Isocyanate Additive for Silicon Negative Electrode Cycle Stability

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Lithium-ion secondary batteries with negative-electrode active materials like Si, Sn, and Pb face challenges in long-term cycle characteristics due to volume expansion, particle size reduction, and electrolyte reactions, which are not adequately addressed by existing nonaqueous electrolytic solutions.

Innovation Solution

A nonaqueous electrolytic solution containing a lithium salt, a nonaqueous solvent, and an isocyanate compound with an aromatic ring, along with monofluorophosphate, difluorophosphate, and carbonate additives, forming a protective film on the negative electrode to enhance cycle characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If negative-electrode active materials containing Si, Sn, Pb are used to increase capacity, then battery capacity is improved, but cycle characteristics deteriorate due to volume expansion and electrolyte reactions

Engineering Contradiction:

Improvebattery capacityVSAvoidcycle characteristics

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent introduces an isocyanate compound as an intermediary substance that forms a protective film between the negative electrode active material (Si, Sn, Pb) and the electrolyte. This film acts as a mediator that prevents direct harmful interactions while allowing lithium ion transport, thereby resolving the contradiction between using high-capacity materials and maintaining cycle stability

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The isocyanate compound performs preliminary action by forming a protective film on the surface of the negative electrode active material before significant degradation occurs. This preliminary protective layer prevents volume expansion damage and electrolyte reactions during subsequent charging-discharging cycles, maintaining both capacity and cycle characteristics

Inventive Principle:

Principle #10Preliminary action

2Reliability

If heterocyclic compounds containing sulfur or oxygen are added to form protective films, then cycle characteristics are improved, but the effectiveness is insufficient for Si, Sn, Pb-based electrodes

Engineering Contradiction:

Improvecycle characteristicsVSAvoideffectiveness for different electrode materials

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent changes the chemical parameters of the electrolyte additive by introducing an isocyanate compound with specific functional groups (NCO group) that are more effective for Si, Sn, Pb-based electrodes. This parameter change in the additive's chemical structure provides better adaptability and effectiveness compared to traditional heterocyclic compounds containing only sulfur or oxygen

Inventive Principle:

Principle #35Parameter changes

3Reliability

If isocyanate compounds are incorporated into electrolyte, then cycle characteristics improve, but high-temperature storage characteristics may be affected

Engineering Contradiction:

Improvecycle characteristicsVSAvoidhigh-temperature storage characteristics

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The patent applies local quality by creating a protective film with specific properties at the electrode surface, where the isocyanate compound forms a tailored interface layer that provides cycle stability. The bulk electrolyte composition remains unchanged, allowing the system to maintain cycle characteristics improvement while managing high-temperature storage through localized modification at the critical electrode-electrolyte interface

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

The solution significantly improves the cycle characteristics of lithium-ion secondary batteries with Si, Sn, and Pb-based negative electrodes by inhibiting electrolyte reactions and reducing capacity loss over time.

Implementation Method 1

adding a heterocyclic compound containing a sulfur atom and/or an oxygen atom in its ring to a nonaqueous electrolytic solution to form a film on a surface of a negative-electrode active material

Methodology Applied

Scientific EffectFilm formation: Deposition (physical)

Implementation Method 2

the incorporation of an isocyanate compound into a nonaqueous electrolytic solution improves cycle characteristics and high-temperature storage characteristics

Methodology Applied

Scientific EffectChemical reaction: Chemical Bonding

Data Source

PatentEP2190054B1Nonaqueous electrolyte solution for secondary battery and nonaqueous electrolyte secondary battery

Publication Date: 2016.10.26 MITSUBISHI CHEM CORP

AI summary

A nonaqueous electrolytic solution effective in improving cycle characteristics and used for a nonaqueous electrolyte secondary battery including a positive electrode having a positive-electrode active material capable of storing and releasing metal ions and a negative electrode having a negative-electrode active material containing at least one atom selected from the group consisting of Si, Sn, and Pb includes an electrolyte, a nonaqueous solvent, and an isocyanate compound having at least one aromatic ring in its molecule.