Battery Cell Performance Estimation Using Temperature-Corrected Resistance Components
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Solution Overview
Problem
Existing methods for diagnosing the deterioration of secondary cells, such as lithium-ion batteries, face challenges in accurately estimating cell performance due to temperature fluctuations, which affect internal resistance values, making it difficult to evaluate deterioration over long periods without requiring extensive time or specialized equipment.
Innovation Solution
A cell performance estimation method that corrects for temperature influences by dividing internal resistance into reaction, ohmic, and diffusion components, using equations to adjust these components to a reference temperature, allowing for accurate estimation of cell capacity and deterioration based on charging/discharging curves and AC impedance measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cell performance estimation is performed using charging/discharging curves, then deterioration diagnosis can be conducted, but temperature fluctuations cause internal resistance values to change, reducing measurement precision
Solution Approach 1:
The patent applies parameter changes by dividing the internal resistance into three distinct components (reaction resistance, ohmic resistance, and diffusion resistance), each with different temperature dependencies. By modeling and correcting each component separately using temperature coefficients, the system achieves accurate performance estimation across varying temperatures, resolving the contradiction between measurement precision and temperature fluctuation effects.
2Measurement precision
If comprehensive cell diagnosis is performed, then accurate deterioration evaluation is achieved, but it requires long time and special equipment
Solution Approach 1:
The patent implements self-service by utilizing the cell's own charging/discharging operation data to perform deterioration diagnosis. The system extracts performance information from routine charging/discharging curves without requiring separate diagnostic procedures, special equipment, or additional time, thereby achieving accurate deterioration evaluation through the cell's normal operational data.
3Reliability
If internal resistance is measured to diagnose deterioration, then cell health can be assessed, but temperature dependence makes it difficult to evaluate deterioration progression
Solution Approach 1:
The patent resolves the temperature dependence issue by changing the parameter representation from a single internal resistance value to three distinct resistance components (reaction, ohmic, and diffusion resistance), each with its own temperature correction model. This allows the system to separate temperature effects from deterioration effects, enabling reliable deterioration diagnosis across different operating temperatures.
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 enables precise evaluation of cell performance and deterioration progression, independent of temperature variations, facilitating reliable diagnosis and maintenance of secondary cells in vehicles and other applications.
Implementation Method 1
measuring frequency characteristics of an internal impedance of the battery by an AC impedance method
Implementation Method 2
estimating the capacity and internal resistance of a cell and the degree of deterioration of each active material of the cathode and anode by referring to the open circuit potential-charged amount data of the active material, from a charging/discharging curve (cell voltage-time data) obtained when the cell is actually charged/discharged
Data Source
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AI summary
According to one embodiment, a cell performance estimation method includes storing data obtained by measuring a cell temperature, an electric current, and a voltage while a secondary cell is charged or discharged, estimating an internal resistance value of the cell by using the cell temperature data, the electric current data, and the voltage data, and predetermined data indicating a relationship between a charged capacity and open circuit voltages of a cathode active material and anode active material, calculating a reaction resistance component, an ohmic resistance component, and a diffusion resistance component from the estimated internal resistance value and correcting the estimated internal resistance value based on a value obtained by correcting the reaction resistance component, the ohmic resistance component, and the diffusion resistance component in accordance with a temperature, and adding up the corrected values.