Amorphous Electrolyte-Coated Cathode for Stable Solid-State Ion Transport
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Solution Overview
Problem
Conventional lithium ion batteries using liquid electrolytes face safety issues due to flammability and thermal instability, while sulfide-based solid electrolytes for all-solid-state batteries suffer from electrochemical instability and hinder ion diffusion when in contact with high-voltage positive electrode active materials.
Innovation Solution
A composite positive electrode active material is developed, comprising a core of lithium-rich or high-nickel positive electrode active material coated with an amorphous solid electrolyte layer represented by Chemical Formula 1, which includes elements like F, Cl, Br, I, O, OH, PF6, BF4, S, N, P, ClO4, or CO3, enhancing structural stability and electrochemical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If sulfide-based solid electrolytes are used in all-solid-state batteries, then high ionic conductivity and flexible mechanical characteristics are achieved, but electrochemical instability occurs when in direct contact with high-voltage positive electrode active materials
Solution Approach 1:
The patent introduces an intermediary coating layer comprising Li2SiO3 and Li3PO4 between the sulfide-based solid electrolyte and the high-voltage positive electrode active material. This coating layer acts as a mediator that prevents direct contact and harmful electrochemical reactions while maintaining ion transport capability, thus resolving the contradiction between achieving high ionic conductivity and ensuring electrochemical stability.
Solution Approach 2:
The patent employs a composite coating layer made of Li2SiO3 and Li3PO4 materials combined with the sulfide-based solid electrolyte. This composite structure leverages the electrochemical stability of oxides/phosphates while preserving the high ionic conductivity of sulfides, effectively resolving the stability-conductivity contradiction.
2Reliability
If oxide-based coating layers are formed on the positive electrode active material surface, then electrochemical stability is improved, but ion diffusion is hindered due to low ionic conductivity
Solution Approach 1:
The patent applies local quality by creating a thin coating layer with specific composition (Li2SiO3 and Li3PO4) only at the interface between the positive electrode active material and the solid electrolyte. This localized treatment provides electrochemical stability exactly where needed (at the contact interface) while maintaining high ionic conductivity in this specific region, thus not hindering overall ion diffusion.
Solution Approach 2:
The patent changes the parameters of the coating layer by selecting specific materials (Li2SiO3 and Li3PO4) with appropriate thickness and composition ratios. These parameter adjustments ensure the coating has both electrochemical stability and sufficient ionic conductivity, resolving the contradiction between stability and ion diffusion.
3Reliability
If fluoride-based materials are used for coating, then oxidation stability is improved, but structural stability and ionic conductivity are insufficient
Solution Approach 1:
The patent uses a composite coating of Li2SiO3 and Li3PO4 that combines the oxidation stability benefits of fluoride-based materials with the structural stability and ionic conductivity of oxide/phosphate materials. This composite approach achieves all three desired properties simultaneously.
Solution Approach 2:
The patent adjusts the composition parameters by incorporating specific ratios of Li2SiO3 and Li3PO4, which provides both oxidation stability and sufficient structural stability and ionic conductivity, overcoming the limitations of pure fluoride-based coatings.
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 composite material improves charge/discharge characteristics and cycle-life characteristics of all-solid-state batteries by ensuring high ionic conductivity and electrochemical stability, overcoming limitations of conventional coatings.
Implementation Method 1
sulfide-based solid electrolytes are highlighted to be the most promising materials for the all-solid-state batteries due to high ionic conductivity
Implementation Method 2
the sulfide-based electrolytes are so electrochemically instable as to cause serious side reactions, when in direct contact with positive electrode active materials with a high voltage
Data Source
AI summary
A composite positive electrode active material for an all-solid-state battery, a positive electrode including the composite positive electrode active material, and an all-solid-state battery. The composite positive electrode active material for includes a positive electrode active material core and a coating layer on the core, wherein the coating layer includes an amorphous solid electrolyte represented by Chemical Formula 1:wherein in Chemical Formula 1,X is F, Cl, Br, I, O, OH, PF6, BF4, S, N, P, ClO4, or CO3;m and n satisfy 1≤m≤2 and 1≤n≤2, respectively; anda and b each satisfy 0.01≤a≤1 and 0.01≤b≤1.