Lithium Battery Electrolyte for Stable SEI Layer Formation

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Solution Overview

Problem

Lithium metal anodes in secondary batteries face instability due to the formation of a non-uniform solid electrolyte interphase (SEI) layer with low ionic conductivity and mechanical strength, leading to lithium plating issues and electrolyte depletion, which hinders the achievement of high energy density.

Innovation Solution

An electrolyte composition with a lithium salt containing nitrogen, a first additive with a lower LUMO value, and a second additive with a higher LUMO value, forming a multilayer SEI structure on the lithium electrode, comprising layers of LiF, Li3N, and LiF, to enhance mechanical properties and lithium ion conductivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If lithium metal is used as an anode to increase energy density, then capacity per unit weight is improved, but the electrolyte is reduced and decomposed to form a non-uniform SEI layer with low ionic conductivity and mechanical strength

Engineering Contradiction:

Improvecapacity per unit weightVSAvoidstability of SEI layer

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The SEI layer is segmented into a multilayer structure with distinct functional layers: a first SEI layer formed by the first additive (lower LUMO value) providing mechanical strength and stability, and a second SEI layer formed by the second additive (higher LUMO value) providing ionic conductivity. This segmentation allows each layer to specialize in different functions, resolving the contradiction between mechanical strength and ionic conductivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the SEI layer are given different properties: the first SEI layer (inner layer) is designed with higher mechanical strength and stability to protect the lithium metal, while the second SEI layer (outer layer) is designed with higher ionic conductivity to facilitate lithium ion transport. This local differentiation of properties resolves the contradiction between mechanical strength and ionic conductivity in the overall SEI layer.

Inventive Principle:

Principle #3Local quality

2Object-affected harmful factors

If a SEI layer is formed on lithium metal surface, then reactivity is reduced, but the SEI layer becomes non-uniform with low ionic conductivity and mechanical strength

Engineering Contradiction:

Improvereactivity of lithium metalVSAvoiduniformity and stability of SEI layer

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The electrolyte composition is designed to perform preliminary action by forming a stable, uniform SEI layer during the initial charging cycle (formation process). The first and second additives in the electrolyte preferentially decompose to form a protective SEI layer before the lithium metal can react with the bulk electrolyte, preventing subsequent non-uniform plating and electrolyte depletion.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The SEI layer is formed as a composite structure comprising multiple components from different additives: the first additive contributes to forming a mechanically strong layer, while the second additive contributes to forming an ion-conductive layer. This composite SEI layer combines the benefits of different materials to achieve both uniformity and stability while protecting the lithium metal.

Inventive Principle:

Principle #40Composite materials

3Productivity

If non-uniform SEI layer is formed, then lithium plating becomes non-uniform, but this leads to deterioration of stability and depletion of electrolyte

Engineering Contradiction:

Improvelithium plating efficiencyVSAvoidstability of battery

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The stable, uniform SEI layer formed by the electrolyte composition creates an equipotential surface on the lithium metal anode. This uniform potential distribution prevents localized hot spots and non-uniform lithium plating, ensuring uniform lithium deposition during charging and stripping during discharging, thereby maintaining both productivity and reliability.

Inventive Principle:

Principle #12Equipotentiality

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 electrolyte composition stabilizes the SEI layer, improving lithium plating/stripping efficiency, extending battery lifespan, and maintaining high energy density by suppressing lithium dendrite growth and reducing battery resistance.

Implementation Method 1

lithium metal has very high reactivity, so the electrolyte is reduced and decomposed to form a solid electrolyte interphase (SEI) layer on the surface of the lithium metal

Methodology Applied

Scientific EffectElectrochemical reduction: Reduction

Implementation Method 2

the formation of the SEI layer, which is non-uniform and has low ionic conductivity and mechanical strength

Methodology Applied

Scientific EffectIonic conductivity: Conduction (electrical)

Data Source

PatentUS20230027597A1Anode for lithium secondary battery including stable solid electrolyte interphase layer and electrolyte composition for manufacturing same

Publication Date: 2023.01.26 HYUNDAI MOTOR CO LTD

AI summary

An electrolyte composition for a lithium secondary battery includes a lithium salt comprising a nitrogen element, a first additive having a LUMO (lowest occupied molecular orbital) value lower than a LUMO value of the lithium salt, and a second additive having a LUMO value higher than the LUMO value of the lithium salt.