4 minutes reading time (854 words)

    Energy for the Future

    Galvani and animal electricity

    Some history​

    Luigi Galvani was an Italian biologist in the 18th century. While performing experiments involving frogs, he made some interesting observations. While cutting a frog's leg, his steel scalpel touched a brass hook that was holding the leg in place. The leg twitched. Galvani was convinced the movement was caused by what he called animal electricity, or the "life force" within the muscles.

    Later, a colleague of Galvani, Alessandro Volta, found that if was the two different metals, not the frog's leg that produced the electricity. The leg was just an indicator of the presence of electricity.

    Volta and his pile

    In 1800 Volta developed the Voltaic pile, which was arguably the first battery. It consists of a pile of alternating discs of two dissimilar metals separated by cardboard or cloth soaked in seawater or acid. A wire connecting the top an bottom discs could produce repeated sparks.
    More layers leads to more of a shock when joined together.

    Evolution of batteries​

    ​The biggest problem facing battery developers was how to make them last longer. In 1830 William Sturgeon addressed weaknesses in the Volta cell by developing a long lasting battery that consisted of a single cell cylinder of cast iron into which a cylinder of amalgamated rolled zinc was placed. Discs of millboard located between the cast iron cell and the cylinder of zinc prevented contact by the different metals. Dilute sulfuric acid was used to charge the battery. In 1859 Plante began experiments that resulted in construction of a battery for the storage of electrical energy; his first model contained two sheets of lead, separated by rubber strips, rolled into a spiral, and immersed in a solution containing about 10 percent sulfuric acid. A year later he presented a battery to the Academy of Sciences consisting of nine of the elements described above, housed in a protective box with the terminals connected in parallel. His battery could deliver remarkably large currents.

    Today, new batteries are no longer discovered through experimentation as the principles of battery design are well known. Now efforts are focused on optimising the chemistries at work in cells.

    Some chemistry

    Galvanic Cells explained in terms of Oxidation and Reduction

    Galvanic cells (primary non-rechargeable batteries or voltaic cells) can use the different activity levels of elements to produce electricity. The electrons that are generated and required during the oxidation and reduction reactions, respectively, are transferred through an external circuit. This is a flow of electrons or the production of electricity. Electricity will be produced as long as reduction and oxidation reactions, or simply redox reactions, take place. Once the redox reactions stop or cannot occur, no electrons flow in the external circuit and there is no electricity to use for powering devices. The cell is said to be used or discharged.

    Cathodes and Anodes

    In a galvanic cell, there are two half cells. Oxidation takes place in one half-cell, and reduction takes place in the other. The metal (electrode) that is in the oxidation half-cell is called the anode, while the metal (electrode) in the reduction half-cell is called the cathode. So,

    1. Oxidation occurs at the anode, generates electrons and ions
    2. Reduction occurs at the cathode, gains electrons and ions

    Galvanic Cell Construction and Direction of Electron Flow

    Each anode and cathode is surrounded by an electrolyte solution (solution of ions). In simple galvanic cells, a salt bridge is used to allow ions to flow from one half-cell to the other, and wires are connected to the anode and cathode to allow the electrons to flow from anode to cathode. The greater the difference in activity level between the two electrodes, the greater the "potential difference" or "electromotive force" and thus the greater the voltage that is produced by the galvanic cell. Below are figures for a galvanic cell, lithium-ion battery during discharge and calculations for the voltage of a galvanic cell.

    Comparison of dry cells, lead acid cells and lithium cells, in terms of chemistry, cost and practicality, as well as the impact on society and the environment.

     What do I do?

    I make new and exciting materials. I test these materials in batteries and determine their crystal structures. I use a nuclear reactor and a high energy X-ray source to investigate the materials inside these batteries as the batteries charge/discharge.
    Using this information we can develop better batteries!
    What are some issues with current technology?
    • Environmental considerations - cobalt in the cathode
    • Capacity (energy density) - lithium content in the cathode
    • Lifetime & reversibility
    • Performance at high applied current (fast charge)
    • Cost
    • Lithium reactivity
    A Concerning Statistic
    Currently 1 in 1 million batteries can be "defective".
    BUT emerging applications such as electric vehicles have 2000+ batteries.
    Therefore 1 in <1000 cars may have "defective" batteries!

    What does the Future hold?
    • Better electric cars?
    • Batteries that bend - what applications can you think of for this technology?
    • What else can you think of?

    Batteries can shape the future.
    Chemistry shapes batteries.
    What do you want for the future?

    The Structure of the Atom


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    Sunday, 22 July 2018

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