Unsaturated Cyclic Carbonate Additives for Stable SEI Formation

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Solution Overview

Problem

Conventional lithium ion batteries with simple electrolyte formulations, such as LiPF6 and cyclic carbonates, fail to provide sufficient protection for carbonaceous negative electrodes like graphite and hard carbon, leading to capacity loss and safety issues due to flammability of co-solvents at high temperatures, and incompatibility with graphite electrodes.

Innovation Solution

Incorporating unsaturated cyclic carbonates like 4-methylene-1,3-dioxolan-2-one and 4,5-dimethylene-1,3-dioxolan-2-one as additives in non-aqueous electrolytic solutions to form a stable solid-electrolyte interface (SEI) on negative electrodes, enhancing cycle life and capacity retention.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional electrolytes with simple formulations (LiPF6 in mixtures of EC and linear carbonates) are used, then the electrolyte can be easily manufactured and operated, but the SEI protection is insufficient leading to capacity loss and poor cycle life

Engineering Contradiction:

ImproveSEI protection and cycle lifeVSAvoidelectrolyte formulation complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies preliminary action by introducing unsaturated cyclic carbonate additives that pre-form protective SEI films on the electrode surface before the battery enters normal operation. These additives react first during initial cycles to create a stable interface layer that prevents subsequent solvent decomposition and electrode degradation, thereby improving reliability without significantly increasing operational complexity

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent employs composite materials by combining conventional electrolyte components (LiPF6, EC, linear carbonates) with unsaturated cyclic carbonate additives. This composite formulation creates a synergistic effect where the additive molecules integrate into the SEI structure to enhance protection capabilities while maintaining the overall electrolyte performance and manufacturing simplicity

Inventive Principle:

Principle #40Composite materials

2Temperature

If a large amount of co-solvents with low viscosity and low melting points (linear carbonates and carboxylate esters) are added to improve low temperature performance, then cell performance at low temperatures is improved, but the co-solvents have low boiling points and are highly flammable presenting safety issues

Engineering Contradiction:

Improvelow temperature performanceVSAvoidflammability and safety issues

Core Design Contradiction:

TemperatureVSObject-affected harmful factors

Solution Approach 1:

The patent applies parameter changes by modifying the chemical composition parameters of the electrolyte - specifically incorporating unsaturated cyclic carbonate additives with specific molecular structures that alter the SEI formation characteristics. This changes the protective properties of the interface layer to provide better thermal stability and flame resistance while maintaining low-temperature ionic conductivity, thus improving safety without sacrificing temperature performance

Inventive Principle:

Principle #35Parameter changes

3Temperature

If propylene carbonate (PC) is used to replace EC to reduce the amount of other co-solvents, then the electrolyte remains liquid over a wide temperature window, but LiPF6-PC based electrolytes are not compatible with graphite electrode due to exfoliation of graphite structure by PC intercalation

Engineering Contradiction:

Improvetemperature windowVSAvoidgraphite electrode compatibility

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The patent applies the intermediary principle by introducing unsaturated cyclic carbonate additives as mediator molecules between PC and the graphite electrode. These additive molecules preferentially adsorb onto the graphite surface and form a protective barrier that prevents PC from intercalating into and exfoliating the graphite structure, thereby enabling PC to be used in graphite-based batteries while maintaining its wide temperature window advantage

Inventive Principle:

Principle #24Intermediary (Mediator)

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 these unsaturated carbonates in lithium ion batteries results in improved cycle life and capacity retention, while maintaining stability across a wide temperature range and preventing electrode exfoliation, thus addressing the limitations of conventional electrolytes.

Implementation Method 1

Methodology Applied

Scientific EffectSolid electrolyte interface (SEI) formation:

Implementation Method 2

non-aqueous electrolytic solutions and electrochemical cells comprising the same

Methodology Applied

Scientific EffectElectrochemical reaction:

Data Source

PatentUS8764853B2Non-aqueous electrolytic solutions and electrochemical cells comprising the same

Publication Date: 2014.07.01 SHENZHEN CAPCHEM TECH CO LTD

AI summary

Non-aqueous electrolyte solutions capable of protecting negative electrode materials such as lithium metal and carbonaceous materials in energy storage electrochemical cells (e.g., lithium metal batteries, lithium ion batteries and supercapacitors) include an electrolyte salt, a non-aqueous electrolyte solvent mixture, an unsaturated organic compound 4-methylene-1,3-dioxolan-2-one or 4,5-dimethylene-1,3-dioxolan-2-one, and other optional additives. The 1,3-dioxolan-2-ones help to form a good solid electrolyte interface on the negative electrode surface.