MIT Powers Up New Battery For Hybrid Cars

Source: Massachusetts Institute of Technology
Posted: February 17, 2006

Researchers at MIT have developed a new type of lithium battery that could become a cheaper alternative to the batteries that now power hybrid electric cars.

(Picture Right: The structure of lithium nickel manganese oxide consists of layers of transition metal (nickel and manganese, blue layer) separated from lithium layers (green) by oxygen (red). (Image courtesy of Ceder Laboratory))

Until now, lithium batteries have not had the rapid charging capability or safety level needed for use in cars. Hybrid cars now run on nickel metal hydride batteries, which power an electric motor and can rapidly recharge while the car is decelerating or standing still.

But lithium nickel manganese oxide, described in a paper to be published in Science on Feb. 17, could revolutionize the hybrid car industry -- a sector that has "enormous growth potential," says Gerbrand Ceder, MIT professor of materials science and engineering, who led the project.

"The writing is on the wall. It's clearly happening," said Ceder, who said that a couple of companies are already interested in licensing the new lithium battery technology.

The new material is more stable (and thus safer) than lithium cobalt oxide batteries, which are used to power small electronic devices like cell phones, laptop computers, rechargeable personal digital assistants (PDAs) and such medical devices as pacemakers.

The small safety risk posed by lithium cobalt oxide is manageable in small devices but makes the material not viable for the larger batteries needed to run hybrid cars, Ceder said. Cobalt is also fairly expensive, he said.

The MIT team's new lithium battery contains manganese and nickel, which are cheaper than cobalt.

Scientists already knew that lithium nickel manganese oxide could store a lot of energy, but the material took too long to charge to be commercially useful. The MIT researchers set out to modify the material's structure to make it capable of charging and discharging more quickly.

Lithium nickel manganese oxide consists of layers of metal (nickel and manganese) separated from lithium layers by oxygen. The major problem with the compound was that the crystalline structure was too "disordered," meaning that the nickel and lithium were drawn to each other, interfering with the flow of lithium ions and slowing down the charging rate.

Lithium ions carry the battery's charge, so to maximize the speed at which the battery can charge and discharge, the researchers designed and synthesized a material with a very ordered crystalline structure, allowing lithium ions to freely flow between the metal layers.

A battery made from the new material can charge or discharge in about 10 minutes -- about 10 times faster than the unmodified lithium nickel manganese oxide. That brings it much closer to the timeframe needed for hybrid car batteries, Ceder said.

Before the material can be used commercially, the manufacturing process needs to be made less expensive, and a few other modifications will likely be necessary, Ceder said.

Other potential applications for the new lithium battery include power tools, electric bikes, and power backup for renewable energy sources.

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The lead author on the research paper is Kisuk Kang, a graduate student in Ceder's lab. Ying Shirley Meng, a postdoctoral associate in materials science and engineering at MIT, and Julien Breger and Clare P. Grey of the State University of New York at Stony Brook are also authors on the paper.

The research was funded by the National Science Foundation and the U.S. Department of Energy.

Hybrid Efficiency and Performance

by Julia Layton and Karim Nice

The key to a hybrid car is that the gasoline engine can be much smaller than the one in a conventional car and therefore more efficient. Most cars require a relatively big engine to produce enough power to accelerate the car quickly. In a small engine, however, the efficiency can be improved by using smaller, lighter parts, by reducing the number of cylinders and by operating the engine closer to its maximum load.

There are several reasons why smaller engines are more efficient than bigger ones:

• The big engine is heavier than the small engine, so the car uses extra energy every time it accelerates or drives up a hill.
• The pistons and other internal components are heavier, requiring more energy each time they go up and down in the cylinder.
• The displacement of the cylinders is larger, so more fuel is required by each cylinder.
• Bigger engines usually have more cylinders, and each cylinder uses fuel every time the engine fires, even if the car isn't moving.

This explains why two of the same model cars with different engines can get different mileage. If both cars are driving along the freeway at the same speed, the one with the smaller engine uses less energy. Both engines have to output the same amount of power to drive the car, but the small engine uses less power to drive itself. But how can this smaller engine provide the power your car needs to keep up with the more powerful cars on the road?

Let's compare a car like the Chevy Camaro, with its big V-8 engine, to our hybrid car with its small gas engine and electric motor. The engine in the Camaro has more than enough power to handle any driving situation. The engine in the hybrid car is powerful enough to move the car along on the freeway, but when it needs to get the car moving in a hurry, or go up a steep hill, it needs help. That "help" comes from the electric motor and battery -- this system steps in to provide the necessary extra power.

