Battery Separator With Electroconductive Layer
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Solution Overview
Problem
Lithium ion secondary batteries face abnormalities due to heat shrinkage and potential short circuits when the internal battery temperature rises, leading to safety concerns and reliability issues during overcharging.
Innovation Solution
A secondary battery with a separator having a laminate structure comprising at least two porous layers, one with an electroconductive material dispersed in a porous electroconductive layer, which migrates to form microfine pathways between electrodes, preventing direct contact and managing thermal energy dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional porous separator is used to prevent short-circuiting, then the separator can provide basic separation and shutdown function, but the separator undergoes heat shrinkage and rupture when internal battery temperature rises, causing short circuits
Solution Approach 1:
The separator is constructed as a composite structure combining a polyolefin porous layer (providing shutdown function) with a heat-resistant porous layer containing heat-resistant fibers (providing thermal stability). This composite structure prevents heat shrinkage and rupture at elevated temperatures while maintaining the shutdown function, thereby resolving the contradiction between reliability and temperature resistance.
Solution Approach 2:
The invention changes the thermal parameters of the separator by incorporating heat-resistant fibers with high melting points into the porous layer. This modifies the separator's heat resistance parameter, enabling it to maintain structural integrity at temperatures that would cause conventional separators to shrink and rupture, thus preventing short circuits.
2Reliability
If the separator provides shutdown function by melting at polymer melting point, then ion conduction is stopped to prevent temperature increase, but the separator coverage area declines and rupture occurs, causing direct electrode contact
Solution Approach 1:
The separator combines a polyolefin porous layer (providing shutdown function through melting) with a heat-resistant porous layer containing heat-resistant fibers (maintaining structural integrity). The heat-resistant layer prevents rupture and maintains coverage area even when the polyolefin layer melts, allowing the shutdown function to operate without compromising structural strength.
Solution Approach 2:
The separator is divided into functional segments: a polyolefin porous layer responsible for the shutdown function and a heat-resistant porous layer responsible for maintaining structural integrity. This segmentation allows each layer to perform its specific function independently, resolving the contradiction between shutdown capability and structural strength.
3Productivity
If the separator is made thinner to reduce battery size, then energy density increases, but the separator becomes more susceptible to heat shrinkage and rupture
Solution Approach 1:
The thin separator uses a composite structure where heat-resistant fibers are incorporated into the porous layer. This allows the separator to maintain adequate mechanical strength and heat resistance at reduced thickness, enabling high energy density without sacrificing reliability against heat shrinkage and rupture.
Solution Approach 2:
The invention changes the material composition parameters of the separator to include heat-resistant components, which improves the strength-to-thickness ratio. This allows the separator to be made thinner for higher energy density while maintaining sufficient durability against thermal degradation.
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
The solution effectively prevents short-circuiting and manages internal battery temperature rises, enhancing safety and reliability by creating microfine electroconductive pathways that disperse thermal energy, thus preventing battery abnormalities during overcharging.
Implementation Method 1
the electroconductive material in the porous electroconductive layer migrates with the molten polymer to within the pores in the electroconductive material-free porous layer
Implementation Method 2
when the melting point of the polymer constituting the porous electroconductive layer is reached due to an increase in the internal battery temperature, this polymer melts and the shutdown function is exhibited
Implementation Method 3
the separator itself has an electroconductive material-free porous layer and as a consequence can prevent the short-circuiting that is caused by direct contact between the positive electrode and negative electrode
Implementation Method 4
the formation of these microfine electroconductive pathways results in the production of microfine short circuits between the positive electrode and negative electrode, and the dispersion and consumption of the thermal energy
Data Source
AI summary
Provided is a very safe secondary battery that can prevent the occurrence of battery abnormalities even when the internal battery temperature increases due to, for example, overcharging. A separator 70 in this secondary battery has a laminated structure that is provided with at least two porous layers 76A, 72, 76B, wherein one of these layers forms a porous electroconductive layer 72 in which an electroconductive material 74 is dispersed in the porous layer.