This paper aims to highlight a few extremely sensitive subjects nowadays, such
as: Energy storage; energy storage solutions; storage of electricity; methods
of electricity storage; the impact of storage technologies on the environment;
lithium – ion batteries Ion methods to improve this storage technology.
II) KEY WORDS:
Energy Storage, Storage of Energy, Storage Methods, Storage Technologies,
Environmental Impact, Lithium Ion Batteries, Storage Technologies of the
is the ability of a body, a mobile, to produce an external impact, for example
a force produced at a certain distance. Energy can be found in several forms,
such as mechanical energy, potential energy, thermal energy, nuclear energy,
chemical energy, etc.
energy is indispensable to life. Every body needs energy to move from the
simplest to the most complex. Movement means evolution. Without moving life
would not be possible on Earth.
present, besides producing the most efficient energy, which has the least
impact on the environment, is a problem: What can be done with the excess
it is known that renewable sources (wind, water, sun, biomass, etc.) are
intermittent and that we can not dispose of electricity from these sources
throughout the year. During one year there are times when it is possible to
produce electricity from renewable sources as much as needed. Because of this,
in certain times, either day or year, we have to reduce or stop the production
of electricity from conventional sources (fossil fuels), which entails
current fossil fuel economy is exposed to a serious risk due to a number of
factors, including the continuing increase in oil demand, the depletion of
non-renewable resources, and the dependence on politically unstable
oil-producing countries. Another worrying aspect of the current fossil fuel
economy is associated with CO2 emissions that have grown dramatically over the
past 30 years.
is already known that some plants such as nuclear or thermoelectric power take
a long time to reduce activity or stop, and overloading long distance
transmission lines would cause major damage to the National Energy System, or
even on the Interconnection Network of Europe.
being said, the same question is resumed: How can we use the excess electricity
produced from renewable sources without compromising the production of
conventional electricity (how many still exist)?
are ways to store electricity either in other forms (hydro energy) or store it
in various devices and equipment (storage in batteries), where it can be stored
and used when needed.
investments in the exploitation of renewable energy resources are on the rise
worldwide, paying special attention to wind and solar power plants (RCE), which
are the most mature technologies. Flashing these resources requires high efficiency
energy storage systems. Electrochemical systems, such as batteries and
superconductors, which can efficiently store and supply energy on demand in
independent power plants, but can also provide energy quality and leveling the
load of the grid in integrated systems, play an essential role in this area.
Presentation of produced and unused power storage technologies – description of
various types of storage technology
energy production, largely based on fossil fuels, is a major problem in the
world economy. This includes the steady increase in oil demand, the depletion
of non-renewable resources, and the dependence on politically unstable
oil-producing countries. Another worrying aspect of the current economy on
energy production from fossil fuels is CO2 emissions, which have risen to an
alarming level in recent years.
reduce greenhouse gas emissions and mitigate the effects of climate change, we
need, among other things, an increase in the share of renewable sources in
energy production worldwide. The issue of CO2 emissions and air pollution in
large urban areas can be solved by replacing the internal combustion engine
with the zero-emission CO2, ie electric cars or vehicles with controlled
emissions, ie hybrid electric cars.
a result, investments for the exploitation of renewable sources are growing
worldwide, with particular attention to wind and solar power plants, which are
among the most mature technologies. The blink of these resources requires
high-efficiency electrochemical energy storage systems such as batteries and
super capacitors. They can store and deliver energy on demand in independent
power plants, as well as ensure energy quality and electrical balancing in
integrated systems, their role being crucial in this area.
– Ion batteries are composed of cells that use lithium interlacing compounds as
positive and negative materials. As the battery performs the cycle, the lithium
ions move between positive and negative electrodes. Because this cell is
charged and discharged, lithium ions continuously move back and forth between
positive and negative electrodes.
material from which the positive electrode is composed may be a metallic oxide
with a layered structure such as lithium cobalt oxide (LiCoO2) or a tunnel-like
oxide such as lithium manganese oxide (LiMn2O4) on a collector current from
material from which the negative electrode is composed may be a graphite carbon
or a layered material on a copper foil collector.
the loading – discharge process, lithium ions are introduced or extracted from
the interstitial space between the atomic layers of the active materials.
of the currently marketed batteries use LiCoO2 as a positive electrode
material. Lithium cobalt oxide has the following advantages:
Provides good and very good electrical performance;
It is easy to prepare;
Has safety features;
Not affected by the loading / unloading process and moisture.
low-cost or higher-performance materials such as LiMn2O4 or Cobalt Nickel
(LiNiCoO2) have been introduced to enable the development of enhanced
performance cells and batteries. Batteries that were first marketed contained
coke electrode materials. As improved graphite became available, the industry
focused on graphite carbon to make the negative electrode, as it has a higher
specific capacity and improved lifetime.
