Negative Electrode SEI Layering for Low-Resistance Electrochemical Cells

Solution Overview

Problem

In electrochemical devices using lithium ions, the formation of an excessively thick solid electrolyte interface (SEI) film leads to increased internal resistance, and the use of fluorine-containing electrolytes like LiPF6 results in instability due to decomposition and HF generation, while LiFSI-based electrolytes form SEI films with high resistance.

Innovation Solution

The electrochemical device incorporates a negative electrode with a surface layer containing lithium carbonate, which reduces internal resistance, and an olefin-based separator to prevent separator deterioration, allowing for a stable SEI film with low resistance by forming a layered structure of lithium fluoride and carbonate.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If LiFSI-based electrolyte is used, then SEI film stability is improved, but internal resistance increases

Engineering Contradiction:

ImproveSEI film stabilityVSAvoidinternal resistance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The invention creates a layered SEI film structure where different regions have different compositions and properties. The inner layer contains LiF for stability, while the outer layer contains Li2CO3 for low resistance, allowing each layer to perform its specific function optimally

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The SEI film is designed as a composite structure combining LiF and Li2CO3 phases. This composite approach allows the film to simultaneously exhibit the stability of LiF and the low resistance characteristics of Li2CO3, resolving the contradiction between stability and resistance

Inventive Principle:

Principle #40Composite materials

2Object-affected harmful factors

If LiPF6 electrolyte is used, then initial internal resistance is low, but SEI film stability deteriorates due to HF generation

Engineering Contradiction:

Improveinitial internal resistanceVSAvoidSEI film stability

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The invention preemptively forms a stable LiF-containing SEI film before HF can be generated from LiPF6 decomposition. This preliminary protective layer prevents HF from reaching and degrading the SEI film, countering the harmful effect before it occurs

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The LiFSI acts as an intermediary substance that forms a protective LiF layer between the electrode and the LiPF6 electrolyte. This intermediary layer prevents direct contact between HF and the SEI film, mediating the interaction to prevent degradation

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If SEI film thickness is increased, then electrode protection is improved, but internal resistance increases

Engineering Contradiction:

Improveelectrode protectionVSAvoidinternal resistance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The invention creates a layered SEI film structure where different regions have different compositions and properties. The inner layer contains LiF for stability, while the outer layer contains Li2CO3 for low resistance, allowing each layer to perform its specific function optimally

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The SEI film is designed as a composite structure combining LiF and Li2CO3 phases. This composite approach allows the film to simultaneously exhibit the stability of LiF and the low resistance characteristics of Li2CO3, resolving the contradiction between stability and resistance

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 suppresses the increase in internal resistance and maintains low resistance over time, improving the reliability and performance of the electrochemical device by controlling the distribution and stability of the SEI film.

Implementation Method 1

the negative electrode material layer includes a negative electrode active material into which lithium ions are reversibly doped

Methodology Applied

Scientific EffectIon doping: Absorption (physical)

Implementation Method 2

when the film region is measured by X-ray photoelectron spectroscopy, a peak in an O1s spectrum is observed in a binding energy range of 530 to 534 eV

Methodology Applied

Scientific EffectX-ray photoelectron spectroscopy: Photoelectric Effect

Data Source

PatentUS20250023196A1Electrochemical device

Publication Date: 2025.01.16 PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO LTD

AI summary

A disclosed electrochemical device includes a positive electrode, a negative electrode, an olefin-based separator, and a lithium ion-conductive electrolyte. The negative electrode includes a negative electrode current collector, and a negative electrode material layer supported on the negative electrode current collector. The negative electrode material layer includes a negative electrode active material into which lithium ions are reversibly doped. A surface layer portion of the negative electrode material layer has a film region, and when the film region is measured by X-ray photoelectron spectroscopy, a peak in an O1s spectrum is observed in a binding energy range of 530 to 534 eV. The peak intensity in the O1s spectrum increases from the surface layer of the film region to the inner side.