Polyimide Binder Ring-Opening Suppression in Lithium Cells

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Solution Overview

Problem

Lithium secondary cells using polyimide binders experience ring-opening of imide rings during repetitive charge/discharge, leading to reduced chemical resistance and shortened cell life, necessitating a binder that suppresses this deterioration for improved cycle properties and energy density.

Innovation Solution

A polyimide binder with specific substituents, such as phenylether groups, is used for the negative electrode active material, which enhances electron-donating ability and suppresses ring-opening, allowing reversible reactions with lithium ions and maintaining binding functionality over time.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If polyimide binder is used for negative electrode active material, then binding functionality and adhesion are achieved, but ring-opening of imide rings occurs during charge/discharge leading to reduced chemical resistance and shortened cell life

Engineering Contradiction:

Improvebinding functionalityVSAvoidchemical resistance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent modifies the chemical structure of polyimide by introducing specific substituents (alkyl, alkoxy, acyl, phenyl, or phenoxy groups) at the 3-position of the imide ring. This structural parameter change enhances electron-donating ability to the carbonyl group, which stabilizes the imide ring and suppresses ring-opening reactions during lithium ion insertion/extraction cycles, thereby maintaining chemical resistance while preserving binding functionality.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite binder system by combining modified polyimide with specific structural characteristics (substituted imide rings) to achieve both binding capability and improved chemical stability. The composite structure integrates the binding function of polyimide with the stabilizing effect of electron-donating substituents, resolving the contradiction between binding strength and chemical resistance.

Inventive Principle:

Principle #40Composite materials

2Ease of manufacture

If conventional polyimide binder is used, then cell assembly is simplified, but cycle deterioration occurs due to imide ring opening during repetitive charge/discharge

Engineering Contradiction:

Improvecell assembly simplicityVSAvoidcell life

Core Design Contradiction:

Ease of manufactureVSDuration of action of stationary object

Solution Approach 1:

The patent introduces substituents with electron-donating groups at the 3-position of the imide ring, which changes the electronic parameters of the polyimide structure. This modification increases the stability of the imide ring against nucleophilic attack by lithium ions during charge/discharge cycles, thereby extending cell life while maintaining the ease of manufacture associated with polyimide-based binders.

Inventive Principle:

Principle #35Parameter changes

3Quantity of substance

If polyimide binder undergoes ring-opening during charge/discharge, then chemical resistance deteriorates, but this leads to reduced energy density and poor cycle properties

Engineering Contradiction:

Improveenergy densityVSAvoidchemical resistance deterioration

Core Design Contradiction:

Quantity of substanceVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary anti-action by pre-modifying the polyimide structure with electron-donating substituents before the battery operates. This pre-established structural feature prevents the harmful ring-opening reaction from occurring during subsequent charge/discharge cycles, thereby protecting chemical resistance and enabling the battery to achieve both high energy density and good cycle properties without the detrimental effects of binder degradation.

Inventive Principle:

Principle #9Preliminary anti-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 polyimide binder extends the life of lithium secondary cells by reducing chemical resistance deterioration, enhancing energy density, and improving cycle properties, enabling the production of cells with superior charge/discharge performance and extended lifespan.

Implementation Method 1

the polyimide has the function of a negative electrode active material because it reacts reversibly with lithium ions during charge/discharge

Methodology Applied

Scientific EffectReversible reaction with lithium ions: Absorption (physical)

Implementation Method 2

when polyimide is obtained using diamine substituted with specific substituents as a raw material, the polyimide exhibits reduced ring-opening of imide rings during repetitive charge/discharge and suppresses the deterioration of chemical resistance

Methodology Applied

Scientific EffectElectron-donating effect:

Data Source

PatentUS9325010B2Negative electrode active material for lithium secondary cell, lithium secondary cell employing the same, and method for producing the same

Publication Date: 2016.04.26 NEC CORP

AI summary

Provided is a negative electrode active material for a lithium secondary cell, the material having the function of a binder for the active material, and being capable of stable reversible reactions with lithium. Also, provided are an extended-life lithium secondary cell having improved energy density and stable charge/discharge, and a method for producing the same. The negative electrode active material for a lithium secondary cell is polyimide represented by formula (1) (wherein R1 and R2 independently denote an alkyl, alkoxy, acyl, phenyl, or phenoxy group).