Lithium Battery Cell Matching via Self-Discharge Current Grading
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Solution Overview
Problem
Current methods for equalizing and matching lithium secondary batteries fail to control the range of self-discharge current, leading to inconsistent battery group performance and reduced service life, and are costly due to inefficient equalization processes.
Innovation Solution
A method involving charging battery cells to a fixed voltage within a voltage-sensitive region, measuring voltage differences, and calculating self-discharge currents to grade and match cells based on self-discharge current and voltage differences, with an equalization protection board and charger configuration that matches the self-discharge current range, reducing equalization costs and extending battery group service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If battery cells are selected based on voltage within a certain range, then the pass rate of matched batteries is improved, but the reliability of the matched battery group deteriorates due to uncontrolled self-discharge current differences
Solution Approach 1:
The patent changes the control parameter from voltage range to self-discharge current range. By measuring voltage differences after a preset time period and calculating self-discharge currents, the method groups battery cells based on their self-discharge characteristics rather than just voltage, thereby improving reliability while maintaining pass rate.
Solution Approach 2:
The patent replaces the traditional voltage-based sorting mechanism with a self-discharge current-based sorting mechanism. This substitution allows for more accurate characterization of battery cell behavior during storage and operation, leading to more reliable battery groups.
2Reliability
If the requirement for consistency is set too high, then the reliability of the matched battery group is improved, but the pass rate of available batteries deteriorates
Solution Approach 1:
The patent changes the consistency control parameter from voltage to self-discharge current. This parameter change enables more meaningful grouping of battery cells based on their actual performance characteristics during storage, achieving high reliability without excessively narrowing the selection range.
Solution Approach 2:
The patent performs preliminary measurement of voltage differences after a preset time period to calculate self-discharge currents before final matching. This preliminary action allows for accurate characterization of self-discharge behavior, enabling reliable matching with acceptable pass rates.
3Reliability
If grade dividing is based on voltage difference, then the control of battery self-discharge is improved, but the accuracy of grade division deteriorates due to inherent voltage differences between cells and test points
Solution Approach 1:
The patent replaces voltage-based grade division with self-discharge current-based grade division. By measuring the change in voltage over a preset time period and calculating the corresponding self-discharge current, the method eliminates the influence of initial voltage differences and test point variations, achieving accurate and reliable grade division.
Solution Approach 2:
The patent changes the measurement parameter from static voltage to dynamic self-discharge current (calculated from voltage change over time). This parameter change transforms the grade division basis from one susceptible to measurement errors to one that reflects actual battery performance characteristics.
4Ease of manufacture
If passive equalization method is used, then the equalization cost is reduced, but the equalization efficiency and service life deteriorate
Solution Approach 1:
The patent performs preliminary matching of battery cells based on self-discharge current characteristics before assembly into battery groups. This preliminary action ensures that cells with similar self-discharge rates are grouped together, reducing the equalization burden and extending service life without requiring expensive active equalization systems.
Solution Approach 2:
The patent applies different equalization strategies to different battery groups based on their matched self-discharge characteristics. By grouping cells with similar self-discharge rates, the system optimizes equalization requirements for each group, balancing cost and service life effectively.
5Device complexity
If the range of self-discharge current is not controlled, then the device complexity is reduced, but the consistency of battery group performance and service life deteriorates
Solution Approach 1:
The patent introduces self-discharge current range as a control parameter for battery cell matching. By calculating self-discharge currents from voltage differences measured after a preset time period and grouping cells based on similar self-discharge characteristics, the method achieves consistent battery group performance without significantly increasing device complexity.
Solution Approach 2:
The patent performs preliminary measurement and calculation of self-discharge currents for each battery cell before matching. This preliminary action establishes the basis for consistent battery group performance by ensuring that cells with similar self-discharge characteristics are grouped together, without requiring complex real-time control systems.
Data Source
AI summary
A method includes providing battery cells for secondary batteries. The battery cells are charged to a fixed voltage (Vc). The battery cells are laid aside in an open circuit for a preset self-discharge time period (t). A voltage (Vt) is measured after the period t for each battery cell. A voltage difference (ΔV) is determined for each battery cell, wherein ΔV=Vc−Vt. A self-discharge rate (ρ) is measured for each ΔV. A self-discharge current (Ic) is calculated during the period t, wherein Ic is a function of ρ. The Ic is curve-fitted to the ΔV for each battery cell to obtain an Ic−ΔV equation. The Ic is divided into h number of grades. The Ic−ΔV equation is utilized to determine h number of grades of ΔV associated with each grade of Ic. Battery cells are selected having a same grade of Ic and ΔV for matching.