes, which leads to low specific capacity and poor rate performances. In this work, novel sodium iron hexacyanoferrate nanospheres with a hierarchical hollow architecture have been fabricated as cathode material for sodium-ion batteries by a facile template method. Due to the unique hollow sphere morphology, sodium iron hexacyanoferrate nanospheres can provide large numbers of active sites and high diffusion dynamics for sodium ions, thus delivering a high specific capacity (142 mAh/g), a superior rate capability, and an excellent cycling stability. Furthermore, the sodium insertion/extraction mechanism has been studied by in situ X-ray diffraction, which provides further insight into the crystal structure change of the sodium iron hexacyanoferrate nanosphere cathode material during charge and discharge processes.

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Sodium (Na) metal is one of the most promising electrode materials for next-generation low-cost rechargeable batteries. However, the challenges caused by dendrite growth on Na metal anodes restrict practical applications of rechargeable Na metal batteries. Herein, a nitrogen and sulfur co-doped carbon nanotube (NSCNT) paper is used as the interlayer to control Na nucleation behavior and suppress the Na dendrite growth. The N- and S-containing functional groups on the carbon nanotubes induce the NSCNTs to be highly “sodiophilic,” which can guide the initial Na nucleation and direct Na to distribute uniformly on the NSCNT paper. As a result, the Na-metal-based anode (Na/NSCNT anode) exhibits a dendrite-free morphology during repeated Na plating and striping and excellent cycling stability. As a proof of concept, it is also demonstrated that the electrochemical performance of sodium–oxygen (Na–O2) batteries using the Na/NSCNT anodes show significantly improved cycling performances compared with Na–O2 batteries with bare Na metal anodes. This work opens a new avenue for the development of next-generation high-energy-density sodium-metal batteries.

This short communication presents a method to measure the integral temperature of organic light-emitting diodes (OLEDs). Based on electrochemical impedance measurements at OLEDs, a non-zero intercept frequency (NZIF) can be determined which is related to the OLED temperature. The NZIF is defined as the frequency at which the imaginary part of the impedance is equal to a predefined (non-zero) constant. The advantage of using an impedance-based temperature indication method through an NZIF is that no hardware temperature sensors are required and that temperature measurements can be performed relatively fast. An experimental analysis reveals that the NZIF is clearly temperature dependent and, moreover, also DC current dependent. Since the NZIF can readily be measured this impedance-based temperature indication method is therefore simple and convenient for many applications using OLEDs and offers an alternative for traditional temperature sensing.

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.

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.

The solar energy conversion efficiency of photoelectrochemical (PEC) devices is usually limited by poor interface energetics, limiting the onset potential, and light reflection losses. Here, a three-pronged approach to obtain excellent performance of an InP-based photoelectrode for water reduction is presented. First, a buried p-n+ junction is fabricated, which shifts the valence band edge favorably with respect to the hydrogen redox potential. Photoelectron spectroscopy substantiates that the shift of the surface photovoltage is mainly determined by the buried junction. Second, a periodic array of InP nanopillars is created at the surface of the photoelectrode to substantially reduce the optical reflection losses. This device displays an unprecedented photocathodic power-saved efficiency of 15.8% for single junction water reduction. Third, a thin TiO2 protection layer significantly increases the stability of the InP-based photoelectrode. Careful design of the interface energetics based on surface photovoltage spectroscopy allows obtaining a PEC cell with stable record performance in water reduction. The efficiency of photoelectrochemical (PEC) water splitting devices is usually limited by interface energetics mismatch between the semiconductor and the electrolyte and insufficient light absorption. The highest photocathodic power-saved efficiency of 15.8% reported so far for single junction PEC water reduction is obtained through interface energetics design and photon management of an InP-based photoelectrode.

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 degrees 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. Huguette Penxten is acknowledged for her assistance during the ferrocene reduction experiments. Imec (Leuven, Belgium) and Phillipe Vereecken are acknowledged for providing micro-cylinder substrates. This study was partly supported by the IWT SBO SOS Lion project.

