Cathode Surface Coating for Stable Sulfide Solid-State Battery Interfaces
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Solution Overview
Problem
The use of sulfide-based solid electrolytes in all-solid-state lithium secondary batteries leads to an exchange reaction between oxygen in lithium ion-conducting oxides and sulfur, resulting in reduced battery characteristics such as rate and cycle characteristics, and decreased initial charge and discharge efficiency.
Innovation Solution
A positive electrode active material with a lithium-containing composite oxide surface coated with a LiAO compound containing elements like Ti, Zr, Ta, Nb, Zn, W, and Al, and a halogen, which reduces interfacial resistance and suppresses the exchange reaction between oxygen and sulfur, enhancing rate and cycle characteristics and initial charge and discharge efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lithium ion-conducting oxide layer such as LiNbO3 is formed on the surface of the positive electrode active material, then the output characteristics and battery capacity can be improved by forming a satisfactory interface, but the exchange reaction between oxygen in the oxide layer and sulfur in the sulfide-based solid electrolyte deteriorates the interface and reduces battery characteristics
Solution Approach 1:
The patent introduces a halogen element as an intermediary substance on the surface of the positive electrode active material. This halogen layer acts as a mediator that prevents direct contact and reaction between the oxygen-containing oxide coating and the sulfur-containing solid electrolyte, thereby eliminating the harmful exchange reaction while maintaining good interface properties for lithium ion conduction.
Solution Approach 2:
The patent applies local quality modification by specifically treating the surface of the positive electrode active material with halogen elements. This creates a localized functional layer with distinct chemical properties that differs from both the oxide coating and the solid electrolyte, providing targeted protection at the critical interface region where the exchange reaction occurs.
2Productivity
If a lithium ion-conducting oxide layer is formed on the positive electrode active material, then the initial charge and discharge efficiency can be improved, but the exchange reaction causes irreversible capacity and reduces initial charge and discharge efficiency
Solution Approach 1:
The halogen element serves as a protective intermediary that prevents the irreversible chemical reaction between oxygen and sulfur. By blocking the direct interaction at the interface, the halogen layer eliminates the source of irreversible capacity loss while preserving the beneficial electrochemical performance and initial charge-discharge efficiency.
3Speed
If a lithium ion-conducting oxide layer is formed on the positive electrode active material, then the rate characteristics can be improved, but the exchange reaction with sulfur reduces rate characteristics
Solution Approach 1:
The halogen intermediary maintains the fast lithium ion conduction pathway established by the oxide coating while preventing the detrimental exchange reaction with sulfur. This allows the system to achieve high rate characteristics without the performance degradation caused by chemical instability at the interface.
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 proposed solution effectively improves the rate characteristics, cycle characteristics, and initial charge and discharge efficiency by reducing interfacial resistance and suppressing the exchange reaction, even when using sulfide-based solid electrolytes.
Implementation Method 1
the surface of a lithium-containing composite oxide (referred to as 'present core particles') is coated with a compound (referred to as 'LiAO compound') containing Li, A (A represents one or two or more elements selected from the group consisting of Ti, Zr, Ta, Nb, Zn, W, and Al), and O
Implementation Method 2
by the effect of suppressing the exchange reaction between oxygen (O) in the LiAO compound or in the core particles and sulfur (S) in the sulfide-based solid electrolyte
Implementation Method 3
by the presence of a halogen on the surface of the present core particles, even when used in combination with a sulfide-based solid electrolyte, the initial charge and discharge efficiency and the cycle characteristics can be enhanced by oxygen compensation on the surface region
Data Source
AI summary
A positive electrode active material for an all-solid-state lithium secondary battery, which is capable of improving the rate characteristics, the cycle characteristics, and the initial charge and discharge efficiency even in the case where a sulfide-based solid electrolyte is used, wherein the surface of a lithium-containing composite oxide, referred to as present core particles, is coated with a compound, referred to as, LiAO compound, containing Li, A, where A represents one or more elements selected from the group consisting of Ti, Zr, Ta, Nb, Zn, W, and Al, and O; and a halogen is present on the surface of the present core particles.