Design Of Battery Electrodes Research Articles

Exploring hybrid hard carbon/Bi2S3-based negative electrodes for Na-ion batteries

Exploring hybridization of Bi2S3 nanorods with hard carbon substrate for sodium-ion batteries revealed enhanced performance with MPA modification, elucidating charge storage mechanisms and transformation dynamics, advancing battery electrode design.

A Computational Model for All-Solid-State Batteries Coupling Electrochemistry and Solid Mechanics on Resolved Microstructures Enabling Optimization of Battery Electrode Design

All-Solid-State Batteries (ASSB) are a promising technology to replace conventional Lithium-Ion Batteries (LIB) since the energy density and fast charging capability of LIBs are projected to reach a physical limit soon. In this regard, the ASSB technology is considered superior, especially if the incorporation of the lithium metal anode, or other high-capacity anode materials like silicon is achieved. However, these systems still require intensive research as many physical effects, especially those concerning the interaction of electrochemistry and solid mechanics, are to date not well understood [1]. Most experimental investigations on ASSB cells are performed on laboratory scale and are usually operated at elevated mechanical pre-stress to obtain satisfactory system performance. The delamination of active materials and solid electrolyte during cycling is expected to be one of the key effects for the required mechanical pre-stress. Furthermore, a lot of experimental research focuses on the development of new material classes and their stability in the cell compound, while a systematic optimization of the cell setup is missing.Comprehensive computational models can help to generate insights in these regards as they allow for detailed investigations of local effects, which is often not possible in experimental setups. Another advantage of computational models compared to experiments is the ability to change input parameters in a fast and systematic way to quantify their influence on the battery cell performance and thereby help to speed up the optimization of battery designs. Since the multitude of physical effects that are relevant in ASSB are computationally challenging, a lot of modeling approaches rely on numerous simplifications like spatial homogenization or neglect of mechanical effects to name just two. However, such assumptions can significantly limit the validity of the model.We propose a novel computational model for ASSB [2] to thoroughly investigate the interdependence of electrochemistry and solid mechanics on resolved microstructures that vastly influence the behavior and the performance of an ASSB cell. It is based on nonlinear continuum mechanics and accounts for large deformations due to lithiation dependent volume changes of the active materials. The mass and charge conservations are consistently formulated to also ensure the conservation property in large deformation scenarios. Furthermore, the model is extended by interaction effects of electrochemistry and solid mechanics like a nonlinear contact formulation at the electrode-electrolyte interfaces to account for delamination phenomena and the subsequent absence of charge transfer reaction (see Fig. 1). We thereby show how delamination phenomena drastically change available percolation paths in the microstructure. The efficient parallel implementation of the computational model allows to investigate realistic three-dimensionally resolved microstructures of ASSB cells while accounting for the coupling effects of electrochemistry and solid mechanics. A combination of elaborate physical models and probabilistic methods enables to gain further understanding and to quantify main influencing factors on the cell performance. To showcase these capabilities and how they can be exploited to increase system understanding, we analyze how statistical values like the porosity, or the composition of the electrode microstructure influence the capacity of an ASSB cell and thereby contribute to find optimal electrode designs.

Niobium Oxide Anode with Lattice Structure Self-Optimization for High-Power and Nearly Zero-Degeneration Battery Operation.

Li+ insertion-induced structure transformation in crystalline electrodes vitally influence the energy density and cycle life of secondary lithium-ion battery. However, the influence mechanism of structure transformation-induced Li+ migration on the electrochemical performance of micro-crystal materials is still unclear and the strategy to profit from such structure transformation remains exploited. Here, an interesting self-optimization of structure evolution during electrochemical cycling in Nb2O5 micro-crystal with rich domain boundaries is demonstrated, which greatly improves the charge transfer property and mechanical strength. The lattice rearrangement activates the Li+ diffusion kinetics and hinders the particle crack, thus enabling a nearly zero-degeneration operation after 8000 cycles. Full cell paired with lithium cobalt oxides displays an exceptionally high capacity of 176mAhg-1 at 8000mAg-1 and excellent long-term durability at 6000mAg-1 with 63% capacity retention over 2000 cycles. Interestingly, a unique fingerprint based on the intensity ratio of two X-ray diffraction peaks is successfully extracted as a measure of Nb2O5 electrochemical performance. The structure self-optimization for fast charge transfer and high mechanical strength exemplifies a new battery electrode design concept and opens up a vast space of strategy to develop high-performance lithium-ion batteries with high energy density and ultra-long cycle life.

