Secondary Battery Separator Adhesion via Gel-Sol Transition
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in manufacturing at high temperatures and pressures, which lead to reduced air permeability and swelling of the separator, affecting the battery's performance and rate characteristics.
Innovation Solution
A secondary battery design featuring a separator with an adhesive layer containing a PVdF-HFP copolymer binder, which has a gel-sol transition temperature between 70° C. to 90° C. and a sol-gel transition temperature between 28° C. to 51° C., allowing for adherence to electrode plates at low temperatures and pressures, thereby suppressing swelling and maintaining air permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high temperature and pressure are used for manufacturing, then adhesion strength is improved, but air permeability is reduced and swelling increases
Solution Approach 1:
The patent changes the temperature and pressure parameters during manufacturing by utilizing the gel-sol transition temperature of the binder. By controlling the binder to transition from gel to sol state at specific temperature ranges, adhesion is achieved at lower temperatures and pressures compared to conventional methods, thereby preventing separator swelling and maintaining air permeability.
Solution Approach 2:
The patent uses a composite binder system comprising PVdF-HFP copolymer with specific HFP content (3-7 wt%). This composite material exhibits gel-sol transition behavior that enables low-temperature adhesion while maintaining mechanical strength and preventing separator degradation, thus resolving the contradiction between adhesion strength and air permeability.
2Strength
If high temperature manufacturing is used, then adhesion is improved, but active material deterioration occurs
Solution Approach 1:
The patent utilizes the gel-sol transition temperature of the binder to enable adhesion at lower temperatures (below the gel-sol transition point). This parameter change prevents thermal degradation of active materials while achieving sufficient adhesion strength through the phase transition mechanism of the binder.
Solution Approach 2:
The patent replaces thermal-mechanical adhesion (high temperature and pressure) with a phase-transition-based adhesion mechanism. The gel-sol transition of the binder provides adhesion through molecular reorganization rather than thermal softening, thereby protecting temperature-sensitive active materials from deterioration.
3Strength
If conventional binding methods are used, then adhesion strength is achieved, but manufacturing temperature and pressure must be high
Solution Approach 1:
The patent exploits the gel-sol phase transition of the PVdF-HFP copolymer binder to achieve adhesion at low temperature and pressure. The binder transitions from gel state (providing structural integrity) to sol state (enabling flow and adhesion) at the gel-sol transition temperature, eliminating the need for high temperature and pressure conventional binding methods.
Solution Approach 2:
The patent changes the physical state parameters of the binder by controlling the HFP content and molecular weight to achieve gel-sol transition at specific temperature ranges. This parameter optimization allows adhesion to occur at significantly lower temperatures and pressures compared to conventional thermal bonding methods.
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 battery is manufactured at lower temperatures and pressures, preventing deterioration of active materials, reducing internal resistance, and maintaining high air permeability, thus improving charging and discharging rates.
Implementation Method 1
a gel-sol transition temperature of the binder is in a range of about 70° C. to about 90° C.
Implementation Method 2
the binder may have a sol-gel transition temperature in a range of about 74° C. to about 88° C.
Data Source
AI summary
Provided is a secondary battery, which includes a separator having excellent air permeability such that the separator is adhered to a positive electrode plate and/or a negative electrode plate at a low temperature under a low pressure and swelling in an electrolyte solution is relatively suppressed. The secondary battery includes an electrode assembly including a positive electrode plate, a negative electrode plate and a separator interposed between the positive electrode plate and the negative electrode plate, wherein the separator further includes an adhesive layer formed on its surface, the adhesive layer includes a binder, and a gel-sol transition temperature of the binder is in a range of 70° C. to 90° C.