Terpolymer-Coated Battery Separator for Adhesion and Low Shrinkage
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Solution Overview
Problem
Lithium secondary battery separators face challenges with insufficient adhesiveness to electrodes, leading to potential internal shorts and stability issues due to thermal contraction, and existing solutions using PVDF-based copolymers face complexity in process control and uniformity.
Innovation Solution
A separator with a porous coating layer comprising inorganic particles and a terpolymer binder including vinylidene fluoride (VDF), hexafluoropropylene (HFP), and chlorotrifluoroethylene (CTFE) with specific weight ratios, providing improved adhesiveness, reduced interfacial resistance, and enhanced thermal stability through controlled phase separation and interstitial volumes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If PVDF-based copolymer binder is used to improve adhesiveness, then adhesiveness towards electrode is improved, but process complexity increases and uniformity decreases
Solution Approach 1:
The invention changes the chemical composition parameters of the binder polymer by using a specific copolymer with controlled comonomer content (5-30 mol%). This parameter optimization allows achieving adequate adhesiveness while maintaining processability and uniform phase separation, thus resolving the contradiction between strength and device complexity
Solution Approach 2:
The invention uses a composite binder system combining PVDF-based copolymer with inorganic particles (alumina, silica, titania). This composite structure provides both adhesive functionality and thermal stability, while the inorganic particles also serve as pore-forming agents, simplifying the overall process by multiple functions in one material system
2Reliability
If comonomer content is increased to improve solubility and wetting property, then electrolyte solution wetting property increases, but pore structure formation becomes difficult
Solution Approach 1:
The invention optimizes the comonomer content parameter within a specific range (5-30 mol%). This controlled parameter change ensures sufficient solubility and electrolyte wetting while maintaining the phase transition characteristics necessary for pore structure formation during non-solvent induced phase separation, thus resolving the contradiction between reliability and manufacturing precision
3Reliability
If two types of PVDF-based copolymers are mixed to combine advantages, then binder polymer performance is improved, but uniformity of pore structure and binder distribution decreases
Solution Approach 1:
The invention uses a single homogeneous PVDF-based copolymer with specifically controlled comonomer content rather than mixing different polymer types. This ensures uniform phase separation behavior and consistent binder distribution throughout the coating layer, resolving the contradiction between reliability and compositional stability
Solution Approach 2:
By precisely controlling the comonomer content parameter (5-30 mol%), the invention achieves optimal balance between solubility, phase separation characteristics, and adhesive properties in a single polymer system, eliminating the non-uniformity issues that arise from mixing different polymers
4Temperature
If inorganic coating layer is formed to improve thermal stability, then thermal contraction is reduced, but adhesiveness towards electrode decreases
Solution Approach 1:
The invention creates a composite coating layer where PVDF-based copolymer binder and inorganic particles are integrated. The binder provides adhesive functionality while the inorganic particles provide thermal stability. The organic-inorganic composite structure allows both functions to coexist, resolving the contradiction between temperature stability and strength
Solution Approach 2:
The invention creates local quality differentiation within the coating layer by forming an adhesive layer through binder migration to the separator surface. The region near the surface has higher binder concentration for adhesion, while the bulk contains inorganic particles for thermal stability, thus resolving the contradiction between strength and temperature resistance
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 solution achieves uniform micropores for increased adhesiveness, low interfacial resistance, and improved air permeability, resulting in enhanced performance and stability of lithium secondary batteries.
Implementation Method 1
there is a method that forms an adhesive layer by inducing the binder polymer migration to the separator surface through wet phase separation
Implementation Method 2
the separator commonly used in the lithium secondary battery show severe thermal contraction behaviors in a high temperature
Data Source
Figure 1a
Figure 1b
Figure 1c
AI summary
The present disclosure relates to a separator for a lithium secondary battery comprising a porous substrate, and a porous coating layer disposed on at least one surface of the porous substrate and comprising inorganic particles and binder polymer, wherein the binder polymer is terpolymer including a repeat unit derived from vinylidenefluoride (VDF), a repeat unit derived from hexafluoropropylene (HFP) and a repeat unit derived from chlorotrifluoroethylene (CTFE), the terpolymer includes 65 to 90 weight% of the repeat unit derived from VDF, 1 to 28 weight% of the repeat unit derived from HFP and 5 to 28 weight% of the repeat unit derived from CTFE, and the separator for a lithium secondary battery has adhesiveness towards electrode ranging from 30 gf/25mm to 150 gf/25mm and machine direction (MD) thermal shrinkage of 1 to 18% and transverse direction (TD) thermal shrinkage of 1 to 17%, and a lithium secondary battery comprising the same, wherein the separator for a lithium secondary battery has uniform micropores on the surface, and thus has the increased adhesive surface area with electrode and consequential improved adhesiveness towards electrode.