Other Battery Technologies
In addition to the main advanced rechargeable batteries technologies (Li-Ion, Ni-MH, Ni-Cd), the lead acid technology has been used for a long time to build rechargeable batteries. Their typical application is the automotive industry for starting-lighting-ignition (sli), and back-up energy storage. Recently, new technologies are emerging, such has sodium sulfur Na-S, or sodium-nickel chloride Na-NiCl2 (Zebra).
Lead acid batteries
The lead-acid battery is based on: Lead dioxide as the active material of the positive electrode, Metallic lead, in a high-surface-area porous structure, as the negative active material, Sulphuric acid solution.
Lead-acid technology is composed of several sub-technologies distinguished by battery design and manufacturing process:
Flooded lead-acid batteries, Valve-Regulated Lead-Acid (VRLA) batteries with electrolyte immobilized by a gel, VRLA batteries with the electrolyte immobilized in an absorptive glass mat (AGM)
Flooded lead-acid batteries
In flooded lead-acid batteries, the positive plate (electrode) is comprised of lead dioxide and the negative of finely divided lead. Both of these active materials react with a sulphuric acid electrolyte to form lead sulphate on discharge and the reactions are reversed on recharge. Batteries are constructed with lead grids to support the active material and individual cells are connected to produce a battery in a plastic case. There are, however, major differences in battery construction depending on the duty cycle and application.
Charging: Total material conversion: 2 PbSO4 + 2 H2O 2 H2SO4 + PbO2 + Pb
Discharging: Total material conversion: 2 H2SO4 + PbO2 + Pb 2 PbSO4 + 2 H2O
Valve-regulated lead acid batteries (VRLA) with electrolyte immobilized by a gel or an absorptive glass mat (AGM)
A secondary battery in which the cells are closed but have a valve that allows the escape of gas if the internal pressure exceeds a predetermined value, valve-regulated lead acid batteries (VRLA) have a starved electrolyte either on Glass fibers (Absorptive Glass Mat, or AGM) or as a Gel (Gel technology) which allows for internal gas circulation. Water loss from overcharge is reduced to less than 10 % through recombination. VRLA can be installed in a free orientation and there are no leakages because of the absence of liquids. The construction of these batteries means that they do not require maintenance, making them especially advantageous for remote area installations.
Typical applications for AGM batteries include use in motorcycles due to their safety in the event of an accident, in auto racing due to their resistance to vibration and in fixed position applications in extreme cold environments where their lack of a free electrolyte means the battery is less likely to crack and leak.
Gel VRLAs can be found in application in wheelchairs due to their suitability for use indoors.
Vented Lead-Acid Batteries
Vented lead-acid batteries are covered secondary cells with an opening through which the products of electrolysis and evaporation are allowed to escape freely from the cells. Vented lead-acid batteries have a liquid electrolyte. The battery is closed by a vent plug and has a gassing rate more than 4 times higher than valve regulated batteries. Water loss by electrolysis during overcharge results in the production of hydrogen and oxygen gases. Vented lead-acid batteries are a well established technology and are economical to produce. Maintenance of water refill depends on design features and application (reduction of refill by recombination plugs or custom refilling systems). The state of charge and age can be checked very easily in vented lead-acid batteries.
Vented lead-acid batteries are commonly found in various traction applications.
This technology contains liquid electrolyte in an unsealed container, requiring that the battery be kept upright and the area be well ventilated to ensure safe dispersal of the hydrogen gas it produces during overcharging. The lead–acid battery is also relatively heavy for the amount of electrical energy it can supply. Its low manufacturing cost and its high surge current levels make it common where its capacity (over approximately 10 Ah) is more important than weight and handling issues. A common application is the modern car battery, which can, in general, deliver a peak current of 450 amperes.
The sealed valve regulated lead–acid battery (VRLA battery)
popular in the automotive industry as a replacement for the lead–acid wet cell. The VRLA battery uses an immobilized sulfuric acid electrolyte, reducing the chance of leakage and extending shelf life. VRLA batteries immobilize the electrolyte, usually by one of two means:
Gel batteries (or “gel cell”) use a semi-solid electrolyte.
Absorbed Glass Mat (AGM) batteries absorb the electrolyte in a special fiberglass matting
Sodium–sulfur battery Na-S
The Sodium–sulfur battery (or NaS battery), along with the related lithium sulfur battery, comprises one of the more advanced systems of the molten salt batteries. The NaS battery is attractive since it employs cheap and abundant electrode materials. Thus the first alkali metal commercial battery produced was the sodium–sulfur battery which used liquid sulfur for the positive electrode and a ceramic tube of beta-alumina solid electrolyte (BASE) for the electrolyte. Corrosion of the insulators was found to be a problem in the harsh chemical environment as they gradually became conductive and the self-discharge rate increased.
This technology has been used in large Energy storage systems connected to the grid.
Sodium-nickel chloride Na-NiCl2 battery (ZEBRA)
The ZEBRA battery operates at 245 °C (473 °F) and utilizes molten sodium aluminumchloride (NaAlCl 4), which has a melting point of 157 °C (315 °F), as the electrolyte. The negative electrode is molten sodium. The positive electrode is nickel in the discharged state and nickel chloride in the charged state. Because nickel and nickel chloride are nearly insoluble in neutral and basic melts, intimate contact is allowed, providing little resistance to charge transfer. Since both NaAlCl4 and Na are liquid at the operating temperature, a sodium-conducting β-alumina ceramic is used to separate the liquid sodium from the molten NaAlCl
4. This battery was invented in 1985 by the Zeolite Battery Research Africa Project (ZEBRA) group led by Dr. Johan Coetzer at the Council for Scientific and Industrial Research (CSIR) in Pretoria, South Africa. In 2009, the battery had been under development for more than 20 years. The technical name for the battery is Na-NiCl2 battery.
The ZEBRA battery has a specific energy of 90 Wh/kg and a specific power of 150 W/kg. For comparison, LiFePO4 lithium iron phosphate batteries store 90–110 Wh/kg and the more common LiCoO2 lithium ion batteries store 150–200 Wh/kg. Nano Lithium-Titanate Batteries store 72 Wh/kg energy and can provide a power of 760 W/kg . The ZEBRA’s liquid electrolyte freezes at 157 °C (315 °F), and the normal operating temperature range is 270 °C (518 °F) to 350 °C (662 °F).
The β-alumina solid electrolyte that has been developed for this system is very stable, both to sodium metal and the sodium aluminumchloride. The primary elements used in the manufacture of ZEBRA batteries, Na, Cl and Al have much higher worldwide reserves and annual production than the Li used in Li-ion batteries. Lifetimes of over 1,500 cycles and five years have been demonstrated with full-sized batteries, and over 3,000 cycles and eight years with 10- and 20-cell modules.
Modec Electric Van uses ZEBRA batteries for the 2007 model and the IVECO daily 3.5 ton delivery vehicle was announced in mid 2010. Th!nk City offers a ZEBRA battery option. In 2011, the US Postal Service began testing five delivery vans that had been converted to all-electric power, one of which uses a ZEBRA battery.
When not in use, ZEBRA batteries are typically continuously kept hot, so that they remain molten and ready for use. If shut down and allowed to solidify, reheating takes around 12 hours to restore the battery pack to the desired temperature and impart a full charge (starting from ambient temperature). This reheating time varies depending on the battery-pack temperature, and power available for reheating. After shutdown a fully charged battery pack loses enough energy to cool and solidify in 3–4 days