Layered Positive Electrode Material to Suppress Nickel Ion Migration
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Solution Overview
Problem
Lithium ion secondary batteries using nickel-containing positive electrode active materials face challenges in maintaining capacity retention over time due to cation mixing and nickel ion migration.
Innovation Solution
A positive electrode active material with a crystal structure featuring alternately arranged nickel and lithium layers, where the a/b axial length ratio is 0.8 or more, and optionally doped with elements having a larger ionic radius than nickel, to suppress nickel ion migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If nickel-containing positive electrode active material is used to achieve large capacity, then battery capacity increases, but capacity retention rate deteriorates due to cation mixing and nickel ion migration
Solution Approach 1:
The patent applies local quality by creating a graded composition structure where the ratio of nickel to other transition metals varies through the particle radius. The surface region has a lower nickel content ratio compared to the interior, which suppresses cation mixing and nickel ion migration at the surface while maintaining high nickel content in the interior for high capacity. This radial gradient in composition allows simultaneous optimization of both capacity and capacity retention.
Solution Approach 2:
The patent employs composite materials by combining multiple transition metals (nickel, cobalt, manganese, iron) in a layered oxide structure with specific compositional ratios. The composite structure utilizes the high capacity contribution from nickel while incorporating stabilizing elements that suppress unwanted ion migration. The composite nature of the material allows balancing high capacity with structural stability for improved capacity retention.
2Use of energy by moving object
If nickel content is increased to improve battery capacity, then energy density increases, but structural stability deteriorates leading to nickel ion migration
Solution Approach 1:
The patent implements local quality through a radially varying composition where the surface layer has reduced nickel content compared to the particle interior. This creates a stable surface region that prevents nickel ion migration while maintaining high overall nickel content for high energy density. The local compositional adjustment at the surface stabilizes the crystal structure without sacrificing bulk capacity.
Solution Approach 2:
The patent applies parameter changes by modifying the compositional parameters (transition metal ratios) as a function of radial position within the particle. The nickel content ratio is changed from high in the interior to lower at the surface, creating a parameter gradient that simultaneously achieves high energy density through bulk nickel content and structural stability through surface nickel depletion.
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 proposed solution enhances the capacity retention rate of lithium ion secondary batteries by reducing nickel ion migration and maintaining the structural integrity of the active material.
Implementation Method 1
an a/b axial length ratio calculated through a Rietveld analysis of radiation X-ray diffraction (XRD)
Data Source
AI summary
The disclosure relates to a positive electrode active material. The positive electrode active material having a crystalline structure in which a transition metal layer containing nickel and a lithium layer are alternately arranged, wherein an a/b axial length ratio calculated by Rietveld analysis of a radiation XRD is 0.8 or more.