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.

It is shown that the dissolution of elemental sulfur into, and its diffusion through, the electrolyte allows cycling of lithium–sulfur batteries in which the sulfur is initially far removed and electrically insulated from the current collector. These findings help to understand why liquid electrolyte lithium–sulfur batteries can be efficiently cycled, despite the extremely insulating properties of sulfur.

Li2S has made the concept of Li-S batteries much more promising due to the relatively high storage capacity, the possibility of using Li-free anodes and the increase of microstructural stability. However, similar to S, Li2S also suffers from the insulating nature and polysulfides dissolution problem. The results presented here show a facile and cost-effective approach by using a plasma sparking and chemical S sulfurization process to synthesize core-shell Li2S@C nanocomposites. The nanocomposites show a significantly reduced particle size and well-developed core-shell architecture, effectively shortening the Li-ion diffusion distance, enhancing the electronic conductivity and suppressing the dissolution losses of polysulfides. As a result, a much improved rate and cycling performance has been achieved. The method presented in this study offers good opportunities for scaling up the production of high performance cathode materials in a simple and low-cost way to be applied in future generations Li-S batteries.

Benefiting from the natural abundance and low standard redox potential of potassium, potassium-ion batteries (PIBs) are regarded as one of the most promising alternatives to lithium-ion batteries for low-cost energy storage. However, most PIB electrode materials suffer from sluggish thermodynamic kinetics and dramatic volume expansion during K+ (de)intercalation. Herein, it is reported on carbon-coated K2 Ti2 O5 microspheres (S-KTO@C) synthesized through a facile spray drying method. Taking advantage of both the porous microstructure and carbon coating, S-KTO@C shows excellent rate capability and cycling stability as an anode material for PIBs. Furthermore, the intimate integration of carbon coating through chemical vapor deposition technology significantly enhances the K+ intercalation pseudocapacitive behavior. As a proof of concept, a potassium-ion hybrid capacitor is constructed with the S-KTO@C (battery-type anode material) and the activated carbon (capacitor-type cathode material). The assembled device shows a high energy density, high power density, and excellent capacity retention. This work can pave the way for the development of high-performance potassium-based energy storage devices.

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.

Tin nitride thin films have been reported as promising negative electrode materials for lithium-ion solid-state microbatteries. However, the reaction mechanism of this material has not been thoroughly investigated in the literature. To that purpose, a detailed electrochemical investigation of radio-frequency-sputtered tin nitride electrodes of two compositions (1:1 and 3:4) is presented for several layer thicknesses. The as-prepared thin films have been characterized by Rutherford backscattering spectrometry, inductively coupled plasma optical emission spectrometry, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The electrochemical results point out that the conversion mechanism of tin nitride most probably differs from the conversion mechanism usually observed for other oxide and nitride conversion electrode materials. The electrochemical data show that more than 6 Li per Sn atom can be reversibly exchanged by this material, whereas only about 4 are expected. Moreover, the electrochemical performance of the material is discussed, such as electrode cycle life, and a method for improving the cycle life is presented. Finally, thicker films have been characterized by Mössbauer spectroscopy. This technique opens a new route toward determining the conversion reaction mechanism of this promising electrode material. ©2010 The Electrochemical Society

The deposition feasibility and electrochemical evaluation of highly structured negative electrode stacks for 3D-integrated batteries is demonstrated. The stacks comprise a TiN thin film, serving as both current collector and Li-barrier layer, covered by a polycrystalline Si (poly-Si) thin film as electrode material. In comparison with planar films, these poly-Si films present a storage capacity increase of about 5x for the highest pore aspect ratio electrodes. The step coverage of poly-Si can be considerably improved by growing TiN and poly-Si into wide trenches. This results in much smoother poly-Si films and significantly improved step coverage. Further optimization of the trench dimensions should result in poly-Si films with a Li-storage capacity increase of more than one order of magnitude with respect to planar films.

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.