Wide Negative Electrode SEI Control for Thermal-Stable Li-Ion Batteries
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Solution Overview
Problem
Nonaqueous electrolyte solution secondary batteries with higher capacity face challenges in uniform film formation on the negative electrode active material layer, leading to uneven reactivity and decreased thermal stability, particularly at the central part of the electrode, resulting in increased heat generation during overcharging.
Innovation Solution
Incorporating a boron element into the negative electrode active material layer and employing a specific manufacturing and inspection method that includes initial charging and aging steps under controlled temperature conditions to adjust the black unevenness index to 12 or less, ensuring uniform film formation and improved thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the electrode body width is increased to 15 cm or more to achieve higher capacity, then the battery capacity is improved, but the additive permeation becomes insufficient in the central part, causing uneven film formation and decreased thermal stability
Solution Approach 1:
An aging process is performed before final battery assembly to pre-form the SEI film on the negative electrode. This preliminary action ensures that the film is formed uniformly across the entire electrode surface, including the central part that would otherwise be difficult to reach during normal operation. The aging process involves charging the electrode to a specific state of charge and maintaining it for a predetermined period, allowing the additive to decompose and form the protective film in advance.
Solution Approach 2:
The state of charge (SOC) is controlled within a specific range of 5% to 50% during the aging process. By optimizing this parameter, the film formation is promoted uniformly across the electrode. Additionally, the aging temperature is controlled at 50°C or higher to accelerate the film formation reaction and improve permeation into the central part of the electrode, thereby resolving the thermal stability issue while maintaining high capacity.
2Ease of manufacture
If conventional film formation methods are used, then the manufacturing process is simple, but the film formation is uneven in the central part of the electrode, leading to increased heat generation
Solution Approach 1:
The aging process is introduced as a preliminary step before battery assembly to pre-form the SEI film. This approach maintains manufacturing simplicity by using a straightforward charging and holding process, while effectively preventing uneven film formation and the associated heat generation problems in the central electrode region.
Solution Approach 2:
By controlling the SOC within 5%-50% and maintaining the temperature at 50°C or higher during aging, the film formation is optimized to be uniform across the electrode. This parameter control prevents the formation of defective films that would otherwise lead to localized high reactivity and heat generation during battery operation.
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
The method effectively suppresses heat generation and enhances thermal stability, providing a battery with reliable performance by objectively measuring and adjusting the black unevenness index, which correlates with heat generation quantity.
Implementation Method 1
at initial charging, a part of the nonaqueous electrolyte solution is decomposed and a film including a decomposition product thereof (solid electrolyte interface film: SEI film) is deposited on a surface of a negative electrode active material layer
Implementation Method 2
a surface of the negative electrode is photographed with a camera so as to include a central part of the negative electrode active material layer in a width direction and photographed image data expressed in an RGB color model is acquired
Data Source
AI summary
A nonaqueous electrolyte solution secondary battery disclosed herein includes an electrode body that includes a positive electrode including a positive electrode active material layer and a negative electrode including a negative electrode active material layer, and a nonaqueous electrolyte solution. The negative electrode active material layer has a width of 15 cm or more and includes a film containing a boron element, and a black unevenness index is 12 or less.