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.

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.

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 an insulating nature and polysulfide dissolution problem. The results presented here show a facile and cost-effective approach by using a plasma sparking and chemical 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 generation Li–S batteries.

•MgTi and MgTiX (X = Ni and Si) can be synthesized using mechanical alloying.•Alloying Ti with Mg powders improves the kinetics of (de) hydrogenation of Mg.•Addition of ternary alloying element such as Ni further improves the kinetics of (de)hydrogenation.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 MgyTi1−y (y = 0.80–0.60) and ternary Mg0.63Ti0.27X0.10 (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 Mg0.80Ti0.20 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 Mg0.70Ti0.30. The charge transfer coefficients (α) and the rate constants (K1 and K2) 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 Mg0.65Ti0.35 compared to those of Mg0.80Ti0.20. 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.

•Mathematical modeling of Pressure Composition Isotherms of Hydrogen storage materials.•Thermodynamic model experimentally verified.•Generalized form Van ′t Hoff relationship derived from first principles thermodynamics.•Palladium and intermetallic (non)-stoichiometric compounds modeled.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 method has been developed to deposit Li4Ti5O12 thin film electrodes.•Deposited Li4Ti5O12 film electrodes combine a high storage capacity and excellent rate capability.•3D deposition of Li4Ti5O12 thin film by MOCVD has been investigated.•Storage capacity was improved 2.5 times by applying 3D deposition.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.

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.

•Prolonged ball-milling of NaAlH4–MgH2 leads to enhanced dehydrogenation rates.•Na3AlH6 and NaMgH3 may coexist during the dehydrogenation of NaAlH4–MgH2.•Complex alloying process of Al with Mg or MgH2 has been proposed.•A few Al–Mg alloys, also reported Al12Mg17, participate in the dehydrogenation.The recently developed NaAlH4–MgH2 composite shows improved hydrogen-storage properties compared to MgH2 and NaAlH4. However, the dehydrogenation reaction rates are still too limited, hampering practical applications. Mechanical ball milling is broadly used to improve the dehydrogenation reaction rates of hydrides. Therefore, the hydrogen-storage properties of the NaAlH4–MgH2 (1:1) composite have been investigated as a function of ball-milling time. Expectedly, elongated milling led to a faster dehydrogenation rates. New insights of the structural transformation pathways of the decomposition reaction are provided. A number of Al–Mg alloys, including the only reported Al12Mg17, seem to participate in the dehydrogenation. Thereby, complex alloying process of Al with Mg or MgH2 has been proposed. Our data indicate the possibility that hydrides Na3AlH6 and NaMgH3, which are the intermediate products of the dehydrogenation, coexist. The study shed a light on the complexity of the decomposition pathways of hydride mixtures in which the key role play alloys.

Semiconductor nanowire arrays are expected to be advantageous for photoelectrochemical energy conversion due to their reduced materials consumption. In addition, with the nanowire geometry the length scales for light absorption and carrier separation are decoupled, which should suppress bulk recombination. Here, we use vertically aligned p-type InP nanowire arrays, coated with noble-metal-free MoS3 nanoparticles, as the cathode for photoelectrochemical hydrogen production from water. We demonstrate a photocathode efficiency of 6.4% under Air Mass 1.5G illumination with only 3% of the surface area covered by nanowires.

•A new method is proposed to measure the internal temperature of (Li-ion) batteries.•The temperature measurement is based on electrochemical impedance spectroscopy.•The intercept frequency can be linked to the internal battery temperature.•No hardware temperature sensors are required and heat transfer delay is absent.A new method is proposed to measure the internal temperature of (Li-ion) batteries. Based on electrochemical impedance spectroscopy measurements, an intercept frequency (f0) can be determined which is exclusively related to the internal battery temperature. The intercept frequency is defined as the frequency at which the imaginary part of the impedance is zero (Zim = 0), i.e. where the phase shift between the battery current and voltage is absent. The advantage of the proposed method is twofold: (i) no hardware temperature sensors are required anymore to monitor the battery temperature and (ii) the method does not suffer from heat transfer delays. Mathematical analysis of the equivalent electrical-circuit, representing the battery performance, confirms that the intercept frequency decreases with rising temperatures. Impedance measurements on rechargeable Li-ion cells of various chemistries were conducted to verify the proposed method. These experiments reveal that the intercept frequency is clearly dependent on the temperature and does not depend on State-of-Charge (SoC) and aging. These impedance-based sensorless temperature measurements are therefore simple and convenient for application in a wide range of stationary, mobile and high-power devices, such as hybrid- and full electric vehicles.

