Silicon Negative Electrode Layering for Stable Conductive Networks
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Solution Overview
Problem
Rechargeable lithium batteries face challenges with high energy density and capacity due to the contraction and expansion of silicon-based active materials in the negative electrode, leading to broken conducting networks and increased charge transfer resistance, which affects ionic and electrical conductivity and cycle-life characteristics.
Innovation Solution
A negative electrode design featuring a current collector, a first layer of crystalline carbon, and a second layer with lithium titanium oxide, silicon-based active material, and carbon nanotubes, where the second layer is thinner than the first, optimizing the aspect ratio of lithium titanium oxide to enhance lithium ion transfer speed and maintain conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based active material is used to increase battery capacity and energy density, then the battery capacity and energy density are improved, but the conducting network is broken due to contraction and expansion during charging and discharging, resulting in increased charge transfer resistance and decreased ionic and electrical conductivity
Solution Approach 1:
The patent uses a composite material system consisting of silicon-based active material particles embedded in a carbonaceous matrix. The carbonaceous material serves as both the matrix and conductive network, while silicon particles provide high capacity. This composite structure allows the carbon matrix to maintain conducting network integrity even when silicon expands and contracts, resolving the contradiction between achieving high capacity and maintaining network stability.
Solution Approach 2:
The patent employs a carbonaceous material matrix that acts as a flexible shell or coating surrounding the silicon-based active material particles. This carbon shell accommodates the volume changes of silicon during lithiation and delithiation while maintaining the overall structural integrity and conducting network connectivity, preventing the network breakdown that would otherwise occur.
2Use of energy by moving object
If amount of silicon in negative electrode is increased to achieve high energy density, then energy density is improved, but charge transfer resistance increases due to broken conducting network
Solution Approach 1:
The patent creates a composite where silicon particles are dispersed within a continuous carbonaceous matrix. This structure allows high silicon content for energy density while the carbon matrix provides uninterrupted conductive pathways, preventing the increase in charge transfer resistance that would normally accompany high silicon loading.
Solution Approach 2:
The carbonaceous material acts as an intermediary between silicon particles and the external circuit. It provides a stable conductive network that mediates electron transport, ensuring low charge transfer resistance even when silicon content is high. The carbon matrix buffers the electrical connection against silicon's volume changes.
3Quantity of substance
If silicon-based active material is used to increase battery capacity, then battery capacity is improved, but cracks occur in silicon creating traps for lithium ions and decreasing contact with lithium ions
Solution Approach 1:
The carbonaceous material forms a flexible shell around silicon particles that accommodates volume expansion during lithiation. This shell prevents crack formation in the silicon while maintaining continuous contact with lithium ions, as the carbon matrix remains intact and conductive throughout the charge-discharge cycles.
Solution Approach 2:
The patent changes the physical state and properties of the matrix material from rigid to flexible by using amorphous or disordered carbon structures. This parameter change allows the matrix to deform elastically with silicon volume changes, preventing crack formation and maintaining lithium ion accessibility without requiring the silicon to maintain a rigid crystalline structure.
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 design achieves excellent ionic and electrical conductivity, high-rate charge and discharge characteristics, and improved cycle-life performance by preventing conductive network deterioration and allowing for higher battery capacity with reduced electrode density.
Implementation Method 1
active material capable of intercalating and deintercalating lithium ions
Implementation Method 2
carbon nanotube
Implementation Method 3
lithium titanium oxide having an aspect ratio of about 10:1 to about 2:1
Implementation Method 4
the battery may generate electrical energy due to the oxidation and reduction reaction if lithium ions are intercalated and deintercalated into the positive electrode and the negative electrode
Data Source
Figure 1
AI summary
A negative electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same are provided, and the negative electrode includes a current collector; a first layer including crystalline carbon; and a second layer including lithium titanium oxide having an aspect ratio of about 10:1 to about 2:1, a Si-based active material, and carbon nanotube, wherein the first layer is positioned between the current collector and the second layer and the second layer is thinner than the first layer.