Two hundred years after Volta's invention
of the first electrochemical power source, Ron Dell reviews progress
in battery technology
voltage and stable voltage plateau over most of the discharge
energy content per unit mass (Wh kg1) and
per unit volume (Wh dm3)
power output per unit mass (W kg1) and per
unit volume (W dm3)
temperature range of operation
resistant to abuse
Safe in use
and under accident conditions
readily available materials that are environmentally benign
electrical efficiency (Wh output/Wh input)
many chargedischarge cycles
accept fast recharge
overcharge and overdischarge
The year 2000 is the bicentenary of Volta's
pile, the first source of continuous or current electricity. From
small beginnings, the applications for portable electrical power
have mushroomed in recent years. Sixty years ago domestic uses for
batteries were largely confined to flashlamps, radio sets and
starter batteries for cars and motorcycles. Modern households
typically have 40-50, hidden away in all sorts of consumer
products - from clocks and watches to personal CD players and
mobile phones. Away from the home there are many other
applications, particularly for large batteries. Examples include
the standby batteries for emergency use in hospitals, hotels,
department stores, telephone exchanges etc; traction batteries for
electric vehicles (tugs, tractors, forklift trucks, wheelchairs,
golf carts); batteries for solar panels or wind generators;
defence batteries in armaments, missiles, submarines, torpedos.
Many of these applications demand a performance that is barely
matched by traditional batteries - which explains the ever-present
demand for new and better varieties.
Batteries are of two general types: primary
cells that are discharged once and then discarded and secondary
batteries that are recharged and used again. One of the
interesting features of batteries is the very wide range of sizes
in which they are manufactured, from a stored energy content of
ca 0.1 watt-hour (Wh) for a watch or calculator battery,
to 100MWh for a load-levelling battery in the electrical supply
industry (Table 1). Can there be any other industry in
which products are produced in such a size range? Estimating the
market for batteries is notoriously difficult. In 1991 the world
battery market was estimated at US$21,000m, with 40 per cent by
value attributable to primary batteries and 60 per cent
secondaries. Undoubtedly, the market has grown since then. A more
recent (1999) estimate of the Japanese market is ca
US$8000m, of which 25 per cent is due to primary cells and 75 per
cent to secondary batteries.1
Even if these figures are only approximate, this is clearly a
major industry worldwide.
1. Battery sizes and applications
Watches, calculators, heart pacemakers
Mobile phones, laptops
Portable radio and TV, flashlamps, toys, video cameras,
Starting batteries for cars, trucks, buses, boats etc.
Traction batteries for lawnmowers, golfcarts, invalid chairs
Remote area power supply
Lighting, water pimping, telecommunications etc
Electric vehicles, forklift trucks, tractors, torpedoes
Standby batteries, un-interruptable power supply (UPS)
Electicity supply industry, load levelling, peak shaving,
Someone once described a battery as 'a
livelihood to the manufacturer, an irritation to the user and an
addiction to the researcher'. If the latter attribute is true of
primary batteries, how much more so is it for rechargable
batteries where the technical challenge of developing a battery
capable of being charge-discharge cycled hundreds or thousands of
times is formidable. And we must meet this goal within a framework
of producing a product that is economically viable, safe to use
and environmentally friendly.
The Box above sets out in more
detail the specifications sought in a battery. The problem (and
the challenge) of developing new and better batteries lies in the
complexity of this specification. Not only are there some 20
criteria for a secondary battery, but these are often highly
interactive. For example, the available stored energy and the peak
power output both depend on the temperature; the peak power also
depends on the state of charge of the battery; the
charge-discharge cycle life of a secondary battery depends
critically on the depth to which it is discharged in each cycle,
and so on. All of these factors need to be quantified before we
can decide whether a battery is likely to be commercially viable
for a particular application. However, key factors are the stored
energy per unit mass and volume and it is here that modern
batteries, such as lithium-based batteries, come into their own.
How does a battery operate? A battery is
basically a simple electrochemical device to store electrical
energy as chemicals. It has certain essential components. The
negative electrode consists of a current collector and an active
component, often a metal such as finely divided zinc, lead or
cadmium, which is capable of being oxidised with the release of
electrons. The positive electrode also consists of a metallic
current collector and an active component, generally a higher
valent metallic oxide (eg MnO2,
PbO2, NiOOH, AgO) that is
capable of being reduced. The electrodes are separated by an
electrolyte that conducts ions, but which must be an electronic
insulator to avoid internal short-circuits.
