Siloxane-Coated Silicon Anode Material for Cycle Capacity Retention

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Solution Overview

Problem

Non-aqueous electrolyte secondary batteries using silicon materials as negative electrode active materials face challenges in maintaining high charge-discharge efficiency and capacity retention due to the expansion and contraction of silicon particles during cycling, leading to decreased discharge capacity over repeated cycles.

Innovation Solution

A negative electrode active material is developed with a surface layer containing a reaction product of a compound that forms siloxane bonds, specifically Si—R1—Si structures, where R1 is a hydrocarbon group, and one silicon is bound with alkoxy, oxyalkylene, chloro, and hydroxyl groups, while the other is bound with alkoxy, oxyalkylene, and chloro groups, enhancing the material's ability to withstand expansion and contraction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If silicon materials are used as negative electrode active material to increase lithium ion absorption capacity, then the charge-discharge capacity per unit volume is improved, but the charge-discharge efficiency decreases due to expansion and contraction during cycling

Engineering Contradiction:

Improvelithium ion absorption capacityVSAvoidcharge-discharge efficiency

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

A surface layer with controlled porosity (0.03 to 0.15 mL/g) is formed on the silicon-containing active material particles. This porous surface layer acts as a flexible buffer that can accommodate the expansion and contraction of silicon particles during charge-discharge cycling, reducing mechanical stress and preventing particle degradation, thereby maintaining charge-discharge efficiency while preserving high lithium ion absorption capacity

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The invention creates a composite structure consisting of silicon-containing active material particles coated with a porous surface layer. This composite material combines the high capacity advantage of silicon with the stability benefits of the porous coating, allowing the negative electrode to achieve both high lithium ion absorption and sustained charge-discharge efficiency over multiple cycles

Inventive Principle:

Principle #40Composite materials

2Quantity of substance

If silicon particles undergo expansion and contraction during charge-discharge cycles to absorb lithium ions, then the storage capacity is improved, but the discharge capacity decreases after repeated cycles

Engineering Contradiction:

Improvelithium ion storage capacityVSAvoiddischarge capacity retention

Core Design Contradiction:

Quantity of substanceVSDuration of action of stationary object

Solution Approach 1:

The porous surface layer is formed beforehand on the silicon-containing particles to provide a cushioning effect. This pre-formed porous structure (with specific porosity of 0.03 to 0.15 mL/g) absorbs and distributes the mechanical stress generated during silicon expansion and contraction, preventing particle fracture and maintaining structural integrity throughout the battery's operational life, thus preserving discharge capacity over repeated 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

This solution significantly improves the capacity retention rate in charge-discharge cycling by protecting the active material surfaces and reducing side reactions, leading to enhanced charge-discharge efficiency and stability of the non-aqueous electrolyte secondary battery.

Implementation Method 1

a surface layer containing a reaction product of a compound reacted so as to form a siloxane bond

Methodology Applied

Scientific EffectSiloxane bond formation: Chemical Bonding

Implementation Method 2

the expansion and contraction of silicon particles during cycling, leading to decreased discharge capacity

Methodology Applied

Scientific EffectExpansion and contraction accommodation: Elasticity

Data Source

PatentUS20240356026A1Negative electrode active material for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery using same, and method for producing negative electrode active material for non-aqueous electrolyte secondary battery

Publication Date: 2024.10.24 PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO LTD

AI summary

The disclosed negative electrode active material for a non-aqueous electrolyte secondary battery includes active material particles containing silicon, and a surface layer formed on surfaces of the active material particles. The surface layer contains a reaction product of a compound reacted so as to form a siloxane bond. The compound includes a structure represented by Si—R1—Si. R1 is a hydrocarbon group having 1 to 50 carbon atoms. The two Si's are each bound with at least one atomic group selected from the group consisting of an alkoxy group having 1 to 6 carbon atoms, and the like.