Cathode Active Material Coating for Solid-State Battery Interfaces
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Solution Overview
Problem
The interfacial resistance between the positive electrode active material and the sulfide-based solid electrolyte in all-solid-state batteries is high, leading to degraded lifetime characteristics and side reactions, which are not effectively addressed by existing coatings containing lithium oxides.
Innovation Solution
A coating layer comprising lithium carbon oxide (Li a CO b ) and lithium titanium oxide (Li x Ti y O 4 ) is applied to the positive electrode active material, with specific weight ratios and thicknesses to improve interfacial resistance and inhibit side reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a sulfide-based solid electrolyte is used in all-solid-state batteries, then lithium ion conductivity is improved, but interfacial resistance between the positive electrode active material and the solid electrolyte increases, leading to degraded lifetime characteristics
Solution Approach 1:
A coating layer comprising lithium phosphate and lithium sulfide is introduced as an intermediary between the positive electrode active material (containing cobalt) and the sulfide-based solid electrolyte. This coating layer prevents direct harmful contact between cobalt and sulfur, suppresses component diffusion at the interface, and reduces interfacial resistance, thereby improving both lithium ion conductivity and lifetime characteristics simultaneously
Solution Approach 2:
The coating layer is formed as a composite material containing lithium phosphate and lithium sulfide in a specific weight ratio range (70:30 to 30:70). This composite structure combines the benefits of both materials: lithium phosphate provides structural stability and suppresses cobalt-sulfur reactions, while lithium sulfide enhances lithium ion conductivity, achieving both improved reliability and energy efficiency
2Reliability
If a coating layer containing lithium oxides is applied to the positive electrode active material, then interfacial resistance is reduced, but side reactions at the interface between the positive electrode active material and the sulfide-based solid electrolyte are not effectively suppressed
Solution Approach 1:
The coating layer is designed with specific local composition (lithium phosphate and lithium sulfide) tailored for the interface between the positive electrode active material and solid electrolyte. This localized composition provides different functions: lithium phosphate suppresses cobalt-sulfur reactions at the interface, while lithium sulfide facilitates lithium ion transfer, addressing both interfacial resistance and side reactions through spatially differentiated material properties
Solution Approach 2:
The coating layer acts as an intermediary barrier that physically separates the positive electrode active material containing cobalt from the sulfide-based solid electrolyte containing sulfur. This intermediary structure prevents direct harmful interactions while maintaining ionic conductivity, effectively suppressing side reactions without compromising interfacial contact
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 coating layer enhances the electrochemical properties and life characteristics of all-solid-state batteries by reducing interfacial resistance and suppressing side reactions, facilitating fast lithium ion transfer.
Implementation Method 1
a sulfide-based solid electrolyte is the most promising material in terms of lithium ion conductivity
Implementation Method 2
reactions occur at the interface between the positive electrode active material and the sulfide-based solid electrolyte, resulting in the diffusion of components such as Co, P or S at the interface
Data Source
Figure 1~2
Figure 3
AI summary
The present invention relates to a positive electrode active material for an all-solid-state battery comprising a core capable of reversible adsorption and release of lithium ions and a coating layer formed on a surface of the core, wherein the coating layer comprises lithium carbon oxide represented by the Formula 1 below and lithium titanium oxide represented by Formula 2 below, a positive electrode for an all-solid-state battery comprising the positive electrode active material for an all-solid-state battery and a sulfide-based solid electrolyte, and an all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, wherein the positive electrode comprises the positive electrode for an all-solid-state battery: [Formula 1] LiaCOb, wherein a is 0<a≤4 and b is 0<b≤4; [Formula 2] LixTiyO4, wherein x is 0.8≤x≤1.4 and y is 1.6≤y≤2.2.