nanoelectrodes.qxp
11/14/2005
8:34 PM
Page 2
NANOSTRUCTURED
ELECTRODES
Experts have recognized for years the
advantages of lithium ion technology
over traditional power batteries,
particularly those based on lead acid
chemistry.
charged in five hours. Up to now, for power applications (rates between 10 and 100 C) energy
density has been severely reduced at high discharge rates for reasons explained below. However, the nanostructured electrode materials now
offer, for the first time, a power-dense solution for
passenger vehicles and other power applications.
Alan Gotcher
Fast recharge
Typical rechargeable batteries take from one
to several hours to recharge after depletion. This
is caused by the physical limitations related to the
relatively large size of the microstructure in the
materials in the active elements.
On the other hand, nanostructured materials
allow dramatically reduced charge rates. For the
first time, it is reasonable to consider an electric
vehicle with a range over 200 miles, which can be
recharged in the time it now takes to fill the gasoline tank in a conventional passenger vehicle. The
technology can virtually eliminate much of the
dependence on oil, and much of the infrastructure to support such an electric vehicle is already
in place in the form of the current power grid.
Thus the only additions necessary are “pumps”
at your local filling station that deliver electricity
instead of gasoline!
Altair Nanotechnologies Inc.
Reno, Nevada
N
anostructured electrodes for lithium
ion batteries provide rapid battery
recharge in a few minutes and a lifetime estimated to be more than twelve
years. For electric vehicles, they enable rapid acceleration with an inherently safe design.
Innovative nanostructured materials include
lithium titanate spinel anode materials and manganate oxide spinel cathode materials. The spinel
minerals are a class conforming to the MgAl2O4
crystal structure (from which the class is derived)
and have the generic formula XY2O4. When
placed together in a battery, they provide power
and long life. Figure 1 compares the specific energies of standard lithium ion batteries, lead acid
batteries, and batteries with nanostructure electrodes as a function of power density.
For applications such as hybrid electric vehicles,
electric vehicles, and power tools, the ability to deliver power is of critical importance. Experts have
recognized for years the advantages of lithium ion
technology over traditional power batteries, particularly those based on lead acid chemistry.
The prime advantage is that the lithium ion
chemistry provides much higher energy density
over lead acid. The rate of charging or discharging
a battery at room temperature under constant current is expressed as total capacity, or C, divided
by the time in hours. For example: 1C indicates
that the battery is completely charged or discharged in one hour. In the same way, 0.2C indicates that the battery is completely charged or dis-
How it works
Lithium ion battery performance depends on
active material particle size and surface area in
the electrodes. Conventional lithium ion battery
performance is limited by the low surface area
available for lithium ion activity. This severely
restricts battery performance because the availability of active surface sites is critical to power
applications. Nanostructured materials increase
available surface area by up to two orders of magnitude over conventional materials, from ~ 1m2/g
up to ~ 100 m2/g.
A comparison of macroparticle based electrodes
to nanoparticle based electrodes shows that macro
particles:
• Cannot fill to capacity because of long surface-to-center distances and
Properties of conventional vs. nanostructured lithium ion batteries blocking of lithium ion
pathways.
Property
Conventional electrodes
Nanostructured electrodes
• Have severely retarded
Charge rates
2 hours (1/2 C)
3 minutes (20 C)
charge and discharge rates
Discharge rates
15 minutes (4 C)
1.5 minutes (40 C)
because of the lower surface area relative to
Cycle life
300 – 500 (shallow, not full depth
2000 cycles (full depth of
volume. This creates a
of discharge)
discharge)
traffic-jam effect at the surCalendar life
2 – 3 years
10 – 15 years
face of macro particles at
The rate of charging or discharging a battery at room temperature under constant current is expressed as total capacity, or C, divided
high discharge rates.
by the time in hours. For example: 1C indicates that the battery is completely charged or discharged in one hour. In the same way,
Thus, specially engineered
0.2C indicates that the battery is completely charged or discharged in five hours.
32
ADVANCED MATERIALS & PROCESSES/DECEMBER 2005
11/14/2005
8:34 PM
Page 3
nanostructured materials enable previously
unattainable capacities at very high discharge rates, as well as dramatically higher
charge rates for next-generation lithium ion
batteries. In addition, nanostructured materials can offer advantages now for currentgeneration lithium ion batteries.
