Page 21 - PEN Ebook May 2021

Test & Measurements Test & Measurements

designers are provided with a wealth of evaluation Pressure mapping has been used in multi-month

tools and insights on the impacts of different use studies evaluating the pressure profile during
parameters for their designs. These studies have thousands of charging and discharging cycles —
helped designers find the correct materials and principles that can be applied to evaluating battery
best construction for their needs, leading to better housing materials.
designs with repeatable results.

Figure 2: This model demonstrates how battery designers can use pressure mapping technology to measure pressure that
occurs while charging and discharging a lithium-ion battery. The thin & flexible sensor fits snugly between nearly any fixture or
battery type.

A RESEARCH-SUPPORTED Finding the “sweet-spot” for housing pressure be-
METHOD TO MEASURE comes a challenge. A load cell fixture can charac-
COMPRESSIVE STACK STRESS terize the average pressure on the battery assem-
While many manufacturers make significant efforts bly. While this study was successful in measuring

to maintain constant stack construction during man- average pressure in cycle testing, pressure mapping
ufacturing, many do not validate the stack pressure technology offers engineers an opportunity to gain
as part of their quality procedure. Furthermore, many more insight into this application and identify spe-
do not quantify the internal stresses on the stack as cific regions of pressure.
the battery is charged and discharged.

In a 2013 Princeton study1, researchers found that A NEW MODEL FOR MEASURING

high stack pressures had “a strong effect on long BATTERY STACK STRESS
term cell performance, with higher levels of stress The thin and flexible array of sensing elements pro-
leading to higher rates of capacity fade.” Significant vides comprehensive data of the different pres-
internal pressures were shown to cause plastic sures between nearly any two surfaces. As in Figure
deformation, delamination, and internal impedance 2, in the case of battery charge/discharge cycle
increases when the anode and cathode separate. testing, a 0.01mm thick sensor can be wrapped
While lower stack pressures provided better long- around the battery to provide a 360º view.
term performance, delamination may still occur
Figure 3: Example of a five-hour charge/discharge cycle test. The top two images show the battery placed in the fixture, while
when pressures are too low. With pressure mapping, researchers and battery the screenshot shows the pressure output.

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