Secondary Battery Positive Electrode Layer Segmentation
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Solution Overview
Problem
Secondary batteries experience a decrease in output when positive electrodes with high specific surface area active materials are stored in air due to the formation of resistance components like Li2CO3 from reactions with air moisture and carbon dioxide.
Innovation Solution
A secondary battery configuration with a positive electrode having a first mixture layer with a high BET specific surface area on the core side and a second mixture layer with a lower BET specific surface area on top, inhibiting air moisture entry and suppressing the formation of Li2CO3, is implemented. The first positive electrode mixture layer contains a first active material with a BET specific surface area of 1.6 to 2.8 m2/g, and the second layer contains a second active material with a BET specific surface area of 0.8 to 1.3 m2/g, with a thickness of 5 to 15 μm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a positive electrode mixture layer containing a positive electrode active material with high specific surface area is used to improve output, then the charge-discharge characteristics including output are enhanced, but the output decreases when the positive electrode is stored in air due to formation of resistance components
Solution Approach 1:
The positive electrode mixture layer is divided into two distinct layers: a first positive electrode mixture layer containing active material with high specific surface area (1.6-2.8 m²/g) for improving output, and a second positive electrode mixture layer containing active material with lower specific surface area (0.8-1.3 m²/g) for protecting against air exposure. This segmentation allows each layer to perform its specialized function without compromising the other.
Solution Approach 2:
Different regions of the positive electrode mixture layer are assigned different properties: the first layer (closer to the current collector) has high specific surface area for enhanced power output, while the second layer (outer surface) has lower specific surface area for reduced reactivity with air. This local differentiation of material properties resolves the contradiction between output performance and air stability.
2Productivity
If the specific surface area of positive electrode active material is increased to improve output, then charge-discharge characteristics are enhanced, but resistance components like Li2CO3 form upon air exposure
Solution Approach 1:
The positive electrode mixture layer is segmented into two layers with different specific surface areas. The first layer (1.6-2.8 m²/g) provides high productivity for charge-discharge, while the second layer (0.8-1.3 m²/g) acts as a protective barrier that minimizes the formation of harmful resistance components like Li2CO3 during air exposure.
Solution Approach 2:
The second positive electrode mixture layer with lower specific surface area serves as an intermediary protective layer between the high-specific-surface-area active material and the air environment. This intermediate layer prevents direct contact between air moisture and the highly reactive first layer, thereby suppressing the formation of resistance components while allowing the first layer to maintain its high productivity.
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
This configuration effectively suppresses the decrease in output due to air exposure, maintaining the battery's performance by preventing the formation of resistance components and ensuring initial and retained output efficiency.
Implementation Method 1
The second positive electrode mixture layer contains a second positive electrode active material having a BET specific surface area of 0.8 m2/g to 1.3 m2/g and acts as a protective layer that suppresses a decrease in output due to air exposure
Data Source
AI summary
A secondary battery includes a positive electrode including a positive electrode core; and a positive electrode mixture layer formed on at least one of the surfaces of the positive electrode core. The positive electrode mixture layer has a first positive electrode mixture layer and a second positive electrode mixture layer formed om the surface of the first positive electrode mixture layer. The first positive electrode mixture layer contains a first positive electrode active material having a BET specific surface area of 1.6 m2/g to 2.8 m2/g, and the second positive electrode mixture layer contains a second positive electrode active material having a BET specific surface area of 0.8 m2/g to 1.3 m2/g. The thickness of the second positive electrode mixture layer is 5 μm to 15 μm.