Photoelectrochemical hydrogen production from solar energy and water offers a clean and sustainab... more Photoelectrochemical hydrogen production from solar energy and water offers a clean and sustainable fuel option for the future. Planar III/V material systems have shown the highest efficiencies, but are expensive. By moving to the nanowire regime the demand on material quantity is reduced, and new materials can be uncovered, such as wurtzite gallium phosphide, featuring a direct bandgap. This is one of the few materials combining large solar light absorption and (close to) ideal band-edge positions for full water splitting. Here we report the photoelectrochemical reduction of water, on a p-type wurtzite gallium phosphide nanowire photocathode. By modifying geometry to reduce electrical resistance and enhance optical absorption, and modifying the surface with a multistep platinum deposition, high current densities and open circuit potentials were achieved. Our results demonstrate the capabilities of this material, even when used in such low quantities, as in nanowires.
Mg-Ti-H thin films are found to have very attractive optical properties: they absorb 87% of the s... more Mg-Ti-H thin films are found to have very attractive optical properties: they absorb 87% of the solar radiation in the hydrogenated state and only 32% in the metallic state. Furthermore, in the absorbing state Mg-Ti-H has a low emissivity; at 400 K only 10% of blackbody radiation is emitted. The transition between both optical states is fast, robust, and reversible. The sum of these properties highlights the applicability of such materials as switchable smart coatings in solar collectors.
Measurements of nuclear magnetic resonance (NMR) relaxation times allow the rates of H and D atom... more Measurements of nuclear magnetic resonance (NMR) relaxation times allow the rates of H and D atomic hopping in metal-hydrides to be determined. A first example compares the rates of H hopping in Mg 65 Sc 35 Pd 2.4 H 220 , a promising new battery electrode and storage alloy, to LaNi 5 H x and to the end-members of the alloy system, ScH 2 and MgH 2 . The motion of MgScH is more rapid than in the metallic ScH 2 and the ionic MgH 2 , but slower than in LaNi 5 H x . Magic-angle spinning (MAS) NMR of metal-deuterides is a newer method that can resolve inequivalent D atoms and measure the rate of diffusive exchange between the sites. Examples include the tetrahedral and octahedral sites in YD 2+x and D in ZrNiD x .
ABSTRACT The absorption and desorption isotherms of Mg thin films are determined by electrochemic... more ABSTRACT The absorption and desorption isotherms of Mg thin films are determined by electrochemical techniques at room temperature. Up to now, especially for hydrogen desorption from pure Mg, the temperature range for determining the isotherm has been confined to high temperatures. The enthalpy of hydride formation and hydride decomposition is in agreement with the data reported previously; however, the present data are measured directly at room temperature. The dynamic electrochemical responses during hydrogen extraction reveal that at the beginning of the dehydrogenation reaction the rate is mostly impeded by a nucleation and growth mechanism. The desorption isotherm is simulated with a lattice gas model and excellent agreement between experiment and theory is found. The parameters are used to obtain detailed information about the magnesium–hydrogen system.
LaNi 4.78 Sn 0.22 H x hydride samples were held at a hydrogen content of x > 5.0 (x is H/La atomi... more LaNi 4.78 Sn 0.22 H x hydride samples were held at a hydrogen content of x > 5.0 (x is H/La atomic ratio) and temperatures above 465 K to accelerate the intrinsic degradation processes. Although Sn-substituted alloys are much more resistant to disproportionation than nearly all other LaNi 5 alloys, the present test conditions did produce substantial degradation. Effects observed included reduction in hydrogen storage capacity, decreases in the plateau pressures, increased slopes of the plateaus, and smaller hysteresis ratios. A regeneration process nearly completely restored the behavior of the degraded LaNi 4.78 Sn 0.22 hydride to its initial value. First-principles chemical reaction kinetics and statistical thermodynamics simulations have replicated experimental pressure-composition hydrogen gas absorption isotherms for both initial and degraded LaNi 4.78 Sn 0.22 hydride. Neutron diffraction characterization of phase compositions, crystal structures, and hydrogen content have been performed on undamaged, degraded, and regenerated LaNi 4.78 Sn 0.22 deuterides.
