Silicon-Composite Anode Conductivity via CNT-Nanofiber Network
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Solution Overview
Problem
Current composite electrode materials for lithium ion batteries face challenges in achieving high energy density due to the low electric conductivity of metal elements like Si, which results in reduced initial capacity and short charge-discharge cycle life, and require excessive amounts of conductive auxiliary agents, leading to decreased energy density and poor expansion control.
Innovation Solution
A composite electrode material comprising particles capable of intercalating lithium ions, multi-walled carbon nanotubes, and carbon nanofibers, where the carbon nanotubes are entangled with the particles and nanofibers, forming a network that enhances conductivity and maintains electrical pathways during expansion and contraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If particles containing metal elements like Si are used as negative electrode material to achieve high theoretical capacity, then the theoretical capacity increases to 4200 mAh/g, but the electric conductivity is very low and resistance for intercalation and deintercalation of lithium ions is large
Solution Approach 1:
The patent creates a composite electrode material consisting of Si particles dispersed in a carbon matrix. The carbon component provides high electric conductivity while the Si particles provide high theoretical capacity. This composite structure allows the Si particles to maintain their high capacity advantage while the carbon matrix compensates for the low conductivity, enabling both functions to work together effectively.
2Stability of the object's composition
If Si particles are microparticulated in nano order to ease stress from expansion and contraction, then expansion and contraction stress is reduced, but the number of Si particles per unit weight increases requiring large additive amount of electrically conductive auxiliary agent
Solution Approach 1:
The patent applies local quality by creating a carbon matrix with specific properties that surrounds and supports each Si particle. The carbon material is distributed locally around the Si particles, providing conductivity and structural support exactly where needed. This localized approach means the carbon matrix serves multiple functions simultaneously - providing conductivity, supporting the Si particles during expansion/contraction, and maintaining structural integrity - thereby reducing the total amount of conductive auxiliary agent needed compared to uniform distribution approaches.
3Reliability
If carbon nanofibers are used as conductive auxiliary agent, then electric conductivity can be improved, but a large amount of carbon nanofibers needs to be added to construct electrically conductive networks
Solution Approach 1:
The patent combines carbon nanofibers with other carbon materials (such as carbon black or graphite particles) to create a composite conductive network. This composite approach allows the carbon nanofibers to provide their high aspect ratio and conductivity advantages while the other carbon materials fill in the gaps and provide additional conductive pathways, thereby constructing an effective conductive network with less total conductive auxiliary agent compared to using carbon nanofibers alone.
4Length of moving object
If carbon nanotubes are used as conductive auxiliary agent, then high aspect ratio can be achieved, but they easily entangle to form aggregates that are not untangled and electrically conductive networks are hardly assembled
Solution Approach 1:
The patent merges carbon nanotubes with other carbon materials to form a composite conductive network. The other carbon materials (such as carbon black or graphite) act as spacers and connectors that prevent the carbon nanotubes from forming large aggregates. By combining these materials, the carbon nanotubes can maintain their high aspect ratio and conductivity advantages while the composite structure prevents excessive entanglement and aggregate formation, enabling effective conductive network assembly.
5Reliability
If excessive amount of electrically conductive auxiliary agent is added to build electrically conductive networks, then conductivity can be improved, but energy density as an electrode decreases
Solution Approach 1:
The patent uses a composite electrode structure where Si particles (high capacity) are dispersed in a carbon matrix (high conductivity). This composite approach allows the active Si particles to constitute the majority of the electrode mass, maximizing energy density, while the carbon matrix provides sufficient conductivity with minimal amount. The synergistic combination eliminates the need for excessive conductive auxiliary agents, as the carbon matrix itself serves as both the structural framework and the conductive network.
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 composite electrode material significantly reduces electrode resistance, improves energy density, and maintains high capacity over cycles, achieving both high initial capacity and capacity maintenance ratio.
Implementation Method 1
the carbon nanotubes are entangled with the particles and nanofibers, forming a network that enhances conductivity and maintains electrical pathways during expansion and contraction
Implementation Method 2
The composite electrode material significantly reduces electrode resistance
Data Source
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Figure 5
AI summary
Particles (A) comprising an element capable of intercalating and deintercalating lithium ions, carbon particles (B) capable of intercalating and deintercalating lithium ions, multi-walled carbon nanotubes (C), carbon nanofibers (D) and optionally electrically conductive carbon particles (E) are mixed in the presence of shear force to obtain a composite electrode material. A lithium ion secondary battery is obtained using the above composite electrode material.