Nonaqueous Electrolyte Ionic Liquid Composition for Battery Safety

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Solution Overview

Problem

Lithium secondary batteries using ethylene carbonate as a solvent in their nonaqueous electrolyte face risks of ignition and explosion due to extended constant-voltage charging periods, which can occur if the charging current decreases below a desired value, potentially leading to safety hazards and reduced reliability.

Innovation Solution

A power storage device incorporating a nonaqueous electrolyte with an ionic liquid containing an alicyclic quaternary ammonium cation and a cyclic ester, such as ethylene carbonate, with an ionic liquid content of 70-100 wt% or 50-80 wt% in the electrolyte, which suppresses decomposition reactions and maintains ion conductivity, preventing extended charging periods and enhancing safety and reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If ethylene carbonate is used as a solvent for nonaqueous electrolyte, then ion conductivity is improved, but the constant-voltage charging period becomes extended leading to safety risks

Engineering Contradiction:

Improveion conductivityVSAvoidignition and explosion risk

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the chemical composition parameters of the electrolyte by introducing ionic liquids with specific structures (imidazolium, pyridinium, phosphonium cations) to modify the charging characteristics and suppress decomposition reactions, thereby resolving the contradiction between maintaining ion conductivity and preventing extended charging periods

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite electrolyte system combining ethylene carbonate with ionic liquids, where the ionic liquid component suppresses decomposition reactions and shortens the constant-voltage charging period while the ethylene carbonate maintains ion conductivity, thus resolving the safety-conductivity contradiction

Inventive Principle:

Principle #40Composite materials

2Reliability

If CCCV charging is performed until charging current becomes lower than desired value, then full charging is achieved, but the charging period becomes extended causing temperature rise and safety risks

Engineering Contradiction:

Improvecharging completenessVSAvoidinternal temperature

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The patent changes the electrolyte composition to include ionic liquids that suppress decomposition reactions, allowing the charging current to decrease to the desired threshold value without excessive delay, thereby achieving full charging while controlling the constant-voltage period and preventing temperature rise

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If CV charging is terminated by timer when predetermined period passes, then safety is improved, but charging may be incomplete reducing productivity

Engineering Contradiction:

Improveignition and explosion riskVSAvoidcharging efficiency

Core Design Contradiction:

Object-affected harmful factorsVSProductivity

Solution Approach 1:

The patent changes the electrolyte composition to include ionic liquids that inherently suppress decomposition reactions and shorten the constant-voltage charging period, allowing the timer to be set to a shorter predetermined time while still achieving complete charging, thus improving both safety and productivity

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 use of this electrolyte composition prevents extended charging periods, reduces the risk of ignition and explosion, and provides a power storage device with improved safety, reliability, and charging/discharging rate characteristics.

Implementation Method 1

an ionic liquid which has non-flammability and non-volatility as a solvent for a nonaqueous electrolyte has been proposed

Methodology Applied

Scientific EffectDecomposition reaction suppression:

Implementation Method 2

a nonaqueous electrolyte (also referred to as 'nonaqueous electrolyte solution') including a nonaqueous solvent and a lithium salt containing lithium ions

Methodology Applied

Scientific EffectIon conductivity: Conduction (electrical)

Implementation Method 3

Characteristics such as high energy density, excellent cycle characteristics and safety under a variety of operating environments are necessary for the lithium secondary battery

Methodology Applied

Scientific EffectIon insertion/extraction:

Data Source

PatentUS9577290B2Nonaqueous solvent, nonaqueous electrolyte, and power storage device

Publication Date: 2017.02.21 SEMICON ENERGY LAB CO LTD

AI summary

A power storage device using an organic solvent as a nonaqueous solvent for a nonaqueous electrolyte, in which a CV charging period in CCCV charging can be prevented from being extended and which has high performance, can be provided. The power storage device includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. The nonaqueous electrolyte includes an ionic liquid including an alicyclic quaternary ammonium cation having one or more substituents and a counter anion to the alicyclic quaternary ammonium cation, a cyclic ester, and an alkali metal salt. In particular, in the power storage device, the ionic liquid content is greater than or equal to 70 wt % and less than 100 wt % per unit weight of the ionic liquid and the cyclic ester in the nonaqueous electrolyte, or greater than or equal to 50 wt % and less than 80 wt % per unit weight of the nonaqueous electrolyte.