Secondary Battery Formation SOC Window for Low-Voltage Screening
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Solution Overview
Problem
Existing methods for manufacturing secondary batteries face challenges in accurately detecting low-voltage defects caused by foreign materials or non-uniform formation conditions, leading to voltage drop issues and difficulties in distinguishing good from defective products, which hampers mass production and detection efficiency.
Innovation Solution
A method involving charging secondary batteries to a state of charge (SOC) of 45% to 65% during the formation step, followed by aging and a low-voltage test at SOC 30% or less, with specific charging and pressurizing conditions to stabilize the SEI film and enhance defect detection, including high-temperature aging and degassing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional charging method (10%-30% SOC) is used, then charging time is reduced, but detection precision of low voltage defects deteriorates
Solution Approach 1:
The patent applies preliminary action by performing a formation charging process at 45%-65% SOC before the actual low voltage detection. This preliminary charging to a higher SOC level prepares the battery in a state where low voltage defects can be more effectively detected during subsequent aging and testing phases, thereby improving detection precision without extending the critical production timeline.
2Device complexity
If conventional OCV measurement method is used, then detection process is simple, but reliability of defect detection deteriorates
Solution Approach 1:
The patent segments the defect detection process into multiple distinct phases: formation charging (45%-65% SOC), aging process, and low voltage detection phase. This segmentation allows each phase to be optimized independently - the formation phase prepares the battery state, the aging phase allows defects to manifest, and the detection phase measures voltage drops. This multi-stage approach significantly improves detection reliability while maintaining manageable process complexity through clear phase separation.
Solution Approach 2:
The patent applies preliminary action by implementing a structured formation and aging process before actual defect detection. The battery is charged to 45%-65% SOC during formation, then aged under controlled conditions to allow low voltage defects to develop and manifest. Only after this preliminary preparation is the voltage measurement performed, ensuring that defects are in a detectable state, thereby greatly improving detection reliability.
3Ease of manufacture
If formation conditions are not optimized, then manufacturing process is simple, but manufacturing precision of battery performance deteriorates
Solution Approach 1:
The patent applies parameter changes by optimizing specific formation conditions: charging to 45%-65% SOC instead of conventional levels, controlling aging temperature and duration, and setting specific C-rates for different charging stages. These parameter optimizations ensure uniform SEI film formation, consistent electrolyte distribution, and uniform lithium plating, thereby achieving high manufacturing precision in battery performance without significantly complicating the overall manufacturing process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces voltage drop in good products, increases detection power for low-voltage defects, shortens charging and detection times, and improves mass productivity by stabilizing the SEI film and enhancing defect detection sensitivity.
Implementation Method 1
The lithium secondary battery undergoes an activation process after the electrode assembly is assembled in the battery case together with the electrolyte. The activation process stabilizes the battery structure and makes it usable through charging, aging, and discharging the assembled battery.
Implementation Method 2
In particular, when a metal foreign material such as iron or copper is present in the positive electrode plate of the secondary battery, the metal foreign material may grow as a dendrite at the negative electrode.
Data Source
AI summary
A method for manufacturing a secondary battery includes a formation step for charging an assembled secondary battery to a state of charge (SOC) of 45% to 65%; an aging step for aging the secondary battery for which the formation has been completed; and a low voltage testing step for measuring the change in voltage value, wherein, in the low voltage testing step, a voltage value is measured in an SOC interval of 30% or lower. Since an SEI coating is stably formed in the method for manufacturing a secondary battery, charging time is shortened and thus the secondary battery can be mass-produced. In addition, since a low voltage test is performed in an interval in which the voltage change rate per capacity of a negative electrode is high, a low voltage defect due to non-uniformity of the formation process can be detected in the method for manufacturing the secondary battery.