Battery systems
Lectures
Investigating the thermal runaway and propagation behaviour of commercial lithium ion batteries: Influence of initiation mode and state of charge
Lithium ion batteries (LIBs) are omnipresent in our daily lives. LIBs power our laptops and mobile phones, are the energy storage of choice for the electrification of vehicles, and play a vital role in the layout of the storage devices needed for the balancing of the grid. Research groups all
How temperature inhomogeneities affect the cycle life of Li-ion batteries
Looking at the ageing behaviour of Li-ion batteries, the internal cell temperature is one main influencing factor. The quantification of its influence is one of the key aspects to improve cycle life and is increasingly addressed in literature. In general, an optimum temperature of about 25 °C is given with
Flexible, fast and transparent approaches to battery capacity forecasting
Battery degradation is a complex phenomenon, leading many to use data-driven techniques to predict future battery health [1]. Linear models are transparent, easy to implement and not computationally demanding. However, simple linear models are often combined with Kalman filters and particle filters when modelling battery degradation [1]. The need for
Experimental investigation of the aging invariance of electrode open circuit voltage curves
Exact knowledge of the relationship between open circuit voltage (OCV) and state of charge (SOC), often referred to as OCV curve, is crucial for most algorithms for the estimation of both the SOC and the state of health (SOH) of lithium-ion batteries. Many researchers showed that the form of the
Deep learning-based state-of-health estimation with battery charging data
The scope of this work is the development of a data-driven capacity estimation model for cells under real-world working conditions with recurrent neural networks having long short-term memory capability. Voltage-time sensor data from the constant current phase charging curve is used as input, reflecting input availability in the real world.
Controlling module pressure evolution over lifetime with buffer layers: Design guidelines, prediction and validation for automotive systems
The development of cheap, energy dense lithium-ion battery systems for electric vehicles is pushed with enormous effort. Stacking pouch-type cells in modules achieves the highest energy densities. As a consequence, however, such modules require an outer bracing to provide a medium pressure environment for optimal cell operation in terms of
Posters
Verification and Validation of Thermal Models for Li-ion Pouch Cells
Temperature has significant impact on the dynamic performance, operating limits as well as aging phenomena of Li-ion battery cells. Due to the complex and often limiting heat transport paths and the uneven heat release within the cell core, the inner temperature distribution can be highly inhomogeneous. At the same time,
Thermal runaway initialization temperature of fresh and aged large prismatic lithium-ion cells
Driven by the field of electric vehicles, the energy density of lithium-ion cells is rapidly increasing. Therefore, safety aspects in lithium-ion battery design become even more important. In case of a single cell failure, a thermal runaway (TR) might be triggered which results in an uncontrolled heat release within the
Thermal conductivity characterization considering dependencies on battery states with implication for thermal modeling and management
Extreme fast charging lithium-ion batteries require aggressive thermal management. High heat generation has to be compensated with active cooling to keep the cell temperature below hazardous thresholds. The importance of thermal management is further increased for many new cell designs. Improvements in energy density often bring along weaker thermal performance.
Temperature impact on the current distribution in Li-ion cells
The behaviour of lithium-ion cells strongly depends on their internal temperature. Thereby, a higher temperature enhances the transport processes. An inhomogeneous temperature distri¬bution within the cell thus leads to an inhomogeneous current distribution with higher current densities in the warmer regions of the cell due to the lower resistances. As
State estimation for fast charging applications of lithium-ion batteries
The use of reduced-order electrochemical models creates opportunities for battery management systems to control the battery behavior by monitoring the internal states in electrochemical processes, which are critical for safety enhancement and degradation mitigation. This poster explores a state observer for lithium-ion batteries based on an extended single-particle model, which
Replication of the thermal behaviour of lithium-ion cells with substitute cells
The performance as well as the lifetime of lithium-ion battery cells are strongly temperature-dependent. To achieve optimal results in both aspects, efficient thermal management systems are needed in the automotive application. Along the development process of these systems, manufacturers face certain obstacles considering the validation of battery systems. An extensive
Optimal power split for heterogeneous storage systems – A comparative study of model predictive control and dynamic programming
Li-ion batteries are commonly used in stationary and mobile energy systems, and its markets are growing rapidly. Due to the high impact of energy costs on the economics and life cycle assessment, the efficiency of storing electrical energy becomes one of the main points of interest. This can be reached
Modeling the dimension changes under external pressure of unit cell with a system level approach
Dimensional changes in the electrodes can affect the electrochemical response of the battery and generates stresses which leads to its premature failure. Thus, understanding the volume expansion of Lithium-ion cell during cycling under external pressure is essential to improve cell design and predict aging phenomena. In this work, the volume
Model-based characterization for silicon-carbon blended electrodes
In recent research for the design of better performing lithium-ion batteries, blended electrodes have started gaining relevance, combining beneficial characteristics of different materials. As an example, silicon graphite anodes are good candidates to increase the energy density of lithium-ion batteries. The complexity of transport phenomena increases in blended electrodes and
Li-ion batteries studied with Scanning Electron Microscopy and combined analytical methods
The complex interaction in batteries is most clearly visible at the interfaces between anode, cathode, separator and electrolyte. A post-mortem microstructural examination of changes on the surfaces of the anode, cathode and separator offers great potential on the way to understand the complex interaction in batteries during ageing. The combination
Influence of compression on the accelerated aging of lithium ion battery cells
In this contribution, the influence of external compression on lithium-ion cells with respect to cyclic aging is demonstrated. Currently, cells for EV applications are manufactured in three different designs: pouch bag, cylindrical and prismatic housings. During charge and discharge especially the anode but as well the cathode expands and contracts.