The recently presented Electrochemical Kinetic Model (EKM), describing the electrochemical hydrog... more The recently presented Electrochemical Kinetic Model (EKM), describing the electrochemical hydrogen storage in hydride-forming materials, has been extended by the description of the solid/electrolyte interface, i.e. the charge transfer kinetics and electrical double layer charging. A complete set of equations has been derived, describing the equilibrium hydrogen partial pressure, the equilibrium electrode potential, the exchange current density and the electrical double layer capacitance as a function of hydrogen content in both solid-solutions and two-phase coexistence regions. The model has been applied to simulate isotherms of Pd thin films with a nominal thickness of 200 and 10 nm. The model demonstrates good agreement between the simulation results and experimental data.
ABSTRACT A novel approach in modeling the ionic transport in the electrolyte of Li-ion batteries ... more ABSTRACT A novel approach in modeling the ionic transport in the electrolyte of Li-ion batteries is here presented. Diffusion and migration processes govern the transport of ions in solution in the absence of convection. In the porous electrode theory [1] it is common to model these processes via mass balance equations and electroneutrality. A parabolic set of equations arises, in terms of a non constant electric field which is afflicted by the paradox of being generated without electrical charges. To remedy this contradiction, Maxwell's equations have been used here, coupled to Faraday's law of electrochemical charge transfer. The set of continuity equations for mass and Maxwell's equations lead to a consistent model, with distinctive energy characteristics. Numerical examples show the robustness of the approach, which is well suited for multi-scale analyses [2,3].
Li-ion is currently the most commonly used battery chemistry in portable applications. Accurate s... more Li-ion is currently the most commonly used battery chemistry in portable applications. Accurate state-of-charge ͑SOC͒ and remaining run-time indication for portable devices is important for user convenience and to prolong the lifetime of batteries. The actual SOC algorithms, which the main companies use in practice, make use of the so-called electromotive force ͑emf͒. In these SOC systems it is assumed that the emf of an Li-ion battery only depends on aging to a limited extent. In this paper, novel emf measurement and modeling efforts are presented as a function of battery aging. As will be shown, a better understanding of this dependence is useful for improving SOC accuracy.
The new mathematical model to estimate volumetric and gravimetric energy densities of the recharg... more The new mathematical model to estimate volumetric and gravimetric energy densities of the rechargeable NiMH batteries has been proposed. Application of the new prospective Mg 0.80 Sc 0.20 (1740 mAh/g) hydride forming material for MH electrode has been studied with the help of that model. It was shown that application of the new Mg 0.80 Sc 0.20 material gives 58 % advance in gravimetric energy density (Wh/kg) for AA-size battery those expected capacity reaches 3045 mAh. For the battery having the same weight as normal AA-size battery higher gains have been achieved, namely, 5 % increase in volumetric energy density and 80 % in gravimetric. Thus prospective NiMH battery may compete with majority of the currently available lithium-ion batteries. The new binary (e.g. Mg-Ti) and ternary (e.g. Mg-Ti-Al) alloys having the same capacity as
Mg-based alloys are promising hydrogen storage materials because of the high gravimetric energy d... more Mg-based alloys are promising hydrogen storage materials because of the high gravimetric energy density of MgH 2 (7.6 wt.%). A major disadvantage, however, is its very slow desorption kinetics. It has been argued that, in contrast to the well-known rutile-structured Mg hydride, hydrided Mg-transition metal alloys have a much more open crystal structure facilitating faster hydrogen transport. In this paper, the electrochemical aspects of new Mg-Sc and Mg-Ti materials will be reviewed. Storage capacities as high as 6.5 wt.% hydrogen have been reached with very favourable discharge kinetics. A theoretical description of hydrogen storage materials has also been developed by our group. A new lattice gas model is presented and successfully applied to simulate the thermodynamic properties of various hydride-forming materials. The simulation results are expressed by parameters corresponding to several energy contributions, for example mutual atomic hydrogen interaction energies. A good fit of the lattice gas model to the experimental data is found in all cases.
