Ionic Liquid Electrolyte Composition for Low-Flammability Li-Ion Cells

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Solution Overview

Problem

Lithium-ion secondary batteries face challenges in achieving high charge and discharge capacity, excellent cycle performance, safety, and reliability, particularly due to issues with non-aqueous electrolytes' volatility and flammability, which can lead to explosions or fires.

Innovation Solution

Development of a novel ionic liquid with a specific cation and anion structure, combined with a positive electrode active material having a layered rock-salt crystal structure and additives like magnesium and fluorine, to enhance safety and performance, and the use of additives such as succinonitrile and fluoroethylene carbonate in the electrolyte.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If organic solvents with high dielectric constant and excellent ionic conductivity (e.g., ethylene carbonate) are used in nonaqueous electrolyte, then ionic conductivity and energy density are improved, but volatility and flammability increase leading to safety issues

Engineering Contradiction:

Improveionic conductivityVSAvoidflammability and volatility

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the physical and chemical parameters of the electrolyte by replacing conventional organic solvents with ionic liquids. This substitution fundamentally alters the safety parameters (flammability, volatility) while maintaining or improving ionic conductivity through careful selection of ionic liquid components and ratios

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite electrolyte systems combining ionic liquids with conventional organic solvents or additives. This composite approach allows the system to inherit the high ionic conductivity of organic solvents while the ionic liquid component provides enhanced safety by suppressing flammability and volatility

Inventive Principle:

Principle #40Composite materials

2Object-affected harmful factors

If ionic liquids are used as solvent in nonaqueous electrolyte, then flammability and volatility are reduced improving safety, but manufacturing cost increases

Engineering Contradiction:

Improveflammability and volatilityVSAvoidmanufacturing cost

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The patent optimizes the concentration parameters of ionic liquids in the electrolyte system, using them in specific ratios rather than pure form. This parameter optimization reduces the amount of expensive ionic liquid required while maintaining sufficient safety improvements, thereby lowering manufacturing costs

Inventive Principle:

Principle #35Parameter changes

3Quantity of substance

If lithium-ion secondary batteries are designed for high energy density, then power storage capacity is improved, but charge and discharge cycle performance and reliability deteriorate

Engineering Contradiction:

Improveenergy densityVSAvoidcycle performance

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent changes the electrolyte composition parameters to include ionic liquids that form stable solid electrolyte interface (SEI) films on electrode surfaces. This parameter change enables the battery to achieve both high energy density and excellent cycle performance by preventing electrode degradation during repeated charging and discharging

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses ionic liquids as sacrificial components that form protective films on electrodes during initial cycles. These ionic liquid-derived films act as durable protective layers that enable long-term battery operation, allowing the expensive ionic liquid to serve its purpose efficiently

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 solution provides a lithium-ion secondary battery with improved charge and discharge capacity, excellent cycle performance, enhanced safety, and reduced irreversible capacity, enabling reliable and long-life operation across a wide temperature range.

Implementation Method 1

an ionic liquid with non-flammability and non-volatility has been proposed to be used as a solvent of a nonaqueous electrolyte

Methodology Applied

Scientific EffectIonic conductivity: Conduction (electrical)

Implementation Method 2

a positive electrode active material having a layered rock-salt crystal structure

Methodology Applied

Scientific EffectIon insertion/extraction: Absorption (physical)

Data Source

PatentUS20240097194A1Ionic liquid, secondary battery, electronic device, and vehicle

Publication Date: 2024.03.21 SEMICON ENERGY LAB CO LTD

AI summary

A novel ionic liquid is provided. A highly safe secondary battery with high charge and discharge capacity is provided. The ionic liquid includes a cation represented by General Formula (G1) and an anion represented by Structural Formula (200). In the formula, X1 to X3 each independently represent any one of fluorine, chlorine, bromine, and iodine. One of X1 to X3 may be hydrogen. In addition, n and m each independently represent 0 to 5. Furthermore, a secondary battery including the above-described ionic liquid is provided.