Silicon-Graphite Negative Electrode Composition for Lithium Battery

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Solution Overview

Problem

Silicon-based active materials in lithium secondary batteries suffer from high volume expansion/contraction during charging and discharging, leading to low initial efficiency and deteriorated battery performance compared to carbon-based materials.

Innovation Solution

A negative electrode composition combining silicon-based and carbon-based active materials, including silicon-carbon composites and silicon oxides with natural and artificial graphite, and a conductive material like single-walled carbon nanotubes, is used to improve electrical conductivity and control volume changes, enhancing battery performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If silicon-based active material is used to increase capacity, then battery capacity is improved, but volume expansion/contraction increases and initial efficiency decreases

Engineering Contradiction:

Improvebattery capacityVSAvoidinitial efficiency

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent applies composite materials by combining silicon-based active material with carbon-based active material in a specific weight ratio range (silicon-based: 5-50 wt%, carbon-based: 50-95 wt%). This composite structure allows the silicon component to provide high capacity while the carbon component provides structural stability and conducts electrons efficiently, thereby resolving the contradiction between high capacity and low initial efficiency.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent changes the compositional parameters by precisely controlling the weight ratio of silicon-based to carbon-based active materials. By adjusting this parameter within the specified range, the patent optimizes the balance between capacity (from silicon) and initial efficiency (from carbon), resolving the technical contradiction through parameter optimization.

Inventive Principle:

Principle #35Parameter changes

2Quantity of substance

If silicon-based active material is used to increase capacity, then battery capacity is improved, but cycle characteristics deteriorate

Engineering Contradiction:

Improvebattery capacityVSAvoidcycle characteristics

Core Design Contradiction:

Quantity of substanceVSDuration of action of stationary object

Solution Approach 1:

The patent uses composite materials combining silicon-based and carbon-based active materials where the carbon component provides structural stability during charging/discharging cycles. This composite structure prevents the silicon component from undergoing excessive volume changes that would lead to pulverization and capacity fade, thereby improving cycle characteristics while maintaining high capacity.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The carbon-based active material acts as an intermediary that mediates the volume expansion/contraction of the silicon-based material. The carbon matrix accommodates the silicon's volume changes and maintains structural integrity, preventing direct contact between silicon particles and electrolyte that would cause degradation, thus improving cycle life.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Speed

If silicon-based active material is used, then high-speed charge characteristics are improved, but volume expansion increases

Engineering Contradiction:

Improvecharge speedVSAvoidvolume expansion

Core Design Contradiction:

SpeedVSVolume of moving object

Solution Approach 1:

The carbon-based active material forms a flexible matrix that surrounds and accommodates the silicon-based particles. This carbon shell/film structure allows the silicon to expand and contract during charging/discharging without breaking, while maintaining electrical contact and structural integrity, thus enabling high-speed charge characteristics without excessive volume expansion.

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The composite structure of silicon-based and carbon-based materials allows the silicon component to provide high-speed charge characteristics through its fast lithium ion insertion/extraction kinetics, while the carbon component constrains the overall volume expansion and maintains structural stability.

Inventive Principle:

Principle #40Composite materials

Data Source

PatentEP4629328A1Negative electrode composition, negative electrode, and lithium secondary battery

Publication Date: 2025.10.08 LG ENERGY SOLUTION LTD

AI summary

The present invention relates to a negative electrode composition, a negative electrode comprising same, a lithium secondary battery, a battery module, and a battery pack, the negative electrode composition comprising a negative electrode active material comprising a carbon-based active material and a silicon-based active material including at least one among a silicon carbon composite and a silicon oxide, wherein the carbon-based active material includes natural graphite and artificial graphite, and when powder resistance is measured at a pressure of 800 kgf/cm2, rolling density decreases in the order of the natural graphite > the artificial graphite > the silicon-based active material, and electrical conductivity decreases in the order of the natural graphite > the artificial graphite > the silicon-based active material.