Positive electrode plate and non-aqueous electrolyte secondary battery having the same
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Solution Overview
Problem
Existing secondary batteries face challenges in achieving high capacity and low resistance, particularly in positive electrode plates using lithium-(transition metal) composite oxides.
Innovation Solution
A positive electrode plate design with a double-layer structure, where a first layer composed of a lithium-rich active material with high capacity but high resistance is positioned farther from the current collector, and a second layer composed of a lithium-poor active material with low resistance is closer to the current collector, combined with specific porosity ranges and content ratios, enhances lithium ion diffusion and reduces overall resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a lithium-rich active material is used to increase capacity, then the battery capacity is improved, but the resistance increases
Solution Approach 1:
The positive electrode active material layer is divided into two distinct layers: a first layer containing lithium-rich active material (Li1+a1□1−a1−x1−y1−z1Nix1Co1/3−x1/6Mn1/2−y1/2−z1O2−ε1) and a second layer containing lithium-poor active material (Li1+a2□1−a2−x2−y2−z2Nix2Co1/3−x2/6Mn1/2−y2/2−z2O2−ε2). This segmentation allows each layer to contribute different properties - the lithium-rich layer provides high capacity while the lithium-poor layer provides low resistance, resolving the contradiction between capacity and resistance.
Solution Approach 2:
Different regions of the active material layer are assigned different compositions and properties. The first layer (closer to separator) has high lithium content for capacity, while the second layer (closer to current collector) has low lithium content for conductivity. This local differentiation of material properties enables simultaneous optimization of both capacity and resistance throughout the electrode structure.
2Productivity
If the porosity of the active material layer is increased to enhance electrolyte contact, then the lithium ion diffusion is improved, but the density of active material decreases
Solution Approach 1:
The active material layer is segmented into two layers with different porosity characteristics. The first layer has porosity of 30-45% to facilitate electrolyte penetration and lithium ion diffusion, while the second layer has porosity of 20-35% to maintain higher active material density. This segmentation allows each layer to optimize porosity for its specific function without compromising the other.
Solution Approach 2:
Different porosity values are assigned to different layers based on their functional requirements. The first layer (liathium-rich) has higher porosity to enhance electrolyte contact and ion diffusion pathways, while the second layer (lithium-poor) has lower porosity to maximize active material packing density. This local optimization of porosity resolves the contradiction between diffusion rate and material density.
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 design results in a non-aqueous electrolyte secondary battery with both high capacity and low resistance, improving the battery's performance by optimizing the contact of active materials with the electrolyte solution.
Implementation Method 1
enhances lithium ion diffusion and reduces overall resistance
Data Source
AI summary
A positive electrode plate comprises a current collector, and an active material layer provided on the current collector. The active material layer has a first layer mainly composed of a first active material represented by a formula (I) and a second layer mainly composed of a second active material represented by a formula (II), and the second layer is positioned closer to the current collector than the first layer is. The formula (I) and the formula (II) are as defined in the claims. A content ratio between the first active material and the second active material in the active material layer is (first active material):(second active material)=2.5:7.5 to 6.5:3.5 (in weight). A porosity of the first layer is from 20 to 45%, and a porosity of the second layer is from 18 to 41%.