Laminate Separator Surface Roughness Control
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Solution Overview
Problem
Secondary battery separators made from resin films are thick, limiting battery capacity and durability, and integrating nanofiber films with electrodes leads to peeling issues and self-discharge.
Innovation Solution
A laminate structure with a first film containing inorganic material and a second film with organic fibers, where the absolute difference in surface roughness between the films is 0.6 μm or less, enhancing adherence and suppressing self-discharge by allowing deformation with charging and discharging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resin film separator is used to prevent contact between electrodes, then battery safety is improved, but the film thickness cannot be reduced much due to mechanical strength requirements, which limits battery capacity
Solution Approach 1:
The patent uses a composite separator structure consisting of a polyolefin resin layer and a heat-resistant non-woven fabric layer. The resin layer provides safety through shutdown function, while the heat-resistant fabric layer provides mechanical strength, allowing thinner overall thickness without compromising safety or strength requirements.
Solution Approach 2:
The separator is divided into multiple functional layers: a polyolefin resin layer for safety shutdown function and a heat-resistant non-woven fabric layer for mechanical strength. This segmentation allows each layer to optimize its specific function while reducing the total thickness requirement.
2Reliability
If a resin film separator is used to prevent electrode contact, then battery safety is improved, but the separator deteriorates in repeated charging and discharging, resulting in decreased cycle characteristics
Solution Approach 1:
The composite separator combines a polyolefin resin layer with a heat-resistant non-woven fabric layer. The heat-resistant fabric provides superior durability and resistance to degradation during repeated charging and discharging cycles, while the resin layer maintains the safety shutdown function.
3Productivity
If a nanofiber film is integrated with an electrode to reduce separator thickness, then battery capacity is improved, but the separator peels off from the electrode causing self-discharge
Solution Approach 1:
The heat-resistant non-woven fabric layer is integrated with the electrode, providing both mechanical reinforcement and strong adhesion. This prevents the separator from peeling off during battery operation, eliminating self-discharge issues while maintaining reduced thickness for high capacity.
Solution Approach 2:
The separator structure is designed with different properties in different regions: the polyolefin resin layer provides safety function, while the heat-resistant non-woven fabric layer integrated with the electrode provides mechanical strength and adhesion where needed, preventing peeling.
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 laminate structure improves energy density and reduces self-discharge in secondary batteries by maintaining adherence and preventing peeling, while allowing for thinner films without compromising mechanical strength.
Implementation Method 1
a back surface of the first film is in contact with a front surface of the first active material-containing layer, and one of a front surface and a back surface of the second film is in contact with a front surface of the first film. An absolute value of a difference between surface roughness Ra1 of the front surface of the first active material-containing layer and surface roughness Ra2 of the back surface of the first film is 0.6 μm or less (including 0).
Data Source
AI summary
According to one embodiment, a laminate includes a first active material-containing layer, a first film and a second film. The first film includes an inorganic material, and a back surface thereof is in contact with a front surface of the first active material-containing layer. The second film includes organic fibers, and one of front and back surfaces is in contact with a front surface of the first film. An absolute value of a difference between surface roughness Ra1 of the front surface of the first active material-containing layer and surface roughness Ra2 of the back surface of the first film is 0.6 μm or less (including 0).