Cylindrical Cell Tester

Human visual inspection is a simple test to check for physical defects or abnormalities, although it's prone to subjectivity and human error. An inspector may check electrode coating, weld integrity, and the cell structure.
As automation becomes more prevalent in battery cell manufacturing, robotic systems with cameras and computer vision algorithms can perform visual inspections with speed, consistency, and precision. Automated visual inspection is a valuable tool for streamlining quality control processes, enhancing inspection capabilities, and boosting manufacturing efficiency.

Direct current internal resistance (DCIR) tests measure resistance to direct current flow. The battery is injected with a relatively high intensity current pulse to measure the ohmic response of the cell. Pulses are applied when the battery is at different states of charge to map the response across the cell range, both charging and discharging. This process provides insights into the internal condition of the cell and its functionality.
While DCIR doesn't provide the most comprehensive analysis, it's a quick and simple approach to get a baseline measurement of internal resistance. Alternating current internal resistance (ACIR) and electrochemical impedance spectroscopy (EIS) tests provide more information about battery impedance, but they are more time-consuming and require specialized equipment.

Unlike DCIR, which measures resistance to direct current, ACIR evaluates the impedance of the battery under alternating current flows. A sinusoidal current is applied to the cell, and the voltage reaction is measured at specific frequencies (typically 1 kHz).
By analyzing the voltage response, engineers can characterize the AC dynamic of the cell and detect critical defects. The results reveal information about various electrochemical processes, aging effects, and internal resistance variations across different frequencies.

EIS tests are the most advanced type of impedance test. Instead of applying the sinusoid at one frequency and amplitude like an ACIR test, the stimuli are applied at many frequencies, typically from 0.1 Hz to 10 kHz or more.
Defects that would otherwise go undetected by ACIR and DCIR tests are captured with EIS because these tests evaluate performance across a larger spectrum and wider frequency range. This method can help identify issues like premature aging. These insights improve the lab's diagnostic capabilities and provide deeper insights into battery behavior.

Open circuit voltage (OCV) tests measure the cell voltage when no load is applied to it and no current is flowing outside the battery. This simple, non-intrusive test indicates whether a cell was correctly activated and characterizes how the cell degrades over time. However, this test provides limited insights into the cell's internal condition. A cell with an OCV that is too low or too high indicates a cell quality concern.
OCV tests are often used to estimate the leakage current of a cell in the formation, pack assembly, and throughout the battery's lifecycle, rating its performance and checking its health. For example, OCV tests are used to sort and match cells during pack assembly.

Leakage tests are helpful for the early detection of leaks, cell damage, or deterioration. These tests are performed in numerous ways to assess the quality of battery cells and packs. Most commonly, periodic OCV tests are performed to detect leakage when the cell is left to age in a climatically controlled environment.
The industry is researching advanced methods. For example, a voltage can be imposed on a cell, and an additional current is supplied to stabilize that voltage. The additional current required to stabilize the voltage is an estimate of the internal leakage current. Unfortunately, this technique is time-consuming and does not produce repeatable results.