Self-Discharge Current Measurement Using Dual Voltage Resolution
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Solution Overview
Problem
Current methods for measuring self-discharge current characteristics in lithium ion cells are impractical and inaccurate, especially in a manufacturing environment, due to the complexity and high cost of existing potentiostat systems, and the need for lengthy testing periods and controlled storage conditions.
Innovation Solution
A system utilizing multiple voltage measurement circuits with different resolutions and a current measurement circuit, coupled with a processor, to quickly and accurately determine self-discharge leakage current characteristics by setting precise potentiostat voltages and measuring open and terminal voltages, allowing for rapid identification of self-discharge currents in storage cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If commercially available potentiostat systems are used to measure self-discharge current characteristics, then measurement accuracy can be improved, but device complexity and cost increase significantly
Solution Approach 1:
The patent divides the measurement system into separate functional modules: a voltage measurement circuit with high-resolution ADC, a current measurement circuit with precision shunt resistor, and a control unit. This segmentation allows each module to be optimized independently, achieving high measurement accuracy without the complexity of a complete commercial potentiostat system.
Solution Approach 2:
The patent introduces a precision shunt resistor as an intermediary element to convert the difficult-to-measure self-discharge current into a voltage signal that can be accurately measured by the ADC. This intermediary approach enables accurate current measurement using simpler, more cost-effective components.
2Ease of manufacture
If traditional open circuit voltage measurement method is used, then testing cost can be reduced, but testing duration extends to weeks and reliability decreases
Solution Approach 1:
The patent applies a constant small voltage to the storage cell throughout the measurement process, maintaining continuous electrochemical activity. This continuous action accelerates the self-discharge process and enables accurate measurements to be taken within hours rather than weeks, dramatically reducing testing duration while maintaining cost-effectiveness.
Solution Approach 2:
The patent changes the measurement parameters by applying a small constant voltage during the test rather than leaving the cell in open circuit. This parameter change accelerates the self-discharge current manifestation, allowing rapid detection of latent defects without extending the test period to weeks.
3Productivity
If batch testing of storage cells is performed in manufacturing environment, then productivity can be improved, but measurement accuracy and reliability deteriorate due to practical constraints
Solution Approach 1:
The patent designs a measurement system that can handle multiple storage cells in batch while maintaining measurement accuracy. The system uses a microcontroller to automatically control multiple channels, allowing batch testing without sacrificing precision. This universal approach enables manufacturing environment deployment where both throughput and accuracy are critical.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the voltage across the shunt resistor and adjusting measurements accordingly. This feedback mechanism compensates for variations in batch testing conditions, maintaining measurement accuracy and reliability even when testing multiple cells in parallel in a manufacturing environment.
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 approach provides a cost-effective and accurate method to determine self-discharge current characteristics within a short period, identifying latent defects and contamination in storage cells, while reducing testing duration and eliminating the need for extensive storage and environmental control.
Implementation Method 1
measuring an open circuit voltage across a pair of terminals of a storage cell by using a first voltage measurement circuit
Implementation Method 2
measuring a terminal voltage at one of the pair of terminals of the storage cell by using a second voltage measurement circuit
Implementation Method 3
executing one or more self-discharge leakage current measurements upon the storage cell over a period of time
Data Source
AI summary
In accordance with one illustrative embodiment, a system for determining a self-discharge current characteristic of a storage cell (or a bank of storage cells) includes a voltage source, first and second voltage measurement circuits, a current measurement circuit, and a processor. The voltage source provides a potentiostat voltage to the storage cell coupled to the system. The first voltage measurement circuit provides a first voltage resolution for measuring an open circuit voltage across a pair of terminals of the storage cell. The second voltage measurement circuit provides a second voltage resolution that is significantly higher than the first voltage resolution for measuring a terminal voltage at one of the pair of terminals of the storage cell. The processor executes a test procedure by using the voltage source, the first and second voltage measurement circuits, and the current measurement circuit, to determine the self-discharge leakage current characteristic of the storage cell.