Crosslinked Polyolefin Battery Separator for High-Temperature Stability
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Solution Overview
Problem
Lithium secondary battery separators face challenges in maintaining elasticity at high temperatures, leading to safety concerns due to potential ignition and explosion risks, and existing solutions like PE/PP/PE trilayer separators require complex manufacturing processes or produce undesired byproducts.
Innovation Solution
A porous polyolefin separator with a tan(δ) of 0.3 or less at 230°C, featuring crosslinked fibrils and pores, and an inorganic composite porous layer, which enhances high-temperature stability and safety through UV crosslinking and simplified manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a polyethylene monolayer separator is used, then the manufacturing process is simple, but the separator has low melting point and causes ignition and explosion at high temperature
Solution Approach 1:
The patent uses a PE/PP/PE trilayer composite structure where polyethylene layers provide shutdown function at lower temperatures and polypropylene layer provides structural support at higher temperatures. This composite approach combines the advantages of both materials to achieve both ease of manufacture and high-temperature safety.
Solution Approach 2:
The patent modifies the melting point parameter of the separator by incorporating polypropylene with higher melting point (160-170°C) into the polyethylene structure, thereby changing the thermal properties to resist high-temperature degradation while maintaining the original manufacturing simplicity.
2Reliability
If a PE/PP/PE trilayer separator is used, then the high-temperature safety is improved, but the manufacturing process becomes more complicated
Solution Approach 1:
The patent combines the shutdown function and structural support function into a single trilayer structure that can be manufactured in one continuous process. The PE/PP/PE layers are bonded together to form an integrated separator that achieves high-temperature safety without requiring separate assembly steps.
3Reliability
If crosslinking agent is used to form crosslinked bonds in polyethylene fibrils, then the high-temperature stability is improved, but byproducts are produced and foreign materials are formed in the separator
Solution Approach 1:
The patent extracts and removes the crosslinking agent and byproducts from the system by using physical crosslinking methods such as radiation or plasma treatment instead of chemical crosslinking. This eliminates the formation of harmful foreign materials while achieving the desired high-temperature stability.
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 provides a separator with improved high-temperature safety, maintaining strength and preventing short-circuits, while simplifying the manufacturing process and avoiding byproduct issues, thus enhancing the safety and efficiency of lithium secondary batteries.
Implementation Method 1
the porous polyolefin substrate includes a plurality of fibrils and pores, wherein the pores are formed by the fibrils entangling with one another, and polyolefin chains forming the fibrils are crosslinked directly with one another
Implementation Method 2
A porous polyolefin separator with a tan(δ) of 0.3 or less at 230°C, featuring crosslinked fibrils and pores, and an inorganic composite porous layer, which enhances high-temperature stability and safety through UV crosslinking
Data Source
AI summary
A separator for a lithium secondary battery, a method of making the same, and a lithium secondary battery including the same is disclosed herein. In some embodiments, a separator for a lithium secondary battery including a porous polyolefin substrate having a tan(δ) of 0.3 or less. The tan(δ) is determined by Formula 1 at a temperature of 230° C. and an angular frequency of 0.1 rad/s:tan(δ)=G″/G′ [Formula 1]wherein G′ is a storage modulus of the polyolefin and G″ is a loss modulus of the polyolefin. The separator has a low viscosity but high elasticity at high temperature, maintains strength at high temperature, and has resistance against external force at high temperature. A lithium secondary battery including the separator has improved safety.