Battery Cell HPC Control Using Voltage Decay Feedback
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Solution Overview
Problem
Existing high-precision coulometry (HPC) methods for determining battery cell parameters like service life and self-discharge rate suffer from kinetic effects causing overvoltage fluctuations, which violate the requirement of constant states of charge, leading to inaccurate measurements.
Innovation Solution
A method that controls the battery cell between controllable voltage values, switches off current when reaching these values, determines the rest voltage from decay behavior, and adjusts the voltage differences to minimize overvoltage, allowing precise measurement of open-circuit voltage without relying on resistance models.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current is applied to cycle the battery cell between voltage values in HPC method, then charge levels can be measured to determine service life and self-discharge rate, but kinetic effects cause overvoltage fluctuations that violate the requirement of constant states of charge
Solution Approach 1:
The patent applies preliminary action by allowing the battery cell to rest for a predetermined time period before measuring open-circuit voltage. This rest period enables kinetic effects to subside and overvoltage to equalize, ensuring that measurements are taken only after the cell reaches a stable state with constant open-circuit voltage, thus resolving the contradiction between measurement precision and reliability of constant states of charge
Solution Approach 2:
The patent implements feedback by continuously monitoring the open-circuit voltage of the battery cell during rest periods and using this information to determine when the cell has reached a stable state. The measurement is performed only when the voltage stabilizes within a predetermined time frame, creating a feedback loop that ensures both precise measurements and reliable constant states of charge
2Measurement precision
If waiting time is extended to allow overvoltage to equalize, then accurate open-circuit voltage can be determined, but test duration increases
Solution Approach 1:
The patent applies partial action by implementing a predetermined, limited rest period rather than waiting indefinitely for complete overvoltage equalization. This predetermined time period is sufficient to achieve the necessary measurement accuracy while avoiding excessive waiting time, thus resolving the contradiction between measurement precision and test duration
3Productivity
If higher temperatures and currents are used for accelerated testing, then test duration is reduced, but the behavior under typical operating conditions is not represented
Solution Approach 1:
The patent applies parameter changes by conducting HPC measurements at the actual operating temperature and current conditions rather than using elevated accelerated test conditions. This approach maintains the representativeness of typical operating conditions while still achieving efficient testing through the precision of HPC methodology, resolving the contradiction between productivity and reliability of operating condition representation
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
Enables accurate determination of battery cell parameters by minimizing overvoltage, independent of cell type fluctuations and aging, thus providing precise results without prolonged waiting times.
Implementation Method 1
Determining the respective rest voltage based on a respective decay behavior of the voltage induced by the switching off of the current
Data Source
Figure 1~2
AI summary
A method for controlling an HPC process for a battery cell is proposed, in which the battery cell is cycled between two controllable voltage values V1, V2, wherein two setpoint values of the open-circuit voltage Vmin, Vmax of the battery cell are defined for the control. The method is characterized by at least the following steps: - (S1) switching off the current when the respective voltage value V1, V2 is reached; - (S2) determining the respective open-circuit voltage based on a respective decay behavior (41) of the voltage induced by the switching off of the current; and - (S3) controlling the voltage values V1, V2, wherein the respective amount of the voltage difference ΔV1, ΔV2 (42) between the respective determined open-circuit voltage and its associated setpoint value Vmin, Vmax is used as the control difference. The invention further relates to HPC processes for a battery cell.