Asymmetric Flame-Retardant Separator for Stable Li-Ion Batteries
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Solution Overview
Problem
Existing lithium secondary battery separators face challenges in preventing lithium ion precipitation in the negative electrode, maintaining flame retardancy, and ensuring electrochemical stability, as conventional coatings do not adequately address these issues.
Innovation Solution
A separator with a polyolefin-based substrate featuring a first coating layer of hydroxide inorganic flame retardant on the positive electrode side and a second coating layer of binder material and inorganic particles on the negative electrode side, with specific weight ratios, enhances flame retardancy and maintains electrochemical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hydroxide-based inorganic flame retardant is coated on the separator surface, then flame retardancy is improved, but water release reacts with Li ions causing explosion risk
Solution Approach 1:
The patent applies different coating materials to different surfaces of the separator. The positive electrode-facing surface receives a hydroxide-based inorganic flame retardant coating for flame retardancy, while the negative electrode-facing surface receives a coating layer containing inorganic particles and binder material to prevent water-Li ion reactions. This local differentiation resolves the contradiction by providing flame retardancy where needed while preventing harmful reactions at the critical interface with the negative electrode.
Solution Approach 2:
The patent introduces an intermediary coating layer on the negative electrode-facing surface that acts as a barrier between the flame retardant and Li ions. This intermediary layer prevents direct contact between water released from the flame retardant and Li ions, thereby eliminating the explosion risk while preserving the flame retardant properties on the other surface.
2Ease of manufacture
If the separator uses a symmetric coating structure, then manufacturing simplicity is improved, but lithium ion precipitation prevention and flame retardancy are insufficient
Solution Approach 1:
The patent employs an asymmetric coating structure where the two surfaces of the separator have different coating compositions. The positive electrode-facing surface has a flame retardant coating while the negative electrode-facing surface has a protective coating with inorganic particles and binder material. This asymmetry optimizes both flame retardancy and lithium ion precipitation prevention, resolving the contradiction between manufacturing simplicity and performance reliability.
3Reliability
If a conventional inorganic coating is applied to the separator, then flame retardancy is improved, but electrochemical stability and thermal resistance are insufficient
Solution Approach 1:
The patent uses composite coating materials on both surfaces of the separator. The positive electrode-facing surface uses a composite of hydroxide-based inorganic flame retardant, while the negative electrode-facing surface uses a composite of inorganic particles and binder material. These composite structures provide enhanced electrochemical stability and thermal resistance while maintaining flame retardancy, resolving the contradiction between flame retardancy and compositional 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 asymmetric coating structure prevents lithium ion precipitation, improves flame retardancy, and maintains similar electrochemical properties compared to conventional separators, while ensuring thermal stability and resistance to nail penetration.
Implementation Method 1
The hydroxide-based inorganic flame retardant is a flame retardant that absorbs heat at a certain temperature
Implementation Method 2
The hydroxide-based inorganic flame retardant releases water when it absorbs heat
Implementation Method 3
It is necessary for the separator to electrically isolate the positive electrode and the negative electrode from each other
Implementation Method 4
exhibit high ion permeability, high mechanical strength and stability at high temperature such that an electrolytic solution can pass smoothly through the separator
Data Source
Figure 1a~1d
Figure 2
Figure 3
AI summary
Disclosed herein is a flame retardant separator for secondary batteries having an asymmetric structure, and more particularly, a flame retardant separator for secondary batteries having an asymmetric structure in which a hydroxide-based inorganic flame retardant is coated on only a surface facing a positive electrode. The present invention provides a separator, in which is capable of preventing the risk of lithium ions predominantly precipitated from a negative electrode in a lithium secondary battery, enhancing the flame retardant effect, and maintaining electrochemical properties in contrast with a conventional separator coated with inorganic matters, and a lithium secondary battery including the same.