The gas engine on a conventional car is sized for the peak power requirement (those few times when you floor the accelerator pedal). In fact, most drivers use the peak power of their engines less than one percent of the time. The hybrid car uses a much smaller engine, one that is sized closer to the average power requirement than to the peak power.

Besides a smaller, more efficient engine, today's hybrids use many other tricks to increase fuel efficiency. Some of those tricks will help any type of car get better mileage, and some only apply to a hybrid. To squeeze every last mile out of a gallon of gasoline, a hybrid car can:

Recover energy and store it in the battery - Whenever you step on the brake pedal in your car, you are removing energy from the car. The faster a car is going, the more kinetic energy it has. The brakes of a car remove this energy and dissipate it in the form of heat. A hybrid car can capture some of this energy and store it in the battery to use later. It does this by using "regenerative braking." That is, instead of just using the brakes to stop the car, the electric motor that drives the hybrid can also slow the car. In this mode, the electric motor acts as a generator and charges the batteries while the car is slowing down.

Sometimes shut off the engine - A hybrid car does not need to rely on the gasoline engine all of the time because it has an alternate power source -- the electric motor and batteries. So the hybrid car can sometimes turn off the gasoline engine, for example when the vehicle is stopped at a red light.

Use advanced aerodynamics to reduce drag - When you are driving on the freeway, most of the work your engine does goes into pushing the car through the air. This force is known as aerodynamic drag. This drag force can be reduced in a variety of ways. One sure way is to reduce the frontal area of the car. Think of how a big SUV has to push a much greater area through the air than a tiny sports car.

Reducing disturbances around objects that stick out from the car or eliminating them altogether can also help to improve the aerodynamics. For example, covers over the wheel housings smooth the airflow and reduce drag. And sometimes, mirrors are replaced with small cameras.

(Picture right: The frontal area profile of a small and large car)

Use low-rolling resistance tires - The tires on most cars are optimized to give a smooth ride, minimize noise, and provide good traction in a variety of weather conditions. But they are rarely optimized for efficiency. In fact, the tires cause a surprising amount of drag while you are driving. Hybrid cars use special tires that are both stiffer and inflated to a higher pressure than conventional tires. The result is that they cause about half the drag of regular tires.

Use lightweight materials - Reducing the overall weight of a car is one easy way to increase the mileage. A lighter vehicle uses less energy each time you accelerate or drive up a hill. Composite materials like carbon fiber or lightweight metals like aluminum and magnesium can be used to reduce weight.

All of the hybrid cars on the market utilize some or all of these efficiency tricks. Let's take a look at the hybrid models you can buy right now.

Hybrid Structure

by Julia Layton and Karim Nice

Gasoline-electric hybrid cars contain the following parts:

Gasoline engine - The hybrid car has a gasoline engine much like the one you will find on most cars. However, the engine on a hybrid is smaller and uses advanced technologies to reduce emissions and increase efficiency.

Fuel tank - The fuel tank in a hybrid is the energy storage device for the gasoline engine. Gasoline has a much higher energy density than batteries do. For example, it takes about 1,000 pounds of batteries to store as much energy as 1 gallon (7 pounds) of gasoline.

Electric motor - The electric motor on a hybrid car is very sophisticated. Advanced electronics allow it to act as a motor as well as a generator. For example, when it needs to, it can draw energy from the batteries to accelerate the car. But acting as a generator, it can slow the car down and return energy to the batteries.

Generator - The generator is similar to an electric motor, but it acts only to produce electrical power. It is used mostly on series hybrids (see below).

Batteries - The batteries in a hybrid car are the energy storage device for the electric motor. Unlike the gasoline in the fuel tank, which can only power the gasoline engine, the electric motor on a hybrid car can put energy into the batteries as well as draw energy from them.

Transmission - The transmission on a hybrid car performs the same basic function as the transmission on a conventional car. Some hybrids, like the Honda Insight, have conventional transmissions. Others, like the Toyota Prius, have radically different ones, which we'll talk about later.

(Picture Right: The Mercedes-Benz M-Class HyPer -- a hybrid concept vehicle, Image courtesy DaimlerChrysler)

You can combine the two power sources found in a hybrid car in different ways. One way, known as a parallel hybrid, has a fuel tank that supplies gasoline to the engine and a set of batteries that supplies power to the electric motor. Both the engine and the electric motor can turn the transmission at the same time, and the transmission then turns the wheels.

