Fluorinated Ester Electrolyte for Battery Capacity Retention

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Solution Overview

Problem

Non-aqueous electrolyte secondary batteries face issues with capacity degradation and poor battery characteristics under high temperature due to reactions between the electrolyte and electrodes, particularly with the use of fluorinated solvents which increase viscosity and reactivity with the negative electrode.

Innovation Solution

A non-aqueous electrolyte comprising a solvent with chain fluorinated carboxylic acid ester, such as 2,2-difluoroethyl acetate or 2,2,2-trifluoroethyl acetate, and a film-forming chemical compound decomposed between +1.0 to 3.0 V, along with lithium salts like LiPF6, is used to suppress reactions and maintain battery performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If fluorinated solvents are used to suppress reaction with positive electrode, then oxidation-resistance is improved, but viscosity increases and reactivity with negative electrode increases

Engineering Contradiction:

Improveoxidation-resistanceVSAvoidreactivity with negative electrode

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies local quality by selectively fluorinating specific carbon positions (β or γ carbons) in the carboxylic acid ester chain while leaving the α carbon unfluorinated. This localized fluorination approach optimizes the balance between oxidation-resistance at the positive electrode interface and reactivity control at the negative electrode interface, avoiding the harmful effects of complete chain fluorination.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes the chemical structure parameters of the solvent by introducing fluorine atoms at specific positions (β or γ carbons) in the carboxylic acid ester chain. This parameter modification improves oxidation-resistance while controlling viscosity and reactivity with the negative electrode, resolving the contradiction between these properties.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If chain fluorinated carboxylic acid ester is used as solvent, then reaction with positive electrode is suppressed, but battery capacity decreases under high temperature

Engineering Contradiction:

Improvereaction suppression with positive electrodeVSAvoidbattery capacity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent uses local quality by fluorinating only specific carbon positions (β or γ) rather than the entire chain, including the α carbon. This selective approach maintains sufficient reactivity with the negative electrode for capacity retention while providing adequate oxidation-resistance at the positive electrode, especially under high temperature conditions.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent employs composite materials by combining fluorinated carboxylic acid ester with other non-aqueous solvents in a mixed solvent system. This composite approach balances the oxidation-resistance benefits of fluorination with the capacity-maintaining properties of the other solvents, preventing capacity loss under high temperature storage.

Inventive Principle:

Principle #40Composite materials

3Reliability

If hydrogen at α carbon is replaced with fluorine, then oxidation-resistance is improved, but lithium salt dissolution is poor and reactivity with negative electrode increases

Engineering Contradiction:

Improveoxidation-resistanceVSAvoidreactivity with negative electrode

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies local quality by specifically avoiding fluorination of the α carbon while fluorinating β or γ carbons. This selective local modification preserves the essential properties for lithium salt dissolution and negative electrode compatibility while still providing oxidation-resistance through fluorination at other positions in the molecule.

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

This configuration effectively restricts capacity loss and maintains favorable battery characteristics over time by forming a protective film on the negative electrode and reducing reactions with the positive electrode, enhancing storage properties and load characteristics.

Implementation Method 1

a film forming chemical decomposed in the range of +1.0 to 3.0 V based on an equilibrium potential between metal lithium and lithium ion

Methodology Applied

Scientific EffectDecomposition: Decomposition (biological)

Implementation Method 2

a non-aqueous solvent dissolving lithium salt

Methodology Applied

Scientific EffectDissolution: Solvation

Data Source

PatentUS8097368B2Non-aqueous electrolyte for secondary battery and non-aqueous electrolyte secondary battery

Publication Date: 2012.01.17 PANASONIC ENERGY CO LTD

AI summary

The present invention provides a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte comprises a non-aqueous solvent and lithium salt as an electrolyte, and wherein the non-aqueous solvent contains chain fluorinated carboxylic acid ester represented by the formula CH3COOCH2CH3-xFx (wherein x is 2 or 3) and a film forming chemical decomposed in the range of +1.0 to 3.0 V based on an equilibrium potential between metal lithium and lithium ion.