Illustration of a battery 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 later reveal 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, and pressed into a coin-type casing.
Today's lab protocol will require that we work in small groups in the Belcher lab. You will use their balance to measure very small masses of material and their glove box to assemble your batteries. As visitors to their lab, please be respectful of their time, equipment, and space.
Part 1: Electrode composition
You'll need to make some careful mass measurements and then mix the nanowires: carbon (= Super P): teflon (PTFE) at the correct ratio of 70% nanowires:25% Super P:5% PTFE. All materials should be isolated and ground to form a powder. This powder is what will be used to make the battery electrodes.
- In small groups, visit the Belcher lab (Koch Institute). The mortar with your nanowires will be there drying in their vacuum oven. Bring your notebooks, a calculator, and carry (don't wear) some latex or nitrile gloves.
- Use the Belcher lab's analytical balance to measure the mass of nanowire powder. Add this mass to a clean mortar.
- Grind the nanowires 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 added based on the mass of the nanowires.
- Measure out Super P and add to mortar. Do not add PTFE yet!
- Grind thoroughly with mortar and pestle for about 20 minutes.
- Add PTFE and mix together, use the pestle to press the mixture into a flat sheet that is all one piece.
- Transfer to a stainless steel plate and roll out the electrode to form a uniform electrode.
- Once rolled, transfer to the stainless steel cutting plate and use a circle cutter to make an electrode.
- Measure the mass of the electrode (you'll need this to calculate your battery's capacity).
- The electrodes have to dry before they can be assembled into a battery so before the next lab, this will be done for you in the glove box in the Belcher lab. Today you will have an opportunity to see a demonstration of the assembly with materials that have been prepared in advance.
Part 2: Research proposal review exercise
To help you focus your ideas and develop the details of your project, you will discuss the project description you submitted today with a classmate from another group. As you listen to your classmate's idea, consider the following criteria proposed for small research project grants by the NIH:
Small Research Grant Program: ...small grant supports discrete, well-defined projects that realistically can be completed in two years and that require limited levels of funding. Because the research project usually is limited, the grant application may not contain extensive detail or discussion. Accordingly, reviewers should evaluate the conceptual framework and general approach to the problem. Appropriate justification for the proposed work can be provided through literature citations, data from other sources, or from investigator-generated data. Preliminary data are not required, particularly in application proposing pilot or feasibility studies.
Use the following questions to guide your discussion as you consider both your and your classmate's project. Because you are still in the early stages of developing your research topic, it is okay if you do not have all of the answers to the following questions. This exercise is meant to help you critically think about your proposal...not to point out the additional research you need to complete! Furthermore, this is an informal conversation and you should feel free to look up information during this exercise or just make notes so you know what to research later with your co-investigator.
- Find the partner you were assigned by the teaching faculty and begin by deciding which partner will present first.
- As the presenter, focus on why you believe your topic is important and provide the context needed to convince your listener that it is indeed worth pursuing.
- As the listener, verbally summarize the topic back to the presenter to ensure you understood the proposal. Are you convinced that the topic is important? Why or why not? Discuss this with the presenter.
- Now that you have the needed background information discuss the 'Hows' of the project.
- As the presenter, consider the questions below as you give some details about your proposal.
- As the listener, feel free to ask questions and maybe provide some helpful feedback as the presenter discusses the details of their project.
- What is the novel aspect of your proposal?
- Why do you believe your project is feasible?
- Is there evidence that supports your proposal?
- How will your research advance the field?
- How will you complete your research (what methods might you use)?
- What is the expected result?
- How might you 'double-check' or confirm an expected result?
- What if you do not get the expected result?
- What can be learned if you get the expected result? If you get an unexpected result?
- What are some alternative approaches (methods) for your proposed research?
Once you have completed discussing the presenter's project, switch roles and complete this exercise with the listener's project.
Use the information you gathered during this exercise to drive a discussion with your co-investigator as you further develop your research proposal and prepare the homework assignment due on Day 4.
Next day: Battery testing
Previous day: Phage nanowires