Battery Management Using OCV Shift for LiFePO4 Degradation Diagnosis
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Solution Overview
Problem
Existing methods for diagnosing battery degradation, such as Differential Voltage Analysis (DVA), are not suitable for secondary batteries with lithium iron phosphate as the positive electrode active material due to its stable olivine structure, which results in a flat voltage curve, making it difficult to determine degradation or its extent.
Innovation Solution
A battery management system that measures open circuit voltage during charge/discharge cycles and determines degradation based on a specific condition (Vn-1 - Vn < 0.002 V) over at least five cycles, utilizing the potential difference of the negative electrode in lithium iron phosphate batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Differential Voltage Analysis (DVA) is used to diagnose battery degradation, then degradation can be determined for most battery types, but it fails for lithium iron phosphate batteries due to their flat voltage curve caused by stable olivine structure
Solution Approach 1:
The patent changes the measurement parameter from voltage (which is flat in LiFePO4 batteries) to open circuit voltage difference over charge/discharge cycles. By measuring the difference between charged and discharged open circuit voltages across multiple cycles, the method detects subtle changes that indicate degradation, making it applicable to lithium iron phosphate batteries where traditional voltage-based methods fail.
2Measurement precision
If open circuit voltage measurement is performed continuously, then degradation can be detected accurately, but measurement time and energy consumption increase
Solution Approach 1:
The patent implements periodic measurement by performing open circuit voltage measurements at specific intervals - after the battery reaches charged and discharged states during regular charge/discharge cycles. By accumulating measurements over at least five cycles and applying a statistical criterion (standard deviation threshold), the method achieves accurate degradation detection without requiring continuous measurement, thus reducing time and energy consumption.
3Reliability
If multiple charge/discharge cycles are monitored to ensure accurate degradation diagnosis, then measurement reliability improves, but diagnostic time increases
Solution Approach 1:
The patent uses feedback by continuously monitoring the standard deviation of open circuit voltage differences across charge/discharge cycles and comparing it against a predetermined threshold. When the criterion is satisfied (indicating stable degradation pattern), the diagnosis process can terminate early, providing reliable results without requiring a fixed number of cycles. This adaptive feedback mechanism balances reliability with diagnostic time efficiency.
Data Source
AI summary
A battery management system for diagnosing the degradation of secondary batteries equipped with a positive electrode including lithium iron phosphate as a positive electrode active material is provided. The battery management system includes a sensing part configured to measure the voltage and open circuit voltage of a secondary battery; a memory part configured to store the open circuit voltage measured by the sensing part; and a control part configured to determine that the secondary battery is degraded if the amount of change in the open circuit voltage due to charge/discharge cycles of the secondary battery, for at least five charge/discharge cycles, satisfies the following condition: Vn−1−Vn<0.002V, (where Vn−1 represents the open circuit voltage measured during the (n−1)th charge-discharge cycle, Vn represents the open circuit voltage measured during the nth charge/discharge cycle, and n is an integer.)