Layered High-Nickel Cathode Structure for Longer Battery Cycle Life
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Solution Overview
Problem
High-loading positive electrodes in lithium secondary batteries face rapid degradation due to limited lithium mobility, leading to poor life characteristics, as increased loading amounts result in lithium ions moving primarily on the surface rather than within the active material layer.
Innovation Solution
A two-layer positive electrode structure is implemented, with a first layer having a high nickel-to-cobalt molar ratio of 18 or more and a second layer with a ratio of less than 18, enhancing lithium mobility and preventing rapid structural degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the loading amount of the positive electrode active material is increased to achieve high capacity, then the energy density is improved, but the lithium mobility is reduced and electrode degradation accelerates
Solution Approach 1:
The positive electrode active material layer is divided into two distinct layers: a first layer with high Ni/Co ratio (≥18) and a second layer with low Ni/Co ratio (<18). This segmentation allows each layer to perform specialized functions - the first layer provides high capacity while the second layer ensures good lithium mobility and structural stability, resolving the contradiction between high loading amount and long cycle life
Solution Approach 2:
Different regions of the positive electrode active material layer are assigned different Ni/Co ratios to optimize local properties. The first layer (closer to the separator) has high nickel content for maximum capacity, while the second layer (closer to the electrolyte) has lower nickel content for better lithium ion transport. This local quality differentiation enables the electrode to simultaneously achieve high energy density and good cycle stability
2Quantity of substance
If the nickel content is increased to achieve high capacity, then the energy density is improved, but the structural stability deteriorates and degradation accelerates
Solution Approach 1:
The high-nickel content is segmented and concentrated in the first layer, while the second layer contains lower nickel content. This segmentation allows the electrode to achieve high overall nickel content for high capacity while preventing excessive nickel in any single region from causing rapid structural degradation
Solution Approach 2:
The nickel content is locally optimized by creating a gradient structure where the first layer has high nickel content (≥80% of total metallic components) for maximum capacity and the second layer has lower nickel content for better structural stability and lithium mobility. This local quality approach resolves the contradiction between high nickel content and structural stability
Data Source
AI summary
A positive electrode for a lithium secondary battery includes a positive electrode collector, a first positive electrode active material layer formed on the positive electrode collector and includes a first positive electrode active material, and a second positive electrode active material layer formed on the first positive electrode active material layer and includes a second positive electrode active material. The first positive electrode active material and the second positive electrode active material include a lithium nickel-cobalt-based oxide in which an amount of nickel among total metallic components excluding lithium is 80 atm % or more, the first positive electrode active material has a molar ratio of nickel to cobalt of 18 or more, and the second positive electrode active material has a molar ratio of nickel to cobalt of less than 18.