Silicon-Graphite Composite Anode for Li-Ion Battery Capacity
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Solution Overview
Problem
Lithium ion batteries using graphite as negative electrodes face limitations in initial charge and discharge efficiency, capacity, and cycle characteristics due to the low electric conductivity and significant volume changes of silicon and tin particles during lithium intercalation and deintercalation.
Innovation Solution
A composite negative electrode material comprising silicon-containing particles, graphitic carbon material particles, and a carbonaceous carbon material, with specific ratios and properties optimized to reduce oxidization and enhance conductivity, is developed, including a surface layer of SiOx and a carbonaceous carbon material to buffer volume changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon or tin particles are used as negative electrode material to increase capacity, then charge and discharge capacity is improved, but electric conductivity decreases and volume change increases causing particle breakage
Solution Approach 1:
The patent uses composite materials consisting of silicon particles (5-50 nm) embedded in a carbonaceous matrix. The carbonaceous material provides structural stability and electrical conductivity while the silicon particles provide high capacity. This composite structure resolves the contradiction by combining materials with complementary properties - silicon for capacity and carbon for stability and conductivity.
Solution Approach 2:
The carbonaceous material forms a flexible matrix that accommodates the volume expansion of silicon particles during lithium insertion. The carbon shell/constraint structure allows the silicon to expand and contract without breaking, maintaining structural integrity and continuous electrical contact throughout charge-discharge cycles.
2Reliability
If graphite is used as negative electrode material to ensure structural stability, then reliability is improved, but charge and discharge capacity is limited
Solution Approach 1:
The patent creates a composite where silicon particles (high capacity) are dispersed in a carbonaceous matrix (stable structure). The carbonaceous material includes graphitic and non-graphitic components that provide structural stability similar to pure graphite, while the silicon particles contribute high capacity, achieving both reliability and high capacity simultaneously.
Solution Approach 2:
The electrode structure has local quality variations - silicon particles provide high capacity in specific localized regions, while the surrounding carbonaceous matrix provides structural stability and conductivity. This local differentiation allows the electrode to exhibit both high capacity and stability at the macro level.
3Duration of action of stationary object
If silicon particle size is reduced to improve capacity retention, then charge and discharge cycle characteristics are improved, but electric conductivity further decreases
Solution Approach 1:
The composite material combines ultra-fine silicon particles (5-50 nm) with carbonaceous material. The carbonaceous component acts as a conductive network that compensates for the low conductivity of fine silicon particles. The carbon matrix provides continuous conductive pathways, ensuring adequate electrical conductivity even when silicon particles are reduced to nanometer scale for improved cycle characteristics.
Solution Approach 2:
The carbonaceous material serves as an intermediary between silicon particles, providing both structural support and electrical conductivity. It mediates the electrical contact between isolated silicon nanoparticles, creating a percolating conductive network that maintains overall electrode conductivity despite the small size and low individual conductivity of silicon particles.
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 achieves low initial irreversible capacity, high initial charge and discharge efficiency, large capacity, and excellent charge and discharge cycle characteristics, balancing capacity retention and efficiency.
Implementation Method 1
a volume change associated with intercalation and deintercalation of lithium ions is large
Implementation Method 2
graphitic carbon material particles and a carbonaceous carbon material... to enhance conductivity
Data Source
AI summary
A lithium ion battery is obtained by using a negative electrode material for lithium ion battery comprises a composite material comprising silicon-containing particles, graphitic carbon material particles, and a carbonaceous carbon material, in which the composite material has a ratio (A/B) of an area (A) of a peak near 100 eV derived from metal Si to an area (B) of a peak near 103 eV derived from silicon oxide, as measured by XPS, of not less than 0.10 and not more than 2.30.