1. Discharging an electrochemical cell
In most conventional batteries the
electrolyte is an aqueous solution such as ZnCl2,
KOH or H2SO4,
although some advanced batteries use ion-conducting ceramics,
polymers or molten salts. During discharge, electrons flow from
the negative electrode to the positive via this 'external load',
thereby doing electrical work.
The charging of a secondary battery is the
reverse of discharging (Fig 1). Given the apparent
simplicity of this scheme, and the wide range of elements to
choose from in the Periodic Table, at first sight it is a puzzle
why developing new batteries has proved to be so difficult.
Indeed, it seems ludicrous when considering the sophistication of
the microchip in a modern laptop computer that the simple battery
should be the largest and heaviest component. It is the complex
and demanding user specification (see above) that poses
the challenge. The more the specification can be relaxed for a
particular application, the better the chance of meeting it.
By far the most common primary cells are
based on the zinc-manganese dioxide couple, either so-called
zinc-carbon cells (Leclanché cells) or alkaline manganese
cells. These both give 1.5V open circuit, but differ in a number
of important respects. Zinc-carbon cells (Fig 2a) have a
central carbon current collector immersed in the positive cathode
(a mixture of impure MnO2 and
carbon), a container of metallic zinc as the anode, and an
electrolyte of aqueous NH4Cl
and/or ZnCl2. These cells are
traditional and inexpensive.
Alkaline manganese cells (Fig 2b),
a superior and more expensive product, use finely divided zinc
powder as the anode and this fills the centre of the cell, with a
brass pin to make contact with the base. The electrolyte is
concentrated KOH solution and the cathode material - a mix of
chemically or electrochemically prepared MnO2
and carbon - forms a concentric annulus around the zinc powder and
the separator. Alkaline manganese cells have a long shelf life and
are particularly useful for high drain (power) applications, where
their useful life is several times that of zinc-carbon.
2. (a) Zinc-carbon battery; (b) Alkaline
manganese dioxide battery
The cheaper zinc-carbon cells are adequate
for low drain applications and for intermittent use (such as in
flashlights) where there is recovery time between uses, to allow
diffusion processes to remove polarisation at the electrodes and
restore equilibrium. Both types of cell are made by most
manufacturers in a variety of standard sizes and shapes. The
prismatic 9V cells, as used in smoke detectors, contain six small
cells wired in series.
Several manufacturers are now offering 3V
lithium-MnO2 cells. These
employ a lithium foil negative and an ion-conducting organic
electrolyte. They are available as cylindrical cells, using
spiral-wound electrodes ('jelly roll' configuration), or as button
cells. Their advantages include high gravimetric and volumetric
energy densities, high pulse rate capability, long shelf life and
the ability to operate over a wide temperature range (-40°C to
Button and coin cells are used widely in
watches and pocket calculators. They may be either alkaline
manganese cells (1.5V), zinc-silver oxide cells (1.5V), or 3V
lithium cells with several possible cathodes (usually MnO2
or CFX). There are also
zinc-air button cells, employing a fuel-cell type air cathode,
which find their main application in hearing aids. Altogether
there are over 40 different sizes and chemistries of button and
The lead-acid battery, invented by Planté
in 1859 and further improved by Fauré in 1881, is the most
widely used secondary battery. The electrode reactions of the cell
are unusual because the electrolyte, sulphuric acid, is one of the
reactants, as seen in the following equations for discharge:
| Pb + H2SO4
+ 2e- + 2H+
+ 2H+ + 2e-
| Pb + PbO2
On discharge, sulphuric acid is consumed
and water is formed, with the converse on charging. We can
therefore determine the state of charge of the battery by
measuring the relative density of the electrolyte (1.28-1.30 for a
fully charged cell).
Energy storage options
Ever since the start of the industrial revolution, fossil
fuels have provided the principal source of the world's
energy. Initially, solid fuels (coal) were employed
exclusively, then in the late 19th and early 20th centuries
liquid fuels (petroleum) progressively took over an increasing
share of the market, particularly for transport, and finally
in the latter half of the 20th century gaseous fuels (natural
gas) assumed increasing importance. Fossil fuels are versatile
in that they may be combusted to provide heat, burnt in an
internal combustion engine to provide mechanical energy/power
(eg for transport) or used to generate electricity
in a power station. An important feature of fossil fuels is
that they are not only concentrated sources of energy, but are
also readily transportable energy stores.
