Secondary Battery Impedance Estimation via Dual-Cycle Current Fluctuation
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Solution Overview
Problem
Existing methods for estimating the deterioration state of secondary batteries, particularly lithium-ion batteries, face challenges in accurately isolating reaction resistance from other impedance components, leading to reduced accuracy in estimating battery deterioration modes.
Innovation Solution
A secondary battery system and method that involves an electronic control unit to calculate first and second impedances based on current fluctuations at different cycles, estimating reaction resistance from their difference, ensuring that specific conditions regarding current differences and fluctuations are met to enhance accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If impedance is calculated from current-voltage relationship without distinguishing cycles, then calculation is simple, but reaction resistance cannot be accurately isolated from other impedance components
Solution Approach 1:
The patent segments the impedance measurement into two distinct cycles: a first cycle for measuring total impedance and a second cycle for measuring diffusion resistance. By separating these measurements into different time periods with different current fluctuation characteristics, the reaction resistance can be isolated as the difference between the two impedance values, thereby improving measurement precision without excessive complexity
Solution Approach 2:
The patent employs periodic current fluctuations at different frequencies in alternating cycles. The first cycle uses current fluctuation at a first frequency to measure total impedance, while the second cycle uses current fluctuation at a second frequency to measure diffusion resistance. This periodic action with varying frequencies enables accurate separation of reaction resistance components
2Measurement precision
If current fluctuation is applied without controlling average current difference, then measurement is straightforward, but estimation accuracy of deterioration state decreases
Solution Approach 1:
The patent incorporates feedback control by continuously monitoring the average current difference between the first and second cycles. The electronic control unit adjusts the measurement process based on whether the average current difference remains within the predetermined range, ensuring accurate reaction resistance estimation while maintaining operational simplicity through automated feedback mechanisms
Solution Approach 2:
The patent changes the parameter of average current difference control by maintaining it within a predetermined range during the measurement process. This parameter control ensures that the battery operates in a stable state during impedance measurements, improving the accuracy of deterioration state estimation without significantly complicating the measurement 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
This approach allows for high-accuracy estimation of reaction resistance and subsequent deterioration modes, thereby improving the assessment of battery health and longevity.
Implementation Method 1
calculating a first impedance of the secondary battery based on a voltage value of the secondary battery at a time when a current value of the secondary battery is fluctuated on a first cycle. The second calculation control is control for calculating a second impedance of the secondary battery based on the voltage value of the secondary battery at a time when the current value of the secondary battery is fluctuated on a second cycle that is shorter than the first cycle
Data Source
AI summary
A secondary battery system includes a secondary battery, an electric circuit, and an electronic control unit. The electronic control unit is configured to execute first calculation control, second calculation control, and estimation control when a predetermined condition is satisfied. The first calculation control is control for calculating a first impedance of the secondary battery based on a voltage value of the secondary battery at a time when a current value of the secondary battery is fluctuated on a first cycle. The second calculation control is control for calculating a second impedance of the secondary battery based on the voltage value of the secondary battery at a time when the current value of the secondary battery is fluctuated on a second cycle. The estimation control is control for estimating a reaction resistance of the secondary battery from a difference between the first impedance and the second impedance.