Silicon Negative Electrode Active Material with Amorphous Carbon Coating

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Solution Overview

Problem

The challenge is to prevent oxidation during the preparation of nano-sized silicon-based negative electrode active materials for lithium secondary batteries, which affects their performance due to rapid volume expansion and unstable solid electrolyte interfaces, leading to reduced capacity and efficiency.

Innovation Solution

A method involving chemical vapor deposition of an amorphous silicon layer on a glass substrate, followed by ultrasonic milling, dispersion in a carbon-based precursor solution, spray drying, and heat treatment to form a silicon composite with an amorphous carbon coating, which controls crystallinity and prevents oxidation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If a silicon-based negative electrode active material is used to achieve high capacity, then the discharge capacity is significantly improved (about 10 times that of graphite), but the material undergoes rapid volume expansion during charge and discharge, leading to crushing of particles, formation of unstable SEI, and decreased capacity

Engineering Contradiction:

Improvedischarge capacityVSAvoidstructural stability

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The silicon-based negative electrode active material is divided into nano-sized particles (5-500 nm) to reduce the overall volume expansion stress on each particle. This segmentation allows the material to accommodate volume changes during lithiation and delithiation without crushing, thereby maintaining structural stability while preserving high discharge capacity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention creates a composite structure by coating silicon-based particles with carbon material to form a core-shell structure. The carbon coating layer (5-50 nm thick) provides mechanical strength and structural stability to the silicon core, preventing particle crushing during volume expansion while allowing lithium ion insertion and extraction, thus maintaining both high capacity and structural integrity

Inventive Principle:

Principle #40Composite materials

2Length of moving object

If a nano-sized silicon-based negative electrode active material is prepared by mechanical milling to achieve controlled particle size, then the particle size is reduced to nano-scale, but the silicon-based material is oxidized during the milling process, reducing the initial efficiency of the secondary battery

Engineering Contradiction:

Improveparticle sizeVSAvoidoxidation

Core Design Contradiction:

Length of moving objectVSObject-generated harmful factors

Solution Approach 1:

The invention performs preliminary protective action by coating the silicon-based particles with carbon material before they undergo any milling or processing. This pre-coating prevents oxidation during subsequent mechanical milling processes while allowing the particles to be reduced to the desired nano-scale size. The carbon layer acts as a protective barrier that is applied in advance to prevent the harmful oxidation effect

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention converts the potentially harmful oxidation effect into a beneficial protective coating process. Instead of allowing oxidation to occur during milling, the silicon-based particles are deliberately coated with carbon material under controlled conditions to create a protective shell. This transforms the oxidation issue into a controlled coating process that actually protects the silicon core from oxidation while providing additional structural stability

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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

This approach results in improved discharge capacity, initial efficiency, and life characteristics of lithium secondary batteries by reducing electrode thickness expansion and maintaining the stability of the solid electrolyte interface.

Implementation Method 1

depositing an amorphous silicon layer on a surface of a glass substrate by chemical vapor deposition (CVD) using silane (SiH4) gas as a source

Methodology Applied

Scientific EffectChemical vapor deposition: Chemical Vapour Deposition

Implementation Method 2

preparing amorphous silicon particles by ultrasonic milling of the amorphous silicon layer

Methodology Applied

Scientific EffectUltrasonic milling: Ultrasonic Vibration

Implementation Method 3

spray drying the dispersion solution to prepare a silicon-based composite precursor

Methodology Applied

Scientific EffectSpray drying: Evaporation

Implementation Method 4

heat treating the silicon-based composite precursor to form a silicon composite which includes an amorphous carbon coating layer containing at least one amorphous silicon particle in the inside thereof

Methodology Applied

Scientific EffectHeat treatment: Heat Treatment

Data Source

PatentUS10511048B2Method of preparing negative electrode active material for lithium secondary battery and lithium secondary battery using the same

Publication Date: 2019.12.17 LG ENERGY SOLUTION LTD

AI summary

The present invention relates to a method of preparing a negative electrode active material for a secondary battery which may prevent oxidation during the preparation of nano-sized silicon particles, a negative electrode active material for a secondary battery prepared thereby, and a negative electrode for a secondary battery and a lithium secondary battery including the same.