Silicon-Graphite Composite Anode for Lithium Battery Capacity Retention
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Solution Overview
Problem
Conventional lithium secondary battery negative electrodes using carbon-based materials face limitations in capacity and cycle characteristics due to volume changes during charging and discharging, leading to reduced battery life, while metal-based materials suffer from conductivity issues and poor cycle performance.
Innovation Solution
A negative electrode composition comprising 3-9% silicon-based active material with a specific atomic composition and 87.5-95.5% graphite-based active material, along with a thickener and binder, optimized with carbon nanotubes to enhance capacity retention and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If metal-based negative-electrode active materials (such as silicon) are used to achieve high capacity and high energy density, then the battery capacity and energy density are improved, but the cycle characteristics deteriorate due to volume change during charging and discharging
Solution Approach 1:
The patent applies amorphous carbon coating as a flexible shell around metal-based negative electrode active materials. This amorphous carbon layer accommodates the volume expansion and contraction of silicon during lithiation and delithiation, preventing particle cracking and maintaining structural integrity over multiple charge-discharge cycles. The amorphous structure of carbon provides flexibility to absorb volume changes while maintaining electrical conductivity.
Solution Approach 2:
The patent creates composite materials by combining metal-based negative electrode active materials (such as silicon) with carbon-based materials (graphite, amorphous carbon). This composite structure leverages the high capacity of metal-based materials while the carbon component provides structural stability and conductivity. The composite approach allows the metal particles to expand into the carbon matrix without causing electrode degradation.
2Quantity of substance
If pure silicon is used as negative-electrode active material to achieve high theoretical capacity of 4017 mAh/g, then the capacity is improved, but conductivity deteriorates and electrode active material peels from current collector due to volume expansion to 300-400%
Solution Approach 1:
An amorphous carbon coating is applied as a flexible shell around silicon particles. This thin film accommodates the 300-400% volume expansion of silicon during lithiation while maintaining structural integrity. The amorphous carbon layer prevents particle cracking, maintains electrical conductivity pathways, and anchors the silicon particles to the current collector, preventing peeling during cycling.
Solution Approach 2:
The patent changes the physical and chemical parameters of the carbon material by using amorphous carbon instead of crystalline carbon. The amorphous structure provides greater flexibility and tolerance to volume changes. Additionally, the carbon content and structure are optimized to balance conductivity, flexibility, and mechanical strength to maintain adhesion during extreme volume expansion.
3Quantity of substance
If carbon-based active material is used to achieve high capacity with theoretical limit of 372 mAh/g, then the capacity is improved, but the capacity is insufficient for high capacity lithium battery development
Solution Approach 1:
The patent develops composite negative electrode materials combining metal-based active materials (silicon, germanium, tin) with carbon-based materials (graphite, amorphous carbon). This composite approach enables the battery to exceed the theoretical capacity limit of pure carbon materials. The metal-based particles provide high capacity (silicon: 4017 mAh/g) while the carbon matrix provides structural support and conductivity, achieving overall capacities beyond 372 mAh/g.
Solution Approach 2:
The patent applies different materials with different functions in specific locations: metal-based particles (such as silicon) are distributed throughout the electrode to provide high capacity, while carbon-based materials form the matrix and coating to provide structural stability and conductivity. This local differentiation of material properties allows the electrode to achieve high overall capacity while maintaining stability.
4Use of energy by moving object
If metal-based negative-electrode active materials are used to achieve high energy density, then the energy density is improved, but cycle life reduces due to cracks in active material causing electrical insulation
Solution Approach 1:
An amorphous carbon coating is applied as a protective flexible shell around metal-based negative electrode particles. This shell accommodates volume expansion and contraction during cycling, preventing particle cracking that would otherwise cause electrical insulation and capacity loss. The flexible carbon layer maintains electrical conductivity pathways even during extreme volume changes, preserving battery life while enabling high energy density.
Solution Approach 2:
The amorphous carbon coating is applied beforehand to the metal-based particles before electrode assembly. This pre-applied coating acts as a cushion that absorbs the mechanical stress of volume expansion during lithiation, preventing cracks from forming in the metal particles. This beforehand protection ensures long-term electrical conductivity and structural integrity throughout the battery's operational life.
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 solution achieves high negative electrode efficiency and excellent capacity retention, maintaining performance even after 50 charge/discharge cycles with improved expansion characteristics and structural stability.
Implementation Method 1
the silicon contained in the negative-electrode active material absorbs lithium during charging and thus expands to about 300 to 400% of its original volume
Implementation Method 2
When lithium is released, the inorganic particles thereof shrink
Data Source
AI summary
The present disclosure is to provide a negative electrode for a lithium secondary battery having high negative electrode efficiency and excellent capacity retention, and a lithium secondary battery including the negative electrode. In one aspect, there is provided a negative electrode for a lithium secondary battery, wherein the electrode contains 3 to 9% by weight of a silicon-based negative-electrode active material having a following composition formula (1); and 87.5 to 95.5% by weight of a graphite-based negative-electrode active material:SixTiyFezAlu (1)where x, y, z and u are atomic %, x: 1−(y+z+u), y: 0.09 to 0.14, z: 0.09 to 0.14, u: 0.01 exclusive to 0.2 exclusive.