Fibrous Carbon Active Material Layer for Crack-Resistant Solid-State Batteries
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Solution Overview
Problem
High-pressure pressing of electrode materials in all-solid-state lithium secondary batteries can lead to material breakage and the generation of cracks due to volume changes during charging and discharging, resulting in decreased ionic and electron conductivity and battery performance.
Innovation Solution
Incorporating a predetermined amount of fibrous carbon as a conductive aid into the active material layer with a controlled porosity, specifically a gap, to maintain ionic and electron conductivity despite volume changes during charging and discharging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If the electrode is pressed at high pressure to decrease porosity, then volume energy density is improved, but the active material is broken and cracks are generated
Solution Approach 1:
The invention utilizes a porous conductive aid material with a three-dimensional network structure that creates controlled void spaces within the active material layer. These porous structures accommodate volume changes during charge-discharge cycles, preventing crack formation while maintaining high packing density for improved volume energy density.
Solution Approach 2:
The invention employs a composite structure combining active material particles with a three-dimensional network porous conductive aid. This composite architecture provides both mechanical integrity during volume changes and continuous conductive pathways, resolving the contradiction between density and structural integrity.
2Volume of stationary object
If the electrode is pressed at high pressure to decrease porosity, then volume energy density is improved, but ionic conductivity and electron conductivity decrease
Solution Approach 1:
The three-dimensional network porous conductive aid maintains interconnected void spaces that facilitate ion transport while providing electron conduction pathways. The porous structure ensures that even at high packing densities, conductivity is preserved through the network of conductive material filling the pores.
Solution Approach 2:
The conductive aid is strategically distributed throughout the active material layer, with higher concentrations in regions where conductivity is needed. The three-dimensional network structure ensures local conductivity while maintaining overall high density, allowing different regions to have optimized properties for their specific functions.
3Reliability
If fibrous carbon is added to improve electron conductivity, then electron conductivity is improved, but the contact area between active material and conductive aid decreases
Solution Approach 1:
The invention transitions from traditional two-dimensional planar conductive aids to a three-dimensional network porous structure. This dimensional change allows the conductive aid to extend throughout the volume of the active material layer, increasing contact points in three dimensions while maintaining adequate contact area through the network architecture.
Solution Approach 2:
The three-dimensional network porous conductive aid forms a nested structure where conductive material fills the void spaces between active material particles. This nesting arrangement maximizes contact area by infiltrating the interparticle spaces, ensuring extensive electrical contact while maintaining high electron conductivity through the nested conductive network.
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 use of fibrous carbon in the active material layer with a gap structure effectively suppresses crack generation and maintains high ionic and electron conductivity, enhancing the battery's performance and cycle stability.
Implementation Method 1
a fibrous carbon material that enables long electron conduction in the active material layer
Implementation Method 2
when the active material layer has the gap, generation of a crack in the active material layer is suppressed even when charging and discharging accompanied by a volume change of an active material are repeated
Implementation Method 3
since lithium ions move between the active material and the solid electrolyte
Data Source
AI summary
The present invention provides an active material layer for an all-solid-state lithium secondary battery including at least an active material, a conductive aid, and a solid electrolyte, in which the active material layer has a gap, a ratio of the conductive aid in the active material layer is 0.1% by mass or more and less than 5.0% by mass, the conductive aid contains fibrous carbon having an average fiber diameter of 10 to 900 nm, and a ratio of the fibrous carbon in the conductive aid is 20% by mass or more.