Designing Multi Temperature Thermal Soak Schedules for Commercial Battery Dossiers
Multi temperature thermal soak schedules isolate micro shorts and establish valid cell voltage decay dossiers prior to volume cell procurement.
K Value Calculation
Meaning
Voltage drop measurements determine the self discharge rate of a cell by measuring the voltage change over a fixed period and then normalizing it by time. Executing a k value calculation identifies cells with internal micro short circuits or impurities. A high value suggests that the cell is losing energy faster than the rest of the production lot.
This measurement occurs during the aging period after the initial charging and discharging cycles are complete.
Voltage Stability
Measured changes in potential over a storage period of several days reveal the integrity of the internal insulation. During k value calculation, the system compares the voltage at the start and end of a holding period. A stable cell shows almost no change, whereas a faulty cell drops rapidly due to internal paths.
This test is the most effective way to prevent thermal runaway caused by manufacturing defects. Even a tiny metallic particle can create a bridge that slowly drains the energy of the cell. High precision meters are necessary to detect these microvolt changes in a reliable manner.
Leakage Rate
Self discharge is sensitive to the state of charge and the temperature of the room. Testing happens at a fixed state of charge to ensure that the results across different batches are comparable. A mathematical formula converts the raw voltage drop into a millivolt per day figure.
This allows the quality team to set a hard pass or fail limit for the entire lot.
Screening Efficiency
Incorporating the test into the high volume production line filters out dangerous units before they reach the customer. If the k value calculation indicates a problem, the cell is immediately quarantined. This data also helps identify if a specific coating machine is introducing contaminants into the production flow.
It acts as a final gatekeeper for electrochemical safety.