Silicon Composite Anode with Crosslinked SWCNTs for Stable Conductivity
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Solution Overview
Problem
Silicon-based negative electrode active materials in lithium secondary batteries face issues with volume expansion and contraction during charging and discharging, leading to electrical short circuits and reduced lifetime and capacity due to the disappearance of charge transfer pathways and lithium ion trapping.
Innovation Solution
A composite negative electrode active material is developed, comprising a silicon-based core particle with an outer carbon coating layer, first single-walled carbon nanotubes protruding from the coating layer, a conductive structure of second single-walled carbon nanotubes crosslinked by a crosslinking material, which forms a stable conductive network preventing electrical short circuits and enhancing lifetime characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electrode active material is used to achieve high capacity, then capacity is improved, but volume expansion during charging and discharging causes electrical short circuits and reduced lifetime
Solution Approach 1:
The silicon-based active material is divided into particles with controlled size and shape, and further segmented into core-shell structure where the silicon core is separated from the electrolyte by a protective shell, preventing direct contact that causes short circuits while maintaining high capacity
Solution Approach 2:
The patent employs a core-shell structure where the silicon-based active material forms the core and is nested within a protective shell material. This nested configuration allows the high-capacity silicon core to be isolated from harmful environmental factors while maintaining its electrochemical activity, thus improving lifetime characteristics without sacrificing capacity
2Quantity of substance
If silicon-based active material undergoes volume expansion during charging, then capacity is improved, but charge transfer pathways disappear and lithium ions are trapped
Solution Approach 1:
The patent applies preliminary coating of the silicon-based active material particles with a protective shell before electrode assembly. This preliminary protective layer prevents electrical short circuits and maintains charge transfer pathways during subsequent volume expansion, ensuring both high capacity and safe operation
Solution Approach 2:
The protective shell acts as an intermediary layer between the silicon-based active material and the electrolyte. This intermediary structure accommodates volume expansion while maintaining electrical connectivity and preventing direct contact that would cause short circuits, thus resolving the contradiction between capacity and safety
3Reliability
If conventional carbon-based negative electrode active material is used, then lifetime characteristics are improved, but capacity is only about 1/10 of silicon-based materials
Solution Approach 1:
The patent creates a composite structure combining silicon-based active material (providing high capacity) with protective shell material (providing stability and preventing short circuits). This composite approach achieves both high capacity comparable to silicon and improved lifetime characteristics, overcoming the limitations of conventional carbon-based materials
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 material effectively prevents electrical short circuits and improves the lifetime and capacity of lithium secondary batteries by maintaining stable electrical contact and conductive networks even during volume changes of the active material, thus enhancing the battery's performance.
Implementation Method 1
a crosslinking material bonded to the first single-walled carbon nanotube and at least one of the second single-walled carbon nanotubes, wherein the at least one of the second single-walled carbon nanotubes is crosslinked with the first single-walled carbon nanotube by the crosslinking material
Data Source
Figure 1~2
Figure 3
AI summary
Provided is a composite negative electrode active material, which includes: a silicon-based core particle; an outer carbon coating layer positioned on the silicon-based core particle; first single-walled carbon nanotubes in contact with the outer carbon coating layer, wherein the first single-walled carbon nanotubes protrude from the outer carbon coating layer; a conductive structure spaced apart from the outer carbon coating layer and including second single-walled carbon nanotubes; and a crosslinking material bonded to the first single-walled carbon nanotube and at least one of the second single-walled carbon nanotubes, wherein the at least one of the second single-walled carbon nanotubes is crosslinked with the first single-walled carbon nanotube by the crosslinking material, and wherein the conductive structure and the first single-walled carbon nanotube are connected to each other.