Lithium – Ion battery market has grown in one decade, from research and
development to sales of over 400 million units in 1999. The market value was
estimated at nearly $ 2 billion in 2001.
Ion batteries are widely used on consumer electronics (phones, laptops) and
personal data assistants as well as military electronics (radios, mine
detectors and thermal weapons).
the near future, it is intended to use Lithium Ion batteries in applications
such as aircraft, spacecraft, satellites and electric vehicles or electric
that can affect battery performance
factors influence the operational features, capacity, power consumption and
performance of a battery. It should be noted that due to the many possible
interactions, these effects can only be presented as generalizations and that
the influence of each factor is usually higher under the more stringent
operating conditions. For example, the storage effect is more pronounced not
only with high storage temperatures but also with long shelf-life as well as
more severe evacuation conditions after storage. After a certain storage
period, the observed capacity loss (compared to the fresh battery) will usually
be higher for heavy loads compared to light-discharge loads. Similarly, loss of
capacity observed at low temperatures (compared to normal temperature
discharges) will be greater for heavy loads than for light or moderate
discharges. Battery specifications and standards typically list the specific
test or operating conditions on which standards are based on the influence of
these conditions on the performance of the battery.
addition, it should be noted that even in a cell or battery there will be
performance differences from manufacturer to manufacturer and between different
versions of the same battery (such as standard, heavy or premium). There are
also performance variables in a production batch and from one batch to another
that are inherent in any manufacturing process.
voltage level of a battery
references are made to the voltage of a cell or battery, references such as:
Theoretical voltage is a function of anode and cathode materials, composition
of electrolyte and temperature (usually indicated at 25 degrees Celsius);
Open voltage is the voltage at a non load condition and is usually
approximately equal to the theoretical voltage;
The closed circuit voltage is the voltage in the charging state;
Rated voltage is generally accepted as typical for battery operating voltage,
eg 1.5 V for zinc-manganese dioxide battery;
The working voltage is more representative of the actual operating voltage of
the battery under load and will be less than the open voltage;
Average voltage is the voltage that occurs during battery discharge;
Middle voltage is the center voltage during cell or battery discharge;
The end or decoupling voltage is designated as the end of the discharge. The
end-to-end voltage may also depend on the application requirements. Using the
lead-acid battery as an example, the theoretical and open circuit voltages are
2.1 V, the nominal voltage is 2 V, the working voltage is between 1.8 and 2 V
and the end voltage is usually 1.75 V at moderate and low temperature and 1.5 V
for engine loads. When charging the voltage varies between 2.3 and 2.8 V. When
a battery (battery) is discharged, its voltage is less than the theoretical
voltage. The difference is caused by losses due to cellular resistance and
polarization of active materials during discharge.
is also shown in figure 1. Ideally, discharge the battery is done until the
active materials are consumed and the capacity is fully utilized, after which
the voltage drops to zero. Under actual conditions, the discharge curve is
similar to the other curves in Figure 1. The initial cell voltage under a
discharge load is less than the theoretical value due to the internal
resistance of the cell, as well as polarization effects on both electrodes.
Voltage also decreases during discharge as cellular resistance increases due to
accumulation of discharge products, activation and concentration, polarization,
and related factors. Curve 2 is similar to curve 1 but represents a cell with a
higher internal resistance or a higher discharge rate or both compared to curve
1. As cell resistance or discharge current is increased, download decreases and
download has a more sloping profile.
Figure 1 – Battery
2 – Example of the discharge curve of a Lithium Ion battery
– Ion Batteries
the technologies used to store excess energy produced from renewable sources
are Lithium Ion Batteries. These are considered the best for sustainable
transport, as they can guarantee the progressive dissemination of energy for H.E.V.
(hybrid electric vehicles), P.H.E.V. (electric vehicles with sockets), B.E.V.
(vehicles with electric batteries).
H.E.V. the synergistic combination of I.C.E. (internal combustion vehicles)
with an electrochemical battery ensures high fuel efficiency with proven fuel
economy benefits. Thus, pollutant emissions control as well as driving
performance are similar to pure or even higher gasoline engines.
research is being done to solve the problems of large – scale diffusion of
Lithium – Ion batteries for R.E.P. and E.V., but also for the development of
advanced and efficient Lithium batteries.
