Battery SEI Formation Control Using AC Impedance Aging
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face challenges in forming a good solid electrolyte interface (SEI) film at high current densities, leading to uneven film formation and reduced yield due to the need for prolonged charging times, which hinders mass productivity and stability.
Innovation Solution
A method involving initial charging and high-temperature aging of nonaqueous electrolyte secondary batteries, with AC impedance measurements to evaluate and adjust ionic conductivity, ensuring a uniform SEI film formation and modification, thereby shortening the time required for SEI film formation and improving battery performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If initial charging is performed at a low rate (0.1 to 0.5 C) to form a good SEI film, then the SEI film quality is improved, but the charging time becomes excessively long (10 to 2 hours), reducing productivity
Solution Approach 1:
The patent applies preliminary action by performing initial charging at a low rate (0.1 to 0.5 C) specifically to form a high-quality SEI film before subsequent high-rate charging operations. This preliminary SEI film formation prevents electrolyte decomposition and electrode material damage during later high-rate charging, enabling both good film quality and improved productivity
Solution Approach 2:
The patent utilizes parameter changes by varying the charging rate between different stages: using a low charging rate (0.1 to 0.5 C) during the SEI film formation stage to ensure quality, then switching to a high charging rate for subsequent charging operations to maximize productivity. This dynamic parameter adjustment resolves the contradiction between film quality and charging time
2Productivity
If initial charging is performed at a high rate (1 to 10 C) to shorten charging time, then productivity is improved, but the SEI film formation becomes uneven and unreliable, reducing yield
Solution Approach 1:
The patent applies preliminary action by dedicating an initial charging stage at a low rate (0.1 to 0.5 C) specifically for SEI film formation before high-rate charging. This preliminary step ensures uniform and reliable SEI film formation, preventing the unevenness that would occur with direct high-rate charging, while still allowing subsequent high-rate operations for productivity
Solution Approach 2:
The patent implements dynamics by making the charging rate adjustable and stage-dependent: using a low charging rate during the critical SEI film formation period to ensure uniformity, then dynamically switching to a high charging rate for subsequent operations to maximize productivity. This dynamic control prevents the trade-off between speed and quality
3Manufacturing precision
If high-temperature aging is performed for an extended period to improve SEI film quality, then the SEI film properties are enhanced, but the production time increases, affecting mass productivity
Solution Approach 1:
The patent applies preliminary action by performing high-temperature aging for a limited period (6 to 24 hours) after initial charging to enhance SEI film properties. This preliminary aging treatment improves film quality and stability without requiring excessively long durations, thereby balancing film property enhancement with mass productivity requirements
Solution Approach 2:
The patent utilizes parameter changes by controlling the aging temperature and time parameters: performing aging at elevated temperatures (50 to 60°C) for optimized durations (6 to 24 hours). This parameter optimization enhances SEI film properties while minimizing the time loss, resolving the contradiction between film quality and production efficiency
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 allows for the production of nonaqueous electrolyte secondary batteries with long life and stable high-rate input-output characteristics in a shorter time and at lower costs, by ensuring a uniform and effective SEI film formation.
Implementation Method 1
performing an AC impedance measurement on the nonaqueous electrolyte secondary battery while maintaining the potential, and calculating an ionic conductivity of the SEI film
Implementation Method 2
performing initial charging on the battery after assembly, to form an SEI film on the surface of the negative electrode
Implementation Method 3
performing an aging process at high temperature, after formation of the SEI film
Data Source
AI summary
A method for producing a nonaqueous electrolyte secondary battery, and a production system therefor, that allow forming a SEI film in a shorter time. The method includes assembly, initial charging, and high-temperature aging steps. At least one from the initial charging and the high-temperature aging has the following sub-steps: a step of performing an AC impedance measurement on the battery and, on the basis of the AC impedance measurement, calculating an ionic conductivity of an SEI film that is formed the surface of a negative electrode of the battery; and a step of determining whether the calculated ionic conductivity falls within a predetermined range or not, and terminating the initial charging step or the high-temperature aging step when the ionic conductivity falls within the predetermined range, and continuing the initial charging step or the high-temperature aging step when the ionic conductivity does not fall within the predetermined range.