GM released photos showing the orange T-shaped battery pack of the Volt is not impacted during frontal collision. (Credit: General Motors)

View the full presentation Chevrolet Volt development update Nov 17 2009

More from Autoblog.com article “GM provides update on Volt vehicle and battery development” and CNET News article “For Chevy Volt drivers, battery life will vary.”

GM Photo of Chevy Volt Crash Test Shows Protected Battery Packs is a post from: CleanCarTalk

As the automobile industry moves toward alternative energy vehicles, near-term solutions include the already popular hybrid cars and the upcoming electric cars. Ironically, the single common performance killer among these new breeds of cars turns out to be their energy storage or battery packs that help them achieve their high mileage. Batteries tend to be unreliable and greatly affect the performance of any hybrid or electric car. Reliability of hybrid or electric cars can be improved with proper battery pack balancing.

Why is Battery Pack Balancing Needed?

Battery pack balancing is the maintenance of each battery cell, which centers on preventing the cells from reaching the minimum and maximum limits with every full charge and discharge cycle. Balancing the battery pack’s SOC, or state of charge, and making sure that the battery stays at an optimal level between full charge and full depletion can help your battery stay in great condition and can considerably lengthen the life of a single battery pack.

The full depletion of a battery pack is not advised since the extreme ends of a battery’s charge can sometimes cause changes to the electrode surfaces of the batteries. This sometimes happen due to SOC deposits that affect the original composition of the batteries. This may then lead to battery problems and possibly cell damage. To keep the battery pack balanced, the recommended operation is in the mid 30% to 50% of the SOC.

The Challenge of Battery Pack Balancing

Battery pack balancing is not a straightforward exercise. One of the most commonly advised practices is to charge each battery cell individually using separate low-voltage chargers instead of charging them together using a high-voltage charger. This will help prevent imbalance, though it could be a bit taxing and time-consuming to have to use multiple chargers. It is also advisable to shuffle the charges from high to low SOC, though this would require complex circuits and may be faced with certain limitations.

Battery pack designers also recommend the use of shunt clamps while charging. By shunting the current from one battery to the next each time a battery pack reaches the necessary clamp voltage, every battery will remain in the same maximum starting voltage. Aside from that, the use of a passive network may also be helpful. A passive network is an affordable and a manageable way of equalizing the voltage, but make sure to avoid deep discharges as this may affect the life span of the battery pack.

Battery Pack Monitoring

In order to ensure that the battery pack is optimally balanced, monitoring the pack closely is critical. Failing batteries should be identified and replaced when necessary. If a failing battery is not determined in a timely manner and left to continue to function within the pack, it can weaken the battery and its pack, and adversely affect the performance of your hybrid or electric car.

Battery pack monitoring is thus a significant function for proper battery pack balancing. Read more on “Design Considerations for Keeping Your Battery Pack in Top Performance: Balancing and Equalization vs. Pack Monitoring.”

Battery Pack Balancing – The Key to Maintain Top Hybrid and Electric Car Performance is a post from: CleanCarTalk

Amidst all this excitement about bailout money, new clean diesel, hybrid and electric cars announcements, joint ventures and collaborations, and battery development progress, I though we’d take a brief look at the history of the electric car. We may learn something from it.

An electric car is a vehicle that uses electric motors for propulsion. It needs electricity to operate instead of an internal combustion engine, or ICE, that runs on fossil fuel such as diesel or gasoline. Despite its long history, electric cars never took off in popularity. Fossil fuels have always been cheap enough so there was no reason to look at alternatives. While the electric car (or its concept) has always been a part of the transportation landscape all along, recent momentum for more efficient energy use and better environmental impact has allow the electric car to quickly become prominent as the search for alternative fuel vehicles plays a more dominant role in the car industry.

Electricity that powers an electric car comes mainly from onboard sources such as a rechargeable energy storage system or battery packs. The energy storage system

1. can be charged externally by plugging the vehicle into a power source when not in operation, or
2. it can be charged while the car is in operation via a small engine.

The former is thus called the electric car, or plug-in electric car (among other variations,) and the latter is what we know today as the gasoline-hybrid, diesel-hybrid, or fuel-cell hybrid depending on the fuel source of the ICE. Collectively they are just called hybrid cars or hybrids for convenience.

Electric Cars – the Early Years

Electric cars have been around since the 1830s, dating back to a time even before diesel and gasoline engines were created. Although the exact year is not known, records show that the first electric carriage was created between 1832 and 1839 by Robert Anderson, a Scottish businessman. In 1835, the first electric car was created by Professor Sibrandus Stratingh from the Netherlands. When the 1840s rolled along, two significant contributors, Thomas Davenport and Robert Davidson, invented more advanced electric vehicles using non-rechargeable electric cells.

It took quite some time for this development to be followed. It was only in 1865 that Frenchman Gaston Plante came up with a better storage technology for electric energy. The technology that Plante pioneered made a significant contribution to the flourishing of electric cars. By 1867, a two-wheel cycle created by Franz Kravogl from Austria that used this specific technology was displayed at a Paris World Exhibition showcase. This technology was later on refined by another Frenchman, Camille Faure, several years later in 1881.

