Battery Aging Function Using State of Charge and Depth of Discharge
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Solution Overview
Problem
Existing methods for predicting battery aging, particularly for lithium-ion batteries used in electric vehicles, do not adequately account for the depth of discharge and state of charge, leading to inaccurate capacity estimation and lifespan prediction.
Innovation Solution
A method that determines a cycling aging function by considering the state of charge, depth of discharge, temperature, charge/discharge intensity, and total charge exchanged, allowing for a more precise estimation of battery capacity degradation and resistance increase over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing aging functions are used that do not consider depth of discharge and state of charge, then the method is simpler, but the prediction accuracy of battery aging deteriorates
Solution Approach 1:
The patent applies parameter changes by introducing depth of discharge and state of charge as additional parameters in the aging function. The aging function is transformed from a simple form to a more comprehensive form that includes these parameters: dSOH/dt = f(Q, T, SOC, DOD), where Q is total charge exchanged, T is temperature, SOC is state of charge, and DOD is depth of discharge. This parameter expansion directly addresses the accuracy-complexity contradiction by incorporating critical aging factors.
Solution Approach 2:
The patent transitions from a one-dimensional aging model (time-based) to a multi-dimensional model by adding depth of discharge and state of charge dimensions. This dimensional expansion allows the aging function to capture the complex relationship between operating conditions and battery degradation, resolving the contradiction between prediction accuracy and method complexity.
2Reliability
If depth of discharge and state of charge are incorporated into the aging function, then the evaluation of cycling aging improves, but the complexity of determining the aging function increases
Solution Approach 1:
The patent applies preliminary action by pre-defining the structure of the aging function to include depth of discharge and state of charge parameters. The function is established in the form dSOH/dt = f(Q, T, SOC, DOD) before actual aging prediction, allowing systematic data collection and parameter identification. This preliminary structuring reduces the complexity of subsequent aging evaluations while maintaining high reliability.
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 2C
AI summary
Method for determining an aging function of a battery, the aging function representing an evolution of the capacity or resistance of the battery, as a function of variables representative of the operation of the battery, the method comprising: - a) carrying out several experimental cycles of charging and discharging at least one test battery, each cycle being parameterized by operating parameters of the battery, which vary with time, during the different cycles; - b) during the experimental cycles, determining experimental data, including a value of each variable parameter and determining the capacity or resistance; - c) from the experimental data resulting from b), determining the aging function of the battery;the process being characterized in that: during step a), the variable parameters include at least the state of charge and a depth of discharge, such that following step c), the variables of the aging function include at least the state of charge and the depth of discharge.