Silicon Negative Electrode Composition for Cycle Life and Heat Stability
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Solution Overview
Problem
Lithium secondary batteries using silicon-based negative electrode materials face challenges with poor battery life characteristics and thermal stability due to large volume expansion and lack of thermal stability, limiting their energy density and performance.
Innovation Solution
A silicon-based negative electrode material co-doped with iron and aluminum, where the contents of elements in the active material layer satisfy specific ratios, is used, along with artificial graphite and single-walled carbon nanotubes, to enhance life characteristics and thermal stability, and a method involving stirring and heat treatment is employed to prepare the doped material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electrode material is used to improve energy density, then theoretical capacity increases from 372 mAh/g to 3580 mAh/g, but volume expansion reaches ~400% during repeated charging and discharging
Solution Approach 1:
The silicon-based active material is embedded within a carbon matrix structure, where the carbon material acts as a container that accommodates the silicon particles. This nested configuration allows the silicon to expand and contract within the carbon framework during charge-discharge cycles, preventing structural collapse and maintaining electrode integrity despite volume changes.
Solution Approach 2:
The invention employs a composite structure combining silicon-based active material with carbon materials (graphite, artificial graphite, or carbon black). This composite design leverages the high capacity of silicon while utilizing the structural stability and volume compensation capabilities of carbon to mitigate the 400% volume expansion issue.
2Quantity of substance
If silicon-based negative electrode material is used to improve energy density, then theoretical capacity increases to 3580 mAh/g, but thermal stability deteriorates
Solution Approach 1:
The composite structure of silicon-based material embedded in carbon matrix provides inherent thermal stability. The carbon framework acts as a thermal barrier and structurally stable component that prevents runaway reactions, thereby improving the overall thermal stability of the electrode while maintaining the high capacity benefits of silicon.
3Temperature
If graphite-based negative electrode material is used, then thermal stability is maintained, but energy density is limited due to low theoretical capacity of 372 mAh/g
Solution Approach 1:
The invention merges the advantages of both graphite and silicon-based materials by combining them into a single electrode structure. The graphite provides thermal stability and structural framework, while the silicon-based active material dispersed within it contributes high theoretical capacity, achieving a synergistic effect that surpasses either material alone.
Solution Approach 2:
By creating a composite electrode containing both graphite and silicon-based active material, the invention achieves a balance between thermal stability (from graphite) and high energy density (from silicon), resolving the trade-off between these two critical properties.
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 co-doping of iron and aluminum improves thermal stability and kinetic properties of lithium ions, leading to significantly improved life characteristics and capacity retention rates, especially at high temperatures, while maintaining a uniform voltage distribution.
Implementation Method 1
The co-doping of iron and aluminum improves thermal stability and kinetic properties of lithium ions
Implementation Method 2
b) heat treating the product of the process a), thereby preparing a negative electrode active material co-doped with iron and aluminum
Data Source
AI summary
Provided are a negative electrode for a lithium secondary battery and a method of manufacturing the same. The negative electrode for a lithium secondary battery according to an embodiment of the present invention includes a silicon-based negative electrode active material including iron and aluminum, wherein in ICP analysis of a negative electrode active material layer including the silicon-based negative electrode active material, contents of elements in the negative electrode active material layer satisfy the following Relations (1) to (3):A/(B2+C2)≤4,500 (1)5≤B≤1,500 (2)3≤C≤1,000 (3)wherein A is a Li content in ppm, B is an Fe content in ppm, and C is an Al content in ppm, based on the total weight of the ICP-analyzed negative electrode active material layer.