VDF-HFP Resin Separator Adhesion for Lithium-Ion Batteries
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Solution Overview
Problem
Non-aqueous secondary batteries, particularly lithium ion batteries, face challenges with adhesion between electrodes and separators, especially in larger formats, leading to reduced battery capacity, deteriorated charge-discharge characteristics, and increased production yield issues due to internal stress and decomposition of electrolyte solutions during thermal press processes.
Innovation Solution
A separator with an adhesive porous layer containing a polyvinylidene fluoride type resin, specifically a VDF-HFP copolymer with an acid value of 3.0 mgKOH/g to 20 mgKOH/g, which provides excellent adhesion to electrodes through both wet and dry heat press methods, maintaining adhesion even after electrolyte impregnation and reducing gas generation and deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a separator with an adhesive porous layer containing polyvinylidene fluoride type resin is used in a large-area soft pack battery, then the battery area is increased, but the adhesion between electrode and separator is insufficient leading to reduced battery capacity and deteriorated charge-discharge characteristics
Solution Approach 1:
The invention changes the chemical parameters of the polyvinylidene fluoride type resin by controlling its acid value to be within 3.0-20.0 mgKOH/g. This parameter adjustment enhances the adhesive properties of the resin, enabling it to maintain strong adhesion between the electrode and separator even in large-area batteries where mechanical stresses are higher.
Solution Approach 2:
The invention uses a composite structure consisting of a polyolefin microporous film as the base separator with an adhesive porous layer containing polyvinylidene fluoride type resin as the coating layer. This composite material approach combines the thermal stability and porosity of the polyolefin base with the adhesive properties of the VDF resin coating, achieving both structural integrity and strong bonding in large-area applications.
2Reliability
If a wet heat press process is used to thermally press the separator to the electrode, then good adhesion is achieved, but the electrolyte solution and electrolyte are decomposed producing gas that expands the battery
Solution Approach 1:
The invention optimizes the thermal press temperature parameter by conducting the process at 60-90°C, which is sufficient to activate the adhesion of the VDF resin while remaining below the decomposition temperature of the electrolyte solution and electrolyte. This controlled temperature parameter prevents gas generation while achieving reliable adhesion.
Solution Approach 2:
The adhesive porous layer containing polyvinylidene fluoride type resin acts as an intermediary between the electrode and the separator. This intermediate layer provides the bonding function through its adhesive properties, eliminating the need for high-temperature thermal pressing that would cause electrolyte decomposition. The VDF resin layer mediates the bonding process at lower temperatures.
3Reliability
If the adhesive porous layer contains polyvinylidene fluoride type resin, then adhesion to the electrode is improved, but the resin lacks sufficient adhesiveness to negative electrodes containing aqueous binders
Solution Approach 1:
The invention adjusts the acid value parameter of the polyvinylidene fluoride type resin to be within 3.0-20.0 mgKOH/g. This chemical parameter modification enhances the resin's polarity and surface energy, improving its wettability and adhesion to aqueous binders used in negative electrodes, thereby achieving universal adhesion performance across different electrode types.
4Manufacturing precision
If internal stress in the separator is high, then the separator may deform during manufacturing, but reducing internal stress may compromise the structural integrity of the separator
Solution Approach 1:
The invention uses a composite structure where the polyolefin microporous film provides the structural backbone with high mechanical strength, while the adhesive porous layer containing VDF resin acts as a stress-absorbing interface. This composite design allows the separator to maintain structural integrity while accommodating and dissipating internal stresses, preventing deformation during manufacturing processes.
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 ensures high adhesion to electrodes, improving battery performance and productivity by maintaining adhesion during thermal press, suppressing gas generation, and reducing production yield losses, thus enhancing the manufacturing efficiency and cycle life of non-aqueous secondary batteries.
Implementation Method 1
the battery using the separator having an adhesive porous layer containing a polyvinylidene fluoride type resin is generally manufactured by preparing a laminate of an electrode and a separator, housing this laminate in an exterior material to inject an electrolyte solution, and subjecting this laminate in a wet state with the electrolyte solution to thermal press treatment
Implementation Method 2
when performing the wet heat press at relatively high temperature, sometimes an electrolyte solution and an electrolyte are decomposed to produce gas in the battery
Data Source
AI summary
A separator for a non-aqueous secondary battery, containing a porous substrate, and an adhesive porous layer that is provided on one side or both sides of the porous substrate, in which the adhesive porous layer contains a polyvinylidene fluoride type resin including a vinylidene fluoride monomer unit and a hexafluoropropylene monomer unit, and the polyvinylidene fluoride type resin has an acid value of from 3.0 mgKOH/g to 20 mgKOH/g.