Wound Electrode SEI Formation Under Slow EC Permeation
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Solution Overview
Problem
In power storage devices, such as lithium-ion batteries, uneven permeation of ethylene carbonate (EC) within the electrode body leads to inadequate formation of the negative electrode SEI film near the center, resulting in increased resistance due to its slow permeation speed and high viscosity, which complicates the handling of wound electrode bodies and affects the battery's performance.
Innovation Solution
A method for producing power storage devices where the electrode body is pre-formed with a film-forming material in the center portion, allowing for even SEI film formation despite uneven EC distribution, using a solvent with a lower melting point than EC to facilitate permeation and prevent resistance increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ethylene carbonate (EC) is used as a solvent in the electrolytic solution to form SEI film, then the SEI film formation is improved, but the permeation speed becomes slow and viscosity increases making handling difficult
Solution Approach 1:
The patent applies preliminary action by pre-forming the electrode body structure and performing initial charging before complete EC permeation. The electrode body is prepared with EC-containing electrolytic solution, and initial charging is performed to start SEI film formation while EC is still permeating, ensuring uniform film formation across the entire electrode body including remote portions.
2Use of energy by moving object
If the electrode body width is increased to 180 mm or larger for higher capacity, then the energy storage is improved, but the EC permeation uniformity deteriorates due to slow permeation speed
Solution Approach 1:
The patent performs initial charging before EC completely permeates the entire electrode body, particularly reaching the center portion. This preliminary action initiates SEI film formation in accessible areas while EC continues to permeate, ensuring that even in wide electrode bodies (180 mm or larger), uniform SEI film formation occurs across all portions including remote center areas.
3Productivity
If initial charging is performed immediately after electrolytic solution injection, then the productivity is improved, but the SEI film formation uniformity deteriorates due to insufficient EC permeation
Solution Approach 1:
The patent performs initial charging as a preliminary action while EC is still permeating the electrode body, rather than waiting for complete permeation. This allows the process to proceed efficiently without excessive waiting time, while still ensuring uniform SEI film formation because the continuous EC permeation supplies sufficient solvent to all areas during the charging process.
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 ensures uniform SEI film formation across the negative active material layer, reducing resistance and improving the overall performance of power storage devices like lithium-ion batteries by addressing the permeation issues of EC.
Implementation Method 1
when a power storage device includes an electrode body in which an electrolytic solution permeates over a long distance
Implementation Method 2
a permeation speed of EC is relatively slow compared to that of DMC, EMC, or a supporting electrolyte
Implementation Method 3
performing initial charging for forming a negative electrode SEI film in the negative active material layer
Data Source
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AI summary
A method for producing a power storage device (1) includes an electrolytic solution (6) containing ethylene carbonate (6VE) and a solvent (6VL) having a lower melting point than that of the ethylene carbonate (6VE), a wound-type electrode body (2), and a case (7). The electrode body (2) includes a negative active material layer (4A) having a width dimension (AW) of 180 mm or larger. The method includes an injecting step (S3) to inject the electrolytic solution (6) into the case (7) housed therein with a to-be-permeated electrode body (12), a waiting step (S4) to wait for lapse of a predetermined waiting time (TT), and an initial charging step (S5). A to-be-permeated electrode body forming step (S 1) is a step of forming the to-be-permeated electrode body (12) placed in advance with a film-forming material (CS) for forming a negative electrode SEI film (4AC) on a negative active material layer (4A) in a center portion (12M) in an axial direction (XH) in the to-be-permeated electrode body (12).