Silicon Anode SEI Control for Longer-Life Lithium Batteries

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Solution Overview

Problem

Lithium secondary batteries with silicon-based anode active materials face challenges due to non-uniform solid electrolyte interface (SEI) layer formation, leading to reduced lifespan and capacity retention due to large volume expansion ratios and side reactions with the electrolyte.

Innovation Solution

An anode for lithium secondary batteries is developed with a composite particle including a silicon-based active material and a uniformly formed SEI layer, where the F-density is controlled to 23% or less, and a polyacrylic acid-based copolymer binder is used to enhance the SEI layer uniformity and stability, along with a carbon coating to reduce resistance and side reactions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If silicon-based particles are used as anode active material to increase capacity, then the battery capacity is improved, but the SEI layer becomes non-uniform due to large volume expansion ratio, degrading battery lifespan

Engineering Contradiction:

Improvebattery capacityVSAvoidbattery lifespan

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

A carbon coating layer is applied to the silicon-based particles before battery assembly. This preliminary protective layer prevents direct contact between the silicon surface and electrolyte, controlling SEI layer formation from the outset and preventing non-uniform growth that would occur with bare silicon particles during subsequent charging cycles.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The anode uses composite particles consisting of silicon-based active material coated with carbon. This composite structure combines the high capacity of silicon with the stability and uniform surface properties of carbon, enabling both high battery capacity and uniform SEI layer formation for improved lifespan.

Inventive Principle:

Principle #40Composite materials

2Use of energy by moving object

If silicon-based particles with high capacity are used, then the energy density is improved, but side reactions with electrolyte increase due to non-uniform SEI layer formation

Engineering Contradiction:

Improveenergy densityVSAvoidside reactions with electrolyte

Core Design Contradiction:

Use of energy by moving objectVSObject-generated harmful factors

Solution Approach 1:

The carbon coating layer acts as an intermediary between the silicon-based particles and the electrolyte. It mediates the interaction by providing a stable interface that allows controlled SEI layer formation while preventing direct harmful reactions between the electrolyte and silicon surface, thus reducing side reactions while maintaining high energy density.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If the SEI layer is formed on silicon-based particles, then protection is provided, but the SEI layer is non-uniformly formed due to volume expansion, reducing battery performance

Engineering Contradiction:

Improveprotection of active materialVSAvoiduniformity of SEI layer

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The carbon coating provides locally uniform properties across the silicon particle surface before electrolyte contact. This local uniformity in the carbon layer translates to uniform SEI layer formation across the entire particle surface, even during volume expansion, ensuring consistent protective properties throughout the battery.

Inventive Principle:

Principle #3Local quality

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 improves the capacity and lifespan of lithium secondary batteries by suppressing side reactions and ensuring uniform SEI layer formation, leading to enhanced charge/discharge efficiency and capacity retention.

Implementation Method 1

a solid electrolyte interface (SEI) layer may be formed on a surface of the silicon-based particle

Methodology Applied

Scientific EffectSolid electrolyte interface (SEI) layer formation: Electrochemiluminescence

Implementation Method 2

an F-intensity obtained by scanning a cross-sectional image of the anode active material layer from a scanning electron microscope-energy dispersion X-ray spectroscopy (SEM-EDS) analysis with a fluorine (F) element

Methodology Applied

Scientific EffectEnergy dispersion X-ray spectroscopy (EDS): X-Ray

Data Source

PatentUS20240413300A1Anode for lithium secondary battery, method of manufacturing the same and lithium secondary battery including the same

Publication Date: 2024.12.12 SK ON CO LTD

AI summary

An anode active material for a secondary battery includes an anode current collector, and an anode active material layer on at least one surface of the anode current collector. The anode active material layer includes an anode active material and an anode binder. The anode active material includes a composite particle that includes a silicon-based active material particle and a solid electrolyte interphase (SEI) layer formed on at least a portion of a surface of the silicon-based active material particle. An F-density defined by Equation 1 is 23% or less.