Porous Battery Separator Coating for Low Resistance and Thermal Stability
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Solution Overview
Problem
Current lithium secondary battery separators exhibit high thermal shrinkage and resistance issues due to polyolefin-based porous polymer substrates, posing safety risks and limiting battery performance.
Innovation Solution
A separator with a porous coating layer comprising a binder polymer blend of P(VDF-TrFE-CTFE) and PVDF-CTFE, with a β-phase amount of 0.90 or above, and a weight ratio of 35:65 to 87:13, along with optional inorganic particles, to reduce thermal shrinkage and enhance Lami strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a porous coating layer is formed on a porous polymer substrate to reduce thermal shrinkage, then thermal stability is improved, but resistance increases
Solution Approach 1:
The patent employs a porous coating layer with controlled porosity (30-80%) formed on the porous polymer substrate. The porous structure allows lithium ion transport while the coating material (polymer blend with inorganic particles) provides thermal stability, thus reducing thermal shrinkage without significantly increasing resistance to ion movement
Solution Approach 2:
The coating layer uses a composite material system combining organic binder polymers (such as polyvinylidene fluoride and carboxymethyl cellulose) with inorganic particles (such as alumina, silica, or boehmite). This composite structure provides both thermal stability from the inorganic particles and ion conductivity from the polymer matrix, resolving the contradiction between thermal stability and resistance
2Reliability
If the porous coating layer thickness is increased to improve safety, then thermal runaway risk is reduced, but lithium ion movement speed decreases
Solution Approach 1:
The porous coating layer with optimized thickness (1-15 μm) and high porosity (30-80%) creates multiple ion transport pathways through the coating. The porous network allows lithium ions to move quickly through tortuous paths, maintaining high ion movement speed even at greater thicknesses that enhance safety by preventing thermal runaway
Solution Approach 2:
The patent applies different materials and structures at different locations: the coating layer has varying polymer and inorganic particle distributions to create optimal local ion transport channels while maintaining overall thermal stability. The inorganic particles are distributed to provide localized thermal protection without blocking ion paths
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 low resistance and improved Lami strength, enhancing the safety and performance of lithium secondary batteries by facilitating quick lithium ion movement and maintaining adhesive properties, thereby reducing the risk of thermal runaway and improving energy density.
Implementation Method 1
facilitating quick lithium ion movement
Implementation Method 2
reduce the resistance and improve the properties... reducing the risk of thermal runaway
Data Source
AI summary
A separator including a porous polymer substrate, and a porous coating layer, and an electrochemical device comprising the same. The porous coating layer includes P(VDF-TrFE-CTFE) and PVDF-CTFE as a binder polymer. The separator has a lower resistance by changing the characteristics of the binder polymer.