Nonwoven Separator Pore Structure for Battery Safety
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Solution Overview
Problem
Existing separators for batteries and capacitors face challenges with short circuits due to metal dendrite growth and lack of thermal stability, especially at high temperatures, which can lead to safety risks and reduced performance.
Innovation Solution
A fibrous nonwoven web fabric separator with particles that form second pores with an average diameter greater than the majority of the second pores, creating a labyrinthine pore structure that prevents dendritic growth and maintains high porosity and thermal stability, while using a binder for mechanical flexibility and a coating for enhanced safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the openings in the separator are made as large as possible to increase electrolyte conductivity and power density, then the electrolyte conductivity and power density are improved, but metal dendrites can lead to short circuits between the two electrodes
Solution Approach 1:
The separator is designed with heterogeneous pore size distribution, combining large pores for electrolyte conductivity with localized small pore regions (filled structures) that prevent dendrite penetration. Different regions of the separator have different pore characteristics optimized for their specific functions.
Solution Approach 2:
The separator combines organic polymer fibers with inorganic filler particles to create a composite structure. This composite material provides both the mechanical flexibility and porosity needed for ion transport, and the thermal stability required to prevent short circuits at elevated temperatures.
2Ease of manufacture
If polyethylene is used as the separator material to achieve shutdown mechanism at low cost, then the shutdown mechanism responds to local heating by melting and blinding pores, but the melting point is around 130°C which limits thermal stability
Solution Approach 1:
The separator uses a composite of polyethylene fibers providing shutdown mechanism and low-cost manufacturing, combined with inorganic filler particles that raise the overall thermal stability of the separator structure, allowing it to maintain integrity at temperatures above 130°C while retaining the shutdown safety feature.
3Temperature
If polypropylene is used as the separator material to achieve higher melting point and thermal stability, then the melting point increases to around 150°C, but the shutdown mechanism is less effective compared to polyethylene
Solution Approach 1:
The separator design incorporates polyethylene regions specifically optimized for shutdown mechanism functionality, while polypropylene or other thermally stable materials provide the overall structural framework that maintains integrity at higher temperatures. Each material is placed where its specific properties are most needed.
4Power
If the separator thickness is reduced to achieve lower cell resistance and higher power density, then the power density is improved, but the separator becomes more susceptible to dendrite penetration and mechanical damage
Solution Approach 1:
The separator uses a highly optimized porous structure with controlled pore size distribution and tortuosity. The filled pore regions create a labyrinthine path that increases the effective thickness for dendrite penetration while maintaining thin overall separator thickness for low resistance. The porous structure provides mechanical strength despite reduced thickness.
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 effectively prevents short circuits and maintains high porosity and thermal stability over a wide temperature range, ensuring safe and efficient energy storage in batteries and capacitors with high power and energy density.
Implementation Method 1
the foundational structure consisting of fibers and having first pores formed by the fibers, the foundational structure being at least partially filled with particles, which particles at least partially fill the first pores and form regions filled with particles
Implementation Method 2
using a binder for mechanical flexibility
Implementation Method 3
and also in the form of a coating
Data Source
AI summary
A ply includes a fibrous nonwoven web fabric forming a foundational structure, wherein the foundational structure includes fibers forming first pores and is partially filled with particles, wherein the particles at least partially fill the first pores so as to form regions filled with particles, wherein the particles in the filled regions form second pores, and wherein an average diameter of the particles is greater than an average pore size of more than 50% of the second pores.