Monolithic NMC Cathode Gradient for Solid-State Battery Stability
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Solution Overview
Problem
Conventional lithium ion batteries face challenges in high voltage applications due to safety issues with flammable liquid electrolytes and mechanical instability of polycrystalline positive electrode materials, which lead to cracking and capacity loss in solid state batteries.
Innovation Solution
Development of a monolithic lithium transition metal oxide powder with a cobalt concentration gradient and a quasi-spherical morphology, providing mechanical robustness and improved interfacial contact with solid electrolytes, enhancing cycle stability and energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polycrystalline porous NMC is used to allow liquid electrolyte penetration, then lithium conductivity is improved, but mechanical robustness deteriorates causing cracks in solid state batteries
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the core region has a porous polycrystalline structure optimized for lithium ion conductivity, while the shell region has a dense monolithic structure optimized for mechanical strength. This spatial differentiation of structural properties resolves the contradiction between needing porosity for ionic transport and density for mechanical robustness in solid state batteries
Solution Approach 2:
The patent creates a composite material system combining two distinct microstructural phases: polycrystalline porous regions and monolithic dense regions. This composite approach allows the material to simultaneously exhibit high lithium conductivity from the porous phase and high mechanical strength from the monolithic phase, resolving the inherent trade-off between these two properties
2Use of energy by moving object
If higher working voltage is applied to increase energy density, then battery performance is improved, but electrolyte decomposition and safety issues worsen
Solution Approach 1:
The patent introduces an artificial protective coating layer as an intermediary between the positive electrode active material and the electrolyte. This coating acts as a mediator that allows high voltage operation by preventing direct harmful interactions between the electrolyte and electrode materials, thereby enabling higher energy density without suffering from electrolyte decomposition and safety issues
3Object-affected harmful factors
If solid electrolyte is used to replace liquid electrolyte for safety, then safety is improved, but interfacial contact and mechanical stability worsen
Solution Approach 1:
The patent employs spherical or near-spherical particle morphology for the positive electrode active material. This spherical shape provides superior interfacial contact with the solid electrolyte compared to irregular shapes, as the curved surface distributes contact stresses more uniformly and maintains better contact under compression, thereby resolving the issue of poor interfacial contact while maintaining the safety benefits of solid electrolytes
Data Source
AI summary
A positive electrode active material for a lithium ion battery comprises a lithium transition metal-based oxide powder, the powder comprising single crystal monolithic particles comprising Ni and Co and having a general formula Li1+a (Niz Mny Cox Zrq Ak)1−a O2, wherein A is a dopant, −0.025≤a<0.005, 0.60≤z≤0.95, y≤0.20, 0.05≤x≤0.20, k≤0.20, 0≤q≤0.10, and x+y+z+k+q=1. The particles have a cobalt concentration gradient wherein the particle surface has a higher Co content than the particle center.