High-Nickel Cathode Sheet Layout for Moisture-Stable Energy Density
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Solution Overview
Problem
High-nickel positive electrode active materials in lithium secondary batteries face challenges with structural and chemical stability, leading to rapid deterioration of thermal stability and increased surface resistance due to reactions with moisture, which limits energy density and battery lifespan.
Innovation Solution
The electrode sheet is designed with a first positive electrode mixture layer containing lithium-nickel-cobalt-manganese oxide with a high nickel content (70 mol % or more) in the central portion, and a second positive electrode mixture layer with a lower nickel content (45 to 60 mol %) at the edges. The rolling density of the second positive electrode mixture layer is set to be smaller than that of the first layer to reduce moisture permeation and prevent fine powder generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the nickel content in the positive electrode active material is increased to improve energy density, then the energy density per volume increases, but the structural stability and chemical stability of the active material decrease, leading to rapid deterioration of thermal stability
Solution Approach 1:
The patent applies different nickel content compositions to different regions of the electrode: the central portion uses high-nickel content material (80-90 mol%) for high energy density, while the edge portions use lower nickel content material (60-70 mol%) for better structural stability and moisture resistance. This spatial differentiation of material properties resolves the contradiction between energy density and stability.
2Use of energy by moving object
If the nickel content in the positive electrode active material is increased to improve energy density, then the energy density per volume increases, but the resistance of the surface of the active material increases due to reactions with moisture and carbon dioxide
Solution Approach 1:
The patent reduces surface resistance by applying lower nickel content material (60-70 mol%) specifically at the edge portions of the electrode where surface exposure to moisture and carbon dioxide occurs. This localized protection strategy maintains high energy density in the central region while minimizing harmful surface reactions at the edges.
3Use of energy by moving object
If the nickel content in the positive electrode active material is increased to improve energy density, then the energy density per volume increases, but gas generation during high temperature storage increases
Solution Approach 1:
The patent minimizes gas generation during high temperature storage by using lower nickel content material (60-70 mol%) at the edge portions of the electrode, which are more susceptible to thermal degradation and moisture reactions. The high-nickel central portion (80-90 mol%) contributes to energy density while the edge portions act as protective zones that reduce overall gas generation.
4Reliability
If a second positive electrode active material with low nickel content (20 to 40%) is applied at both ends to suppress lithium precipitation, then lithium precipitation is suppressed, but the desired energy density cannot be implemented
Solution Approach 1:
The patent optimizes the nickel content at edge portions to 60-70 mol%, which is higher than the conventional 20-40 mol% but still lower than the central high-nickel region. This intermediate nickel content provides sufficient lithium precipitation suppression while maintaining higher energy density compared to conventional approaches, thus resolving the contradiction between reliability and energy density.
Data Source
AI summary
The present invention relates to an electrode sheet comprising: a first cathode mixture layer which is formed in a central portion of a holding part and contains a first cathode active material of lithium nickel cobalt manganese oxide; and a second cathode mixture layer which is formed at one end or both ends of the first cathode mixture layer and contains a second cathode active material lower in nickel content than the first cathode active material, wherein a rolling density b of the second cathode mixture layer is lower than a rolling density a of the first cathode mixture layer, whereby the electrode sheet has the effect of improving the energy density while suppressing a reaction with water.