Amorphous-Coated Graphite and Lithium Fluorosulfonate for Battery Performance

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Solution Overview

Problem

Nonaqueous electrolyte secondary cells, particularly those used in electric vehicles and hybrid vehicles, face challenges in achieving high Li precipitation resistance and high-rate characteristics simultaneously, especially when using amorphous-coated graphite with low oil absorption amounts, which can lead to deteriorated Li precipitation resistance and capacity retention.

Innovation Solution

Incorporating lithium fluorosulfonate (FSO3Li) in the nonaqueous electrolytic solution at a specific weight proportion (0.65 wt % to 0.85 wt %) and using amorphous-coated graphite with an oil absorption amount of 35 ml/100 g to 50 ml/100 g to stabilize the electrolyte chemically and electrochemically, forming a negative electrode SEI film that enhances both Li precipitation resistance and high-rate characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If amorphous-coated graphite with low oil absorption amount is used to improve high-rate characteristic, then rapid charge/discharge capability is enhanced, but Li precipitation resistance deteriorates

Engineering Contradiction:

Improvehigh-rate characteristicVSAvoidLi precipitation resistance

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent optimizes the oil absorption amount parameter of amorphous-coated graphite to a specific range (35-50 ml/100g) to balance high-rate characteristic and Li precipitation resistance. This parameter adjustment resolves the contradiction by finding the optimal value that satisfies both requirements simultaneously.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses amorphous-coated graphite as a composite negative electrode active material, combining graphite particles with amorphous carbon coating. This composite structure improves both high-rate characteristic and Li precipitation resistance compared to uncoated graphite, resolving the technical contradiction through material composition optimization.

Inventive Principle:

Principle #40Composite materials

2Productivity

If amorphous-coated graphite is used to suppress electrolytic solution decomposition products deposition, then occlusion/release of lithium ions is improved, but capacity retention deteriorates in long-term use

Engineering Contradiction:

Improveocclusion/release of lithium ionsVSAvoidcapacity retention

Core Design Contradiction:

ProductivityVSDuration of action of stationary object

Solution Approach 1:

The patent specifies the oil absorption amount of amorphous-coated graphite within the range of 35-50 ml/100g to optimize both lithium ion occlusion/release performance and capacity retention. This parameter control ensures long-term stability while maintaining high ion transfer efficiency.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The amorphous carbon coating on graphite particles creates a composite structure that prevents electrolytic solution decomposition products from depositing on the graphite surface, thereby maintaining both ion transfer capability and capacity retention over extended periods.

Inventive Principle:

Principle #40Composite materials

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

This configuration effectively prevents deterioration of Li precipitation resistance while maintaining excellent high-rate characteristics, enabling the construction of high-performance nonaqueous electrolyte secondary cells with improved capacity retention and rapid charge/discharge capabilities.

Implementation Method 1

the nonaqueous electrolytic solution includes lithium fluorosulfonate (FSO3Li)... to stabilize the electrolyte chemically and electrochemically

Methodology Applied

Scientific EffectChemical stabilization:

Implementation Method 2

forming a negative electrode SEI film that enhances both Li precipitation resistance and high-rate characteristics

Methodology Applied

Scientific EffectSEI film formation:

Implementation Method 3

Amorphous-coated graphite in which the surface of graphite particles is coated with amorphous carbon has been studied for use as a negative electrode active material... to suppress the deposition of electrolytic solution decomposition products

Methodology Applied

Scientific EffectSurface coating protection: Coatings

Data Source

PatentUS10897064B2Nonaqueous electrolyte secondary cell including negative electrode active material made of amorphous-coated graphite and electrolytic solution including lithium fluorosulfonate

Publication Date: 2021.01.19 TOYOTA JIDOSHA KK

AI summary

A cell assembly before initial charging, including an electrode body having a positive electrode and a negative electrode, a nonaqueous electrolytic solution including a nonaqueous solvent and a supporting salt, and a case housing the electrode body and the nonaqueous electrolytic solution. The negative electrode has a negative electrode mixture layer including a particulate negative electrode active material made of amorphous-coated graphite in which the surface of graphite particles is coated with amorphous carbon, and the nonaqueous electrolytic solution includes lithium fluorosulfonate. The oil absorption amount of the negative electrode active material is 35 ml/100 g to 50 ml/100 g, and a weight proportion of the lithium fluorosulfonate in the nonaqueous electrolytic solution is 0.65 wt % to 0.85 wt %. As a result, it is possible to provide a high-performance nonaqueous electrolyte secondary cell in which both the high-rate characteristic and the Li precipitation resistance are realized at a high level.