Battery System Design Research Articles

Investigation of the influence of different bracing of automotive pouch cells on cyclic liefetime and impedance spectra

Abstract Lithium-Ion pouch cells are types of cells with great potential regarding energy and power densities to design of battery systems and battery modules in electromobility. These cells pose a high demand on their placement and bracing in the module to compensate their expansion and therefore guarantee a long lifetime. The challenge is to identify optimal bracing for the individual pouch cells. Thus, this work studies the cyclic aging of four identical automotive pouch cells under different bracing conditions while measuring cell-specific force, distance and impedance parameters. This measurement shows an improved mechanical integration of this type of battery cell in modules. Furthermore there is a recognizable correlation between the different conditions of strain and the impedance spectra along different states of aging. From this results a specific parameter is identified which can be used for rapid test procedures.

Marriage of an Ether-Based Electrolyte with Hard Carbon Anodes Creates Superior Sodium-Ion Batteries with High Mass Loading

Inferior rate performance, insufficient cycle life, and low mass loading have restricted the practical application of hard carbon (HC) anodes in sodium-ion batteries (NIBs). Here, a compatible strategy is developed by matching HC anodes with an ether-based electrolyte. Systematical investigation reveals that good compatibility of the electrode-electrolyte systems forms thinner but a more sustainable solid-electrolyte interphase and delivers a higher ionic conductivity and Na+ ion diffusion coefficient than the commonly used ester-based electrolytes. Therefore, an excellent electrochemical performance is demonstrated with a long cycle life (∼196 mA h/g and 90% capacity retention after 2000 cycles at 1 A/g), a super rate capability (∼51% capacity retention at 10 A/g) at a mass loading of 1.5 mg/cm2, and a high initial Coulombic efficiency of 85.9%. More importantly, a high reversible areal capacity of 4.3 mA h/cm2 can be achieved at an ultrahigh mass loading of 17 mg/cm2, superior to all reported HC anodes. Our findings not only shed light on the design of high-performance battery systems but also promise a commercial transformation from the lab test to mass production of NIBs.

Residential Demand Forecasting With Solar-Battery Systems: A Survey-Less Approach

Due to the push to reduce greenhouse gas emissions in the residential sector, new precincts are likely to include a higher uptake of solar and battery systems. One fundamental tool required to assess the impact and cost of solar and battery systems in residential precincts is a reliable model that can simulate electricity demand for individual homes. That model should capture the time-series complexity and the unique demographic composition of a precinct. In response, this research contributes to state-of-the-art demand forecasting by presenting a time-series, survey-less, demographically focused model formulation. The model achieves the survey-less feature by substituting household surveys for geodemographic profiling data, avoiding comprehensive surveying used in other research. This increases the usability for developers and network operators. The research applies the adaptive boost regression tree algorithm as an alternative to traditional methods, such as feed forward neural network (FFANN). The results investigate three case study precincts and show that this algorithm improves over an FFANN in aspects such as peak event estimation and daily variability, achieving an R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> value of 0.86. Finally, the research implements an MILP battery model and demonstrates the demand model is robust to provide real value battery system design, cost, and impact estimations.

Mechanisms for the evolution of cell variations within a LiNixCoyMnzO2/graphite lithium-ion battery pack caused by temperature non-uniformity

Cell variations always undermine the efficiency of energy utilization of battery pack. How does the temperature non-uniformity affect the status of cell variations remains unclear. This paper investigates the underlying mechanisms of the status change of cell variations caused by temperature non-uniformity in a battery pack. First, the status of cell variations has been defined using a graphical model, in which each cell has a coordinate of (capacity, electric quantity). Second, the status transformation caused by temperature non-uniformity has been clarified. Dynamics that describes the thermal-electrochemical effect on the movement of the coordinate for individual cells are firstly established by transformation functions. The movement of the cell locations in the graphical model can vividly interpret the evolution of cell variations caused by temperature non-uniformity with the help of the built transformation functions. Modelling analysis points out that 5 °C increase in the maximum temperature difference among the battery pack can lead to 1.5%–2% capacity loss of the battery pack, therefore the capacity loss caused by cell variations due to temperature non-uniformity should be considered in battery system design. The methodology can be further used to analyze the status change of cell variations in a battery pack caused by all kinds of temperature non-uniformities, benefiting the design of battery management system with high efficiency of energy utilization.

Multiphysics Simulation for the Design and Optimization of High-performance Battery Systems

Multiphysics Simulation for the Design and Optimization of High-performance Battery Systems

Impact of pore size, interconnections, and dynamic conductivity on the electrochemistry of vanadium pentoxide in well defined porous structures.

