PVA Graft Copolymer Binder for Silicon Anode Volume Expansion

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Solution Overview

Problem

Conventional binders used in lithium-ion batteries, particularly those with silicon-based negative electrode materials, face challenges such as volume expansion and contraction, leading to reduced adhesion in alkaline environments, which affects the cycle life and performance of the battery.

Innovation Solution

A polyvinyl alcohol graft copolymer is developed, comprising a polyvinyl alcohol main chain with branched chains derived from fluorine-containing ethylenically unsaturated monomers, ethylenically unsaturated carboxylic acid monomers, and ethylenically unsaturated amide monomers, which forms hydrogen bonds and covalent bonds to maintain adhesion in alkaline environments, addressing the issues of volume expansion and contraction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If silicon-based materials are used as negative electrode active material to increase energy density, then the energy density of the lithium-ion battery is greatly increased, but the severe volume expansion and contraction during charging and discharging destroy the structure of the negative electrode plate, resulting in conductive network collapse and electrode plate peeling

Engineering Contradiction:

Improveenergy densityVSAvoidstructure stability

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent modifies the chemical composition parameters of the binder by incorporating carboxyl groups with specific content ranges (0.1-10 mmol/g) to change the binding mechanism from physical adhesion to chemical bonding, enabling the binder to withstand volume expansion and contraction of silicon-based materials

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses a composite binder system comprising polyvinylidene fluoride and carboxymethyl cellulose sodium salt in specific weight ratios (95:5 to 50:50), combining the adhesive properties of PVDF with the structural stability and carboxyl functionality of CMC to simultaneously achieve strong bonding and volume expansion resistance

Inventive Principle:

Principle #40Composite materials

2Strength

If a binder is used to bind electrode active material and conductive material, then the adhesion is improved, but the binder may swell in electrolyte causing the stability of the electrode to decrease

Engineering Contradiction:

ImproveadhesionVSAvoidelectrode stability

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent controls the carboxyl group content parameter within specific ranges (0.1-10 mmol/g) to optimize the balance between adhesion strength and electrolyte stability, preventing excessive swelling while maintaining sufficient bonding capability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces carboxyl groups specifically at the binder interface with the electrode materials, creating localized chemical bonding zones that provide strong adhesion without requiring the entire binder volume to be highly reactive, thus maintaining overall stability

Inventive Principle:

Principle #3Local quality

3Reliability

If PAA is used as binder to form hydrogen bonding force with silicon-based material surface to inhibit volume expansion, then the volume expansion is inhibited, but the PAA is hygroscopic requiring high temperature drying for long time and needs to be used together with CMC and/or SBR to avoid brittleness

Engineering Contradiction:

Improvevolume expansion inhibitionVSAvoiddrying process complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent uses CMC sodium salt as a more manufacturable alternative to PAA, achieving volume expansion inhibition through carboxyl groups without the severe hygroscopicity and brittleness problems of PAA, simplifying the manufacturing process

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The patent modifies the chemical structure parameters by using CMC with controlled carboxyl group content (0.1-10 mmol/g) instead of PAA, reducing hygroscopicity while maintaining volume expansion inhibition capability

Inventive Principle:

Principle #35Parameter changes

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 polyvinyl alcohol graft copolymer enhances the adhesion and flexibility of electrode plates, reducing pulverization and cracking, thereby increasing the cycle life and electrochemical performance of lithium-ion batteries.

Implementation Method 1

The PAA has a carboxyl group, which can form a hydrogen bonding force with the surface of the silicon-based material to inhibit the volume expansion of the silicon-based material

Methodology Applied

Scientific EffectHydrogen bonding: Chemical Bonding

Implementation Method 2

forms hydrogen bonds and covalent bonds to maintain adhesion in alkaline environments

Methodology Applied

Scientific EffectCovalent bonding: Chemical Bonding

Data Source

PatentUS11827730B2Graft copolymer and use thereof

Publication Date: 2023.11.28 ETERNAL MATERIALS CO LTD

AI summary

The present invention provides a polyvinyl alcohol graft copolymer including a polyvinyl alcohol main chain. The polyvinyl alcohol graft copolymer includes branched chains including structural units derived from the following monomers: (a) a fluorine-including ethylenically unsaturated monomer, (b) an ethylenically unsaturated carboxylic acid monomer, and (c) an ethylenically unsaturated amide monomer. The present invention also provides an aqueous binder composition, and an electrode slurry composition including the polyvinyl alcohol graft copolymer.