Batteries For EVs and HEVs

Name: Satyajeet Udavant

Course: Energy Storage and Devices

IUPUI, INDIANAPOLIS

Abstract: Lithium ion batteries are a great success to grow to become a leader in the battery

industry. Battery Sales is reaching $80‐billion annually. This report discusses a brief

history of the batteries for EVs and HEVs. It discusses why and how Battery powered EVs

and HEVs could become a reality. New advances in technologies like regenerative

breaking, mass production that reduces cost, battery management system, and higher

battery life and battery efficiency are the few of the techies that made this possible, at

length in the following report.

Introduction:

Environmental impact of traditional mode of transport -Our personal and luxury vehicles

are a major reason to global warming. Together, cars and trucks account for almost one-

fifth of all U.S. emissions, emitting more than 25 pounds of carbon dioxide, NOx, CFCs

and other global-warming gases for every gallon of gas. Almost 6-7 pounds comes from

various process of extraction, production, and delivery of the fuel, while the biggest of

all is of heat-trapping emissions which accounts more than 19 pounds per gallon it

comes from cars. Increasing number of cars used and with advancing technologies

substitute for traditional way of transport was necessary. As the following figure

suggest;

As you can see the graph is getting more steep with growing demand of the cars.

Need of Electric Vehicles and Hybrid Electric vehicles:

Electric Vehicles (EVs) are considered “zero emission” as they don’t release harmful

gases. They are said to be free from greenhouse gases or other pollutants and harmful

chemicals during usage.

“Based on electricity rates in 50 cities across the United States, the analysis found

drivers can save $750 to $1,200 dollars a year compared to operating an average new

compact gasoline vehicle (27 mpg) fueled with gasoline at $3.50 per gallon. Higher gas

prices would mean even greater EV fuel cost savings. For each 50 cent increase in gas

prices, an EV driver can expect save an extra $200 a year.”[1]

Comparison Table:

Characteristics Lead Acid Li-polymer

Specific energy 33–42 Wh/kg 100–265 W·h/kg

Energy density 60–110 Wh/L 250–676 W·h/L

Specific power 180 W/kg ~250-~340 W/kg

Charge/discharge

efficiency 50–95% 80–90%

Energy/consumer-

price 7(sld)to 18(fld) Wh/US$ 2.5 W·h/US$

Self-discharge rate 3–20%/month 31% at 60 °C

Cycle durability 500–800 cycles 400–1200 cycles

Nominal cell voltage 2.0 V 3.6 / 3.8 V

Charge temperature

interval min. −35 °C, max. 45 °C

1. Description of the project Provide some basic information on the topic such as the

working principles, structure, composition, etc. Background information.

What has been done for this topic, advantages and disadvantages of the current

work/approaches, what is the state-of-art of this topic? What is the problem?

Various Technology Advances:

Regenerative breaking.

In electric and hybrid cars, the regenerative brakes can do an amazing function, it can

charge the main battery pack, and therefore, it effectively extends the vehicle's range

between successive charges.

Most of the vehicles now use bulks of supercapacitors or ultracapacitors for storing

energy instead of batteries. The reason being supercapacitors can store energy more

quickly and can discharge it quickly. It is also better in storing large amount of energy.

The only disadvantage is that it can store it for long time. Also the wear and tear causes

more maintenance.

Working[2] : When you're driving along, energy flows from the batteries to the motors,

turning the wheels and providing you with the kinetic energy you need to move. When

you stop and hit the brakes, the whole process goes into reverse: electronic circuits cut

the power to the motors.

Now, your kinetic energy and momentum makes the wheels turn the motors, so the

motors work like generators and start producing electricity instead of consuming it.

Power flows back from these motor-generators to the batteries, charging them up.

Graphs talks about the comparison between the kinetic energy and the power to and

from the battery

Idle speed :Start-Stop In Urban areas due to heavy traffic cars are constantly under start and stop condition.

For conventional cars it uses the gasoline and due to less requirement of power a lot of

fuel is wasted. In hybrid and complete electric cars the powertrain is modified as per the

different driving conditions like in urban drive, the gasoline engine remains dormant

while at rest. Whenever cars come to a halt in traffic or signal scenarios the engine is

shut. Next time when the drive requires power to start it draws this power from the

battery .Battery technology has made cars more fuel efficient. Battery management

system deals with the management of the charge and discharge of the battery, heat

dissipation and temperatures effects are all countered and efficiency is increased.[5]

Above fig talks about the Start-stop Engine technology, Ideal for Urban areas where cars

are frequently run and stopped at signals.

