Silicon-Silicon Oxide Negative Electrode Active Material for High-Rate Discharge
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Solution Overview
Problem
Lithium ion secondary batteries face a challenge in achieving high discharge capacity at high rates due to the poor electric conductivity of silicon-silicon oxide mixtures used as negative electrode active materials, which leads to significant decreases in discharge capacity when current density is high, making them unsuitable for high-power applications like hybrid and electric vehicles.
Innovation Solution
A negative electrode active material primarily composed of silicon and silicon oxide, characterized by an Ar-laser Raman spectrum with specific peak intensities and ratios, is developed to maintain high strength, suppress excessive cross-linking, and provide sufficient lithium diffusion paths, ensuring high discharge capacity at high rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon and silicon oxide mixture is used as negative electrode active material, then cycle characteristics are improved, but electric conductivity deteriorates
Solution Approach 1:
The patent applies local quality by creating a non-uniform carbon distribution where carbon is concentrated at specific locations (particle surfaces and internal structures) rather than uniformly distributed. This localized carbon placement provides conductivity enhancement exactly where needed for electrochemical reactions while preserving the bulk silicon-silicon oxide structure for mechanical stability and cycle life.
Solution Approach 2:
Carbon acts as an intermediary substance that mediates between the silicon-silicon oxide active material and the electrolyte. The carbon component provides conductive pathways and facilitates lithium ion transport without directly participating in the main electrochemical reactions, thus improving conductivity while maintaining the integrity of the silicon-based active material.
2Loss of energy
If carbon coating is applied to increase discharge capacity at high rate, then electric conductivity is improved, but contact area with electrolyte solution decreases
Solution Approach 1:
The patent uses local quality by applying carbon selectively at specific locations rather than creating a thick uniform coating. Carbon is concentrated at particle surfaces and internal structures where conductivity is most needed, while leaving other areas accessible to electrolyte. This localized approach provides conductivity enhancement without significantly reducing the effective contact area with electrolyte.
Solution Approach 2:
The carbon structure incorporates porous or hollow features that increase surface area and electrolyte accessibility. The porous carbon component provides extensive internal surface area for lithium ion insertion while maintaining overall particle porosity that allows electrolyte penetration, thus improving conductivity without reducing external contact area.
3Quantity of substance
If silicon content is increased to achieve higher capacity, then theoretical capacity is improved, but expansion and shrinkage stress increases
Solution Approach 1:
The patent employs composite materials by combining silicon and silicon oxide in a controlled ratio within the active material. This composite structure leverages silicon's high capacity and silicon oxide's mechanical stability to resist expansion and shrinkage stresses. The composite also includes carbon components that provide structural support and stress distribution, enabling high silicon content while managing mechanical stresses.
Solution Approach 2:
The patent applies beforehand cushioning by incorporating silicon oxide and carbon structures that anticipate and cushion against the expansion and shrinkage stresses of silicon during cycling. These cushioning components are built into the particle structure in advance, providing mechanical support and stress distribution before the expansion-shrinkage cycles begin, thus preventing particle degradation.
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 enables lithium ion secondary batteries to maintain high discharge capacity at high rates, addressing the limitations of previous technologies by optimizing the bonding between silicon and oxygen in the negative electrode active material, thereby enhancing the battery's performance and cycle characteristics.
Implementation Method 1
the stress caused by expansion and shrinkage of silicon during charging and discharging is relaxed by silicon oxide
Implementation Method 2
optimizing the bonding between silicon and oxygen in the negative electrode active material, thereby enhancing the battery's performance
Data Source
AI summary
A negative electrode active material mainly contains silicon and silicon oxide. In the negative electrode active material, an Ar-laser Raman spectrum thereof includes a peak A corresponding to 950±30 cm−1 and a peak B corresponding to 480±30 cm−1, and an intensity ratio of the peak B to the peak A (B/A) is in the range of 1 to 10.