Separator Porous Coating Layer Thermal Stability
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Solution Overview
Problem
Lithium secondary batteries face issues with thermal stability and capacity due to the disintegration of filler particles in the porous coating layer during the assembly process, leading to potential short circuits and reduced battery performance, especially at low temperatures.
Innovation Solution
A separator with a porous coating layer made of a mixture of electrochemically oxidized and reduced electrode active material particles and a binder polymer, which includes a copolymer with specific monomer units, is used to enhance thermal stability and prevent filler particle disintegration, thereby improving battery capacity and safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a porous coating layer is formed on the porous substrate to prevent thermal shrinkage, then thermal stability is improved, but filler particles disintegrate during assembly process
Solution Approach 1:
The patent uses a composite porous coating layer made of inorganic filler particles (such as Al2O3, SiO2, TiO2, ZrO2, BaTiO3, or PZT) dispersed in a polymer matrix (such as polyvinylidene fluoride, polyacrylonitrile, carboxymethyl cellulose, or starch). This composite structure combines the thermal stability of inorganic fillers with the binding capability of polymers, preventing filler disintegration while maintaining thermal resistance. The synergistic effect of the composite material resolves the contradiction between improving thermal stability and maintaining filler particle integrity during assembly.
Solution Approach 2:
The patent employs a porous coating layer with controlled porosity formed on the porous substrate. The porous structure allows the coating layer to maintain flexibility and adhesion to the substrate while preventing thermal shrinkage. The porous architecture reduces stress concentration during assembly, preventing filler particle disintegration. This approach maintains both thermal stability and filler particle integrity by designing the coating layer with appropriate pore structure that accommodates thermal and mechanical stresses.
2Stability of the object's composition
If filler particles are used as spacers in the porous coating layer to maintain physical shape, then thermal shrinkage is restrained, but manufacturing complexity increases
Solution Approach 1:
The patent optimizes key parameters of the porous coating layer including filler particle size (0.1-10 μm), filler content (1-50 wt% of total coating layer), and coating layer thickness (1-20 μm). By controlling these parameters, the separator achieves thermal shrinkage resistance with a relatively simple structure. The optimized parameter range ensures that filler particles effectively restrain thermal shrinkage while maintaining a straightforward coating process and simple separator architecture, thus resolving the contradiction between thermal shrinkage resistance and manufacturing complexity.
3Object-affected harmful factors
If a porous coating layer is formed to improve safety, then thermal runaway is prevented, but battery capacity decreases
Solution Approach 1:
The patent applies the porous coating layer selectively on specific surfaces of the porous substrate (one surface or both surfaces) with controlled thickness (1-20 μm). This local application provides thermal protection where most needed (at the electrode interface) while minimizing the volume occupied by the coating layer. The localized coating approach prevents thermal runaway at critical interfaces without significantly reducing the overall active material content in the separator, thus resolving the contradiction between safety improvement and battery capacity maintenance.
Solution Approach 2:
The patent uses inorganic filler particles that can be easily synthesized and replicated in the coating layer. These filler particles (Al2O3, SiO2, TiO2, ZrO2, BaTiO3, PZT) serve as thermal stability components that can be incorporated through standard coating processes. The use of readily available, easily replicable filler materials allows the separator to achieve thermal runaway protection without complex manufacturing, and the coating thickness is optimized to minimize capacity loss while maintaining safety.
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 increases battery capacity and prevents short circuits by maintaining the integrity of the porous coating layer during assembly, ensuring improved thermal stability and safety of the electrochemical device.
Implementation Method 1
a binder polymer, which includes a copolymer having (a) a first monomer unit with a contact angle to water of 5 to 30° and (b) a second monomer unit with a contact angle to water of 70 to 120°
Implementation Method 2
the filler particles 3 in the porous coating layer formed on the porous substrate 1 act as a kind of spacer that keeps a physical shape of the porous coating layer, so the filler particles 3 restrain thermal shrinkage of the porous substrate when the electrochemical device is overheated
Data Source
Figure 1~2
AI summary
A separator includes a porous substrate having a plurality of pores, and a porous coating layer formed on at least one surface of the porous substrate and made of a mixture of a plurality of filler particles and a binder polymer. The filler particles include electrode active material particles that are electrochemically oxidized and reduced. The binder polymer includes a copolymer having (a) a first monomer unit with a contact angle to water of 0 to 49° and (b) a second monomer unit with a contact angle to water of 50 to 130°. This separator is useful for an electrochemical device, particularly a lithium secondary battery. This separator ensures improved thermal stability and increased capacity of the electrochemical device. Also, inorganic particles in the porous coating layer formed on the porous substrate are not disintercalated due to excellent peeling resistance of the porous coating layer while the electrochemical is assembled.