Battery Separator Adhesive Coating for Thin-Layer Electrode Bonding
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Solution Overview
Problem
Current lithium secondary battery separators face challenges in achieving sufficient electrode adhesion and phase separation, especially when the coating layer thickness is reduced to 3µm or less, leading to inadequate bonding and increased interfacial resistance due to humidity sensitivity and phase separation issues.
Innovation Solution
A coating composition comprising a solvent, inorganic particles, a dispersant, and a binder with specific molecular weights and HFP-derived unit ratios, applied under controlled humidity conditions to ensure strong bonding and phase separation, even at low humidity, enhancing electrode adhesion and air permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the coating layer thickness is reduced to 3µm or less, then the battery weight and size are reduced, but the electrode adhesion and bonding strength become insufficient
Solution Approach 1:
The patent changes the chemical composition parameters of the binder by incorporating specific functional groups (carboxyl, hydroxyl, amine groups) and using copolymers with controlled HFP content (5-30 wt%). This allows the binder to maintain strong adhesion properties even at reduced coating thickness of 3µm or less, resolving the contradiction between weight reduction and adhesion strength
Solution Approach 2:
The patent uses composite binder materials comprising multiple polymer components including PVDF-HFP copolymer and other polymers with complementary properties. This composite approach enables the thin coating layer to achieve sufficient bonding strength by combining the advantages of different material properties, maintaining electrode adhesion while reducing overall separator thickness
2Ease of manufacture
If conventional binders are used in thin coating layers, then manufacturing is simpler, but phase separation occurs and interfacial resistance increases during cycling
Solution Approach 1:
The patent modifies binder parameters by selecting polymers with specific functional groups and controlling HFP content within 5-30 wt%. This parameter optimization prevents phase separation during battery cycling while maintaining ease of coating application, as the modified binders retain good processability and coating characteristics
Solution Approach 2:
The patent employs binders with controlled molecular weights and functional group contents that provide sufficient performance for the application without requiring complex manufacturing processes. The optimized composition allows standard coating equipment and procedures to be used, maintaining manufacturing simplicity while achieving reliable long-term performance
3Strength
If the HFP content in the binder is increased to improve adhesion, then bonding strength increases, but the coating becomes less stable and more sensitive to humidity
Solution Approach 1:
The patent optimizes the HFP content parameter within a specific range of 5-30 wt% rather than using high HFP content. This controlled parameter adjustment achieves sufficient bonding strength while preventing excessive humidity sensitivity and coating instability that would result from higher HFP concentrations
Solution Approach 2:
The patent creates a composite binder system combining PVDF-HFP copolymer with other polymers containing complementary functional groups. This composite formulation balances the adhesion enhancement from HFP with the stabilizing effects of other polymer components, achieving both strong bonding and coating stability
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 effectively achieves strong bonding between the separator and electrode, suppresses interfacial resistance, and improves air permeability, ensuring reliable battery performance and safety, even at reduced coating thicknesses and low humidity levels.
Implementation Method 1
the binder present in the porous coating layer and the binder layer contains two or more kinds of polyvinylidene fluoride (PVDF) homopolymer or polyvinylidene fluoride-co-hexafluoropropylene (P(VDF-HFP))-based copolymer, the difference in the amount of the hexafluoropropylene (HFP) being 3 wt% or more
Data Source
Figure 1(a)
Figure 1(b)
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AI summary
Disclosed is a coating composition for a porous substrate, the coating composition including a solvent, inorganic particles, a dispersant, and a binder, wherein the binder includes a binder B("B") and a binder A("A"), both the B and the A include a VDF unit and a HFP unit, the HFP unit constitutes 8 to 50 wt% of the B and constitutes 5 wt% or more of the A under the condition that a proportion of the HFP unit in the A is 80% or less of a proportion of the HFP unit in the B, the B has a total Mn of 200,000 to 2 million, and the A has a total Mn corresponding to 70% or less of that of the B, and a weight ratio of the A : the B in the coating composition is 0.1 to 10 : 1.