Silyl Compound Electrolyte for Graphite Battery Resistance

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Solution Overview

Problem

The use of graphite with a small specific surface area in non-aqueous electrolyte secondary batteries leads to increased internal resistance due to surface film formation and substance buildup, which affects cycle characteristics and capacity retention.

Innovation Solution

Incorporating a silyl compound represented by the formula (R1R2R3Si—O)m-M=(O)n in the non-aqueous electrolyte, where M is P, B, or S, and R1 to R3 are alkyl, fluoroalkyl, alkenyl, or aryl groups, to suppress the rise in resistance by forming a conductive surface film at the positive electrode, reducing substance migration to the negative electrode.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If graphite with small specific surface area is used in negative electrode, then cycle characteristics are improved, but internal resistance increases due to thick surface film formation

Engineering Contradiction:

Improvecycle characteristicsVSAvoidinternal resistance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A silyl compound is introduced as an intermediary substance in the non-aqueous electrolyte. This compound mediates between the graphite negative electrode and the electrolyte, forming a protective surface film that prevents excessive substance deposition while maintaining low resistance, thus resolving the contradiction between cycle life and internal resistance

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention changes the chemical composition parameters of the electrolyte by adding a silyl compound with specific molecular structure (formula (1)). This parameter change modifies the surface film formation characteristics, enabling the film to be both protective (improving cycle characteristics) and conductive (maintaining low internal resistance)

Inventive Principle:

Principle #35Parameter changes

2Loss of substance

If graphite with small specific surface area is used, then side reaction with electrolyte is reduced, but surface film becomes thick and resistance increases

Engineering Contradiction:

Improveside reactionVSAvoidsurface film thickness

Core Design Contradiction:

Loss of substanceVSObject-affected harmful factors

Solution Approach 1:

The silyl compound acts as an intermediary that modifies the interface between graphite and electrolyte. It forms a surface film with optimized properties that reduces side reactions while preventing excessive thickness, thus resolving the contradiction between substance loss and film thickness

Inventive Principle:

Principle #24Intermediary (Mediator)

3Quantity of substance

If intercalation/deintercalation amount of Li ions per unit area increases, then capacity is improved, but surface film thickens and resistance increases

Engineering Contradiction:

ImproveLi ion intercalation amountVSAvoidsurface film resistance

Core Design Contradiction:

Quantity of substanceVSObject-affected harmful factors

Solution Approach 1:

By changing the electrolyte composition to include a silyl compound, the surface film properties are modified to accommodate higher Li ion intercalation amounts without proportionally increasing resistance. The silyl compound enables the film to maintain conductivity even as thickness increases due to higher ion traffic

Inventive Principle:

Principle #35Parameter changes

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 approach effectively reduces the increase in negative electrode resistance and improves cycle characteristics and capacity retention by minimizing substance buildup on the graphite surface, while maintaining high capacity retention ratios.

Implementation Method 1

by containing a silyl compound represented by a formula (1): (R1R2R3Si—O)m-M=(O)n in the non-aqueous electrolyte, the rise in the resistance can be suppressed

Methodology Applied

Scientific EffectSurface film formation: Deposition (physical)

Data Source

PatentUS20220029164A1Nonaqueous electrolyte secondary battery and nonaqueous electrolytic solution

Publication Date: 2022.01.27 PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO LTD

AI summary

A non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The negative electrode includes a graphite. The graphite has a BET specific surface area of 3 m2/g or less. The non-aqueous electrolyte includes a silyl compound represented by a formula (1): (R1R2R3Si—O)m-M=(O)n. In the formula (1), M is P, B or S, n is 0, 1 or 2, m is 2 or 3, and each of R1 to R3 is independently an alkyl group, a fluoroalkyl group, an alkenyl group, a fluoroalkenyl group, an aryl group, a fluoroaryl group, or a hydrogen atom.