Composite Cathode Material with Nanocrystalline M2S for Solid-State Batteries
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Solution Overview
Problem
Lithium batteries with liquid electrolytes pose safety risks due to the likelihood of overheating and fires, prompting the development of all-solid secondary batteries with solid electrolytes to enhance safety, but these batteries face challenges in achieving high energy density and cycle stability.
Innovation Solution
A composite cathode active material comprising M2S, an alkali metal salt, and a carbon-based material is developed, with M2S crystallites sized less than 9.9 nm, forming a solid solution that improves ionic and electronic conductivity, reducing internal resistance and enhancing cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solid electrolyte is used instead of a liquid electrolyte, then safety is improved, but energy density and cycle stability deteriorate
Solution Approach 1:
The patent uses composite cathode active material comprising M2S, alkali metal salt, and carbon-based material to achieve both high energy density and good cycle stability while maintaining the safety benefits of solid electrolytes. The composite structure allows synergistic effects of different materials to overcome the limitations of individual components.
Solution Approach 2:
The patent controls the crystallite size of M2S to be less than 9.9 nm, which is a critical parameter change that significantly improves ionic conductivity and electrochemical performance. This nanoscale dimension control enables the solid electrolyte system to achieve high energy density and cycle stability.
2Productivity
If M2S crystallite size is reduced, then specific capacity and cycle characteristics are improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent specifies a precise crystallite size range (less than 9.9 nm) for M2S to optimize ionic conductivity and electrochemical performance. This parameter control is achieved through controlled synthesis methods that navigate the trade-off between performance improvement and manufacturing complexity.
Solution Approach 2:
The composite structure incorporates porous carbon-based materials that provide both high surface area for electrochemical reactions and pathways for ion transport. The porosity at controlled scales helps achieve high specific capacity while the hierarchical structure simplifies the manufacturing process compared to dense nanomaterials.
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 cathode active material increases specific capacity, cycle stability, and high-rate characteristics of all-solid secondary batteries, while reducing the risk of overheating and fires, thereby improving safety and performance.
Implementation Method 1
the composite includes a solid solution of the M 2S and the alkali metal salt
Implementation Method 2
a size of an M 2S crystallite obtained from an X-ray diffraction (XRD) spectrum of the composite is less than 9.9 nm
Data Source
Figure 1
Figure 2A~2B
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AI summary
A composite cathode active material, a cathode including the same, and an all-solid secondary battery are provided. The composite cathode active material includes a composite of M2S, an alkali metal salt, and a carbon-based material, wherein M is an alkali metal, the alkali metal is Li or Na, a size of an M2S crystallite obtained from an X-ray diffraction (XRD) spectrum of the composite is less than 9.9 nm, and the composite includes a solid solution of the M2S and the alkali metal salt.