Nuclear fuels (uranium, plutonium, thorium) are of use only
for the central generation of electricity in a nuclear
reactor. Although nuclear fuels themselves may be stored, the
electricity produced from them cannot be stored directly.
Renewable energy sources (wind energy, solar PV energy, wave
energy, biomass, tidal energy, geothermal energy) are also
best exploited via electricity generation, although in a
dispersed mode and on a smaller scale than nuclear
electricity. Again, electricity from these sources is not
As concern grows over fossil fuel usage, in terms of global
warming and resource depletion, there will be a progressive
swing to renewable energy. This will necessitate the
development of improved methods of storing electricity, from
periods when it is available (eg sunny or windy days) to when
it is needed (night-time or periods of calm weather). Because
electricity cannot be stored directly (except on a very small
scale in capacitors), it must first be converted to some other
energy form for storage. There are four options:
energy: Pumped-hydro schemes, as currently operated by
electricity utilities in mountainous regions; compressed air
energy: Storage in high-speed flywheels of advanced design,
and made from fibre-reinforced composites.
energy: Night storage heaters of high thermal capacity, as
commonly used in the UK for space heating.
energy: Conversion to fuels such as hydrogen or methanol, or
storage as chemicals in batteries. In the 21st century, the
requirement for electricity storage will grow and it is likely
that batteries will play a key role.
If a battery
is to be charged-discharged for hundreds, or even thousands,
of cycles, it is essential that the chemical reactions that
take place at the electrodes are quantitatively reversible.
Even if as little as 0.1 per cent irreversibility (or side
reaction) occurs, this will soon add cumulatively to a major
loss in capacity. Many, if not most, electrode reactions
involve a reconstructive phase change in the crystal chemistry
of the active materials. A typical positive electrode reaction
Solid (A) + Anion « Solid
(B) + e- (charged)
(eg Ni(OH)2 + OH-
« NiOOH + H2O +
ionic diffusion processes in the crystal structure of the
solids, leading to phase change and recrystallisation. From
the viewpoint of the solid state chemist, the requirement to
reverse this reaction quantitatively during each cycle is
exceedingly demanding. The severity of the specification is
apparent when one considers the many possible processes or
side reactions leading to battery deterioration and failure.
and swelling of the electroactive material with loss of
formation of inactive phases, isolating active material;
metallic needles (dendrites) at the negative electrode,
causing internal short circuits;
shedding of active material from electrode plates;
dry-out through over-heating;
current collectors, resulting in increased internal
electrode plates on overcharge.
other degradation processes may result in precipitous battery
failure, through an internal short circuit, or may lead to
progressive loss in capacity and performance. Generally the
degradation steps are interactive and accumulative, so that
when the performance starts to deteriorate it soon accelerates
and the battery becomes unusable. Despite this gloomy
prognosis, some remarkable success has been achieved in
designing batteries of long cycle life (ca 1000 cycles) for
several different chemistries. The nickel-hydrogen battery has
been demonstrated to last for >20000 cycles and is the
preferred type in low Earth orbit satellites, as used for
meteorology and Earth surveillance. For this application the
batteries are required to undergo 16 charge-discharge cycles
per day (5840 cycles per year, with no loss in capacity and no
opportunity to exchange failed batteries!). Modern weather
forecasts and military defences are dependent on the
performance of the batteries in these satellites.
Lead-acid batteries find wide application
in vehicles. Originally known as 'starting, lighting and ignition
batteries', they are now more commonly referred to as 'automotive
batteries' because of the range of other duties they must perform
in the modern car. Other engine starting applications are in
aircraft, boats and stationary engines for local electricity
generation. These batteries are recharged by the engine's
alternator and in normal use are not subjected to 'deep' discharge
(see Glossary). They are of the 'pasted plate' (Fauré)
design, in which the positive active material is pasted on to a
lead grid current collector. This design is cheap to construct and
gives a high power output, but the life of the battery is
considerably shortened by repeated deep discharge. A modified
version of the pasted plate battery is the so-called 'leisure
battery' used in caravans, boats and so on for supplying the
'house electrics'. This is essentially an improved pasted plate
battery which, at higher cost, will give a reasonable life when
subjected to deep discharge duties.
