Search

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”.

Advanced energy materials 12(44), 2202094 (2022). doi:10.1002/aenm.202202094, Published by Wiley-VCH, Weinheim

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.

Thin-film lithium-ion batteries (LIBs) have attracted much attention as one of the state-of-the-art energy storage technologies. However, most research regarded the current collector as infinitely conductive or with no separate simulation for this part. Herein, a model is proposed to simulate thin-film current collectors’ potential distribution and resistance. The effects of changing the aspect ratio and the thickness on the thin-film current collector are investigated. The experimental results obtained are in excellent agreement with the model. At the same time, this method is quite generic and can also be used for other types of batteries.

Electrochimica acta 398, 139316 (2021). doi:10.1016/j.electacta.2021.139316, Published by Elsevier, New York, NY [u.a.]

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.

ACS applied energy materials 4(9), 10333-10343 (2021). doi:10.1021/acsaem.1c02278, Published by ACS Publications, Washington, DC

© 2019 American Chemical Society. Silicon (Si) has been regarded as one of the most promising anode materials to fulfill the growing demand of high performance lithium-ion batteries based on its high specific capacity. However, Si is not yet capable of replacing the widely used graphite anode due to solid-electrolyte interphase (SEI) formation and extreme volume expansion during lithiation. In this work, advanced in situ electrochemical atomic force microscopy has been applied to track simultaneously the topographical evolution and mechanical properties of thin-film polycrystalline Si electrodes during SEI formation and initial lithiation. At first, a uniform flattening of the Si surface has been found, attributed to the SEI formation. This is followed by a nonuniform expansion of the individual particles upon lithiation. The experimental findings allow defining a detailed model describing the SEI layer formation and lithiation process on polycrystalline silicon thin-film electrodes. Our results support further research investigations on this promising material.

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.

© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Lithium–sulfur batteries (Li–S) have become a viable alternative to future energy storage devices. The electrochemical reaction based on lithium and sulfur promises an extraordinary theoretical energy density, which is far higher than current commercialized Li-ion batteries. However, the principal disadvantage impeding the success of Li–S batteries lies in the severe leakage and migration of soluble lithium polysulfide intermediates out of cathodes upon cycling. The loss of active sulfur species incurs significant capacity decay and poor battery lifespans. Considerable efforts have been devoted to developing various sulfur host materials that can effectively anchor lithium polysulfides. Herein, a comprehensive review is presented of recent advances in sulfur host materials. On the basis of the electrochemistry of Li–S batteries, the strategies for anchoring polysulfides are systematically categorized into physical confinement and chemical bonding. The structural merits of various sulfur host materials are highlighted, and the interaction mechanisms with sulfur species are discussed in detail, which provides valuable insights into the rational design and engineering of advanced sulfur host materials facilitating the commercialization of Li–S batteries. Future challenges and promising research prospects for sulfur host materials are proposed at the end of the review.

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.

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.

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.

ACS applied energy materials 3(7), 6583-6590 (2020). doi:10.1021/acsaem.0c00765, Published by ACS Publications, Washington, DC

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.]

Several efficient analytical methods have been developed to solve the solid-state diffusion problem, for constant diffusion coefficient problems. However, these methods cannot be applied for concentration-dependent diffusion coefficient problems and numerical methods are used instead. Herein, grid-based numerical methods derived from the control volume discretization are presented to resolve the characteristic nonlinear system of partial differential equations. A novel hybrid backward Euler control volume (HBECV) method is presented which requires only one iteration to reach an implicit solution. The HBECV results are shown to be stable and accurate for a moderate number of grid points. The computational speed and accuracy of the HBECV, justify its use in battery simulations, in which the solid-state diffusion coefficient is a strong function of the concentration.

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.

Journal of power sources 509, 230345 (2021). doi:10.1016/j.jpowsour.2021.230345, Published by Elsevier, New York, NY [u.a.]

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.

ACS applied energy materials 2(11), 8153-8162 (2019). doi:10.1021/acsaem.9b01621, Published by American Chemical Society, Washington, DC

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

© 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.

Advanced energy materials 11(13), 2003939 (2021). doi:10.1002/aenm.202003939, Published by Wiley-VCH, Weinheim

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.