A three-dimensional pore-scale model for redox flow battery electrode design analysis

A three-dimensional (3-D) pore-scale model has been developed to construct multiscale fibrous electrodes for redox flow batteries (RFB). New designs, such as biporous electrodes modify electrode structures by creating secondary pores on single carbon fiber to reduce internal battery resistance. Existing pore-scale models only resolve electrodes to the single carbon fiber scale and cannot incorporate recent multiscale electrode designs into numerical models. Our new model aims to bridge this gap and provide a tool to rapidly screen new electrode configurations. Two multiscale electrodes, laser-perforated and biporous electrodes, were investigated at varying operation conditions with the proposed 3-D pore-scale models. The laser-perforated electrode exhibits a reduced pressure drop, but follows the same permeability correlation compared to the corresponding pristine electrode. For the biporous electrode, the added specific surface area and faster reaction kinetics from the secondary pores are the most influential factors leading to improved battery efficiency. However, operating the biporous electrode in limiting current density conditions should be avoided due to the decreased mass transfer efficiency and a more significant voltage loss. We believe that our 3-D pore-scale model can accelerate the flow battery electrode design process and provide new insights into electrode geometry optimizations.

Influence of Polymeric Binders on Robust Performance of Lithium-Ion Electrodes

Lithium-ion batteries have become ubiquitous in a variety of energy storage applications ranging from grid storage to consumer electronics to electric vehicles. However, their continued usage in a vastly dynamic world predicates on their ability to be not only safe, sustainable, and reliable, but also contain high capacity under a variety of fast charge/discharge conditions. Multiple studies have shown that increased performance at fast charge/discharge rates can be achieved through systematic manipulation of key interfaces at various nano-, micro- and mesoscales of the electrode. Through careful tuning of the processing and chemical modification of polymeric binders, capping agents, and conductive additives, rational design of battery electrodes with specific performance characteristics can be achieved. Careful manipulation of interfacial chemistries can help push the boundaries of electrochemical performance in a wide variety of cell components. This presentation will focus on the chemical manipulation of polymers within a composite electrode to gain fundamental insights needed for the realization of next-generation battery systems.

A Review on Digitalization Approaches for Battery Manufacturing Processes

Lithium ion batteries (LiBs) continue to be the most advanced technology in the battery systems as the world rushes to meet the diverse and expanding demands of the energy storage solutions. Research institutions, academia and industries requires a safer, high-performance and cheaper LiBs to accelerate the transition from oil-based to an electrical-based economy. Because of some interdependent electrochemical kinetics involved in the LiB chemistry, and time it takes for the fabrication process it became one of the challenging aspects in this modern day life as it is time consuming and needs to be updated with upcoming materials and methodologies[1]. To overcome these challenges quickly, introduction of digital tools [2] which can optimize the parameters of making LiBs are being researched and are trying to implement them in the battery manufacturing industry. Typically, the state of art manufacturing of batteries is a sequence of intermittent steps like slurry preparation, coating and drying, electrode cutting, calendaring, stacking pouch cell formation, electrolyte filling, sealing and mechanical and electrochemical testing which have to be precisely controlled and optimize each dependent parameters carefully and reorganize them for the fabrication to adopt to new systems which takes a lot of effort and machine handling for new innovative battery technologies. Automation of this manufacturing process with Artificial Intelligence (AI), Machine learning(ML) or Internet of Things (IoT) is the new way of approach [3]. These approaches can help the research and battery manufacturing plants to meet the demands of cost effectiveness, sustainability, time needs and scalability. Digitalization of these techniques on one hand can reduce the time to market and provide a profitable manufacturing and on the other hand it can guide the cell prototyping and advanced cell chemistry to the new manufacturing tools in the virtual way. Thus the designing tools cost, prototyping cost also can be reduced. The abstract reviews both experimental and computational approach to undergo smooth transition in the battery manufacturing process.References Witt, D. et al. Myth and Reality of a Universal Lithium-Ion Battery Electrode Design Optimum: A Perspective and Case Study. Energy Technol. 9, (2021).Ramakrishna, S., Khong, T. C. & Leong, T. K. Smart Manufacturing. Procedia Manuf. 12, 128–131 (2017).dos Reis, G., Strange, C., Yadav, M. & Li, S. Lithium-ion battery data and where to find it. Energy AI 5, (2021).

