LiF/h-BN Interfacial Layer for Lithium Metal Anode Stability

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Solution Overview

Problem

Lithium metal anodes in lithium-sulfur and lithium-air batteries face challenges due to chemical and mechanical instabilities, leading to dendritic Li plating/stripping, low Coulombic efficiencies, and safety concerns, primarily because of the strong reactivity with electrolytes and the formation of a weak solid electrolyte interphase (SEI) that is prone to mechanical deformation.

Innovation Solution

A lithium metal anode with a current collector and an interfacial layer composed of a 2D material like hexagonal boron nitride (h-BN) and a reinforcing material such as lithium fluoride (LiF), where LiF is selectively deposited on defect sites using atomic layer deposition to create a stable and conformal SEI, reducing dendrite formation and enhancing mechanical stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If lithium metal anode is used to achieve high specific capacity, then energy density is improved, but chemical stability deteriorates due to strong reactivity with electrolytes

Engineering Contradiction:

Improveenergy densityVSAvoidchemical stability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

A 2D material film (such as h-BN) is introduced as an intermediary layer between the lithium metal anode and the electrolyte. This intermediate layer acts as a protective barrier that prevents direct contact and chemical reactions between the highly reactive lithium metal and the electrolyte, thereby maintaining chemical stability while preserving the high energy density benefits of lithium metal anodes.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The anode structure is designed as a composite system combining lithium metal with a 2D material film. This composite structure integrates the high capacity advantage of lithium metal with the chemical stability and protective properties of the 2D material, creating a hybrid anode that simultaneously achieves high energy density and improved reliability.

Inventive Principle:

Principle #40Composite materials

2Quantity of substance

If lithium metal anode undergoes volume change during cycling, then capacity is improved, but mechanical stability deteriorates due to SEI layer deformation

Engineering Contradiction:

ImprovecapacityVSAvoidmechanical stability

Core Design Contradiction:

Quantity of substanceVSStability of the object's composition

Solution Approach 1:

A thin 2D material film is applied to the lithium metal anode surface. This thin film structure is capable of accommodating the volume changes and mechanical deformation that occur during lithium insertion and extraction cycles, while maintaining the structural integrity and preventing SEI layer breakdown. The film acts as a flexible protective shell that maintains mechanical stability throughout cycling.

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The 2D material film is applied in advance to the lithium metal anode before cycling begins. This pre-applied protective layer cushions and absorbs the mechanical stresses and deformations that will occur during subsequent volume changes, preventing direct damage to the SEI layer and maintaining mechanical stability throughout the battery's operational life.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Productivity

If high-surface area lithium metal is used to enhance reaction kinetics, then electrochemical performance is improved, but thermal stability deteriorates leading to lower runaway temperature

Engineering Contradiction:

Improvereaction kineticsVSAvoidthermal stability

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The 2D material film serves as an intermediary layer that enables beneficial electrochemical reactions while blocking harmful thermal reactions. The film allows lithium ion transport for high reaction kinetics but acts as a thermal barrier that prevents direct contact between lithium metal and electrolyte, thereby maintaining thermal stability and raising the temperature at which thermal runaway occurs.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 LiF/h-BN hybrid film effectively suppresses lithium dendrite formation, maintains high Coulombic efficiency over 300 cycles, and reduces side reactions with the electrolyte, thereby improving the cycle life and safety of lithium metal anodes.

Implementation Method 1

performing atomic layer deposition to deposit a reinforcing material selectively on certain regions of the film

Methodology Applied

Scientific EffectAtomic layer deposition:

Data Source

PatentUS11499228B2Stitching two-dimensional atomic crystals by atomic layer deposition as stable interfaces for batteries

Publication Date: 2022.11.15 THE BOARD OF TRUSTEES OF THE LELAND STANFORD JUNIOR UNIV

AI summary

An anode includes: (1) a current collector; and (2) an interfacial layer disposed over the current collector. The interfacial layer includes a film of a layered material and a reinforcing material selectively disposed over certain regions of the film, while other regions of the film remain exposed from the reinforcing material.