Battery State Estimation Using Voltage Fade Correction
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Solution Overview
Problem
Current techniques fail to accurately estimate the internal state of energy storage devices with active materials exhibiting voltage fade (VF) and hysteresis, making it difficult to determine the state of charge (SOC) and health (SOH) due to non-uniquely determined voltage and electrochemical characteristics.
Innovation Solution
An estimation device that acquires and stores energy storage amount-voltage characteristics and their changes during charge-discharge cycles, using these characteristics to estimate the internal state of the energy storage device, including the counter electrode, by referencing feature values such as charge or discharge capacity and average discharge potential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium-rich active material with Mn/Me > 0.5 is used to achieve higher capacity, then discharge capacity increases, but voltage fade and hysteresis occur causing SOC estimation difficulty
Solution Approach 1:
The system performs preliminary characterization of the electrode material to establish the relationship between voltage characteristics and SOC before actual battery operation. Multiple voltage characteristics (open circuit voltage, average discharge voltage, dV/dQ) are measured and stored in advance for different SOC levels, creating a reference database that accounts for hysteresis and voltage fade effects. This preliminary action enables accurate SOC estimation during battery operation without being affected by the material's inherent voltage instability.
2Productivity
If current integration method is used for SOC estimation, then continuous monitoring is achieved, but measurement error accumulates over time
Solution Approach 1:
The system implements a feedback mechanism where the estimated SOC from current integration is continuously corrected using voltage-based SOC estimation. The voltage characteristics (OCV, average discharge voltage, dV/dQ) provide feedback information about the actual SOC state, which is used to correct cumulative errors from current integration. This dual-estimation approach with feedback correction maintains continuous monitoring capability while preventing error accumulation over time.
3Measurement precision
If OCV method is used for SOC estimation, then accurate SOC determination is achieved, but it cannot be applied to materials with hysteresis and voltage fade
Solution Approach 1:
The system creates a universal SOC estimation approach that works for both conventional and lithium-rich electrode materials. By measuring and utilizing multiple voltage characteristics (OCV, average discharge voltage, dV/dQ) and establishing their relationships with SOC through preliminary characterization, the method becomes adaptable to different material types including those with hysteresis and voltage fade. The system universally applies voltage-based correction to current integration results regardless of the specific electrode material properties.
Data Source
AI summary
An estimation device include: an acquisition unit that acquires information relating to a part of a third characteristic that is an energy storage amount-voltage charge characteristic and/or a fourth characteristic that is an energy storage amount-voltage discharge characteristic, of an energy storage device; a storage unit that stores a plurality of energy storage amount characteristics that are at least any of first characteristics, second characteristics, third characteristics that are energy storage amount-voltage charge characteristics, fourth characteristics that are energy storage amount-voltage discharge characteristics, and pieces of V−dQ/dV in correspondence with a change in a feature value, which is changed by repeated charge-discharge, or stores as a function of the feature value; and a first estimation unit that estimates an internal state of the energy storage device on the basis of the information and the energy storage amount characteristics.