Lithium Ion Cell Life Estimation Using Dynamic Voltage-Based Equation Switching
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Solution Overview
Problem
Current methods for estimating the remaining life of lithium ion secondary cells, such as those combining linear and root degradation rules, still exhibit significant differences between estimated and actual values, necessitating improved accuracy.
Innovation Solution
A life estimation apparatus that acquires cumulative cycle or capacity data and calculates remaining capacity using specific exponential equations (Equation 1 and Equation 2) based on the change in open circuit voltage, voltage rise width, or voltage rise rate, with exponents ranging from 0.9 to 1.1 and 0.4 to 0.6 respectively, to switch between estimation equations dynamically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If linear rule or root rule is used for capacity degradation estimation, then the estimation method is simple, but the estimation accuracy is insufficient with large difference from measured values
Solution Approach 1:
The patent dynamically switches between different degradation equations (Equation 1 with n1=0.9-1.1 and Equation 2 with n2=0.4-0.6) based on the sign of the amount of change in voltage characteristics. This dynamic adaptation allows the system to select the most appropriate model for the current cell state, improving estimation accuracy without requiring a single complex model
Solution Approach 2:
The patent changes the exponent parameters (n1 and n2) in the degradation equations based on voltage characteristic changes. By adjusting these parameters according to the amount of change in open circuit voltage, voltage rise width, or voltage rise rate, the system adapts to different degradation stages and improves measurement precision
2Measurement precision
If combined linear and root degradation rules are used, then estimation accuracy is improved compared to single rule, but large difference still exists between estimated and measured values
Solution Approach 1:
The system dynamically selects between Equation 1 and Equation 2 based on real-time voltage characteristic monitoring. This dynamic selection mechanism improves both accuracy and reliability by adapting to the actual degradation behavior rather than relying on a fixed combined model
Solution Approach 2:
The patent uses feedback from voltage characteristic measurements (open circuit voltage, voltage rise width, voltage rise rate) to determine which degradation equation to apply. This feedback mechanism ensures the estimation model aligns with actual cell behavior, improving reliability
Data Source
AI summary
A life estimation apparatus includes a second calculation unit that calculates a remaining capacity, which is a capacity with which the lithium ion secondary cell is capable of being charged or which the lithium ion secondary cell is capable of discharging, based on Equation 1 having an exponent n1 of 0.9 to 1.1 and Equation 2 having an exponent n2 of 0.4 to 0.6. The second calculation unit calculates the remaining capacity using Equation 1 if the amount of change of open circuit voltage, the amount of change of a voltage rise width, or the amount of change of a voltage rise rate has a positive value and calculates the remaining capacity using Equation 2 if the amount of change of the open circuit voltage, the amount of change of the voltage rise width, or the amount of change of the voltage rise rate has a negative value.