Infrared imaging has undergone significant evolution since the 1970s, transforming from a niche military and industrial tool into a critical diagnostic method for battery thermal analysis. The progression of IR technology has been closely tied to the increasing energy densities of batteries, where thermal management became a pivotal factor in performance, safety, and longevity. This chronicle outlines key advancements in IR imaging and their impact on battery research and development.
The 1970s marked the early adoption of infrared imaging for industrial applications, primarily using first-generation cooled detectors such as mercury cadmium telluride (MCT). These systems operated in the long-wave infrared (LWIR) spectrum (8-14 µm) and required liquid nitrogen cooling, making them bulky and expensive. Despite limitations, they provided the first glimpses into thermal behavior in early lead-acid and nickel-cadmium batteries. Resolution was coarse, typically around 100x100 pixels, but allowed researchers to identify hotspots during charge-discharge cycles.
By the 1980s, advances in detector materials and cooling mechanisms improved sensitivity and reduced pixel sizes. Indium antimonide (InSb) detectors emerged, offering better response in the mid-wave infrared (MWIR, 3-5 µm). This decade saw the first systematic studies of thermal runaway in lithium-based systems, where IR imaging helped correlate internal short circuits with surface temperature spikes. Spatial resolution improved to 320x240 pixels, enabling more precise localization of thermal anomalies. However, frame rates remained slow, often below 30 Hz, limiting dynamic analysis.
The 1990s introduced focal plane array (FPA) technology, eliminating the need for mechanical scanning and enabling real-time imaging. Microbolometer-based uncooled detectors became commercially viable, reducing costs and power consumption. This democratized IR use in academic labs, where researchers began mapping temperature distributions in lithium-ion cells under varying loads. A pivotal study in 1995 demonstrated how non-uniform electrode heating accelerated degradation, linking thermal gradients to capacity fade. Resolution reached 640x480 pixels, while thermal sensitivity improved to below 50 mK.
The early 2000s saw the integration of high-speed IR cameras capable of 1,000 Hz or more, critical for capturing rapid thermal events like internal shorts during nail penetration tests. Researchers leveraged these tools to validate thermal models predicting runaway propagation in multi-cell packs. MWIR cameras gained prominence for their ability to detect electrolyte combustion signatures at high temperatures. Parallel advancements in lithium-ion energy densities—from 100 Wh/kg in 2000 to over 200 Wh/kg by 2010—necessitated finer thermal monitoring, pushing IR systems to sub-20 mK sensitivity.
Between 2010 and 2020, hyperspectral IR imaging emerged, combining spatial and spectral data to differentiate thermal emissions from various battery components. This proved invaluable in studying solid-state batteries, where interfacial heating between ceramic electrolytes and electrodes required micron-scale resolution. High-definition IR cameras (1024x768 pixels) became standard, alongside software advancements like lock-in thermography, which isolated periodic thermal signals from noise. A landmark 2016 study used IR to map lithium plating in real-time, revealing how charging protocols influenced dendritic growth.
Recent developments (2020-present) focus on AI-enhanced thermal analytics. Modern systems integrate machine learning to predict thermal runaway from early warning signs, achieving >90% accuracy in experimental setups. Portable IR microscopes now offer 5 µm resolution, enabling in-situ analysis of single electrode particles. These tools have been critical in optimizing fast-charging protocols for 350 Wh/kg lithium-ion cells, where thermal homogeneity dictates cycle life.
The trajectory of IR imaging has mirrored battery innovation. As energy densities climbed from 50 Wh/kg in the 1970s to over 300 Wh/kg today, thermal analysis evolved from coarse hotspot detection to predictive, multi-scale diagnostics. Each leap in IR capability—resolution, speed, sensitivity—has provided deeper insights into battery behavior, cementing its role as an indispensable tool in energy storage research. Future advancements will likely focus on combining IR with other modalities, such as X-ray or acoustic imaging, for holistic battery assessment.