Influence of (meta-)parameters on the behavior of state of charge estimation using an extended Kalman Filter
State estimation is a core function of any battery management system (BMS) in order to ensure safe operating conditions and to prolong the lifetime of the energy storage system. In this context the state of charge (SOC) is an important indicator for the remaining useable battery capacity. This variable is
Impact of Level of Homogenization in 3D Thermal Simulation of Li-ion battery cells [1]
Temperature has a large impact on the performance and aging behavior of Li-ion batteries. Therefore, the temperature range for optimal performance and minimum aging of Li-ion batteries should be ensured during operation. The knowledge of the internal temperature field in Li-ion batteries is essential in this respect. Since in-situ measurements
Identification of Degradation Mechanisms for Lithium Titanate Oxide based Cells
The cyclic and calendar aging of in total 43 same-typed prismatic LTO cells are investigated. Therefore, measurements over a period of more than 600 days were carried out. Regarding the calendar aging, 19 cells were stored at 8 different operating conditions, under variation of state of charge and temperature. Considering
High-Voltage-Safe Digital Temperature Measuring System for the Verification and Characterization of HV Batteries
Batteries are of central importance to electric vehicles. Their temperature behavior has to be investigated precisely and temperature models have to be verified. For the development of suitable temperature management systems, the thermal behavior of all components within the battery housing must be known. The thermal characterization of high-voltage batteries
High duty use and fast charging of power tool battery packs: A simulation based study to improve cooling strategies
In the fast growing, but also highly competitive market of battery-powered power tools short charging times are essential to achieve a high customer acceptance. To prevent loss of performance and rapid charging capability due to cell aging the knowledge of proper use conditions in everyday practice is important. In this
Float Current Analysis for fast calendar aging detection investigating 18650 NCA/ Graphite varying temperature and voltage
Converting our electricity and transportation strategy into a sustainable system, we need high-quality battery electric storage. The most popular candidate up to now is the lithium-ion bat-tery family as it provides high energy density combined with long cycle life at low costs. The lifetime is targeted e.g. for e-mobility to
Experimental validation of Parallel-Connected Lithium-Ion Cells with Controllable Interconnection Resistance
Due to the broad use of parallel-connected cells across multiple applications, it is essential to understand the current distribution between them. Variations in resistance, temperature and capacity can lead to an inhomogeneous current distribution and have a deleterious influence on ageing and safety. It is therefore crucial to investigate the
Evolution of Mobility
As electric mobility is increasingly shaping our daily mobility, it is also starting to conquer special vehicle applications. Although technology, design and manufacturing of battery systems are despite the system complexity well understood, it remains a challenge to have fitting solutions for this wide range of applications. Especially while the
Equivalent circuit model of a 180 Ah LFP/graphite home storage cell for model-based state diagnostics
State of Charge (SOC) and State of Health (SOH) are important parameters for the users and manufacturers of home storage systems. The state diagnostics of LFP/graphite cells is challenging due to the inherent thermodynamic hysteresis and the flat, but unsymmetrical discharge/charge characteristics. Battery models allow a knowledge-based and therefore more
Electrical and structural characterization of large-format lithium iron phosphate cells used in home-storage systems
Installed energy capacity of home storage systems, which is used to store excess energy produced by renewable sources, mainly photovoltaic (PV), has expanded rapidly in Germany in last years. Lithium ion batteries make up for more than 95 % of the new installations [1]. Home storage systems are typically constructed
Effects of High Acceleration Mechanical Shocks on 94 Ah Large Format Lithium-Ion Battery Cells
In regular operation and especially in the case of crashes, lithium-ion batteries have to withstand severe mechanical shock loads. To ensure their safety, they are tested according to various norms and regulations with procedures depending on the country of usage, the field of the application and the mass of the
Diagnosis of Battery Condition Using Ultrasonic Measurements
In lithium-ion batteries (LIBs), mechanical alteration of the composites can cause a safety-critical state during battery operation. These alterations can be caused by deformation, inhomogeneous straining, or lithium plating just to name a few. Besides a safety risk, such alterations can lead to a massive loss of capacity, accelerate the
Decay of Open Circuit Voltage during Storage of Lithium Ion Batteries
Calendaric ageing of lithium-ion battery (LIB) is relevant to most applications of LIB. Classical testing methods, which involve long-term storage with regular check-up (CU) are slow and cost intensive. New methods have been presented in the past, such as float current measurement [1] or the high precision coulometry (HPC) [2].
