Ceramic-Coated Separator for Lithium Battery Overcharge Safety
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Solution Overview
Problem
Lithium rechargeable batteries face safety issues during overcharge due to metal-ion elution, particularly at high temperatures, which affects their performance and cycle-life characteristics.
Innovation Solution
A rechargeable lithium battery design featuring a silicon-based negative active material, a ceramic-containing coating layer on a polymer substrate separator, and an ethylene carbonate-based organic solvent, where the ceramic-containing coating layer is positioned between the polymer substrate and the positive active material, enhancing safety and ion mobility while controlling metal-ion elution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a polymer substrate separator is used in lithium rechargeable batteries, then the battery structure is simple and manufacturing is easy, but metal-ion elution occurs at high temperatures during overcharge reducing safety
Solution Approach 1:
The patent applies composite materials by combining a polymer substrate with a ceramic-containing coating layer to create a separator that maintains the simplicity of polymer manufacturing while adding the thermal stability and metal-ion elution prevention properties of ceramic materials. The coating layer contains ceramic particles dispersed in a binder resin, forming a composite structure that resolves the contradiction between ease of manufacture and overcharge safety.
Solution Approach 2:
The patent applies local quality by positioning the ceramic-containing coating layer only on the positive electrode side of the separator, where it directly contacts the positive active material. This localized application provides metal-ion elution prevention exactly where it is needed during overcharge, while maintaining the simplicity and cost-effectiveness of the polymer substrate for the remainder of the separator structure.
2Reliability
If a ceramic-containing coating layer is added to prevent metal-ion elution, then overcharge safety is improved, but the separator structure becomes more complex
Solution Approach 1:
The ceramic-containing coating layer is applied locally only on the positive electrode side of the separator where it is needed to prevent metal-ion elution from the positive active material. This localized approach improves overcharge safety without requiring the entire separator to be redesigned, thereby limiting the increase in structural complexity.
Solution Approach 2:
The coating layer is designed with porous characteristics that allow it to maintain ion permeability while providing the protective function. The porous structure enables the coating layer to perform its safety function without requiring a dense, complex structure that would impede ion transport, thus balancing safety improvement with structural simplicity.
3Speed
If the coating layer porosity is increased to facilitate ion transfer, then ion mobility is improved, but the ability to prevent metal-ion elution may be reduced
Solution Approach 1:
The coating layer is designed with controlled porosity in the range of 30-80%, creating a porous structure that facilitates ion transfer while maintaining the protective function. The porous architecture allows ions to pass through the coating layer efficiently, preventing it from becoming a transport barrier, while the ceramic particles within the porous matrix continue to prevent metal-ion elution.
Solution Approach 2:
The composite structure of ceramic particles dispersed in a binder resin within a porous matrix enables simultaneous achievement of ion permeability and metal-ion elution prevention. The ceramic provide structural integrity and elution prevention, while the porous binder resin matrix allows ion transport, resolving the contradiction between ion mobility and safety.
4Reliability
If the coating layer thickness is increased to improve metal-ion elution prevention, then overcharge safety is enhanced, but ion transfer resistance increases
Solution Approach 1:
The coating layer employs a porous structure that allows ions to pass through tortuous paths within the porous matrix, effectively increasing the functional thickness for metal-ion elution prevention while maintaining reasonable ion transfer rates. The porosity compensates for the increased thickness by providing multiple transport channels.
Solution Approach 2:
The coating layer thickness is optimized within a specific range (3-20 μm) rather than being maximized, and this parameter is combined with controlled porosity (30-80%) to achieve the desired balance. By adjusting these parameters together rather than independently, the patent achieves both adequate metal-ion elution prevention and acceptable ion transfer rates.
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 battery achieves excellent overcharge safety, improved cycle-life characteristics, and high capacity per volume, with the ceramic-containing coating layer providing suitable porosity and thickness to facilitate ion transfer and prevent excessive metal-ion elution.
Implementation Method 1
the ceramic-containing coating layer has porosity at or between about 60% and about 80%
Implementation Method 2
the ceramic-containing coating layer is positioned only between the polymer substrate and facing the positive active material
Data Source
Figure 1
AI summary
Disclosed is a rechargeable lithium battery that includes a positive electrode including a positive active material, a negative electrode including a silicon-based negative active material, an electrolyte including a lithium salt and a non-aqueous organic solvent, and a separator including a polymer substrate and a ceramic-containing coating layer on the polymer substrate. The ceramic-containing coating layer has a porosity at or between about 50% and about 90%, and a thickness at or between about 2µm and about 6µm. The rechargeable lithium battery has a capacity per volume of more than or equal to about 700Wh/ℓ .