Hydrofluoroether Liquid Electrolyte for Stable Lithium Metal Cycling

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Solution Overview

Problem

Lithium metal batteries face performance obstacles due to high reactivity between battery components and traditional electrolytes, leading to irreversible reactions, structural instability, and shortened cycle life, primarily caused by the formation of thick solid electrolyte interphase (SEI) layers and volumetric changes in the lithium metal anode.

Innovation Solution

A liquid electrolyte comprising an aprotic solvent, an ionic liquid, a lithium salt, and 8 mol % to 30 mol % hydrofluoroether, with specific molar ratios, which enhances chemical compatibility, thermodynamic stability, and non-flammability, suppressing electrolyte decomposition and improving cell reversibility.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional electrolytes are used in lithium metal batteries, then the battery can operate with basic electrolyte properties, but the high reactivity between battery components and electrolyte causes irreversible reactions, thick SEI layer formation, and shortened cycle life

Engineering Contradiction:

Improvecycle lifeVSAvoidreactivity between battery components and electrolyte

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent introduces a fluorinated cyclic carbonate additive as an intermediary substance that mediates the interaction between lithium metal and the electrolyte. This additive preferentially reacts with lithium to form a stable fluorinated SEI layer that acts as a protective barrier, preventing direct contact and harmful reactions between lithium metal and the bulk electrolyte, thereby extending cycle life while maintaining basic electrolyte functionality

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent modifies the chemical composition parameters of the electrolyte by incorporating fluorinated cyclic carbonate compounds with specific molecular structures and ratios. This parameter change transforms the electrolyte's chemical properties to create a more stable interface with lithium metal, reducing reactivity and preventing the formation of thick, unstable SEI layers that would otherwise shorten battery cycle life

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If conventional electrolytes are used, then the battery structure remains simple, but volumetric changes in lithium metal anode during cycling cause structural instability due to frail SEI films

Engineering Contradiction:

Improvestructural stabilityVSAvoidvolumetric changes during cycling

Core Design Contradiction:

Stability of the object's compositionVSDuration of action of moving object

Solution Approach 1:

The patent applies beforehand cushioning by pre-forming a robust fluorinated SEI layer on the lithium metal surface before significant volumetric changes occur during cycling. This pre-formed protective layer acts as a cushioning barrier that accommodates and buffers the mechanical stress from lithium's volumetric expansion and contraction, preventing structural instability and maintaining integrity throughout the battery's operational life

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Reliability

If traditional electrolyte compositions are used, then the electrolyte maintains basic ionic conductivity, but irreversible reactions consume lithium and electrolyte, increasing internal resistance

Engineering Contradiction:

Improvecapacity retentionVSAvoidconsumption of lithium and electrolyte

Core Design Contradiction:

ReliabilityVSLoss of substance

Solution Approach 1:

The patent converts the harmful irreversible reactions between lithium metal and traditional electrolytes into a beneficial process by introducing fluorinated cyclic carbonate additives. These additives deliberately undergo controlled reactions to form stable fluorinated SEI layers, converting what would be continuous harmful consumption of lithium and electrolyte into a one-time beneficial formation process that protects against future substance loss and maintains capacity retention

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 electrolyte composition achieves at least a 50% improvement in cycle life, extends capacity retention, and delays increases in internal resistance, demonstrating improved stability and performance compared to conventional electrolytes.

Implementation Method 1

the thermodynamic instability of lithium metal can cause irreversible and continuous reactions between lithium metal and the electrolyte that generate thick solid electrolyte interphase (SEI) layers on the lithium metal surface

Methodology Applied

Scientific EffectSolid electrolyte interphase (SEI) layer formation:

Implementation Method 2

Methodology Applied

Scientific EffectChemical compatibility and thermodynamic stability:

Data Source

PatentUS11908998B2Liquid electrolyte for lithium metal battery

Publication Date: 2024.02.20 APPLE INC

AI summary

Liquid electrolytes for a lithium metal battery comprise an aprotic solvent, an ionic liquid, a lithium salt, 8 mol % to 30 mol % hydrofluoroether and up to 5 mol % additives. A molar ratio of the hydrofluoroether to the lithium salt is 0.22:1 to 0.83:1. The liquid electrolytes achieve at least a 50% improvement in cycle life over conventional electrolytes, extend capacity retention and delay increases in internal resistance.