Capacity Grading

Measurement Protocol

Laboratory conditions must be strictly controlled to ensure that the discharge and charge cycles used for evaluation are consistent across every batch. Specialized automated equipment performs these cycles at a fixed temperature to minimize the impact of environmental variables on the results of the capacity grading. Each cell undergoes a full discharge to its lower voltage limit followed by a constant current charge to determine its total usable energy.

This data allows the manufacturer to identify outliers that might indicate a flaw in the electrode coating or electrolyte filling process.

Binning Logic

Software algorithms analyze the discharge curves to assign each cell to a specific bin based on its measured ampere hour rating. While a production line might target a nominal value, capacity grading results follow a normal distribution that requires the sorting of units into narrow tolerance groups. Combining cells from different bins in the same module would lead to electrical imbalances and accelerated degradation of the weakest unit.

Precise binning allows for the construction of packs with uniform state of charge behavior and predictable heat generation during high power events. This logic helps the factory maximize its yield by finding a home for every cell that meets the safety standards regardless of its exact capacity.

Commercial Value

Market pricing for lithium ion products is often tied directly to the precision and transparency of the data generated during the sorting phase. High performance electric vehicle manufacturers require very tight capacity grading tolerances to guarantee the range and longevity of their battery systems. Cells that fall into lower bins are frequently sold for stationary storage or consumer electronics where the weight and volume constraints are less restrictive.

Providing a detailed grade report for each shipment builds trust with the integrator and reduces the risk of contract disputes regarding delivered performance. Clear grading criteria allow for a more efficient secondary market for cells that do not meet the primary specification.