Positive Electrode Binder Composition With Controlled Swelling

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Solution Overview

Problem

There is a need for a composition that balances the suppression of battery performance degradation, high-temperature storage properties, and DC resistance in lithium ion secondary batteries, which existing binders fail to achieve effectively.

Innovation Solution

A graft copolymer composition is developed, comprising a stem polymer with a polyvinyl alcohol structure and a branch polymer containing (meth)acrylonitrile or (meth)acrylic acid monomer units, with a specific swelling rate and crosslinking agent content, to create a binder that maintains battery performance and resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional binders are used, then battery assembly is straightforward, but battery performance degradation is not sufficiently suppressed

Engineering Contradiction:

Improvebattery performance degradation suppressionVSAvoidbinder structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention uses a graft copolymer comprising polyvinyl alcohol as the stem polymer and (meth)acrylonitrile/(meth)acrylic acid as the branch polymer, creating a composite material structure that combines the advantages of both polymer systems to suppress battery performance degradation while maintaining manufacturability

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The invention specifies precise parameter ranges including swelling rate (105-200% at 25°C for 15 days), content ratios of stem polymer to branch polymer (95:5 to 50:50 by mass), and saponification degree (70-100%), thereby optimizing binder performance through controlled parameter variations

Inventive Principle:

Principle #35Parameter changes

2Quantity of substance

If high-capacity electrode is used, then energy density increases, but battery performance degradation accelerates

Engineering Contradiction:

Improveenergy densityVSAvoidbattery performance degradation

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The invention optimizes the swelling rate parameter to 105-200% at 25°C for 15 days and controls the content ratio of stem polymer to branch polymer within 95:5 to 50:50 by mass, thereby achieving optimal binder performance that supports high-capacity electrodes while suppressing performance degradation

Inventive Principle:

Principle #35Parameter changes

3Reliability

If binder composition is optimized for performance, then battery performance improves, but manufacturing complexity increases

Engineering Contradiction:

Improvebattery performanceVSAvoidbinder manufacturing complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The invention defines specific parameter ranges including swelling rate (105-200%), content ratios (95:5 to 50:50 by mass), and saponification degree (70-100%), which can be controlled during synthesis to achieve optimal performance while maintaining manufacturing feasibility

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention applies different functional properties to different parts of the binder molecule, with the polyvinyl alcohol stem providing structural integrity and the (meth)acrylonitrile/(meth)acrylic acid branches providing electrochemical compatibility, thereby optimizing performance through localized functional differentiation

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 composition effectively suppresses battery performance degradation, enhances high-temperature storage properties, and reduces DC resistance, improving the overall performance of lithium ion secondary batteries.

Implementation Method 1

the composition has a swelling rate to an electrolytic solution of 105 to 200% at 25° C. for 15 days; the swelling rate is a swelling rate after immersing the composition in the electrolytic solution at 25° C. for 15 days

Methodology Applied

Scientific EffectSwelling: Absorption (physical)

Data Source

PatentUS20230317951A1Composition, positive electrode composition, positive electrode slurry, positive electrode, and secondary battery

Publication Date: 2023.10.05 DENKA CO LTD

AI summary

A composition, serving as a binder with a good balance between suppression of battery performance degradation at a high-capacity electrode, high-temperature storage property, and DC resistance, a slurry for a positive electrode using the composition, a positive electrode, and a secondary battery. The composition includes a graft copolymer, wherein: the graft copolymer has a stem polymer and a branch polymer; the stem polymer contains a polyvinyl alcohol structure, the branch polymer contains a first monomer unit containing a (meth)acrylonitrile monomer unit and/or a (meth)acrylic acid monomer; the composition has a swelling rate to an electrolytic solution of 105 to 200% at 25° C. for 15 days; the swelling rate is a swelling rate after immersing the composition in the electrolytic solution at 25° C. for 15 days; and the electrolytic solution is obtained by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 1:2.