Electrodes are necessary in the creation of any battery. All electrodes can be classified into two categories: anodes and cathodes. Each of these electrode types needs the other to facilitate the conventional current that allows a battery to function properly.
How is an anode different from a cathode?
The main difference between an anode and a cathode can be observed in their relationship with electrons, and, by extension, how they contribute to a redox reaction.
During an electrochemical reaction, an anode will lose electrons to the circuit, becoming oxidized in the process; whereas a cathode will gain these electrons to be reduced. Read on to explore their differences in depth!
What is an Anode?
An anode, in the strictest sense, is the electrode that releases electrons, and is consequently the site that is oxidized during a redox reaction. For clarity, recall that oxidation simply refers to a loss of electrons.
When electrons exit an anode and flow out into the circuit, the anode gains a positive charge. This attracts negative ions – or anions – to the anode, which will subsequently be able to gain their extra electrons to replace the ones it loses as it remains active. For this reason, anodes are also referred to as electron acceptors.
Oxidizing metals are used for anodes; the most common metals being zinc, aluminum and magnesium.
What is a Cathode?
Cathodes function in the exact opposite way as an anode. It is an electrode that receives the electrons coming in through the circuit. This influx of electrons leads to the reduction of a cathode, completing the other half of a redox reaction.
With the addition of these new electrons, the cathode acquires a negative charge. This causes the positive ions – also known as cations - to move towards the cathode. While the circuit remains active, it will donate the extra electrons that it receives to these cations; in light of this, cathodes are called electron donors.
Materials used for making cathodes include lithium, cobalt, nickel and manganese.
Differences Between an Anode and a Cathode
Michael Faraday was the first to name both electrodes in conducting an electrochemical study in 1834, although he enlisted the help of fellow scientist William Whewell who created the terms “anode” and “cathode” for Faraday’s paper.
The term “anode” is derived from the Greek word for ascent, which was “anodos” (ἄνοδος). Likewise, “cathode” came from the word for descent in Greek, “kathodos” (κάθοδος).
With the discovery of the electron, modern etymologists justify using these words as electrons “ascend” from anodes and “descend” into cathodes.
In a circuit, the electric potential difference within a battery induces electrons to move out of the anode and flow through the circuit.
These electrons will pass through the loads and any other circuit components before reaching and entering the cathode.
You can contrast this with the conventional current model, which runs opposite to electron flow; instead of electrons moving from anodes and into cathodes, it considers the current flow to begin from the cathodes.
The movement of electrons from an anode to a cathode causes both electrodes to acquire charges.
Anodes acquire a positive charge through the loss of electrons. This attracts negatively-charged ions from the electrolyte solution or material.
In contrast, the inflow of added electrons leads cathodes to become negatively-charged, which pulls the positive-charge cations towards the electrode.
As a battery discharges, it leads to the movement of an electron from a donor species to an acceptor. This movement is the basis for redox reactions.
The anode is the oxidizing electrode as it gives away electrons to the circuit. Likewise, the reducing electrode, which receives said electrons, is the cathode.
Whether an electrode is positively or negatively charged in a given setup is a common cause of confusion.
When a battery is being charged, the anode is positively polarized, and the cathode has a negative charge. Their charges are reversed when the battery is used.
In lithium-ion batteries, graphite – a highly conductive form of carbon - is the most commercially viable material for anodes.
Cathodes in a lithium-ion battery are typically derived from metal oxides. The most common of these is lithium cobalt oxide (LiCoO2), or other layered oxides. Polyanions such as lithium iron phosphate (LiFePO4), or magnesium/aluminum spinels such as lithium manganese oxide (Li/MgO2), are also regularly used.
Comparison Chart: Anode vs Cathode
|Etymology||“Anodos,” Greek for “ascent”||“Kathodos,” Greek for “descent”|
|Electron Flow||Electrons move out of anodes||Electrons move into cathodes|
|Charge||Positive (charging)Negative (discharging)||Negative (charging)Positive (discharging)|
|Components||Carbon (graphite)||Metal oxides, e.g. lithium cobalt oxide (LiCoO2)|
How are Anodes and Cathodes similar?
Anodes and cathodes, despite being literal polar opposites in charge and half-reactions, are still a vital part of any battery. Without these electrodes, a battery would be unusable.
Electrodes facilitate the movement of electrons through a circuit. Both anodes and cathodes are also involved in oxidation-reduction reactions, albeit through opposite half-reactions. In addition, the two electrodes become charged when the circuit is active, and attract their respective ions.
As a final note, both electrodes owe their names to the works of Michael Faraday and William Whewell, seminal contributors to the field of electrochemistry.
Who invented the first modern battery?
Italian chemist Alessandro Volta is credited with the creation of the first modern electrochemical battery, the voltaic pile, in 1800.
A simple electric cell made of a zinc and copper disc with a thin layer of electrolyte in between, was the basic unit of the voltaic pile. Several of these pairs would be stacked on top of each other, increasing the voltage of the entire battery.
By connecting the contacts at the top and bottom with a wire, an electric current would be observed to flow.
Why are lithium-ion batteries so common?
Lithium-ion batteries are currently the most used type of battery for powering a wide range of electronics, from earbuds to phones and laptop computers.
A Li-ion battery holds several advantages to other competing battery types, such as the nickel-cadmium battery. Because they can store much more energy in a small package, they are considerably energy-dense. They are also able to output larger amounts of current, and boast longer battery lives.
Furthermore, unlike Ni-Cd models, Li-ion batteries don’t use cadmium, which is a toxic element.
Anodes and cathodes are two kinds of electrodes that are indispensable parts to any battery.
The key differences between both are found in their half-reaction, role in the electron flow, and the ions they attract.
Anodes release electrons into the circuit. In the process, it oxidizes and gains a positive charge, attracting anions from which it takes extra electrons.
On the opposite end, cathodes receive electrons. They are subsequently reduced, acquiring a negative charge which pulls in cations that gain its extra electrons.