1000
TDT = Total discharge time
TDT = 100 hours,
C/100 rate
TDT = 10 hours,
C/10 rate
TDT = 1 hour,
C rate
TDT = 6 minutes,
10C rate
Specific energy, Wh/kg
nanoelectrodes.qxp
Safety advantages
Altairnano’s
Traditional lithium power batteries exdisruptive
100
hibit potentially explosive thermal runtechnology
away problems above 130ºC (266°F). The
problem is exacerbated by high internal impedances normally present at the electrode
surfaces. Thus, the safety of the battery at
TDT = 36 seconds,
Altairnano technology
practical charge and discharge rates is lim100C rate
Conventional Li-ion
ited by heating caused by passing current
Lead-acid
through the high resistance. In addition,
expensive and sophisticated electronic circuitry is required to keep cells in charge and
10
1
10
100
1000
10000
the voltage balanced, as well as to avoid the
Specific power , W/kg
dangerous states of overcharge, under disFig. 1 — This graph shows the performance comparison of standard lithium-ion, leadcharge, and reverse discharge.
Nanostructured electrode materials and acid, and Altairnano’s battery technology. The rate of charging or discharging a batbatteries eliminate thermal runaway below tery at room temperature under constant current is expressed as total capacity, or C,
250ºC (480°F). This is partially due to their divided by the time in hours. For example: 1C indicates that the battery is completely
charged or discharged in one hour. In the same way, 0.2C indicates that the battery is
very low internal impedance, which allows completely charged or discharged in five hours.
for minimal heating during both charge
and discharge at high currents. Also, these
generator will start in eight seconds to provide
batteries do not need the high level of expensive further backup.
control circuitry necessary with standard lithium
Altairnano’s Titanium Backup System is a solid
ion systems, because they can be safely over- state replacement for flywheel UPS systems and
charged and are not damaged when fully dis- requires no regular maintenance. The batteries
charged. The need for cell voltage balancing can are expected to last up to 15 years in normal use.
be minimized from the control circuitry, greatly The batteries are designed to operate over a wide
reducing cost.
temperature range of -40 to +65°C (-40 to +150°F).
As with all Altairnano products, the batteries are
Power hand tools
friendly to the environment.
Traditional portable power tools are too heavy
because of the required size of the battery pack. Hybrid electric vehicles
In addition, the size of the pack limits the operTraditional HEV battery systems are limited by
ating time per battery, and the recharge time for heavy and/or toxic lead-acid, cadmium, or nickelthese packs can run from one to two hours. Typ- based batteries. At a minimum, these batteries
ically, today’s power tools include cadmium and must be replaced every five to seven years at a
nickel as part of the battery system in addition to cost of several thousand dollars. Performancea caustic electrolyte.
wise, the limited power capabilities of current batIn contrast, Altairnano’s power tool battery pack teries limits the acceleration possible from battery
weighs one to two pounds, and may be carried power alone. This is exacerbated by the relatively
on a suspender belt. The battery pack is optimized heavy weight of current HEV battery systems.
for five to six hours of operation, and the battery
Altairnano’s batteries are based on nanostrucpack can be recharged in a phenomenal 10 to 15 tured titanate and manganate spinels. In addiminutes. The power tool pack is safe because it tion to their environmental and weight advancontains no nickel, cadmium, or other hazardous tages, these materials possess exceedingly high
materials.
discharge rates (up to 100C and more) and currently unavailable charge rates of up to 40C. This
Uninterruptible power supplies
40C charge rate allows for a complete charge in
Uninterruptible power supplies (UPS) sys- about 1.5 minutes! Thus, not only do hybrid vetems use lead acid batteries or mechanical fly- hicles benefit from these breakthrough material
wheels to provide backup power, and opera- advancements, but also practical fully electric vetion is hindered because of the lead-acid hicles become a real-world option.
battery’s tendency to fail. Constant maintenance is required, and lead-acid batteries need For more information: Alan Gotcher, Altair Nanotechto be replaced every 1.5 to 4 years. Mechanical nologies Inc., 204 Edison Way, Reno NV 89502; tel:
flywheels provide only 15 to 20 seconds of 775/858-3714; e-mail: agotcher@altairnano.com; Web
backup power, under the assumption that a site: www.altairnano.com.
ADVANCED MATERIALS & PROCESSES/DECEMBER 2005
33