New plastic films offer an option for hybrid vehicle batteries

Lead-acid batteries, invented in 1859, are not very respected by environmentalist as they contain lead. They are heavy for the energy they store, and they degrade easily if not cycled properly. This crucial under-the-hood part has not seen any major advances in the technology over the decades. As a result, substitution/replacement technologies are being developed. In the late 1990s, hybrid cars that used a 60-volt lead-acid pack and a separate 150-volt supercapacitor pack were designed and tested. The lead-acid system allowed the vehicles to drive in all-electric mode in the city, while the supercapacitors gave the cars the jolt that was needed for acceleration and the ability to quickly absorb energy from braking. Though the car functioned well, the heavy weight of all the power electronics required to control the two power systems were also very expensive. As a result, Lamb's team decided to eliminate the need for all external electronics - one of the plates (the negative electrode) in the lead-acid battery was made half of lead and half of carbon, converting the battery into a supercapacitor-lead-acid hybrid.
Nickel-metal hydride batteries account for 97% of the hybrid electric vehicle market, by revenue. But the nickel-metal hydride technology has reached its maturity and battery makers and auto manufacturers have begun turning their attention to lithium-ion batteries because they are smaller, lighter, able to hold a charge longer and have a higher energy density. A newer generation of batteries, notably lithium-ion batteries are an improvement over the lead-acid batteries. Developments are underway to make these batteries efficient, inexpensive and safe. Hybrid vehicles use both battery and gas for powering the car- wherein the lithium-ion batteries store the electricity to power these vehicles. Plastics play a vital role in such batteries, particularly in their use as separator membranes between the anodes and cathodes of these devices. Separator films are membranes that keep the battery's positive and negative fields, which are wrapped in a jelly-roll configuration, from touching. Typical hybrid vehicles contain between 50 and 70 batteries; plug-in electric vehicles with range-extending motors have 80 to more than 200 batteries; and fully electric vehicles carry 150 or more. Within each battery, the separator is a sheet positioned between the two electrodes. It functions as a barrier that prevents the electrodes from touching and shorting while letting lithium ions pass back and forth to allow the charge and discharge of the battery. To meet the performance criteria of advanced lithium-ion vehicle batteries, separator membranes are required to be porous, so that ions can pass through them easily when the battery is being charged or discharged. However, if the battery starts to overheat, the membranes must lose that porosity, thus shutting off the flow of current. Such overheating can occur if a battery is overcharged, or due to a short circuit caused by manufacturing defects. Most separators, whether commercial or developmental, are based on microporous polyolefin films, which are light-weight and low in cost. The emerging separator materials are based on polyamide, fluoropolymers, or plastic-ceramic composites.
Exxon Mobil Corp�s new development has led to rechargeable lithium-ion batteries to power cars and trucks, akin to batteries in cell phones and laptops. A super-thin plastic sheeting that can improve the power, safety and reliability of lithium-ion batteries for use in automobiles. The film allows battery makers to build smaller and cheaper battery systems- removing key obstacles that have kept automakers from building hybrid and electric vehicles on a wide scale. The film was developed with Japanese affiliate Tonen Chemical and is the first to squeeze multiple layers of plastic into a single white sheet the width of a human hair. The added layers enable the batteries to run at higher temperatures and produce more power, while still protecting them from overheating. It also incorporates features that cause it to shut down if there is a short circuit in the battery. By 2012, hybrid sales will grow to 1 million, or nearly 6% of the market. A hybrid like the Toyota Prius, combines a gasoline engine with an electric motor to achieve better fuel economy and lower emissions than vehicles with only a traditional internal combustion engine. But hybrids cost almost US$3000 more than their gas-powered counterparts, and weigh 900 lbs more, leading to sluggish performance. If Exxon's film separator can reduce the costs and weight of battery systems, then hybrids could become more than a niche market.
