Lithium-Ion Negative Electrode Particle Size Control

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Solution Overview

Problem

Lithium-ion secondary batteries face challenges in cyclability and discharge capacity due to volumetric changes in negative-electrode active-material particles, leading to film cracking and electrolyte degradation, which affects charging and discharging performance.

Innovation Solution

Controlling the particle diameters of negative-electrode active-material particles to 85% or more at 1 μm or larger, with a specific surface area of 6 m2/g or less and a D50 of 4.5 μm or more, and using a fluorinated ethylene carbonate solvent in the electrolyte to stabilize the film and prevent electrolyte degradation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the particle diameter of negative-electrode active-material particles is reduced to increase discharge capacity, then the discharge capacity is improved, but the film cracks due to volumetric changes, leading to electrolyte degradation and reduced cyclability

Engineering Contradiction:

Improvedischarge capacityVSAvoidcyclability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent applies parameter changes by optimizing the particle size distribution of negative-electrode active material particles. Specifically, it controls the volume ratio of particles with diameter ≤1 μm to be 15% or less, and sets the D50 (median diameter) to 4.5 μm or more. This parameter optimization reduces volumetric changes during lithium ion insertion/extraction, preventing film cracking while maintaining high discharge capacity, thus resolving the contradiction between productivity and reliability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite materials by combining negative-electrode active material particles with specific surface area characteristics (6 m²/g or less) with a binder containing fluorinated ethylene carbonate. This composite structure creates a stable film that accommodates volumetric changes without cracking, allowing both high discharge capacity and good cyclability to be achieved simultaneously

Inventive Principle:

Principle #40Composite materials

2Productivity

If the specific surface area of negative-electrode active-material particles is increased to improve discharge capacity, then the discharge capacity is improved, but the film stress increases causing cracks and electrolyte contact

Engineering Contradiction:

Improvedischarge capacityVSAvoidfilm cracking and electrolyte degradation

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent applies parameter changes by controlling the specific surface area of negative-electrode active material particles to be 6 m²/g or less. This parameter optimization reduces film stress during volumetric changes, preventing film cracking and electrolyte degradation, while maintaining high discharge capacity through optimized particle size distribution

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the potentially harmful effect of high specific surface area (which causes film stress) into a benefit by combining particles with controlled surface area characteristics with fluorinated ethylene carbonate binder. This combination creates a flexible film that can accommodate volumetric changes without cracking, transforming the stress issue into a mechanism for maintaining film integrity during charging/discharging cycles

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 approach enhances cyclability and discharge capacity by reducing film stress and cracking, maintaining electrolyte stability, and improving the overall performance of lithium-ion secondary batteries.

Implementation Method 1

a negative electrode, which comprises: a current collector; and a negative-electrode active-material layer formed on a surface of the current collector, and including negative-electrode active-material particles... capable of sorbing and desorbing lithium ions

Methodology Applied

Scientific EffectSorption: Sorption

Implementation Method 2

A film is formed on a surface of the negative-electrode active-material particles at the time of charging, and thereby an electrolytic solution is prevented from contacting directly with the negative-electrode active-material particles so that the electrolytic solution is suppressed from deteriorating

Methodology Applied

Scientific EffectFilm formation and stabilization:

Data Source

PatentUS9819008B2Negative-electrode stuff and negative electrode for use in lithium-ion secondary battery as well as lithium-ion secondary battery

Publication Date: 2017.11.14 TOYOTA INDUSTRIES CORP

AI summary

A negative electrode for lithium-ion secondary battery including a negative electrode that includes a current collector; and a negative-electrode active-material layer formed on a surface of the current collector, and including negative-electrode active-material particles. The negative-electrode active-material particles include an element being capable of sorbing and desorbing lithium ions, and being capable of undergoing an alloying reaction with lithium; or/and an elementary compound being capable of undergoing an alloying reaction with lithium, the negative-electrode active-material particles include particles whose particle diameter is 1 μm or more in an amount of 85% by volume or more thereof when the entirety is taken as 100% by volume, and exhibit a “D10” being 3 μm or more. The negative-electrode active-material layer having a thickness that is 1.4 times or more of a “D90” that said negative-electrode active-material particles exhibit.