Finally, there is the traction battery as
used to propel electric vehicles (milk floats, tractors, fork-lift
trucks etc). This is a more expensive battery type in
which the positive active material (PbO2)
is contained in a row of polyester or braided glass fibre tubes.
Co-axially, in the centres of the tubes, are vertical lead alloy
spines that act as the current collectors. Figure 3
shows the two principal lead-acid types.
3. Lead-acid batteries with (a) flat plates and (b)
Over the years, many improvements have been
made to the lead-acid battery. Although the essential
electrochemistry remains unchanged, the modern battery bears
little resemblance to that of 50 years ago. Major advances have
been made in the lead alloys used, in the materials and design of
the separators, in the packaging (polypropylene containers rather
than glass or hard rubber/pitch), and in the methods of
construction. All these changes have led to batteries of improved
performance, lower mass and lower cost. In recent years sealed
lead-acid batteries have been developed that require no
maintenance and may be used in any orientation.
Rechargeable alkaline electrolyte batteries
were invented at the end of the 19th century by Jungner in Sweden
and Edison in the US. These were based on nickel oxide cathodes
and either iron or cadmium anodes, and are popularly known as the
nickel-iron and nickel-cadmium batteries, respectively. The
electrolyte is concentrated KOH solution. The overall chemistry of
each cell is analogous:
| Fe + 2NiOOH + 4H2O
| Cd + 2NiOOH + 4H2O
Both batteries were commercialised early in
the 20th century, though the nickel-cadmium battery has proved
more successful. This is because the iron electrode is more
susceptible to corrosion and to self-discharge on standing. Also,
the electrical efficiency is poor and a low over-potential for
hydrogen evolution leads to excessive gassing during recharge.
Nickel-cadmium batteries are best known as
small (AA size) rechargeable cells for use in childrens' toys.
Much larger 6V batteries (5 cells in series) are available for
engine-starting, for stationary battery applications, and for
electric traction. These have several advantages over lead-acid:
stable discharge voltage, long operational life (ca 1000
cycles), low maintenance, faster discharge rate, better
low-temperature performance and excellent reliability. However,
they are considerably more expensive and there are environmental
concerns over the disposal of batteries containing toxic cadmium.
This disposal problem may be easier to solve for the larger
batteries used by industry, which can easily be recycled, than for
domestic AA size cells that tend to be discarded with the domestic
For this reason, at least, two recent
developments in rechargeable alkaline batteries are welcome.
Traditionally, alkaline Zn-MnO2
cells have always been seen as primary cells, but rechargeable
cells of this type are now being marketed. This has come about as
a result of advances in separator materials, which prevent the
formation of elongated zinc needles or dendrites, which lead to
internal short-circuiting. Changes in cell design prevent
discharge from occurring beyond the first electron removal step
Mn3+). In addition it is
necessary to use special chargers that taper-charge the cell to a
maximum of 1.7V per cell, to prevent over-charge and gassing. Such
cells are capable of relatively few charge-discharge cycles, but
have several times the capacity of comparably sized Ni-Cd cells
and are cheaper. They may be seen as intermediate between primary
alkaline manganese cells and rechargeable Ni-Cd cells.
The second major advance in rechargeable
alkaline batteries was the development of the nickel-metal hydride
battery. This retains the nickel oxide positive electrode and the
KOH electrolyte, but uses a metallic hydride rather than cadmium.
Effectively, the negative electrode is hydrogen (as in a fuel
cell), immobilised in the form of a metallic hydride. The hydride
is a complex alloy of rare-earth elements and other metals that
may be decomposed and reformed reversibly. The operating voltage
of a Ni-MH cell is almost the same as that of Ni-Cd (1.2-1.3V),
making for ready interchangeability. The specific energy of Ni- MH
batteries (60-70 Whkg-1) is up
to double that of Ni-Cd and their specific power may be as high as
250Wkg-1. These batteries are
resilient to overcharge and overdischarge and operate from -30 to
+45°C. Cells of both cylindrical and prismatic design are now
manufactured in a range of sizes; small cells are used in portable
electronic devices (eg mobile phones), while prismatic
cells of 100Ah capacity are available for assembly into 12-14V
modules (eg for use as traction batteries). The new material
technology involved in developing Ni- MH batteries is almost
entirely associated with the hydride negative electrode.