In current work, the ionic transport limitations in the Li-ion battery liquid electrolyte with se... more In current work, the ionic transport limitations in the Li-ion battery liquid electrolyte with separator are studied by a finite element method. This theoretical approach is based on the Nernst-Planck equation. It is shown that instead of solving coupled PDE system for concentration and potential, it is sufficient to calculate only the concentration profile in a three-dimensional (3D) structure to obtain a full description of the diffusion-migration ionic transport in the electrolyte in the steady-state. Subsequently, the overpotential and electric field can be calculated by using the provided equations. It was found that diffusion and migration overpotentials are equal in the steady-state. Consequently, two algorithms exploiting electrolyte simulations are proposed and successfully used to calculate the limiting current for the simulated battery system. In the present study a single perforated layer of the separator is inserted into the electrolyte and the simulations are carried out by increasing the complexity of the membrane holes. The ionic transportation dependence on the pore shape was found to be local and limited by the spatial area around the perforated separator.
2011 IEEE Vehicle Power and Propulsion Conference, 2011
ABSTRACT Successful introduction of Plug-in Electrical Vehicles (PEV) increases the requirements ... more ABSTRACT Successful introduction of Plug-in Electrical Vehicles (PEV) increases the requirements for advanced on-board Battery Management Systems (BMS) significantly. Modern BMS provides the driver for a number of important indications, such as remaining operation time, adaptive State-of-Charge and State-of-Health. The core of an advanced BMS is a mathematical model for the battery (pack). However, the high complexity and the large amount of computing power necessary for a proper implementation of such models creates a barrier for their introduction to automotive applications. In the present paper a simple dynamic model, describing the behavior of the battery voltage is therefore proposed. The approach is experimentally validated for 18650-type of Li-ion cells.
Nowadays, portable telecommunication, computing and entertainment equipments rely strongly on lit... more Nowadays, portable telecommunication, computing and entertainment equipments rely strongly on lithium-ion batteries for providing on-board energy. Silicon is attracting a lot of attention as a negative electrode material for lithiumion batteries due to its extremely high storage capacity. Two companies recently even announced the development of nanocomposite negative electrode materials based on Si. [ 2 , 3 ] Si particles suffer from severe mechanical degradation due to huge volume expansion/shrinkage of the material induced by Li-ion insertion/extraction. In order to prevent this degradation process, nano-sizing the material has been proposed as a crucial requirement. For use in microbatteries, nanostructuring can be achieved in several ways. The material can be prepared in the form of, for instance, thin fi lms. It is well-known that Si thin fi lms can reversibly accommodate the mechanical stresses accompanying Li-ion insertion/extraction, however, the amount of active material and, therefore, the storage capacity in planar thin fi lms batteries remains low. Thus, covering 3D structures such as trenches and pores with thin fi lms of active electrode materials is a promising route to increase the storage capacity, as has been recently demonstrated. Other architectures, for instance porous structures, or structures based on the inverse template, such as vertical pillars [ 11 , 12 ] or nanowires, have also been considered and have recently been reviewed. Although large improvements have been achieved by nanostructuring, the material integrity, and thus its lifetime, still remains a critical issue. The design of an alternative robust architecture that can withstand repeated expansion/shrinkage cycles is therefore the next challenge.
A mathematical model for all-solid-state Li-ion batteries is presented. The model includes the ch... more A mathematical model for all-solid-state Li-ion batteries is presented. The model includes the charge transfer kinetics at the electrode/electrolyte interface, diffusion of lithium in the intercalation electrode, and diffusion and migration of ions in the electrolyte. The model has been applied to the experimental data taken from a 10 Ah planar thin-film all-solid-state Li-ion battery, produced by radio frequency magnetron sputtering. This battery consists of a 320 nm thick polycrystalline LiCoO 2 cathode and a metallic Li anode separated by 1.5 m Li 3 PO 4 solid-state electrolyte. Such thin-film batteries are nowadays often employed as power sources for various types of autonomous devices, including wireless sensor nodes and medical implants. Mathematical modeling is an important tool to describe the performance of these batteries in these applications. The model predictions agree well with the galvanostatically measured voltage profiles. The simulations show that the transport limitations in the solid-state electrolyte are considerable and amounts to at least half of the total overpotential. This contribution becomes even larger when the current density reaches 0.5 mA cm −2 or higher. It is concluded from the simulations that significant concentration gradients develop in both the positive electrode and the solid-state electrolyte during a high current ͑dis͒charge.
