Hydrogen-Bonded Battery Separator Coatings for Cell Expansion Control
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Solution Overview
Problem
Lithium ion batteries face challenges in maintaining high-rate discharge performance and cycle performance due to the expansion of bare cells during processing and cycling, which affects energy density and safety.
Innovation Solution
A battery design incorporating a separator with a base film coated on both surfaces with polar substances that form hydrogen bonds with the positive and negative electrodes, enhancing binding forces and reducing expansion, achieved by optimizing the mass ratios and types of polar substances and reinforcing agents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a traditional separator is used that is only in physical contact with the electrodes, then the separator structure is simple, but the bare cell is prone to expansion which does not facilitate shaping of the cell
Solution Approach 1:
The separator is constructed as a composite material system consisting of a base film layer and a polar substance coating layer. The base film provides mechanical strength and thermal stability, while the polar substance coating layer (containing groups like -OH, -COOH, -NH2) provides hydrogen bonding capability with the electrode binder, creating a composite structure that simultaneously ensures structural integrity and strong electrode adhesion to prevent cell expansion.
Solution Approach 2:
The polar substance coating layer acts as an intermediary between the separator and the electrode. This intermediate layer contains polar groups that form hydrogen bonds with the electrode binder, serving as a chemical bridge that strengthens the interface bonding without requiring direct contact between the base film and electrode, thus facilitating cell shaping while maintaining structural simplicity.
2Ease of manufacture
If the separator is not strongly bound to the electrodes, then the separator is easy to manufacture, but the binding forces are insufficient leading to cell expansion during processing and cycling
Solution Approach 1:
The invention changes the chemical parameter of the separator surface by coating it with polar substances that have specific functional groups (-OH, -COOH, -NH2). This parameter change enables hydrogen bonding interaction with the electrode binder, significantly enhancing the binding force between separator and electrode without complicating the manufacturing process, as the coating can be applied through conventional coating methods.
3Reliability
If the bare cell expands during processing and cycling, then the separator and electrode contact is maintained, but the energy density decreases and safety performance deteriorates
Solution Approach 1:
The polar substance coating layer is pre-applied to the separator before battery assembly. This preliminary action creates a ready-to-bond surface that will form hydrogen bonds with the electrode binder during battery assembly and cycling, preventing cell expansion from occurring in the first place rather than attempting to correct it after expansion has begun.
4Strength
If the separator coating contains high content of polar substance, then the hydrogen bonding capability is enhanced, but the lithium ion transport may be hindered
Solution Approach 1:
The separator is designed with non-uniform local properties: the polar substance coating layer is applied only on the surfaces that contact the electrodes, while the central base film region remains thick and porous to facilitate lithium ion transport. This local differentiation ensures that hydrogen bonding capability is concentrated where needed (at the electrode interface) while maintaining high ion conductivity in the bulk separator region.
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 significantly improves the high-rate discharge capacity and cycle performance by reducing cell expansion, ensuring better lithium ion transport and maintaining consistent tension across the separator, thus enhancing the battery's overall performance.
Implementation Method 1
hydrogen bonds are formed between the first polar substance and a positive binder of the positive electrode
Implementation Method 2
hydrogen bonds are formed between the second polar substance and a negative binder and/or a negative active component of the negative electrode
Data Source
AI summary
A battery, a battery module, a battery pack and an electric device are provided. In some embodiments, the battery includes: a positive electrode, a separator and a negative electrode, wherein the separator includes a base film, a first coating provided on a first surface of the base film, and a second coating provided on a second surface of the base film, the first coating includes a first polar substance, and hydrogen bonds are formed between the first polar substance and a positive binder; hydrogen bonds are formed between the second polar substance and a negative binder and/or a negative active component. In the present disclosure, binding forces between the separator and the positive electrode and the negative electrode may be increased by the hydrogen bonds, thus reducing a cycle expansion rate of a bare cell and improving a high-rate discharge performance and a cycle performance of the battery.