Lithium, with an atomic mass of 6.94, is
the lightest of all the metals and is therefore an obvious
candidate for battery use. It has a high specific capacity
(3.86Ahg-1) and a much higher
electrochemical reduction potential (-3.045V) than zinc (-0.76V).
The problems in developing lithium batteries stem from the high
reactivity of lithium metal. It is necessary to use a non-aqueous
electrolyte, which may be either an organic liquid or a solid
polymer - each with a dissolved lithium salt to make it ionically
conducting - or a fused lithium salt.
Some key manufacturers
and alkaline manganese primary batteries
Duracell, Ever Ready (Energizer), Panasonic, UCAR, Vidor,
Varta, Kodak, Rayovac
Duracell, Ultralife, Energizer, Sanyo
and coin cells
Duracell, Varta, Hitachi
Hawker (Tungstone), CMP, Johnson Controls, Varta, Tudor, CEAC
SAFT, Varta, Eagle-Picher
SAFT, GM-Ovonics, Varta, Panasonic, Matsushita
AEA Technology, Sony, Sanyo, Varta
Primary lithium batteries using a lithium
foil negative electrode, an organic liquid electrolyte and any one
of several positive electrode materials are commercially available
from several suppliers. The difficulties arise when one tries to
develop a rechargeable lithium battery of this type. Much work has
been done in this field with oniy limited success. In general,
lithium is not electrodeposited as a smooth layer on the metal
current collector, but as a mossy deposit.
Lithium foil that has been exposed to air is
covered with a thin layer of hydroxide-nitride, which limits its
reactivity. Freshly electrodeposited lithium is finely divided and
highly reactive, and decomposes the electrolyte. Some of the
deposit becomes electrically isolated from the electrode and so
capacity is lost rapidly. Lithium metal may also be plated out as
crystalline dendrites that ultimately penetrate the separator and
cause an internal short-circuit of the cell. Finally, these
processes constitute a fire risk and cells have been known to
ignite spontaneously during recharge. For all these reasons, the
commercial prospects for rechargeable cells based on liquid
electrolytes and lithium metal negatives do not seem too bright,
although much research is still in progress. The lithium ion
battery, the rising star of the 1990s, circumvents most of these
The essential feature of the lithium ion
battery is that at no stage in the charge-discharge cycle should
there be any lithium metal present. Rather, lithium ions are
intercalated into the positive electrode in the discharged state
and into the negative electrode in the charged state and move from
one to the other across the electrolyte. The latter is a solution
of a lithium salt in an organic solvent. The origin of the cell
voltage is then the difference in free energy between Li+
ions in the crystal structures of the two electrode materials.
Commercial cells use carbon as the negative
electrode: lithium ions will intercalate readily into graphite up
to a composition approaching C6Li,
at a voltage of zero to 1V with respect to a lithium reference
electrode. Using a positive electrode of LiCoO2
or LiNiO2, the cells are
assembled in the discharged state and a 3V lithum ion cell
results. After a few initial cycles, approximately half of the
intercalated lithium may be removed reversibly, as shown:
+ 0.45Li+ + 0.45e-
+ 0.5Li+ + 0.5e-
The solid state chemistry of the LiNiO2
structure is more complex than that of LiCoO2
and the fully lithiated compound is not stable during
electrochemical cycling. Nevertheless, the practical Ah capacities
are much the same, as are the cell voltages. When cycling Li+
ion cells it is important to control the top-of-charge voltage
carefully (4.1V for LiNiO2 and
4.2V for LiCoO2). Failure to
do so results in decomposition of the 'positives' to give oxygen
gas and Co3O4
or LiNi2O4, a hazardous situation in a sealed cell. For this
reason, lithium ion cells must be recharged using a specially
designed charger incorporating both voltage and temperature
control. Over-discharge must also be avoided and it is usual to
have a limiting cut-off voltage on discharge of ca 2.7V.
(In this regard the NiMH battery has the advantage of being much
better able to withstand overcharge and overdischarge.)