In the same year, Gustave Trouve, a French inventor, also revealed a three-wheeled car that ran on electricity at the International Exhibition of Electricity in Paris. Thanks to the support of France and Great Britain, widespread development of electric cars became possible. It was only later on, around 1891, that the Americans paid attention to the electric cars following the creation of an electric wagon that can hold six people by William Morrison and A. L. Ryker.

The Growth of Electric Cars

During their heyday, electric cars performed rather well in terms of speed, distance, and overall performance. In fact, in 1899, Camille Jenatzy was able to go up to 62 miles per hour (mph) or 100 km/h in an electric car called Jamais Contente, which can even go as fast as 66 mph (105.88 km/h) at maximum speed. Due to the great potential of electric cars in the market, the vehicles increased in number steadily through the early 1900s. By 1897, electric taxis were roaming the New York City streets.

Even with the Internal Combustion Engine (ICE) vehicles in the picture, the electric cars progressed continuously. For a time, the electric cars sold more than the gas-based cars. The electric cars were warmly embraced by the upper class market and mostly in urban areas where light city driving is the norm. The easy to use nature of these vehicles also made them highly ideal for women drivers. However, due to the various limitations of the early electric cars, especially the limited speed, the electric cars could not prove its usefulness as driver demands continued.

Overall, the automotive industry was very much alive, and soon there came steam- and gasoline-powered vehicles in the late 1800s and early 1900s. Electric cars were found to be greatly advantageous over the other types of vehicles in the market because they produced no vibration, no noise, and no smell. They were also easy to use and to maintain unlike gas-powered cars that required gear shifting and steam cars that required longer start-up time and had less range. But since the electric cars were mostly sold to the upper classes, some of the vehicles featured luxurious and ornate carriages and very extravagant materials. All the way until the 1920s, the electric cars enjoyed great popularity.

Early 20th Century Decline of Electric Cars

The electric cars soon met their downfall, brought about by several factors. As more roads were developed, long distance travel became widespread, and the electric cars, which had limited range, could not match up to the needs of the new age. At around the same time, the Texas crude oil was discovered, and gasoline prices significantly fell, making gas-powered vehicles easily within reach of regular consumers. The gas-powered vehicles also received several various improvements (including the invention of the electric starter for automobile by Charles Kettering in 1912) that made them almost as easy to use as the electric cars. Gone were the days of hand-cranking the engine just to be able to drive somewhere.

Soon enough, the demand for ICE, or internal combustion engine, vehicles rose at such a rate that car companies started mass-producing the vehicles to answer to this growing demand. Led by Henry Ford, consumers welcomed several ICE vehicles into the market, and these vehicles were just more affordable and practical than the electric cars.

Despite its fate, the electric cars did not fade into oblivion. They were still used in special cases where the range is expectedly limited. However, when the 1930s came, the electric cars have all but disappeared and cease to be a viable commercial product.

Modern Revival of Electric Cars

It wasn’t until 1966 that U.S. Congress introduced a bill recommending electric cars as solutions to reduce air pollution What followed were a period of hits and misses that included various congressional laws and mandates, car industry attempts at making electric cars viable for consumers, and fleet operators trying out several electric car options in test programs. None proved successful enough as electric cars struggled against yet-ready electric drive technologies, fossil-fuel conglomerates including fuel producers and unwilling car manufacturers, and the general political environment that did not see strong values in electric cars.

In the early 1990s, California passed its Zero Emission Vehicle (ZEV) Mandate that required two percent of the state’s vehicles to have no emissions by 1998 and 10 percent by 2003. But the law did not hold its mandate and became weaker over the years with lower and lower number of ZEVs it required.

During this time frame, a few thousand electric cars were made available from various manufacturers. There were the Chrysler TEVan, the GM EV1, the GM S10 EV, the Honda EV Plus hatchback car, the Ford Ranger EV, the Toyota Rav4 EV, and the Nissan Altra EV. The Toyota Prius sold nearly 18,000 units during its first production year in 1997. Despite this, the car makers did not strongly market the electric cars. The mandate was eventually revoked, faced by the protests of major oil companies, and most electric cars released were recalled and destroyed except for some Toyota Rav4 EV models that still circulated in the used market.

This brings us to the present day.

The Prius is now in its third generation after 12 years on the market; undeniably a great achievement! The Prius now has a true and serious competitor in the Honda Insight 2010. Other hybrid, electric and clean diesel cars by both new and existing carmakers have been announced to hit the market in the next several years. We may now have the perfect environmental, financial, political and technical conditions to truly foster an explosive growth of electric cars.

