Incoming Batch Inspection and Degradation Testing Procedures for Sodium Ion Shipments
Immediate AC-IR screening and differential capacity testing reveal hidden transit degradation and cell capacity variance in sodium ion shipments.
Degradation Testing
Meaning
This experimental procedure evaluates how a battery cell’s performance and capacity decline over time and under specific stress conditions. Engineers use degradation testing to estimate the operational lifespan of cells and to identify the primary failure mechanisms within the cell chemistry. The process involves subjecting the cells to repeated charge and discharge cycles, elevated temperatures, and prolonged storage states.
It is measured in terms of capacity retention and internal resistance rise over hundreds or thousands of test cycles. This testing provides the data needed to formulate warranties, establish safety parameters, and justify the long-term investment in specific cell technologies.
Testing Protocol
The laboratory setup utilizes multi-channel battery cyclers housed in thermal chambers to simulate real-world operating environments. Conducting degradation testing requires defining the exact cycle parameters, including charge rates, discharge rates, depth of discharge, and temperature limits. Cells are tested under continuous cycling to accelerate the aging process, which can take several months or even years to complete.
Periodically, the testing is paused to run diagnostic checks such as electrochemical impedance spectroscopy and incremental capacity analysis. These diagnostic steps allow researchers to track the growth of the solid electrolyte interphase and the loss of active lithium without damaging the cell. This detailed tracking reveals the specific electrochemical changes that occur as the cell approaches its end of life.
Lifetime Prediction
Sourcing departments rely on these laboratory results to verify the lifetime claims made by battery manufacturers. The results from degradation testing are used to build mathematical models that predict how cells will perform over ten or fifteen years in the field. These models help system integrators design appropriate thermal management strategies and decide on the initial over-sizing of the battery pack.
If a cell exhibits rapid degradation under specific conditions, the system controls can be programmed to avoid those states. This predictive capability reduces the financial risks for project developers by ensuring that the batteries can meet the performance requirements of the power purchase agreement.
Material Selection
The choice of battery chemistry directly influences how the cell responds to these aging tests. Running degradation testing on different cell chemistries reveals their unique strengths and weaknesses under identical load profiles. Sourcing teams use this comparison to select the most appropriate battery technology for their specific application, balancing cost and longevity.
For instance, some chemistries excel in high-temperature environments, while others are better suited for continuous, deep cycling. Having access to independent testing data allows companies to make informed purchasing decisions that align with the specific requirements of their end users.