Types of Battery

1.) Lead–Acid battery

It has very low energy-to-weight ratio and a low energy-to-volume ratio, power-to-weight

ratio is the ability to supply high surge currents.

Negative plate reaction:

Pb(s) + HSO− 4(aq) → PbSO 4(s) + H+ (aq) + 2e−

Positive plate reaction:

PbO 2(s) + HSO− 4(aq) + 3H+(aq) + 2e− → PbSO4(s) + 2H2O(l)

The total reaction can be written as

Pb(s) + PbO2(s) + 2H2SO 4(aq) → 2PbSO4(s) + 2H 2O(l)

The sum of the molecular masses of the reactants is 642.6 g/mol, so theoretically a cell

can produce two faradays of charge (192,971 coulombs) from 642.6 g of reactants, or

83.4 ampere-hours per kilogram (or 13.9 ampere-hours per kilogram for a 12-volt

battery)For a 2 volts cell, this comes to 167 watt-hours per kilogram of reactants, but a

lead–acid cell in practice gives only 30–40 watt-hours per kilogram of battery, due to the

mass of the water and other constituent parts.[3]

Application:

It is used in motor vehicles to provide the high current required by automobile starter

motors.

Risk:

Excessive charging causes electrolysis, it results in gassing. Process of emitting

hydrogen and oxygen is known as "gassing’’.

Also corrosion on the positive terminal is caused by electrolysis, this happens because

of the existant mismatch of metal alloys that are used in the manufacture of the battery

terminal.

2.) Nickel Metal Hydride battery

The NiMH battery is termed an alkaline storage battery due to the use of potassium hydroxide (KOH) as the electrolyte. Electrically, NiMH batteries are very similar to nickel cadmium batteries. Rechargeable alkaline storage batteries are a dominant factor in the market for several technically important reasons:

High electrolyte conductivity allows for high power applications

The battery system can be sealed, minimizing maintenance and leakage issues

Operation is possible over a wide temperature range

Long life characteristics offset higher initial cost than some other technologies

Higher energy density and lower cost per watt or watt-hour (depending on design)

3.) Li-ion battery:

The cathode

The anode

The overall reaction

Overdischarge supersaturates lithium cobalt oxide, leading to the production of lithium

oxide possibly by the following irreversible reaction:

[4]

Disadvantage:

However, one downside to lithium-ion batteries is that they require longer to charge

than other batteries. But there is always room for improving the efficiency

4.)Lithium Polymer Battery:

It has most advantages of that of the lithium ion battery. The solid polymer is

transparent to Li+ and opaque to electrons. This gives safety by giving a battery more

resistant to overcharge. Less chance to spill the electrolyte. Flexibility in shape and size

as thin strips or sheets are used. Therefore creating light weight cell.

Disadvantages: It has low ionic conductivity.

Few others:

Zinc Air Battery:

Sodium Metal Chloride Battery

Nickel Cadmium Battery:

Discussions:

Maintenance:

Hybrids have the components of a regular gas engine along with their electric aspects,

they do require the same routine maintenance as any other gas vehicle.

One of the biggest attacks made on hybrids has to do with battery life. It is said that the

battery life is very short, and if something were to happen to it, it is very expensive to

replace

Need of skilled labors to work on advanced systems that these cars possessed.

Fire hazards from overheating the battery

2. Conclusion

With the advances in technology hybrid cars are becoming a reality.

Regenerative breaking

Engine idle- start stop

Downsizing of the car components

Different battery types and the increased efficiency due to low consumption of fuel

Reference:

[1] http://www.ucsusa.org/clean-vehicles/electric-vehicles/emissions-and-

charging-costs-electric-cars#.Vxh_2DFu32I

[2] http://www.explainthatstuff.com/how-regenerative-brakes-work.html

[3] 3.014 MATERIALS LABORATORY MODULE – BETA 1

NOVEMBER 13 – 17, 2006 GEETHA P. BERERA LEAD-ACID STORAGE CELL

[4] Thin, Flexible Secondary Li-Ion Paper Batteries

Liangbing Hu,† Hui Wu,† Fabio La Mantia, Yuan Yang, and Yi Cui*

Department of Materials Science and Engineering, Stanford University, Stanford,

California 94305

[5] An Intelligent Regenerative Braking Strategy for Electric Vehicles

Guoqing Xu 1,2, Weimin Li 3,*, Kun Xu 3 and Zhibin Song 3