Battery Pack End-of-Life Determination via Multi-Frequency Impedance
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Solution Overview
Problem
Measuring the full-charge capacity and direct-current resistance of battery packs, especially in power-assisted electric bicycles, is challenging due to varying current flow and temperature conditions, making it difficult to predict the deterioration state of secondary battery cells, particularly for manganese spinel lithium-ion cells.
Innovation Solution
A battery pack with a determination unit that measures index values such as capacity reduction rate, cycle count, time elapsed, and cell voltages to determine if the battery has reached its end of life, and a suspension unit that halts usage when the battery is deemed deteriorated.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If direct-current resistance measurement is used to predict battery deterioration, then protection can be provided, but measurement becomes unreliable under varying temperature and current conditions
Solution Approach 1:
The patent changes the measurement parameters from direct-current resistance to alternating-current impedance measurement at multiple frequencies. This allows accurate battery state assessment under varying temperature and current conditions by measuring impedance across different frequency ranges, which remains reliable even when DC resistance measurements fail due to environmental variations.
2Reliability
If full-charge capacity measurement is used to determine battery end of life, then deterioration state can be assessed, but measurement becomes difficult when battery is not fully discharged
Solution Approach 1:
The patent performs preliminary impedance measurements at multiple frequencies before full discharge is required. By measuring impedance characteristics at different frequencies during partial discharge states, the system can predict full-charge capacity and determine battery health without requiring complete charge-discharge cycles, making the process easier to operate.
Solution Approach 2:
The patent replaces the mechanical/chemical process of full charge-discharge cycling with electrical impedance spectroscopy. By using AC impedance measurements at multiple frequencies, the system can infer capacity information electrically without requiring the battery to undergo complete charge-discharge cycles, thus simplifying operation.
3Device complexity
If protection circuit halts battery use based on single measurement parameter, then simple control is achieved, but accurate deterioration prediction becomes difficult under varying usage conditions
Solution Approach 1:
The patent segments the impedance measurement into multiple frequency components (e.g., high frequency, medium frequency, low frequency). Each frequency range provides different information about battery health, and by analyzing the combination of these segmented measurements, the system achieves accurate deterioration prediction while maintaining relatively simple control logic.
Data Source
AI summary
Provided is a battery pack capable of more reliably preventing adverse effects from being externally exerted. MCU (26) measures, as index values pertaining to the deterioration state of battery unit (1), at least two or more from among: a capacity reduction rate that is the reduction rate of the full-charge capacity of battery unit (1) from an initial value; a cycle count representing the number of times that a cycle, in which battery unit (1) is charged until the cumulative value of charge quantities charged to battery unit (1) reaches a prescribed charge quantity, has been performed; the number of times that battery unit (1) has been charged; time elapsed from the manufacturing of battery unit (1); cell voltages that are the voltages of secondary battery cells 11; and determines whether battery unit (1) has reached its end of life by using the measured index values. Monitoring IC 25 suspends the use of battery unit (1) when battery unit (1) has reached its end of life.