Fluorite-structured Mg–Ti hydrides are interesting for hydrogen storage applications because of their high gravimetric hydrogen storage capacity, and improved (de)hydrogenation kinetics compared to MgH2. In the present study we have investigated the potential catalytic effect of Ni and Si as third element on the siting and mobility of electrochemically loaded deuterium in ball-milled Mg0.63Ti0.27Ni0.10 and Mg0.63Ti0.27Si0.10 alloys. Magic angle spinning (MAS) 2H NMR reveals that Ni and Si induce new types of deuterium sites in addition to the Mg-rich and Ti-rich sites already present in Mg0.65Ti0.35D1.2. 2D exchange NMR spectroscopy shows a substantial deuterium exchange between the various types of sites, which reflects their close interconnectivity in the crystal structure. Furthermore, the time scale and temperature dependence of the deuterium mobility have been quantified by 1D exchange NMR. The obtained effective residence times for deuterium atoms in the Mg-rich and Ti-rich nanodomains in Mg0.65Ti0.35D1.2, Mg0.63Ti0.27Ni0.10D1.3, and Mg0.63Ti0.27Si0.10D1.1 at 300 K are 0.4, 0.3, and 0.8 s, respectively, and the respective apparent activation energies 17, 21, and 27 kJ mol–1. The addition of Ni promotes deuterium mobility inside Mg–Ti hydrides, which is in agreement with the observed catalytic effect of Ni on the electrochemical (de)hydrogenation of these materials.

•A simple, accurate and adaptive thermal model is proposed for Li-ion batteries.•Equilibrium voltages, overpotentials and entropy changes are quantified from experimental results.•Entropy changes are highly dependent on the battery State-of-Charge.•Good agreement between simulated and measured heat development is obtained under all conditions.•Radiation contributes to about 50% of heat dissipation at elevated temperatures.An accurate thermal model to predict the heat generation in rechargeable batteries is an essential tool for advanced thermal management in high power applications, such as electric vehicles. For such applications, the battery materials’ details and cell design are normally not provided. In this work a simple, though accurate, thermal model for batteries has been developed, considering the temperature- and current-dependent overpotential heat generation and State-of-Charge dependent entropy contributions. High power rechargeable Li-ion (7.5 Ah) batteries have been experimentally investigated and the results are used for model verification. It is shown that the State-of-Charge dependent entropy is a significant heat source and is therefore essential to correctly predict the thermal behavior of Li-ion batteries under a wide variety of operating conditions. An adaptive model is introduced to obtain these entropy values. A temperature-dependent equation for heat transfer to the environment is also taken into account. Good agreement between the simulations and measurements is obtained in all cases. The parameters for both the heat generation and heat transfer processes can be applied to the thermal design of advanced battery packs. The proposed methodology is generic and independent on the cell chemistry and battery design. The parameters for the adaptive model can be determined by performing simple cell potential/current and temperature measurements for a limited number of charge/discharge cycles.

Cobalt oxide thin films have been deposited with remote plasma atomic layer deposition (ALD) within a wide temperature window (100–400 °C), using CoCp2 as cobalt precursor and with a remote O2 plasma as oxidant source. The growth rate was relatively high at 0.05 nm per ALD-cycle and resulted in the deposition of high density (∼5.8 g cm−3), stoichiometric Co3O4. For the electrochemical analyses, Co3O4 was deposited on a Si substrate covered with an ALD-synthesized TiN layer to prevent Li diffusion. The as-deposited electrodes were investigated in a three-electrode electrochemical cell using constant current (CC) charge/discharge cycling and Galvanostatic Intermittent Titration Technique (GITT) in combination with Electrochemical Impedance Spectroscopy (EIS). Compared to the literature, ALD-deposited Co3O4 exhibited a high electrochemical activity (∼1000 mAh g−1) and the formation of a solid electrolyte interface has been identified by EIS.Highlights► Preparation of cobalt oxide within a wide temperature window employing atomic layer deposition. ► Consistent material properties for deposition between 100 °C and 400 °C. ► Interesting anode material for application in all-solid-state microbatteries because of a high electrochemical activity. ► Extensive electrochemical investigation and evaluation of a conversion anode material (Co3O4) for application in microbatteries.

An electrochemical kinetic model (EKM) is developed, describing the electrochemical hydrogen storage in hydride-forming materials under equilibrium conditions. This model is based on first principles of electrochemical reaction kinetics and statistical thermodynamics and describes the complex, multi-stage, electrochemical (de)hydrogenation process. A complete set of equations have been derived, describing the equilibrium hydrogen partial pressure and equilibrium electrode potential as a function of hydrogen content in both solid-solution and two-phase coexistence regions. The EKM has been applied to simulate the isotherms of thin film Pd electrodes of various thicknesses. Good agreement between experiment and theory is found in all cases. Relevant energy and kinetic parameters are obtained from the simulations.

We consider the process of chemical vapor deposition on a trenched Si substrate. To understand the process (including e.g. the layer conformality) at the trench scale (microscale), we need solutions at both the trench and reactor scales (macroscale). Due to the huge difference in size of these scales, straightforward numerical computations are very challenging. To overcome this difficulty, we consider a multiscale approach by introducing an intermediate scale (the mesoscale). We start with a time-continuous model describing the transport processes and then perform time discretization. At each time step, using the ideas of domain decomposition inspired from Lions (1988) [4], we provide iterative coupling conditions for these three different scales. Using a weak formulation for the time-discrete equations, we prove the convergence of this iterative scheme at each time step. The approach also provides an alternative proof for the existence of the solutions for the time-discrete formulation.

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 an insulating nature and polysulfide dissolution problem. The results presented here show a facile and cost-effective approach by using a plasma sparking and chemical 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 generation Li–S batteries.