Research shows metal catalysts play important role in improving efficiency
CAMBRIDGE, Mass. — A team of researchers at MIT has made significant progress on a technology that could lead to batteries with up to three times the energy density of any battery that currently exists.
Yang Shao-Horn, an MIT associate professor of mechanical engineering and materials science and engineering, says that many groups have been pursuing work on lithium-air batteries, a technology that has great potential for achieving great gains in energy density. But there has been a lack of understanding of what kinds of electrode materials could promote the electrochemical reactions that take place in these batteries.
Lithium-oxygen (also known as lithium-air) batteries are similar in principle to the lithium-ion batteries that now dominate the field of portable electronics and are a leading contender for electric vehicles. But because lithium-air batteries replace the heavy conventional compounds in such batteries with a carbon-based air electrode and flow of air, the batteries themselves can be much lighter. That’s why leading companies, including IBM and General Motors, have committed to major research initiatives on lithium-air technology.
Test battery has inlet and outlet on the sides to provide a flow of air, providing oxygen for the battery’s operation. Photo: Patrick Gillooly/MIT
In a paper published this week in the journal Electrochemical and Solid-State Letters, Shao-Horn, along with some of her students and visiting professor Hubert Gasteiger, reported on a study showing that electrodes with gold or platinum as a catalyst show a much higher level of activity and thus a higher efficiency than simple carbon electrodes in these batteries. In addition, this new work sets the stage for further research that could lead to even better electrode materials, perhaps alloys of gold and platinum or other metals, or metallic oxides, and to less expensive alternatives.
Doctoral student Yi-Chun Lu, lead author of the paper, explains that this team has developed a method for analyzing the activity of different catalysts in the batteries, and now they can build on this research to study a variety of possible materials. “We’ll look at diffe
rent materials, and look at the trends,” she says. “Such research could allow us to identify the physical parameters that govern the catalyst activity. Ultimately, we will be able to predict the catalyst behaviors. ” Why it matters: Lightweight batteries that can deliver lots of energy are crucial for a variety of applications — for example, improving the range of electric cars. For that reason, even modest increases in a battery’s energy-density rating — a measure of the amount of energy that can be delivered for a given weight — are important advances.
Next Steps: One issue to be dealt with in developing a battery system that could be widely commercialized is safety. Lithium in metallic form, which is used in lithium-air batteries, is highly reactive in the presence of even minuscule amounts of water. This is not an issue in current lithium-ion batteries because carbon-based materials are used for the negative electrode. Shao-Horn says the same battery principle can be applied without the need to use metallic lithium; graphite or some other more stable negative electrode materials could be used instead, she says, leading to a safer system.
A number of issues must be addressed before lithium-air batteries can become a practical commercial product, she says. The biggest issue is developing a system that keeps its power through a sufficient number of charging and discharging cycles for it to be useful in vehicles or electronic devices.
Researchers also need to look into details of the chemistry of the charging and discharging processes, to see what compounds are produced and where, and how they react with other compounds in the system. “We’re at the very beginning” of understanding exactly how these reactions occur, Shao-Horn says.
Gholam-Abbas Nazri, a researcher at the GM Research & Development Center in Michigan, calls this research “interesting and important,” and says this addresses a significant bottleneck in the development of this technology: the need find an efficient catalyst. This work is “in the right direction for further understanding of the role of catalysts,” and it “may significantly contribute to the further understanding and future development of lithium-air systems,” he says.
While some companies working on lithium-air batteries have said they see it as a 10-year development program, Shao-Horn says it is too early to predict how long it may take to reach commercialization. “It’s a very promising area, but there are many science and engineering challenges to be overcome,” she says. “If it truly demonstrates two to three times the energy density” of today’s lithium-ion batteries, she says, the likely first applications will be in portable electronics such as computers and cell phones, which are high-value items, and only later would be applied to vehicles once the costs are reduced.
The Di Pietro motor concept is based on a rotary piston. Different from existing rotary engines, the Di Pietro motor uses a simple cylindrical rotary piston (shaft driver) which rolls, without any friction, inside the cylindrical stator. The space between stator and rotor is divided in 6 expansion chambers by pivoting dividers. These dividers follow the motion of the shaft driver as it rolls around the stator wall. The motor shown is effectively a 6 cylinder expansion motor.