(Invited, Digital Presentation) Phase Interactions and Degradation in Battery Composite Electrodes

The composite electrodes of lithium-ion and sodium-ion batteries must balance complex interactions between the many physical phenomena that underpin battery operation. Active materials host electroactive species. Porous regions support the movement of ions, and secondary phases containing binders and conductive additives provide a supporting electron conducting matrix. Cycling and aggressive operating conditions drive changes in these phases and the balance between them. The alteration of these electrode phases manifests in declining performance and ultimately battery failure. Here, we present an overview of research on degradation processes observed in a diverse set of battery materials using X-ray imaging methods—nanotomography, microtomography, and X-ray absorption near edge structure (XANES) imaging—complemented by electrochemical experiments and other materials characterization methods.Metallic anodes offer a high-capacity alternative to carbon-based anodes for lithium-ion and sodium-ion batteries. Among these metallic anodes tin-based active materials present high-capacity and electrochemical activity in both lithium and sodium chemistries. However, high capacity comes at the price of excessive volume expansion and attendant performance degradation. Studies of Cu6Sn5 alloy anodes in lithium-ion batteries performed using X-ray tomography and nanoscale 2D XANES reveal material volume expansion, fracture, and dissolution as key failure mechanisms within the active material. However, the expansion and contraction of the metallic active material during cycling also leads to significant changes in the supporting carbon-binder domains of the electrodes. Such changes are also observed in the cycling of tin-based composite anodes in both lithium-ion and sodium-ion applications. Active material pulverization of tin due to lithiation and sodiation processes is evident in phase size distributions observed with X-ray microtomography. These changes are accompanied by alteration of the supporting carbon-binder regions.Low cobalt layered oxide cathode materials for lithium-ion batteries present an opportunity for maintaining desirable theoretical capacities while removing cobalt, a metal that presents significant humanitarian issues within its supply chain. However, removal of cobalt from these layered oxide systems removes its stabilizing influence on the electrode structure, especially when cycling at voltages above 4.0 V vs. Li/Li+. Degradation of the low cobalt cathode material Li(Ni0.8Mn0.1Co0.1)O2 has been assessed under different cut-off voltage and operating temperatures using a suite of electrochemical and materials characterization techniques. Higher cycling temperature was found to accelerate degradation mechanisms within the active material, specifically rock-salt phase formation and active material dissolution. Elevated temperature was found to cause significant changes in the supporting carbon-binder domains as well. These changes in both the active material and supporting phases manifest in degradation of electrochemical performance with respect to lost capacity and altered electrode impedances.Taken together, the above studies provide a picture of battery degradation that is driven by anticipated changes in the active material and more nuanced variations that occur in the supporting phases. These observations motivate holistic approaches for the analysis and design of battery electrodes that fit their status as heterogeneous functional materials.

Data-Based Interpretable Modeling for Property Forecasting and Sensitivity Analysis of Li-ion Battery Electrode

Lithium-ion batteries have become one of the most promising technologies for speeding up clean automotive applications, where electrode plays a pivotal role in determining battery performance. Due to the strongly-coupled and highly complex processes to produce battery electrode, it is imperative to develop an effective solution that can predict the properties of battery electrode and perform reliable sensitivity analysis on the key features and parameters during the production process. This paper proposes a novel tree boosting model-based framework to analyze and predict how the battery electrode properties vary with respect to parameters during the early production stage. Three data-based interpretable models including AdaBoost, LPBoost, and TotalBoost are presented and compared. Four key parameters including three slurry feature variables and one coating process parameter are analyzed to quantify their effects on both mass loading and porosity of battery electrode. The results demonstrate that the proposed tree model-based framework is capable of providing efficient quantitative analysis on the importance and correlation of the related parameters and producing satisfying early-stage prediction of battery electrode properties. These can benefit a deep understanding of battery electrodes and facilitate to optimizing battery electrode design for automotive applications.

