Designing Pouch Cell Batteries

 

 

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Overview:

Designing Pouch Cell Batteries

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The aim of this lesson/project is to have students create their own set of pouch cell batteries that will power a motor that will raise a load of weights. The end goal is to have students compete to see whose batteries can raise the heaviest load.

Essential Question.

What combination of metals coupled with which concentration of sulfate solutions will produce a battery that will provide the maximum amount of current to lift the heaviest load using a small DC motor?

Background:

Batteries are devices that harness electrochemical potential differences (measured as voltage) between materials in order to generate a stream of electrons (i.e. current).

These reactions are often classified as oxidation-reduction (redox) reactions. Because batteries are galvanic cells, reduction (gaining electrons) occurs at the cathode and oxidation (losing electrons) occurs at the anode. Through careful selection of materials, scientists can maximize the voltage and current of their batteries.

Research Connection:

The current drive in the battery industry is to make small, lightweight batteries that hold a considerable charge, and can be recharged multiple times. One of the techniques researchers use to achieve these goals is the use of a pouch cell—a thin, lightweight battery often used in devices like phones and other small electronic devices. It is this technique that we will mimic in order to provide students with the opportunity to connect to current, real-world research.

NGSS Standards:

Standard Number

Standard text

MS-PS3-3

Design, build, and refine a device that works within given constraints to convert one form of energy into another form of energy.

Materials:

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Part 2: Making the Pouch Cell (Figure 1)

  1. Cut a strip of vacuum sealing bag wide enough to comfortably fit your metal electrodes (you can always cut excess plastic at the end). Cut that strip in half so that you have two pieces sealed on one side.

  2. Cut your metal electrodes near the top to

    create “tabs” for your pouch battery (this will also prevent the metals from touching).

  3. Prepare a saturated solution of KCl/NaCl in a 40 mL beaker.

  4. Carefully scrape your sulfate gel onto your first metal electrode, keeping your electrolyte as smooth and flat as possible. Carefully place the bottom of the electrode inside your piece of vacuum seal bag as close to the sealed edge as possible (see pictures below).

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  5. Cut two or three strips of filter paper wide enough and long enough to just hang over the edge of your electrodes. Soak the filter paper in the saturated KCl/NaCl solution. When the filter paper is thoroughly soaked, layer the two pieces of filter paper on top of the electrode in the vacuum seal bag (see pictures below).

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  6. Turn on the hair straightener to 310 F.

  7. Carefully scrape your sulfate gel onto your second metal electrode, keeping your electrolyte as smooth and flat as possible. Carefully place the electrode on top of the filter paper, ensuring that the two electrodes do not come in contact with each other (see pictures below).

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  8. Seal one side of the pouch cell just below the “tabs” at the top of the electrodes by clamping the hair

    straightener for ~10 seconds (see picture below).

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  9. Carefully ensure that your electrodes are packed into the corner of vacuum seal bag that you’ve just

    made. Using the hair straightener, seal the other side of your pouch cell.

  10. Carefully trim the plastic on the final unsealed side of the pouch cell to allow the electrode “tabs” to stick out of the top of the plastic. Carefully remove as much air as possible from your pouch cell, then seal the top of the pouch cell using the hair straightener (see picture below). You may hear some sizzling. If it looks like your gel is liquefying/boiling, increase the length of the electrode “tabs” so that the hair straightener is further from the gels during the final sealing process.

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Discussion

Each group needs to create at least two prototypes of their pouch cells. At the end of the project, each group will turn in the following:

After testing each prototype, answer the following questions:

  1. Describe two specific things that worked well? Describe two specific things that didn’t work well?

  2. What could you change to make the battery better? Identify the variable/aspect of the battery you

will change. Explain why you’re changing it and how that will affect the battery’s output.

After you’ve created your final prototype, answer the following questions:

  1. Justify your choice of the two metals used (with supporting calculations) and concentrations of electrolytes (with calculations) in your batteries.

  2. What should the voltage of your cells be vs. what is the actual voltage?

    1. Propose an explanation for the discrepancy.

  3. How did the viscosity of your electrolyte affect your battery? Propose an explanation for why.

  4. What mass were you batteries able to lift with the motor? What was the overall mass of your battery pouches? How did your batteries compare to other groups’ batteries?

  5. What are two specific changes you would make to your batteries in order to improve their efficacy (i.e. lift a heavier load)?

Create a general diagram of your pouch cell. Label each component of your pouch cell and write a 1-2 sentence description of the purpose/function of each component of the battery.

Extensions:

If time permits, it would be interesting for students to test different thickening agents for the electrolyte gel. Agar was used due to availability and prior experience with the substance, but it would be interesting to see if/how these changes would affect the battery’s output. Other simple thickening agents include: pectin, corn starch, and gelatin.

Resources:

Different Types of Batteries – https://batteryuniversity.com/learn/article/types_of_battery_cells

Applications of Pouch Cells – https://www.epectec.com/batteries/prismatic-pouch-packs.html

How a Lithium Pouch Cell is Made in Lab – https://www.youtube.com/watch?v=f_OoK_yPVLo

Sources:

This lesson would not have been possible without the help and guidance of the UW Material Science and Engineering Yang Lab.