Lithium Secondary Battery Low-Voltage Screening by Microcurrent Cycling
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Solution Overview
Problem
Conventional methods for screening low-voltage defective lithium secondary batteries are time-consuming, requiring several days to tens of days, which decreases productivity.
Innovation Solution
A microcurrent charging/discharging process is applied in multiple sections with current rates of 0.000001 C to 0.0001 C, followed by measuring voltage changes and screening based on these changes to identify defective batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional OCV measurement method is used to screen low-voltage defective batteries, then measurement precision is improved, but loss of time increases significantly
Solution Approach 1:
The patent applies preliminary action by performing microcurrent charging/discharging cycles before final OCV measurement to activate and reveal low-voltage defective batteries. The microcurrent stress treatment (charging/discharging at 0.01C to 0.1C rate for 1-24 hours) prepares the battery in advance, causing defective batteries to exhibit voltage drop characteristics that can be detected quickly afterward, thus reducing the overall inspection time while maintaining detection accuracy
Solution Approach 2:
The patent changes the measurement parameters by introducing microcurrent charging/discharging cycles with specific current rates (0.01C to 0.1C) and time durations (1-24 hours) before OCV measurement. This parameter transformation converts the inspection process from direct long-term monitoring to a staged approach where controlled electrical stress reveals defects, enabling faster screening without sacrificing measurement precision
2Productivity
If microcurrent charging/discharging process is applied, then productivity is improved by reducing inspection time, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the inspection process into distinct stages: microcurrent charging phase, resting phase, and discharging phase, with multiple cycles (N≥2). Each phase has controlled duration and current parameters. This segmented approach simplifies control by breaking down the complex inspection into manageable, repeatable modules while achieving high productivity through systematic cycling
Solution Approach 2:
The patent employs periodic action through repeated charging/discharging cycles with defined periods. Each cycle includes charging at microcurrent for a set time, followed by resting and discharging phases. This periodic structure enables automated, high-throughput inspection where defective batteries reveal their characteristics through repeated stress cycles, increasing productivity while maintaining manageable system complexity through rhythmical operation
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
The method significantly reduces inspection time from days to several hours, improving productivity by accurately distinguishing between good and defective batteries.
Implementation Method 1
a microcurrent charging/discharging process consisting of N (N is an integer of 2 or more) charging/discharging sections, and applying a microcurrent to a battery cell in each of the charging/discharging section
Implementation Method 2
some of the secondary batteries that have been manufactured show a phenomenon in which a voltage drop behavior is higher than the self-discharge rate
Data Source
AI summary
An inspection method for a low-voltage defect of a lithium secondary battery includes performing a microcurrent charging/discharging process having N charging/discharging sections, N being an integer of 2 or more, and for each charging/discharging section, applying a microcurrent to the lithium secondary battery; measuring a change in voltage of the lithium secondary battery before and after each charging/discharging section; and screening for the low-voltage defect of the lithium secondary battery based on the measured change in voltage. The lithium secondary battery having the low-voltage defect is not shipped. The microcurrent for each charging/discharging section is at a current rate of 0.000001 C to 0.0001 C.