Battery Internal Resistance Measurement by Polarization Separation
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Solution Overview
Problem
Current methods for measuring internal resistance in batteries, such as DC and AC methods, lack accuracy in distinguishing between ohmic, electrochemical, and concentration polarizations, and fail to provide clear standards for determining when ohmic polarization disappears, leading to inaccurate results and inability to differentiate between polarization types.
Innovation Solution
A method involving controlled temperature and constant-current discharging/charging of batteries, with high-speed data acquisition to record specific voltage points (V1, V2, V3, V4) based on voltage change rates, allowing for separate calculation of ohmic, charge-transfer, and diffusion internal resistances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If DC method is used to measure internal resistance by recording voltage at first point after discharge/charge ends, then measurement can be conducted, but the result is inaccurate because the first point depends on measuring instrument resolution and does not accurately reflect when ohmic polarization disappears
Solution Approach 1:
The patent uses a criterion based on voltage change rate (|dV/dt| < threshold) to determine when ohmic polarization disappears. This feedback mechanism continuously monitors voltage changes and automatically identifies the correct measurement point, eliminating dependence on instrument resolution and providing accurate, reproducible results for internal resistance measurement.
2Productivity
If conventional DC method is used to measure internal resistance, then measurement can be performed, but it fails to distinguish between different polarization types (ohmic, electrochemical, concentration)
Solution Approach 1:
The patent segments the internal resistance measurement into three distinct components by identifying specific voltage points: V1 (initial voltage), V2 (voltage when ohmic polarization disappears), V3 (voltage when electrochemical polarization disappears), and V4 (stable voltage). This segmentation allows calculation of separate resistance values for ohmic (R0), charge-transfer (Rct), and diffusion (Rdiff) polarizations, providing comprehensive diagnostic information while maintaining measurement efficiency.
3Productivity
If voltage measurement points are determined arbitrarily based on instrument resolution, then measurement can be completed, but the results have great arbitrariness and uncertainty
Solution Approach 1:
The patent changes the determination criterion from arbitrary time-based selection to a parameter-based criterion using voltage change rate (|dV/dt|). By setting a threshold for voltage change rate, the method objectively identifies when ohmic polarization disappears, eliminating arbitrariness and ensuring reliable, reproducible results across different instruments and operators.
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 method provides accurate separation and measurement of internal resistances due to its ability to account for different polarization types, improving battery design, failure analysis, and heat generation estimation.
Implementation Method 1
there are three types of polarizations existing: ohmic polarization, electrochemical polarization and concentration polarization
Implementation Method 2
ohmic polarization (also called resistance polarization) is very short, generally of the order of magnitude of about 10 microseconds
Implementation Method 3
concentration polarization caused by diffusion of electric charge in solid and liquid phases
Implementation Method 4
since there is an electric double layer exists on electrode surface, at initial phase where discharge/charge current ends, the electric double layer needs to be charged/discharged, just because of this, the voltage would not rise/drop promptly but slowly
Data Source
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AI summary
The present disclosure provides a method for measuring an internal resistance of a battery, after discharging/charging the battery under a preset constant-current, acquiring voltages of the battery within a period from ending the discharging/charging to a time when the voltage reaches stable, and then calculating different corresponding internal resistances caused by ohmic polarization, electrochemical polarization and concentration polarization separately. Since it is different for the orders of the magnitude of the characteristic time which these different polarizations need to get back into new equilibrium state after ending the discharging/charging, the method of the present disclosure classifies the internal resistances caused by these polarizations and calculated different internal resistances corresponding to the polarizations. Both the comparison with a result measured by other method and multiple embodiments in the application justify that the method in the present disclosure has high reliability and strong practicability.