Core-Shell NMC Precursor for Stable Ni-Rich Cathodes
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Solution Overview
Problem
Ni-rich lithium nickel manganese cobalt oxide (NMC) cathode materials in lithium-ion batteries face instability due to high nickel content, leading to degradation in air atmospheres with carbon dioxide and moisture, and increased production costs, along with poor thermal stability and electrochemical performance.
Innovation Solution
A core-shell structured precursor with a Ni-rich core and a Co-rich shell is used, where the core has a composition of Ni0.8Mn0.1Co0.1 and the shell has a composition of Mn0.1Co0.9 or Mn0.05Co0.95, sintered at low temperatures to produce a lithiated Ni-rich NMC compound with improved electrochemical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high nickel content (Ni-rich) is used in NMC cathode material to increase reversible capacity, then energy density is improved, but thermal stability and structural integrity deteriorate
Solution Approach 1:
The cathode material is segmented into core and shell regions with different compositions. The core contains high Ni content (Ni0.8Mn0.1Co0.1) for high capacity, while the shell has lower Ni content and higher Co/Mn content to provide thermal stability. This spatial segmentation allows each region to fulfill its specific function without compromising the other.
Solution Approach 2:
Different regions of the particle are assigned different local qualities: the core has high Ni concentration for energy storage, while the shell has tailored composition (enriched in Co and/or Mn) for structural stability and thermal resistance. This local differentiation resolves the contradiction by allowing high Ni content where needed while maintaining stability at the surface.
2Ease of manufacture
If high nickel content is used to reduce production cost, then manufacturing cost is improved, but stability in air atmosphere deteriorates
Solution Approach 1:
The shell region is designed with specific local quality (enriched in Co and Mn, depleted in Ni) to provide chemical stability in air atmosphere. This protective shell allows the use of cost-effective high-Ni core material while preventing degradation during storage and processing.
Solution Approach 2:
The cathode material is constructed as a composite structure combining Ni-rich NMC core with a shell having different composition characteristics. This composite approach leverages the cost advantage of high-Ni materials while incorporating stability-providing elements (Co, Mn) in the shell region.
3Use of energy by moving object
If high nickel content is used to achieve higher reversible capacity, then energy density is improved, but particle structural integrity during charge-discharge deteriorates
Solution Approach 1:
The particle is segmented into core and shell, where the high-Ni core provides capacity while the shell acts as a structural reinforcement. The shell region with lower Ni content and higher Co/Mn content maintains structural integrity during volume changes, preventing particle cracking.
Solution Approach 2:
The shell structure serves as a pre-established protective layer that cushions the high-Ni core against mechanical stress and volume expansion during charge-discharge cycles. This beforehand cushioning prevents structural degradation before it occurs.
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 approach results in a positive electrode material with enhanced first cycle efficiency, cycle stability, and thermal stability, achieving higher discharge capacity and safety, with first cycle efficiency exceeding 94% and improved heat resistance.
Implementation Method 1
sintered at low temperatures to produce a lithiated Ni-rich NMC compound
Data Source
AI summary
A precursor compound for manufacturing a lithium transition metal based oxide powder usable as an active positive electrode material in lithium-ion batteries, the precursor being either one of a metal-bearing M′-hydroxide, -oxyhydroxide or -carbonate, with M′=Ni1-x-y-zMnxCOyAz with x>0, y>0, 0.70≤1-x-y-z≤0.95 and 0≤z<0.1, the precursor comprising having a core comprising a metal-bearing compound M′c and a shell comprising a metal-bearing compound M′s, wherein M′c=Ni1-xc-yc-zcMnxcCOycAzc with 0<xc≤0.2, 0<yc≤0.2, 0≤zc<0.1 and 0.75≤1-x-y-z≤0.95, and M′s=Ni1-xs-ys-zsMnxsCOysAzs with 0<xs≤0.25, 0.75<ys≤0.95, 0≤zs<0.1 and 0≤1-xs-ys-zs≤0.10.