Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas).
Michael Faraday coined the term "electrode" in 1833; the word recalls the Greek ἤλεκτρον (ḗlektron, "amber") and ὁδός (hodós, "path, way").
The electrophore, invented by Johan Wilcke in 1762, was an early version of an electrode used to study static electricity.
[2] This battery consisted of a stack of copper and zinc electrodes separated by brine-soaked paper disks.
'Anode' was coined by William Whewell at Michael Faraday's request, derived from the Greek words ἄνο (ano), 'upwards' and ὁδός (hodós), 'a way'.
It is the positive electrode, meaning the electrons flow from the electrical circuit through the cathode into the non-metallic part of the electrochemical cell.
We can represent the problem as calculating the transfer rate for the transfer of an electron from donor to an acceptor The potential energy of the system is a function of the translational, rotational, and vibrational coordinates of the reacting species and the molecules of the surrounding medium, collectively called the reaction coordinates.
This classically derived result qualitatively reproduced observations of a maximum electron transfer rate under the conditions
This is needed in order to explain why even at near-zero absolute temperature there are still electron transfers,[11] in contradiction with the classical theory.
Without going into too much detail on how the derivation is done, it rests on using Fermi's golden rule from time-dependent perturbation theory with the full Hamiltonian of the system.
It is possible to look at the overlap in the wavefunctions of both the reactants and the products (the right and the left side of the chemical reaction) and therefore when their energies are the same and allow for electron transfer.
Skipping over a few mathematical steps the probability of electron transfer can be calculated (albeit quite difficult) using the following formula
The efficiency of electrochemical cells is judged by a number of properties, important quantities are the self-discharge time, the discharge voltage and the cycle performance.
An integral part of the Li-ion batteries are their anodes and cathodes, therefore much research is being done into increasing the efficiency, safety and reducing the costs of these electrodes specifically.
There is much research being done into finding new materials which can be used to create cheaper and longer lasting Li-ion batteries [18] For example, Chinese and American researchers have demonstrated that ultralong single wall carbon nanotubes significantly enhance lithium iron phosphate cathodes.
By creating a highly efficient conductive network that securely binds lithium iron phosphate particles, adding carbon nanotubes as a conductive additive at a dosage of just 0.5% by weight helps cathodes to achieve a remarkable rate capacity of 161.5 mA⋅h⋅g−1 at 0.5 C and 130.2 mA⋅h⋅g−1 at 5 C, whole maintaining 87.4% capacity retention after 200 cycles at 2 C.[19] The anodes used in mass-produced Li-ion batteries are either carbon based (usually graphite) or made out of spinel lithium titanate (Li4Ti5O12).
[18] Graphite anodes have been successfully implemented in many modern commercially available batteries due to its cheap price, longevity and high energy density.
[21] Li4Ti5O12 has the second largest market share of anodes, due to its stability and good rate capability, but with challenges such as low capacity.
Furthermore, Silicon has the advantage of operating under a reasonable open circuit voltage without parasitic lithium reactions.
[23] As a result, composite hierarchical Si anodes have become the major technology for future applications in lithium-ion batteries.
In the early 2020s, technology is reaching commercial levels with factories being built for mass production of anodes in the United States.
It boasts a higher specific capacity than silicon, however, does come with the drawback of working with the highly unstable metallic lithium.
These SWCNTs help to preserve electron conduction, ensure stable electrochemical reactions, and maintain uniform volume changes during cycling, effectively reducing anode pulverization.
[36] The method is able to analyze how the stresses evolve during the electrochemical reactions, being a valuable tool in evaluating possible pathways for coupling mechanical behavior and electrochemistry.
[35][37] While the chemical driving forces are usually higher in magnitude than the mechanical energies, this is not true for Li-ion batteries.
[38] A study by Dr. Larché established a direct relation between the applied stress and the chemical potential of the electrode.
The term γ inside the logarithm is the activity and x is the ratio of the ion to the total composition of the electrode.
The novel term Ω is the partial molar volume of the ion in the host and σ corresponds to the mean stress felt by the system.
The result of this equation is that diffusion, which is dependent on chemical potential, gets impacted by the added stress and, therefore changes the battery's performance.
[40] In a vacuum tube or a semiconductor having polarity (diodes, electrolytic capacitors) the anode is the positive (+) electrode and the cathode the negative (−).