Sources:

• PBS.org “NOW”: Timeline: Life & Death of the Electric Car
• Wikipedia “Electric car“
• About.com: Inventors “The History of Electric Vehicles“

History of the Electric Car is a post from: CleanCarTalk

Elkhart, Indiana – Further accelerating the manufacturing and deployment of electric vehicles, batteries, and components here in America, and creating tens of thousands of new jobs, President Obama today announced 48 new advanced battery and electric drive projects that will receive $2.4 billion in funding under the American Recovery and Reinvestment Act. These projects, selected through a highly competitive process by the Department of Energy, will accelerate the development of U.S. manufacturing capacity for batteries and electric drive components as well as the deployment of electric drive vehicles, helping to establish American leadership in creating the next generation of advanced vehicles.

View listing of award recipients. View map showing award recipients.

“If we want to reduce our dependence on oil, put Americans back to work and reassert our manufacturing sector as one of the greatest in the world, we must produce the advanced, efficient vehicles of the future,” said President Obama.

“For our nation and our economy to recover, we must have a vision for what can be built here in the future – and then we need to invest in that vision,” said Vice President Biden. “That’s what we’re doing today and that’s what this Recovery Act is about.”

The announcement marks the single largest investment in advanced battery technology for hybrid and electric-drive vehicles ever made. Industry officials expect that this $2.4 billion investment, coupled with another $2.4 billion in cost share from the award winners, will result directly in the creation tens of thousands of manufacturing jobs in the U.S. battery and auto industries.

The new awards cover the following areas:

• $1.5 billion in grants to U.S. based manufacturers to produce batteries and their components and to expand battery recycling capacity;
• $500 million in grants to U.S. based manufacturers to produce electric drive components for vehicles, including electric motors, power electronics, and other drive train components; and
• $400 million in grants to purchase thousands of plug-in hybrid and all-electric vehicles for test demonstrations in several dozen locations; to deploy them and evaluate their performance; to install electric charging infrastructure; and to provide education and workforce training to support the transition to advanced electric transportation systems.

Today, President Obama visited Navistar International Corporation, in Elkhart, Ind., to make the announcement. Navistar will receive a $39 million grant to manufacture electric trucks which the company reports will ultimately will create or save hundreds of jobs when full scale manufacturing at the site commences. Overall, seven projects in Indiana will receive grants totaling more than $400 million. The applications from the companies and from one university engaged in this technology research anticipate that these awards will create or save thousands of jobs.

Vice President Joe Biden and four Members of the Cabinet, also fanned out across the country to discuss the historic announcement.

Vice President Biden was in Detroit to announce over $1 billion in grants to companies and universities based in Michigan. Reflecting the state’s leadership in clean energy manufacturing, Michigan companies and institutions are receiving the largest share of grant funding of any state. Two companies, A123 and Johnson Controls, will receive a total of approximately $550 million to establish a manufacturing base in the state for advanced batteries, and two others, Compact Power and Dow Kokam, will receive a total of over $300 million for manufacturing battery cells and materials. Large automakers based in Michigan, including GM, Chrysler, and Ford, will receive a total of more than $400 million to manufacture thousands of advanced hybrid and electric vehicles as well as batteries and electric drive components. And three educational institutions in Michigan, the University of Michigan, Wayne State University in Detroit, and Michigan Technological University in Houghton in the Upper Peninsula, will receive a total of more than $10 million for education and workforce training programs to train researchers, technicians and service providers, and to conduct consumer research to accelerate the transition towards advanced vehicles and batteries.

Energy Secretary Steven Chu, whose Department selected the 48 award winners, visited Celgard, in Charlotte, NC, to announce a $49 million grant for the company to expand its separator production capacity to serve the expected increased demand for lithium-ion batteries from manufacturing facilities in the U.S. Celgard will be expanding its manufacturing capacity in Charlotte, NC and nearby Aiken, SC, and the company expects the new separator production to come online in 2010. Celgard expects that approximately hundreds of jobs could be created, with the first of those jobs beginning as early as Fall 2009.

EPA Administrator Lisa Jackson was in St. Petersburg, FL, to announce a $95.5 million grant for Saft America, Inc. to construct a new plant in Jacksonville on the site of the former Cecil Field military base, to manufacture lithium-ion cells, modules and battery packs for military, industrial, and agricultural vehicles.

Deputy Secretary of the Department of Transportation John Porcari visited East Penn Manufacturing Co., in Lyon Station, Penn., to award the company a $32.5 million grant to increase production capacity for their valve regulated lead-acid batteries and the UltraBattery, a lead-acid battery combined with a carbon supercapacitor, for micro and mild hybrid applications. East Penn Manufacturing is a third-generation family business with over 63 years in battery manufacturing.

Commerce Secretary Gary Locke visited Kansas City, Missouri, to announce a $10 million grant for Smith Electric to build and deploy up to 100 electric vehicles, including vans, pickups, and their “Newton” brand medium duty trucks. In addition, Secretary Locke announced three other grants supporting manufacturing and educational programs in Missouri: a $30 million grant to Ford Motor Company supporting the manufacturing of plug-in hybrid electric vehicles in Kansas City and in Michigan; a $73 million grant to Chrysler, for the manufacturing of 220 plug-in hybrid and electric pickup trucks and minivans in St. Louis and in Michigan; and a $5 million grant to Missouri University of Science and Technology, in Rolla, Missouri, to fund educational and workforce training programs on advanced vehicles technologies.

