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 Many different battery technologies have been developed, each replacing the previous technology to some extent, but not completely. Application requirements dictate certain technologies, for example Lead Acid batteries are almost exclusively used for automotive applications; they are not surpassed for price, lifetime and performance characteristics. Despite toxic components, Nickel Cadmium cells (Ni-Cad) are still sometimes used for high energy and fast charge rugged applications. Nickel-Metal Hydride batteries were developed in the 1970s and have higher energy density than Ni-Cad. Despite disadvantages Ni-MH battery had its own issues and so not too many years after its introduction its use has now largely been replaced with Lithium Ion Batteries and other related Lithium based technologies including the now widely used Lithium Polymer batteries. Lithium based batteries are used in everyday modern electronics including smart phones, tablets and laptop computers.
Battery Separators
The growth of the fully electric car industry fuels a demand for high power, long life and low price battery systems. Advanced Lithium based batteries offer a promising solution. The Lithium Ion technology requires advanced materials. Quantachrome instruments can help with understanding and measuring pore structure of many materials used in Lithium Ion and other technology power systems.
All batteries use some form of porous “separator” that isolates the electrode “circuits”. The material for this is carefully chosen to be highly insulating yet able to easy pass ions between electrodes. The separator must be porous to retain enough liquid to allow free passage of ions to complete the electrical circuit.
The battery separator plays a key role in determining the capacity of the battery. Separator materials and pore structure are topics of much research and development. Many different materials are used both individually and together. Their properties including pore size and permeability characteristics are critical to battery life and performance. These vary according to battery technology although current emphasis is mostly on Lithium Ion Systems. The separator should be highly porous but also strong and mechanically stable at elevated temperatures. Polyolefin membranes such as Polyethylene (PE) and Polypropylene (PP) have been used extensively. Polyethylene has a lower melting point than Polypropylene. A laminated combination of both PE and PP is now commonly used for small lithium ion batteries. Choosing a low melting point polymer like Polyethylene adds safety since it effectively adds a thermal fuse. Under elevated temperature conditions such as with a short, it melts and the pores fuse together. The PP layer or layers retain the overall structure of the separator to avoid shrinkage and possible fires.
The Quantachrome Porometer 3G models measure pore size and permeability of through-pores and are the ideal technology for measurement of lithium ion and other battery separators. The polymeric separators discussed are only approximately 25 microns thick and are very easy to measure with the Porometer 3G models.
Summary Table, Battery Components
Table of example pore sizes
| Separator Material - |
|
Application- |
Thickness- |
Max. Pore Size- |
Mean Pore Size- |
Min. Pore Size |
| |
|
µm |
nom.µm |
µm |
µm |
µm |
| Polyethylene (PE): |
|
Li-ion |
25 |
0.0722 |
0.0595 |
0.0534 |
| Polypropylene (PP): |
|
Li-Ion |
25 |
0.0619 |
0.0525 |
0.0473 |
| PP-PE-PP laminate 1: |
|
Li-Ion |
25 |
0.0313 |
0.0284 |
0.0266 |
| PP-PE-PP laminate 2: |
|
Li-Ion |
25 |
0.0369 |
0.0347 |
0.0328 |
| PVDP component: |
|
Li-Ion Gel |
30 |
0.7934 |
0.5207 |
0.4084 |
| Polyethylene component: |
|
Lead-Acid |
250 |
0.0557 |
0.0420 |
0.0328 |
| Ceramic Coating : |
|
Hydrophilic |
200 |
5.6637 |
1.2551 |
9.2167 |
Polyethylene Separator
Single layer thin film separators, such as this polyethylene film can be characterized using the Porometry method that measures the dimensions of through-pores.
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Porometry measures flow rates and pressures and presents data as the flow through empty pores over a range of pressures. The pores are filled with wetting fluid and progressively emptied as the pressure is increased. The pressure is converted to pore size and the flow rate data can then be presented as capillary flow %. The cumulative and differential % flow distributions are presented. |
 |
Summary data is most often used and is given in the following format |
Calculations from 0.107 µm to 0.043 µm
Maximum Pore Size: |
0.0722 (µm) |
Mean Flow Pore Size: |
0.0595 (µm) |
Minimum Pore Size: |
0.0534 (µm) |
Bubble Point Pressure: |
6.3417 bar |
Bubble Point Flow Rate: |
0.0006 (l/m) |
Polypropylene Separator
 |
Pore size data is presented as the number of pores / cm2
|
Calculations from 0.067 µm to 0.034 µm
Maximum Pore Size: |
0.0619 (µm) |
Mean Flow Pore Size: |
0.0525 (µm) |
Minimum Pore Size: |
0.0473 (µm) |
Bubble Point Pressure: |
6.9500 bar |
Bubble Point Flow Rate: |
0.0675 (l/m) |
Pore Density (Number): |
2.47E+11 /cm² |
Tri-Layer Laminated PP/PE Separator
Calculations from 0.080 µm to 0.032 µm
Maximum Pore Size: |
0.0369 (µm) |
Mean Flow Pore Size: |
0.0347 (µm) |
Minimum Pore Size: |
0.0328 (µm) |
Bubble Point Pressure: |
17.3322 bar |
| Bubble Point Flow Rate: |
0.0368 (l/m) |
|
Fuel Cells Components | Standards
Fuel Cell Substrate
There are many different types of fuel cells but all generate electricity rather than store energy; as batteries do. All fuels cells function through electrochemical action with an oxidizing agent (such as oxygen gas) and fuel such as Hydrogen.
PEM fuel cells are one of the most common types and contain one or more porous components.
Quantachrome Instruments offers several applicable methods for measure the pore structure of fuel cell components. The example given shows the through-pore size distribution of a fuel cell substrate sample measured with the Porometer 3Gzh pore size analyzer.
Run Data, Wet Run with Porofil and Dry Run
Calculations from 78.144 µm to 24.124 µm
Maximum Pore Size: |
56.8384 (µm) |
Mean Flow Pore Size: |
37.7836 (µm) |
Minimum Pore Size: |
35.5556 (µm) |
Bubble Point Pressure: |
0.0113 bar |
Bubble Point Flow Rate: |
0.0847 (l/m) |
