Batteries are systems that store chemical energy and then release it as electrical energy when they are connected to a circuit. Batteries can be made from many materials, but they all share three main components: a metal anode, a metal cathode and an electrolyte between them. The electrolyte is an ionic solution that allows charge to flow through the system. When a load, such as a light bulb, is connected, an oxidation-reduction reaction occurs that releases electrons from the anode while the cathode gains electrons (see reference 1).
Batteries can be remarkably simple. Potatoes contain enough phosphoric acid to act as an electrolyte and you can use them to make a simple, low-voltage battery. To make a potato battery, you will need a piece of zinc, such as a zinc-plated nail, and a piece of copper, such as a copper wire or a penny. Stick both items into the potato and attach them to whatever you want to power, such as a clock or an LED light. The zinc acts as the anode, the copper acts as the cathode and you have a battery. It will also work with the citric acid in a lemon (see references 2 and 5).
You don’t need produce to make a simple battery. One of the first batteries, invented by Alessandro Volta, is the voltaic pile. It is a stack of alternating zinc and copper sheets separated by paper soaked in salt water or vinegar, creating a series of thin battery cells. Connecting wires from the top and bottom of the pile to a load completes the circuit. The voltage produced is limited because the weight of the stack can eventually squeeze out the electrolyte from between the bottommost layers (see reference 3 and 5).
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If you need more voltage, make a Daniell’s cell, invented by John Fredric Daniell. A Daniell’s cell is made up of a copper strip in a copper sulfate solution and a zinc strip in a zinc sulfate solution. A salt bridge connects the two electrolyte solutions. The cells can be linked together in series for higher voltages. As with other simple batteries, the zinc loses electrons while the copper gains electrons (see references 4 and 5).
Commercial Battery Materials
Commercially available batteries use a variety of metals and electrolytes. Anodes can be made of zinc, aluminum, lithium, cadmium, iron, metallic lead, lanthanide, or graphite. Cathodes can be made of manganese dioxide, mercuric oxide, nickel oxyhydroxide, lead dioxide or lithium oxide. Potassium hydroxide is the electrolyte used in most battery types, but some batteries use ammonium or zinc chloride, thionyl chloride, sulfuric acid or lithiated metal oxides. The exact combination varies by battery type. For example, common single-use alkaline batteries use a zinc anode, a manganese dioxide cathode, and potassium hydroxide as the electrolyte (see reference 6).