President Obama Announces $2.4 Billion in Grants to Accelerate the Manufacturing and Deployment of the Next Generation of U.S. Batteries and Electric Vehicles is a post from: CleanCarTalk

Ever find yourself driving behind a hybrid car?

With larger number of hybrids sharing the public roads, hybrid cars are becoming common sights everyday. So here’s the question: if you’re “caught” driving behind a hybrid, do you find your blood pressure soaring, or do you feel this is actually good for your health?

Now before everyone jumps on me for being mean or arrogant, let me explain. By design hybrid cars like the Toyota Prius, Honda Civic Hybrid and the Honda Insight Hybrid get higher mileage due in large part to the electric motor drive and regenerative braking, or regen.

Regen is the capability of the electric motor and battery systems to recapture the forward momentum of the car during deceleration and convert the energy back into electricity that can be stored in the battery packs. Depending on specific car design, regen can occur as soon as you let off the accelerator pedal (simulating engine braking,) when you “ride” the brake pedal lightly (regen only with no friction brake,) and when you push harder on the brake to activate both friction and regen. Typically, regen is not active below certain low speed range, like around 7 mph.

By definition, then, when you’re coasting, you’re recharging your battery packs. It’s also a known technique among hybrid drivers that while coasting, either on flat road or downhill, lightly riding the brakes to activate just regen and not friction braking will give you more energy capture. Drivers can do this safely and only use friction brake to finally come to a complete stop.

So regen is an important part of the overall hybrid system performance. In fact slowly coming to a stop without hard braking has always been an age-old advice for conventional car drivers. We just choose to occasionally forget efficient driving techniques, that’s all. Hybrid car or not.

I guess driving behind a hybrid car, or driving like driving a hybrid car, is actually good for your health, and a lot of other people’s health too. Now if I can just deal with those hybrids driving faster than the speed limit on the highway, just because they can still get great mileage at high speeds with their more efficient engines.

For those interested, here’s some hard core hybrid drivers discussing regenerative braking on the GREENhybrid.com Forum on the Toyota Prius versus the Honda Civic Hybrid.

Driving Behind a Hybrid – Soaring Blood Pressure or Good For Your Health? is a post from: CleanCarTalk

Battery pack technology is all about managing the temperature of the cells and low resistance of the interconnecting conductors, connectors, and switches. Battery pack technology is not the same as battery chemistry technology. The latter is about building functional individual battery units, while the former is about making those units work together effectively and safely to provide much higher capacities.

There is still a lot of room for creative pack designs in electric and hybrid-electric vehicles with different form, fit and function topologies and connection schemes. The most common requirement is the need for temperature management for high power performance and operational life of a pack. High current charging and discharging through parasitic resistances in the cells, connections, switches, and wire cables generate heat that must be dissipated without damaging the surrounding materials.

Here are some key factors governing good battery pack design.

Internal Heating Factor

Knowing where the heat originates is the first step in designing a cooling system. Just like ultracapacitors, cylindrical cells are rolled up like a jelly roll with an outside cover and dissipate the most heat through the electrode connections in the center at either end of the cylinder. Again just like ultracapacitors, prismatic cells are in the form of flat sheets and dissipate the most heat through the sides of the cell. Cells in the middle of the pack and at the end of the circulating air or coolant stream will be the hottest and deserve the most attention. The most stress on a cell occurs at high temperature and high voltage such as immediately after braking regeneration charging while going down a hill.

Quick, low cost, low resistance connections between cells are a challenge. One bad or corroded high resistance connection can create enough heat to destroy an entire pack very quickly during high current charging or discharging operations. Even if the cell chemistry can accept high current “quick” charging and discharging, resistive heating losses in the connections and wires can easily drop the stored energy efficiency to 50% from the 80%-90% efficiency of more moderate power operations.

MES-DEA Zebra Z5 battery pack Courtesy MES-DEA.

The challenge is to keep all the cells at a uniform cool temperature to prevent uneven cell aging and premature pack failure. It would be clever if the cooling system would start early in anticipation of high current downhill charging and startup accelerations. Today’s position locations systems make this a real possibility.

Low Ambient Temperature Factor

Keeping a pack warm is generally not a problem except during cold weather startups. Some batteries lose a significant amount of capacity at extremely low temperatures. Using part of the stored energy to power a heating blanket could work nicely prior to startup.

The “Zebra” Nickel Sodium Chloride (NiNaCl) battery requires an internal temperature of 300 °C (572 °F) to keep the NaCl electrolyte melted. Using the stored energy of the battery pack and excellent insulation, the temperature can be maintained over a number of days from the stored energy alone. The downside is that the battery must be preheated before use. Prematurely charging a cold Zebra will destroy an expensive pack.

