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Enhancing Sodium-Ion Batteries Through Calorimetry and Safety Testing

In this article, Dr Carlos Ziebert, head of IAM-AWP’s Calorimeter Center at the Karlsruhe Institute of Technology (KIT), delves into the world of battery calorimetry and its role in the development of improved sodium-ion batteries. By providing thermal characterisation and safety testing, battery calorimeters play a crucial role in advancing the performance and safety of post-lithium battery technologies.

Introduction: Sodium-ion batteries as a viable alternative

The POLiS (Post Lithium Storage) Cluster of Excellence, jointly acquired by KIT and Ulm University, aims to revolutionize energy storage through the development of post-lithium battery technologies. One promising option is the sodium-ion battery (SIB), which offers several advantages over traditional lithium-ion batteries. These include the use of more abundant and environmentally friendly materials such as sodium, magnesium, or calcium. Driven by the need for sustainable and scalable energy storage solutions, the research focus of the cluster is on advancing the SIB technology.

Understanding the working principle of a sodium-ion battery

The working principle of a sodium-ion battery is similar to that of a lithium-ion battery, with the key difference being the transfer of sodium ions instead of lithium ions. In a SIB, sodium ions are transferred via an organic electrolyte through a separator between the two electrodes, where they are intercalated and deintercalated. The cathode, typically a transition metal oxide, provides defined diffusion paths for the sodium ions, enabling efficient charge and discharge cycles.

Optimizing cathode and anode materials

Researchers are exploring various cathode and anode materials to improve the performance of sodium-ion batteries. Layered cathode materials with P2-type and O3-type structures show promise due to their high specific capacity, wide working voltage range, and ease of synthesis. However, these materials often suffer from phase transformations that result in a reduction of reversible capacity. On the anode side, options include metal alloys, metal oxides, and carbonaceous materials.

The importance of thermal studies in battery development

In addition to electrochemical characterisation, understanding the thermal properties of battery materials is crucial for optimizing performance and safety. Calorimetry techniques, such as differential scanning calorimetry (DSC) and Tian-Calvet calorimeters, enable researchers to determine thermophysical parameters like heat capacity and thermal conductivity. These measurements provide insights into possible phase transformations and the thermal stability of materials, aiding in the development of safer and more efficient battery systems.

Characterising heat generation during cycling

Tian-Calvet calorimeters play a vital role in measuring the heat generation during charging and discharging cycles of sodium-ion batteries. By directly measuring heat flow, these calorimeters offer valuable information about the underlying electrochemical processes occurring at the electrodes. This data is crucial for predicting the state-of-health (SOH) and ageing of batteries, allowing for informed design improvements.

Ensuring safety through calorimetry and safety testing

Safety is a paramount concern in battery development, and battery calorimeters are instrumental in ensuring the safety of new battery systems. Small-scale cell-level studies using highly sensitive calorimeters provide insights into thermal behavior and potential hazards. As the technology progresses, larger-scale calorimeters known as Accelerating Rate Calorimeters (ARCs) allow for safety tests, including thermal runaway, overcharging, internal/external short circuits, and mechanical impact.

Thermal abuse testing and its implications

One example of safety testing is the Heat-Wait-Seek (HWS) test, which involves heating the battery cells in controlled increments and monitoring their response. The test detects whether the cell generates excessive heat that could lead to a thermal runaway. The temperature curves and pressure measurements obtained from these tests help identify critical stages and potential failure mechanisms, contributing to the design of safer battery systems.

Unlocking the potential of sodium-ion and post-lithium batteries

Battery calorimetry, coupled with safety testing, provides quantitative thermal and thermodynamic data essential for the development of sodium-ion and other post-lithium batteries. By understanding the temperature, heat, and pressure characteristics of battery materials and cells, researchers can optimize their performance and safety profiles. This knowledge is crucial in creating advanced energy storage systems that meet the growing demands for sustainable and reliable energy solutions.

Conclusion

Battery calorimetry plays a crucial role in the development of improved sodium-ion batteries. By providing insights into thermal behavior, characterizing heat generation, and ensuring safety through testing, calorimeters enable researchers to optimize battery performance and safety. This, in turn, paves the way for the widespread adoption of sodium-ion and other post-lithium battery technologies in our quest for a sustainable energy future.