Batteries have become one of the essential devices in our day to day life. We use them to wake up, brush our teeth, communicate with our relatives, listen to music while doing sports, play a video game while waiting for the bus, work from our laptop or get around on a scooter.
They practically go unnoticed throughout the day, but there they are, giving us energy coverage and a lot of trouble when they run out. We probably haven’t realized it, but a person living in a developed country may need several dozen batteries in their daily life. In the European Union (EU) alone, more than 200 tons of batteries enter each day for use in electronic devices. If we include other applications such as industrial or automotive, this figure exceeds one million tons per year.
even more batteries
The use of this energy storage technology, based on electrochemistry, experienced strong growth accompanied by the development of consumer electronics. However, its growth will be even greater in the coming years, since it is called to lead the new change in energy and mobility paradigm.
Batteries will allow us to store the energy obtained from renewable sources and use it when it cannot be produced, and they are an essential part of electric cars. In terms of global energy demand, it is expected that in 2030 it will reach 2,600 GWh. In short, in this decade we are going to need more batteries, with greater storage capacity, faster to charge and, also, more durable.
One of the most pressing problems with batteries is their durability. In fact, we have all experienced the gradual loss of the capacity of some portable electronic device, such as our mobile phone. This is usually presented as a loss of autonomy (duration). This phenomenon also worsens with the passage of time. To understand how batteries degrade, we need to understand how they work.
How Lithium Ion Batteries Work
A lithium ion battery is made up of a set of cells stacked in a prismatic or cylindrical shape. Each cell is in turn made up of two electrodes (one negative and one positive), separated by a membrane and an electrolyte, which is a solution through which the ions move to the electrodes during the battery charging and discharging processes. In addition, the electrodes are connected to electronic conductors (current collectors) through which the electrons circulate.
The anode is made of graphite, while the cathode is usually graphite with lithium and a metal compound, such as NMC (a combination of nickel, manganese, and cobalt). During the charging process, lithium ions are inserted into the anode, while when we use the battery (actively or passively), these ions go to the cathode. Therefore, in a battery there is always a flow of species and electrons from one side to the other. As we will see below, this movement has its consequences on the cell, causing its deterioration.
Why do batteries degrade?
The trips made by the lithium ions through the electrolyte, the membrane and, above all, the electrodes, involve many phenomena that end up degrading these components and, finally, the battery.
The first of these is known as solid electrolyte formation. In the process of charging and discharging, lithium ions are inserted into the electrodes. This is known as collation. When the electrodes are full, the ions that cannot enter react with the graphite on the surface, giving rise to a whitish layer which, as its name suggests, is a solidification of the electrolyte.
This process usually occurs from the first charge of the battery and is responsible for a loss of 10% of its capacity, since this layer acts as a kind of barrier for the diffusion of ions. The phenomenon increases with the increase in battery temperature and can also give rise to what is known as thermal runawaya series of chain reactions that give off heat and are very difficult to stop.
electrodes
Regarding the electrodes, by definition, the positive one is the one with the highest potential. In the case of lithium-ion batteries, the cathode is positive and the anode is negative. In the electrodes there is also a deposition of metallic lithium on the surface of the anode. This occurs at low temperatures and high current levels (such as fast charging).
The intercalation and deintercalation of the ions also cause important structural changes in the electrodes. Some internal stresses are produced in the material that end up with the cracking of the electrodes and, therefore, the loss of storage capacity. In addition, new surfaces may appear where the two previous phenomena may occur, further aggravating the problem.
In addition to the above, there are other phenomena, such as oxidation, electrolyte decomposition or acid attack, which cause both the electrodes and the electrolyte to degrade. All of them are aggravated both by use and by temperature or charging speed.
Can we prevent its deterioration?
Once we have identified the mechanisms of battery degradation, we can monitor their state of health. In addition to controlling the above aspects, it is possible to introduce agents that, either autonomously or driven by a precursor, start a battery healing process.
Just as blood heals our wounds, it is possible to manipulate materials to incorporate self-repair mechanisms. Precisely, this line of work is one of the main proposals of the new European battery strategy and the use of microencapsulated repair agents, carbon nanotubes or active carbon to fix the cracks is proposed.
In order for the self-repair process to start at the right time, it will be essential to properly monitor the state of health of the batteries. For this, fiber optics can be used, for example. In addition, it is essential to better protect the components. This can be done using two-dimensional materials, such as graphenewhich will exert a passive internal defense, minimizing deterioration.
In short, thanks to nanotechnology, there are several routes that are currently being explored to considerably improve the health of batteries. Therefore, it will be possible in a reasonable period of time to have devices with greater durability. Our problem will then be different: we will have to look for alternative, more sustainable manufacturing materials, so as not to replicate dependence on fossil fuels. In this sense, new technologies are being considered, such as sodium batteries, silicon electrodes or double graphite electrodes of recycled origin.
Reference article: https://theconversation.com/podran-manufacture-batteries-that-do-not-degrade-with-use-175452
