Silicon Negative Electrode Elastic Deformation for Cycle Life

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Solution Overview

Problem

Lithium-ion secondary batteries using silicon or silicon oxide as negative electrode materials face significant volume expansion issues during charging and discharging, leading to exfoliation and fracture of the electrode layer, which severely limits their cycle durability.

Innovation Solution

A negative electrode with a specific tensile strength and thickness ratio for the active material layer and current collector, optimized to reduce interface stress through elastic deformation, ensuring the product of tensile strength and thickness falls within a range of 3.8 to 9.0 N/mm and the ratio of these products is between 1.06 and 1.29, thereby suppressing exfoliation and enhancing cycle characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If silicon-based negative electrode active material is used to achieve high capacity, then the theoretical discharge capacity is significantly improved (11 times that of graphite), but volume expansion occurs during lithium intercalation leading to exfoliation and fracture of the electrode

Engineering Contradiction:

Improvedischarge capacityVSAvoidelectrode structural stability

Core Design Contradiction:

Quantity of substanceVSStability of the object's composition

Solution Approach 1:

The invention changes the physical parameters of the current collector (tensile strength ≥250 N/mm², surface roughness Rz 0.6-10 μm, thickness 5-20 μm) to create an optimized substrate that can accommodate the volume expansion of silicon-based active material while maintaining electrode integrity and adhesion

Inventive Principle:

Principle #35Parameter changes

2Strength

If the tensile strength of the negative electrode current collector is increased to suppress fracture, then the electrode mechanical strength is improved, but a large amount of interface stress is generated between the current collector and active material layer during expansion and shrinkage, causing cracks and fracture

Engineering Contradiction:

Improvecurrent collector tensile strengthVSAvoidinterface stress

Core Design Contradiction:

StrengthVSStress or pressure

Solution Approach 1:

The invention uses a thin film current collector with optimized thickness (5-20 μm) and high tensile strength that provides sufficient mechanical support while maintaining flexibility to accommodate volume changes, thereby reducing interface stress during expansion and shrinkage cycles

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The invention applies surface roughening treatment (Rz 0.6-10 μm) to create localized surface features that enhance adhesion between the current collector and active material layer, distributing interface stress more evenly and preventing crack propagation

Inventive Principle:

Principle #3Local quality

3Strength

If the surface roughness is increased to improve adhesion between active material layer and current collector, then the bonding strength is improved, but the manufacturing precision and surface uniformity become more difficult to control

Engineering Contradiction:

Improveadhesion strengthVSAvoidsurface roughness control

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The invention specifies an optimized surface roughness range (Rz 0.6-10 μm) that balances adhesion improvement with manufacturability, providing sufficient bonding strength while remaining achievable through conventional surface treatment processes

Inventive Principle:

Principle #35Parameter changes

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 significantly improves the charging/discharging cycle characteristic of lithium-ion secondary batteries, achieving capacity retention of 50% or more after 500 cycles and maintaining high charging/discharging rate performance.

Implementation Method 1

Silicon can electrochemically intercalate and deintercalate lithium ions and charging and discharging with a very large amount of capacity compared with graphite

Methodology Applied

Scientific EffectIntercalation: Absorption (physical)

Implementation Method 2

a value which is obtained by dividing the product of the tensile strength and the thickness of the negative electrode by a product of tensile strength and thickness of a negative electrode current collector is 1.06 to 1.29

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Data Source

PatentUS9166223B2Negative electrode for lithium-ion secondary battery and lithium-ion secondary battery

Publication Date: 2015.10.20 TDK CORP

AI summary

The negative electrode for lithium-ion secondary battery is used in which a product of tensile strength and thickness of a negative electrode having a negative electrode active material layer containing silicon and silicon oxide as main components is 3.8 to 9.0 N/mm and a value obtained by dividing the product of the tensile strength and the thickness of the negative electrode by a product of tensile strength and thickness of a negative electrode current collector is 1.06 to 1.29.