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11.4.1: Battery Storage

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    84609
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    According to the orthodox definition, the the current i basic “building block” of an electric battery is an electrochemical cell. The battery consists of several such cells connected together to increase their performance. Accordingly, the popular AA or C “batteries” are not betteries, but single cells. Yet, today little attention is paid to this orthodox division and we use the term “battery” for single cells as well. In this Chapter we will stick to that habit and a single cell will often be referred to as a “battery”.

    A conventional electrochemical cell consists of essential parts: two electrodes and electrolyte. The electrodes are made of metals or current-conducting solids. The electrolyte is an ion-conducting substance placed between the two electrodes. Most often it’s a liquid or it has consistency of a gel. A potential difference (the same as voltage) arises between the electrodes immersed in the electrolyte. The one with a higher potential is called the positive electrode or the “plus” (+) electrode. The other is the negative electrode or the “minus” one. Now, if the two electrodes are connected by a metal wire, an electric current starts flowing1. Electrons in the wire travel from the “minus” electrode to the “plus” one. But the charge cannot accumulate, therefore it must be carried back – now, through the electrolyte, by ions.

    In texts describing galvanic cells as well as other electric devices two important terms are often found: namely, the anode and the cathode. How are they defined? Suppose that the electrodes of the device in question are connected by a wire. Then, current flows: as mentioned above, it’s the electrons flowing from the “minus” electrode to the “plus” electrode. But the “conventional current” – the concept introduced by Franklin – “flows” in the opposite direction. The concepts of the anode and the cathode refer specifically to this “conventional current”. Namely, the anode is the electrode into which the “conventional current” enters from outside. And the cathode is the electrode from which the “conventional current” flows out. Accordingly, if we think of an AA battery or any other disposable one, the “+” terminal is the cathode, and the “-” terminal is the anode. But with rechargeable batteries, as will be discussed below, things become more tricky.

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    1. Benjamin Franklin, one of the Founding Fathers of the United States, was also a great scientist. He conducted research of fundamental importance on electricity. In the 18th century when he lived it was impossible to determine what was the exact nature of the charges carrying electric current. Franklin assumed that the current flowed from the positive electrode to the negative one – and it became an established rule. Only 150 years later it have been proved beyond any doubts that in metals the current is carried by negative particles, the electrons, who travel from the negative electrode to the positive one. But that doesn’t mean Franklin was completely wrong because there are non-metallic conductors in which electric currents are carried by positive particles – e.g., by positive ions, or by holes in p-type semiconductors


    11.4.1: Battery Storage is shared under a CC BY 1.3 license and was authored, remixed, and/or curated by Tom Giebultowicz.

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