Wound Nonaqueous Battery Electrode Structure for Outer-Layer Crack Control
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Solution Overview
Problem
Cracks in the mixture layer on the outer peripheral surface side of the current collector in winding-type non-aqueous electrolyte secondary batteries can lead to degradation of charge-discharge cycle characteristics, particularly when the thickness of the mixture layer is increased for higher capacity.
Innovation Solution
The battery design includes carbon nanotubes in the mixture layers on the outer periphery side with a larger average fiber length than those on the inner periphery side, ranging from 5 μm to 30 μm, to enhance adhesive bonding strength and prevent cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the thickness of the mixture layer is increased to achieve higher capacity, then the energy density is improved, but cracks occur in the mixture layer on the outer peripheral surface side due to tensile stress
Solution Approach 1:
The patent applies different average fiber lengths of carbon nanotubes to different radial positions within the mixture layer. Specifically, carbon nanotubes with larger average fiber lengths are used in the outer peripheral region (5-30 μm) compared to the inner peripheral region, creating local quality differentiation that addresses the specific tensile stress conditions at different locations.
Solution Approach 2:
The patent changes the physical parameter of carbon nanotube average fiber length based on radial position within the electrode. By increasing the average fiber length parameter in the outer peripheral region where tensile stress is highest, the mixture layer's resistance to crack formation is enhanced without compromising the overall capacity.
2Quantity of substance
If cracks occur in the mixture layer on the outer peripheral surface side, then the capacity increases initially, but charge-discharge cycle characteristics degrade due to isolation of active material
Solution Approach 1:
The patent implements preventive measures by incorporating carbon nanotubes with larger average fiber lengths in the outer peripheral region before cracks can form. This beforehand cushioning strengthens the mixture layer in advance against tensile stress, preventing crack formation and the subsequent isolation of active material that would degrade cycle characteristics.
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 design effectively restrains the degradation of charge-discharge cycle characteristics by preventing cracks in the mixture layers, thereby maintaining battery performance.
Implementation Method 1
carbon nanotubes of the mixture layer on the outer periphery side have a larger average fiber length than the carbon nanotubes of the mixture layer on the inner periphery side and have 5 μm to 30 μm of average fiber length
Data Source
AI summary
The purpose of the present invention is to provide a winding-type nonaqueous electrolyte secondary battery which is capable of minimizing degradation of charge-discharge cycle characteristics. The winding-type nonaqueous electrolyte secondary battery according to an embodiment of the present invention is provide with a negative electrode that has a negative electrode current collector, an inner-circumference-side negative electrode mixture layer which is disposed, of the two surfaces of the negative electrode current collector, on the inner-circumference-side surface, and an outer-circumference-side negative electrode mixture layer disposed on the outer-circumference-side surface, wherein the inner-circumference-side negative electrode mixture layer and the outer-circumference-side negative electrode mixture layer each include a negative electrode active material and carbon nanotubes, and the carbon nanotubes in the outer-circumference-side negative electrode mixture layer have an average fiber length of 5-30 um, which is longer than that of the carbon nanotubes in inner-circumference-side negative electrode mixture layer.