Electrochemical Separator with Dual-Layer Shutdown and Heat Resistance
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Solution Overview
Problem
Current electrochemical device separators, such as those used in lithium secondary batteries, face challenges in providing adequate safety and reliability due to thermal shrinkage and the risk of internal short-circuits, especially when exposed to high temperatures or during abnormal heating events, as they lack sufficient shutdown characteristics and are prone to deformation.
Innovation Solution
A separator comprising a porous film with a first layer that includes a resin with a melting point of 80°C to 130°C to initiate a shutdown by melting and closing pores, and a second layer with a heat-resistant filler to prevent direct contact between electrodes and suppress thermal shrinkage, enhancing safety and reliability by increasing the tortuosity factor and using flakes to hinder lithium dendrite penetration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a polyethylene separator is stretched to provide strength and porosity, then the mechanical strength is improved, but the shutdown temperature is raised up to the thermal runaway temperature, reducing safety margin
Solution Approach 1:
The separator is divided into multiple functional layers: a heat-resistant base layer (polypropylene nonwoven fabric) that maintains dimensional stability, and a shutdown layer (polyethylene porous film) that provides the shutdown function. This segmentation allows each layer to perform its specific function without compromising the other, resolving the contradiction between mechanical strength and safety margin.
2Quantity of substance
If a polyethylene separator is stretched to provide porosity, then the porosity is improved, but distortion occurs due to residual stress, causing thermal shrinkage at high temperature
Solution Approach 1:
The separator structure separates the porosity function (provided by the stretched polyethylene shutdown layer) from the dimensional stability function (provided by the non-stretched polypropylene nonwoven fabric base layer). This segmentation eliminates the contradiction by assigning each function to the appropriate layer.
Solution Approach 2:
Different regions of the separator have different properties: the base layer has high dimensional stability and heat resistance, while the shutdown layer has high porosity and shutdown capability. This local differentiation of properties resolves the contradiction between porosity and dimensional stability.
3Stability of the object's composition
If heat-resistant resin separators are used to prevent thermal shrinkage, then dimensional stability is improved, but the shutdown characteristic is lost, reducing safety during abnormal heating
Solution Approach 1:
The separator is segmented into a heat-resistant base layer that provides dimensional stability and a separate shutdown layer that provides the shutdown characteristic. The base layer uses heat-resistant polypropylene nonwoven fabric while the shutdown layer uses polyethylene porous film with melting point 80-130°C, allowing both functions to coexist without compromise.
4Device complexity
If a single-layer separator is used to simplify structure, then device complexity is reduced, but it cannot simultaneously provide adequate shutdown function and resistance to internal short-circuit
Solution Approach 1:
The separator is segmented into two functional layers: a base layer for structural integrity and heat resistance, and a shutdown layer for thermal safety. This segmentation enables the separator to provide both shutdown function and resistance to internal short-circuit, overcoming the limitations of single-layer designs.
Solution Approach 2:
The separator uses a composite structure combining polypropylene nonwoven fabric and polyethylene porous film. This composite material approach allows the separator to integrate multiple functions (heat resistance, dimensional stability, shutdown capability, and short-circuit prevention) that cannot be achieved with a single material.
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 proposed separator design significantly improves safety and reliability by ensuring a shutdown mechanism is triggered at elevated temperatures, preventing internal short-circuits and maintaining structural integrity, thus ensuring the electrochemical device's safety and performance.
Implementation Method 1
the resin A melted on a surface of the separator forms a film to inhibit the conduction of the Li ion, thereby causing a shutdown
Implementation Method 2
a porous film having a thickness of 20 to 30 μm is used as a separator to be interposed between a positive electrode and a negative electrode
Data Source
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AI summary
An electrochemical device having excellent safety at a high temperature is provided by using a separator for an electrochemical device, which is made of a porous film including a first separator layer and a second separator layer. The first separator layer includes, as a main ingredient, at least one kind of resin selected from the group consisting of resin A that has a melting point in a range of 80°C to 130°C, and resin B that absorbs a nonaqueous electrolyte and swells due to heating and whose swelling degree is increased as the temperature rises, the second separator layer includes, as a main ingredient, a filler that has a heat-resistant temperature of not lower than 150°C, and at least one of the first separator layer and the second separator layer includes flakes.