Detecting Battery Defects With High-Speed Microscopy

The global battery market is experiencing a remarkable expansion, with a projected annual growth of about 15.8% from 2023 to 2030. Lithium-ion batteries are at the forefront of this surge and are expected to dominate the market share by 2024. This growth trajectory is largely fueled by the burgeoning sectors of electric vehicles and battery energy storage systems, which are integral to the transition toward renewable energy sources and electric mobility. 

 

Lithium-ion batteries used for energy storage. Image used courtesy of National Renewable Energy Laboratory

 

However, this rapid expansion brings an acute challenge: ensuring the integrity and safety of battery cells through meticulous defect detection. One technology to address this challenge is scanning acoustic microscopy (SAM), which can provide detailed insights into the structure of battery cells for improved defect detection. But what is SAM, and why is it so powerful?

 

Challenges With Battery Defect Detection

In the intricate process of manufacturing battery cells, defects are common. These can range from microscopic cracks in electrode materials or separators to electrode coating inconsistencies and gaps between a battery cell's layers. Such defects can significantly impair battery performance, leading to reduced capacity and efficiency or even serious safety hazards.

Unfortunately, traditional methods for defect detection in battery manufacturing have encountered several challenges. Conventional techniques, such as visual inspection or basic electronic testing, often lack the precision necessary to detect minute flaws, especially those not visible to the naked eye. These methods can be labor-intensive, time-consuming, and inherently limited in scope and accuracy. Moreover, techniques like X-ray imaging, while more detailed, can be expensive, require extensive safety protocols, and may still miss smaller yet critical internal inconsistencies.

 

Different forms of battery structural defects. Image used courtesy of Li et al.

 

Another significant challenge is the throughput speed. Inspecting each battery cell thoroughly without slowing down the production line in a high-volume production environment is a formidable task. Traditional methods often compromise the depth of inspection and production speed. This trade-off can lead to situations where only a sample of the total production is inspected, potentially allowing defective products to pass through.

These challenges are further exacerbated when considering battery cell components' diverse and complex nature. The intricate layers and materials within a battery cell, such as electrodes and separators, require nuanced and detailed inspection methods to identify inconsistencies like microscopic cracks, gaps, or improper alignments.

 

SAM for Defect Detection

SAM is a non-invasive ultrasonic testing method that employs focused sound waves to inspect the internal structure of battery cells. 

SAM's primary advantage lies in its ability to conduct thorough inspections without damaging the batteries. It works by directing ultrasonic pulses from a transducer at the target object, with the interaction of these pulses with the material's internal structure providing critical information about the presence and nature of defects. The reflected echoes and their time delays reveal details about the material's density, attenuation, and acoustic impedance, indicating any internal inconsistencies.

 

Scanning acoustic microscopy. Image used courtesy of Yu et al.

 

Unlike traditional inspection methods that often require a trade-off between speed and resolution, recent advancements in SAM have successfully enhanced both, making it possible to inspect batteries at high throughput speeds without sacrificing image resolution. For example, the technology can identify defects as small as 50 microns.​ This is crucial in large-scale manufacturing operations where 100% inspection is essential to ensure safety and optimal performance. 

SAM's capabilities also extend far beyond defect detection. It offers a multidimensional view of a battery's internal structure, enabling highly sensitive layer-by-layer inspection. This method is advantageous over other techniques like X-ray or infrared thermography, as it allows for three-dimensional tomography of the inner structure of non-transparent materials.

 

SAM as a Catalyst

As demand grows for lithium-ion batteries, so does the need for defect-free battery manufacturing. SAM has emerged as a vital technology in this context, offering a non-invasive, efficient, and comprehensive solution for detecting defects in battery cells. With SAM, battery manufacturers hope to improve battery safety and reliability without sacrificing production throughput.