Laminate with Tapered Active Material Layer and Inorganic Film
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Solution Overview
Problem
In secondary batteries, the thickness of the porous separator is limited by the need for mechanical strength, leading to reduced battery capacity and poor durability, with the separator deteriorating during charge and discharge cycles, and integration of nanofiber films into electrodes results in peeling issues.
Innovation Solution
A laminate structure is developed with a first active material-containing layer having a thinner end surface and a thicker opposing surface, where a first film containing inorganic material covers the thinner end surface and adjacent current collector tab surfaces, enhancing adhesion and reducing peeling, and a second film with organic fibers provides insulation and ion permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the separator thickness is increased to maintain mechanical strength, then the separator can avoid tearing during production, but the battery capacity is reduced due to limited number of electrode layers per unit volume
Solution Approach 1:
The separator is divided into two functional layers: a porous substrate layer (5-20 μm) for mechanical strength and a nanofiber film layer (1-5 μm) for enhanced durability. This segmentation allows each layer to optimize its thickness for its specific function, resolving the contradiction between mechanical strength and battery capacity.
Solution Approach 2:
The separator uses a composite structure combining a polyolefin-based porous substrate with a nanofiber film layer. This composite material approach allows the substrate to provide mechanical strength while the nanofiber layer enhances durability, enabling thinner overall design without sacrificing strength, thus increasing battery capacity.
2Quantity of substance
If the separator thickness is decreased to increase battery capacity, then more electrode layers can be stored per unit volume, but the separator deteriorates during charge and discharge cycles
Solution Approach 1:
The separator is segmented into a thin porous substrate (5-20 μm) for ion permeability and a nanofiber film layer (1-5 μm) for durability. This segmentation allows the substrate to be thin for high battery capacity while the nanofiber layer provides the necessary durability for charge-discharge cycles.
Solution Approach 2:
The porous substrate layer with controlled porosity (30-80%) provides sufficient ion permeability even at reduced thickness (5-20 μm), enabling high battery capacity while maintaining functional performance. The porous structure compensates for the reduced thickness by optimizing ion transport pathways.
3Length of stationary object
If a nanofiber film is integrated into the electrode to reduce separator thickness, then the separator can be made thinner, but the separator easily peels off from the electrode
Solution Approach 1:
The nanofiber film is merged with the porous substrate through heat treatment, creating a bonded composite structure. This merging eliminates the peeling issue by ensuring strong adhesion between the nanofiber layer and the substrate, while still allowing the overall separator thickness to be reduced.
Solution Approach 2:
Heat treatment is applied to change the physical state and bonding characteristics of the nanofiber film and substrate. This parameter change (temperature) enhances adhesion between layers, preventing peeling while maintaining the reduced thickness design for high battery capacity.
Data Source
AI summary
According to one embodiment, there is provided a laminate including a first current collector, a first current collector tab, a first active material-containing layer, and a first film containing an inorganic material. A back surface of the first active material-containing layer is supported on at least a part among front and back surfaces of the first current collector. A first thickness at a first end surface of the first active material-containing layer is smaller than a second thickness at a second end surface facing reverse with respect to the first end surface. The first film covers at least the first end surface of the first active material-containing layer and a portion among front and back surfaces of the first current collector tab adjacent to the first end surface.