Silicon Negative Electrode Active Material Lattice Mismatch Control
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Solution Overview
Problem
Lithium-based secondary batteries using silicon-based negative electrode active materials face challenges with volume change during charging/discharging, leading to electric insulation and reduced cycle stability due to lattice mismatch and conductivity issues.
Innovation Solution
A silicon-based negative electrode active material with a crystal lattice mismatch ratio of the matrix layer to the Si layer within 20%, featuring a three-layer structure comprising a crystalline Si layer, an amorphous matrix layer, and a nano grain matrix layer, which suppresses dispersal and maintains capacity over cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electrode active material is used to achieve high capacity and high energy density, then the battery capacity and energy density are improved, but volume change during charging/discharging causes electric insulation and cycle stability degradation
Solution Approach 1:
The patent applies the nesting principle by embedding Si particles within a matrix layer structure. The Si particles are contained within the matrix layer, forming a nested configuration where the active Si material is protected by the surrounding matrix structure. This nested arrangement allows the high-capacity Si to be utilized while the matrix layer constrains volume expansion and prevents electric insulation, resolving the contradiction between capacity and cycle stability.
Solution Approach 2:
The patent employs composite materials by creating a layered structure comprising a matrix layer and Si particles. This composite structure combines the high capacity advantage of Si with the structural stability of the matrix material, achieving both high battery capacity and improved cycle stability simultaneously.
2Quantity of substance
If silicon is used as negative electrode active material to occlude and discharge lithium ions, then high capacity is achieved, but conductivity deteriorates due to volume change during charging/discharging
Solution Approach 1:
The Si particles are nested within the matrix layer structure, which provides a conductive pathway network. This nested configuration ensures that even when Si particles undergo volume changes during lithium occlusion and discharge, they remain electrically connected through the matrix layer, preventing conductivity deterioration while maintaining high lithium ion capacity.
Solution Approach 2:
The matrix layer acts as an intermediary between Si particles, maintaining electrical connectivity during volume changes. The matrix material serves as a mediating structure that accommodates Si expansion/contraction while preserving the conductive network, thus preventing electric insulation despite significant volume fluctuations.
3Reliability
If thin film coating is applied to silicon surface to control reaction speed and improve stability, then cycle efficiency is improved, but electric resistance increases when film thickness is larger
Solution Approach 1:
The patent utilizes a matrix layer structure that functions as a flexible protective shell around Si particles. This matrix layer provides mechanical support and stabilizes the structure during cycling, improving cycle efficiency. The layer is designed with appropriate thickness and composition to maintain electrical conductivity while providing structural stability, thus avoiding the electric resistance problem associated with thicker coating films.
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 effectively reduces volume change and electric insulation, enhancing the initial efficiency and capacity maintenance of the battery, thereby improving the lifespan and performance of lithium secondary batteries.
Implementation Method 1
a crystal lattice mismatch ratio of a matrix layer to a Si layer is controlled in the Si layer which is a crystal layer and the matrix layer mixed with the Si layer
Data Source
AI summary
Provided are a negative electrode active material for a secondary battery, which suppresses a dispersal phenomenon of a negative electrode active material during charging/discharging by controlling a lattice mismatch ratio of an amorphous matrix layer to a silicon layer in a silicon-based negative electrode active material.