Si-Al-Fe Alloy Negative Electrode for Lithium Battery

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Solution Overview

Problem

Lithium secondary batteries using non-carbonaceous materials like Si-based alloys face issues with unstable structure and reduced cycle-life due to volumetric expansion and high raw material costs, while carbonaceous materials also have limitations in intercalation and deintercalation processes.

Innovation Solution

A Si—Al—Fe alloy with a specific atomic ratio is developed, which includes a Si phase and an alloy phase that registers specific X-ray diffraction peaks, allowing for uniform dispersion and improved reaction with lithium ions, thereby stabilizing the battery structure and enhancing cycle-life characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If non-carbonaceous materials like Si-based alloys are used as negative active material, then initial discharge capacity is improved, but structural stability deteriorates due to volumetric expansion and contraction

Engineering Contradiction:

Improveinitial discharge capacityVSAvoidstructural stability

Core Design Contradiction:

Quantity of substanceVSStability of the object's composition

Solution Approach 1:

The Si-based alloy is segmented into fine particles with an average diameter of 0.1 to 10 μm, which divides the volumetric expansion stress into smaller units, preventing catastrophic structural failure and maintaining stability during charge-discharge cycles

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

An amorphous carbon coating layer is applied on the surface of the Si-based alloy particles, providing a flexible protective shell that accommodates volumetric changes while maintaining structural integrity and preventing direct exposure to electrolyte

Inventive Principle:

Principle #30Flexible shells and thin films

2Quantity of substance

If Si-based alloys are used as negative active material, then initial discharge capacity is improved, but cycle-life deteriorates due to repeated volumetric changes

Engineering Contradiction:

Improveinitial discharge capacityVSAvoidcycle-life

Core Design Contradiction:

Quantity of substanceVSDuration of action of stationary object

Solution Approach 1:

The amorphous carbon coating acts as a flexible shell that expands and contracts with the Si-based alloy core during lithium insertion/extraction, maintaining structural integrity over hundreds of cycles and preventing particle disintegration

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The alloy is subjected to rapid cooling at 10³ to 10⁶ K/sec to form an amorphous carbon phase in advance, which pre-establishes a stable structure that can accommodate subsequent volumetric changes during battery cycling

Inventive Principle:

Principle #10Preliminary action

3Stability of the object's composition

If Si—Ti—Ni alloy is used, then negative electrode structure is stabilized, but raw material cost increases

Engineering Contradiction:

Improveelectrode structure stabilityVSAvoidraw material cost

Core Design Contradiction:

Stability of the object's compositionVSEase of manufacture

Solution Approach 1:

The patent replaces expensive Ti and Ni elements with cheaper Fe and Al elements in the alloy composition, using abundant and low-cost raw materials while maintaining the stabilizing effect through optimized atomic ratios (Fe: 5-30 at%, Al: 5-30 at%)

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The alloy composition parameters are optimized with specific atomic ratios of Si (50-90 at%), Fe (5-30 at%), and Al (5-30 at%), which changes the material properties to achieve structural stability at lower cost by forming stable intermetallic phases in the desired composition range

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

The Si—Al—Fe alloy improves the initial discharge capacity and cycle-life of lithium secondary batteries by preventing structural destruction from volumetric changes and optimizing the reaction with lithium ions, leading to higher capacity and longer battery life.

Implementation Method 1

The positive and negative electrodes each include an active material that allows lithium ions to be intercalated and deintercalated

Methodology Applied

Scientific EffectIntercalation and deintercalation:

Implementation Method 2

when lithium ions are intercalated and deintercalated between the positive and negative electrodes, oxidation and reduction reactions occur, and thus, electrical energy is generated

Methodology Applied

Scientific EffectOxidation and reduction reactions: Redox Reactions

Implementation Method 3

The alloy phase may register an X-ray diffraction peak at a Bragg angle 2θ of about 20° to about 60° when measured using a CuK-α X-ray wavelength of 1.541 Å

Methodology Applied

Scientific EffectX-ray diffraction: Bragg Diffraction

Data Source

PatentUS9306216B2Negative active material, method of preparing the same, negative electrode for lithium secondary battery including negative active material, and lithium secondary battery including negative electrode

Publication Date: 2016.04.05 SAMSUNG SDI CO LTD

AI summary

A negative active material for a rechargeable lithium battery includes a Si—Al—Fe alloy represented by Formula 1. The Si—Al—Fe alloy includes a Si phase and an alloy phase, and the alloy phase includes Si, Al, and Fe in a ratio of atomic percentages of about 3:3:2:xSi-yAl-zFe Formula 1wherein 50 at %≦x≦90 at %, 5 at %≦y≦30 at %, 5 at %≦z≦30 at %, and x+y+z=100 at %.