Li-ion is the most commonly used battery chemistry in portable applications nowadays. Accurate st... more Li-ion is the most commonly used battery chemistry in portable applications nowadays. Accurate state-of-charge ͑SOC͒ and remaining run-time indication for portable devices is important for the user's convenience and to prolong the lifetime of batteries. A new SOC indication system, combining the electromotive force ͑EMF͒ measurement during equilibrium and current measurement and integration during charge and discharge, has been developed and implemented in a laboratory setup. During discharge, apart from simple Coulomb counting, the effect of the overpotential is also considered. Mathematical models describing the EMF and the overpotential functions for a Li-ion battery have been developed. These models include a variety of parameters whose values depend on the determination method and experimental conditions. In this paper the battery measurement and modeling efforts are described. The method of implementing the battery model in an SOC indication system is also described. The aim is an SOC determination within 1% inaccuracy or better under all realistic user conditions, including a wide variety of load currents and a wide temperature range. The achieved results show the effectiveness of our novel approach for improving the accuracy of the SOC indication.
All-solid-state 3D integrated batteries can reach the energy storage capacity required for future... more All-solid-state 3D integrated batteries can reach the energy storage capacity required for future wireless devices by exploiting the third dimension. Conformal deposition techniques such as atomic layer deposition (ALD) are needed to deposit the battery materials. In this work, the current development of ALD processes for 3D integrated batteries is reviewed. We have developed both the TiN diffusion barrier and Pt cathode current collector processes. TiN showed good barrier properties in 3D, although a higher than expected charge density was observed, which could be attributed to a lower thickness and/or different material properties at the bottom of the 3D structures. The remote plasma ALD process for Pt showed fast growth initiation and good adhesion of the films. Furthermore, sufficient step coverage for the battery application was found. ALD is also potentially able to deposit the active battery layers, although the deposition of Li-containing materials is expected to be challenging.
Photoelectrochemical hydrogen production from solar energy and water offers a clean and sustainab... more Photoelectrochemical hydrogen production from solar energy and water offers a clean and sustainable fuel option for the future. Planar III/V material systems have shown the highest efficiencies, but are expensive. By moving to the nanowire regime the demand on material quantity is reduced, and new materials can be uncovered, such as wurtzite gallium phosphide, featuring a direct bandgap. This is one of the few materials combining large solar light absorption and (close to) ideal band-edge positions for full water splitting. Here we report the photoelectrochemical reduction of water, on a p-type wurtzite gallium phosphide nanowire photocathode. By modifying geometry to reduce electrical resistance and enhance optical absorption, and modifying the surface with a multistep platinum deposition, high current densities and open circuit potentials were achieved. Our results demonstrate the capabilities of this material, even when used in such low quantities, as in nanowires.
Mg-Ti-H thin films are found to have very attractive optical properties: they absorb 87% of the s... more Mg-Ti-H thin films are found to have very attractive optical properties: they absorb 87% of the solar radiation in the hydrogenated state and only 32% in the metallic state. Furthermore, in the absorbing state Mg-Ti-H has a low emissivity; at 400 K only 10% of blackbody radiation is emitted. The transition between both optical states is fast, robust, and reversible. The sum of these properties highlights the applicability of such materials as switchable smart coatings in solar collectors.
Measurements of nuclear magnetic resonance (NMR) relaxation times allow the rates of H and D atom... more Measurements of nuclear magnetic resonance (NMR) relaxation times allow the rates of H and D atomic hopping in metal-hydrides to be determined. A first example compares the rates of H hopping in Mg 65 Sc 35 Pd 2.4 H 220 , a promising new battery electrode and storage alloy, to LaNi 5 H x and to the end-members of the alloy system, ScH 2 and MgH 2 . The motion of MgScH is more rapid than in the metallic ScH 2 and the ionic MgH 2 , but slower than in LaNi 5 H x . Magic-angle spinning (MAS) NMR of metal-deuterides is a newer method that can resolve inequivalent D atoms and measure the rate of diffusive exchange between the sites. Examples include the tetrahedral and octahedral sites in YD 2+x and D in ZrNiD x .
