All-solid-state Battery Cell Degradation Estimation via SOC-OCV Mapping
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Solution Overview
Problem
Secondary batteries with multiple unit cells connected in series face challenges in estimating individual cell degradation states under total voltage monitoring, leading to potential over-discharge or over-charge, which accelerates degradation.
Innovation Solution
A method and device that calculate the state of charge and open circuit voltage of an all-solid-state lithium secondary battery, select a matching state of charge-open circuit voltage curve from a pre-established map, and estimate individual unit cell degradation based on this curve, allowing for precise determination of charging and discharging limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage and other parameters of individual unit cells are measured to estimate degradation states, then degradation state estimation accuracy is improved, but device configuration and system complexity become complicated
Solution Approach 1:
The patent creates a virtual model (copy) of the battery pack's SOC-OCV characteristics by integrating individual unit cell curves. This virtual model allows estimation of individual cell degradation states using only total voltage measurements, eliminating the need for complex individual cell monitoring hardware while maintaining estimation accuracy.
Solution Approach 2:
The patent introduces SOC-OCV curves as an intermediary representation that bridges the gap between simple total voltage measurements and individual cell degradation states. By using these curves as a mediator, the system can infer detailed cell information without directly measuring each cell, thus reducing device complexity while improving estimation capability.
2Device complexity
If only total voltage monitoring is used for battery management, then device complexity is reduced, but individual unit cell degradation states cannot be estimated leading to over-discharge and over-charge
Solution Approach 1:
The patent creates a virtual representation of individual cell behavior through integrated SOC-OCV curves, allowing the system to monitor each cell's degradation state using only total voltage measurements. This copying approach enables reliable safety monitoring without requiring complex individual cell measurement hardware.
Solution Approach 2:
The patent establishes a feedback mechanism where the integrated SOC-OCV curves continuously provide information about individual cell states based on total voltage measurements. This feedback loop enables real-time detection of over-discharge and over-charge conditions, maintaining battery safety while using a simple monitoring system.
3Device complexity
If individual unit cell degradation is not properly estimated, then device complexity remains low, but deteriorated unit cells become over-discharged and overcharged promoting further degradation
Solution Approach 1:
The patent creates virtual models of individual cell degradation patterns through integrated SOC-OCV curves, enabling the system to identify and protect deteriorated cells without complex monitoring hardware. This prevents over-discharge and over-charge of weak cells, stopping the degradation acceleration cycle while maintaining low device complexity.
Solution Approach 2:
The patent performs preliminary analysis by integrating individual unit cell SOC-OCV curves to create predictive models before actual degradation problems occur. This preliminary action enables the system to anticipate which cells are deteriorating and take preventive measures, avoiding the harmful effects of over-discharge and over-charge before they accelerate degradation.
Data Source
AI summary
A method for estimating, under total voltage monitoring, degradation states of individual unit cells connected in series of an all-solid-state lithium secondary battery includes: calculating, at several timings, a state of charge and open circuit voltage of the battery to acquire an actual state of charge-open circuit voltage curve representing the relationship between the state of charge and the open circuit voltage, selecting, from a map of state of charge-open circuit voltage curves, a curve for which a degree of matching with the actual state of charge-open circuit voltage curve is equal to or greater than a predetermined value or is greatest. The map curves are obtained by integrating as many state of charge-open circuit voltage curves of the unit cell corresponding to different degrees of degradation of the unit cell as the number of unit cells, and estimating the individual unit cells degradation states based on the selected curve.