Fluorine-Containing Coating Film for Negative Electrode

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Solution Overview

Problem

In nonaqueous electrolyte secondary batteries, the introduction of fluorine in the solvent leads to increased negative electrode resistance and internal resistance due to irreversible reactions between the nonaqueous solvent and lithium salt, and the generation of a solid electrolyte interface (SEI) on the negative electrode.

Innovation Solution

A nonaqueous electrolyte secondary battery with a negative electrode coated with a lithium ion-permeable film containing elements like P, Si, B, V, Nb, W, Ti, Zr, Al, Ba, La, or Ta, and S, O, or Br, along with lithium, and a nonaqueous electrolyte containing a lithium salt and a solvent with a fluoro group, which reduces internal resistance by selectively covering the negative electrode active material layer and suppressing excessive SEI generation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If fluorine is introduced in the nonaqueous solvent to suppress oxidative decomposition on the positive electrode, then oxidation resistance is improved, but negative electrode resistance and internal resistance are increased due to excessive SEI generation

Engineering Contradiction:

Improveoxidation resistanceVSAvoidnegative electrode resistance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A coating film containing lithium compound and fluorine is formed on the negative electrode surface before battery operation. This preliminary coating prevents excessive SEI generation during initial charging cycles, suppressing negative electrode resistance increase while allowing fluorinated solvent to provide oxidation resistance on the positive electrode.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The coating film is applied selectively to the negative electrode surface, creating a localized fluorine-rich region. This local fluorine concentration provides protection against SEI over-generation at the negative electrode without requiring fluorine throughout the entire electrolyte, thus avoiding excessive resistance increase while maintaining oxidation resistance where needed.

Inventive Principle:

Principle #3Local quality

2Stability of the object's composition

If fluorine is introduced in SEI to improve stability, then SEI stability is improved, but negative electrode resistance is increased

Engineering Contradiction:

ImproveSEI stabilityVSAvoidnegative electrode resistance

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The coating film contains lithium compound with specific fluorine content and composition ratios. By controlling the fluorine concentration and chemical composition parameters in the coating film, stable SEI is formed without excessive resistance increase, optimizing both stability and conductivity.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The coating film is composed of lithium compound combined with fluorine-containing compounds, creating a composite structure. This composite material provides both the stability of fluorinated SEI and the conductivity needed to minimize resistance, balancing stability and resistance characteristics.

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

The solution effectively reduces negative electrode resistance and internal battery resistance while maintaining high durability and oxidation resistance, even when fluorine is introduced, by forming a coating film with appropriate thickness and composition that promotes lithium ion conductivity.

Implementation Method 1

a coating film having a lithium ion permeability

Methodology Applied

Scientific EffectLithium ion permeability: Permeation

Implementation Method 2

the nonaqueous solvent and the lithium salt partially irreversibly react with each other by reductive decomposition, and a solid electrolyte interface (SEI) is generated

Methodology Applied

Scientific EffectReductive decomposition: Reduction

Data Source

PatentUS11063254B2Negative electrode including lithium and fluorine containing coating film covering negative electrode active material layer

Publication Date: 2021.07.13 PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO LTD

AI summary

A nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a nonaqueous electrolyte having a lithium ion conductivity, and the negative electrode includes a negative electrode collector, a negative electrode active material layer provided on a surface of the negative electrode collector, and a coating film which at least partially covers a surface of the negative electrode active material layer and which has a lithium ion permeability. The coating film contains a lithium compound which contains an element M, an element A, an element F, and lithium; the element M is at least one selected from the group consisting of P, Si, B, V, Nb, W, Ti, Zr, Al, Ba, La, and Ta; and the element A is at least one selected from the group consisting of S, O, N, and Br.