The cylindrical shaft driver, forced by the air pressure on its outer wall, moves eccentrically, thereby driving the motor shaft by means of two rolling elements (not shown) mounted on bearings on the shaft. The rolling motion of the shaft driver inside the stator is cushioned by a thin air film. Timing and duration of the air inlet and exhaust is governed by a slotted timer which is mounted on the output shaft and rotates with the same speed as the motor.
Variation of performance parameters of the motor is easily achieved by varying the time during which the air is allowed to enter the chamber: A longer air inlet period allows more air to flow into the chamber and therefore results in more torque. A shorter inlet period will limit the air supply and allows the air in the chamber to perform expansion work at a much higher efficiency. In this way compressed air (energy) consumption can be exchanged for higher torque and power output depending on the requirements of the application.
Motor speed and torque are simply controlled by throttling the amount or pressure of air into the motor. The Di Pietro motor gives instant torque at zero RPM and can be precisely controlled to give soft start and acceleration control.
Angelo Di Pietro
“There is no other motor as good as ours, years of research and analysing other motors around the world gave me the confidence and obligation to say so. Obligation in the sense that people have been waiting for ages in relation to efficiency in order to take care of our environmental situation.
100% more efficiency than our competitor is a very serious claim and should not be confused with some kind of publicity stunt were the interest is purely to try and make money out of some ridiculous claim.
The invention has a long list of important improvements over other motors.
The concept has the capability to change the method we use for transportation, apart from the benefits of energy saving in stationary applications.
We have verification of its performance
We have patents issued
It has outstanding efficiency
It has constant high torque
It has low parts count
It has low number of moving parts
It is compact and light
It has virtually no friction
It has virtually no vibration
It has smooth speed control characteristics
Only 1 PSI of pressure is needed to overcame the friction
More info can be found on this at their website here:
A compressed air car is a car that uses a motor powered by compressed air. The car can be powered solely by air, or combined (as in a hybrid electric vehicle) with gasoline, diesel, ethanol, or an electric plant with regenerative braking.
Compressed air cars are powered by engines fueled by compressed air, which is stored in a tank at high pressure such as 30 MPa (4500 psi or 300 bar). Rather than driving engine pistons with an ignited fuel-air mixture, compressed air cars use the expansion of compressed air, in a similar manner to the expansion of steam in a steam engine.
Storage tanks are often made of carbon-fiber for weight reduction while maintaining strength; if penetrated carbon fiber will crack but not produce shrapnel.
There have been prototype cars since the 1920s and compressed air has been used in torpedopropulsion as well.
The major manufacturers that are developing air cars have designed safety features into their containers.[citation needed] In contrast to hydrogen’s issues of damage and danger involved in high-impact crashes, air, on its own, is non-flammable. It was reported on Seven Network’sBeyond Tomorrow that on its own,[clarification needed] carbon-fiber is brittle and can split under sufficient stress, but creates no shrapnel when it does so. Carbon-fiber tanks safely hold air at a pressure somewhere around 4500 psi, making them comparable to steel tanks.
Compressed air is also relatively space inefficient of storing energy when compared to conventional gasoline. Air at 30 MPa (4,500 psi) contains about 50 Wh of energy per liter. Gasoline contains about 9411 Wh per liter.[1]
Emissions
Compressed air cars are emission-free at the exhaust. Since a compressed air car’s source of energy is usually electricity, its total environmental impact depends on how clean the source of this electricity is. Different regions can have very different sources of power, ranging from high-emission power sources such as coal to zero-emission power sources such as wind. A given region can also update its electrical power sources over time, thereby improving or worsening total emissions.
However a study showed that even with very optimistic assumptions, air storage of energy is less efficient that chemical (battery) storage.[2]
Advantages
The principal advantages of an air powered vehicle are:
Refueling can be done at home using an air compressor [3] or at service stations. The energy required for compressing air is produced at large centralized plants, making it less costly and more effective to manage carbon emissions than from individual vehicles.