Considering the tortuous, random porous nanostructures existing in many battery electrodes, it is essential to understand electronic and ionic behaviors in such a confined nanoscale porous geometry in which electron and ion transports can change dynamically. Here, we have carefully designed three dimensional (3D) interconnected porous electrode structures and performed experiments to probe how the ion and electron transport is impacted within these controlled geometries. By using anodized aluminum oxide as a template, we were able to fabricate both 1D array electrodes and 3D electrodes with varying numbers of interconnections, utilizing vanadium oxide (V2O5) as the active material. We demonstrate that the inherent properties of the electrode material in combination with the structural properties of the electrodes can both positively and negatively impact electrochemical characteristics. Most notably, electrodes with seven interconnecting layers in their structure had 19.7% less capacity at 25C than electrodes with zero interconnecting layers, demonstrating the negative effect of interconnections combined with poor electronic conductivity of V2O5 upon lithiation beyond one Li insertion. These results indicate that a careful consideration of the material and structural properties is needed for the design of high performance battery systems.

Lithium-Ion Battery Storage for the Grid—A Review of Stationary Battery Storage System Design Tailored for Applications in Modern Power Grids

Battery energy storage systems have gained increasing interest for serving grid support in various application tasks. In particular, systems based on lithium-ion batteries have evolved rapidly with a wide range of cell technologies and system architectures available on the market. On the application side, different tasks for storage deployment demand distinct properties of the storage system. This review aims to serve as a guideline for best choice of battery technology, system design and operation for lithium-ion based storage systems to match a specific system application. Starting with an overview to lithium-ion battery technologies and their characteristics with respect to performance and aging, the storage system design is analyzed in detail based on an evaluation of real-world projects. Typical storage system applications are grouped and classified with respect to the challenges posed to the battery system. Publicly available modeling tools for technical and economic analysis are presented. A brief analysis of optimization approaches aims to point out challenges and potential solution techniques for system sizing, positioning and dispatch operation. For all areas reviewed herein, expected improvements and possible future developments are highlighted. In order to extract the full potential of stationary battery storage systems and to enable increased profitability of systems, future research should aim to a holistic system level approach combining not only performance tuning on a battery cell level and careful analysis of the application requirements, but also consider a proper selection of storage sub-components as well as an optimized system operation strategy.

A Project-Based Cooperative Approach to Teaching Sustainable Energy Systems

Engineering education is undergoing a restructuring driven by the needs of an increasingly multidisciplinary engineering profession. At the same time, power systems are transitioning toward future smart grids that will require power engineers with skills outside of the core power engineering domain. Since including new topics in the existing curriculum while maintaining the existing requirements is difficult, this paper proposes a project-based cooperative learning approach to promote soft skills in an engineering course. This paper then shows how to construct a realistic open-ended multidisciplinary problem whose solution requires a wide range of skills, which is not a trivial task. The design and technoeconomic viability assessment of a small-scale photovoltaic battery system is used as a case study. The effectiveness of the approach and students’ satisfaction were assessed over two years. Survey results after the first year revealed that the students did not feel sufficiently prepared for multidisciplinary work. After appropriate adjustments in the second year, the survey results improved noticeably. Statistical analysis reveals that the project teaches skills that are complementary to the core domain skills, which confirms the validity of the approach.

Hybrid Vehicle Battery Pack Useful Life Simulation

A systematic approach has been used to develop a computational model of a traction battery system, including series and/or parallel cell design configuration in the pack, cell energy/power performance, thermal and electrical controls, and interfaces to the vehicle and external environment. The model is capable of estimating the battery performance and predicting the battery life under a variety of use cases in different environmental and application conditions. Simulation results are verified with variety of laboratory and vehicle test data. The accuracy of the model predicted battery life performances is further validated with real field application vehicle data. The availability of this battery model enables rapid optimization of battery pack size, electrical and thermal controls design to maximize battery usage and/or minimize battery cooling needs while still meeting the battery’s life targets, and allow the majority of the life cycle analyses to be conducted before battery packs and vehicles are actually assembled.

Hybrid Vehicle Battery Pack Useful Life Simulation

This paper describes the development of a computational model of a traction battery system for hybrid vehicle application. The battery model simulates the electrical and thermal performance of the entire battery system, including series and/or parallel cell design configuration in the pack, cell energy/power performance, thermal and electrical controls, and interfaces to the vehicle and external environment. The battery model is capable of estimating the battery performance and predicting the battery life under a variety of use cases in different environmental conditions. The model enables rapid optimization of battery pack size, electrical and thermal controls design to maximize battery usage and/or minimize battery cooling needs while still meeting the battery’s life targets. A systematic approach has been developed in which this vehicle-level information is quantified and ranked to be able to identify and simulate the battery usage for varieties of customer. Simulation results are verified with variety of laboratory and vehicle test data. The availability of this battery pack model enables minimizing of costly and time-consuming pack-level performance and life testing, allowing the majority of the life cycle analyses to be conducted before battery packs and vehicles are actually assembled. The model aims to ensure that when the battery pack model is utilized for life simulations, compliance with the battery pack warranty and fuel economy targets, as well as other vehicle standards, may be quickly and reliably assessed. The accuracy of the model predicted battery life performances is further validated with real field application vehicle data from customer return pack.

