Battery Separator Coating for Adhesion and Heat Resistance
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Solution Overview
Problem
Secondary batteries face challenges with separators that have high heat resistance coatings but poor adhesion to electrode sheets, requiring high temperature and pressure for assembly, which is difficult to meet adhesion strength requirements.
Innovation Solution
A composite polymer coating is applied to the separator, comprising a high melting point core layer and a low softening temperature cladding layer, enhancing adhesion strength and heat resistance through a synergistic effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If inorganic particle coatings with high heat resistance are applied on the base membrane, then heat resistance is improved, but density becomes high which is not conducive to improving battery performance
Solution Approach 1:
The patent applies a composite polymer coating consisting of multiple polymer components (first polymer, second polymer, and third polymer) with different functional properties. This composite structure provides high heat resistance through the first polymer while maintaining low density and good adhesion through the combination of multiple polymer materials, avoiding the high density problem of inorganic particle coatings.
2Strength
If conventional coating designs are used to improve adhesion, then adhesion strength may be improved, but high temperature and pressure are required which are difficult to meet for power battery assembly
Solution Approach 1:
The patent changes the chemical composition parameters of the coating by using a specific composite polymer formulation containing polymers with different glass transition temperatures and functional groups. This allows the coating to achieve high adhesion strength through chemical affinity and physical interlocking at lower processing temperatures, eliminating the need for high temperature and pressure treatment.
3Strength
If a single polymer coating is used, then the structure is simple, but it cannot achieve both high adhesion strength and high heat resistance simultaneously
Solution Approach 1:
The patent employs a composite polymer coating system where the first polymer provides heat resistance, the second polymer enhances adhesion, and the third polymer adjusts mechanical properties. This multi-component composite structure enables the simultaneous achievement of high adhesion strength (1-5 N/m) and high heat resistance, which cannot be achieved with a single polymer material.
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 composite polymer coating achieves high adhesion strength and heat resistance, reducing the risk of polymer detachment during cycling and improving thermal stability, ionic conductivity, and liquid retention.
Implementation Method 1
the adhesion strength between the separator and the positive electrode sheet is 1-5 N/m; the adhesion strength between the separator and the negative electrode sheet is 1-5 N/m
Implementation Method 2
the core layer adopts a first polymer with a melting point of 180-400° C.... The combination of high melting point polymer and low softening temperature polymer exhibits a synergistic effect, enabling the constructed composite polymer coating material to achieve high adhesion strength and high heat resistance
Implementation Method 3
the cladding layer adopts a second polymer with a softening temperature of 40-70° C.... the thermal shrinkage rate of the separator in the MD and TD directions is less than 5% at 130° C. for 0.5 h
Data Source
AI summary
A secondary battery, including a positive electrode sheet, a negative electrode sheet, and a separator. The separator includes a base membrane and a coating arranged on at least one surface of the base membrane; the coating includes a composite polymer and a binder, and the composite polymer includes a first polymer for an inner core layer and a second polymer for a cladding layer arranged on the surface of the inner core layer; the peel strength between the separator and the positive electrode sheet is 1-5 N/m, and the thermal shrinkage rate of the separator in MD and TD directions is less than 5% at 130° C. for 0.5 h.