Core-Shell Cathode for All-Solid Battery Sulfide Interface Stability
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Solution Overview
Problem
All-solid secondary batteries with sulfide-based solid electrolytes face stability issues due to reactions between cobalt and sulfur, leading to deterioration of lifetime characteristics, especially when using cobalt-based cathode active materials.
Innovation Solution
A cathode with a core-shell structure, where the core is a nickel-rich transition metal-based active material and the shell is cobalt-rich, combined with a lithium ion conductor coating film, reduces interfacial resistance and prevents lithium depletion, allowing for the use of cobalt in sulfide-based batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a cobalt-based cathode active material is used in an all-solid secondary battery with sulfide-based solid electrolyte, then the battery can achieve high energy density and good electrochemical performance, but the reaction between cobalt and sulfur occurs at the interface, leading to deterioration of lifetime characteristics
Solution Approach 1:
An aluminum oxide coating layer is introduced as an intermediary between the cobalt-based cathode active material and the sulfide-based solid electrolyte. This coating layer prevents direct contact and chemical reaction between cobalt and sulfur, eliminating the harmful interface reaction while maintaining ionic conductivity for lithium ions, thus preserving both high energy density and improving lifetime characteristics
Solution Approach 2:
The surface properties of the cathode active material are modified by coating with aluminum oxide, changing the chemical composition and surface characteristics at the interface. This parameter change prevents the harmful cobalt-sulfur reaction while maintaining the electrochemical performance necessary for high energy density
2Quantity of substance
If a nickel-rich transition metal-based active material is used in the core to achieve high capacity, then the battery capacity increases, but the stability and lifetime characteristics deteriorate due to interface reactions
Solution Approach 1:
The cathode active material is divided into a core-shell structure where the nickel-rich core provides high capacity and the aluminum oxide coating shell provides stability. This segmentation allows the high-capacity nickel-rich material to function while being protected from harmful interface reactions, thus achieving both high capacity and improved lifetime characteristics
Solution Approach 2:
Different regions of the cathode material are assigned different functions: the core region contains nickel-rich material optimized for high capacity, while the surface region is coated with aluminum oxide optimized for stability and reaction prevention. This local quality differentiation allows simultaneous achievement of high capacity and long lifetime
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 solution improves the lifetime characteristics and capacity retention of all-solid secondary batteries by suppressing the diffusion of cobalt, phosphorus, and sulfur at the interface, thereby enhancing the battery's stability and performance.
Implementation Method 1
a coating film containing a lithium ion conductor on a surface of the shell
Implementation Method 2
suppressing the diffusion of cobalt, phosphorus, and sulfur at the interface
Data Source
AI summary
A cathode for an all-solid secondary battery including a sulfide-based electrolyte, wherein the cathode includes a cathode active material and a solid electrolyte, the cathode active material includes a core and a shell and further includes a coating film containing a lithium ion conductor on a surface of the shell. The core includes a first transition metal-based active material containing about 50 mol % or more of nickel (Ni) based on the total mol (mole) amounts of transition metals included in the first transition metal-based active material, and the shell includes a second transition metal-based active material containing about 30 mol % or more of cobalt (Co) based on the total mol amount of transition metals included in the second transition metal-based active material. Further, an all-solid secondary battery including the cathode is provided.