Battery Testing in Thermal Analysis
Battery testing encompasses a series of evaluations conducted to ascertain the performance, capacity, and endurance of batteries, ensuring they align with the requirements of their designated applications. This includes critical assessments like charge and discharge testing, cycle life testing, and temperature testing, all of which are instrumental in gauging battery performance.
Moreover, battery testing serves a dual purpose. It not only verifies that batteries operate in accordance with specified parameters but also plays a vital role in ensuring safety and reliability in various applications.
Battery Calorimeter
A battery calorimeter is a specialized device employed to measure the heat generated by a battery throughout its charging and discharging processes. This measurement is referred to as the “heat of reaction” and plays a pivotal role in assessing a battery’s efficiency. The heat of reaction corresponds to the difference in enthalpy (heat content) between the reactants and products involved in a chemical reaction.
Battery calorimeters find extensive application in research and development to evaluate new battery chemistries and optimize the design of existing batteries. They are equally valuable in the manufacturing process, ensuring that batteries adhere to performance and safety standards.
For comprehensive thermal monitoring of batteries, Linseis offers a modular calorimeter. This system comprises a flexible array of practically identical components, allowing for the examination of various battery cell sizes (as illustrated in Fig. 1). These modules are highly scalable in terms of their geometry, effectively covering a range of sizes without necessitating the purchase of a new device. Notably, the battery calorimeter can be seamlessly integrated into existing systems at minimal cost, providing the versatility needed for testing batteries of various dimensions.
Scalable Battery Calorimeter:
The calorimetric water-cooled modules fully envelop the battery cell, ensuring excellent thermal contact and efficient heat transfer.
Scalable Battery Calorimeter – The calorimetric water-cooled modules fully enclose the battery cell and ensure good thermal contact
In the figure below, a typical heat flow pattern is presented, exemplifying the behavior of a lithium rechargeable battery (C//LiCoO2 pouch cell) during both discharge and charge processes.
These data are invaluable for the design and optimization of thermal management systems.
Heat flow stemming from Joule heating and heat flow induced by the heat of a reaction exhibit opposing signs during charge and discharge processes (negative and positive signs, respectively). The heat flow patterns, as they vary with cell charge, demonstrate a strong correlation with phase transitions occurring within the carbon anode and the LiCoO2 cathode (refer to Fig. 3).
Effects arising from factors such as temperature, charge and discharge currents, electrode and electrolyte compositions, battery age, and more are readily discernible in the heat flow curves. This information is instrumental in enhancing the cell’s performance. As an illustrative example, Fig. 4 presents a measurement from a subpar, low-cost Li-ion battery.
Differential Scanning Calorimeters (DSC)
Differential Scanning Calorimetry (DSC) measurements find extensive application in the research and development of various battery chemistries.
Each battery chemistry boasts its unique characteristics and properties, tailored for specific applications. The selection of a battery chemistry hinges on the precise requirements of the application, encompassing factors like energy density, power density, safety, and cost considerations.
As depicted in Fig. 5, the DSC measurement curve illustrates the thermal behavior of a solid ceramic electrolyte used in solid-state batteries, which enable the creation of safer, high-energy batteries. These materials often necessitate high-temperature heat treatment to establish the necessary interconnections between the electrolyte, electrodes, and other components, such as current collectors.
Differential Scanning Calorimetry (DSC) of a ceramic electrolyte used in solid-state batteries. The red line corresponds to the measurement from room temperature to 1200°C, the dotted line to the cooling curve.
Thermogravimetric Analyzer (TGA)
Thermogravimetric Analysis (TGA) is a technique that measures the changes in weight of a material in relation to temperature and time. TGA proves to be a valuable tool in battery testing, enabling the determination of thermal stability and various other material properties relevant to battery performance.
For instance, Fig. 6 provides an illustration of TGA measurements conducted on diverse lithium-ion battery cathode materials.
In battery applications, it is crucial for the electrode materials to exhibit stability at elevated temperatures. As shown in the solid measurement curve, an excellent electrode material displays no weight changes up to approximately 800°C. Beyond this point, the material begins to decompose.
The upper dashed curve highlights an increase in mass, indicating oxidation. Electrodes experiencing corrosion tend to rapidly lose their performance.
