Positive Electrode Layering for Battery Energy Density and Cycle Life
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Solution Overview
Problem
Secondary batteries face challenges in achieving both high energy density and high cycle characteristics simultaneously due to limitations in the compressive strength and distribution of positive electrode active materials during the rolling process, which affects electrolyte permeability and material durability.
Innovation Solution
A positive electrode for secondary batteries is designed with a mixture layer containing two active materials of different compressive strengths, where the first material with a compressive strength of 400 MPa or less is concentrated in one region and the second material with a lower compressive strength in another region, allowing for optimized distribution and increased density without crushing, thereby enhancing energy density and cycle retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the positive electrode mixture layer uses a single type of active material, then the structure is simple, but both high energy density and high cycle characteristics cannot be achieved simultaneously
Solution Approach 1:
The patent applies local quality by creating two distinct regions within the positive electrode mixture layer. The first region (near the current collector) contains active material with compressive strength ≥400 MPa to maintain structural integrity during rolling, while the second region (near the surface) contains active material with compressive strength <400 MPa to achieve high energy density. This spatial differentiation of material properties resolves the contradiction between structural reliability and energy density.
Solution Approach 2:
The patent uses composite materials by combining two different positive electrode active materials with distinct compressive strength characteristics. The first active material (high compressive strength) provides mechanical stability, while the second active material (low compressive strength) enables higher density packing. This composite approach allows simultaneous achievement of high cycle characteristics and high energy density.
2Quantity of substance
If the positive electrode mixture layer is densely packed to increase energy density, then the energy density improves, but the cycle characteristics deteriorate due to material crushing and loss of electrolyte permeability
Solution Approach 1:
The patent implements local quality by assigning different material properties to different regions of the mixture layer. The first region near the current collector uses high compressive strength material to withstand rolling pressure and maintain electrolyte permeability pathways, while the second region near the surface uses low compressive strength material to achieve dense packing and high energy density. This resolves the contradiction between density and cycle life.
3Quantity of substance
If the positive electrode mixture layer undergoes rolling to increase density, then the energy density improves, but the compressive strength of active material particles decreases causing particle crushing and reduced cycle characteristics
Solution Approach 1:
The patent applies local quality by positioning high compressive strength active material in the first region that undergoes maximum rolling pressure near the current collector, while placing low compressive strength material in the second region that experiences less rolling pressure near the surface. This spatial distribution allows the density-enhancing rolling process to occur while protecting the most vulnerable materials from crushing.
Data Source
AI summary
A positive electrode for a secondary battery including a positive electrode current collector, and a positive electrode mixture layer containing a positive electrode active material and disposed on a surface of the positive electrode current collector in which the positive electrode mixture layer contains a first positive electrode active material having a compressive strength of 400 MPa or less, a second positive electrode active material having a compressive strength smaller than the compressive strength of the first positive electrode active material, and when the positive electrode mixture layer is zoned into a first region and a second region having the same thickness, the first positive electrode active material is contained more in the first region than in the second region, and the second positive electrode active material is contained more in the second region than in the first region is used.