Lithium Ion Factor

Lithium ion (Li ion) titanate is a unique battery chemistry that is endothermic (cools by absorbing heat from the environment) during moderate to low operational power currents. However, at high currents and with corroding connections over time a Li ion titanate pack has the same heat dissipation problems.

Tesla Roadster battery system – Courtesy TeslaMotors.com

The Tesla electric sports car battery pack uses an older Li ion battery chemistry that is more susceptible to thermal runaway. Even when passively sitting fully charged in a garage the Tesla pack uses the equivalent of two refrigerators power to continuously keep the pack cool.

Electromagnetic Radiation Factor

Often ignored, one final consideration in pack design is the high magnetic field surrounding the high current carrying conductors. The high current DC power of the battery leads to an inverter controller for control of the AC induction motor used in most electric vehicles. The high current AC coming out of the inverter creates enough electromagnetic radiation to drown out any nearby AM radio, so good shielding practices have to be followed in the wire and cable installation. Alternatively, this problem can be ignored if functioning AM radio reception is not a priority.

The Bottom Line

Very few battery pack manufacturers have successfully integrated all the pack thermal and electrical requirements into a mechanical structure that has to withstand the shock and vibration environment of transportation applications. With at least five new plug-in battery cars coming on the market within the next two years, resulting in thousands of electric cars driving on our roads, let’s hope the manufacturers are successful with their battery pack integration.

Design Considerations For Good Battery Pack Design & Integration is a post from: CleanCarTalk

Ultracapacitors are super high capacity versions of electric capacitor components that store energy in an electric field. These are devices that have raised the “capacity” of a capacitor so high that ultracapacitors or “supercapacitors” are now thought of as energy storage devices that can replace batteries in some applications. They are available in various cylindrical, square, and flat shapes and sizes. With increasing production volumes and economies of scale, their prices can be competitive with batteries.

Ultracapacitor Characteristics

Ultracapacitors, sometime called Ucaps, are high-power/low-energy devices while batteries tend to be high-energy/low-power devices. The lower equivalent series resistance of an ultracapacitor gives it higher roundtrip (in and out) energy storage efficiency, especially with lower losses at high currents. Ultracapacitor packs are ideal for storing high power braking regeneration energy and supplying quick acceleration energy. The original Honda FCX hybrid fuel cell car used ultracapacitors for the energy storage, as do some of the new hybrid electric transit buses.

Being a capacitor, the state of charge (SOC) energy is precisely determined by the square of the voltage (E=½CV²), where C is the capacitance. The SOC discharge profile is significantly different from a battery, but offers some unique characteristics and advantages. Low temperature performance down to a -40°C (-40°F) shows little degradation. Above 89°C (192°F) internal temperature the electrolyte will vaporize and cause a flash explosion. In general the cycle life is limited by the temperature history of the electrolyte, which slowly decomposes. Over a million complete 100% charge/discharge cycles can be expected.

Ultracapacitor Construction

Capacitors are electric components that store energy in an electric field between two electrically conducting plates or “electrodes”. Ultracapacitors or “supercapacitors” have electrodes are made from a high porosity carbon much like the carbon in air and water filters. This high porosity carbon (in some new devices carbon nanotubes) is somewhat like a microscopic sponge that has extremely high surface areas that increase the “capacity” of a capacitor to such a high density that ultracapacitors are now thought of as energy storage devices that can replace some battery applications.

Ultracapacitors are known as double layer carbon devices because the actual construction is like a layer cake with carbon electrodes on the top and bottom. In between the electrodes is an electrolyte to facilitate the movement of charged microparticles. A special separator sheet lies in the middle of the electrolyte to isolate the voltage between the top and bottom electrodes. Ultracapacitors are rolled up like a “jelly roll” to make cylindrical devices and stacked in flat sheets to make prismatic devices. The cylindrical devices dissipate most of the charging/discharging heat through the end electrode connections while the prismatic devices dissipate most of the heat through the flat sides.

Unlike some modern batteries of similar construction no chemical reaction takes place to store or release energy. One of the electrodes in a battery is made from a different material and different electrolytes are chosen to act as catalysts for the chemical reaction.

Ultracapacitor and Batteries

The combination of ultracapacitors with batteries offers potential advantages in power, energy, temperature range, and life. However, the different SOC voltage profiles make such combinations challenging especially in high power vehicle applications. There have been over 50 technical papers published on combining batteries and ultracapacitors.

I maintain that, for many applications, a simple parallel ultracapacitor pack combination with a battery pack could double the life of the battery pack and pay for the extra complexity.

At least one manufacturer is developing a type of hybrid battery/ultracapacitor cell for use in vehicles. An actual vehicle test using an energy storage pack built with hybrid battery/ultracapacitor cells more than doubled the pack life. The AFS Trinity hybrid SUV offered a combination of battery and ultracapacitor packs. Small scale testing in a camera circuit demonstrated the combination advantages and I suspect that there are some small cordless tool applications that have already implemented this design.