ABSTRACT The absorption and desorption isotherms of Mg thin films are determined by electrochemic... more ABSTRACT The absorption and desorption isotherms of Mg thin films are determined by electrochemical techniques at room temperature. Up to now, especially for hydrogen desorption from pure Mg, the temperature range for determining the isotherm has been confined to high temperatures. The enthalpy of hydride formation and hydride decomposition is in agreement with the data reported previously; however, the present data are measured directly at room temperature. The dynamic electrochemical responses during hydrogen extraction reveal that at the beginning of the dehydrogenation reaction the rate is mostly impeded by a nucleation and growth mechanism. The desorption isotherm is simulated with a lattice gas model and excellent agreement between experiment and theory is found. The parameters are used to obtain detailed information about the magnesium–hydrogen system.
LaNi 4.78 Sn 0.22 H x hydride samples were held at a hydrogen content of x > 5.0 (x is H/La atomi... more LaNi 4.78 Sn 0.22 H x hydride samples were held at a hydrogen content of x > 5.0 (x is H/La atomic ratio) and temperatures above 465 K to accelerate the intrinsic degradation processes. Although Sn-substituted alloys are much more resistant to disproportionation than nearly all other LaNi 5 alloys, the present test conditions did produce substantial degradation. Effects observed included reduction in hydrogen storage capacity, decreases in the plateau pressures, increased slopes of the plateaus, and smaller hysteresis ratios. A regeneration process nearly completely restored the behavior of the degraded LaNi 4.78 Sn 0.22 hydride to its initial value. First-principles chemical reaction kinetics and statistical thermodynamics simulations have replicated experimental pressure-composition hydrogen gas absorption isotherms for both initial and degraded LaNi 4.78 Sn 0.22 hydride. Neutron diffraction characterization of phase compositions, crystal structures, and hydrogen content have been performed on undamaged, degraded, and regenerated LaNi 4.78 Sn 0.22 deuterides.
The recently presented Electrochemical Kinetic Model (EKM), describing the electrochemical hydrog... more The recently presented Electrochemical Kinetic Model (EKM), describing the electrochemical hydrogen storage in hydride-forming materials, has been extended by the description of the solid/electrolyte interface, i.e. the charge transfer kinetics and electrical double layer charging. A complete set of equations has been derived, describing the equilibrium hydrogen partial pressure, the equilibrium electrode potential, the exchange current density and the electrical double layer capacitance as a function of hydrogen content in both solid-solutions and two-phase coexistence regions. The model has been applied to simulate isotherms of Pd thin films with a nominal thickness of 200 and 10 nm. The model demonstrates good agreement between the simulation results and experimental data.
ABSTRACT A novel approach in modeling the ionic transport in the electrolyte of Li-ion batteries ... more ABSTRACT A novel approach in modeling the ionic transport in the electrolyte of Li-ion batteries is here presented. Diffusion and migration processes govern the transport of ions in solution in the absence of convection. In the porous electrode theory [1] it is common to model these processes via mass balance equations and electroneutrality. A parabolic set of equations arises, in terms of a non constant electric field which is afflicted by the paradox of being generated without electrical charges. To remedy this contradiction, Maxwell's equations have been used here, coupled to Faraday's law of electrochemical charge transfer. The set of continuity equations for mass and Maxwell's equations lead to a consistent model, with distinctive energy characteristics. Numerical examples show the robustness of the approach, which is well suited for multi-scale analyses [2,3].
Li-ion is currently the most commonly used battery chemistry in portable applications. Accurate s... more Li-ion is currently the most commonly used battery chemistry in portable applications. Accurate state-of-charge ͑SOC͒ and remaining run-time indication for portable devices is important for user convenience and to prolong the lifetime of batteries. The actual SOC algorithms, which the main companies use in practice, make use of the so-called electromotive force ͑emf͒. In these SOC systems it is assumed that the emf of an Li-ion battery only depends on aging to a limited extent. In this paper, novel emf measurement and modeling efforts are presented as a function of battery aging. As will be shown, a better understanding of this dependence is useful for improving SOC accuracy.