Data Driven Approach for Sensorless Temperature Estimation for Lithium-Ion Cells based on Pulse Resistance Measurements
Knowing the temperature distribution within a battery pack is crucial, because of the impact of temperature on capacity loss, power degradation and safety issues. Temperature measurements are usually realized with external temperature sensors attached to a few crucial cells throughout the battery pack, leaving the majority of cells in bigger
Data compression techniques applied to long-term recordings of battery data from electric vehicles
Data compression offers the possibility to decrease the amount of storage or the bandwidth of a communication channel required to save or transmit collected data. In battery packs of electric vehicles (EV), the data over time contains values of voltage, current, temperature, state of charge and others depending on the
Challenges and solutions in battery system prototyping
Within the framework of the research project „Lebenszykluskostenreduktion im elektrischen Verteilerverkehr durch individuell adaptierbaren Antriebsstrang“ (LiVe), modular battery systems for commercial vehicles are being developed at the PEM of the RWTH Aachen University. Based on the proclaimed project objective of optimizing life cycle costs, different core requirements for battery system
Anode-Controlled Fast Charging Optimization of Lithium Ion Batteries
Electric vehicles are an important element for a sustainable environmentally and climate-friendly mobility. But charging of these takes considerably more time than refueling of a conventional one. This can be an obstacle for many consumers. For an increased acceptance of electric vehicles, the general objective is to charge the battery
Analysis of isotope labeled lithium-ion battery electrolytes – tracing solvent molecule decomposition during first cycles
The instability of state-of-the-art lithium-ion battery (LIB) electrolytes against applied electrode potentials results in redox reactions at the electrode/electrolyte interfaces. Especially during the first charge and discharge cycles, the solid electrolyte interphase (SEI) is formed on the negative electrode caused by solvent molecule and conducting salt decomposition. A sufficient interphase
Analysis of Impedance Spectra of Aged Commercial LTO Cells
The impedance spectra of aged commercial LTO cells have been fitted with an equivalent circuit model. The model contains an inductive part, a constant phase element and resistance for the charge transfer process and a Warburg element and addition RC-element for the slower frequency tail. The serial resistance, charge transfer
A Comparison of Different Methods for Physically Motivated Parameterization of High Power Lithium-Ion Battery Cells
The development of lithium-ion batteries with high power density is currently being driven by their potential applications in mild hybrid vehicles. A 48 V electrical system in passenger cars can provide an efficiency advantage and reduce CO_2 emissions by about 10 % to 15 %. Pouch bag cells having a
A Comparison of Different Methods for Physically Motivated Parameterization of High Power Lithium-Ion Battery Cells
The development of lithium-ion batteries with high power density is currently being driven by their potential applications in mild hybrid vehicles. A 48 V electrical system in passenger cars can provide an efficiency advantage and reduce CO_2 emissions by about 10 % to 15 %. Pouch bag cells having a
A comparative study of impedance based modelling of lithium-ion batteries on half and full cell level
The dynamic performance of lithium-ion cells is strongly dependent of the underlying loss processes such as contact resistances, charge transfer and ion diffusion. Electrochemical impedance spectroscopy (EIS) is a well-known characterisation method for quantifying the complex impedance of electrochemical systems such as lithium-ion cells. In combination with an equivalent circuit