Battery Cell SOC Calibration Using Thickness Inflection Points
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Solution Overview
Problem
Estimating the state of charge (SOC) for lithium iron phosphate (LFP) and graphite-based battery cells is challenging due to their flat voltage profile, leading to inaccuracies in existing methods like coulombic counters, which require time-consuming recalibration and are prone to error accumulation.
Innovation Solution
Calibrate SOC by detecting inflection points in battery cell thickness changes during charging and discharging, using pressure sensors to identify known SOC values, thereby improving accuracy and speed of calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage-based estimation methods are used for SOC estimation, then the system is simple to operate, but the measurement precision is poor due to flat voltage profile of LFP and graphite-based battery cells
Solution Approach 1:
The patent introduces pressure sensors as an intermediary measurement tool to detect battery cell thickness changes. This mediator enables indirect SOC estimation through mechanical deformation detection rather than direct voltage measurement, resolving the contradiction by providing accurate SOC data without relying on voltage-based methods that fail with flat voltage profiles.
Solution Approach 2:
The patent replaces the traditional electrical measurement system (voltage-based SOC estimation) with a mechanical measurement system (pressure sensors detecting thickness changes). This substitution allows accurate SOC estimation for LFP and graphite-based cells by measuring physical deformation instead of relying on electrical potential differences.
2Reliability
If coulombic counters are used for SOC estimation, then the device complexity is low, but the reliability deteriorates due to error accumulation requiring time-consuming recalibration
Solution Approach 1:
The patent implements a feedback mechanism where pressure sensor data continuously monitors battery thickness changes and provides real-time SOC correction. This feedback loop prevents error accumulation by constantly comparing estimated SOC with actual physical state, eliminating the need for periodic recalibration and maintaining high reliability over time.
Solution Approach 2:
The system performs self-calibration by using its own pressure sensor measurements to correct SOC estimation errors. The battery management system automatically detects thickness inflection points and adjusts SOC values without external intervention, making the system self-correcting and eliminating time-consuming manual recalibration procedures.
3Measurement precision
If pressure sensors are used to detect thickness changes for SOC calibration, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent makes the pressure sensor system multi-functional by using it for both SOC estimation and battery health monitoring. The same sensor infrastructure serves multiple purposes, including detecting thickness inflection points for SOC calibration and monitoring overall battery mechanical state, thereby justifying the added complexity through enhanced system versatility and reduced need for separate monitoring systems.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method provides a more accurate and faster SOC calibration by utilizing thickness inflection points, reducing reliance on voltage-based estimation and addressing errors in coulombic counters.
Implementation Method 1
A battery system includes a pressure sensor configured to sense pressure changes corresponding to thickness changes of at least one of a plurality of battery cells
Data Source
AI summary
A battery system includes a pressure sensor configured to sense pressure changes corresponding to thickness changes of at least one of a plurality of battery cells of a battery. A battery management module includes a state of charge (SOC) estimator configured to estimate the SOC of the battery. Based on sensed pressure, the SOC estimator detects at least one of a first inflection point and a second inflection point during one of charging and discharging of the battery, and calibrates the SOC of the battery based on at least one of a first SOC value and a second SOC value corresponding to the at least one of the first inflection point and the second inflection point, respectively.