Silicon Powder for Li-Ion Anodes via Wet Classification

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Solution Overview

Problem

Silicon anodes for lithium-ion batteries face significant volume changes during lithiation and de-lithiation, leading to degradation and poor cycle life due to the presence of undersized particles and inhomogeneous carbon coating, which compromises electrode integrity.

Innovation Solution

A silicon powder with a well-defined particle size distribution, produced by jet milling and subsequent wet classification, ensuring no or minimal undersized particles are attached to the surface, allowing for homogeneous carbon coating and improved performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If silicon powder is used as anode material for high energy density batteries, then the theoretical capacity increases beyond 4000 mAh/gSi, but the large volume change during lithiation and de-lithiation causes degradation and poor cycle life

Engineering Contradiction:

Improvetheoretical capacityVSAvoidcycle life

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The silicon anode is segmented into very fine particles with D10 between 1-3 μm and D50 between 3-10 μm. This segmentation reduces the overall volume change impact on electrode integrity while maintaining high theoretical capacity, as the fine particles can better accommodate expansion and contraction during cycling

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A carbon coating is applied specifically to the surface of silicon particles to create a protective interface. This local modification at the particle surface prevents direct contact between silicon and electrolyte, reducing degradation while allowing lithium ion transport, thus improving cycle life without sacrificing capacity

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If conventional drying methods are used after jet milling, then the production process is simple, but undersized particles attach to the surface of larger particles creating inhomogeneous structure

Engineering Contradiction:

Improveprocess simplicityVSAvoidparticle size distribution uniformity

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

Wet classification using liquid medium (water or alcohol) is employed instead of conventional drying methods. The liquid medium allows undersized particles to be separated and removed from the surface of larger particles through fluid dynamics, achieving uniform particle size distribution without particle attachment while maintaining process efficiency

Inventive Principle:

Principle #29Pneumatics and hydraulics

3Manufacturing precision

If jet milling is used to produce fine silicon particles, then the particle size can be controlled, but the process complexity increases compared to conventional methods

Engineering Contradiction:

Improveparticle size controlVSAvoidmilling process complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The harmful undersized particles are extracted and removed from the particle surface through wet classification. This extraction process simplifies the overall structure by eliminating the problematic attachment of fine particles, allowing the use of jet milling for precise particle size control without the penalty of increased complexity in particle morphology management

Inventive Principle:

Principle #2Taking out (Extraction)

4Productivity

If inhomogeneous carbon coating is applied on silicon particles, then the coating process is faster, but the electrode integrity deteriorates due to cracking and degradation

Engineering Contradiction:

Improvecoating speedVSAvoidelectrode integrity

Core Design Contradiction:

ProductivityVSStrength

Solution Approach 1:

The silicon particles are pre-treated through wet classification to achieve uniform size and remove surface attachments before carbon coating. This preliminary action ensures that the subsequent carbon coating process produces homogeneous coverage, preventing cracking and degradation while maintaining reasonable coating speed through optimized process parameters

Inventive Principle:

Principle #10Preliminary action

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 silicon powder with a particle size distribution between 3 and 30 μm and no undersized particles attached to the surface provides enhanced performance and cycle life in lithium-ion batteries by ensuring a homogeneous carbon coating, reducing degradation and cracking.

Implementation Method 1

coarse silicon particles are jet milled and thereafter subjected to wet classification

Methodology Applied

Scientific EffectJet milling:

Implementation Method 2

coarse silicon particles are jet milled and thereafter subjected to wet classification to remove silicon particles having a particle size below the lower cut-off particle size

Methodology Applied

Scientific EffectWet classification:

Data Source

PatentUS11322741B2Silicon powder for use in anodes for lithium-ion batteries and method for production of silicon powder

Publication Date: 2022.05.03 ELKEM

AI summary

The present invention relates to a silicon powder, where the size of the silicon powder particles are between 3 and 30 μm, a particle size fraction D10 of the silicon powder particles is between 3 and 9 μm, and where the silicon powder particles have no, or substantially no, silicon particles with a size smaller than D10 attached to the surface. The silicon powder according to the present invention is produced by wet classifying produced silicon powders.