Lithium Battery Separator Coating for Low Shrinkage Resistance
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Solution Overview
Problem
Rechargeable lithium batteries face challenges in achieving high energy density and capacity while maintaining stability and longevity due to issues with membrane resistance and heat shrinkage.
Innovation Solution
A separator for lithium batteries comprising a porous substrate with a coating layer containing a (meth)acryl-based binder and a mixture of boehmite and barium titanate, where the barium titanate is substantially spherical and has a low specific surface area, reducing membrane resistance and heat shrinkage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional separator is used, then the battery can operate, but the membrane resistance is high and heat shrinkage is excessive
Solution Approach 1:
The separator employs a porous substrate structure that allows efficient ion transport while maintaining mechanical integrity. The porous configuration reduces membrane resistance by providing multiple pathways for lithium ion conduction, directly addressing the harmful effect of high resistance in conventional separators.
Solution Approach 2:
The separator utilizes a composite structure combining organic binder polymers with inorganic heat-resistant particles (such as alumina or silica). This composite material approach simultaneously achieves low membrane resistance through the porous organic matrix and low heat shrinkage through the thermally stable inorganic framework, resolving the contradiction between operational reliability and resistance reduction.
2Object-affected harmful factors
If the separator thickness is reduced to improve ionic conductivity, then membrane resistance decreases, but mechanical strength and thermal stability deteriorate
Solution Approach 1:
The reinforced composite separator integrates inorganic particles (alumina, silica, or boehmite) within the polymer matrix to maintain mechanical strength at reduced thickness. These rigid particles provide structural support and thermal stability, enabling the separator to be thinner while preserving both strength and low resistance properties.
Solution Approach 2:
The separator design implements local quality enhancement by strategically distributing inorganic particles and optimizing the porous structure in different regions. The coating layers on both sides of the porous substrate provide localized reinforcement and controlled porosity, allowing thin overall thickness while maintaining mechanical integrity and ionic conductivity where needed.
3Strength
If the binder content is increased to improve coating adhesion, then coating strength increases, but membrane resistance increases
Solution Approach 1:
The coating composition uses a balanced composite of polymer binder and inorganic particles. The inorganic particles provide structural framework and heat resistance while the polymer binder ensures adhesion. This composite approach achieves sufficient coating strength without excessive binder content that would block ion transport pathways and increase membrane resistance.
Solution Approach 2:
The coating layer maintains a porous structure that balances adhesion and ion conductivity. The porous configuration allows the coating to adhere strongly to the substrate while preserving channels for lithium ion transport, preventing the trade-off between coating strength and membrane resistance that occurs in dense non-porous coatings.
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 achieves low dry shrinkage rates and improved thermal stability with reduced membrane resistance, enhancing the battery's ionic conductivity and overall performance.
Implementation Method 1
The filler includes a mixture of boehmite and barium titanate... the separator achieves low dry shrinkage rates and improved thermal stability with reduced membrane resistance, enhancing the battery's ionic conductivity
Implementation Method 2
The separator may have a low membrane resistance and a high heat resistance, resulting in low heat shrinkage
Data Source
AI summary
Examples of the present disclosure include a separator for a rechargeable lithium battery, and a rechargeable lithium battery including the separator. The separator for a rechargeable lithium battery includes a porous substrate and a coating layer on at least one surface of the porous substrate. The coating layer includes a binder and a filler. The binder includes a (meth)acryl-based binder including a sulfonate group-containing structural unit. The filler includes a mixture of boehmite and barium titanate in a weight ratio in a range of about 20:80 to about 80:20 with respect to 100 parts by weight of the mixture of boehmite and barium titanate.