The new mathematical model to estimate volumetric and gravimetric energy densities of the recharg... more The new mathematical model to estimate volumetric and gravimetric energy densities of the rechargeable NiMH batteries has been proposed. Application of the new prospective Mg 0.80 Sc 0.20 (1740 mAh/g) hydride forming material for MH electrode has been studied with the help of that model. It was shown that application of the new Mg 0.80 Sc 0.20 material gives 58 % advance in gravimetric energy density (Wh/kg) for AA-size battery those expected capacity reaches 3045 mAh. For the battery having the same weight as normal AA-size battery higher gains have been achieved, namely, 5 % increase in volumetric energy density and 80 % in gravimetric. Thus prospective NiMH battery may compete with majority of the currently available lithium-ion batteries. The new binary (e.g. Mg-Ti) and ternary (e.g. Mg-Ti-Al) alloys having the same capacity as
Mg-based alloys are promising hydrogen storage materials because of the high gravimetric energy d... more Mg-based alloys are promising hydrogen storage materials because of the high gravimetric energy density of MgH 2 (7.6 wt.%). A major disadvantage, however, is its very slow desorption kinetics. It has been argued that, in contrast to the well-known rutile-structured Mg hydride, hydrided Mg-transition metal alloys have a much more open crystal structure facilitating faster hydrogen transport. In this paper, the electrochemical aspects of new Mg-Sc and Mg-Ti materials will be reviewed. Storage capacities as high as 6.5 wt.% hydrogen have been reached with very favourable discharge kinetics. A theoretical description of hydrogen storage materials has also been developed by our group. A new lattice gas model is presented and successfully applied to simulate the thermodynamic properties of various hydride-forming materials. The simulation results are expressed by parameters corresponding to several energy contributions, for example mutual atomic hydrogen interaction energies. A good fit of the lattice gas model to the experimental data is found in all cases.
In current work, the ionic transport limitations in the Li-ion battery liquid electrolyte with se... more In current work, the ionic transport limitations in the Li-ion battery liquid electrolyte with separator are studied by a finite element method. This theoretical approach is based on the Nernst-Planck equation. It is shown that instead of solving coupled PDE system for concentration and potential, it is sufficient to calculate only the concentration profile in a three-dimensional (3D) structure to obtain a full description of the diffusion-migration ionic transport in the electrolyte in the steady-state. Subsequently, the overpotential and electric field can be calculated by using the provided equations. It was found that diffusion and migration overpotentials are equal in the steady-state. Consequently, two algorithms exploiting electrolyte simulations are proposed and successfully used to calculate the limiting current for the simulated battery system. In the present study a single perforated layer of the separator is inserted into the electrolyte and the simulations are carried out by increasing the complexity of the membrane holes. The ionic transportation dependence on the pore shape was found to be local and limited by the spatial area around the perforated separator.
2011 IEEE Vehicle Power and Propulsion Conference, 2011
ABSTRACT Successful introduction of Plug-in Electrical Vehicles (PEV) increases the requirements ... more ABSTRACT Successful introduction of Plug-in Electrical Vehicles (PEV) increases the requirements for advanced on-board Battery Management Systems (BMS) significantly. Modern BMS provides the driver for a number of important indications, such as remaining operation time, adaptive State-of-Charge and State-of-Health. The core of an advanced BMS is a mathematical model for the battery (pack). However, the high complexity and the large amount of computing power necessary for a proper implementation of such models creates a barrier for their introduction to automotive applications. In the present paper a simple dynamic model, describing the behavior of the battery voltage is therefore proposed. The approach is experimentally validated for 18650-type of Li-ion cells.
