Lithium Alloy Core-Shell Composites for Battery Anodes

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Solution Overview

Problem

Lithium ion batteries face reduced initial charge-discharge efficiency and battery capacity due to the formation of a surface electrolyte interface (SEI) on carbon materials, and the volume expansion of lithium alloys in negative electrodes, which affects cycling properties.

Innovation Solution

The development of lithium alloy composites with a core-shell structure, where lithium alloy granules are coated with a carbon shell, limiting volume expansion and improving cycling properties, achieved through a fabrication process involving stirring, drying, and calcination in an inert environment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If lithium alloy is added to the negative electrode material to solve the problem of decreasing battery capacity, then battery capacity is improved, but the lithium alloy volume expands continuously during charge-discharge processes causing material loosening and detachment

Engineering Contradiction:

Improvebattery capacityVSAvoidelectrode material stability

Core Design Contradiction:

Quantity of substanceVSStability of the object's composition

Solution Approach 1:

A carbon coating layer with controlled thickness (50-1000 Å) is applied to the lithium alloy granule surface. This thin film shell accommodates the volume expansion of lithium alloy during charge-discharge cycles while maintaining structural integrity, preventing material loosening and detachment, and improving cycling stability.

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The invention creates a composite structure combining lithium alloy granules (10-40 wt% Li) with carbon coating material. This composite approach leverages the high capacity of lithium alloy while the carbon shell provides structural stability and prevents harmful reactions with the electrolyte, resolving the contradiction between capacity and stability.

Inventive Principle:

Principle #40Composite materials

2Stability of the object's composition

If carbon materials are used for negative electrodes, then the battery structure is stable, but a SEI layer forms on the surface reducing initial charge-discharge efficiency

Engineering Contradiction:

Improveelectrode structure stabilityVSAvoidinitial charge-discharge efficiency

Core Design Contradiction:

Stability of the object's compositionVSLoss of energy

Solution Approach 1:

Instead of using pure carbon material throughout, the invention applies a thin carbon coating (50-1000 Å) only on the surface of lithium alloy granules. This localized carbon layer provides sufficient structural stability and SEI formation control without the excessive energy loss associated with bulk carbon materials, improving initial charge-discharge efficiency while maintaining adequate structure stability.

Inventive Principle:

Principle #3Local quality

3Duration of action of stationary object

If a thick carbon coating is applied to limit lithium alloy volume expansion, then cycling properties improve, but the internal resistance increases and affects battery performance

Engineering Contradiction:

Improvecycling lifeVSAvoidinternal resistance

Core Design Contradiction:

Duration of action of stationary objectVSObject-affected harmful factors

Solution Approach 1:

The invention optimizes the carbon coating thickness to a specific range (50-1000 Å) and lithium content (10-40 wt%). This parameter optimization ensures sufficient coating to limit volume expansion and improve cycling life, while maintaining thin enough thickness and appropriate composition to minimize internal resistance and preserve electrical conductivity.

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 lithium alloy composites enhance initial charge-discharge efficiency, increase battery capacity, and extend cycling life by reducing lithium ion detachment and internal resistance, while allowing for effective handling and cost reduction in the fabrication process.

Implementation Method 1

lithium alloy granules are coated with a shell of carbon material... effectively limit the volume expansion of lithium alloys

Methodology Applied

Scientific EffectVolume expansion constraint:

Implementation Method 2

calcining the dried product to obtain the negative electrode material with lithium alloy composites

Methodology Applied

Scientific EffectCalcination:

Data Source

PatentUS7524586B2Materials for negative electrodes of lithium ion batteries

Publication Date: 2009.04.28 BYD AMERICA CORP

AI summary

The present invention provides materials for negative electrodes of lithium rechargeable batteries. These materials include lithium alloy composites. Each lithium alloy composite has a core-shell structure with one or more lithium alloy granules as its core and a carbon material as its shell. The average granule diameter of the lithium alloy granule is between 5 μm and 40 μm. The average thickness of the shell layer is between 50 Å and 1000 Å. The average diameter of the lithium alloy composite is between 10 μm to 50 μm. The methods of fabrication for the material includes the following steps: stirring lithium alloy granules in an organic solution with a coating substance, drying the solid product in the organic solution with a coating substance, calcining the dried product to obtain the negative electrode material with lithium alloy composites.