Solvent-Based Binder and No-Pressing for Graphite Anode Capacity Retention
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Solution Overview
Problem
Energy storage devices with carbon-based negative active materials and water-based binders, such as SBR, exhibit low capacity retention ratios when charged, due to uneven ion migration and reaction issues caused by the binder's low swellability and resistance characteristics, as well as potential surface peeling and stress-related expansion during the manufacturing process.
Innovation Solution
The use of graphite as a negative active material with a solvent-based binder in the energy storage device, avoiding pressing of the negative active material layer to maintain uniform ion migration and suppress reaction unevenness, thereby enhancing capacity retention. Additionally, the ratio of surface roughness with and without the active material layer is maintained at 0.90 or more to ensure consistent performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a water-based binder (SBR) is used in the negative active material layer, then the manufacturing process is simplified, but the capacity retention ratio deteriorates due to low swellability and high resistance causing uneven ion migration
Solution Approach 1:
The invention changes the binder type from water-based (SBR) to solvent-based binder, which has different swelling characteristics and resistance properties. This parameter change enables uniform ion migration throughout the negative active material layer, significantly improving capacity retention ratio while maintaining ease of manufacture through similar application processes
2Ease of manufacture
If the negative active material layer is subjected to pressing during manufacturing, then the manufacturing process follows conventional methods, but the capacity retention ratio deteriorates due to uneven expansion and peeling
Solution Approach 1:
The invention extracts the pressing step from the conventional manufacturing process. By eliminating the pressing operation, the negative active material layer maintains its uniform structure without experiencing the uneven expansion and peeling that would otherwise occur, thereby improving capacity retention ratio while still allowing for straightforward manufacturing
3Ease of manufacture
If a water-based binder is used, then the manufacturing process is conventional, but surface peeling and stress-related expansion occur reducing durability
Solution Approach 1:
The invention changes the binder chemistry from water-based to solvent-based, which fundamentally alters the swelling behavior and adhesion properties. This parameter change prevents surface peeling and stress-related expansion by ensuring uniform distribution and binding of the negative active material, thereby improving durability and compositional stability
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 configuration results in a high capacity retention ratio for the energy storage device after being left in a charged state, with improved charge-discharge performance and reduced material deterioration, as the solvent-based binder ensures uniform ion migration and the absence of pressing prevents uneven expansion and peeling.
Implementation Method 1
uniform ion migration
Data Source
AI summary
An energy storage device according to one aspect of the present invention is an energy storage device including a negative electrode having a negative electrode substrate and a negative active material layer stacked on the negative electrode substrate directly or via another layer, and a nonaqueous electrolyte solution, in which the negative active material layer contains graphite and a solvent-based binder, and the negative active material layer is not subjected to pressing.