Composite Anode Active Material with Dual Graphite for Stable Conductivity
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Solution Overview
Problem
Existing high-capacity silicon-carbon composite materials for anode active materials in lithium secondary batteries face issues with reduced silicon particle size and conductivity degradation, leading to volume expansion and sudden efficiency drops during charging and discharging cycles.
Innovation Solution
A composite anode active material is developed, comprising a silicon-carbon composite with large-particle graphite and a specific structure, including a porous silicon composite cluster coated with carbon, and mixed with artificial and natural graphite, maintaining a balanced particle diameter ratio and density to enhance silicon dispersion and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon particle size is reduced to increase capacity, then energy density is improved, but conductivity deteriorates and volume expansion occurs
Solution Approach 1:
The patent uses a composite material structure where silicon particles are embedded in a graphite matrix. The graphite component provides structural stability and conductivity pathways, while the silicon particles provide high capacity. This composite approach allows the silicon to expand and contract during lithiation/delithiation without losing electrical contact, thus maintaining conductivity while achieving high energy density.
Solution Approach 2:
The graphite matrix acts as a flexible shell or matrix that accommodates the volume expansion of silicon particles during charging. The graphite structure can elastically deform to absorb the expansion stress, preventing particle disintegration and maintaining the integrity of the conductive network throughout the battery cycle.
2Quantity of substance
If silicon particle size is reduced to increase capacity, then energy density is improved, but particle disintegration occurs during cycling
Solution Approach 1:
The composite structure of silicon particles embedded in graphite provides both high capacity and particle stability. The graphite matrix reinforces the silicon particles, preventing them from disintegrating during the repeated expansion and contraction cycles. This is achieved through the strong interfacial bonding between silicon and graphite while maintaining the ability to accommodate volume changes.
Solution Approach 2:
The graphite matrix serves as a flexible shell that surrounds and protects the silicon particles. This shell can elastically deform to accommodate the volume expansion of silicon during lithiation, preventing particle disintegration while maintaining structural integrity throughout the battery's charge-discharge cycles.
3Reliability
If graphite particle diameter is increased to improve conduction pathways, then conductivity is improved, but surface area for lithium intercalation decreases
Solution Approach 1:
The patent applies local quality by having different graphite particle sizes in different regions of the anode. Larger graphite particles provide long-range conductivity pathways, while smaller graphite particles provide high surface area for lithium intercalation. This spatial differentiation of particle sizes allows the system to simultaneously achieve both high conductivity and high reactive surface area.
Solution Approach 2:
The graphite component is segmented into multiple particle size fractions that are distributed throughout the anode structure. This segmentation allows different size classes to perform different functions: larger particles for conductivity and smaller particles for surface area, thereby resolving the contradiction between these two requirements.
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 superior lifespan characteristics and battery efficiency by preventing particle disintegration, increasing conductivity, and maintaining uniform conduction pathways, thus overcoming early cycle deterioration.
Implementation Method 1
silicon particles are reduced in particle size and thus conductivity is degraded, resulting in volume expansion
Implementation Method 2
a carbon coating film including amorphous carbon on the porous silicon composite cluster
Implementation Method 3
oxidation/reduction reactions of lithium ions which are intercalated/deintercalated in a cathode and an anode
Implementation Method 4
a porous silicon composite cluster including a porous core including a porous silicon composite secondary particle
Data Source
AI summary
A composite anode active material, an anode, and a lithium secondary battery, the composite anode active material including a silicon-carbon composite; a first graphite; and a second graphite that is different from the first graphite, wherein the first graphite has an average particle diameter D50 of about 10 μm or greater, and the second graphite has an average particle diameter D50 of about 18 μm or greater.