To reduce the use of fossil fuels and to meet the growing demand for hybrid and electric vehicles, DuPont has introduced the first nanofiber-based polymeric battery separator that boosts performance and safety of lithium ion batteries. DuPont� Energain� battery separators can increase power 15-30%, increase battery life by up to 20% and improve battery safety by providing stability at high temperatures. With more battery power, the car can travel farther on a single charge and accelerate more quickly and safely. For automobile and battery manufacturers, more battery power can reduce the number of batteries typically required in today�s hybrid and electric vehicles. The Energain� separators boost performance and safety of lithium ion batteries. It is a sheet between two electrodes to prevent them from touching while letting lithium ions pass back and forth to allow the charge and discharge of the battery. DuPont estimates that, by 2015, the market for high-performance lithium ion batteries alone will total more than US$7 bln pa, primarily for electric vehicle applications and some photovoltaics and grid storage. DuPont^� Energain� battery separators are produced into a web using a proprietary spinning process that creates continuous filaments with diameters between 200 and 1,000 nanometers. The separators exhibit stability and low shrinkage in high temperatures and are highly saturable in electyrolyte liquids. The result is more efficient operation, longer battery life and improved safety. Batteries containing Energain� separators can be quickly recharged, deliver improved performance and reduce the number of batteries needed by up to one-third for hybrid vehicles.
Innovative new grades from Solvay have been developed for hybrid and electric cars- a new series of Polyvinylidene Fluoride (PVDF) for use in Lithium-ion batteries. PVDF Solef® was already recognized as a key component in the Li ion batteries used in mobile phones, computers or electric tools. Solvay's R&D efforts have resulted in a new generation of PVDF which significantly increase battery energy density and cycle life, making it possible to store more electrical power in batteries with the same volume and weight. Increasing energy density and driving down Li ion battery costs support the use of these batteries in new applications, such as hybrid cars. Li ion batteries are significantly lighter than the currently used car batteries. Battery weight reduction leads to lighter cars, consuming less energy.
Hybrid cars and EVs rely on batteries for power, but batteries are bulky and heavy, causing the car to use up more energy. Researchers are working on the car's bodywork of a strong, lightweight material that could store and discharge electrical energy just as a conventional battery does. Researchers at the Imperial College London are developing a key building block for the hybrid car of the future, on the principles of wafer thin mobile phones and laptops that do not need a separate battery because they draw power from their casing. Imperial College has been working on the idea as part of a �3.4 mln, 3 year European Union-funded project which includes researchers from a number of European partners, including automotive firm Volvo. The prototype material is a composite of carbon fibers and a polymer resin which can store and discharge large amounts of energy much faster than conventional batteries. Unlike these there is little degradation in the material over time because there is no chemical process involved, and this also aids more rapid recharging. It is lightweight and strong enough to make car body parts, and could be plugged into the household power supply for recharging. Researchers say the next stage is to further develop the composite in order to store more energy. This may be achieved by growing carbon nanotubes on the surface of the carbon fibers which will increase the surface area, thus improving its storage capacity. They also hope to find alternative options for recharge such as recycling energy created during braking while the car is on the move. Their first test in-situ will be to exchange the metal floor in the car boot, or wheel well, for the composite, and Volvo is investigating the possibility of rolling this out in prototype cars for testing purposes. The addition of the composite combined with a reduced need for heavy batteries could see the car's overall weight drop by up to 15%, consequently increasing the range of future hybrids. The most effective method for manufacturing the composite material at an industrial level is also being investigated. The team is at the first stage of this project and opines that the composite material shows promise.
The future market for hybrid-electric vehicles, at least those that are affordable, isn't necessarily paved with lithium. Researchers in Australia have created � a lead-acid battery on steroids�, capable of performing as well as the nickel-metal hydride systems found in most hybrid cars but at a fraction of the cost. The so-called UltraBattery combines 150 year old lead-acid technology with supercapacitors, electronic devices that can quickly absorb and release large bursts of energy over millions of cycles without significant degradation. As a result, the new battery lasts at least four times longer than conventional lead-acid batteries, and its creators say that it can be manufactured at one-quarter the cost of existing hybrid-electric battery packs.