Positive Electrode Gas Discharge via CNT Network
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face reduced charge and discharge efficiency due to gas generated during charging and discharging, particularly in the early stages, when using electrode active materials with small particle diameters, as the gas tends to remain within the electrode active material layer, hindering efficient discharge.
Innovation Solution
Incorporating carbon nanotubes with an average length of 1 μm to 2 μm and an average diameter of 10 nm or less, along with another electroconductive carbon material like carbon black, into the positive electrode active material layer to form a network that facilitates the discharge of generated gas, ensuring higher charge and discharge efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the density of the electrode active material layer is increased to achieve higher energy density, then the energy density is improved, but gas generated during charging and discharging remains within the electrode active material layer, making it difficult to be discharged outside, which reduces battery performance
Solution Approach 1:
The patent introduces a porous structure within the electrode active material layer by incorporating a foam material. This foam material creates interconnected voids and channels that allow gas to escape from the dense electrode structure during charging and discharging, preventing gas accumulation while maintaining high energy density.
Solution Approach 2:
The patent creates a composite structure by combining the electrode active material with a foam material. This composite approach allows the dense electrode material to maintain high energy density while the foam component provides gas escape pathways, resolving the contradiction between density and gas dischargeability.
2Quantity of substance
If an electrode active material with a relatively small mean particle diameter (10 μm or less) is used to increase the thickness of the electrode active material layer, then the energy density is improved, but gas generated in charging and discharging tends to remain, causing reduction in charge and discharge efficiency
Solution Approach 1:
The foam material creates a porous network within the electrode active material layer that provides continuous pathways for gas to escape. This porous structure is particularly effective for fine particle materials where gas trapping is more severe, as the foam channels extend throughout the entire electrode thickness, enabling efficient gas discharge while maintaining high energy density.
3Quantity of substance
If the thickness of the electrode active material layer is increased to achieve high energy density, then the energy density is improved, but gas generated during charging and discharging remains within the layer, causing abnormal behavior of charge and discharge curves and reduced efficiency
Solution Approach 1:
The foam material creates a three-dimensional porous network that spans the entire thickness of the electrode active material layer. This network provides multiple escape routes for gas throughout the electrode, preventing gas accumulation that would otherwise cause abnormal charge and discharge curves. The porous structure ensures reliable gas discharge even in thick electrodes with high energy density.
Data Source
AI summary
The nonaqueous electrolyte secondary battery disclosed herein includes an electrode assembly including a positive electrode and a negative electrode, and a nonaqueous electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The positive electrode active material layer has an average film thickness of 100 μm or more. The positive electrode active material layer includes a positive electrode active material having a mean particle diameter of 10 μm or less, and, as an electroconductive material, carbon nanotubes and another electroconductive carbon material. The carbon nanotubes have an average length of 1 μm or more to 2 μm or less, and an average diameter of 10 nm or less. In a cross-sectional electron microscope image of the positive electrode active material layer, the electroconductive material is dispersed.