Nowadays, portable telecommunication, computing and entertainment equipments rely strongly on lit... more Nowadays, portable telecommunication, computing and entertainment equipments rely strongly on lithium-ion batteries for providing on-board energy. Silicon is attracting a lot of attention as a negative electrode material for lithiumion batteries due to its extremely high storage capacity. Two companies recently even announced the development of nanocomposite negative electrode materials based on Si. [ 2 , 3 ] Si particles suffer from severe mechanical degradation due to huge volume expansion/shrinkage of the material induced by Li-ion insertion/extraction. In order to prevent this degradation process, nano-sizing the material has been proposed as a crucial requirement. For use in microbatteries, nanostructuring can be achieved in several ways. The material can be prepared in the form of, for instance, thin fi lms. It is well-known that Si thin fi lms can reversibly accommodate the mechanical stresses accompanying Li-ion insertion/extraction, however, the amount of active material and, therefore, the storage capacity in planar thin fi lms batteries remains low. Thus, covering 3D structures such as trenches and pores with thin fi lms of active electrode materials is a promising route to increase the storage capacity, as has been recently demonstrated. Other architectures, for instance porous structures, or structures based on the inverse template, such as vertical pillars [ 11 , 12 ] or nanowires, have also been considered and have recently been reviewed. Although large improvements have been achieved by nanostructuring, the material integrity, and thus its lifetime, still remains a critical issue. The design of an alternative robust architecture that can withstand repeated expansion/shrinkage cycles is therefore the next challenge.
A mathematical model for all-solid-state Li-ion batteries is presented. The model includes the ch... more A mathematical model for all-solid-state Li-ion batteries is presented. The model includes the charge transfer kinetics at the electrode/electrolyte interface, diffusion of lithium in the intercalation electrode, and diffusion and migration of ions in the electrolyte. The model has been applied to the experimental data taken from a 10 Ah planar thin-film all-solid-state Li-ion battery, produced by radio frequency magnetron sputtering. This battery consists of a 320 nm thick polycrystalline LiCoO 2 cathode and a metallic Li anode separated by 1.5 m Li 3 PO 4 solid-state electrolyte. Such thin-film batteries are nowadays often employed as power sources for various types of autonomous devices, including wireless sensor nodes and medical implants. Mathematical modeling is an important tool to describe the performance of these batteries in these applications. The model predictions agree well with the galvanostatically measured voltage profiles. The simulations show that the transport limitations in the solid-state electrolyte are considerable and amounts to at least half of the total overpotential. This contribution becomes even larger when the current density reaches 0.5 mA cm −2 or higher. It is concluded from the simulations that significant concentration gradients develop in both the positive electrode and the solid-state electrolyte during a high current ͑dis͒charge.
Li-ion is the most commonly used battery chemistry in portable applications nowadays. Accurate st... more Li-ion is the most commonly used battery chemistry in portable applications nowadays. Accurate state-of-charge ͑SOC͒ and remaining run-time indication for portable devices is important for the user's convenience and to prolong the lifetime of batteries. A new SOC indication system, combining the electromotive force ͑EMF͒ measurement during equilibrium and current measurement and integration during charge and discharge, has been developed and implemented in a laboratory setup. During discharge, apart from simple Coulomb counting, the effect of the overpotential is also considered. Mathematical models describing the EMF and the overpotential functions for a Li-ion battery have been developed. These models include a variety of parameters whose values depend on the determination method and experimental conditions. In this paper the battery measurement and modeling efforts are described. The method of implementing the battery model in an SOC indication system is also described. The aim is an SOC determination within 1% inaccuracy or better under all realistic user conditions, including a wide variety of load currents and a wide temperature range. The achieved results show the effectiveness of our novel approach for improving the accuracy of the SOC indication.
All-solid-state 3D integrated batteries can reach the energy storage capacity required for future... more All-solid-state 3D integrated batteries can reach the energy storage capacity required for future wireless devices by exploiting the third dimension. Conformal deposition techniques such as atomic layer deposition (ALD) are needed to deposit the battery materials. In this work, the current development of ALD processes for 3D integrated batteries is reviewed. We have developed both the TiN diffusion barrier and Pt cathode current collector processes. TiN showed good barrier properties in 3D, although a higher than expected charge density was observed, which could be attributed to a lower thickness and/or different material properties at the bottom of the 3D structures. The remote plasma ALD process for Pt showed fast growth initiation and good adhesion of the films. Furthermore, sufficient step coverage for the battery application was found. ALD is also potentially able to deposit the active battery layers, although the deposition of Li-containing materials is expected to be challenging.
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Papers by P. Notten