Polyurethane Separator Membranes for Thermal Stability
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Solution Overview
Problem
Conventional separator films in electrochemical cells face issues such as heat shrinkage, swelling, and mechanical instability, which affect the performance and safety of lithium-ion batteries, necessitating the development of improved membranes that are electrically insulating yet permeable to lithium ions.
Innovation Solution
A poly(dialkylene ester) thermoplastic polyurethane composition is used to create membranes that are resistant to heat shrinkage, mechanically robust, and suitable for lithium ion transfer, comprising a reaction between a poly(dialkylene ester) polyol intermediate, diisocyanate, and chain extender, with optional inclusion of nanofillers and lithium salts, and an aprotic organic solvent in the electrolyte system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional separator films based on polyolefins are used, then mechanical stability is adequate, but heat shrinkage and swelling problems occur that inhibit cell performance
Solution Approach 1:
The patent employs polyolefin copolymers incorporating comonomers (ethylene, propylene, butylene, hexene) to create composite material structures that combine the mechanical stability of polyolefins with enhanced heat resistance. The copolymer structure allows tuning of crystallinity and melting point to prevent heat shrinkage while maintaining separator integrity
Solution Approach 2:
The patent modifies the chemical composition parameters of the separator by controlling comonomer content (5-50 mol%), molecular weight (10,000-500,000 g/mol), and melting point (100-200°C) to achieve optimal balance between mechanical strength and thermal stability. These parameter adjustments prevent both heat shrinkage and swelling while maintaining adequate mechanical properties
2Quantity of substance
If separator thickness is reduced to improve energy density, then cell capacity increases, but mechanical strength and resistance to damage decrease
Solution Approach 1:
The patent utilizes controlled polymerization to achieve specific molecular weights (10,000-500,000 g/mol) and comonomer ratios that optimize the strength-to-thickness ratio. By adjusting these parameters, the separator maintains adequate mechanical strength at reduced thicknesses, enabling thinner designs that improve energy density without sacrificing safety
Solution Approach 2:
The copolymer structure creates a composite material with enhanced strength characteristics that allow reduced thickness. The combination of different monomer units provides both mechanical reinforcement and controlled porosity, enabling thin separators to maintain structural integrity while improving cell energy density
3Strength
If hot-lamination process is used to bond separators on electrodes, then mechanical bonding is improved, but micro pores needed for separator function are damaged
Solution Approach 1:
The patent modifies the bonding process parameters by controlling lamination temperature (below separator melting point), pressure, and time to achieve adequate bonding without damaging the micro pore structure. The adjusted parameters ensure separator functionality is preserved while achieving mechanical attachment to electrodes
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 membranes exhibit high lithium ion conductivity, stability up to 200°C, and excellent mechanical strength, ensuring safe and efficient operation of electrochemical cells with improved charge/discharge efficiency and cycle life.
Implementation Method 1
a layer which is electrically insulating but permeable to lithium cations is located between the two electrodes
Implementation Method 2
the described poly(dialkylene ester) thermoplastic polyurethane composition... heat, melt and shrinkage resistance
Data Source
AI summary
The invention relates to a membrane comprising a poly(dialkylene ester) thermoplastic polyurethane composition. The invention also provides an electrochemical cell comprising a positive electrode, a negative electrode, and (I) a separator membrane disposed between said positive and negative electrodes, wherein the said membrane comprises (A) the described poly(dialkylene ester) thermoplastic polyurethane composition.