Yttrium-Modified Lithium Phosphate Coating for Battery Interface Resistance

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Solution Overview

Problem

Current non-aqueous electrolyte secondary batteries face challenges in reducing internal resistance and improving overcharge characteristics, particularly in lithium ion batteries, where the interface resistance between the solid electrolyte and the positive electrode active material remains high, leading to inefficient lithium ion conductivity and potential heat generation issues during overcharge.

Innovation Solution

A positive electrode active material is developed with a coating layer containing a lithium ionic conductor composed of trilithium phosphate (LPO) and yttrium, featuring regions with varying yttrium concentrations, which enhances lithium ion conductivity and oxygen trapping capabilities, thereby reducing interface resistance and heat generation during overcharge.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a coating material containing elements such as Sc, Ti, V, Y, Zr, Nb, Ca, Sr, Ba, Hf, Ta, Cr, Mo, and W is used to coat the positive electrode active material, then lithium ion conductivity between the solid electrolyte layer and positive electrode layer is improved, but interface resistance remains high and overcharge characteristics are insufficient

Engineering Contradiction:

Improvelithium ion conductivityVSAvoidinterface resistance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The coating portion is designed with non-uniform yttrium concentration, creating Y-rich region A and Y-poor region B. This local quality variation optimizes different regions for specific functions: Y-rich regions enhance oxygen trapping capability to prevent heat generation during overcharge, while Y-poor regions maintain lithium ion conductivity. This resolves the contradiction by having different local zones address different problems rather than using a uniform coating.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The coating material is a composite consisting of lithium ionic conductor containing lithium, phosphoric acid group, and yttrium. This composite structure combines the high lithium ion conductivity of lithium phosphate with the oxygen-trapping capability of yttrium, achieving both low interface resistance and improved overcharge characteristics simultaneously.

Inventive Principle:

Principle #40Composite materials

2Productivity

If the positive electrode active material is coated with a lithium ionic conductor, then lithium ion insertion/extraction efficiency is improved, but heat generation during overcharge increases due to insufficient oxygen trapping

Engineering Contradiction:

Improvecharge/discharge efficiencyVSAvoidheat generation

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

Yttrium is selectively concentrated in region A of the coating portion to create local oxygen-trapping zones. These Y-rich regions specifically address heat generation during overcharge by trapping released oxygen, while maintaining overall charge/discharge efficiency through the conductive Y-poor region B. This localized approach resolves the contradiction between productivity and heat generation control.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The coating structure converts the potentially harmful effect of oxygen release during overcharge into a beneficial trapping mechanism. Yttrium in the coating captures the oxygen that would otherwise react with the electrolyte to generate heat, transforming a harmful byproduct into a controlled element that enhances safety without compromising charge/discharge efficiency.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 improved lithium ion conductivity and oxygen trapping properties result in reduced resistance characteristics and enhanced overcharge safety, enabling high-rate charge/discharge capabilities and thermal stability in lithium ion batteries, suitable for applications like hybrid and electric vehicles.

Implementation Method 1

a lithium ion is efficiently conducted between a solid electrolyte layer and a positive electrode layer

Methodology Applied

Scientific EffectIonic conductivity: Conduction (electrical)

Implementation Method 2

Y can become a trivalent cation, and hence can probably trap, at a time of overcharge, oxygen released due to excessive lack of lithium in the positive electrode active material to suitably reduce a heat generating reaction between oxygen and the electrolyte

Methodology Applied

Scientific EffectOxygen trapping: Absorption (physical)

Implementation Method 3

a reaction between the sulfide-based solid electrolyte layer and the positive electrode layer can be reduced

Methodology Applied

Scientific EffectChemical reaction inhibition:

Data Source

PatentUS11508954B2Non-aqueous electrolyte secondary battery and positive electrode active material

Publication Date: 2022.11.22 TOYOTA JIDOSHA KK

AI summary

A non aqueous electrolyte secondary battery includes a positive electrode containing a positive electrode active material, a negative electrode, and a non aqueous electrolyte, and the positive electrode active material includes a positive electrode active material particle containing a lithium transition metal compound, and a coating portion coating at least a part of a surface of the positive electrode active material particle. The coating portion contains a lithium ionic conductor containing lithium, a phosphoric acid group, and yttrium. The lithium ionic conductor includes a region A in which a ratio of yttrium is relatively rich and a region B in which the ratio of yttrium is relatively poor.