You'll notice that the fuel tank and gas engine connect to the transmission. The batteries and electric motor also connect to the transmission independently. As a result, in a parallel hybrid, both the electric motor and the gas engine can provide propulsion power.

Typical Parallel Hybrid

4-cylinder Engine, Simillar to the engine in most cars, but smaller and more efficient.

Electric Motor, Simillar to the motor in electric car, but usually smaller since it doesn't have to power the by itself.

Transmission, Some hybrids have conventional transmissions, others use more exotic technology like CVTs.

Batteries, The batteries store energy recovered from braking or generated by the motor.

Fuel Tank, The main energy storage device for the hybrid, usually gives the car a range of 500 miles or more.

Typical Series Hybrid

By contrast, in a series hybrid (below), the gasoline engine turns a generator, and the generator can either charge the batteries or power an electric motor that drives the transmission. Thus, the gasoline engine never directly powers the vehicle.

Take a look at the explanation below of the series hybrid, starting with the fuel tank, and you'll see that all of the components form a line that eventually connects with the transmission.

Fuel Tank, The main energy storage device for the hybrid, the fual tank usually gives the car a range of 500 miles or more.

Electric Motor, Simillar to the motor on an electric car, the motor on a series hybrid provides all of the propultion power.

Transmission, Simillar to the transmission on electric vehicle, the motor can spin fast enough so that the transmission only needs one generator.

Batteries, The batteries store energy recovered from braking or generated by the motor.

Generator, This is where the gas engine's power gets converted to electrical power to drive the motor or charge the batteries.

Four-cylinder Engine, The engine on a series hybrid turns the generator. It is not able to power the car directly.

The structure of a hybrid car harnesses two sources of power to increase efficiency and provide the kind of performance most of us are looking for in a vehicle.

What Makes it a

by Karim Nice

Any vehicle is a hybrid when it combines two or more sources of power. In fact, many people have probably owned a hybrid vehicle at some point. For example, a mo-ped (a motorized pedal bike) is a type of hybrid because it combines the power of a gasoline engine with the pedal power of its rider.

Hybrid vehicles are all around us. Most of the locomotives we see pulling trains are diesel-electric hybrids. Cities like Seattle have diesel-electric buses -- these can draw electric power from overhead wires or run on diesel when they are away from the wires. Giant mining trucks are often diesel-electric hybrids. Submarines are also hybrid vehicles -- some are nuclear-electric and some are diesel-electric. Any vehicle that combines two or more sources of power that can directly or indirectly provide propulsion power is a hybrid.

The gasoline-electric hybrid car is just that -- a cross between a gasoline-powered car and an electric car. Let's start to explain the differences.

Gas-powered Car

A gas-powered car has a fuel tank, which supplies gasoline to the engine. The engine then turns a transmission, which turns the wheels.

A typical four-cylinder engine for gasoline-powered car engines typically produce more than 100 ht and operate at speeds up to 8000 rpm.

The energy storage device for the car, it usually gives the car a range of 300 miles or more.

The transmission allows the engine to operate in a narrow speed range while allowing the car to drive at speeds 0 to 150 mph.

Electric Car

Electric car has a set of batteries that provides electricity to an electric motor. The motor turns a transmission, and the transmission turns the wheels.

The electric motor can spin at speeds up to 15000 rpm and has up to 100 KW of power, giving some electric cars a sport-car-like acceleration.

The energy-storage device for the electric car, the batteries usually give the car a range of 5-100 miles.

Since the motors can operate from 0 to 15000 rpm, most electric vehicle transmission have only one gear ratio.

Introduction to How Hybrid Cars Work

by Karim Nice

Have you pulled your car up to the gas pump lately and been shocked by the high price of gasoline? As the pump clicked past $20 or $30, maybe you thought about trading in your car for something that gets better mileage. Or maybe you're worried that your car is contributing to the greenhouse effect.

(Picture right: The 2000 Honda Insight hybrid electric car)

The auto industry has the technology to address these concerns. It's the hybrid car. You're probably aware of hybrid cars because they've been in the news a lot. Most automobile manufacturers have announced plans to manufacture their own versions.

How does a hybrid automobile work? What goes on under the hood to give you 20 or 30 more miles per gallon than the standard automobile? And does it pollute less just because it gets better gas mileage? In this article, we'll help you understand how this amazing technology works, and we'll even give you some tips on how to drive a hybrid car for maximum efficiency.