State-of-Charge and Deformation-Rate Dependent Mechanical Behavior of Electrochemical Cells

The state-of-charge and deformation-rate dependent mechanical behavior of cylindrical lithium-ion battery cells was investigated. The research revealed that both state of charge and deformation rates affected the stiffness of the battery cells. Battery mechanical failure load was only weakly dependent on the state of charge. For the deformation-rate dependency on the mechanical integrity of battery cells, the battery mechanical failure load was either decreased significantly at high state of charge or decreased slightly at low state of charge as deformation rate increased. For the correlation between mechanical integrity and electrical failure, the displacement at the battery mechanical failure load coincided with a voltage drop. However, at high state of charge, premature and incomplete voltage drops were observed before the definite final voltage drop. No such premature voltage drop was observed in low state-of-charge specimens. The results of this research may be used as a reference for the design of impact and damage tolerant electric vehicle battery systems.

Optimal capacity design of battery and hydrogen system for the DC grid with photovoltaic power generation based on the rapid estimation of grid dependency

This paper presents a fast and novel method to determine the optimal capacity of a battery and a hydrogen system for a grid-connected photovoltaic (PV) system based on the required grid dependency (GD) and the minimum Levelized Cost of Energy (LCE). The GD is calculated from the weather data at 9 locations throughout Japan during 25years considering different sizing of PV, battery, and hydrogen system. Based on the results, the relationship between the GD and the capacities of the devices and the weather parameter is established. The results show that the GD depends on the annual total solar insolation and the devices’ capacities as well. The empirical GD formula is then examined at a different location in Japan. The proposed GD calculation agrees well with the GD obtained from the real 25 – year weather data and shows great advantages over the conventional method in the simplicity and calculation time. In addition, the optimal capacity of the system can be obtained directly from the GD formula and the objective function of the LCE.

Efficient and Extensible Quasi-Explicit Modular Nonlinear Multiscale Battery Model: GH-MSMD

Complex physics and long computation time hinder the adoption of computer aided engineering models in the design of large-format battery cells and systems. A modular, efficient battery simulation model—the multiscale multidomain (MSMD) model—was previously introduced to aid the scale-up of Li-ion material & electrode designs to complete cell and pack designs, capturing electrochemical interplay with 3-D electronic current pathways and thermal response. This paper enhances the computational efficiency of the MSMD model using a separation of time-scales principle to decompose model field variables. The decomposition provides a quasi-explicit linkage between the multiple length-scale domains and thus reduces time-consuming nested iteration when solving model equations across multiple domains. In addition to particle-, electrode- and cell-length scales treated in the previous work, the present formulation extends to bus bar- and multi-cell module-length scales. Example simulations are provided for several variants of GH electrode-domain models.

Protective Oxide Coating for Ionic Conductive Solid Electrolyte Interphase.

To employ Li-based batteries to their full potential in a wide range of energy-storage applications, their capacity and performance stability must be improved. Si is a viable anode material for Li-based batteries in electric vehicles due to its high theoretical capacity and good economic feasibility. However, it suffers from physical and chemical degradation, leading to unstable electrochemical performance and preventing its incorporation in new Li-based battery systems. Herein, we applied a poly(vinyl alcohol)-PO4 protective coating for Si-graphite anodes and confirmed an improvement in the electrochemical performance. The experimental results revealed that the polymer acts as a binder to alleviate the pulverization of the electrode. Furthermore, the oxide coating reduces the loss of Li2O, which has high ionic conductivity, during operation, resulting in the formation of a stable solid electrolyte interphase. Our findings suggest that a stable and ion-conducting anode/interphase can be developed by applying an oxide and polymer coating in combined approach. Therefore, this study is expected to provide a basis for the further development and design of high-performance Li-based battery systems.

