Solid Electrolyte Cathode Porous Structure Cracking

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Solution Overview

Problem

All-solid-state secondary batteries face challenges with low ion conductivity and capacity retention due to the limited interface area between cathode active material and solid electrolyte, which is exacerbated by the expansion and contraction of cathode active material during charge and discharge, leading to cracking and decreased contact properties.

Innovation Solution

A cathode active material layer is formed with a specific oil absorption amount of 35 to 50 ml per 100 g and a solid electrolyte with an average particle diameter of 1.5 to 2.5 μm, mixed without solvent and pressure-formed to enhance contact properties and prevent cracking, using a sulfide-based solid electrolyte for improved ion conductivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high pressure is applied to increase contact between cathode active material and solid electrolyte, then interface area is improved, but the expansion and contraction space of cathode active material is reduced, causing cracking

Engineering Contradiction:

Improvecontact propertyVSAvoidmechanical strength

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The porous structure of the cathode active material provides internal void space that can accommodate expansion and contraction during charge-discharge cycles, reducing mechanical stress and preventing cracking while maintaining good contact with solid electrolyte particles

Inventive Principle:

Principle #31Porous materials

Solution Approach 2:

The porous structure acts as a pre-designed cushioning space that absorbs the mechanical stress from expansion and contraction before it can cause cracking, protecting the structural integrity of the cathode active material

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

2Quantity of substance

If cathode active material particles are densely packed to increase capacity, then energy density is improved, but the space for solid electrolyte penetration is reduced, decreasing ion conductivity

Engineering Contradiction:

ImprovecapacityVSAvoidion conductivity

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The cathode active material maintains a porous structure with optimized pore volume and diameter that allows solid electrolyte particles to penetrate deeply into the material, ensuring sufficient ion conduction pathways even when particles are densely packed for high capacity

Inventive Principle:

Principle #31Porous materials

Data Source

PatentUS9601759B2Cathode for secondary batteries, method for producing cathode for secondary batteries, and all-solid-state secondary battery

Publication Date: 2017.03.21 TOYOTA JIDOSHA KK

AI summary

To provide: a cathode for secondary batteries, which has a high capacity retention rate; a method for producing a cathode for secondary batteries; and an all-solid-state secondary battery comprising the cathode. This object has been achieved providing by a cathode for secondary batteries, which is characterized by comprising a cathode active material layer containing at least a cathode active material and a solid electrolyte, wherein the cathode active material has an oil absorption amount of 35 to 50 ml per 100 g; wherein the solid electrolyte has an average particle diameter of 1.5 to 2.5 μm; and wherein the cathode active material layer is formed by mixing the cathode active material and the solid electrolyte in the absence of solvent and pressure-forming the resulting mixture.