Polyolefin Separator Thermal Stability in Lithium-Ion Batteries
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Solution Overview
Problem
Lithium ion secondary batteries with high energy density or large size are prone to thermal runaway due to potential melting or fracturing of the separator during abnormal current events, leading to concerns about short-circuit resistance.
Innovation Solution
A lithium ion secondary battery design featuring a separator with a porous resin layer containing polyolefin, where the layer maintains a specific thickness and structure after a nail penetration test, ensuring the positive and negative electrodes remain separated even under high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous polyolefin separator is used in high energy density or large-sized lithium ion secondary batteries, then the separator provides shut-down function and basic separation, but the separator may be melted or fractured due to plasticization during abnormal current events, leading to thermal runaway
Solution Approach 1:
The patent applies composite materials by combining polyolefin base material with inorganic particles (such as alumina, silica, or boehmite) to create a separator that maintains structural integrity at high temperatures. The inorganic particles form a heat-resistant skeleton that prevents melting and fracturing of the polyolefin matrix during abnormal current events, thereby resolving the contradiction between reliability and strength under thermal stress.
Solution Approach 2:
The patent changes the physical and chemical parameters of the separator by controlling the pore size distribution (average pore diameter of 0.01 to 10 μm), porosity (30 to 80%), and thickness (5 to 50 μm) of the porous resin layer. These parameter optimizations ensure the separator maintains adequate mechanical strength and thermal stability while providing effective ion transport, thus improving short-circuit resistance without compromising separator integrity.
2Reliability
If the separator thickness is increased to prevent melting and fracturing during abnormal current events, then short-circuit resistance improves, but the battery energy density decreases due to increased non-active material volume
Solution Approach 1:
The patent applies local quality by creating a heat-resistant skeleton structure through inorganic particles that is concentrated at critical locations where thermal stress and mechanical stress are highest. This localized reinforcement provides enhanced short-circuit resistance at the separator without uniformly increasing thickness throughout, thereby maintaining energy density while improving reliability.
Solution Approach 2:
The patent optimizes the thickness parameter of the porous resin layer to a specific range (5 to 50 μm) and controls porosity (30 to 80%) to balance mechanical strength and ion conductivity. By precisely controlling these parameters, the separator achieves adequate short-circuit resistance with minimal thickness, preserving battery energy density while ensuring safety.
3Productivity
If the porous resin layer structure is optimized for ion transport, then battery performance improves, but the separator becomes more susceptible to melting and fracturing under thermal stress
Solution Approach 1:
The patent uses composite materials by integrating inorganic particles into the polyolefin matrix to create a dual-function structure. The porous resin layer maintains high porosity (30 to 80%) and appropriate pore size (average 0.01 to 10 μm) for excellent ion conductivity, while the inorganic particles provide thermal stability and structural reinforcement, preventing melting and fracturing under thermal stress.
Solution Approach 2:
The patent applies local quality by distributing inorganic particles throughout the porous resin layer to create localized heat-resistant zones. These zones maintain the overall porous structure for ion transport while providing localized thermal stability, thus resolving the contradiction between productivity and strength.
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 design enhances short-circuit resistance and prevents thermal runaway by maintaining the separator's integrity and preventing electrode contact, even at elevated temperatures.
Implementation Method 1
the porous resin layer maintains a specific thickness and structure after a nail penetration test, ensuring the positive and negative electrodes remain separated even under high temperatures
Implementation Method 2
an average thickness of the porous resin layer in a range of 1 mm to 3 mm in an in-plane direction from a peripheral edge of a nail hole is equal to or greater than 10% of an average thickness of the porous resin layer before the nail penetration test
Implementation Method 3
the porous membrane has a shut-down function of blocking a current flow. According to this, the porous membrane becomes effective from the viewpoint of avoiding battery thermal runaway
Implementation Method 4
a metal nail having a diameter of 3 mm penetrates through a central portion of the lithium ion secondary battery at 80 mm/sec for short-circuiting of the lithium ion secondary battery
Data Source
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AI summary
Provided is a lithium ion secondary battery including, as components accommodated in a container, a positive electrode that intercalates and deintercalates lithium, a negative electrode that intercalates and deintercalates lithium, a nonaqueous electrolytic solution that contains a lithium salt, and a separator that is interposed between the positive electrode and the negative electrode. The separator includes a porous resin layer containing polyolefin as a main component. In a full charge state, when observing a cross-section of the lithium ion secondary battery after performing a nail penetration test in which a metal nail having a diameter of 3 mm penetrates through a central portion of the lithium ion secondary battery at 80 mm/sec for short-circuiting of the lithium ion secondary battery, an average thickness of the porous resin layer in a range of 1 mm to 3 mm in an in-plane direction from a peripheral edge of a nail hole is equal to or greater than 10% of an average thickness of the porous resin layer before the nail penetration test, and the porous resin layer remains at a position within 1 mm in the in-plane direction from the peripheral edge of the nail hole.