3 – Lithium Ion battery (right) and its use in H.E.V. (Left)
– Ion batteries are light, compact and operate at a voltage of 4 V with an
energy of between 100Wh / kg and 150Wh / kg. In its most conventional
structure, a lithium-ion battery contains a graphite anode (e.g., mesh carbon
microbes, MCMB), a cathode formed of a lithium metal oxide (LiMO2, e.g. LiCoO2)
and an electrolyte consisting of a lithium salt solution) in a mixed organic
solvent (e.g., ethylene carbonate-dimethyl carbonate, EC-DMC) incorporated into
a separating felt. This pattern is shown in the figure above.
Due to the high energy content, lithium – ion batteries have triggered the
growth of popular devices, such as mobile phones, MP3s, etc. In the figure
below we find the production of Lithium Ion batteries per year, divided by the
most popular fields.
4 – Evolution of lithium – ion battery production on the most demanding areas
first glance, the electrochemical process underlying the operation of the
Lithium Ion battery seems rather simple, consisting of the reversible exchange
of Lithium Ion between the two electrodes. However, in practice, operation of
this battery requires the central processes to continue. In Figure 5 (A) it can
be seen that the REDOX process at the MCMB anode evolves around 0.05 V against
Li and that of the LiCoO2 cathode evolves to about 4 volts to Li. The onset of
current in the electrolyte is evidenced by the occurrence of reduction or
oxidation processes that define its range of stability. The figure shows how
the electrolyte range extends from about 0.8 V to Li at 4.5 V to Li and that
the MCMB anode works well beyond the electrolyte stability and the cathode is
only at its limit.
is also shown in Figure 5 (B), which shows the voltage intervals of the MCMB
anode and of the LiCoO2 cathode compared to the stability interval of the most
common organic liquid electrolytes. In conclusion, the C / LiCoO2 battery is
thermodynamically unstable at these electrolytes.
in practice, the battery operates under kinetic stability.
5 (A) – Volume profiles – Cyclic metric (potential against Li / Li +)
components of the Lithium Ion battery: anode and cathode (green), electrolyte
(blue). Contra-electrodes: Super P carbon; electrolyte: EC – DMC, LiPF6
– C / LiCoO2 electrode combination voltage ranges compared to the most common
liquid electrolyte stability range
initial decomposition of the electrolyte results in the formation of a
protective film on the surface of the anode, thus ensuring the continuity of
the loading and unloading processes. A potential hazard is represented by the
oxidation processes at the cathodic side. Under suitable conditions, the
battery operates below the oxidant limit of the electrolyte. However, if
unexpected events, such as accidental overload, this limit is exceeded, no
cathode protection film is formed and the electrolyte continues to oxidize,
which greatly contributes to the acceleration of cell damage.
the whole, both the anode and cathode decomposition processes involve the
consumption of active masses and electrolytes, accompanied by gas evolution.
This results in loss of battery capacity (irreversible initial capacity) and
hazards. Both loss of capacity and gas evolution are undesirable phenomena,
which must be carefully controlled (especially during the production process)
to ensure adequate battery performance.
6 – Operating principle of S.E.I. in a Lithium-Ion battery C / LiCoO2. Source:
US Department of Energy
short – term progress of Lithium – Ion battery technology
scaling of standard Lithium Ion battery chemistry for their application in the
field of transport (sustainable vehicles) or energy (renewable power plants) is
problematic. Issues such as safety, life cycle, cost, wide temperature range
and availability of materials hinder their good implementation. On the other
hand, the intrinsic benefit of lithium technology and its use in these
important evolutionary markets have spawned worldwide efforts to solve these
problems in order to place the lithium ion battery in a dominant position in
both E.V. and R.E. sectors.
is now universally accepted that advances in lithium battery technology require
innovative chemists for both electrode and electrolyte components. The goal is
to identify materials with higher performance than those offered by the anode and
cathode used in common variants. Indeed, the chemistry of Lithium Ion batteries
has not changed constantly since their introduction in the early nineties. As
already mentioned, most of the production is still based on a graphite anode
and a lithium cobalt oxide cathode, separated into a liquid solution of a
lithium salt (e.g. LiPF6), in a mixture of organic solvents CE – DMC).
general, the performance of any device depends directly on the properties of
the materials it is made of, and this also applies to Lithium Ion batteries.
