Lithium Battery Electrode Assembly Impact Resistance
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Solution Overview
Problem
Lithium secondary batteries face issues with capacity loss due to impacts like dropping, and they struggle to maintain high capacity while ensuring resistance to short-circuits and heat.
Innovation Solution
The battery design incorporates a porous heat-resistant layer with an insulating filler and binder between the positive and negative electrodes, along with a specific B/A ratio for the negative electrode width to distance from the restricting part, which enhances resistance to short-circuits and impacts, and maintains high capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the B/A ratio is increased to enhance battery capacity, then the battery capacity is improved, but the electrode assembly becomes susceptible to distortion causing direct contact between electrodes
Solution Approach 1:
A lower insulator is introduced as an intermediary component between the electrode assembly and the battery can bottom. This insulator acts as a cushion that absorbs impact forces and prevents electrode distortion, allowing the B/A ratio to be increased to 0.97 while maintaining resistance to short-circuits during impact
Solution Approach 2:
The lower insulator is positioned in advance at the bottom of the battery can to provide cushioning protection. By pre-placing this protective element, the electrode assembly is protected from impact-induced distortion before any short-circuit can occur, enabling higher B/A ratios for increased capacity
2Quantity of substance
If the separator is made thinner to increase battery capacity, then the battery capacity is improved, but the resistance to internal short-circuits is reduced
Solution Approach 1:
The lower insulator serves as an additional intermediary protective layer between the electrode assembly and the battery can bottom. This extra insulating layer provides enhanced protection against internal short-circuits, compensating for the reduced protection from thinner separators and enabling higher battery capacity
Solution Approach 2:
The lower insulator is pre-positioned to cushion the electrode assembly against impact forces that could cause separator failure. By providing this protective cushioning in advance, the system can use thinner separators for higher capacity while maintaining safety through the insulator's impact absorption
3Reliability
If the B/A ratio is set to 0.97 with a lower insulator, then the resistance to short-circuits is improved, but the electrode assembly may still experience distortion under impact
Solution Approach 1:
The B/A ratio is optimized to 0.97, balancing the electrode assembly dimensions to maximize capacity while maintaining structural stability. This parameter optimization, combined with the lower insulator, achieves both short-circuit resistance and improved impact resistance by reducing electrode distortion
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 prevents capacity loss due to impacts and ensures excellent resistance to short-circuits and heat, allowing for a high-capacity lithium secondary battery.
Implementation Method 1
a porous heat-resistant layer which contains an insulating filler (solid fine particles) and a binder is formed on a surface of at least one of the positive electrode active material layer and the negative electrode active material layer
Implementation Method 2
Since the porous heat-resistant layer is resistant to shrinking even at high temperature, it has the function of suppressing the overheating of the battery in the event of an internal short-circuit
Implementation Method 3
the filler particles are bonded to one another with a relatively small amount of a binder
Data Source
AI summary
A lithium secondary battery that is excellent in resistance to short-circuits and heat, is unlikely to suffer a capacity loss due to impact such as dropping, and has a high capacity. The lithium secondary battery includes an electrode assembly including a strip-like positive electrode and a strip-like negative electrode that are wound together with a porous heat-resistant layer interposed therebetween, a non-aqueous electrolyte, and a battery can. The battery has a restricting part for restricting vertical movement of the electrode assembly. The distance A from the restricting part to the inner bottom face of the battery can and the width B of the negative electrode satisfy the relation: 0.965≦B/A≦0.995.