Bilayer Negative Electrode Structure for Silicon Cycle Stability

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Solution Overview

Problem

Lithium secondary batteries face challenges with silicon-based negative electrodes due to low charge/discharge efficiency and significant volume changes during charge/discharge cycles, leading to conductive path disconnection and poor cycle characteristics.

Innovation Solution

A bilayer negative electrode structure is implemented, with a first layer containing a carbonaceous active material and a second layer comprising a silicon-based active material and carbon nanotubes, where carbon nanotubes are used as a conductive material to maintain contact with the silicon-based material and prevent conductive path isolation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If a silicon-based material is used as a negative electrode active material to increase theoretical capacity, then the energy density is improved, but the charge/discharge efficiency deteriorates and volume change during charge/discharge increases

Engineering Contradiction:

Improvetheoretical capacityVSAvoidcharge/discharge efficiency

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent uses a composite structure where silicon-based active material particles are embedded in a carbonaceous matrix. The carbonaceous material serves as both the matrix and conductive network, combining the high capacity of silicon with the stability and conductivity of carbon, thereby resolving the contradiction between high theoretical capacity and reliable charge/discharge efficiency

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The carbonaceous material forms a flexible matrix that accommodates the volume expansion of silicon during lithiation. This carbon shell or matrix structure allows the silicon particles to expand and contract without losing electrical contact or structural integrity, maintaining reliability despite significant volume changes

Inventive Principle:

Principle #30Flexible shells and thin films

2Quantity of substance

If a silicon-based material is used as a negative electrode active material to increase theoretical capacity, then the energy density is improved, but the volume change during charge/discharge increases leading to conductive path disconnection

Engineering Contradiction:

Improvetheoretical capacityVSAvoidconductive path stability

Core Design Contradiction:

Quantity of substanceVSStability of the object's composition

Solution Approach 1:

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The carbonaceous material acts as an intermediary between silicon particles, providing a stable conductive network that remains intact during volume changes. This intermediary matrix ensures continuous electrical contact even as silicon expands and contracts, preventing conductive path disconnection

Inventive Principle:

Principle #24Intermediary (Mediator)

3Stability of the object's composition

If carbon nanotubes are added as a conductive material to maintain conductive path stability, then the conductive path stability is improved, but the device complexity increases

Engineering Contradiction:

Improveconductive path stabilityVSAvoidelectrode structure complexity

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The carbonaceous material serves multiple functions simultaneously: it acts as the matrix holding silicon particles, provides electrical conductivity through its inherent conductive network, and accommodates volume expansion. By combining these functions in a single component rather than adding separate carbon nanotube additives, the patent avoids increasing device complexity while maintaining conductive path stability

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 configuration enhances the cycle characteristics and inhibits degradation of discharge capacity by maintaining conductivity and preventing silicon-based material isolation, even after repeated charge/discharge cycles.

Implementation Method 1

carbon nanotubes are used as a conductive material to maintain contact with the silicon-based material and prevent conductive path isolation

Methodology Applied

Scientific EffectConduction (electrical): Conduction (electrical)

Implementation Method 2

a silicon-based material shows a change in volume of 300% or more during charge/discharge

Methodology Applied

Scientific EffectThermal Expansion: Thermal Expansion

Data Source

PatentUS12002949B2Negative electrode and secondary battery including the same

Publication Date: 2024.06.04 LG ENERGY SOLUTION LTD

AI summary

A negative electrode including: a current collector; a first negative electrode active material layer positioned on at least one surface of the current collector for a negative electrode and containing a first carbonaceous active material; and a second negative electrode active material layer positioned on a surface of the first negative electrode active material layer and containing a silicon-based active material and carbon nanotubes. A lithium secondary battery including the negative electrode is also disclosed.