Thus, steps before lithium rechargeable batteries can only be achieved by
discovering new electrodes and electrolytes.
the world’s R & D efforts are geared to replacing the current battery components
with more energy-efficient, power-efficient, cost-effective, durable, and safe
approaches to achieving this goal are focused on two main directions:
1) Replacement of graphite
and cobalt lithium oxide with alternative anodic and cathode materials with
higher capacities and lower costs;
2) Replacement of liquid
electrolyte solutions with organic carbonate with safer and more reliable
in specific energy
now, the specific energy of Lithium Ion batteries has increased mainly by
improving manufacturing, by using progressive lighter cases (eg switching from
stainless steel to aluminum) or optimizing cell design, electrode materials. A
limit has been reached beyond which the additional increase in specific energy
requires modification of cellular chemistry.
metal alloys (eg Lithium – Silicon, Lithium – Staniu) are among the most
promising in making negative electrodes, replacing carbon-based common
materials. These alloys have a specific capacity that exceeds that of graphite
– lithium (about 4000mAh / g Li – Si and about 990 mAh / g Li – Sn versus 370
mAh / g Li – C. Unfortunately, Lithium alloys can not be used as such in
lithium cells, the main problem being expansion – the high volume contraction
that occurs during load-discharging processes, these volume changes induce
mechanical stresses with the resultant disintegration of the electrode with
consecutive failures during the loading / unloading cycles.
7 – Effects of volume change associated with the process of loading and
unloading of metal alloy electrodes into lithium-ion cells. Figure shows the
scheme for introducing the lithium ion and changing the corresponding volume
during discharge (left-hand side); compared to volume changes: clean material
(dark columns) Li + interleaved material (light columns – left image) and LiM
image before and after cycle (right)
problem has been solved by optimizing the electrode morphology by developing
nanostructured configurations capable of buffering large volume changes and
thus ensuring a long life of the combined cycle with a high specific capacity.
A good example is provided by electrode structures based on metal carbon nanoparticles
(eg tin – carbon).
approaches have been adopted to promote the performance of Li – Si metal
electrodes. The results obtained by various laboratories around the world have
demonstrated that the long cycle life can be achieved by exploiting appropriate
electrode changes. Due to these important achievements, lithium metal alloys
are now ready for use in the production of lithium batteries. An example is the
Sn – Co – C alloy, which is already used as a new material in the anode construction
of a commercial battery. The actions for promoting anodic amplification are
also directed to graphite modification by coating the surface with thin metal
layers. It is expected that this treatment, by promoting the improvement of
conductivity, will lead to improved electrode performance – especially in the
low temperature range.
into new anodic materials also addresses titanium oxides. In this range of
materials, anatase titanium oxide (TiO2 or TO) and lithium titanium oxide (Li4Ti5O12
or LTO) are attractive negative electrodes for advanced Lithium Ion batteries.
The lithium insertion potential of these oxides is between 1.2 V and 2 V,
relative to Simple lithium (i.e., in the window of regular organic electrolyte
stability). LTO has a rich Li structure. This electrode material is
characterized by an electrochemical process in two phases that develops with a
flat voltage profile. The theoretical capacity is lower and the voltage level
is higher than conventional graphite, ie 170 mAh / g versus 370 mAh / g and 1.5
V vs. 0.05 V. Both differences can lead to lower specific energy; however,
interest in Li4Ti5O12 remains high due to its specific properties including:
1) a very low volume change
(<1%) during the cycle, which leads to a high stability of the cycle; 2) no electrolyte decomposition, hence no S.I.I. formation; 3) high speed and very low temperature load / discharge capacity; 4) high thermal stability in both loaded and unloaded state. Indeed, the LTO is currently virtually exploited to develop batteries for P.H.E.V. (electric vehicles with a socket). Titanium oxide (TO) has a brookite structure. This anodic material offers important benefits in terms of cost efficiency, safety and environmental compatibility. The maximum theoretical capacity is 335mAh / g, corresponding to the introduction of one gram of Li per TiO2, associated with a complete reduction of Ti4 + to Ti3 +. The electrochemical performance of TO strongly depends on the particle morphology. Consequently, research on this material focuses on the manufacturing process appropriate to be produced in nanoscale or nanotreated forms, as can be seen in Figure 8. Attempts to develop morphologies that provide efficient electronic pipeline networks to increase utilization mass and kinetics of electrodes are in progress.