Cathode Material Precursor Density Gradient for Lithium Diffusion
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Solution Overview
Problem
Existing cathode active materials do not achieve high charge/discharge efficiency, cycle life, and thermal stability due to ineffective lithium diffusion during charge/discharge cycles, despite improvements in other characteristics.
Innovation Solution
A precursor for cathode active materials is designed with a center portion having a higher density and a surface portion with a lower density, achieved through differences in porosity and element composition, allowing for efficient lithium diffusion and structural stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high Ni content (70% or more) is used to increase capacity and output, then charge/discharge efficiency improves, but capacity decreases upon repeated charge/discharge due to crystal structure shrinkage, oxygen release, cation mixing, and gelation
Solution Approach 1:
The precursor particle is designed with non-uniform density distribution where the surface portion has lower density than the center portion. This local quality differentiation allows the surface to accommodate volume changes during lithium intercalation/deintercalation, reducing stress on the crystal structure and preventing degradation mechanisms such as shrinkage, oxygen release, cation mixing, and gelation, thereby maintaining high capacity over repeated charge/discharge cycles while preserving high charge/discharge efficiency
Solution Approach 2:
The invention changes the density parameter of the precursor particle by creating a gradient structure where surface density is lower than center density. This parameter change is achieved through controlled precipitation processes that result in different porosity levels in different regions of the particle, allowing the material to exhibit both high initial performance and improved cycling stability
2Stability of the object's composition
If a dense intermediate layer is added between porous core and shell to reduce stress from volume changes, then structural stability improves, but lithium ion diffusion distance increases and charge/discharge efficiency decreases
Solution Approach 1:
Instead of adding a dense intermediate layer between porous core and shell as in conventional approaches, this invention inverts the density distribution by making the surface portion less dense than the center portion. This inversion eliminates the need for a separate intermediate layer while still providing stress relief during volume changes, and simultaneously maintains short lithium ion diffusion paths throughout the particle, achieving both structural stability and high charge/discharge efficiency
3Reliability
If the entire precursor particle has high density to improve structural stability, then resistance characteristics improve, but lithium diffusion to the center becomes ineffective and charge/discharge efficiency decreases
Solution Approach 1:
The precursor particle exhibits local quality differentiation with the center portion having high density for structural stability and resistance characteristics, while the surface portion has lower density to facilitate lithium diffusion. This spatial variation in density ensures that lithium ions can effectively reach the high-density center region, maintaining both structural integrity and high charge/discharge efficiency
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 precursor structure enhances lithium diffusion, suppresses structural cracks, and improves charge/discharge efficiency, cycle lifespan, and thermal stability of the cathode active material.
Implementation Method 1
the surface portion has a lower density than the center portion... provides excellent cycle life and thermal stability as well as high charge/discharge efficiency
Data Source
AI summary
Disclosed is a precursor for preparing a cathode active material, more specifically, a precursor for preparing a cathode active material including a center portion and a surface portion sequentially formed from a center of a particle toward an outer surface, wherein the surface portion has a lower density than the center portion.