Compressed air engines reduce the cost of vehicle production, because there is no need to build a cooling system, spark plugs, starter motor, or mufflers.[4]
The rate of self-discharge is very low opposed to batteries that deplete their charge slowly over time. Therefore, the vehicle may be left unused for longer periods of time than electric cars.
Expansion of the compressed air lowers its temperature; this may be exploited for use as air conditioning.
Air turbines, closely related to steam turbines, are a technology over 50 years old.
Reduction or elimination of hazardous chemicals such as gasoline or battery acids/metals
Some mechanical configurations may allow energy recovery during braking by compressing and storing air.
Disadvantages
The principal disadvantage is the indirect use of energy. Energy is used to compress air, which – in turn – provides the energy to run the motor. Any conversion of energy between forms results in loss. For conventional combustion motor cars, the energy is lost when chemical energy in fossil fuels is converted to heat energy, most of which goes to waste. For compressed-air cars, energy is lost when chemical energy is converted to electrical energy, and then when electrical energy is converted to compressed air.
When air expands in the engine it cools dramatically (Charles law) and must be heated to ambient temperature using a heat exchanger. The heating is necessary in order to obtain a significant fraction of the theoretical energy output. The heat exchanger can be problematic: while it performs a similar task to an intercooler for an internal combustion engine, the temperature difference between the incoming air and the working gas is smaller. In heating the stored air, the device gets very cold and may ice up in cool, moist climates.
Conversely, when air is compressed to fill the tank it heats up: as the stored air cools, its pressure decreases and available energy decreases. It is difficult to cool the tank efficiently while charging and thus it would either take a long time to fill the tank, or less energy is stored.
Refueling the compressed air container using a home or low-end conventional air compressor may take as long as 4 hours, though specialized equipment at service stations may fill the tanks in only 3 minutes.[3]. To store 14.3 kWh @300 bar in 300 l (90 m3 @ 1 bar) reservoirs, you need at least 93 kWh on the compressor side (with an optimum compressor working on the ideal adiabatic limit, which is what industrial compressors can do at best). That means, a compressor power of over 1 Megawatt (1000 kW) is needed to fill the reservoirs in 5 minutes. This also means that the overall efficiency of a compressed air vehicle cannot exceed 14 % (with a 100 % efficient engine- which will likely be closer to 10-20 %) (Ref: see http://www.druckluft-effizient.de/downloads/fakten/02-thermodynamik.pdf and http://cair.wikia.com/wiki/Compressed_air_energy_storage)
Early tests have demonstrated the limited storage capacity of the tanks; the only published test of a vehicle running on compressed air alone was limited to a range of 7.22 km.[5]
A 2005 study demonstrated that cars running on lithium-ion batteries out-perform both compressed air and fuel cell vehicles more than three-fold at the same speeds.[6] MDI has recently claimed that an air car will be able to travel 140 km in urban driving, and have a range of 80 km with a top speed of 110 km/h (68 mph) on highways,[7] when operating on compressed air alone, but in as late as mid 2009, MDI has still not produced any proof to that effect.
A 2009 University of Berkeley Research Letter found that “Even under highly optimistic assumptions the compressed-air car is significantly less efficient than a battery electric vehicle and produces more greenhouse gas emissions than a conventional gas-powered car with a coal intensive power mix.” [8]
Crash safety
Safety claims for light weight vehicle air tanks in severe collisions have not been verified. North American crash testing has not yet been conducted, and skeptics question the ability of an ultralight vehicle assembled with adhesives to produce acceptable crash safety results. Shiva Vencat, vice president of MDI and CEO of Zero Pollution Motors, claims the vehicle would pass crash testing and meet U.S. safety standards. He insists that the millions of dollars invested in the AirCar would not be in vain. To date, there has never been a lightweight, 100-plus mpg car which passed North American crash testing. Technological advances may soon make this possible, but the AirCar has yet to prove itself, and collision safety questions remain.[9]
The key to achieving an acceptable range with an air car is reducing the power required to drive the car, so far as is practical. This pushes the design towards minimizing weight. In a collision the occupants of a heavy vehicle will, on average, suffer fewer and less serious injuries than the occupants of a lighter vehicle.[10] An accident in a 2000 lb (900 kg) vehicle will on average cause about 50% more injuries to its occupants than a 3000 lb (1350 kg) vehicle.[11] Air cars may use low rolling resistance tires, which typically offer less grip than normal tires.[12][13] In addition, the weight (and price) of safety systems such as airbags, ABS and ESC may discourage manufacturers from including them.