A Short Primer on Ultracapacitors is a post from: CleanCarTalk

The Institute of Electrical and Electronics Engineers (IEEE), the Society of Automotive Engineers (SAE), and others periodically publish magazine articles that provide update summaries on the leading candidate energy storage technologies. Research and Development (R&D) and production is on the upswing getting a kick from increased funding and tax credit support for electric vehicles (EVs) to reduce oil consumption and the generation of CO2 and other air quality contaminants. The American Recovery and Reinvestment Act of 2009 (ARRA 09) has designated $400 million for electric transportation technology and $2 billion for advanced car battery manufacturing.

Batteries or battery packs can make or break a hybrid or electric car. Here’s a look at the different battery options and their characteristics together with notes on key manufacturers. The list is in no particular order.

Lead-acid or valve regulated lead-acid (VRLA)

• Most widely used for starting engines.
• Cheapest option.
• Good power capability.
• Low energy density making it too heavy or too low capacity for some applications.
• Reduced capacity at low and high temperatures.
• Lead must be recycled.
• Good shelf life.
• Poor cycle life unless SOC (state of charge) range is limited during operation.
• Improvements are still being developed, look for various “hybrid” energy cells.
• Requires desulfation charge to extend the life an extra 25 to 50%.
• Deep cycle versions are used for electric vehicles to keep the cost down.

Nickel Cadmium (NiCad)

• Is going away because the biggest problem is the recycling of heavy metal cadmium.
• Has a memory problem without deep cycling.
• Requires watering maintenance.
• Average cycle and shelf lives, power and energy densities, with reasonable temperature performance and cost.

Nickel Metal Hydride (NiMH)

• Today’s standard for power and energy capacities and densities.
• Millions of packs in use.
• Shelf life requires charge maintenance.
• Cycle life several times better than lead-acid, but SOC range must be limited during cycles to attain HEV and EV life goals.
• Performance falls off at low temperature.
• Cooling is required for high current charge and discharge cycles.
• Panasonic is dominant producer and Toyota Prius dominant user.
• U.S. producer Cobasys has yet to prove it can supply good reliable packs.

Lithium Ion (Li Ion)

• High energy and power capacities and densities (lightweight) ideal for hybrid and EV applications. Ten-year shelf life and extremely high cycle life if SOC range is limited (40% to 70% or tighter); some low temperature performance drop off. Look for widespread production use by the middle of 2010.
• Most of the world supply of lithium carbonate source material is located in Bolivia, Chile and Argentina. Early abundance reports suggested the supply was insufficient to supply the potential global demand. Later reports suggest otherwise.
• Widely used in small electronics, early chemistries had a potential thermal runaway problem that led to a few explosions. More recent recipes must pass rigorous cell testing and have all but eliminated the problem, however there remains some residual concern about heat generated in pack designs.
• Nissan now in partnership with NEC to develop and produce an in house pack design for an EV starting with fleet deliveries in 2010 and the general public in 2012. A 26-minute “quickie” is one of the charging options. Nissan and others will offer pack leasing to control fears about the cost of replacing a failed battery pack.
• Magna Steyr in Austria is in volume pack production using A123 batteries for some European vehicle manufacturers. A123 is also developing some of its own pack designs.
• Toyota delayed introducing Li Ion packs, but may do so in their new plug-in Prius.
• Valence Technology Inc in Texas is in high volume production for electric bikes and scooters and has supplied larger packs to a limited number of plug-in hybrid school buses. The one negative is that these batteries tend to be a bit pricey. But I guess for extended EV range you get what you pay for at least for now.
• ThunderStruck, a Chinese company, is in high volume low cost cell production with limited quality control; about 10% of delivered cells are bad.
• Altairnano is leading the way in fast rechargeable cells with the lithium titanate chemistry. They give up some energy density to gain fast charging and high cycle life.

Nickel Zinc (NiZ)

• Powergenix, headquarters in San Diego and production in China, offers AA and sub C size cylindrical cells with D size in preproduction testing.
• The primary application so far is hand held power tools where they are a less expensive alternative to Li Ion and NiMH cells.
• Higher energy density than NiMH because of higher cell voltage of the chemistry.
• Easy recycle handling.
• Apparently good shelf life.
• Good efficiency (low cell resistance).
• Good lower temperature performance.
• Powergenix built a Prius replacement pack (it needs more R&D) and may find a niche market as a less expensive replacement pack supplier.

Ultracapacitors

• These devices have extremely low internal resistance (~0.2 milliohm) per cell and extremely high capacitance (~3000 Farads) per cell, making them ideal high power devices.
• However, they are generally low energy and need to work with a battery to achieve any driving range.
• Ideally the combination of batteries and ultracapacitors offer the best of both worlds, but the voltage versus SOC profiles don’t match and there has been very little development of large pack combinations.
• Hybrid cells may offer a way out.

This list represents a snapshot of various energy storage technologies available for upcoming hybrid and electric cars. Development in the industry is expected to move quickly in the next few years due to demands of the market and with the help of government regulations and financial stimulus packages. There are several major battery conferences on battery technology every year, both in the United States and around the world. For additional details, your favorite Internet search engine may be your best window into this fast moving, and critical, industry.