First-Principles Study of Amorphous Al2O3 ALD Coating in Li-S Battery Electrode Design

The Li-S battery is exceptionally appealing as an alternative candidate beyond Li-ion battery technology due to its promising high specific energy capacity. However, several obstacles (e.g., polysulfides’ dissolution, shuttle effect, high volume expansion of cathode, etc.) remain and thus hinder the commercialization of the Li-S battery. To overcome these challenges, a fundamental study based on atomistic simulation could be very useful. In this work, a comprehensive investigation of the adsorption of electrolyte (solvent and salt) molecules, lithium sulfide, and polysulfide (Li2Sx with 2 ≤x≤ 8) molecules on the amorphous Al2O3 atomic layer deposition (ALD) surface was performed using first-principles density functional theory (DFT) calculations. The DFT results indicate that the amorphous Al2O3 ALD surface is selective in chemical adsorption towards lithium sulfide and polysulfide molecules compared to electrolytes. Based on this work, it suggests that the Al2O3 ALD is a promising coating material for Li-S battery electrodes to mitigate the shuttling problem of soluble polysulfides.

Sparse data machine learning for battery health estimation and optimal design incorporating material characteristics

State of health estimation and optimal electrode design are two critical challenges in battery research, yet few work addressed them together. In this work we demonstrate a machine learning approach for next generation high capacity batteries with black phosphorus anodes. Experimentally 90 coin cells with various material properties are fabricated and cycled at different conditions, generating so far the most comprehensive dataset. For the first time, material characteristics are incorporated for state of health estimation in a data-driven framework. A virtual sample generator is developed to address sparse data by generating virtual samples, which significantly improves state of health prediction. Incorporating easy-to-measure material properties, the model is able to accurately predict state of health after a given number of cycles using only the first 2 cycles. The approach provides quantitative insights of feature importance, resulting in a multi-objective optimization framework for battery electrode design, achieving long cycling life, high active material loading and fast kinetics at the same time.

Layered-Rocksalt Intergrown Cathode for High-Capacity Zero-Strain Battery Operation

The continuous dependence on high-performance lithium-ion batteries leads to a pressing demand for advanced cathode materials of high energy density along with excellent cycling stability. Here we demonstrate a new concept of layered-rocksalt intergrown structure that harnesses the combined figures of merit from each individual phase, including the high capacity of layered and rocksalt phases, good kinetics of layered oxide and structural advantage of rocksalt phase. Based on this concept, lithium nickel ruthenium oxide of a main layered structure (R-3 m) with intergrown rocksalt (Fm-3 m) is developed, which delivers a high capacity with good rate performance. More importantly, the interwoven rocksalt structure successfully prevents the anisotropic structural change that is typical for the layered oxide, enabling a nearly zero-strain operation upon high-capacity cycling. Furthermore, a general design principle is successfully extrapolated and experimentally verified in a series of compositions. The success of such layered-rocksalt intergrown structure exemplifies a new concept of battery electrode design and opens up a vast space of compositions to develop high-performance intergrown cathodes for advanced energy storage devices.

(Invited) Towards Model-Based Predictive Battery Electrode Design

Lithium ion batteries contain porous electrodes, whose design determines battery performance, cost and life-time.Yet, we are far from knowing what is the best structure, and it is prohibitively time- and resource-consumingto do experimental trial and error production, as there are too many parameters in the production process and in the electrode itself.This motivates to use physico-chemical models that yield insight into performance and limitations of given electrode structures as well asallow optimal design. The need for models that allow structure optimisation, i.e. rapid evaluation of many design variants, basically excludes large 3-dimensional models with complex inhomogeneous structures. On the other hand, homogeneous pseudo-two-dimensional models face limitations regarding the prediction of new electrode designs as the crucial influence of conducting additives and binder are not considered sufficiently.This talk will elucidate a pathway that allows model-based predictive battery design.It shows the application of microstructure models to identify the effective electric and ionic conductivity and electroactive area ofelectrode structures containing additives, and the transfer of this knowledge via surrogate models into electrochemical P2D models to evaluate the respective electrochemical performance. The effect of additive and active material content and distribution is demonstrated at the example of Li ion battery cathode and all solid state Li battery electrodes. The models are applicable to predict the performance of electrodes in cells. We further elucidate how uncertainties in the production process of electrodes lead to distributed electrode design parameters and performance.Finally, we show and compare two pathways of identifying optimal electrode designs at the example of dual layer electrodes: a coarse-grained scanning of thousands of design variants using 8 parameters reveals strongly different designs for optimal charge and discharge, whereas a high resolution optimisation of two design parameters shows flat performance plateaus.Model-based design optimization without extensive experimental studies will reduce costs and experimental efforts in the development of next-generation batteries.

