Binder-Free Positive Electrode With CNT-Rich Collector Interface
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Solution Overview
Problem
Conventional positive electrodes for secondary batteries, despite using carbon nanotubes to reduce resistance, experience a significant increase in resistance during repeated charging and discharging cycles.
Innovation Solution
A positive electrode configuration with a positive-electrode active material layer on a current collector, containing carbon nanotubes with a higher concentration in a layer-like region in contact with the current collector, which reduces initial resistance and prevents resistance increase during cycling, by optimizing the content and thickness of carbon nanotubes in both the layer-like and other regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon nanotubes are used as conductive material and binder to eliminate resin binder, then initial resistance of positive electrode is reduced, but resistance increases significantly when charging and discharging are repeated
Solution Approach 1:
The patent applies local quality by creating a layer-like region at the interface between the positive-electrode active material layer and current collector with a carbon nanotube content of at least 3 mass% and no greater than 10 mass%. This localized high concentration of carbon nanotubes in the layer-like region (which is 5-20% of total layer thickness) provides enhanced conductive pathways and structural stability at the critical interface, preventing resistance increase during cycling while maintaining low initial resistance.
2Reliability
If resin binder is eliminated to reduce resistance, then conductive performance improves, but structural stability and resistance durability deteriorate
Solution Approach 1:
The patent changes the parameter of carbon nanotube concentration from uniform distribution to non-uniform distribution with specific thresholds. The layer-like region contains carbon nanotubes at 3-10 mass% (higher than other regions), and this parameter change creates both the conductive network needed for low resistance and the structural framework for durability during repeated charging and discharging.
Solution Approach 2:
The patent creates a composite structure where carbon nanotubes serve dual functions as both conductive material and binder in the layer-like region. This composite approach eliminates the need for separate resin binder while providing both electrical conductivity and structural stability, as the carbon nanotube network performs multiple functions simultaneously.
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 configuration achieves a significant reduction in initial resistance and effectively suppresses resistance increase during repeated charge-discharge cycles, enhancing the battery's performance and longevity.
Implementation Method 1
carbon nanotubes, which are a conductive component and function as both a conductive material and a binder
Data Source
AI summary
Provided is a positive electrode for a secondary battery in which carbon nanotubes are used, of which an initial resistance is small, and that suppresses an increase in resistance when charging and discharging are repeated. The positive electrode for a secondary battery disclosed herein includes a positive-electrode current collector and a positive-electrode active material layer provided on the positive-electrode current collector. The positive-electrode active material layer contains a positive-electrode active material and carbon nanotubes, and substantially does not contain a resin binder. The positive-electrode active material layer includes a layer-like region that is in contact with the positive-electrode current collector, and a region other than the layer-like region. Both of the layer-like region and the region other than the layer-like region contain carbon nanotubes. A content of carbon nanotubes in the layer-like region is larger than a content of carbon nanotubes in the region other than the layer-like region.