Silicon-Based Negative Electrode Active Material with Fluorine Coating

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Solution Overview

Problem

Lithium-ion secondary batteries using silicon materials face challenges in achieving cycle stability comparable to those using carbon materials, with issues such as surface layer breakage and electrolyte decomposition affecting battery performance.

Innovation Solution

A negative electrode active material comprising a silicon-based material (SiOx where 0.5≤x≤1.6) with a crystalized fluorine compound, specifically bis(trifluoromethyl) dicarbonate, and optionally compounds containing -CF2-CF2 units, such as polytetrafluoroethylene, is used to enhance cycle performance and initial charge/discharge performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If silicon is used as a negative electrode active material to increase battery capacity, then the battery capacity is improved, but the negative electrode active material expands or shrinks during charging or discharging, making it easy to break particularly near its surface layer

Engineering Contradiction:

Improvebattery capacityVSAvoidsurface layer strength

Core Design Contradiction:

Quantity of substanceVSStrength

Solution Approach 1:

The invention uses a composite material consisting of silicon particles coated with a carbon-containing layer. The carbon layer acts as a protective shell that maintains structural integrity during silicon expansion and contraction, preventing surface layer breakage while preserving the high capacity benefits of silicon.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The carbon-containing layer forms a flexible protective shell around the silicon particles. This shell can accommodate the volume changes of silicon during charging and discharging cycles without breaking, thereby protecting the silicon from mechanical failure.

Inventive Principle:

Principle #30Flexible shells and thin films

2Quantity of substance

If the surface layer of the negative electrode active material breaks, then a new surface is created, increasing the reaction area, but this causes decomposition reaction of the electrolyte and consumes electrolyte, reducing cycle performance

Engineering Contradiction:

Improvereaction areaVSAvoidcycle performance

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The carbon-containing layer forms a stable protective shell that prevents uncontrolled surface breakage. This shell allows controlled reaction areas to exist while preventing the catastrophic surface failures that lead to electrolyte decomposition and poor cycle performance.

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The carbon-containing layer acts as an intermediary between the silicon particles and the electrolyte. It provides a stable interface that prevents direct contact between the electrolyte and fresh silicon surfaces, thereby preventing electrolyte decomposition while still allowing necessary electrochemical reactions.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If various materials and configurations are used to improve initial efficiency and cycle performance, then the cycle performance is improved, but the device complexity increases

Engineering Contradiction:

Improvecycle performanceVSAvoidmaterial configuration complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention employs a relatively simple composite structure of silicon particles with a carbon-containing coating layer. This straightforward composite approach achieves improved cycle performance without requiring complex multi-layer configurations or sophisticated material combinations.

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 improves the battery's capacity, cycle stability, and initial charge/discharge performance by inhibiting surface layer breakage and electrolyte decomposition, leading to higher volume energy density and longer battery life.

Implementation Method 1

A negative electrode active material for a negative electrode material of a non-aqueous electrolyte secondary battery includes a silicon-based material expressed by SiOx where 0.5≤x≤1.6 and a crystalized fluorine compound in at least a part of a surface layer of the negative electrode active material

Methodology Applied

Scientific EffectChemical passivation:

Data Source

PatentEP3104440B1Negative electrode active material for negative electrode material of non-aqueous electrolyte secondary battery, negative electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

Publication Date: 2019.10.02 SHIN ETSU CHEMICAL CO LTD

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Figure 4~6

AI summary

The present invention is a negative electrode active material for a negative electrode material of a non-aqueous electrolyte secondary battery, including a silicon-based material expressed by SiOx where 0.5≤x≤1.6 and either or both of a crystalized fluorine compound and a compound containing -CF2-CF2- units in at least a part of a surface layer of the negative electrode active material, the silicon-based material containing at least one of Li6Si2O7, Li2Si3O5, and Li4SiO4. There can be provided a negative electrode active material that can increase the battery capacity and improve the cycle performance and initial charge and discharge performance when used for a lithium-ion secondary battery, as well as a lithium-ion secondary battery having a negative electrode using this negative electrode active material.