Hi-Ni Positive Electrode Crystallite Gradient for Cycle Stability
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Solution Overview
Problem
Conventional Hi-Ni-type positive electrode active materials with small crystallite diameters reduce particle breakage but have low initial efficiency, while those with large diameters have high efficiency but are prone to particle breakage during charge and discharge, compromising both endurance and efficiency.
Innovation Solution
A positive electrode design featuring a layered metal oxide with a nickel-to-metallic elements ratio of 70 mol% or more, where the surface layer has a smaller crystallite diameter and the base material layer has a larger crystallite diameter, creating a double-layer structure to balance endurance and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a small crystallite diameter is used, then particle breakage is reduced and endurance is improved, but specific surface area increases causing decreased initial efficiency
Solution Approach 1:
The patent applies local quality by creating a positive electrode active material layer with non-uniform crystallite diameter distribution. Specifically, the crystallite diameter is controlled to be smaller near the surface (closer to electrolyte contact) and larger toward the base material side. This spatial variation in crystallite size allows the surface region to resist particle breakage while the interior region maintains high charge-discharge efficiency, thus resolving the contradiction between endurance and initial efficiency.
2Productivity
If a large crystallite diameter is used, then initial efficiency is improved, but particle breakage increases during charge and discharge reducing endurance
Solution Approach 1:
The patent resolves this contradiction by implementing local quality through spatially differentiated crystallite diameters. The larger crystallite diameter regions are positioned toward the base material side where they enable efficient charge-discharge processes, while smaller crystallite diameter regions are positioned near the surface to prevent particle breakage during cycling. This localized optimization allows each region to perform its specific function effectively.
Data Source
AI summary
The present disclosure relates to a positive electrode comprising a positive electrode active material layer and a positive electrode base material, wherein the positive electrode active material layer includes a positive electrode active material, the positive electrode active material includes a layered metal oxide, the ratio of nickel to the total amount of nickel and a transition metal in the layered metal oxide is 70% or more, and the positive electrode active material present near a surface of the positive electrode active material layer closer to the positive electrode base material has a crystallite diameter that is 200 Å to 500 Å greater than the positive electrode active material present near a surface of the positive electrode active material layer opposite to the positive electrode base material. According to the present disclosure, a positive electrode and a battery each of which is excellent in both endurance and efficiency are provided.