Battery Options for Hybrid Vehicles and Electric Vehicles is a post from: CleanCarTalk

The history of battery packs for electric vehicles is filled with stories of early failures and fires. Optimum and safe pack performance requires balancing and equalization management of the pack state of charge (SOC). A battery pack SOC is the equivalent of a fuel gauge which tells you how much usable charge remains in the pack.

Battery pack balancing and equalization management is the regulation or protection of individual battery cells from hitting the maximum or minimum limits when fully charging or discharging the whole pack.

Here are several methods used by battery pack designers to keep a battery pack in balance in order to get top performance out of the pack.

1. Ignore it – For only few cells in series and a limited number of charge/discharge cycles (like a 12-volt starting battery with six cells) that don’t deplete the battery, balancing doesn’t add much to the battery life. For large numbers of individual batteries in a full parallel and series matrix connection the distribution of cells may be good enough to average out variations and provide some fault tolerance without balancing, however, it can create a huge connection and cooling problem. For example, the Tesla Roadster sports car is thought to have a matrix connected type of battery pack with over 8,000 small AA batteries and connections. It almost always turns out that the cells in the middle of the pack are the hottest and hardest to cool. I’ve suggested that a good university student project would be to model such a design and determine sensitivities to manufacturing tolerances, aging, and failures of individual cells.
    
2. Charge each cell or sub pack separately – For example, if a number of 12-volt packs are connected together for a higher voltage pack, each 12-volt battery is charged to a full voltage SOC with a separate 12-volt charger rather than charging the whole pack with a single high voltage charger. If this is done periodically, like once a day, the assumption is that the charge/discharge cycles during the day won’t result in enough unbalance to be a problem. Multiple chargers and connection points can make this a bit cumbersome and time consuming.
    
3. Use a shunt clamp - During charging, as each battery in the pack reaches a predetermined clamp voltage, shunt (switch) the current around the battery to the next battery in line. This process is better known as equalization because every battery in the pack is “equalized” to the same maximum beginning voltage. This requires extra switching circuits that can be tricky for high voltage and high current applications.
    
4. Shuffle the charge - During operation constantly move some charge (current) from batteries with a high SOC to batteries with a low SOC. This requires even more complex circuits and can be limited by how much current can be moved at any time. It works well if the batteries don’t go through a lot of rapid deep cycling because it could take a while to complete all the shuffling. A failing battery in the pack could put a heavy demand on the shuffling system.
    
5. Monitor the pack - Continuously monitor the individual battery voltages in the pack and create a maintenance flag to replace the failing battery. This can cause disruptive and costly down time if not well planned, and typically requires many sensors, extra wiring connections, data acquisition network, some form of processing and reporting (display). This approach is commonly used in addition to balancing and equalization.
    
6. Use a passive network - Connect a resistor in parallel with each cell in the pack. This is a cheap and easy equalizing voltage divider that may work well depending on the resistor value and the length of time available for voltage equalization. However, it can create inefficiencies, generate extra undesired heat, and shorten the battery pack life because of extra deep discharges.
    
7. Others - Dozens of issued patents and published patent applications offer a source reference for finding other schemes to solve this problem.

By managing the battery pack SOC and limiting the operation to stay between a full charge and full charge depletion, battery pack life can be significantly extended.

Why is it bad to fully deplete the pack? Some battery chemistries change the composition of the electrode surfaces at the extreme ends of the SOC (fully charged or full depletion). For example, lead acid batteries at a depleted SOC deposits a sulfate coating on the plates thereby reducing the available electrode surface area. The electrode surface area is where the electric action takes place and the amount available determines the battery performance. Other chemistries such as Li Ion seem to be much less susceptible to electrode damage. However, all chemistries are susceptible to individual cell damage due to imbalances at the extreme ends of the SOC. Most battery pack manufacturers will recommend operating in the middle 30% to 50% SOC for optimum battery pack life.

Take the Toyota Prius as an example. Toyota does extremely well in the battery pack design and operation in the Prius hybrid car. The Prius Nickel Metal Hydride (NiMH) battery pack has 800 to 2000 full charge cycles because of the nature of the battery chemistry. However, by allowing use of only 7% of available battery capacity (usually in the middle of the SOC, about 50-60%), Prius’ battery packs are achieving 8 to 10 years and 100,000 to over 300,000 mile life of the pack. When Toyota says you can drive the Prius on electric alone, this really means the system allows you to drive on electricity alone using 7% of available SOC before the engine comes on for recharging. Because pack life performance has been much better than expected, Toyota has increased the operating SOC range to 15% to increase driving efficiency by capturing more of the braking energy.

The only downside of all of this complex battery pack SOC management is the fact that you are carrying around all the extra battery weight that it appears does not get used. You charge the battery pack only to 50-60% SOC, then use only 7% of that before recharging again. You may be tempted to somehow shave off battery weight to lighten the load the car has to lug around. In reality, it’s actually cheaper to extend the life of the battery pack (through maintaining ideal SOC range, hence heavy battery pack weight) than to save fuel by carrying around less weight.

