Polymer Separator Blocking Layer to Prevent PVdF Pore Penetration

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Solution Overview

Problem

The existing polyvinylidene fluoride (PVdF) coating technology for lithium-ion battery separators using acetone as a solvent faces safety concerns due to its low boiling point, leading to permeability issues and reduced battery performance, as the PVdF polymer solution penetrates the separator, blocking pores and reducing ionic conductivity.

Innovation Solution

A polymer separator is developed with a hydrophilic blocking layer between the porous substrate and the porous polar polymer bonding layer, which suppresses the penetration of the PVdF polymer solution, enhancing permeability and porosity, and a method involving coating a hydrophilic blocking slurry and a polar polymer binder solution onto the substrate to form the separator.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If acetone is used as solvent in PVdF coating technology, then the coating process can be completed, but operational safety deteriorates due to low boiling point

Engineering Contradiction:

Improvecoating processVSAvoidoperational safety

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent changes the solvent parameter from acetone (low boiling point) to high-boiling solvents such as N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), or dimethyl carbonate (DMC). This parameter change maintains the coating process effectiveness while significantly improving operational safety by eliminating the fire and explosion hazards associated with low-boiling-point solvents.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If high-boiling solvents are used instead of acetone, then operational safety is improved, but battery performance deteriorates due to polymer solution penetration

Engineering Contradiction:

Improveoperational safetyVSAvoidbattery performance

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent introduces a hydrophilic blocking layer as an intermediary between the porous substrate and the PVdF coating layer. This blocking layer acts as a mediator that prevents the high-boiling solvent and PVdF polymer solution from penetrating into the porous substrate, thereby maintaining battery performance while allowing the use of safe high-boiling solvents.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent segments the coating structure into three distinct layers: (1) porous substrate, (2) hydrophilic blocking layer, and (3) PVdF coating layer. This segmentation allows each layer to perform its specific function - the blocking layer prevents penetration while the PVdF layer provides safety functions, resolving the contradiction between safety and performance.

Inventive Principle:

Principle #1Segmentation

3Ease of manufacture

If PVdF polymer solution penetrates the separator, then coating is achieved, but ionic conductivity deteriorates due to pore blocking

Engineering Contradiction:

Improvecoating achievementVSAvoidionic conductivity

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The hydrophilic blocking layer serves as an intermediary that allows the PVdF coating to be achieved on its surface while preventing the polymer solution from penetrating into and blocking the pores of the porous substrate. This maintains ionic conductivity while enabling the coating process.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent applies local quality by making different layers have different properties: the hydrophilic blocking layer has pore-blocking properties to prevent penetration, while the PVdF coating layer has safety properties. This localized differentiation allows coating achievement without compromising ionic conductivity.

Inventive Principle:

Principle #3Local quality

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 significantly improves the permeability and ionic conductivity of the polymer separator, leading to better performance and safety of lithium-ion batteries by preventing polymer solution penetration and maintaining high operational safety.

Implementation Method 1

the polyvinylidene fluoride polymer solution is extremely permeable, and the polymer solution easily penetrates the separator to reach the other surface opposite to the coating surface, carrying the polyvinylidene fluoride polymer into the pores of the separator

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 2

the fluidity and permeability of the polyvinylidene fluoride polymer is much lower than those of the organic solvent, the polyvinylidene fluoride polymer carried into the separator by the organic solvent usually remains in the pores of the separator

Methodology Applied

Scientific EffectEvaporation: Evaporation

Data Source

PatentUS11824225B2Separator including substrate, hydrophilic blocking layer, and polar polymer bonding with nodal structure, and method of preparing the same

Publication Date: 2023.11.21 BYD CO LTD

AI summary

The present disclosure provides a polymer separator and preparation method thereof, and a lithium-ion battery including the polymer separator and preparation method thereof. The polymer separator includes a porous substrate, a hydrophilic blocking layer, and a porous polar polymer bonding layer. The hydrophilic blocking layer is disposed between the porous substrate and the porous polar polymer bonding layer. Pore walls in the porous polar polymer bonding layer are provided with node structures.