Battery Separator Coating With Core-Shell Binder for Thermal Stability
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Solution Overview
Problem
Lithium secondary batteries face safety concerns due to their high ignition hazard and thermal instability, particularly as they transition from small-scale to medium to large-scale applications such as electric cars and energy storage systems.
Innovation Solution
A coating composition for the separator of a secondary battery is developed, comprising a core-shell structured binder system where an emulsion-type binder forms a core and a solution-type binder forms a shell, chemically bonded and radially crosslinked, with ceramic particles dispersed in the aqueous binder solution to enhance thermal and mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a nonaqueous electrolyte is used in lithium secondary batteries, then high energy density and performance are achieved, but ignition hazard and thermal instability increase
Solution Approach 1:
A coating layer comprising ceramic particles (alumina, boehmite, silica, titania, zirconia) dispersed in a binder solution is applied to the separator surface as an intermediary barrier. This coating layer physically separates the nonaqueous electrolyte from the separator, preventing direct contact and reducing ignition hazard while maintaining ion conductivity for high energy density operation
2Quantity of substance
If the battery size is increased from small-scale to medium to large-scale, then energy storage capacity is improved, but safety problems and thermal instability become more significant
Solution Approach 1:
The separator system is segmented into two functional layers: the base separator for ion transport and the coated separator surface for safety enhancement. This segmentation allows the bulk separator to maintain porosity for ion conductivity while the surface coating provides thermal stability and safety, enabling safe operation in large-scale batteries with higher energy storage capacity
3Temperature
If ceramic particles are added to the binder solution, then thermal stability is improved, but particle agglomeration occurs
Solution Approach 1:
The binder solution parameters are optimized by selecting specific binder polymers (carboxymethyl cellulose, styrene-butadiene rubber, or nitrile rubber) with appropriate molecular weights and functional groups. These parameter changes enhance the wetting and dispersing capabilities of the binder, preventing ceramic particle agglomeration while maintaining thermal stability in the coating layer
4Strength
If a coating layer is applied to the separator, then thermal and mechanical stability are improved, but ion conductivity may be reduced
Solution Approach 1:
The coating layer is designed with a porous structure where ceramic particles are dispersed in the binder matrix, creating interconnected voids that allow lithium ion transport. The porosity is controlled by optimizing the ceramic-to-binder ratio and particle size distribution, ensuring mechanical strength enhancement while maintaining sufficient ion conductivity for battery operation
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 thermal stability and mechanical strength of the separator, ensuring safer operation and longer lifespan of lithium secondary batteries by maintaining ion conductivity and preventing agglomeration of ceramic particles, thus addressing the safety and performance issues.
Implementation Method 1
the emulsion-type binder and the solution-type binder are chemically bonded
Implementation Method 2
a polymer chain radially crosslinked from the coating layer
Implementation Method 3
dispersing a first monomer and a surfactant in a solvent to form micelles
Implementation Method 4
adding a first initiator to the solvent and performing first polymerization reaction to form a precursor solution
Implementation Method 5
dispersing ceramic particles in the aqueous binder solution to form a slurry
Data Source
AI summary
Provided is a method of preparing a coating composition for a separator of a secondary battery, and particularly a method including dispersing a first monomer and a surfactant in a solvent to form micelles, adding a first initiator to the solvent and performing first polymerization reaction to form a precursor solution including an emulsion-type binder, and adding a second monomer and a second initiator to the precursor solution and performing second polymerization reaction to form an aqueous binder solution including a solution-type binder, wherein the emulsion-type binder has a core shape, the solution-type binder has a shell shape wrapping the emulsion-type binder, and the emulsion-type binder and the solution-type binder are chemically bonded.