Path Dependence in Lithium-Ion Batteries Degradation - a Comparison of Cycle and Calendar Aging

The Hawai‘i Natural Energy Institute (HNEI) is leading research efforts to understand the degradation of lithium-ion batteries under two distinct projects. The first research project is focused on grid-scale battery energy storage systems (BESS) while the second project is targeting electric vehicles (EVs) and their synergy with the grid. Both applications require a combination of long cycle-life (1000 cycles or more) and long shelf-life (10 to 20 years in operation) to meet the expectations of the customers. To determine whether these durability goals are realistic or not, we performed accelerated testing of different lithium-ion battery technologies in the laboratory. For each technology, we conducted a series of cycle and calendar aging experiments. The results of these studies will be used to develop predictive performance models. The concept of accelerated aging is only valid if the degradation the cell underwent is the same than of the one it experienced in real life. In this presentation, we want to share our preliminary observations regarding the differences between cycle aging and calendar aging across the different chemistries and across the industries (EVs, BESS). Our primary objective is to showcase the different degradation pathways, whether calendar-driven or cycle-driven, which can lead to identical capacity losses. This concept is better known as path dependence and this talk will highlight its implications for the design of long-life battery systems, the laboratory testing it requires and the validity of accelerated testing strategies. [1] M. Dubarry, N. Vuillaume and B. Y. Liaw, J. Power Sources 186(2), (2009) 500-507. [2] M. Dubarry, C. Truchot and B.Y. Liaw, J. Power Sources 219 (2012) 204-216. [3] https://www.soest.hawaii.edu/HNEI/alawa/[4] M. Dubarry, C. Truchot, A. Devie and B. Y. Liaw, J. Electrochem. Soc 162(6), (2015) A877-A884.

Two-Dimensional Thermal Modeling of Lithium-Ion Battery Cell Based on Electrothermal Impedance Spectroscopy

Thermal modeling of lithium-ion batteries is gaining its importance together with increasing power density and compact design of the modern battery systems in order to assure battery safety and long lifetime. Thermal models of lithium-ion batteries are usually either expensive to develop and accurate or equivalent thermal circuit based with moderate accuracy and without spatial temperature distribution. This work presents initial results that can be used as a fundament for the cost-efficient development of the two-dimensional thermal model of lithium-ion battery based on multipoint electrothermal impedance spectroscopy.

Bi-objective optimal design of a damage-tolerant multifunctional battery system

In current electric vehicles (EVs), battery systems only serve the role of electrical energy storage. Heavy protecting structures surround the batteries. To enhance the overall performance of EVs one desires multifunctional battery systems with structural and energy storage functionalities. Our research centers on the design methodology to enable such multifunctional material systems. An architectured multifunctional battery-structure material system, namely the Cellular Battery Assembly (CBA), is introduced. The CBA is composed of cylindrical battery cells surrounded by hollow tubes. The CBA inherits features of the energy absorbing characteristics of periodic cellular materials while maintaining an electrical energy storage. The energy absorbing mechanism is activated when intentional collapse of hollow tubes dissipates energy and protects battery units from high compressive stress. Depending on loading conditions to be applied, the multi-functionalities of CBA can be optimized by morphological or dimensional control of the building blocks through a multi-objective optimization process. The present study focuses on a multi-objective optimization design process to achieve optimal configurations in specific applications where energy storage and energy absorption are objective functions to be maximized simultaneously. Results show that CBA can possess energy absorption performance that compares well to other energy absorbing materials while a desirable energy storage capability is maintained.

Mission Profile-Oriented Design of Battery Systems for Electric Vehicles in MATLAB/Simulink

Mission Profile-Oriented Design of Battery Systems for Electric Vehicles in MATLAB/Simulink

An online method for lithium-ion battery remaining useful life estimation using importance sampling and neural networks

An accurate battery remaining useful life (RUL) estimation can facilitate the design of a reliable battery system as well as the safety and reliability of actual operation. A reasonable definition and an effective prediction algorithm are indispensable for the achievement of an accurate RUL estimation result. In this paper, the analysis of battery terminal voltage curves under different cycle numbers during charge process is utilized for RUL definition. Moreover, the relationship between RUL and charge curve is simulated by feed forward neural network (FFNN) for its simplicity and effectiveness. Considering the nonlinearity of lithium-ion charge curve, importance sampling (IS) is employed for FFNN input selection. Based on these results, an online approach using FFNN and IS is presented to estimate lithium-ion battery RUL in this paper. Experiments and numerical comparisons are conducted to validate the proposed method. The results show that the FFNN with IS is an accurate estimation method for actual operation.

Capacity Degradation Mechanisms in Nickel/Metal Hydride Batteries

The consistency in capacity degradation in a multi-cell pack (&gt;100 cells) is critical for ensuring long service life for propulsion applications. As the first step of optimizing a battery system design, academic publications regarding the capacity degradation mechanisms and possible solutions for cycled nickel/metal hydride (Ni/MH) rechargeable batteries under various usage conditions are reviewed. The commonly used analytic methods for determining the failure mode are also presented here. The most common failure mode of a Ni/MH battery is an increase in the cell impedance due to electrolyte dry-out that occurs from venting and active electrode material degradation/disintegration. This work provides a summary of effective methods to extend Ni/MH cell cycle life through negative electrode formula optimizations and binder selection, positive electrode additives and coatings, electrolyte optimization, cell design, and others. Methods of reviving and recycling used/spent batteries are also reviewed.