Electrode Undercoat Composition for Adhesion and Ion Migration Control
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Solution Overview
Problem
Lithium ion secondary batteries face issues with adhesiveness of binders to current collectors, leading to material stripping and increased contact resistance, which affects battery capacity and safety, and ion migration from current collectors causing early device deterioration.
Innovation Solution
A thin film forming composition comprising conductive carbon material, a heterocyclic compound with two or more nitrogen atoms, a dispersant, and a solvent is used to form an undercoat layer that enhances adhesion and suppresses ion migration between the current collector and electrode mixture layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional binder is used to bond active material and conductive material to the current collector, then the electrode structure is formed, but the adhesiveness is insufficient causing material stripping and increased contact resistance
Solution Approach 1:
A conductive undercoat layer is introduced as an intermediary between the current collector and the electrode mixture layer. This undercoat layer comprises a binder and conductive filler, where the binder provides strong adhesion to the current collector and the conductive filler ensures low contact resistance. This intermediary layer resolves the contradiction by simultaneously achieving both strong bonding and low electrical resistance that a single conventional binder cannot provide.
Solution Approach 2:
The undercoat layer is formed as a composite material combining a binder (such as polyvinylidene fluoride or carboxymethyl cellulose) with conductive filler (such as carbon black or carbon nanotubes). This composite structure allows the binder to provide mechanical adhesion while the conductive filler provides electrical conductivity, thereby simultaneously improving both adhesiveness and contact resistance.
2Duration of action of stationary object
If the binder swells by the electrolyte solution during long-term use, then the electrode mixture volume changes, but this causes increased contact resistance and material stripping leading to battery capacity deterioration
Solution Approach 1:
The conductive undercoat layer acts as a cushioning layer between the current collector and the electrode mixture layer. During long-term use, when the binder swells and the electrode mixture volume changes, this undercoat layer absorbs and distributes the mechanical stress, preventing direct contact loss between the electrode mixture and current collector. This beforehand cushioning effect maintains stable electrical contact and prevents material stripping, thereby preserving battery capacity over time.
3Reliability
If a conductive undercoat layer is introduced to reduce contact resistance, then adhesion between current collector and electrode mixture is improved, but the device complexity increases
Solution Approach 1:
The conductive undercoat layer is applied as a preliminary coating on the current collector surface before the electrode mixture layer is formed. This preliminary action ensures that the current collector surface is pre-equipped with both adhesive and conductive properties, simplifying the subsequent electrode fabrication process. The undercoat layer is applied in advance using conventional coating methods, making the overall process manageable despite the additional layer.
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 composition effectively reduces ion migration and improves adhesion, thereby enhancing the stability and performance of lithium ion secondary batteries by maintaining battery capacity and safety over time.
Implementation Method 1
a heterocyclic compound including two or more nitrogen atoms constituting a ring... effectively reduces ion migration
Implementation Method 2
a conductive carbon material... reduces the resistance of a battery by increasing the adhesion
Implementation Method 3
The binder is used for bonding the active material, the conductive material, and the metal foil to each other
Data Source
AI summary
Provided is a composition, which is for forming a thin film for an energy storage device electrode and contains a conductive carbon material, a heterocyclic compound containing at least two nitrogen atoms constituting a ring, a dispersant, and a solvent, as a composition which is for forming a thin film for an energy storage device electrode and can be suitably used for forming a conductive thin film, and from which an undercoat layer exhibiting the effect of suppressing migration can be provided, in particular, in an energy storage device.