Editorial Team   |   September 12, 2017

The Hemp Battery Construction as a Coin Cell and its Comparison to the Lithium Counterpart

This article outlines the process on how to construct a hemp cell and how the discharge curve compares against a lithium cell.

This article outlines the process on how to construct a hemp cell and how the discharge curve compares against a lithium cell.

Construction Process of the Hemp Coin Cell

The main components that make a hemp battery includes the negative side cap which is the top cap with nylon seal, the anode material, the separator, the active material plate, the spacer, the spring and finally a positive plate that is the bottom plate. 

 

 

To make the separator, first place the separator material between the two plates of a hole puncher equipment and tighten the plates down. Next, fit the cutter of desired size into the hole puncher and push it through the separator disc. Similarly, for the active material place the active material plate between the two plates of a hole puncher equipment and tighten the plates down. Next, fit the cutter of desired size into the hole puncher and push it through the active material plate. If the separator is 20 mil then the active material should be 15 mil. 

 

 

For the current collector which is a metal collector, you need the vise device. Place the current collector between the two plates and insert the cutter tool. Place it between the jaws of the vise and push through it. 

 

 

Before putting all the components together, soak the separator in salt electrolyte overnight. Begin with the negative side cap, and place the anode material within in. Next, fit in the separator. After that, put a couple of electrolyte drops on the active material and fit it in. Fit in the spacer, spring and finally the positive plate, pressing until you get a click.

 

Place the cell within the jaws of the cell fitting machine with the positive side facing downwards. Pump the handle of the machine for the jaws to close and then pumping until the pressure reaches between 500-600 psi. Unlock the jaws and remove the cell.  The cell is now ready.

 

 

Hemp Coin Cell Comparison with Lithium Coin Cell

After the construction of hemp cell, you will definitely want to analyse it to compare it with the lithium cell. To test it, place the hemp cell in the cell holder within a circuit and monitor the discharge curve. Simultaneously, monitor the lithium cell having the same size and form factor.

This test was done with 0.029 grams of active material in the hemp cell. The entire weight of the lithium cell was 2.775 g and that of the hemp cell was 2.997 g. Both the cells had 20 mm diameter and 3 mm thick.

The resulting discharge curves are as below:

 

Comparison Conclusion

The lithium one showed a reading of 4.26 while the hemp one showed a reading of 3.77 which is an almost identical value.

 

More from Robert Murray-Smith:

https://www.youtube.com/watch?v=pcj-TPQqKTo&t=162s

 

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