20.109(F09): Mod 3 Day 4 Battery assembly

Battery Assembly

Introduction

Figure from Lt. Col. F. John Burpo

Though some nice micrographs like what you can find on the front page of this module would be great, your TEM results may have revealed nanowires that are not uniform in their appearance or in their gold coating. Fortunately, even ugly-duckling nanowires may serve beautifully when assembled into a battery. The question you'd like to address is if a battery electrode made from gold nanowires (+ some percentage of silver) performs better than a battery made with a solid, gold foil electrode. And having included silver in the templating, how does the % of that metal affect the voltage potential and the charging of the battery? To answer these questions, you will assemble your nanowires into a battery, mixing a known percentage of the active nanowire material, with a small amount of conducting material and a small amount of binding material. The conducting material we'll use is a graphite carbon called “Super P”. The binder is a kind of teflon called polytetrafluoroethylene, or PTFE for short, that will hold the nanowires and carbon conductor together. The nanowires, carbon and teflon will form a flexible film that you'll roll out like cookie dough and that will serve as the electrode (shown in black in this image) for your battery. The electrode will then be moved into a glovebox to be assembled with the lithium and the electrolyte, pressed into a coin-type casing, and dry until testing next time.

Protocols

Some of today's lab protocol will require that we work in small groups in the Belcher lab. We'll be using their balance to measure very small masses of material and their glove box to assemble the batteries. As visitors to their lab, please be respectful of their time, equipment and space.

Part 1: Examining TEM images

Images from your TEM grids are here. They are organized with the following numbering scheme:

Lab section	Team color	.tif #
T/R	Red	1-4
	Green	5-8
	Blue	9-12
	Orange	13-16
	Pink	17-20
	Yellow	21-24
	Purple	25-28
W/F	Pink	29-32
	Purple	33-36
	Green	37-40
	Red	41-44
	Blue	45-48

Part 2: Electrode Composition

You'll need to make some careful mass measurements and then mix the nanowires: carbon (= Super P): teflon (PTEF) at the correct ratio of 70% nanowires:25% Super P:5% PTFE. All material should be isolated and ground to form a powder. This powder is what will be used to make the battery electrodes.

1. Measure the mass of nanowire powder and add to a clean mortar.
2. Grind for 5 minutes. You and your lab partner(s) can take turns grinding. While you're not grinding determine the mass of Super P and PTFE to be add based on the mass of the nanowires.
3. Measure out Super P and add to mortar. Do not add PTFE yet!
4. Grind thoroughly with mortar and pestle for about 20 minutes.
5. Add PTFE and mix together, use the pestle to press the mixture into a flat sheet that is all one piece.
6. Transfer to a stainless steel plate and roll out the electrode to form a uniform electrode.
7. Once rolled, transfer to the stainless steel cutting plate and use a circle cutter to make an electrode.
8. Measure mass of the electrode (you'll need this to calculate your battery's theoretical capacity).
9. Assembly of the electrodes into batteries will be done for you in the glove box in the Belcher lab.

For Next Time

1. Based on the mass of the electrode, determine the theoretical capacity (amps) of the electrode, using the loading factor of 50mA/g, a value that is in accordance with previously tested gold nanowire electrodes.
2. You should be well on your way to your final presentations of a research idea. Review the required elements for your presentation that are noted here.