Silicon Nanowire Anode Structure for Volume-Change Stability
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Solution Overview
Problem
Lithium-ion secondary batteries using silicon as a negative electrode active material face issues with deformation and breakage due to volume changes during charge and discharge cycles, leading to reduced reliability and capacity.
Innovation Solution
A negative electrode is fabricated with a current collector and an active material layer comprising silicon nanowires grown with graphene and polyimide, where graphene is in contact with the nanowires and polyimide, preventing deformation and breakage by direction-dependent volume changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as a negative electrode active material to increase capacity, then the theoretical capacity increases significantly (4200 mAh/g vs 372 mAh/g for carbon), but the volume changes during charge and discharge cycles cause deformation and breakage of silicon
Solution Approach 1:
The silicon is divided into fine particles with a maximum diameter of 50 μm, and further into nanowire structures. This segmentation reduces the overall volume change impact on the electrode structure and prevents large-scale deformation and breakage while maintaining high capacity.
Solution Approach 2:
The patent uses a composite structure where silicon particles are combined with carbon materials (graphite, carbon black) and binder resins. The carbon components provide structural stability and conductivity while the silicon provides high capacity, creating a balanced composite that maintains both performance and reliability.
2Quantity of substance
If the number of received carrier ions is increased to enhance capacity, then the theoretical capacity increases, but the adhesion between current collector and silicon deteriorates due to volume expansion and contraction
Solution Approach 1:
The silicon particles are pre-treated by forming them into fine particles with controlled size (maximum diameter ≤ 50 μm) before electrode fabrication. This preliminary size control prevents excessive volume expansion that would cause adhesion loss, while still allowing sufficient carrier ion reception for high capacity.
Solution Approach 2:
The use of binder resins and carbon materials forms a flexible matrix around the silicon particles that can accommodate volume changes during charge-discharge cycles. This flexible structure maintains adhesion between the silicon and current collector even when carrier ion reception causes expansion.
3Quantity of substance
If silicon particles are used as active material, then high capacity is achieved, but deformation and breakage occur during repeated charge and discharge cycles
Solution Approach 1:
Dividing silicon into fine particles (maximum diameter ≤ 50 μm) and nanowire structures segments the material into smaller units that experience reduced stress during volume changes. This prevents crack propagation and maintains structural integrity over many charge-discharge cycles while preserving high capacity.
Solution Approach 2:
Combining silicon with carbon materials and binder resins creates a composite structure where the carbon and resin components provide mechanical strength and flexibility. This composite approach enables the electrode to withstand repeated cycling without deformation or breakage of the silicon particles, ensuring long-term cycle stability.
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 enhances the reliability and charge-discharge capacity of lithium-ion secondary batteries by preventing silicon deformation and breakage, maintaining battery performance over multiple cycles.
Implementation Method 1
a negative electrode active material layer including a negative electrode active material, graphene, and polyimide is formed over a negative electrode current collector
Implementation Method 2
a material capable of receiving and releasing lithium ions is used as an active material for a positive electrode and a negative electrode
Data Source
AI summary
A highly reliable electrode for a lithium-ion secondary battery is provided. A highly reliable lithium-ion secondary battery is also provided using the electrode for a lithium-ion secondary battery. The electrode for a lithium-ion secondary battery includes a current collector and an active material layer. The active material layer includes an active material, graphene, and polyimide. The active material includes a plurality of nanowires each of which grows with a silicon particle used as a nucleus and extends in one direction into a fine needle. The graphene includes a region in contact with the plurality of nanowires, and polyimide includes a region in contact with the graphene. The lithium-ion secondary battery uses the electrode as a negative electrode.