Layered-rocksalt intergrown cathode for high-capacity zero-strain battery operation

The dependence on lithium-ion batteries leads to a pressing demand for advanced cathode materials. We demonstrate a new concept of layered-rocksalt intergrown structure that harnesses the combined figures of merit from each phase, including high capacity of layered and rocksalt phases, good kinetics of layered oxide and structural advantage of rocksalt. Based on this concept, lithium nickel ruthenium oxide of a main layered structure (Rbar{3}m) with intergrown rocksalt (Fmbar{3}m) is developed, which delivers a high capacity with good rate performance. The interwoven rocksalt structure successfully prevents the anisotropic structural change that is typical for layered oxide, enabling a nearly zero-strain operation upon high-capacity cycling. Furthermore, a design principle is successfully extrapolated and experimentally verified in a series of compositions. Here, we show the success of such layered-rocksalt intergrown structure exemplifies a new battery electrode design concept and opens up a vast space of compositions to develop high-performance intergrown cathode materials.

Low-Tortuosity, Highly Conductive, Vertically Aligned, Ultra-Thick Composite Electrode Design for Batteries

Ultra-think electrode is very important for high-energy batteries. It requires to increase the volume ratio of active material to inactive material and to improve the electrochemical reaction kinetics with low-tortuous ion and electron transfer pathways. In this talk, I will introduce a vertically aligned carbon fibers framework to structurally and electrically reinforce electrode structure to obtain high conductivity and low tortuosity. Compared with the traditional LFP electrodes composed of randomly dispersed LFP particles and carbon black particles, the CF-LFP electrodes show significant improvements in active material loading, structural stability and electrochemical performance due to the unique vertical arrangement of carbon fibers inside composite electrode. Because the vertical arrangement of carbon fibers provides a fast electron/ion transport channel, it promotes the redox reaction kinetics in the electrodes. CF-LFP electrodes significantly enhance the capacity and rate capability. The thickness of the electrode can be up to 1 mm with a loading of ~128 mg/cm2 and a specific capacity of 154 mAh/g.

Energy-Dispersive X-ray Diffraction: Operando Visualization of Electrochemical Activity of Thick Electrodes

Effective utilization of the electroactive material in thick electrodes could enable Li-based batteries to be developed with higher energy densities while simultaneously reducing the overall cost of the battery. Herein, we explore the lithiation of a multiple electron transfer conversion material, Fe3O4, and report tomographic-like mapping of the electroactive material utilization under operando electrochemical lithiation using energy-dispersive X-ray diffraction. A challenge for thick electrodes is limited Li+ diffusion resulting in an inability to fully access the active material. Our strategy to surmount this obstacle is the deliberate incorporation of acicular carbon nanotubes to the electrode where the design maximized the electron and ion access to the Fe3O4 active material within a thick electrode (∼500 μm). Based on whole pattern fitting of the diffraction data, the phase composition was determined with both spatial and temporal resolutions. The data allow identification of the electrochemical conversion products, Li2O and Fe metal, where interestingly, the Li2O crystallites increase in size after initial formation. The observation of increased crystallite size of Li2O after initial formation provides new insight into the time-dependent phenomena of conversion-type active materials and their reversibility. This investigation contributes to our understanding of Li+ transport in thick electrodes and provides insight into the design of battery electrodes that facilitate electroactive material utilization of energy storage systems crucial for the development of next-generation batteries.

