Polyolefin Separator with Isotropic Deformation for Battery Internal Resistance
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges in maintaining low internal resistance and high battery performance due to issues with separator materials that affect ion permeability and mechanical strength, particularly during charging and discharging cycles.
Innovation Solution
A separator with a first layer made of porous polyolefin, characterized by specific viscoelastic properties and a white index range, is designed to prevent increased internal resistance by ensuring isotropic deformation and optimal ion permeability, incorporating a porous structure that shuts down ion transport at high temperatures to prevent short-circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous polyolefin separator is used to ensure ion permeability, then ion transport is improved, but mechanical strength and structural stability deteriorate
Solution Approach 1:
The separator is constructed as a composite material consisting of a polyolefin base layer providing mechanical strength and a silane-modified polyethylene coating layer providing enhanced ion permeability and thermal shutdown function. This composite structure resolves the contradiction by combining materials with complementary properties.
Solution Approach 2:
The separator incorporates a porous structure with controlled pore size distribution (average pore diameter of 0.03-0.10 μm) and porosity (30-80%) to facilitate ion transport while maintaining structural integrity. The porous silane-modified polyethylene layer specifically enhances ion permeability without compromising the mechanical foundation.
2Reliability
If the separator structure is optimized for ion transport, then battery performance is improved, but resistance to thermal deformation worsens
Solution Approach 1:
The separator utilizes controlled parameter changes including crystallinity (40-80%) and crosslinking degree (5-50%) to achieve optimal balance between ion transport and thermal stability. The silane modification introduces crosslinked structures that maintain dimensional stability at elevated temperatures while preserving ion permeability pathways.
Solution Approach 2:
The separator exploits the phase transition properties of polyolefin materials, utilizing the melting and crystallization behavior to achieve thermal shutdown function at specific temperatures while maintaining structural stability during normal operation. The crosslinked silane network moderates excessive deformation during phase transitions.
3Productivity
If the separator is made thinner to reduce battery size, then energy density is improved, but manufacturing precision requirements increase
Solution Approach 1:
The separator is divided into multiple functional layers: a polyolefin base layer providing mechanical strength and a thinner silane-modified polyethylene coating layer (1-10 μm) providing ion transport pathways. This segmentation allows the overall structure to be optimized for both thinness and manufacturing feasibility, with each layer performing its specific function.
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 separator effectively suppresses the increase in internal resistance and maintains high battery performance by ensuring suitable ion permeability and mechanical strength, while the shutdown function at high temperatures enhances safety by preventing short-circuits.
Implementation Method 1
The separator separates the positive electrode and the negative electrode from each other and also functions as a film transmitting the electrolyte solution and carrier ions
Implementation Method 2
a first layer which has a parameter X, defined by the following equation, equal to or more than 0 and equal to or less than 20... MD tan δ and TD tan δ are respectively a loss tangent in a flow direction and a loss tangent in a width direction
Implementation Method 3
incorporating a porous structure that shuts down ion transport at high temperatures to prevent short-circuits
Data Source
AI summary
Provided is a separator capable of suppressing an increase in internal resistance and a decrease in a battery performance. A separator having a first layer consisting of a porous polyolefin and an organic antioxidant and a secondary battery including the separator are provided. The first layer has a parameter X, defined by the following equation, equal to or more than 0 and equal to or less than 20,X=100MDtanδ-TDtanδMDtanδ+TDtanδ2where MD tan δ and TD tan δ are respectively a loss tangent in a flow direction and a loss tangent in a width direction which are obtained by a viscoelasticity measurement of the first layer at a temperature of 90° C. and a frequency of 10 Hz. A white index of the first layer is equal to or more than 85 and equal to or less than 98.