Sodium Ion Solid Electrolyte Sheet Thickness Flatness Control

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Solution Overview

Problem

Reducing the thickness of solid electrolytes in sodium ion all-solid-state batteries increases internal resistance, leading to decreased battery characteristics such as discharge capacity and operating voltage, and results in low ionic conductivity due to surface layer Na2O concentration gradients and flatness issues during the production of sodium ion-conductive crystal-containing solid electrolyte sheets.

Innovation Solution

A sodium ion-conductive crystal-containing solid electrolyte sheet with a thickness of 500 μm or less and a flatness of 200 μm or less, using β″-alumina and NASICON crystals, with controlled Na2O concentration gradients to maintain high ionic conductivity, and a pre-firing method to reduce contraction and volatilization of sodium components during firing, ensuring uniform electrode application and reduced cracking.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If the thickness of the solid electrolyte is reduced to increase energy density, then the energy density per unit volume increases, but the internal resistance of the battery increases and battery characteristics deteriorate

Engineering Contradiction:

Improveenergy density per unit volumeVSAvoidbattery characteristics

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The patent changes the physical parameters of the solid electrolyte by controlling thickness (50-500 μm) and flatness (≤200 μm) to optimize both energy density and battery performance. By precisely controlling these geometric parameters, the invention achieves high energy density while maintaining acceptable internal resistance and discharge capacity.

Inventive Principle:

Principle #35Parameter changes

2Volume of moving object

If the thickness of the solid electrolyte is reduced, then the energy density increases, but the internal resistance increases leading to decreased discharge capacity and operating voltage

Engineering Contradiction:

Improveenergy densityVSAvoiddischarge capacity and operating voltage

Core Design Contradiction:

Volume of moving objectVSPower

Solution Approach 1:

The patent optimizes the thickness parameter within a specific range (50-500 μm) to balance energy density and power output. This parameter control ensures that the solid electrolyte is thin enough for high energy density but not so thin that internal resistance becomes excessive, thereby maintaining adequate discharge capacity and operating voltage.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If the green sheet method is used to produce sheet-form solid electrolyte, then the production efficiency increases, but the ionic conductivity decreases due to Na2O concentration gradient

Engineering Contradiction:

Improveproduction efficiencyVSAvoidionic conductivity

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent controls the Na2O concentration parameter to minimize the concentration gradient between the surface and interior of the solid electrolyte. By maintaining Na2O concentration difference at ≤10% (mole ratio) between depths of 5 μm and 20 μm from the surface, the invention preserves high ionic conductivity while utilizing the efficient green sheet production method.

Inventive Principle:

Principle #35Parameter changes

4Ease of manufacture

If the flatness of the solid electrolyte is large, then the manufacturing is easier, but the electrode application becomes uneven leading to increased internal resistance

Engineering Contradiction:

ImprovehandleabilityVSAvoidelectrode thickness uniformity

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent optimizes the flatness parameter to ≤200 μm, which represents a balanced value that maintains adequate handleability during manufacturing while ensuring sufficiently uniform electrode application. This flatness control prevents excessive local variations in electrode thickness that would otherwise increase internal resistance.

Inventive Principle:

Principle #35Parameter changes

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 enables sodium ion all-solid-state batteries with improved discharge capacity, operating voltage, and energy density while minimizing internal resistance and mechanical strength loss, achieving high ionic conductivity and enhanced handleability.

Implementation Method 1

contains at least one type of sodium ion-conductive crystal selected from β″-alumina and NASICON crystal

Methodology Applied

Scientific EffectIonic conductivity: Conduction (electrical)

Implementation Method 2

making a raw material powder for the solid electrolyte into a slurry, forming a green sheet from the slurry, and then firing the green sheet

Methodology Applied

Scientific EffectThermal heating: Heating

Data Source

PatentUS11552329B2Solid electrolyte sheet, method for producing same and all-solid-state secondary battery

Publication Date: 2023.01.10 NIPPON ELECTRIC GLASS CO LTD

AI summary

Provided are a sodium ion-conductive crystal-containing solid electrolyte sheet capable of giving excellent battery characteristics even when reduced in thickness, and an all-solid-state battery using the same. The solid electrolyte sheet contains at least one type of sodium ion-conductive crystal selected from β″-alumina and NASICON crystal and has a thickness of 500 μm or less and a flatness of 200 μm or less.