How a lithium battery works

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Martí Micolau

What is a lithium battery

Basically, one lithium battery (or rather, a lithium-ion battery, or Li-ion) is composed of a series of chemical components enclosed in a casing, connected to the outside through two metal ends, one positive and the other negative.

When these two ends are brought into contact with each other (through a conductive material), a reaction is triggered that causes the internal particles of the battery to join and separate continuously, in order to produce other chemical elements, called ions.

In particular, the ions are responsible for producing the energy to power the battery, while the electrons are responsible for generating the electricity necessary to operate the device to which it is connected (smartphone, tablet, notebook and so on).

Lithium batteries, thanks to their particular structural and chemical characteristics, are currently widely used both in the field of electronics (smartphones, tablets, notebooks, uninterruptible power supplies, wearables and so on) and in very different sectors, such as that of hybrid and electric cars.

The aim of this guide will be to explain, in simple terms, the criterion underlying the operation of rechargeable lithium-ion batteries and the reasons for the most common problems encountered on them.

A brief history of lithium batteries

The history of lithium batteries begins way back 1912, when the first accumulator of this type was invented by Gilbert N. Newis: these were non-rechargeable cells, but able to provide much higher voltages than the other batteries in use at the time, thanks to the presence of lithium.

This invention, however, was not considered particularly useful until 1970, when the chemist M. S. Whittingham managed to develop a prototype of rechargeable battery exploiting, in fact, lithium.

However, even this invention did not find the desired success: since lithium is a light metal but extremely unstable, the batteries designed at the time carried with them a high risk of explosion; therefore complicit in the dangers associated with the manipulation of lithium in this sector, and the collapse of the price of oil (basic element for all rechargeable batteries in use at the time), the development of rechargeable lithium batteries was shelved.

This was until 1991, the year in which J.B. Goodenough made the first Li-Ion battery for Sony, changing the construction material of the cathode and increasing its power; the project was further refined, in the same year, by Akira Yoshino, which succeeded in completely eliminating lithium in pure form from rechargeable batteries, replacing it with lithium ions, that is, with particles capable of "detaching" from the lithium atom following a chemical reaction.

This last step was of fundamental importance for the safety of what, to date, are the most used rechargeable batteries in the world: starting from that year, thanks to continuous studies on the chemical structure of the battery components and the With the gradual introduction of safety mechanisms, the risks associated with lithium-ion batteries have been extremely reduced, in the face of an increase in power, energy storage capacity and duration over time.

Note: Whittingham, Goodenough and Yoshino were awarded the Nobel Prize in Chemistry in 2019, precisely for the development of Li-ion batteries.

How a lithium battery works

A lithium-ion battery is made up of one or more electronic parts capable of generating energy, called celle; each cell is mainly composed of three elements: a positive electrode, called cathode; a negative electrode, called anode; and a chemical, called electrolyte.

Batteries of this type are generally rechargeable, therefore capable of both accumulating energy (in the charging phase) and releasing it (in the discharge phase): this mechanism is made possible by the flow of ions and electrons, ie small particles that "detach" from the atoms, which they travel from the anode to the cathode - and vice versa - through the electrolyte.

Let me better explain the dynamics of this mechanism. When the battery collects energy and is, that is, in charging phase, cathode "Gives" some of its lithium ions, which travel through the electrolyte material, following the internal circuit, and are accumulated inside theanode, in which they flow continuously, generating energy and being negatively charged. When the lithium ions from the cathode stop circulating through the electrolyte material, the process stops and the battery is charged.

When, on the other hand, the battery gives up energy and is in discharge phase, the reverse process takes place: the ions, following the external circuit of each cell in the opposite direction, circulate from the anode to the cathode, supplying energy to the battery (and to the connected device); when they reach their destination, they combine with the electrons present in the cathode, depositing there. When the anode has no more lithium ions to release, the process stops: the battery is completely discharged.

It is precisely the distance traveled by the lithium ions that determines the time required to charge and discharge a battery: since the first of the two phases takes place on an internal circuit and the other on an external "path", it goes without saying that the battery charging is much faster than discharging.