The third electrode material experiences a loss of mass even at lower temperatures, rendering it unsuitable for high-performance batteries subject to substantial temperature fluctuations during charging and discharging.
Moreover, beyond assessing thermal stability, TGA results serve the purpose of identifying the composition of battery materials, providing further insights into their characteristics.
Simultaneous TG-DSC/DTA (STA)
The DSC and TGA measurements described above can also be performed simultaneously with the Linseis STA instruments. Simultaneous TG-DSC allows to measure both, the weight changes and heat generated by a material as a function of temperature and time.
Combining TGA and DSC measurements can provide more information than either technique alone and give a deeper understanding of the thermal behavior of batteries.
Application:
The safety risk of different anode and cathode materials was evaluated by using a simultaneous TG-DSC system coupled with gas analysis in a temperature range from room temperature to 600°C (Fig. 7). The decomposition processes can be monitored and indicate how stable the materials are and how much energy can evolve during the thermal runaway.
Heating Microscope
Heating microscopy proves to be a valuable tool in battery testing, enabling researchers to observe the reactions that underlie a battery’s performance. Through subjecting a specimen to a controlled thermal treatment that mimics the battery’s operational conditions, it becomes possible to monitor the reactions and assess the battery’s performance in real-time.
As depicted in Fig. 8, the decomposition of a cathode material utilized in a Li-ion battery is clearly visible. This material was heated in a Linseis heating microscope, which allows for the capture of individual images or videos during the course of the measurements.
Thermal properties for batteries
The thermal characteristics of batteries play a critical role in determining their performance and safety. Linseis provides a comprehensive selection of instruments designed for the measurement of thermal conductivity, thermal diffusivity, and thermal resistances in both bulk and thin-film materials.
Laser Flash (LFA)
Linseis Laser Flash Instruments (LFA) enable the precise measurement of thermal diffusivity and thermal conductivity across a wide temperature range spanning from -180°C to 2800°C. This versatile tool can be applied to analyze the thermal properties of diverse materials and, with the addition of the Periodic Laser Heating extension (PLH), can also be used to study thin films with micrometer-scale thickness.
For instance, in a specific application involving battery testing, the data presented in Figure 9 illustrates the thermal behavior of a Na-ion cathode material. Notably, the thermal diffusivity and thermal conductivity exhibit a pronounced peak at approximately 90°C, followed by a significant decline in their values.
Dilatometry and Thermomechanical Analysis (TMA)
When assessing the mechanical properties of battery materials, Linseis Dilatometers and Thermomechanical Analyzers (TMA) prove to be highly suitable instruments. In particular, the push rod dilatometer applied to a Na-ion cathode material, as shown in Figure 10, records changes in length, from which temperature-induced variations in density can be derived. Notably, the density of the material experiences an initial increase up to 150°C, primarily due to water evaporation. Subsequently, after the water has evaporated, the density stabilizes. However, at temperatures exceeding 300°C, the sample undergoes expansion, indicating a decrease in density.
The measured densities obtained from these experiments are invaluable for Laser Flash measurements, facilitating the calculation of thermal conductivities when combined with the simultaneously measured thermal diffusivity. Additionally, the determination of specific heat capacity, a crucial parameter, can be accomplished using a Differential Scanning Calorimeter (DSC).
Moreover, the TMA serves as an extension of the Dilatometers, offering the capability to assess the elastic modulus of the sample in both compression and tension directions, dynamically and under static conditions.
Thin Film Analytics
Linseis provides specialized instrumentation for the precise characterization of thin films, ranging from a mere few nanometers to micrometer thickness. Thin Film Batteries are a prime example of applications within this scope, featuring solid electrodes and a solid electrolyte, typically with thicknesses in the range of several hundred nanometers.
These compact Thin Film Batteries offer distinct advantages over their bulk solid-state counterparts, as they enable the development of smaller electronic devices. Furthermore, they often exhibit enhanced energy density and extended operational lifecycles.
Within Linseis’ thin film analytics portfolio, you can find state-of-the-art tools such as Thin Film Laser Flash instruments for the comprehensive assessment of thermal properties. Additionally, the unique Thin Film Analyzer is designed to accurately measure the thermoelectric properties of thin films, offering valuable insights into their performance characteristics.