Developers and manufacturers
Various companies are investing in the research, development and deployment of Compressed air cars. Overoptimistic reports of impending production date back to at least May 1999. For instance, the MDI Air Car made its public debut in South Africa in 2002,[14] and was predicted to be in production “within six months” in January 2004.[15] As of January 2009, the air car never went into production in South Africa. Most of the cars under development also rely on using similar technology to Low-energy vehicles in order to increase the range and performance of their cars.
MDI has proposed a range of vehicles made up of AirPod, OneFlowAir, CityFlowAir, MiniFlowAir and MultiFlowAir..[16] One of the main innovations of this company is its implementation of its “active chamber”, which is a compartment which heats the air (through the use of a fuel) in order to double the energy output.[17]
Tata Motors
As of May 2007[update]Tata Motors of India had planned to launch a car with an MDI compressed air engine in 2008.[18] . Tata subsequently announced that the technology was still in development stage and the launch of a commercially viable vehicle in the near future was not possible[19].
In December 2009 Tata’s vice president of engineering systems confirmed that the limited range and low engine temperatures were causing difficulties [20].
Air Car Factories
Air Car Factories SA is proposing to develop and build a compressed air engine.[21] This Spanish based company was founded by Miguel Celades. Currently there is a bitter dispute between Motor Development International, another firm called Luis which developed compressed-air vehicles, and Mr. Celades, who was once associated with that firm.[22][23]
Energine
The Energine Corporation was a South Korean company that claimed to deliver fully-assembled cars running on a hybrid compressed air and electric engine. These cars are more precisely named pneumatic-hybrid electric vehicles.[24] Engineers from this company made, starting from a Daewoo Matiz, a prototype of a hybrid electric/compressed-air engine (Pne-PHEV, pneumaticplug-in hybrid electric vehicle[citation needed]). The compressed-air engine is used to activate an alternator, which extends the autonomous operating capacity of the car.
The CEO is the first compressed air car promoter to be arrested for fraud.[25]
A similar (but only for braking energy recovery) concept using a pneumatic accumulator in a largely hydraulic system has been developed by U.S. government research laboratories and industry, and is now being introduced for certain heavy vehicle applications such as refuse trucks.[26]
K’Airmobiles
K’Airmobiles has presented two running prototypes of VPA (Vehicles with Pneumatic Assistance). Their leaders now seek to gain the means of developing several projects of urban or leisure VPP (Vehicles with Pneumatic Propulsion). K’Airmobiles propose a different technology with their VPP , which may allow a reasonable range, generally with compressed air tanks of about 50L-100L/3000 psi capacity only.
These ecological vehicles use the technology of the compressed-air engine K’Air, developed in France by a small group of researchers, which thus proposes a range of projects around an idea: that of the urban or leisure compressed-air vehicles.
K’Airmobiles is the name given to a set of projects relating to “VPA” (Vehicles with Pneumatic Assistance) and “VPP” (Vehicles with Pneumatic Propulsion), These models are conceived like ultra light vehicles (limited to 250 kg (551 lb) max.), and their consumption of compressed air was calculated to remain lower than 120 L/min., although developing a dynamic push able to reach 4 kN.
Two VPA prototypes are operational today, the “K’AirBike” and the K’AirKart. Two new VPP prototypes, the one-seater “K’AirTrike” and the three-seater “K’AirMobile Max” were intended for public presentation in October and November 2007 respectively.
Electro-Tech Enterprises
Electro-Tech Enterprises is a small company that specializes in electric air vehicles using a new technology discovered by themselves that is currently in the proto-type phase.[dubious – discuss]
Engineair
Engineair is an Australian company which manufactures small industrial vehicles using an air engine of its own design. http://www.engineair.com.au
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