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Building Science

The Science of Batteries

It started with copper and iron, but the future of batteries is likely lithium ion

Tesla's Powerwall batteries store electricity for residential PV systems.

All batteries work in the same basic way, creating the magic of electricity through the wizardry of chemical reactions. When two chemicals react to form a third compound, the individual atoms can gain, lose, or share electrons in an attempt to balance the positive and negative charges at the atomic level. Batteries pair two reactions—one that causes a loss of electrons and one that requires a gain of them—to create a flow of electrons that can be used to start cars or run cell phones. Each reaction occurs at an electrode at opposite ends of the battery.

The flow of electrons is called current, and that current is what makes things light up or spin. For electrons to flow, there needs to be a circuit, typically a wire, between the electrode that has a surplus of electrons and the one that has a need of them. The spot with the surplus of electrons is said to be negatively charged (the anode), while the electron-poor spot is positive (the cathode). One anode and one cathode make up a cell, and a battery is a collection of cells. The more cells a battery has, the higher its voltage.

Anodes and cathodes are metals or metal oxides of differing electrical potential. In addition to an anode and a cathode, a battery cell requires an electrolyte in which the anode and cathode are placed. The chemical reactions occur between the metals of the electrodes and the electrolyte. Electrolytes can be a variety of substances. Over two millennia ago, batteries were made in Mesopotamia by submerging iron and copper electrodes in a vinegar electrolyte. As the Mesopotamian civilizations weren’t known for their advanced electronics, the guess is that this was done as a novelty or in some religious ceremony. In the 1780s, Alessandro…

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  1. Nathan_Kipnis_FAIA | | #1

    I'm not a battery expert, but the weight of a battery is not critical for home use (generally assuming the battery will be put in the basement on a concrete floor). The better chemistry, from what I have heard, is Lithium Iron Phosphate. As the name implies with the iron, it is very heavy. But again, weight isn't the issue. This is the formulation that companies like Sonnen use, and I have heard that Tesla is looking into using it for its next generation PowerWall. That formulation has a battery life closer to 45 years based on the charts from Sonnen.

  2. iconoclast2222 | | #2


    With household storage batteries becoming practical, is there a future for an all-DC house? I suppose that there is considerable loss when converting DC AC between PV systems and the grid. Many of our major appliances already use DC motors to modulate their output. Lighting sources using LEDs basically rectify AC current in their operation. It seems reasonable that a zero-net-energy home might benefit further from appliances and systems based largely upon DC.
    I’m no kinda expert on this, just thinking......

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