Battery Separator Coating for Heat-Resistant Cycle Life
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Solution Overview
Problem
Conventional separators for rechargeable lithium batteries face challenges in maintaining ion conductivity and cycle-life characteristics, particularly at high temperatures, due to issues with moisture absorption and mechanical stability.
Innovation Solution
A separator comprising a porous substrate with a coating layer containing a binder mixture of polyurethane and polyvinyl alcohol, along with inorganic particles and a cross-linking agent, which enhances ion conductivity, heat resistance, and adhesion, while minimizing moisture absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional separator is used, then the battery can operate, but moisture absorption occurs and cycle-life characteristics deteriorate at high temperatures
Solution Approach 1:
The patent applies composite materials by combining polyurethane and polyvinyl alcohol in a specific weight ratio (5:5 to 9:1) to create a binder that simultaneously provides moisture resistance and thermal stability. This composite binder system resolves the contradiction by integrating two materials with complementary properties: polyurethane for moisture barrier performance and polyvinyl alcohol for thermal stability, thereby improving cycle-life characteristics while preventing moisture absorption at high temperatures.
Solution Approach 2:
The patent employs parameter changes by optimizing the weight ratio of polyurethane to polyvinyl alcohol in the binder (5:5 to 9:1 range) and controlling the molecular weight parameters (polyurethane: 1,000-150,000, cross-linked polymer: 500-80,000 g/mol). These parameter optimizations enable the binder to achieve both low moisture absorption and high thermal stability, resolving the contradiction between moisture resistance and cycle-life performance at elevated temperatures.
2Temperature
If the separator uses a simple binder, then manufacturing is easier, but heat resistance and adhesion are insufficient at high temperatures
Solution Approach 1:
The patent uses composite materials by formulating a binder containing polyurethane and polyvinyl alcohol in a specific weight ratio (5:5 to 9:1). This composite binder provides superior heat resistance and adhesion properties compared to simple binders, while the defined ratio range keeps the composition manageable for manufacturing processes.
Solution Approach 2:
The patent applies local quality by introducing a coating layer on at least one surface of the porous substrate. This coating layer contains the polyurethane-polyvinyl alcohol binder with inorganic particles and cross-linking agents, providing localized enhancement of heat resistance and adhesion properties where they are most needed, while the rest of the separator structure remains relatively simple.
3Stability of the object's composition
If the separator maintains mechanical stability, then structural integrity is preserved, but ion conductivity may be compromised
Solution Approach 1:
The patent uses porous materials by employing a porous substrate as the base structure of the separator. This porous structure inherently provides ion conductivity pathways while maintaining mechanical stability through the substrate's architecture. The coating layer with cross-linked polymer further reinforces mechanical stability without blocking ion transport channels.
Solution Approach 2:
The patent applies composite materials by combining the porous substrate with a coating layer containing polyurethane-polyvinyl alcohol binder, inorganic particles, and cross-linking agents. This composite structure achieves a balance where the porous substrate ensures ion conductivity and the coating layer with cross-linked polymer provides enhanced mechanical stability and thermal resistance.
4Strength
If a cross-linked polymer with high molecular weight is used, then strength is improved, but manufacturing precision and processing become more difficult
Solution Approach 1:
The patent employs parameter changes by controlling the weight average molecular weight of the cross-linked polymer within a specific range (500-80,000 g/mol) and optimizing the cross-linking agent content (0.03-10 parts by weight per 100 parts binder). These parameter controls enable the formation of a strong coating layer while maintaining manufacturability and coating precision.
Solution Approach 2:
The patent applies local quality by concentrating the cross-linking and polymerization processes within the coating layer on the porous substrate surface. This localized approach allows the cross-linked polymer to provide strength enhancement where needed (in the coating layer) without requiring the entire separator structure to be complex, thereby maintaining manufacturing precision.
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 improves the thermal stability and cycle-life characteristics of rechargeable lithium batteries by reducing moisture content and preventing shrinkage at high temperatures, ensuring both heat resistance and prolonged battery performance.
Implementation Method 1
the cross-linking agent being bound to the polyurethane and/or the inorganic particles. The cross-linking agent may be bound to the polyurethane to form a cross-linked polymer
Implementation Method 2
a coating layer on at least one surface of the porous substrate, wherein the coating layer includes a binder and inorganic particles
Implementation Method 3
a porous substrate; and a coating layer on at least one surface of the porous substrate
Data Source
AI summary
A separator for a rechargeable lithium battery and a rechargeable lithium battery, the separator including a porous substrate; and a coating layer on at least one surface of the porous substrate, wherein the coating layer includes a binder and inorganic particles, the binder including a polyurethane and a polyvinyl alcohol, and the polyurethane and the polyvinyl alcohol are included in a weight ratio of about 5:5 to about 9:1.