Analysis of Lithium Battery Capacity Matching Standards

I. Definition of Lithium Battery Consistency

The consistency of lithium batteries refers to the similarity of key characteristics within a group of batteries. It is a relative concept where “the more consistent, the better” applies. Ideally, all parameters of the multiple cells in a battery pack should fall within a narrow range to ensure good consistency. For instance, each of the cells in a parallel series should exhibit similar voltage, internal resistance, and capacity.

If we introduce the time dimension, consistency refers to the uniformity of all parameters of each cell throughout its entire lifecycle. This includes accounting for inconsistencies in capacity decay, internal resistance increase, and aging rate. Ultimately, the life of the entire battery pack is the main focus of our consistency assessment. Researchers often visualize the interaction of these parameters over time, plotting them on a graph where time is on the x-axis and the parameters are on the y-axis. This graph shows how different parameters evolve over time, creating an interconnected network to serve as a foundation for our understanding of battery consistency.

In the context of lithium batteries, “battery grouping” refers to assembling multiple cells to form a battery pack (for example, one cell may have 3.7V and 2000mAh). If a battery pack needs to achieve a configuration of 14.8V and 6000mAh, the grouping might involve 4 cells in parallel and 3 in series.

Consistency in lithium battery grouping is essential. When batteries are connected in series or parallel, poor consistency can cause uneven discharge rates. If one cell discharges completely while another is only halfway discharged, this will prevent the battery pack from delivering its maximum power. To ensure optimal performance, it is essential to match the cells carefully.

II. Lithium Battery Capacity Matching Standards

1. Lithium Cell Charging and Discharging Rate Testing
   • Cells with a capacity of less than 2000mAh: charge and discharge at a rate of 1C.
   • Cells with a capacity of 2000mAh or more: charge and discharge at a rate of 0.5C.
   • Cells with a capacity of 4000mAh or more: charge and discharge at a rate of 0.2C.
   Only cells of the same class (i.e., within the same capacity range) can be paired together.
2. Lithium Battery Cell Matching StandardsThe following parameters are used to determine the compatibility of battery cells:

Matching Item	1C Discharge Matching Requirements	0.5C Discharge Matching Requirements	0.2C Discharge Matching Requirements
Allowable Internal Resistance Difference	≤ 3mΩ	≤ 3mΩ	≤ 3mΩ
Allowable Voltage Difference	≤ 3mV	≤ 3mV	≤ 3mV
Allowable Capacity Difference	≤ 10mAh	≤ 15mAh	≤ 30mAh
Allowable Platform Difference	≤ 1 min	≤ 3 min	≤ 5 min

3. Precautions
   • Safety precautions should be strictly observed during testing. If cells overheat or short-circuit, they should be immediately moved to a safe area away from personnel and flammable or explosive materials.
   • During the testing process, it is necessary to differentiate and label cells from different suppliers, models, specifications, as well as distinguish between good and defective products.
   • For cells that have been in stock for 2 or 3 months, the “Cell Activation Standard” should be applied.
   • Voltage testing should be conducted using a four-and-a-half-digit digital voltmeter.