All-solid-state sodium-sulfur battery cathode mixture
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Solution Overview
Problem
All-solid-state sodium-sulfur batteries face challenges in maintaining charge/discharge capacity at normal temperatures due to low electron conductivity and sodium ion conductivity in the cathode mixture layer, which limits the reactivity of sulfur and sodium ions.
Innovation Solution
A cathode mixture containing an ion-conductive material with phosphorus at a specific weight ratio, sulfur, and a conductive material with a high specific surface area is used to enhance reaction conductivity and reactivity, ensuring charge/discharge capacity at normal temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If sulfur is used as cathode active material in all-solid-state sodium-sulfur battery, then theoretical capacity is high (1672 mAh/g), but electron conductivity and sodium ion conductivity in cathode mixture layer are low at normal temperature
Solution Approach 1:
The patent introduces a eutectic mixture of Li2S and P2S5 as an intermediary substance in the cathode mixture layer. This eutectic mixture acts as a mediator that enhances both electron conductivity and sodium ion conductivity at normal temperatures, enabling the sulfur cathode to function effectively without requiring high temperature operation. The eutectic mixture facilitates the charge/discharge reactions by providing conductive pathways while maintaining the high theoretical capacity of sulfur.
2Ease of operation
If conventional sodium-sulfur battery uses molten sodium and sulfur, then charge/discharge reaction can proceed, but high temperature operation (300°C to 350°C) is required
Solution Approach 1:
The patent fundamentally changes the physical state parameters of the battery components. Instead of using molten sodium and sulfur at high temperatures (300°C to 350°C), the invention employs solid-state materials: a sodium-containing compound as anode, a solid electrolyte layer, and a cathode mixture layer containing sulfur, conductive material, and eutectic mixture. This parameter change from liquid/molten state to solid state enables normal temperature operation while maintaining charge/discharge functionality.
Solution Approach 2:
The patent creates a composite cathode mixture layer comprising sulfur, conductive material, and eutectic mixture of Li2S and P2S5. This composite structure combines multiple materials with complementary properties: sulfur provides high theoretical capacity, the conductive material enhances electron conductivity, and the eutectic mixture improves both electron and ion conductivity. The composite material approach enables the battery to operate at normal temperatures with maintained reactivity.
3Stability of the object's composition
If solid electrolyte layer is used to separate anode and cathode, then all-solid-state configuration is achieved, but sodium ion conductivity is limited at normal temperature
Solution Approach 1:
The patent changes the temperature parameter at which the battery operates, enabling sodium ion conductivity at normal temperatures through the solid electrolyte layer. The solid electrolyte is designed to maintain adequate ion conductivity without requiring high temperature operation, thus preserving the solid-state structure while ensuring reliable sodium ion transport for charge/discharge reactions.
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 cathode mixture increases reaction points between sulfur and conductive materials, improving charge/discharge characteristics and maintaining capacity even at normal temperatures, thus overcoming the limitations of existing sodium-sulfur batteries.
Implementation Method 1
an ion-conductive material (A) containing phosphorus in a specific amount (weight ratio)... to ensure the charge/discharge capacity of the all-solid-state sodium-sulfur battery even during operation at normal temperature
Implementation Method 2
a conductive material (C) including a conductive material (C1) with a predetermined specific surface area... the number of reaction points between sulfur and/or its discharge product (B) and the conductive material (C) is increased
Data Source
Figure 1
AI summary
The present invention aims to maximize the advantageous physical properties of sulfur and provide a cathode mixture that can be suitably used in a cathode mixture layer of an all-solid-state sodium-sulfur battery in which charge/discharge capacity can be ensured even during operation at normal temperature. The present invention also aims to provide an all-solid-state sodium-sulfur battery including a cathode mixture layer containing the cathode mixture. The present invention relates to a cathode mixture for use in a cathode mixture layer of an all-solid-state sodium-sulfur battery, the cathode mixture including the following components (A) to (C): (A) an ion-conductive material containing phosphorus at a weight ratio of 0.2 to 0.55; (B) sulfur and/or its discharge product; and (C) a conductive material, the component (C) containing a conductive material (C1) having a specific surface area of 1000 m2/g or more.