Alkali Metal Battery Separator with Reactive TFE Layer
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Solution Overview
Problem
Existing secondary batteries using alkali metals, such as lithium, face challenges with dendrite growth, which can lead to short circuits and reduced cycle characteristics, as current separators either cannot completely prevent dendrite growth or require hydrophilizing treatments that compromise battery performance.
Innovation Solution
A secondary battery design featuring a separator with a tetrafluoroethylene (TFE) polymer or copolymer layer that reacts with alkali metal dendrites, combined with a hydrophilizing treatment at a specific rate to maintain porosity and prevent dendrite growth, and a layer that does not react with dendrites between the negative electrode and separator to ensure high ionic conductivity and prevent short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separator with smaller pore size is used to inhibit dendrite growth, then dendrite penetration is prevented, but ionic conductivity is reduced
Solution Approach 1:
The separator employs a dual-layer structure where the first layer (facing negative electrode) has smaller pore size (0.01-0.1 μm) to prevent dendrite penetration, while the second layer has larger pore size (0.1-1.0 μm) to maintain high ionic conductivity. Each layer performs its specific function locally without compromising the other.
Solution Approach 2:
The separator is divided into two distinct layers with different pore size characteristics. The first layer segment handles dendrite blocking, while the second layer segment handles ion transport, allowing both contradictory requirements to be satisfied in different segments of the same component.
2Productivity
If hydrophilizing treatment is applied to improve ion transport, then ionic conductivity increases, but dendrite growth inhibition is compromised
Solution Approach 1:
Hydrophilizing treatment is applied selectively only to the second layer of the separator, not the first layer. This localized treatment enhances ionic conductivity in the region where it benefits ion transport, while the first layer remains untreated to maintain its dendrite-blocking functionality.
Solution Approach 2:
The hydrophilizing treatment is segmented to affect only specific regions (the second layer) of the separator, allowing different chemical properties in different segments to address different functional requirements.
3Reliability
If reactive polymer layer is used to inhibit dendrite growth, then dendrite penetration is blocked, but defluoridation occurs reducing battery performance
Solution Approach 1:
The reactive polymer layer is segmented into a thin first layer (1-10 μm) positioned between the negative electrode and the bulk separator. This thin reactive layer provides dendrite blocking functionality while minimizing the amount of reactive material that could undergo defluoridation, thus balancing protection with performance.
Solution Approach 2:
The reactive polymer functionality is localized to the first layer that directly interfaces with the negative electrode, where dendrite formation occurs. The second layer lacks this reactivity, preventing defluoridation in the bulk separator material while maintaining dendrite blocking at the critical interface.
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 inhibits dendrite growth, significantly increasing the number of charge and discharge cycles before a short circuit occurs, while maintaining high ionic conductivity and preventing defluoridation of the separator, thus enhancing battery performance and safety.
Implementation Method 1
a separator comprising a layer of tetrafluoroethylene (TFE) polymer or copolymer that reacts with a dendrite of the alkali metal
Implementation Method 2
the separator being hydrophilized by a hydrophilizing treatment material at a rate of not less than 10% and not more than 80% of the separator
Implementation Method 3
a layer that does not react with a dendrite of the alkali metal located between the separator and the negative electrode
Data Source
Figure 1~2.
Figure 3
AI summary
Problem to be Solved An object of the present invention is to provide a secondary battery that is able to inhibit the growth of a dendrite that can generate from an electrode comprising alkali metal and a separator used therein. Solution A secondary battery, comprising: a positive electrode; a negative electrode comprising alkali metal; a separator comprising a layer of tetrafluoroethylene (TFE) polymer or copolymer that reacts with a dendrite of the alkali metal, the separator being hydrophilized at a rate of not less than 10% and not more than 80%; and a layer that does not react with a dendrite of the alkali metal located between the separator and the negative electrode, wherein the standard deviation of opening areas of pores on the negative electrode side surface of the layer that does not react with a dendrite of the alkali metal is 0.1 µm2 or less, and a separator used therein.