Graphite-Silicon Composite Negative Electrode for Lithium Batteries

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Solution Overview

Problem

Rechargeable lithium batteries face challenges in achieving uniform current density characteristics, which affects their cycle-life and output performance, particularly due to the volume expansion of non-carbon based negative active materials like silicon, leading to non-uniform distribution and contact resistance issues.

Innovation Solution

A negative electrode comprising a graphite-silicon composite with a carbon coating layer, where the silicon particles are distributed within a specific weight percentage range and particle size, and the graphite particles are buffered by the carbon coating to maintain uniform distribution and electrical conductivity, along with a binder and conductive material for improved binding and conductivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If non-carbon based negative active materials like silicon are used to increase capacity, then battery capacity is improved, but volume expansion occurs leading to non-uniform current density distribution

Engineering Contradiction:

Improvebattery capacityVSAvoidcurrent density uniformity

Core Design Contradiction:

Quantity of substanceVSStability of the object's composition

Solution Approach 1:

The patent uses a composite structure where silicon particles are embedded in a graphite matrix. The graphite provides structural stability and uniform electron conductivity, while silicon contributes high capacity. This composite approach allows the battery to achieve high capacity from silicon without suffering from its volume expansion issues, maintaining uniform current density distribution throughout the electrode.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The graphite matrix acts as an intermediary between the silicon particles and the electrolyte. It buffers the volume expansion of silicon during lithium insertion/extraction, preventing direct mechanical stress on the electrode structure. This intermediary role of graphite maintains the structural integrity and uniformity of the electrode, ensuring stable current density characteristics.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Quantity of substance

If silicon particles are added to increase capacity, then battery capacity is improved, but contact resistance increases due to non-uniform distribution

Engineering Contradiction:

Improvebattery capacityVSAvoidelectrical conductivity

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent achieves homogeneous distribution of silicon particles within the graphite matrix. The graphite particles are used in sufficient quantity to ensure complete dispersion of silicon particles, preventing aggregation. This homogeneous distribution ensures uniform electrical conductivity throughout the electrode, maintaining reliable electron transport pathways while incorporating high-capacity silicon material.

Inventive Principle:

Principle #33Homogeneity

3Quantity of substance

If high concentration of silicon is used to achieve high capacity, then battery capacity is improved, but cycle-life deteriorates due to volume expansion

Engineering Contradiction:

Improvebattery capacityVSAvoidcycle-life

Core Design Contradiction:

Quantity of substanceVSDuration of action of stationary object

Solution Approach 1:

The graphite matrix serves as a pre-established cushioning structure that accommodates the volume expansion of silicon particles during lithium insertion. The graphite's layered structure and mechanical properties absorb the expansion stress, preventing structural degradation of the electrode. This beforehand cushioning effect allows high concentrations of silicon to be used without compromising cycle-life, as the graphite protects against repeated mechanical stress during charging cycles.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 solution results in a rechargeable lithium battery with uniform current density characteristics, enhanced cycle-life, and high-capacity performance, capable of operating at high rates without performance deterioration, by ensuring smooth lithium ion intercalation and inhibiting volume expansion of the silicon particles.

Implementation Method 1

a carbon coating layer surrounding the Si particle on the surface of the graphite particle

Methodology Applied

Scientific EffectPhysical containment: Physical Containment

Implementation Method 2

a negative active material capable of intercalating/deintercalating lithium ions

Methodology Applied

Scientific EffectIntercalation: Absorption (physical)

Data Source

PatentUS9496549B2Negative electrode and rechargeable lithium battery including same

Publication Date: 2016.11.15 SAMSUNG SDI CO LTD

AI summary

A negative electrode for a rechargeable lithium battery includes: a current collector; and a negative active material layer on the current collector. The negative active material layer includes a negative active material including a graphite-silicon composite including a graphite particle, a silicon (Si) particle on a surface of the graphite particle, and a carbon coating layer surrounding the graphite particle on the surface of the silicon (Si) particle. A rechargeable lithium battery includes the negative electrode.