Battery Technology for Electric Vehicles

An electrical battery comprises of one or more electrochemical cells that convert stored chemical energy into electrical energy using electrochemical processes. The energy density of such batteries is mentioned in Joule/kg or Watt-Hour/kg or Watt-Hour/Litre. Energy density denotes how much energy a battery can mass and provide for the vehicle with a given size of the battery. So the higher the Watt-Hour/kg the better the battery becomes for traction since the weight of the battery does play a significant role, especially in electric vehicles as the batteries need to be carried along. Batteries with higher energy density need less volume and weight, making it possible to develop light weight electric cars.  Also as such batteries use less material they will help lower costs too.

 

Impetus to Industry

 

There is a huge market and growing trend of battery technology, especially for use in the automotive industry. World’s leading car manufacturers are looking at various options and coming up with different ideas to build cars that run on electricity, due to the dependence of most countries on a foreign land for oil. The electric cars  lead to lesser oil consumption and lower carbon-dioxide emissions, working towards a green environment. Considering similar benefits having immediate as well as long-term impact, several governments and countries are adopting a multi-pronged approach to encourage manufacturing and sales of electric and hybrid-electric vehicles to curb oil consumption, air pollution and greenhouse gas emissions. A recent announcement from the UK government to establish and support a new ‘UK Energy Storage R&D Centre’ for the advancement of electric and hybrid vehicle batteries serves as an illustrative example. The £13m research centre aims to boost development of electric and hybrid vehicle batteries. The federal government in the United States too has financed $2.4 billion in electric battery production facilities and closely $80 million a year for electric battery research and development.

 

Industry Scenario

 

Developing suitable batteries is a prime challenge to boost sales of electric, hybrid and fuel-cell vehicles, for this could be the tipping point of bringing electric cars to the mainstream car owners. Batteries for such electric cars vary significantly from traditional lead-acid batteries used in internal combustion engine vehicles: they are larger, heavier and costlier. Besides these limitations, they come with safety concerns that necessitate use of electronically controlled cooling systems. Presently the most common rechargeable battery used in the automotive industry is the lead-acid battery and is known as Start-Lighting-Ignition (SLI) battery as this is its main purpose. The battery in this case consists of 6 galvanic cells connected in series, for a 12V system, with each providing 2.1V and hence a total of 12.6V at full charge. In heavier vehicles there are 24V systems where 2 such batteries are connected in series. Generally diesel vehicles require higher energy capacity batteries since these engines require heavy duty starter motors and also require that the head of the engine be heated for starting.

 

But the energy density in KWh/kg for these lead-acid batteries is very low and although they can be used in electric vehicles for traction, their weight becomes a limiting factor for distance to be travelled. A typical family car, for example, would require a battery with capacity of 40KWh for a single run of 200 miles. If the battery chosen is a lead-acid one, the weight of the battery would be around 1.5tons. This makes it impractical.

 

The energy density of gasoline on the other hand is 124KWh/kg. The only battery, presently available in the market, which comes anywhere close to this requirement is the Lithium Thionyl Chloride (Tadiran) battery with density of 1.1KWh/kg, however, the cost of this battery at present is too high.

 

The predicted demand for automotive traction batteries in 2020 is over $55 billion. The US government has pledged substantial financial assistance for batteries and electric motion projects as discussed earlier. Also they have announced a goal to have one million electric vehicles on the road by 2015. To this end, the feds have also announced tax credits worth up to $7,500 on the purchase of each new electric vehicle (EV) to encourage consumers and businesses to attain this goal.

 

Some car manufacturers have moved to fuel cells. This technology provides electricity by combining hydrogen with oxygen in a controlled manner. The technology offers very good energy density and can provide very long driving ranges. However, the main disadvantage of this system is that hydrogen cylinders need to be large for long drive ranges and also there are no readily available refueling stations for hydrogen.

 

It is for this reason battery operated cars have become more popular since it is easy to find plugs anywhere for recharging the batteries. Some car manufacturers are also working on developing hybrid vehicles where although the main source of electricity is from the battery, there are other resources on the vehicle to intermittently charge the on-board batteries and hence provide long driving ranges.

 

The industry has also experimented with other options such as the following.

 

  • Solar panels on the roof top of vehicles – Although a good option, the size of the panels need to be very large to provide appropriate voltage and charging current
  • Small hydrogen cylinders with fuel cells – Here the idea is to fast charge the battery for a couple of times
  • Diesel generators sets – Here although gasoline is used, it is used only for small intervals to charge the battery

 

The most important aspect for a battery driven vehicle is to use as little power for all other functions while retaining the majority for traction. Also the use of regenerative systems to return power to the battery will help increase the drive range.

 

An R&D Initiative by Ascenten for an Electric Vehicle

 

Now Ascenten is developing a system to sense key parameters in an electric vehicle and provide only that minimal power required for the relevant function/system within the vehicle.

 

For example, when the driver switches on the turning indicator, the system senses the daylight available and accordingly decides the intensity of the turning bulbs that blink. During the day, the bulb blinks quite rapidly, but with low intensity, accompanied by a low power beeper to catch the attention of other vehicle drivers. When the ambient light is low, the blinker frequency is low and intensity is higher. This is also true for the headlights used in the vehicle.

 

The system will also sense the vehicle’s angle of motion and accordingly apply the generator to the wheels. In other words, it will not apply any load on the wheels when the vehicle is moving up a slope, but will apply the generator when the vehicle is moving down the slope when the power for the electric motor is almost zero and therefore the generator can return the power back to the battery.

 

The unit is a microprocessor based system which also takes care of all the safety options on an electric vehicle. The most important being the disconnection of all power sources during an accident so there is no chance of electric shock or any other hazard because of electric power running through the vehicle.

 

Features discussed above represent only a partial list of full features being developed for proper battery power management, thereby enhancing the drive range of batteries used in electric vehicles.

 

About The Author

Abhaya Venugopal (Senior Project Manager, Ascenten) is responsible for Project Management and all customer engagements. He brings over 20 years of leadership experience in operations and delivery management. Abhaya also contributes in technical support, training and business development.

No Comments