Lithium Cell Sorting by Parallel Current Self-Discharge Screening
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Solution Overview
Problem
Current methods for sorting lithium cells are costly and time-consuming, particularly when aiming to ensure consistency in self-discharge rates, which is crucial for maintaining the performance and cycle life of battery packs in electric vehicles, as existing methods are not scalable or efficient for large-scale sorting.
Innovation Solution
A method involving quick and high-precision sorting of lithium cells by equalizing factory-fresh cells and using a single- or multi-ammeter parallel circuit setup to identify and eliminate cells with large self-discharge rates, employing an equivalent circuit model to connect high-precision ammeters to each branch for accurate sorting into groups based on self-discharge rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional screening methods measuring voltage after long open-circuit time are used, then self-discharge rate can be evaluated, but time consumption is long and cost is high
Solution Approach 1:
The patent applies preliminary action by performing a constant current charging process before the self-discharge measurement. The battery is charged to a specific voltage range (3.0-4.2V) in advance, which prepares the battery in a standardized state for subsequent self-discharge rate measurement, eliminating the need for long open-circuit time and reducing overall testing time
Solution Approach 2:
The patent changes the measurement parameters by using voltage change rate (dV/dt) during constant current charging as the evaluation criterion instead of traditional open-circuit voltage measurement. This parameter change allows for faster measurement while maintaining evaluation accuracy, as the voltage change rate directly reflects the self-discharge characteristics during the charging process
2Measurement precision
If Li Gechen's method with 12 hours calculation time and hundreds of thousands of calculations is used, then self-discharge rate can be measured, but calculated amount is extremely large and equipment requirements are high
Solution Approach 1:
The patent extracts only the essential voltage data points during the constant current charging process to evaluate self-discharge rate. By focusing on voltage change rate at specific charging stages rather than performing comprehensive calculations on all possible parameters, the method simplifies the computational burden and reduces equipment requirements while maintaining measurement precision
Solution Approach 2:
The patent employs a simplified measurement approach that uses basic voltage monitoring during charging rather than complex calculation systems. This disposable-like simplicity in measurement methodology reduces the need for high-performance computing equipment and complex analytical tools, making the system more accessible and cost-effective
3Measurement precision
If Jeff Dahn's ultra-high-precision coulomb efficiency measurement method is used, then coulomb efficiency can be measured accurately, but cost is high and it is difficult for large-scale cell sorting
Solution Approach 1:
The patent creates a universal measurement platform that uses constant current charging with voltage change rate monitoring to evaluate both self-discharge rate and, by extension, coulomb efficiency. This multi-functional approach allows the same simple setup to serve multiple measurement purposes, enabling large-scale sorting without requiring specialized ultra-high-precision equipment for each measurement type
Solution Approach 2:
The patent replaces complex measurement systems with a simplified electrical measurement approach. By substituting sophisticated coulomb efficiency measurement instrumentation with basic voltage monitoring during constant current charging, the method achieves adequate precision for large-scale sorting applications while dramatically reducing cost and improving scalability
4Measurement precision
If Zheng's method studying coulomb efficiency differences between series batteries is used, then coulomb efficiency can be compared, but consumed time is longer
Solution Approach 1:
The patent employs periodic action by conducting measurements on multiple batteries simultaneously during a single constant current charging process. By monitoring voltage change rates of series-connected batteries in real-time during their normal charging cycle, the method enables time-efficient comparison of coulomb efficiency and self-discharge characteristics without requiring separate extended measurement periods for each battery
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
This method allows for rapid and accurate classification of cells, reducing costs and enabling large-scale sorting by efficiently identifying and grouping cells with similar self-discharge rates, thereby improving the consistency and performance of battery packs.
Implementation Method 1
connecting the plurality of cells into a single-ammeter parallel circuit in parallel, monitoring a current change of an ammeter
Implementation Method 2
employing an equivalent circuit model with self-discharge, finding out cells with greatly different self-discharge rates
Data Source
AI summary
The present invention provides a method for sorting lithium cells, which includes quick sorting and high-precision sorting. The method provided by the present invention can be used for quickly and accurately classifying cells based on self-discharge, and is applicable to large-scale self-discharge sorting due to low cost of adopted equipment. Through the quick sorting method and the high-precision sorting method in the present invention, cells with large self-discharge rates can be eliminated from a batch of cells, cells with similar self-discharge rates can be sorted into groups, and an application range is wider.