CNT-Binder Negative Electrode Structure for Stable Battery Cycling
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Solution Overview
Problem
Metal-based active material particles in non-aqueous electrolyte secondary batteries, such as SiOx, are less conductive and undergo significant expansion and shrinkage during charge and discharge, leading to deterioration of conductive paths and degradation of cycling performance, even when carbon nanotubes are used to form conductive paths.
Innovation Solution
A negative electrode with an active material layer comprising metal-based and carbon-based active material particles, carbon nanotubes, and a first binder, where the carbon nanotubes have an average length of 1.5 μm or more, and at least part of the first binder is not mixed with the carbon nanotubes, allowing them to cover the surface of the active material particles and form good conductive paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon nanotubes are used to form conductive paths between metal-based active material particles, then electrical conductivity is improved, but the conductive paths are easily deteriorated due to expansion and shrinkage of metal-based particles during charge and discharge
Solution Approach 1:
The patent introduces a binder as an intermediary substance between the metal-based active material particles and carbon nanotubes. This binder absorbs the mechanical stress from expansion and shrinkage of metal particles, preventing direct transmission of stress to the carbon nanotube conductive paths. The binder layer acts as a cushion that maintains the structural integrity of the conductive network while accommodating volume changes of the active material.
Solution Approach 2:
The patent creates a composite structure consisting of metal-based active material particles, carbon nanotubes, and binder materials working together. The carbon nanotubes provide electrical conductivity, the binder provides mechanical stability and stress absorption, and the metal particles provide electrochemical activity. This composite approach allows each component to fulfill its specific function while compensating for the weaknesses of other components, particularly protecting the conductive paths from degradation.
2Reliability
If carbon nanotubes are mixed with binder uniformly, then manufacturing process is simplified, but carbon nanotubes cannot effectively connect active material particles due to being covered by binder
Solution Approach 1:
The patent applies local quality by creating different mixing states in different regions of the slurry. Carbon nanotubes are kept relatively free from binder coverage in critical regions where they need to connect active material particles, while binder is present in other regions for structural support. This spatial variation in mixing quality ensures that carbon nanotubes maintain their conductive function while the binder provides mechanical stability where needed.
Solution Approach 2:
The patent uses partial mixing rather than complete uniform mixing of carbon nanotubes and binder. By controlling the mixing process to achieve only partial incorporation of binder with carbon nanotubes, the patent ensures that enough carbon nanotubes remain exposed and available to form conductive bridges between active material particles, while still having sufficient binder for structural support. This partial action approach balances conductive path formation with mechanical 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
The proposed negative electrode structure enhances the cycling performance of non-aqueous electrolyte secondary batteries by maintaining the integrity of conductive paths and reducing degradation, even with metal-based active material particles that undergo significant volume changes.
Implementation Method 1
Carbon nanotubes connect active material particles to each other and thereby can form good conductive paths
Implementation Method 2
first carbon nanotubes adhered to and lying over the first binder that is not mixed with the carbon nanotubes and covers a surface of the active material particle
Data Source
AI summary
A negative electrode has an active material layer including active material particles, carbon nanotubes (CNTs), and a first binder. The active material particles include metal-based active material particles and carbon-based active material particles. An average length of the CNTs determined by analysis of a scanning transmission electron microscope image of the active material layer is 1.5 μm or more. At least part of the first binder is not mixed with the CNTs and covers at least part of a surface of the active material particle. The CNTs include first CNTs adhered to and lying over the first binder, and second CNTs each connecting a pair of the active material particles to each other.