Reaction-diffusion-stress coupling model for Li-ion batteries: The role of surface effects on electrochemical performance

Recent years, nanostructured design for battery electrodes has emerged as a promising solution to improve rate capability and reliability of the high-capacity electrodes. However, the surface effects arising from small feature size may affect the multi-physical features of electrodes subject to non-equilibrium electrochemical cycles. In this study, a reaction-diffusion-stress coupling model is developed with the contribution of surface effects, which can capture the interactions between surface electrode reaction, diffusion and solid deformation in a nanoparticle of an electrode under non-equilibrium cyclic charge and discharge. Numerical results show that compressive stress at the surface of an electrode particle during insertion inhibits lithium absorption, while tensile stress at the surface of an electrode particle due to ion extraction suppresses lithium desorption with regard to surface electrochemical reactions. When surface mechanics is taken account into nanoscale electrode study, surface tension is found to be responsible for the increase in mechanical stability, as well as the significant reduction in charge capacity during both the galvanostatic and potentiostatic operation in the meantime. By further introducing tunable surface modulus effects, it is shown that the positive surface modulus aggravates charge capacity loss, whereas the negative surface modulus remedies it for a given potential. The results of the study provide a new idea for nano-surface engineering to optimize the design of electrode to meet required durability and electrochemical performance.

Deterministic Design of Chemistry and Mesostructure in Li-Ion Battery Electrodes.

All battery electrodes have complex internal three-dimensional architectures that have traditionally been formed through the random packing of the electrode components. What is now emerging is a new concept in battery electrode design, where the important electronic and ionic pathways, as well as the chemical interactions between the components of the electrode, are deterministically designed. Deterministic design enables far better properties than are possible through random packing, including dramatic improvements in both power and energy. Such a design approach is particularly attractive for emerging high-energy-density materials, which require available free volume as they swell during cycling. In addition to controlled structure, another important facet of the design of such systems is the stable chemical linkages between the active material and the conductive network that survive the lithiation and delithiation processes. In this Perspective, we discuss and provide our views on deterministically designed battery electrodes.

Simulated impedance of diffusion in porous media

This paper describes the use of a frequency domain, finite-difference scheme to simulate the impedance spectra of diffusion in porous microstructures. Both open and closed systems are investigated for a range of ideal geometries, as well as some randomly generated synthetic volumes and tomographically derived microstructural data. In many cases, the spectra deviate significantly from the conventional Warburg-type elements typically used to represent diffusion in equivalent circuit analysis. A key finding is that certain microstructures show multiple peaks in the complex plane, which may be misinterpreted as separate electrochemical processes in real impedance data. This is relevant to battery electrode design as the techniques for nano-scale fabrication become more widespread. This simulation tool is provided as an open-source MatLab application and is freely available online as part of the TauFactor platform.

Corrugated Electrode/Electrolyte Interfaces in SOFC: Theoretical and Experimental Development

The development routes to improve the performances of SOFCs are globally well identified and lead to shift the characteristic i/v curve towards higher potentials and current densities, an effect that is consistent with a lowering of the three overpotentials (activation, resistance and concentration). An increase of the Triple Phase Boundary (TPB) density at the electrodes, a reduction of the materials thickness, the development of materials with improved performances, the optimization of electrodes microstructure all serve as guidelines that aim to this goal. Taking as an example the specific design of battery electrodes, we have explored how the corrugation of electrode/electrolyte interfaces at a mesoscopic scale in a SOFC could improve the electrochemical performances, from theoretical and experimental points of view. First, an electrochemical model was established and implemented in the COMSOL Multiphysics software, taking into account masses and charges conservation, gas transport and electrochemical reaction kinetics. The model results demonstrated that the presence of a periodic pattern (parallelepipeds, pyramids, ellipsoids) at the electrolyte/electrode interfaces, along with an electrolyte the thickness of which is significantly smaller than the dimensions of the pattern, could lead to a strong increase of the exchange surface, hence to higher exchange currents and cell performances. To that extent, it is theoretically shown that the patterns must have concave and convex singularities so as to confine the cathode material on the cathode side and the anode material on the anode side, hence the active layers on both sides, so that a much larger number of TPB are solicited and involved in the chemical reactions, reducing then the activation overpotential, as compared with a flat surface. It is also shown that the geometrical feature can be chosen so that it minimizes the concentration overpotential. In addition, the modeling provided us with key information regarding the characteristics of the patterns (shape, width and depth, distance between them, …) that should lead to a large gain in exchange current throughout the interface. For example, an increase of the exchange current of about 60% was calculated for a parallelepipedic pattern with 70 μm width and 100 μm depth, each geometric feature separated from the other by a few hundred microns. With the use of laboratory standard ceramic processes (tape casting, screen printing, bar coating, cold pressing, cold stamping), we have implemented such mesoscopic architectures on green self supported anodes (YSZ + Ni) on top of which a thin layer of electrolyte (YSZ) was deposited. As anticipated the electrical testing and impedance spectroscopy results show that such corrugation at anode/electrolyte interfaces improves significantly the electrochemical performances of the cell even though the sintering tends to alter and blunt the geometrical features of the pattern. Based on the electrochemical performances and modeling, the geometry of the pattern and its evolution during sintering is discussed in terms of activation and concentration overpotentials.

