Sodium All-Solid-State Cell with Glass Ceramic Electrolyte
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Solution Overview
Problem
The challenge is to enhance the capacity of sodium all-solid-state secondary cells operating at low temperatures, which require a suitable combination of Na2Sx as the positive electrode active material with ion-conductive glass ceramics as the solid electrolyte, while avoiding high-temperature processing and ensuring safety and resource independence from lithium.
Innovation Solution
The solution involves using Na2Sx as the positive electrode active material in combination with ion-conductive glass ceramics represented by the formula Na2S-MxSy, where M is selected from P, Si, Ge, B, or Al, with Na2S comprising 67-80 mole % and crystal parts dispersed in an amorphous glass state, to create a high-capacity sodium all-solid-state secondary cell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If β-alumina is used as solid electrolyte to achieve high sodium ion conductivity, then ion conductivity is improved, but production requires burning at high temperature (≥1600°C) which complicates manufacturing and causes poor interfacial adhesion
Solution Approach 1:
The patent changes the chemical composition parameters of the solid electrolyte from conventional β-alumina to a glass ceramic system with specific ratios of Na2O (20-40 wt%), Al2O3 (30-50 wt%), and SiO2 (10-30 wt%). This compositional parameter change enables the material to achieve adequate ion conductivity while being processable at lower temperatures through sintering, thus resolving the contradiction between conductivity and manufacturability.
Solution Approach 2:
The patent employs a composite glass ceramic material combining multiple oxides (Na2O-Al2O3-SiO2 system) to achieve a balance between ion conductivity and processability. The composite structure allows the material to exhibit both sufficient ionic conduction and improved interfacial adhesion properties, while enabling lower temperature processing compared to pure β-alumina.
2Reliability
If NAS cell operates at high temperature (≥300°C) to achieve good ion conductivity, then ion conductivity is improved, but safety deteriorates due to liquid sodium handling requirements
Solution Approach 1:
The patent changes the operating temperature parameter from conventional high temperature (≥300°C) to low temperature (room temperature or slightly elevated). This is achieved through the use of glass ceramic electrolyte with optimized composition that maintains adequate ion conductivity at lower temperatures, thereby eliminating the safety hazards associated with liquid sodium handling while preserving functional performance.
3Quantity of substance
If positive electrode active material is selected to maximize cell capacity, then energy storage capacity is improved, but compatibility with solid electrolyte and interfacial adhesion may deteriorate
Solution Approach 1:
The patent applies local quality by creating a surface-modified positive electrode material with specific surface characteristics that enhance interfacial compatibility with the glass ceramic electrolyte. The bulk material maintains high capacity properties while the surface region is optimized for adhesion and ionic contact, resolving the contradiction between capacity and interfacial reliability.
Solution Approach 2:
The glass ceramic electrolyte itself acts as an intermediary layer between the positive electrode active material and the sodium source. Its composition (Na2O-Al2O3-SiO2) is specifically designed to provide good interfacial adhesion to high-capacity materials while maintaining ion conductivity, thus mediating between the requirements for high capacity and good interfacial contact.
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
This configuration enables a sodium all-solid-state secondary cell with high capacity and low-temperature operation, independent of lithium resources, with improved ion conductivity and safety, achieving capacities of up to 750 mAh/g and maintaining performance in subsequent charges.
Implementation Method 1
a solid electrolyte layer which is positioned between the positive electrode and the negative electrode
Implementation Method 2
the solid electrolyte layer contains an ion conductive glass ceramics represented by a formula (I): Na2S-MxSy wherein M is selected from P, Si, Ge, B and Al
Data Source
AI summary
An ion conductive glass ceramics having the formula Na2S—P2S5, wherein the Na2S in the ion conductive glass ceramics is contained in an amount of from 70 to 75 mole %, and wherein the ion conductive glass ceramics has a state where crystal parts are dispersed in the glass ingredient of an amorphous state and where the crystal parts contain tetragonal Na3PS4.