- [Narrator] Today there are
different kinds of batteries based on the application
for which they will be used. These visuals show the
popular applications for each kind of battery technology. And it is clear from this chart
that lithium-ion batteries, invented back in the year
1991 are the most popular with over 35% share of energy storage. In this video, we are going to see why lithium-ion batteries
will continue their domination and in the future may even overshadow gasoline-powered
technologies by understanding the technology enhancements
happening in this area. Let's take a lithium-ion
cell used in a DSLR camera and explore its internal parts. You can see that electrons will flow between the sheets when we connect a load across the battery. This natural electron flow means that the electrons were stored
in an unstable condition before the load was connected. We need to better understand
this basic principle to understand the
technological advancements happening in lithium-ion batteries. Here, the unstable electrons are stored in a kind of container called graphite with a higher electrochemical potential, and before storing the
electrons should be separated from the atomic structure of an element. There is a metal called lithium
which has a high tendency to lose electrons from its outer shell and due to this lithium is
very reactive in nature. However, as part of a metal oxide, lithium atoms are very stable. Let's use an external power source. The positive side of the power source attracts the electrons. We use an electrolyte too, which blocks any electron flow through it, so instead they flow
through the external circuit and get trapped between
the graphite layers. Similarly, the negative
side of the power source attracts the lithium-ions
and they also get trapped in the graphite layers. Eventually the lithium-ions are stored with a higher electrochemical potential. As soon as we remove the power source and connect it to a load, all the electrons in the graphite
will flow through the load and hence we can get
electricity from this. There are three good characteristics
for an energy source. Low cost, high energy
density and longer life. Let's explore how the lithium-ion cell fares in these three aspects and what are the future trends. Let's first consider the cost factor of lithium-ion batteries. The capital cost required to set up a lithium-ion based
technology is way higher than its counterparts. However, when we compare the running cost of electric cars to gasoline cars, electric cars run at 1/3 of
the price of gasoline cars. The main reason for the high capital cost is the presence of nickel and cobalt in the metal oxide compound. Moreover, battery makers
use these two metals in greater quantities than lithium. Due to this reason, the cost
of a lithium-ion battery is almost six times
that of a lead acid one and three times that of a
nickel metal hydride battery. However, the good news is that the cost per kilowatt hour of a
lithium-ion battery technology has been dropping at a rapid
rate over the last few years, so that in the future it might overcome the capital cost hurdle. Lithium-ion batteries provide
much higher energy density than any other battery technologies but are greatly inferior to
gasoline's energy density. The most crucial part which
affects the energy density is the storage medium of
lithium-ions and electrons. In a Tesla cell, the
storage medium is graphite. Scientists are now trying
a breakthrough technology by replacing the storage
medium graphite with silicon. With this technique it
is possible to multiply the energy density by almost 4.4 times. However, silicon causes
an unacceptable level of volume expansion and compression during each cycle. To take advantage of the high
energy density of silicon but to avoid its negative effects, some manufacturers have
started using 5% silicon mixed in with the graphite. Now let's get it to the most crucial part, the life of lithium-ion batteries. The lithium-ion batteries
of your old laptops used to die in one year. However, now they are easily giving three to four years of life. How do lithium-ion batteries die? To understand how researchers
have been able to improve the longevity of lithium-ion batteries and why they are continuing
this improvement, we need to understand the mechanism behind the death of a lithium-ion battery. Generally, a lithium-ion
battery fails after a few years even if you don't use it. This capacity loss is not abrupt. In fact, the process is electroless which means it does not
require any electricity flow. As per the operation discussed earlier, when the lithium ions are
flowing through the electrolyte, they are covered with a coating
called a solvent molecule. During the very first charge, the lithium-ions along
with the solvent molecules react with the graphite
and form an SEI layer. The SEI layer is a blessing in disguise because it allows the
lithium-ions to pass through it. The SEI layer helps to
avoid direct contact between the electrons and the electrolyte, thus saving the electrolyte
from degradation. Assume after the lithium-ion
cell is charged for some time, we remove the power supply, now the lithium-ion
cell is an open circuit. Even though the SEI layer tries to prevent the electrons from entering it, a small amount of
electrons in the graphite can still tunnel through it. Due to some porous
portions of the SEI layer, the solvent molecules
present in the electrolyte can easily enter into it. The solvent molecule reacts and forms an SEI layer again. Here we can observe that the SEI layer becomes thicker than before and simultaneously the
electrolyte is consumed. It is interesting to note that the degradation process
of your lithium-ion battery is a very slow process when
there is an open circuit. This process of lithium-ion cell death that we discussed above
will be accelerated many times during an actual operation. Let's see how. This is because the
movements of the lithium-ions bring more solvent molecules, thus the thickening of the
SEI layer is accelerated. This process consumes active
lithium-ions and electrolyte and that's why the life of the battery is significantly shortened depending on the number of cycles. From this discussion, it can be seen that the
SEI plays a dual role in the battery performance. On the one hand, it
protects the electrolyte from degradation and will support the main working of the battery. While on the other hand, it
consumes cyclable lithium-ions and electrolyte inside the cell which leads to the death of the battery. However, the longevity of
battery can be scalable up to a certain limit with the help of an electrolyte additive. This is like a secret sauce in a recipe that slows down the degradation process and helps to improve the battery life. Currently, Tesla batteries last for around 3,000 cycles
or around seven years and researchers are
putting their best efforts into extending this to 10,000 cycles, which is equivalent to
25 years of battery life. Today, almost all valuable
electronic gadgets are using lithium-ion batteries but it is interesting to note that there are slight changes in the chemical composition
of the metal oxides used. This is because factors
like cost, life cycles, and energy density vary depending upon the type of application. The discussions so far
have clearly explained how lithium-ion batteries
are getting better in terms of energy density and longevity. A recent innovation in
lithium-ion battery technology has given a big boost to the safety of lithium-ion batteries. This technology uses
an aqueous electrolyte with halogen intercalation. In this technique, the
addition of the helper halogen to the metal oxide side increases the mobility
of the lithium-ions. As the electrolyte is
a salt in water type, it can resolve the issues of flammability and it also increases the
mobility of the lithium-ions. The automobile industry will decide the future of lithium-ion batteries. To achieve greater adoption
in the automobile industry, lithium-ion batteries need
to be more competitive in terms of cost, life and energy. A new technology called
a lithium-air battery has shown an energy density
equivalent to gasoline under laboratory conditions. With its continuing improvements and all of the three aspects, the lithium-ion battery can definitely become the future power source
of the automobile industry. We hope this video has given
you a clear understanding about the future of lithium-ion batteries. Thank you!
