Asymmetric Positive Electrode Loading for Stack-Type Lithium Batteries
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Solution Overview
Problem
Rechargeable lithium batteries with high nickel-based or cobalt-free positive electrode active materials face challenges in achieving high energy density while maintaining charge/discharge efficiency due to cation mixing during synthesis, leading to suboptimal cycle-life characteristics and capacity.
Innovation Solution
A stack-type rechargeable lithium battery design featuring a positive electrode with a first active material layer having a higher loading level and larger secondary particles, and a second active material layer with a lower loading level and smaller single particles, both composed of specific lithium composite oxides, optimizing the N/P ratio and particle distribution to enhance cycle-life characteristics and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high nickel-based or cobalt-free positive electrode active materials are used to increase energy density, then capacity is improved, but charge/discharge efficiency deteriorates due to cation mixing
Solution Approach 1:
The patent applies local quality by creating asymmetric loading levels on the two surfaces of the positive electrode current collector. The first surface has a higher loading level (20-30 μg/cm²) while the second surface has a lower loading level (15-25 μg/cm²), optimizing local electrochemical performance to compensate for cation mixing effects and improve overall charge/discharge efficiency while maintaining high capacity
Solution Approach 2:
The patent implements asymmetry by deliberately designing unequal loading levels on the two surfaces of the positive electrode. This asymmetric structure (first surface loading > second surface loading) creates different electrochemical environments that optimize both high capacity utilization and charge/discharge efficiency, resolving the contradiction between quantity and reliability
2Quantity of substance
If positive electrode materials with relatively low charge/discharge efficiency are used, then energy density is maintained, but cycle-life characteristics deteriorate significantly
Solution Approach 1:
The patent uses local quality by varying the loading level across different regions of the positive electrode. The first surface maintains higher loading (20-30 μg/cm²) for energy density while the second surface uses lower loading (15-25 μg/cm²) to reduce stress and improve stability, thereby extending cycle-life characteristics without sacrificing overall energy density
Solution Approach 2:
The patent introduces a dimensional variation by considering the bidirectional structure of the positive electrode (two surfaces). By optimizing each surface independently with different loading levels, the patent transforms a single-parameter optimization problem into a multi-dimensional solution that simultaneously addresses energy density and cycle-life characteristics
Data Source
AI summary
A positive electrode for a stack-type rechargeable lithium battery includes a current collector, a first positive electrode active material layer on one surface of the current collector, and a second positive electrode active material layer on the other surface of the current collector, wherein a loading level of the first positive electrode active material layer is about 5% or more higher than a loading level of the second positive electrode active material layer, each of the first positive electrode active material layer and the second positive electrode active material layer includes a first positive electrode active material in the form of secondary particles and a second positive electrode active material in the form of single particles, an average particle diameter of secondary particles of the first positive electrode active material is larger than an average particle diameter of single particles of the second positive electrode active material.