Battery Testing in Thermal Analysis
Battery testing involves testing the performance, capacity, and durability of batteries to ensure that they can meet the needs of their intended applications. Tests such as charge and discharge testing, cycle life testing, and temperature testing are all important for evaluating the performance of batteries.
Battery testing is also necessary to ensure that batteries are performing as expected and for safety considerations.
A battery calorimeter is a device used to measure the heat generated by a battery during charging and discharging. This measurement is known as the “heat of reaction” and is an important indicator of the efficiency of a battery. The heat of reaction is the difference in the enthalpy (heat content) of the reactants and products in a chemical reaction.
Battery calorimeters are used in research and development to evaluate new battery chemistries and to optimize the design of existing batteries. They are also used in the manufacturing process to ensure that batteries meet performance and safety standards.
For the thermal monitoring of batteries, Linseis offers a modular calorimeter. It consists of a variable number of practically identical components and allows the most diverse battery cell sizes to be examined (Fig. 1). The modules are easily scalable with regard to their geometry. Different types of sizes are covered without having to buy a new device. The battery calorimeter can be integrated into existing systems at low cost. Practically all sizes of batteries can be tested.
A typical heat flow pattern of a lithium rechargeable battery (C//LiCoO2 pouch cell) during discharge and charge is shown in the next figure.
These information can be used to design and optimize the thermal management system.
Heat flow due to Joule heating and heat flow caused by heat of a reaction have a different sign during charge and discharge (negative and positive signs). The pattern of the heat flow as a function of the charge of the cell correlates well with phase transitions within the carbon anode and the LiCoO2 cathode (see Fig. 3).
Effects due to temperature, charge and discharge current, electrode and electrolyte composition, age etc. can easily be seen in the heat flow curves and used to improve the performance of the cell. Fig. 4 shows a measurement example of a poor, low-cost Li-ion battery.
Differential Scanning Calorimeters (DSC)
DSC measurements are mainly used in the research and development of battery chemistries.
Each battery chemistry has its own specific characteristics and properties and are designed to be used in different applications. The choice of a battery chemistry depends on the specific requirements of the application, such as energy density, power density, safety, and cost.
Fig 5 shows a DSC measurements curve of a solid ceramic electrolyte used in solid-state batteries enabling safer high-energy batteries. High temperature heat treatment is necessary to interconnect electrolyte, electrodes and other components like current collectors.
Thermogravimetric Analyzer (TGA)
Thermogravimetric Analysis (TGA) is a technique which measures the weight changes of a material as a function of temperature and time. TGA is a valuable tool in battery testing and can be used to determine thermal stability and other properties of the battery material.
As an example, Fig. 6 illustrates a TGA- measurement on different lithium-ion battery cathode materials.
The electrode should be stable up to high temperatures. The solid measurement curve shows a good electrode material which shows no weight change up to around 800°C. At higher temperatures the material decomposes.
The upper dotted curve shows an increase in mass caused by oxidation. Corroded electrodes quickly lose their performance.
The third electrode material loses mass even at low temperatures. This material is therefore not suitable for high-performance batteries that are subject to high temperature fluctuations during charging and discharging.
In addition to these thermal stability tests, results obtained from TGA can help to identify the composition of the battery materials.
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.
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 microscopy can be used for battery testing, as it allows researchers to observe the reactions that are responsible for the battery’s performance. By subjecting a specimen to a thermal treatment reproducing the battery’s operation, it is possible to monitor the reactions and performance of the battery in real time.
In Fig. 8 the decomposition of a cathode material used in a Li-ion battery is visible. The material was heated up in a Linseis heating microscope. Individual images or videos can be recorded during the measurements.
Thermal properties for batteries
The thermal properties of batteries affect its performance and safety. Linseis offers a broad range of instruments to measure the thermal conductivity, thermal diffusivity and thermal resistances on bulk and thin film materials.
Laser Flash (LFA)
With Linseis Laser Flash Instruments (LFA) the thermal diffusivity and thermal conductivity can be measured inn a broad temperature range (-180 to 2800 °C). It can be applied on all materials and with the Periodic Laser Heating extension (PLH) also to thin films in the low micrometer range.
As an example, for battery testing with the LFA, the measurement in Fig. 9 was performed on a Na-ion cathode material. The thermal diffusivity and thermal conductivity reach a maximum at around 90°C and then decrease quite strongly.
Dilatometry and Thermomechanical Analysis (TMA)
To test the mechanical properties of battery materials, the Linseis Dilatometers or Thermomechanical Analyzers (TMA) are very suitable.
The push rod dilatometer on a Na-ion cathode material in Fig. 10 shows the length change from which also the density change with the temperature can be calculated. The density increases until 150° due to water evaporation. After the water evaporation the density is more or less constant. However above 300°C the sample expands referring for a decreasing density.
The measured densities can be used for Laser Flash measurements to calculate the thermal conductivities together with the measured thermal diffusivity. The specific heat capacity which is also necessary can be measured with a DSC.
The TMA is in fact an extension of the Dilatometers. As an add-on it can measure the elastic modulus of the sample in both compression and tension direction, dynamically and statically.
Thin Film Analytics
Linseis offers instruments to measure thin films in the range of a few nanometers to the micrometer range. Thin Film Batteries consist of solid electrodes and a solid electrolyte, both with thicknesses in the range of a few hundred nanometers.
Thin Film Batteries are much smaller in size compared to bulk solid-state batteries. They can be used to create smaller electronic devices. They often possess a higher energy density and longer life cycles.