Low-Sodium Ceramic-Coated Separator for Lower Battery Internal Resistance
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Solution Overview
Problem
Existing ceramic-coated lithium battery separators have high internal resistance, which affects battery performance and discharge efficiency, and current methods fail to adequately address this issue through adjustments in thickness and air permeability, while neglecting the influence of the composition ratio of the coating slurry.
Innovation Solution
A low-internal-resistance ceramic-coated separator is developed using a polymer base film with a ceramic layer having a sodium content less than 1000 ppm and no sodium carboxymethyl cellulose (CMC), featuring a peel strength of 20 N/m or above and ionic conductivity of 1.4 mS/cm or higher, achieved by optimizing the ceramic slurry composition and coating process to reduce viscosity and water content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the separator is reduced to lower internal resistance, then ion conductivity improves, but mechanical strength and safety deteriorate
Solution Approach 1:
The patent applies composite materials by coating a ceramic layer (alumina, silica, or boehmite particles) onto the polyolefin base film. This composite structure allows the separator to maintain thin thickness (15-20 μm) for low internal resistance while the ceramic coating provides mechanical reinforcement and thermal stability, preventing puncture and maintaining structural integrity.
Solution Approach 2:
The ceramic coating is applied locally on the inner surface of the base film, creating a functional gradient structure. The base film provides mechanical strength and shutdown function, while the thin ceramic coating (3-10 μm) provides thermal stability and surface porosity for ion conduction, allowing each layer to optimize its specific function without compromising the other.
2Temperature
If ceramic coating is applied to improve high temperature shrinkage resistance and liquid absorption, then thermal stability improves, but internal resistance increases
Solution Approach 1:
The patent optimizes the ceramic coating parameters by controlling particle size (0.1-10 μm), coating thickness (3-10 μm), and porosity (30-70%). The slurry composition is carefully adjusted with specific binder ratios (5-20 wt%) and solvent content to achieve optimal pore structure. These parameter optimizations ensure the coating provides thermal stability while maintaining sufficient porosity for ion conduction, preventing excessive internal resistance.
3Strength
If conventional ceramic slurry with CMC and high sodium content is used to enhance adhesion, then peel strength improves, but internal resistance and moisture absorption increase
Solution Approach 1:
The patent replaces conventional CMC binders with alternative binders (polyvinylidene fluoride, polyacrylonitrile, or carboxymethyl cellulose with controlled sodium content <1000 ppm). The binder content is optimized at 5-20 wt% of ceramic particles, and the slurry is prepared with controlled water content and pH (8-10). These parameter changes reduce sodium introduction and improve ion conductivity while maintaining adhesion through optimized binder-ceramic-base film interactions.
Solution Approach 2:
The patent extracts and removes the harmful CMC component from conventional ceramic slurry, replacing it with alternative binders that do not introduce excessive sodium or increase moisture absorption. This extraction eliminates the source of high internal resistance while maintaining the necessary adhesion through carefully selected alternative binding agents.
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 reduces the internal resistance of the separator, enhancing the power performance and discharge efficiency of lithium batteries by minimizing sodium content and eliminating the negative effects of CMC on ion diffusion and moisture absorption.
Implementation Method 1
Ion conduction inside the battery depends on the diffusion of Li ions in the electrolyte through the porous separator
Implementation Method 2
a CMC solution is usually added. At the same time, CMC, as a suspension agent, can improve the particle settlement after the slurry is prepared
Data Source
AI summary
The present disclosure provides a low-internal-resistance ceramic-coated separator, a preparation method thereof, and a lithium battery. The low-internal-resistance ceramic-coated separator of the present disclosure includes a polymer base film, and a ceramic layer coated on one or two sides of the polymer base film. The ceramic layer adopts low-sodium boehmite and does not contain sodium carboxymethyl cellulose (CMC). A sodium content of the ceramic layer is less than 1000 ppm, so that a Gurley increase value of the separator is significantly lowered. When applied to the lithium battery, the ceramic layer can greatly reduce an internal resistance of a cell, thereby improving the power performance and discharge efficiency of the battery.