Strictly speaking, current lithium battery manufacturing cannot achieve complete “capacity testing-free” operation. The core purpose of capacity testing is screening and grading. As long as there are minor, unavoidable differences in the manufacturing process (such as fluctuations in coating thickness or batch-to-batch material variations), this “quality control” step of capacity testing is indispensable. However, in order to reduce costs and shorten production cycles, the industry has indeed developed several process approaches that “weaken” or “replace” capacity testing:
1. Optimized Process: Replacing “Scoring” with “Testing” This is currently the most pragmatic alternative. The core is to use data from the formation process to infer capacity, or to use settling parameters to screen for anomalies.
- Integrated Formation and Capacity Testing: Capacity data is collected synchronously during the formation process (first battery activation). By analyzing voltage, time, and other curves, the capacity is directly determined after formation to ensure it is up to standard. This doesn’t completely eliminate capacity grading, but rather transforms it from a separate “full inspection” into an “incidental result.”
- OCV/IR Screening Method: By optimizing the formation and aging processes (e.g., long-term settling), only the open-circuit voltage (OCV) and internal resistance (IR) of the cells are tested. Cells with abnormal capacity are indirectly eliminated through precise voltage ranges (e.g., 15 20mV) and internal resistance differences (e.g., 5mΩ). This method is fast, but less accurate than a full charge-discharge cycle.
2. Data-Driven: Statistical Process Control (SPC) This method combines statistics and attempts to replace “full inspection” with “sampling,” requiring extremely high stability in the production process.
- SPC Dynamic Monitoring: Monitors the AC internal resistance difference before and after formation, constructs an SPC control chart, and first eliminates cells with abnormal internal resistance fluctuations.
- Model-Based Capacity Estimation: Only a small number of cells are sampled for complete charge and discharge to establish a universal SOC-OCV curve (State of Charge-Open Circuit Voltage curve) and initial coulombic efficiency. For other cells, the total discharge capacity is estimated using the measured open circuit voltage and charging capacity, and then they are categorized.
3. Ultimate Solution: Structural Innovation This method fundamentally changes the battery structure, rendering “capacity grading” meaningless, but it is currently mainly in the cutting-edge research and development stage.
- Post-Assembly Formation: Uncharged cells are shipped directly to downstream customers (such as car manufacturers). After the customers assemble the cells into packs, they use the initialization function on the protection board to perform the first charge activation of the battery. Since the battery cells leave the factory with zero charge, there’s no need for capacity testing at the cell factory. This transfers risk, but places high demands on the equipment and technology of downstream customers.
- New materials/structural systems: Separatorless batteries: These replace traditional separators by coating the electrode surfaces with a solid electrolyte layer. If solid-state battery technology matures in the future, its extremely high uniformity and consistency are expected to fundamentally solve the “consistency anxiety” of current liquid batteries, making capacity testing redundant.
- Current collector-free design: This involves directly fusing the cathode material with the separator, simplifying the structure and reducing performance differences caused by current collector corrosion.
In summary, the current feasible path is to optimize capacity testing, for example, by shortening the time by 70%-80% through “integrated formation and capacity testing.” True capacity testing-free operation requires revolutionary breakthroughs in materials or structure (such as solid-state batteries), but this is still a long way off.
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