The Sony Corporation in Japan first
commercialised lithium ion cells in the early 1990s, and they have
since been marketed by many other battery manufacturers. They are
extensively employed in laptop computers, mobile phones and other
portable electronic equipment. In 1997 alone it is estimated2
that 190m cells were manufactured in Japan with a value exceeding
US$2000m. With worldwide R&D in progress, we may hope for
future improvements in performance as well as price reductions for
lithium ion cells.
From this brief survey it is clear that
battery research is a dynamic and challenging field for chemists,
working closely with material scientists and design engineers. The
rapid advances of the past 20 years augur well for new power
sources in the 21st century.
Ronald Dell worked in applied
electrochemistry for 20 years, and may be contacted at 2 Tullis
Close, Sutton Courtenay, Abingdon, Oxfordshire OX14 4BD.
- K. Tamura and T. Horiba, J. Power
Sources. 1999, 81-82, 156.
- T. Kodama and H. Sakaebe, J. Power
Sources, 1999, 81-82, 144.
International. London: Euromoney Publications.
Acta. London: Elsevier Science.
of Applied Electrochemistry. The Netherlands: Kluwer
of the Electrochemical Society USA. Pennington, NJ: The
of Power Sources. London: Elsevier Science.
the ninth international meeting on lithium batteries, J.
Power Sources, vol 81-82, 1999.
State lonics. London: Elsevier Science.
Maintenance-free batteries, 2nd edn. Taunton:
Research Studies Press, 1997.
S. U. Falk and
A. J. Salkind, Alkaline storage batteries.
Chichester: John Wiley, 1969.
batteries, J.-P. Gabano (ed). Maidenhead: Academic Press,
of batteries and fuel cells, 2nd edn, D. Linden (ed). New
York: McGraw-Hill, 1995.
D. A. J. Rand,
R. Woods and R. M. Dell, Batteries for electric vehicles.
Taunton: Research Studies Press, 1998.
and J. G. Smith, Batteries for automotive use.
Taunton: Research Studies Press, 1997.
state batteries, C. A. C. Sequeira and A. Hooper (eds).
NATO ASI series. The Netherlands: Martinus Nijhoff
J. L. Sudworth
and A. R. Tilley, The sodium sulfur battery. London:
Chapman & Hall, 1985.
battery technology, C. D. S. Tuck (ed). Chichester: Ellis
C. A. Vincent,
Modern batteries, 2nd edn. Maidenhead: Edward
International Power Sources
Society of Chemistry links
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material: The electrode material that takes part in the
electrochemical reactions that store/deliver electrical energy.
Active material utilisation: The fraction of
active material that reacts during discharge before the battery
can no longer deliver the required current at a useful voltage.
Anode: The negative electrode from which
electrons flow during discharge.
Battery management: The regulation of charging
and discharging conditions (eg control of temperature, cut-off
Capacity: The amount of charge (measured in
ampere-hours, Ah) that can be withdrawn from a fully charged
battery under specified conditions.
Cathode: The positive electrode to which
electrons flow during discharge.
Current collector: The metallic part of an
electrode which conducts electrons to and from the active
Depth of discharge: The ratio of the
ampere-hours discharged from a battery to the available capacity
measured at the same temperature and discharge rate.
Energy density: The energy output from a
battery per unit volume, expressed in Wh dm3.
Energy efficiency: The fraction of the energy
used in charging the battery, expressed in watt-hours, which is
available on discharge.
voltage: The voltage of a battery when there is no net
Over-discharge: The discharge of a battery
beyond the level specified for correct operation.
Passivation: The formation of a surface layer
that impedes the electrochemical reactions at an electrode.
Power density: The power output of a battery
per unit volume, usually expressed in W dm3
and quoted at 80 per cent depth of discharge.
Self-discharge: The loss of capacity of a
battery under open-circuit conditions as a result of internal
chemical reactions and/or short-circuits.
Separator: An electronically non-conducting,
but ion-permeable, material that prevents electrodes of opposite
polarity making contact.
Shelf-life: The period over which a battery
may be stored and still meet specified performance criteria.
Specific energy: The energy output of a
battery per unit weight, usually expressed as Wh kg1.
Specific power: The power output of a battery
per unit weight, usually expressed as W kg1.
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