Similar considerations apply to plug-in hybrids and all electric vehicles that we are going to look at in future posts. You probably don’t need to know all this to drive your hybrid or electric car, but you can give yourself extra battery life by taking advantage of every convenient charging opportunity and not waiting until the battery is fully depleted. We’ll talk more about leakage depletion and how to avoid shelf life damage.

Design Considerations for Keeping Your Battery Pack in Top Performance: Balancing and Equalization vs. Pack Monitoring is a post from: CleanCarTalk

For the most part, today’s car batteries are driven by low cost mass production economies of scale. They are still the same fast discharge, slow charge energy storage device required to start an engine. Technology improvements have evolved in the areas of chemistries, shelf and cycle life, performance environment, maintenance, packaging, and recycling. They all contribute toward offering more choices to the discriminating battery consumer.

Lead-acid is still the most popular choice for battery chemistry because the elements are cheap and production techniques are well known. Recycling efforts have reduced much of the damage previously done by discarding old lead-acid batteries. 

No matter what the chemistry, however, battery selection always starts with power and energy; the good old P and E. The battery has to have sufficient power over a long enough time to meet the peak load demand, e.g., turn the starter motor for a minimum of 3 10-second starting attempts. Because power equals current times voltage

P=IV, and

resistance heat losses (which is also expressed as a form of power) equal the current squared times the resistance

P(loss)=(I²R),

it is desirable to keep the voltage high and the current low for better efficiencies. Also, I²R not only describes the quantitative losses but also is real heat that must be dissipated to prevent high temperature damage to nearby materials. The resistance that causes heat loss can come from many components within the electrical system including parts of the battery itself or the wiring or connections. 

Minimizing the resistance is always a challenge. And because there is a limit to minimizing resistance in the battery or heavy-duty cables, the discriminating vehicle designer must look toward using higher voltage batteries to get the power needed to drive the hybrid or electric car. That is why over 50 years ago car manufacturers switched from 6-volt starting batteries to the 12-volt car battery that is now common. Many heavy-duty buses and trucks use two 12-volt batteries in series to provide electrical power for 24-volt accessories. Several years ago there was an attempt to move to 42-volt car and truck batteries, but it didn’t catch on because of the proliferation of inexpensive 12-volt and 24-volt accessories. 

In practice, for vehicle applications it is highly desirable to keep power currents less than 200 amps with only momentary spikes going higher. For example, if the power circuit has the small resistance of 1 ohm, at 200 amps the waste heat generated (I2R) is 40 kW, about the same heat put out by 40 hairdryers.

Making Battery Packs – The Key to Higher Voltage

The only way to get higher voltage battery packs is to “stack” or connect battery cells in series. Cells are essentially individual chemical batteries, and can be technically defined as “a vessel containing various chemicals which produce electricity as a result of the reactions taking place between these chemicals.”

So far so good, we’ll just stack the cells in series to get higher voltage and use larger cells or parallel stacks to get higher current and the problem is solved, right? Not so fast.

The first real world problem is that each of the stacked cells is not identical to the other cells in the stack because of slight differences in the fabrication processes and materials, i.e. manufacturing tolerances. The net result of differences in cell capacity, cell resistance, and leakage current is to cause the voltage to vary across each battery cell in a stacked pack. 

When charging or discharging a series connected battery pack, each cell has exactly the same current as the whole pack.  Because of the difference in resistance from cell to cell, repeated charge/discharge cycles of the pack cause the voltage variations between the cells to increase. Also, for the same charging current a lower capacity cell will wind up with a higher voltage than a cell with higher capacity; and for the same discharging current the lower capacity cell will have a voltage that drops faster than the cell with a higher capacity. Even if the pack sits on the shelf, over time the cells will have different voltages because of the variation in leakage currents (parasitic self discharge).

All this means that, as the state of charge (SOC) variations among the cells increase over time, some cells will eventually get excessively charged and some cells will get excessively discharged. In either case the cell is destroyed, typically resulting in a high cell resistance. Higher resistance means more heat generated during high currents and can result in a high enough temperature to melt materials and cause battery fires. If we’re lucky enough, the damaged cell will just short out, and the overall pack voltage and corresponding power capability will just be reduced. In either case, “unbalanced” voltages can result in destruction of the pack rather quickly as the best cells and the worst cells continue to be picked off from either overcharging or over-discharging. In a series connected pack it only takes one cell to fail in the open condition or “burn out” for the whole pack to fail. 

So now you have some understanding on how high voltage battery packs can be built to power hybrid and electric cars. There are always challenges involved, and the best designs will have to take advantage of new materials, designs, and compromises between many important physical and operational considerations the system must withstand in both typical usage and worst-case driving scenarios.

How does all this affect my hybrid and electric car? Look for my next post.

Building Reliable High Power Battery Packs: Here Are Some Practical Considerations is a post from: CleanCarTalk