However, as you certainly know, the autonomy of a lithium-ion battery is extremely variable, based on the type of device it powers and the activities that are carried out!

Each cell also implements some security mechanisms aimed at reducing problems due to overheating: if the cell and / or the battery reaches a temperature that is too high during the charging phase, the flow of incoming energy is immediately interrupted and, consequently, it can no longer receive charge.

Although lithium-ion batteries are dominated by the same operating principle, they are not all the same: there are in fact different types and characteristics, which vary mainly due to the materials with which the anode, cathode and electrolyte are made.

For example, most of the batteries found on smartphones, tablets, notebooks and power banks are of the type Lithium-Cobalt Oxide / LCO (o LiCoO2): it is formed by a cobalt oxide cathode and a graphite anode; electric car batteries, on the other hand, exploit the chemical combination lithium, nickel, manganese e cobalt oxide / LiNMC (LiNiMnCoO2): the cathode, in this case, is made of nickel, manganese and cobalt; the cathode present in the batteries used for modern uninterruptible power supplies, on the other hand, uses a cathode atlithium and manganese oxide, usually with addition of cobalt.

Pros and cons of lithium batteries

The introduction of lithium-ion batteries has brought several benefits to the world of electronics. To begin with, unlike nickel-cadmium batteries (or NiCd, pronounced "nicad"), Li-Ion batteries they do not suffer from the memory effect: if I had never heard of it, it is a phenomenon that "makes a battery believe" that it is less capacious than its initial condition.

The memory effect is extremely frequent in NiCd batteries and is “activated” when, for some reason, the battery is recharged when there is still residual energy inside it; to get things back to normal, you have to completely discharge the battery and recharge it immediately afterwards.

Another big advantage of lithium-ion batteries is that they are relatively read compared to the amount of energy they are able to store; again, to build batteries of this type the use of cadmium is not foreseen, an extremely toxic material and still used today, albeit to a much lesser extent than in the last decade, for the production of rechargeable batteries.

Not everything, however, "is roses and flowers": although, over time, safety mechanisms have been implemented capable of minimizing the possibility of overheating and consequent fires, you must always pay attention to heat, as lithium batteries suffer a lot from this effect: the battery should always be kept at room temperature and the cells should not be recharged when the device is already hot, as performance drops may occur due to the difficulty of " retain ”energy.

Also, the batteries should be charged at a appropriate voltage: the use of too “powerful” battery chargers could significantly reduce the life and efficiency of each cell, as well as cause danger accumulations of gas (naturally released during the charging / discharging phases), which could cause sudden and dangerous explosions.

Another aspect to pay attention to, especially with regard to electronic devices such as smartphones, tablets and notebooks, is the minimum charge level. Let a lithium-ion battery reach it 0% of charge can negatively affect its life: if the transit of ions from the cathode to the anode is completely interrupted, the lithium particles could irreparably damage the latter, decreasing the performance of the battery. Furthermore, the device may have some difficulty or take longer to turn on again, since the transit of ions must be restarted "from scratch".

For this reason, it is good practice avoid completely discharging an electronic device powered by a Li-ion battery, before recharging it; for the same reason, if you plan not to use an electronic device for a long time, take care to store it with the battery charged to at least 50%: the small and inevitable loss of charge due to inactivity, in this way, will hardly cause damage of the cells.

Given its characteristics, it must be said that a lithium-ion battery has a limited duration: manufacturers generally define this parameter in terms of charge cycles, after which the battery cells may not be able to accumulate more energy properly, due to the wear of the anodes or the chemical material inside. Don't worry, though: a well-managed battery - the ideal would be to constantly maintain a 30-80% charge range of your device - can remain "healthy" even for more than five years (despite an obvious drop compared to the original capacity , but not so drastic as to compromise its use)!

For more "practical" information, I invite you to read my tutorials on how to charge the smartphone battery and how to increase the battery life of a notebook.

How a lithium battery works

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