Silicon-Tin Alloy Negative Electrode Carbon Cover Layer Cycle Durability
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Solution Overview
Problem
Existing negative electrodes for lithium ion secondary batteries lack sufficient cycle durability, leading to performance degradation after repeated charge and discharge cycles.
Innovation Solution
A negative electrode design featuring a carbon cover layer with a specific particle size ratio to a silicon-containing alloy, along with a negative electrode electric conducting additive, which reduces direct contact with the electrolyte and enhances electrical conductivity, thereby improving cycle durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-containing alloy is used as negative electrode material, then capacity is improved, but cycle durability deteriorates due to excessive contact with electrolyte causing decomposition
Solution Approach 1:
A carbon cover layer is introduced as an intermediary between the silicon-containing alloy and the electrolyte. This carbon layer reduces direct contact between the alloy and electrolyte, preventing excessive decomposition while maintaining electrical conductivity through appropriate particle size selection (D50 ratio of 100-500). The carbon material acts as a mediator that protects the silicon alloy from harmful electrolyte interaction.
Solution Approach 2:
The invention optimizes the particle size parameters by controlling the D50 ratio of silicon-containing alloy to carbon material to be within 100-500. This parameter change ensures adequate coverage of the alloy particles by carbon material, reducing electrolyte contact area while maintaining conductivity. The specific particle size ratio is critical for achieving both high capacity and long cycle durability.
2Reliability
If carbon cover layer is added to reduce electrolyte contact, then cycle durability is improved, but electrical conductivity may deteriorate
Solution Approach 1:
The invention carefully controls the particle size parameters (D50 ratio of 100-500) and carbon content (0.1-5 mass%) to optimize the balance between protection and conductivity. By adjusting these parameters, the carbon cover layer provides sufficient electrolyte barrier while maintaining adequate electrical conductivity for battery operation.
Solution Approach 2:
The carbon cover layer is applied with specific local characteristics through controlled particle size distribution. The carbon material particles are sized to provide appropriate coverage density, creating local regions with optimized protection-conductivity balance. This local quality control ensures that the carbon layer protects against electrolyte while maintaining electron transport pathways.
3Reliability
If carbon content is increased to improve coverage, then cycle durability is improved, but manufacturing cost and complexity increase
Solution Approach 1:
The invention optimizes the carbon content parameter to a specific range (0.1-5 mass%) to achieve the minimum effective coverage. This parameter optimization avoids excessive carbon addition while ensuring sufficient protection. The controlled particle size ratio (D50 of 100-500) further enhances coverage efficiency, reducing the need for high carbon content and simplifying manufacturing processes.
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 proposed design significantly enhances the cycle durability of lithium ion secondary batteries by minimizing contact between the silicon-containing alloy and the electrolyte, preventing excessive decomposition and maintaining electrical conductivity, resulting in improved charge and discharge efficiency.
Implementation Method 1
a carbon cover layer including a carbon material and covering a silicon-containing alloy
Implementation Method 2
the amount of DBP oil absorption of the carbon material is 240 mL/100 g or greater, wherein the amount of DBP oil absorption is obtained according to JIS K6221 (1975)
Implementation Method 3
the average particle diameter of the silicon-containing alloy and the carbon material are particle diameters when a cumulative value of particle size distribution is 50% by mass, measured by a laser diffraction method
Data Source
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AI summary
A negative electrode (10) for an electric device includes a silicon-containing alloy (1) containing silicon and tin, a carbon cover layer (2) including a carbon material and covering the silicon-containing alloy (1), and a negative electrode electric conducting additive (3). A ratio of an average particle diameter of the silicon-containing alloy (1) to an average particle diameter of the carbon material is 240 or greater. The negative electrode (10) for an electric device and an electric device (100) using the negative electrode (10) can improve cycle durability.