Silicon Negative Electrode Layer Structure for Stable High-Rate Batteries
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Solution Overview
Problem
Rechargeable lithium batteries face challenges with the negative active material, particularly due to the contraction and expansion of silicon, which leads to broken conducting networks, lithium ion trapping, and increased charge transfer resistance.
Innovation Solution
A negative electrode for rechargeable lithium batteries is designed with a current collector, a first layer of crystalline carbon, and a second layer containing lithium titanium oxide, a Si-based active material, and carbon nanotubes, where the second layer is thinner than the first layer, optimizing ionic and electrical conductivity and high-rate charge/discharge characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If silicon-based active material is used to increase capacity, then energy density is improved, but conducting network is broken due to contraction and expansion
Solution Approach 1:
The patent uses a composite structure combining silicon-based active material with crystalline carbon and amorphous carbon. The carbon components form a stable conducting network that maintains electrical connectivity even when silicon expands and contracts during charging and discharging cycles, thus preserving both high energy density and network integrity
Solution Approach 2:
The patent employs an amorphous carbon coating layer that acts as a flexible buffer around the silicon-based active material. This thin film accommodates the volume changes of silicon during lithiation and delithiation, preventing crack formation and maintaining the conducting network while allowing high silicon content for increased capacity
2Use of energy by moving object
If silicon-based active material is used to increase capacity, then energy density is improved, but cracks occur creating lithium ion traps
Solution Approach 1:
The amorphous carbon coating serves as a flexible shell that conforms to the expanding and contracting silicon particles. This flexible layer prevents crack formation that would otherwise create traps for lithium ions, while still allowing efficient lithium ion transport to and from the silicon active material
Solution Approach 2:
The patent utilizes the porous structure of amorphous carbon that provides pathways for lithium ion diffusion. The porous network allows lithium ions to access the silicon particles without being trapped in cracks, maintaining fast ion transport kinetics while enabling high capacity
3Use of energy by moving object
If silicon-based active material is used to increase capacity, then energy density is improved, but charge transfer resistance increases
Solution Approach 1:
The composite of silicon-based active material with conductive carbon components creates a synergistic structure where the carbon phases provide efficient electron transport pathways. This reduces charge transfer resistance at the electrode-electrolyte interface while maintaining the high capacity benefits of silicon, enabling both high energy density and low resistance
Solution Approach 2:
The amorphous carbon coating acts as an intermediary layer between the silicon-based active material and the electrolyte. This intermediate phase facilitates charge transfer by providing a conductive interface that reduces resistance, while also protecting the silicon from direct contact with the electrolyte that would cause side reactions
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 configuration enhances ionic conductivity, electrical conductivity, and high-rate charge/discharge capabilities, while maintaining cycle-life characteristics, thus improving the overall performance of rechargeable lithium batteries.
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
contraction and expansion of silicon during charging and discharging
Data Source
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.