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.
Capacity Retention Criteria
Meaning
Performance thresholds establish the minimum percentage of initial discharge capacity a secondary cell must maintain after a specified number of cycles. Manufacturers use capacity retention criteria to define the end of life for a particular application. Most automotive standards set this limit at eighty percent of the original rated value.
A cell falling below this mark is unsuitable for primary propulsion and usually transitions to stationary storage.
Evaluation Metric
Measured values from a standard discharge test are compared against the initial beginning of life figures. When applying capacity retention criteria, the discharge must occur at a fixed rate and temperature to ensure the comparison is valid. A drop in retention usually indicates the growth of a solid electrolyte interface layer or the loss of active lithium.
This percentage is the primary indicator of the health of the electrochemical system.
Cycle Lifetime
Testing protocols define the number of charge and discharge events a cell undergoes before the retention is checked. If the capacity retention criteria are met after one thousand cycles, the cell is certified for long duration use. Different chemistries show varying decay curves over time.
Lithium iron phosphate often maintains high retention for more cycles than nickel cobalt manganese. These results allow for the calculation of the total energy throughput over the life of the battery. Extensive cycling reveals the durability of the electrode structure under mechanical strain.
Quality Target
Production batches are sampled to ensure that the entire lot meets the minimum retention levels. If a sample fails the capacity retention criteria, the entire batch is investigated for manufacturing errors. This standardizes the product performance for the end user.
Clear performance limits protect the buyer and the seller during the warranty period.