Secondary Battery Capacity Degradation Estimation via OCV
Solution Overview
Problem
Existing methods for estimating capacity degradation and state of charge (SOC) of secondary batteries in real-world usage are inaccurate and affected by temperature changes, making it difficult to monitor battery health effectively.
Innovation Solution
An apparatus and method that measures open circuit voltage (OCV) at various depths of discharge (DoD) using sensors and control units, calculating anode voltage from original cathode and OCV values to determine capacity degradation, allowing for accurate estimation of DoD and SOC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If full discharge events are performed to accurately calculate capacity degradation, then measurement precision is improved, but productivity is worsened due to rare occurrence in actual usage
Solution Approach 1:
The patent performs preliminary action by measuring and storing open circuit voltage at known depth of discharge points when the battery is new (before capacity degradation occurs). These preliminary measurements create a reference profile that can be used later to calculate capacity degradation without requiring full discharge events, thus resolving the contradiction between measurement precision and productivity.
2Productivity
If indirect estimation methods are used for capacity degradation, then productivity is improved, but measurement precision deteriorates due to temperature sensitivity
Solution Approach 1:
The patent uses open circuit voltage as an intermediary parameter to indirectly measure capacity degradation. By measuring OCV at a known depth of discharge and comparing it to the reference profile, the system can calculate capacity degradation without direct full discharge events. This intermediary approach maintains measurement precision while improving productivity, and the method is less sensitive to temperature changes compared to other indirect estimation methods.
Data Source
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AI summary
Disclosed is an apparatus and method for estimating a parameter of a secondary battery. The apparatus includes a sensor configured to measure an open circuit voltage (OCVm) of the secondary battery at a first depth of discharge (DOD'), the open circuit voltage (OCVm) corresponding to a difference between a predetermined original cathode voltage (Vc,o) at the first depth of discharge (DOD') and an anode voltage (Va), and a control unit configured to calculate an anode voltage (Va) from the original cathode voltage (Vc,o) and the open circuit voltage (OCVm), determining that the original anode voltage (Va,o) is identical to the anode voltage (Va), determining a second depth of discharge (DOD") corresponding to the original anode voltage (Va,o), and determining capacity degradation (Δcapa) of the secondary battery according to a difference between the first depth of discharge (DOD') and the second depth of discharge (DOD").