Positive Electrode CNT Purification by Magnetic Metal Separation
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Solution Overview
Problem
Existing methods for improving the conductivity of carbon nanotubes (CNTs) in positive electrodes of secondary batteries, such as oxidation in nitric acid or magnetic separation, can damage the CNT structure or leave residual catalytic metals, leading to suboptimal electrical conductivity and battery output characteristics.
Innovation Solution
A method involving the preparation of a CNT paste with a dispersing agent, followed by magnetic separation to remove metals from the CNTs without damaging them, and subsequent mixing with a positive electrode active material and binder to form a conductive layer on a current collector, ensuring improved conductivity and output characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oxidation in nitric acid solution is used to open end portions of CNTs, then conductivity is improved, but CNT structure is damaged and electrical conductivity is lowered
Solution Approach 1:
The patent extracts catalytic metals from inside CNTs using magnetic separation, removing the harmful impurities without chemically treating or damaging the CNT structure. This extraction approach improves conductivity by eliminating metal contaminants while preserving the intact CNT framework, avoiding the structural damage caused by oxidation methods.
Solution Approach 2:
The patent replaces the chemical oxidation method with a physical magnetic separation method. Instead of using chemical reactions (oxidation in nitric acid) to open CNT ends, the invention uses magnetic fields to selectively remove metal particles from CNTs, substituting a mechanical/physical process for a chemical one that damages the CNT structure.
2Reliability
If magnetic separation method is used to remove catalytic metals, then metal removal is achieved, but large amount of catalytic metal remains inside CNT tubes
Solution Approach 1:
The patent performs preliminary action by opening the CNT end portions through controlled oxidation before magnetic separation. This preliminary step creates openings in the CNT structure that allow magnetic fields to penetrate and access metals trapped inside the CNT tubes, enabling more effective metal removal in subsequent magnetic separation steps.
Solution Approach 2:
The patent implements continuous metal removal through repeated cycles of oxidation and magnetic separation. Instead of relying on a single magnetic separation step, the invention performs multiple sequential treatments, each cycle further reducing metal content until the desired purity is achieved, ensuring complete removal of both surface and internal metals.
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 approach enhances the conductivity of CNTs by removing metals while maintaining their structure, resulting in improved output characteristics and performance of secondary batteries, specifically reducing output resistance and enhancing Li ion mobility.
Implementation Method 1
a carbon nanotube (CNT) paste preparation step of preparing a CNT paste containing at least CNTs and a dispersing agent
Implementation Method 2
a magnetic separation step of exerting a magnetic force on the CNT paste to adsorb metal existing inside the CNTs and separating the CNTs and the metal
Data Source
AI summary
A method for manufacturing a positive electrode disclosed here includes: a CNT paste preparing step of preparing a CNT paste containing at least carbon nanotubes (CNT) and a dispersing agent; a magnetic separating step of exerting a magnetic force on the CNT paste to adsorb metal existing inside the CNTs and separating the CNTs and the metal; a positive electrode active material layer forming paste preparing step of mixing the CNTs subjected to the magnetic separating step, a positive electrode active material, and a binder to prepare a positive electrode active material layer forming paste; and a positive electrode active material layer forming step of applying the prepared positive electrode active material layer forming paste to a positive electrode current collector to form a positive electrode active material layer on the positive electrode current collector.