Dual-Layer Positive Electrode for Battery Safety
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Solution Overview
Problem
Lithium secondary batteries face limitations in thermal stability and safety due to poor resistance against external penetration, leading to potential ignition or explosion from overcurrent.
Innovation Solution
A positive electrode structure with a first and second mixture layer, where the second layer has a smaller average particle diameter and a controlled ratio of specific surface area of conductive material to active material, increasing resistance and reducing electrical conductivity to prevent overcurrent and ignition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a lithium nickel composite oxide is used as positive electrode active material to achieve high reversible capacity, then the battery capacity increases, but the thermal stability deteriorates leading to safety issues
Solution Approach 1:
The positive electrode is divided into two distinct mixture layers: a first layer containing lithium nickel composite oxide particles and a second layer containing smaller particles. This segmentation allows each layer to serve different functions - the first layer provides high capacity while the second layer improves thermal stability and safety by increasing resistance to external penetration.
Solution Approach 2:
Different regions of the positive electrode are given different properties. The first mixture layer (with larger particles) is positioned to provide high capacity, while the second mixture layer (with smaller particles and lower conductive material ratio) is positioned to provide thermal stability and overcurrent protection. This local differentiation resolves the contradiction between capacity and safety.
2Power
If the specific surface area ratio of conductive material to active material is increased to improve electrical conductivity, then the output performance improves, but the resistance against external penetration decreases causing safety hazards
Solution Approach 1:
The electrode is segmented into two layers with different conductive material ratios. The first layer has a higher ratio for good output performance, while the second layer has a lower ratio (9 or less) to provide high resistance against external penetration. This segmentation allows both conductivity and safety to be optimized in different regions.
Solution Approach 2:
The conductive material distribution is made non-uniform across the electrode thickness. The first layer (closer to current collector) has higher conductivity for power output, while the second layer (upper layer) has lower conductivity to increase resistance to nail penetration and prevent short circuits. This local quality differentiation resolves the contradiction between power and safety.
3Power
If the average particle diameter of active material is reduced to increase specific surface area, then the electrical conductivity improves, but the resistance against external penetration decreases leading to overcurrent issues
Solution Approach 1:
The active material particles are segmented into two size groups distributed in different layers. The first layer contains particles with larger average diameter providing structural stability and penetration resistance, while the second layer contains particles with smaller average diameter (5 to 80% of first layer) providing higher specific surface area and electrical conductivity. This segmentation allows both conductivity and penetration resistance to be optimized.
Solution Approach 2:
Particle size is varied locally across the electrode structure. The first mixture layer uses larger particles for mechanical strength and penetration resistance, while the second mixture layer uses smaller particles for enhanced conductivity. This local quality variation in particle size resolves the contradiction between electrical conductivity and penetration resistance.
Data Source
AI summary
Provided is a positive electrode for a secondary battery, the positive electrode including a positive electrode current collector, a first positive electrode mixture layer laminated on the positive electrode current collector and including a first positive electrode active material and a first conductive material, and a second positive electrode mixture layer laminated on the first positive electrode mixture layer and including a second positive electrode active material and a second conductive material, wherein the average particle diameter (D50) of the second positive electrode active material is 5 to 80% of the average particle diameter (D50) of the first positive electrode active material, and the ratio of the specific surface area of the second conductive material to the specific surface area of the second positive electrode active material is 9 or less.