Electric Cars and Straight Talk on Lithium-Ion Batteries
Is Lithium-Ion a Safe Bet to Run Your Hybrid Car?
For decades, researchers have been working to create electric cars. To do so would free America from its dependence on foreign oil, slow the degradation of our atmosphere, and help the auto industry compete on a global scale.
Electric cars depend on an extremely powerful and durable electric motor. And this motor is turned by a similarly amazing battery. Ironically, what makes batteries effective also makes them a threat to safety. Incredible voltage levels could do incredible harm if not expertly and frequently checked.
Unfortunately, danger is inherent in transportation. Driving is the most dangerous activity that most people do. So the best engineers can do is to make electric cars safe before they hit the road. Part of ensuring safety comes from predicting what kinds of external accidents may occur, such as collisions or abrupt breaking, and how they would affect the battery.
The two main foci are minimizing charge and containing chemicals. Batteries do this with active and passive monitoring, through combinations of many safety features. A single battery pack may utilize rupture disk, pouches, thermistors, current interrupt devices, pressure monitoring, closing separators, placement and protection, cooling fans and heaters, and then hopefully be recycled when removed from the vehicle.
When dealing with incredibly effective yet dangerous technology, engineers and designers employ a slew of safety features; redundancy is not a bad thing. Active monitoring is used extensively in automobile batteries. Microprocessors are constantly checking for abnormal activity. Because a slight malfunction can quickly escalate in a multi-cellular pack, the computers check for risks at a high rate: thousands of times per second. A CPU monitors energy use so that the
battery supplies an appropriate amount of charge. It also takes signals from sensors that measure impact, air bag release, and the difference between hot and neutral wires.
In the Tesla model, it constantly connects to the batteries to keep the circuit closed. Without the computer’s command, the battery won’t deliver power. Thus, if the CPU is disabled, energy flow will shut down, not remain unwatched. Pressure and temperature vary directly in an enclosed volume. So a device that measures pressure levels can inform a system about when the temperature is rising. A current interrupt device does even better; the device itself prevents dangerous current.
Without relying on a computer, the CID itself opens the circuit when triggered by a rise in pressure. The current flows through a ring made of a pressure disk and a rupture disk. When the pressure rises sufficiently, the rupture disk is pushed outwards, breaking the connection.
For batteries that lack CID’s or for the purpose of redundancy, pouches around the battery allow gas to escape when the internal pressure becomes too great. They also contain the juices in case of explosion; battery electrolytes are very corrosive or at least very hot. A third feature of the pouch is to keep external chemicals from contacting the cell. If a foreign substance contacts an integral part of the battery’s circuitry, unforeseen and
potentially dangerous reactions could occur.
Between the positive and negative electrodes lies a separator. This piece of electrolyte-soaked plastic l, only 25 micrometers at the thickest, has pores that allow the passage of ions but not electrons. The charged ions maintain an electrochemical equilibrium, which prevents a short circuit. The pores will shut, preventing further electric flow. Alternatively, the entire separator may be designed to melt at a significantly high temperature. When melted, the separator prevents the movement of any molecules, ions, or charges. It does so mechanically, by permanently closing the passageway.
Another ingenius passive device recognizes the danger of heat on the battery. A resistor with a positive temperature coefficient, also called a thermistor, is a material in which change in resistance and change in temperature are directly related. Thusly, when a cell gets hot, the resistance increases. At dangerously high temperatures, the resistance will be so great that hardly any current can flow. This will stop large amounts of electricity from harming passengers in the event that batteries melt.
Heat isn’t always a problem for batteries. Each type has a unique temperature that maximizes efficiency. Considering the wide range of temperatures in which consumers drive, from freezing mountains to baking beaches, batteries can get far above or below that optimum temperature. When below freezing, lithium will plate on the separator; a process that is irreversible. When the battery is too hot, there is an obvious threat of fire and explosion. To maintain a temperature that is less dangerous and more efficient, batteries are equipped with a fan, a heater, or both.
In addition to temperature monitoring, the location of the battery also determines how safe it will be during an accident. The battery pack is tucked away from the passengers and enclosed in heavy metal, which would contain any spilled battery acids. Another locational feature is to maintain sufficient space between the battery and the chassis. Otherwise, a malfunctioning battery could send pulses of high voltage energy throughout the car and its surroundings.
Another concern is how close the battery pack should be to the driver and passengers. The National Institute of Health and the American Cancer Society cite dangers of electro-magnetic radiation, the same reason that cell phones have been in the media as of late. Because all-electric vehicles have just been discovered, there are no studies showing a correlation between cancers or other diseases and electric-car usage. Toyota claims that the Prius has easily complied with the European standard of electromagnetic field emission.
Finally, an environmental safety concern is the impact of the battery after it leaves the car. Chemicals that are damaging to people are just as bad for plants and ecosystems. Technology exists to recycle the components but the process is currently more expensive than finding new materials. Some wonder if we are simply replacing oil with an equally detrimental technology, trading one dependence for another. The most crucial difference is that oil is used up, whereas lithium and other substances are mostly still present when the battery pack is discarded. A government subsidy could help cross this monetary gap.
Even if batteries aren’t properly disposed of, lithium-ion is far more friendly than previous types of batteries. “Lithium manganate is like sand. It has almost no environmental impact — unlike lead acid batteries that contain poisonous heavy metal,” claims Tim Boyle of the United States Department of Energy’s Sandia National Laboratory. “Also, the lithium battery can be recharged – meaning that it isn’t thrown out, but used over and over again.” In addition, batteries can be improved by using safer materials, whereas oil is relatively unalterable.
However, according to former Bell Labs director Don Murphy, lithium-ion capacity improves by only 7% per year. This rate of advancement pales in comparison to the typical increase in electronic technologies, like Intel’s computer chips that double in capability every two years. Considering that the batteries inability to power vehicles for extended distances is preventing the mass transition to all electric vehicles, designers will be more focused on a material’s energy density and less concerned with its environmental side effects.
Battery engineers will have nature as a higher priority once the lithium-ion battery is capable enough to meet demand, has achieved its theoretical energy density, or has surpassed the ability of the drive train. Yet even then, government interference may be necessary to foster environmental consideration. Hopefully, car manufacturers realize that desire for a healthy environment is a major factor behind consumers choosing to go all-electric.
In essence, all a battery needs is a potential difference, separated in a way that sends electrons through a device. But electricity is tricky-if possible, it’ll find a new stream down which to flow. Solely of importance is the shortest path, the path of least resistance, the fastest way to reach the lowest energy level.
These alternate routes can be dangerous, even deadly, for users of a battery-powered apparatus. Likewise, the potential difference is created by certain corrosive anions. When uncontrolled, such liquids pose a threat to life. So significant technological research is focused on the safety features of such powerful batteries.
Many strategies are combined to create layers of redundancy, so if electricty outsmarts one method, another will prevent further damage. We go to such lengths because portable energy is incredibly useful. Consider the popularity and rapid integration of cell phones, laptops, and other battery-dependent devices.
In fact, the progress we have made towards efficient batteries in consumer electronics has made implementation possible in vehicles. Research that produces more powerful batteries should occur in tandem with research on battery protection. While great electrical capability provides incredible benefits to mankind, without meticulous safety inspection and care it poses incredible threats to individuals.
Hopefully, our current safety technology will prove exhaustive and yet keep improving. Electric cars will be a huge improvement over the internal-combustion engine thanks to batteries that are both safer and more efficient than ever before.