Insights from industry

Exploring Li-Ion Battery Testing Materials for Thermal Analysis

In this interview with Doctor Angela Hammer from METTLER TOLEDO, discover the thermal analysis techniques used to characterize materials for Li-ion batteries.insights from industryDoctor Angela HammerApplication SpecialistMETTLER TOLEDO

Which thermal analysis techniques used to characterize materials for lithium-ion batteries?

Global demand to reduce fossil resource use has surged in recent years, as this shift is widely seen as a promising solution to the climate crisis. Significant progress is underway in developing new materials for lithium-ion batteries, particularly for electric vehicle applications.

Thermal analysis techniques—including Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), Thermomechanical Analysis (TMA), and Dynamic Mechanical Analysis (DMA)—play a vital role in characterizing the materials and compounds used in lithium-ion batteries.

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What are the key materials used in lithium-ion batteries, and how have they evolved since the 1980s?

The demand for metal-ion accumulators continues to grow, with lithium-ion batteries widely used in consumer electronics, household appliances, and electric vehicles.

The first commercially available lithium-ion battery was developed in the 1980s. In the early 1990s, lithium cobalt dioxide was introduced as a cathode material, valued for its high energy density, long service life, stable discharge properties, and broad operating temperature range.                                                                                                                       

In addition to lithium cobalt dioxide, lithium iron phosphate, and lithium nickel manganese cobalt oxide are now commonly used cathode materials.

Could you please explain the working principle of a lithium-ion battery (LIB)?

Lithium-ion batteries are made up of a positive electrode (cathode), a negative electrode (anode), a separator, and an electrolytic solution. During charging, the cathode—typically lithium cobalt oxide—undergoes oxidation, while the anode, usually graphite, undergoes reduction.

During discharge, this process is reversed. The separator keeps the anode and cathode electrically isolated, ensuring electrons flow only through the external circuit. Positively charged lithium ions migrate between the anode and cathode by diffusing through the liquid electrolyte, which contains organic solvents, lithium salts, and addatives such as binders.

The separator’s porosity is crucial, allowing the free movement of the electrolyte and lithium ions.

What are the key components of lithium-ion batteries, and how are thermal analysis techniques used to characterize their properties?

Lithium-ion batteries consist of several key components that require detailed thermal characterization: the anode, cathode, electrolyte, binder material, separator, various additives, and the battery housing. Each of these elements plays a vital role in battery performance, making thermal analysis techniques an essential tool.

Thermal analysis offers valuable insights into the thermal stability of cathode and anode materials. In addition, thermogravimetric analysis combined with evolved gas analysis, allows decomposition gases from these materials to be identified.

For electrolyte solutions, understanding the glass transition, crystallization, and melting behaviors are useful for process optimization and quality control testing. The typically inert binder material maintains a solid connection between the electrode and contacts, making its thermal stability and melting behavior particularly important.

For separators, which are thin membrane materials, it is essential to evaluate expansion, shrinkage, and modulus—using DMA—to understand behavior in electrolyte solutions as a function of temperature. Lastly, the housing material’s thermal stability and decomposition properties are also critical to ensuring reliable battery performance.

Could you explain Differential Scanning Calorimetry (DSC) in more detail?

Differential Scanning Calorimetry, or DSC, measures the energy absorbed or released by a sample as it is heated or cooled. DSC instruments can have different temperature ranges, sensor types, and heating and cooling rates.

The METTLER TOLEDO DSC instruments operate from -150 °C to 700 °C, with heating rates up to 300 kelvin per minute. Samples are typically measured in small aluminum, alumina, or other crucibles, in amounts between 2 and 20 milligrams.

High-pressure DSC (HPDSC) is another technique that allows the analysis of samples under inert or reactive gases at pressures from 10 millibar to 100 bar, thus preventing sample vaporization and enabling stability studies under increased pressure.

DSC is used to study thermal behaviors such as melting and chemical reactions. Applications include analyzing electrolyte composition, min/max usage temperature recommendations, oxidative stability, and the influence of additives.

How does Thermogravimetric Analysis (TGA) provide information on material composition and thermal stability?

In TGA, the mass of a sample is continuously monitored as it is heated or cooled in a controlled atmosphere, such as nitrogen or air. This technique provides valuable insights into the composition of materials, including polymer and filler content.

TGA is particularly effective for investigating processes such as vaporization and decomposition. Some TGA instruments can also generate a DSC signal. Evolved gases are analyzed online through hyphenated techniques such as TGA-MS, TGA-FTIR, and TGA-GC-MS.

For example, a useful TGA/DSC application is to analyze thermal stability and decomposiiton of cathode material. The resuting mass-loss steps in the measurement curve as a function of temperature indicate moisture loss and the decomposition of electrolyte in the sample. The DSC measurement curve shows the temperature at which decomposition takes place, showing the maximum temperature at which the cathode material can operate. The thermal stability of cathode materials often depends on the stability of the electrolytic solution used.

What role does Thermomechanical Analysis (TMA) play in characterizing materials?

Thermomechanical Analysis, or TMA, measures the dimensional changes of a sample under a specified load as it is heated or cooled. TMA is particularly valuable for determining a material's expansion behavior and coefficient of thermal expansion, as well as identifying its glass transition temperature and analyzing softening behavior, creep, or swelling in a solvent.

In lithium-ion batteries, TMA is a useful technique for evaluating polyolefin membrane films used as separator material. TMA provides essential quality control testing by checking shrinkage and melting behaviors—critical factors in preventing thermal runaway in batteries. By characterizing the thermal stability of a membrane, TMA is also a useful tool for determining the usable temperature range.

How does Dynamic Mechanical Analysis (DMA) function, and what are its primary applications?

Dynamic Mechanical Analysis, or DMA, measures the mechanical properties of viscoelastic materials across time, temperature, and frequency while applying an oscillating stress. DMA is essential for evaluating modulus, compliance, damping, and the viscoelastic behavior of materials.

This technique identifies softening points and beta relaxation temperatures, often observed as peaks in the tan delta or shifts in modulus. For lithium-ion batteries, DMA plays a critical role in assessing the stability of battery separators, particularly in electrolyte solutions over specific temperature ranges.

How does METTLER TOLEDO support thermal analysis needs?

METTLER TOLEDO offers various resources to support thermal analysis, including UserCom, a technical magazine with articles and applications published twice a year, available online.

Additional resources, such as handbooks, webinars, applications, and training, are accessible through the company’s website.

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This information has been sourced, reviewed and adapted from materials provided by METTLER TOLEDO - Thermal Analysis.

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