Composite Cathode Reducing Interfacial Resistance
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Solution Overview
Problem
Oxide-based solid electrolytes in all-solid-state batteries have insufficient ductility, leading to increased interfacial resistance when in contact with cathode active materials, resulting in reduced discharge capacity and capacity retention due to the formation of pores during heat treatment.
Innovation Solution
A composite cathode is developed using a crystalline phosphate solid electrolyte and a phosphate-based cathode active material with significantly higher electrical conductivity, forming an interphase without the need for conductive materials, which enhances electronic conduction pathways and reduces interfacial resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conductive material is added to lower interfacial resistance, then electrical conductivity is improved, but contact formation between solid electrolyte and cathode is disturbed and pores are generated
Solution Approach 1:
The patent removes the conductive material component from the cathode composite, relying instead on the inherent electrical conductivity of the phosphate-based cathode active material itself to provide the necessary conductive pathways, thereby avoiding the pore formation issue associated with conductive material addition
Solution Approach 2:
The patent changes the electrical conductivity parameter of the cathode active material by selecting phosphate-based materials with inherently high conductivity, eliminating the need for separate conductive additives and maintaining both good contact formation and low interfacial resistance
2Manufacturing precision
If heat treatment is performed to prepare the cathode, then material densification is achieved, but pores are generated due to disturbed contact formation
Solution Approach 1:
The patent performs preliminary mixing of the phosphate-based cathode active material and oxide-based solid electrolyte to ensure uniform distribution and intimate contact before heat treatment, preventing pore formation during the subsequent densification process while achieving the desired material consolidation
3Stability of the object's composition
If oxide-based solid electrolyte is used, then atmospheric stability is improved, but ductility is insufficient leading to increased interfacial resistance
Solution Approach 1:
The patent creates a composite material system combining phosphate-based cathode active material with oxide-based solid electrolyte, where the phosphate material provides both the necessary electrical conductivity and compatibility with the oxide electrolyte, achieving low interfacial resistance while maintaining atmospheric stability
Solution Approach 2:
The patent applies local quality by using phosphate-based materials specifically at the interface between the cathode and solid electrolyte, where high electrical conductivity is needed, while the bulk oxide-based solid electrolyte maintains its atmospheric stability properties
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 composite cathode achieves improved initial capacity and cycle stability in secondary batteries by forming a dense structure with reduced porosity and increased conductivity, enhancing lithium ion movement between the cathode active material and solid electrolyte.
Implementation Method 1
a crystalline phosphate cathode active material having an electrical conductivity that is about 10 times to about 106 times greater than an electrical conductivity of the crystalline phosphate solid electrolyte
Implementation Method 2
heat treating the composition at a temperature of 700° C. or greater and at a pressure of 150 megapascals or less to form the composite cathode
Implementation Method 3
heat treating the composition at a temperature of 700° C. or greater and at a pressure of 150 megapascals or less to form the composite cathode
Implementation Method 4
enhancing lithium ion movement between the cathode active material and solid electrolyte
Data Source
AI summary
A composite cathode, including: a cathode current collector; and a cathode active material layer on the cathode current collector. The cathode active material layer includes: a crystalline phosphate solid electrolyte; a crystalline phosphate cathode active material having an electrical conductivity about 10 times to about 106 times greater than an electrical conductivity of the crystalline phosphate solid electrolyte; and an interphase between the crystalline phosphate solid electrolyte and the crystalline phosphate cathode active material.