The Secret to Optimizing the Performance of Lithium-Ion Batteries Our expertise

The materials that make up a battery must work within a temperature range of −20 °Celsius to 60 °Celsius, so thermal tolerance is one of the most critical parameters in material selection. Thermal analysis is an ideal technique for testing the thermal tolerance and stability of battery materials.

Thermal analyzers can be used to quantify many material characteristics, such as decomposition temperature, chemical composition, degree of oxidation, solvent composition, melting temperature, glass transition, and thermal stability.

Before performing thermal analysis, first, determine the battery component of interest and its material identity. The component’s decomposition temperature, composition determination, oxidation, and solvent drying can be studied by thermogravimetric analysis (TGA).

Differential scanning calorimetry (DSC) can help to identify a material’s melting temperature, the heat of fusion, heat capacity, and glass transition. If the material melts at a high temperature (more than 1,200 °Celsius), a simultaneous DSC/TGA can analyze high-temperature melting and stability and determine composition.

When it comes to studying the stability of the material’s shape and size, a thermomechanical analyzer (TMA) can be used to analyze thermal expansion and shrinkage. The mechanical properties of the battery (deformation study) should be qualified by a dynamic mechanical analyzer (DMA) during manufacturing, which often requires working with slurries of solid particles, binders, and solvents.

Rheology provides critical insights into battery slurries at each manufacturing stage, including storage, mixing, coating, and drying. A rheological profile measurement can help ensure a uniform, defect-free coating that leads to the production of consistent, high-quality electrodes with high batch-to-batch repeatability and low scrap rates. Furthermore, the quantitative thermodynamic and kinetic behavior of electrolytes can be studied simply by using a thermal activity monitor (TAM) system, which is shown in the second case study.

A typical separator is made from polypropylene (PP). TGA is used to determine thermal stability. DSC yields important information about thermal transitions, including the glass transition, heats of fusion and crystallization, and melting and crystallization temperatures. TMA is used to determine expansion as a function of temperature in both the machine direction (MD) and cross direction (TD).

In the case of our sample, which is a uniaxially stretched film, shrinkage in the MD is part of the safety engineering. To prevent thermal runaway, the pores collapse, stopping ionic transport and effectively shutting down the battery. Evaluation of dimension change in the TD is also important, as excessive shrinkage could lead to electrode contact and short circuit.

Following a protocol established by NASA, the shrinkage onset temperature, deformation temperature, and rupture temperature were determined. DMA determines the mechanical properties of the separator, which is important for maintaining mechanical integrity across battery operating conditions without excessive deformation or mechanical failure.

Working with Waters Corporation, scientists at the Amanchukwu Laboratory began using the TA Instruments TAM IV microcalorimeter system to directly measure the universal heat signal and, therefore, the quantitative thermodynamic and kinetic behavior of electrolytes. The heat flow sensitivity and long-term temperature stability of the TAM IV enabled the team to measure many processes that were undetectable by other techniques.

“It is quite exciting to work with the TAM IV microcalorimeter system. No other instrument has the heat flow sensitivity we need for this research,” said Dr. Chibueze Amanchukwu, Principal Investigator of Amanchukwu Laboratory and Assistant Professor at the University of Chicago.

He added: “We discovered we can use microcalorimetry to gather a lot of information and it is extremely easy to use. But when we couple it with other techniques, it provides us with even more insight for our research. Another benefit is the ease of use, even for those with minimal or no training, as it is very simple for users to grasp the instrument quickly.”