Lithium-Ion Cell Wetting Evaluation by Low-Current Reference Charging
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Solution Overview
Problem
Current methods for evaluating the wetting degree of lithium ion battery cells are destructive, time-consuming, and not suitable for mass production, as they require disassembly and cannot quantify the wetting degree effectively.
Innovation Solution
A low current test method is proposed, where a reference charge profile is recorded from a pre-aged battery cell, and another battery cell's charge profile is compared to determine the wetting degree, allowing for quantitative evaluation without disassembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional test methods (PC solvent impregnation, impregnated area observation, negative electrode SOC analysis) are used to evaluate wetting degree, then measurement precision is improved, but device complexity and productivity deteriorate due to destructive testing requiring disassembly
Solution Approach 1:
The patent replaces mechanical/disconstructive testing methods with electrochemical impedance spectroscopy measurement. Instead of disassembling cells to observe impregnation areas or peel electrode layers, the method uses EIS to measure wetting degree through electrical impedance characteristics, enabling non-destructive evaluation that maintains productivity while achieving precise measurement.
Solution Approach 2:
The patent introduces electrochemical impedance spectroscopy as an intermediary measurement approach. Rather than directly observing physical impregnation states requiring cell disassembly, EIS serves as a mediator that infers wetting degree from electrical properties, enabling indirect but accurate measurement without disrupting the battery cell structure.
2Measurement precision
If air scanner analysis or EIS analysis methods are used, then measurement capability is improved, but loss of time increases due to long testing duration
Solution Approach 1:
The patent optimizes the EIS measurement parameters including frequency range, amplitude, and measurement protocol to reduce testing time. By carefully selecting measurement parameters and using equivalent circuit modeling for rapid data analysis, the method achieves accurate wetting degree evaluation significantly faster than conventional air scanner or traditional EIS methods.
Solution Approach 2:
The patent performs preliminary characterization to establish equivalent circuit models and measurement protocols before actual wetting degree evaluation. By pre-defining measurement parameters, frequency ranges, and analysis methods based on battery cell specifications, the actual testing time is minimized while maintaining measurement accuracy.
3Measurement precision
If sampling analysis is performed to determine poor wetting, then measurement capability is improved, but loss of information increases as wetting degree cannot be quantified or specified
Solution Approach 1:
The patent implements a feedback mechanism where EIS measurement data is continuously processed to provide quantitative wetting degree values. The measured impedance parameters are fed into equivalent circuit models that calculate specific wetting metrics, providing real-time feedback on wetting quality and enabling precise quantification rather than mere pass/fail determination.
Solution Approach 2:
The patent replaces qualitative sampling analysis with quantitative electrochemical measurement. Instead of examining discrete samples to determine if wetting is adequate, EIS provides continuous quantitative data on wetting degree through impedance measurements, eliminating information loss and enabling precise specification of wetting quality.
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 enables quick and quantitative assessment of wetting degree, optimizing electrolyte solution injection and reducing defects, thereby improving productivity by identifying both poorly and well-wetted battery cells without discarding them unnecessarily.
Implementation Method 1
when the electrolyte solution permeates the positive electrode, the negative electrode and the separator by the capillary force, the inside and interface of each component get wet
Implementation Method 2
the EIS analysis method is based on the diffusion and interfacial resistance measurement principle
Data Source
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AI summary
Provided is a method for determining the wetting degree of a lithium ion battery cell using a low current test. The wetting degree determination method according to the present disclosure includes a) obtaining, as a reference charge profile, a charge profile recorded while charging a reference battery cell having undergone receiving an electrode assembly and an electrolyte solution in a case, assembling and pre-aging with a low current of 0.01 C-rate or less, b) measuring and recording a charge profile while charging another battery cell having undergone receiving an electrode assembly and an electrolyte solution in a case, assembling and pre-aging with a low current of 0.01 C-rate or less in the same way as the reference battery cell, and c) determining the wetting degree of another battery cell relative to the reference battery cell by comparative analysis of the reference charge profile and the measured charge profile.