The Effect of Kinetic Nonlinearity on Battery Electrode Design: A Closer Look at Electrode Processes

The idea of using modeling in battery design was first introduced by W. Tiedemann and J. Newman in 19751. They used an ohmically limited porous electrode model to maximized the cell effective capacity by controlling electrode thickness and porosity. Newman later applied the reaction-zone model to maximize the specific energy of the system by considering mass as well2. V. Ramadesigan et al.3went one step further with the ohmic resistance model in the electrode by including electrode kinetics. They assumed the linear kinetics, and minimized the ohmic resistance in the positive electrode by varying porosity using control vector parameterization (CVP) method. They also introduced the idea of using layered graded electrode to get a porosity distribution to further reduce the ohmic resistance in the system. Since the introduction of the pseudo-2D (P2D) model3, many efforts have been made in applying the P2D model in battery design. W. Du et al. applied an optimization framework based on surrogate method4. S. Golmon et al. performed the multi-objective and multi-design-parameter optimization problem with adjoint sensitivity analysis5 with expanded P2D model incorporating mechanical stress-strain relationship. S. De and his coworkers6 used a reformulated model developed by the Subramanian group7, to perform simultaneous optimization of multiple design parameters. N. Xue et al. 8 applied the gradient-based algorithm framework to optimize the cell design. More recently, Y. Dai and V. Srinivasan9used a gradient-free direct search method to maximize the specific energy. Generally, there are two purposes of using models to simulate the battery system; one is to develop a better understanding of the system, and the other is to use the models as guidance to achieve better performance. For the latter purpose, a model with fewer assumptions and more equations capturing as many processes as possible is desired to simulate the system better. However, for a better understanding of the system, it may be worth taking a step back, and examining a simpler model where the effects of different processes can be observed clearly, even though more detailed physical models with much less assumptions would be used to guide the actual design. This is the purpose and idea behind this study. The model used in this study is an ohmic resistance model, with the assumption that the electrolyte concentration is uniform and double-layer charging can be ignored. Ohm’s law for both solid and electrolyte phases was included in the model, as well as a polarization equation representing the electrode kinetics. The polarization equation describes the charge transfer between the two phases, of which the linear form together with Ohm’s law for the two phases can be found in Ref10. In such a model, the trade-off between ohmic potential drop and reaction kinetics can be captured by current distribution between the two phases. In this work, we want to quantify the impact of nonlinearity on the architecture design by carefully examining the effect of nonlinearity on the ohmic resistance model. For linear kinetics, the optimal design to minimize overall resistance is independent of operation conditions (Fig. 1). However, for nonlinear kinetics, the optimal porosity is bigger for higher charge/discharge rates. This suggests that for batteries built for different applications, the optimal design varies depending on the operation conditions, especially at high rates, where the kinetics fall outside the linear regime. Figure 1 . Optimal Porosity under Different Charge/Discharge Rates for Linear and Nonlinear Polarization Acknowledgements The authors are thankful for the financial support of this work by the Clean Energy Institute (CEI) at the University of Washington.