Composite Battery Separator for Dendrite Puncture Resistance
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Solution Overview
Problem
Lithium battery separators are prone to breaking under external forces in a vertical direction due to lithium dendrite accumulation, leading to physical damage and short circuits between the anode and cathode.
Innovation Solution
A separator design comprising a bonding layer with a base film and a gel film on either side, enhancing ductility and deformation resistance, and a base film with good shape-retaining capability to prevent breakage under external forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a polyolefin separator is used, then the separator has low physical deformation in a direction perpendicular to the film surface, but it is prone to breaking under external force in a vertical direction
Solution Approach 1:
The separator is constructed as a composite structure comprising a base film layer and a gel film layer. The base film provides shape stability and low perpendicular deformation, while the gel film enhances vertical direction breaking resistance and ductility. This composite material approach resolves the contradiction by combining materials with complementary properties.
Solution Approach 2:
The separator is divided into functional segments: a base film segment for maintaining shape and providing structural support, and a gel film segment for enhancing puncture resistance and ductility. Each segment performs its specific function, and their combination resolves the contradiction between shape stability and breaking resistance.
2Quantity of substance
If the separator is made thinner to improve energy density, then the energy density increases, but the piercing resistance decreases
Solution Approach 1:
The gel film layer, even at thin thicknesses (1-12 μm), provides disproportionate puncture resistance enhancement due to its viscoelastic properties and ability to deform without breaking. This allows the overall separator to maintain high energy density while achieving superior piercing resistance that would be impossible with a single thin polyolefin layer.
Solution Approach 2:
The introduction of the gel film changes the mechanical parameters of the separator, particularly its stress-strain behavior. The gel film exhibits high elongation at break and can undergo significant deformation before failure, fundamentally changing the separator's response to puncture forces and enabling thin designs with high piercing resistance.
3Reliability
If lithium dendrites accumulate during battery use, then the separator is physically damaged in the vertical direction, but this causes short circuit between anode and cathode
Solution Approach 1:
The gel film layer acts as a cushioning layer that absorbs and distributes the mechanical stress from lithium dendrite accumulation before it can cause through-puncture damage. The gel's viscoelastic properties allow it to deform and accommodate dendrite growth, preventing the sharp stress concentrations that would otherwise lead to immediate separator failure and short circuits.
Solution Approach 2:
The gel film's ability to deform and stretch under stress converts the harmful puncture action of lithium dendrites into a beneficial deformation mechanism. Instead of the dendrites creating immediate through-holes, the gel film stretches and accommodates them, maintaining separator integrity and preventing short circuits even in the presence of dendrite accumulation.
Data Source
AI summary
Disclosed in the present application are a separator, a preparation method for a separator, and an electrochemical device. The separator comprises a bonding layer, and a base film and a gel film which are respectively arranged on two sides of the bonding layer. In the present application, the gel film has relatively good ductility and deformation resistance, is not prone to be being pierced or still completely covers a pierced position after being pierced, such that the separator still plays a role in separating positive and negative electrodes; and the base film has relatively good shape-retaining capability and self-supporting performance. The base film and the gel film are respectively provided on the two sides of the bonding layer, such that the gel film and the base film are bonded into a whole under the bonding action of the bonding layer, and thus when there is an external force acting in the vertical direction of the separator, the separator deforms but is not prone to breaking, thereby delaying the breakage of the separator and improving the stability and safety of a battery.