Batteries aiming for energy efficiency

energy efficiency , lithium battery , electric cars , batteryThe fact that they are part of our everyday life should not let us forget that only after countless experiments could electric batteries come to life. Over one-and-a-half century went by between the invention of the first battery by the Italian scientist Alessandro Volta in 1799 and this of the first rechargeable battery by the French physicist Gaston Planté. The history of this technology was interspersed with successive works by William Cruikshank, who invented the electric battery in 1802, William Grove as well as Robert Bunsen, with the purpose of making safer, cheaper and more powerful batteries. But what is actually referred to as a battery? What are the most promising technologies to make them more energy efficient?

A battery is an accumulator capable of storing electricity using metallic and chemical components so as to use it in the future. This is made possible by a chemical reaction between the components. A battery includes three elements: an anode or negative pole, a cathode or positive pole and an electrolyte, that is to say a solid or liquid substrate allowing electric current to flow between these two poles. When the battery is in use, electrons travel from one pole to the other thanks to ions. Once all ions have been transferred, the battery is “flat” (depleted). The term “oxidation” refers to the reaction through which the anode lets go of electrons and the word “reduction” means the reaction through which the cathode catches them back.

The kinds of metal and chemical components present in a battery are its DNA and determine its energy efficiency

  • The lead-acid battery is the oldest kind. It includes two layers of lead and rubber dipped in acidic water. It is still frequently used in the automobile industry. Its main advantage lays in its cost and its capacity to be recharged at all times with no loss in performance.
  • There is a whole range of nickel batteries, among which the most used are the nickel-cadmium (NiCd), the nickel-metal-hydride (NiMh) and the nickel-zinc (NiZn) batteries. The first of the aforementioned is less and less used because of cadmium-induced pollution, with this component banned by the European Commission in 2006 (Directive 2006/66/CE). The NiMh, which has been on the market since 1990, has an energy value 30% superior to that of the NiCd battery. Furthermore, towards the end of its life it pollutes less than its counterparts, which is why it has been used for a long time in hybrid or electric cars. Although its lifetime is shorter than the NiCd battery’s, it is more efficient and little prone to the so-called “memory effect”, a physic-chemical phenomenon which slows down the accumulator’s energy delivery capacity. The NiZn battery’s most obvious assets are its low cost and toxicity. Nevertheless, it has a shorter life-cycle (number of possible charge/discharge repetitions).
  • The lithium battery is currently the most advanced technology. There are two main sorts: metallic lithium batteries with a negative electrode made of lithium metal, and lithium-ion batteries which use distinct components in each electrode to preserve the ionic state of lithium. Whereas metallic lithium batteries are known to be dangerous, the lithium-ion technology has many advantages, for instance its higher energy output and the absence of memory effect. However, it is still expensive today.

The automobile industry, main seeker of powerful, self-reliant and dependable batteries

The development of electric vehicles made efficiency and safety crucial for manufacturers. The sodium-nickel-chloride zebra battery, based on a combination of sodium chloride (that is to say, salt), nickel and iron, is an interesting solution available. However, it operates optimally only if its components are subjected to high temperature, ranging from 270 to 350 degrees Celsius. It is a limitation of its use in the automobile, since cold-start cycle damages it prematurely.

To address the issues intrinsic to electric cars, several experiments are being held in order to make always more powerful and economical batteries. Lithium batteries, for instance, are expected to yield a higher ion storage capacity thanks to manganese oxide (LiMnO2) and nickel oxide (LiNiO2). Their power could rise from 150 Wh/kg to 350 and even 500 Wh/kg.

Although lithium batteries have proved their worth, researchers plan on doing without this component. The last stage of research consists in using enzymes from the biomass in order to produce electrodes already electro-chemically charged. Super condensers are another solution: they operate based on static, have a virtually unlimited life time and require more basic and cheaper materials. However, their electric density (and so their power) is still too low for them to be used in today’s battery-based devices.

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