Silicon Composite Negative Electrode for Li-Ion Batteries
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Solution Overview
Problem
Current negative electrode materials for lithium ion secondary batteries, such as silicon and silicon oxide, face challenges in maintaining high coulomb efficiency during repeated charge/discharge cycles due to the size of silicon particles, which affects their cycle performance and energy density.
Innovation Solution
A silicon composite is developed where microcrystals or microparticles of silicon are dispersed in a different composition, such as silicon dioxide, with a crystallite size of up to 8.0 nm, and optionally coated with a conductive material like carbon, to enhance coulomb efficiency and cycle performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon oxide is used as negative electrode material to increase charge/discharge capacity, then energy density is improved, but cycle performance deteriorates due to increased irreversible capacity on first charge/discharge cycle
Solution Approach 1:
The invention divides the silicon oxide material into microparticles with controlled size distribution (D10≥3μm, D50≥6μm, D90≥9μm) to optimize both capacity and cycle performance. This segmentation allows sufficient surface area for high capacity while maintaining structural integrity for good cycle performance
Solution Approach 2:
The invention changes the particle size parameters of silicon oxide microparticles to specific ranges (D10≥3μm, D50≥6μm, D90≥9μm) and controls the SiOx composition ratio to achieve optimal balance between irreversible capacity and cycle performance, resolving the contradiction between high capacity and good cycle stability
2Reliability
If silicon particles are micronized to improve cycle performance, then various properties are enhanced, but the relationship between particle size and coulomb efficiency remains indefinite
Solution Approach 1:
The invention optimizes particle size parameters (D10≥3μm, D50≥6μm, D90≥9μm) to achieve the best balance between cycle performance and coulomb efficiency, preventing excessive micronization that would harm efficiency while maintaining sufficient size reduction for performance enhancement
3Loss of energy
If smaller silicon crystallite size is used to improve coulomb efficiency, then charge/discharge capacity increases, but manufacturing precision requirements increase
Solution Approach 1:
The invention controls silicon crystallite size within specific ranges (3-8nm) through heat treatment processes, achieving optimal coulomb efficiency while maintaining feasible manufacturing precision through controlled thermal processing
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 silicon composite material improves coulomb efficiency and cycle performance by preventing the formation of non-contributing particles, leading to higher charge/discharge capacity and energy density in lithium ion secondary batteries.
Implementation Method 1
microcrystals or microparticles of silicon are dispersed in a substance of a different composition from the microcrystals or microparticles, the microcrystals or microparticles having a crystallite size of up to 8.0 nm as determined by the Scherrer equation on the basis of the half width of a diffraction peak assigned to Si(220) on X-ray diffractometry
Data Source
AI summary
The present invention relates to a negative electrode material for nonaqueous electrolyte secondary batteries, which is composed of a silicon composite body that has a structure wherein microcrystals or fine particles of silicon are dispersed in a substance having a composition different from that of the microcrystals or fine particles, said silicon composite body having a crystallite size of the microcrystals or fine particles of 8.0 nm or less as calculated using Scherrer's equation on the basis of the half width of the diffraction peak belonging to Si(220) in an X-ray diffraction. The present invention is able to provide a negative electrode material for nonaqueous electrolyte secondary batteries, which has excellent coulombic efficiency, and a nonaqueous electrolyte secondary battery.