A broad range of different electrochemical systems and battery technologies exist today.
There are currently four battery families dominating the automotive and industrial battery market:
The selection of one of these technologies depends on application requirements regarding performance, life, safety and cost.
Lead based battery technologies
Lead-acid technology is the most widely used electrochemical system, used in numerous applications from back-up for uninterruptible power supplies and grid energy storage, to traction in battery electric vehicles and for starting, lighting and ignition (SLI) in conventional combustion engine vehicles.
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.
Total material conversion: 2 PbSO4 + 2 H2O 2 H2SO4 + PbO2 + Pb
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.
Rechargeable alkaline batteries employ a nickel hydroxide based cathode, with either a metallic anode (Nickel-Cadmium (Ni/Cd), Nickel-Iron (Ni/Fe), Nickel-Zinc (Ni/Zn) or a hydrogen storing anode (Nickel/H2, Nickel-Metal Hydride (Ni/MeH)). Due to technical limitations on maintenance and long term cycling performance, Ni/Fe and Ni/Zn batteries cannot be used for automotive or stationary applications. Ni/MeH is technically superior to Ni/Cd in a number of technical aspects and it can be used in many applications.
Both Nickel/Hydrogen (Ni/H) and Ni/MeH batteries are, in principle, the same battery system, utilising nickel hydroxide (NiOOH) as positive and hydrogen (H2) as negative electrode materials. In Ni/MeH batteries a hydrogen storage alloy is used. Both systems have an excellent cycle life.
Nickel based batteries are used for standby as well as other applications, including Electric Vehicles (EV), Hybrid Electric Vehicles (HEV) and for starting aircraft. They are available with pocket-plate or sintered electrodes in steel or plastic containers. A full range of applications is served and nickel based batteries are especially suited to electrically or mechanically arduous applications.
Nickel based batteries have a positive electrode of nickel hydroxide and a negative electrode of cadmium. On discharge the nickel hydroxide is reduced to a different form of nickel hydroxide with a lower oxidation state and the cadmium is oxidised to cadmium hydroxide. The reverse reactions take place on recharge. The electrolyte is a potassium hydroxide solution. The construction of the battery differs for particular applications but there are two basic types; either a pocket-plate type or types using a sintered or bonded electrode structure. For pocket-plate types, a perforated nickel-plated steel pocket is used to contain the active material. For sintered or bonded types, a porous partially sintered nickel substrate may be used but various plastic bonded structures and fibrous constructions are also offered. The pocket-plate construction is highly reliable and offers moderate performance but the other types offer higher levels of electrical performance. Nickel based batteries may also be constructed in a fully sealed form similar to VRLA batteries.
Nickel based batteries offer good resistance to electrical use as they can be left in a discharged condition for long periods without permanent damage and also offers good performance in higher ambient temperatures.
Lithium-Ion (Li-Ion) is currently the dominant battery system for portable applications. It was introduced to the market by SONY in 1991. Due to the high capacity of active materials and a single cell voltage of 3.6V, Li-Ion provides the highest energy density of all rechargeable systems operating at room temperature. Li-Ion batteries are also available as lithium polymer batteries using a solid or gel-type electrolyte.
The Li-Ion battery employs a Lithium metal oxide cathode and a carbon anode with an organic electrolyte. Over the last years tremendous improvements on battery parameters have been achieved. Both the high level of energy and power makes the Li-Ion system very suitable for various applications, ranging from high energy to high power. The high single cell voltage not only results in high performance, but also allows the use of fewer cells, compared to other battery systems.
Lithium based batteries can be found in electric vehicles and aerospace applications.
In lithium based batteries, the anode is made of carbon, while the cathode is a lithiated metal oxide (LiCoO2, LiMO2, etc.). The electrolyte is made up of lithium salts (such as LiPF6) dissolved in organic carbonates. When the battery is being charged, the Lithium atoms in the cathode become ions and migrate through the electrolyte toward the carbon anode where they combine with external electrons and are deposited between carbon layers as lithium atoms. This process is reversed during discharge. Because lithium reacts to water, non-aqueous solutions are used.
Sodium based batteries have a high energy density, long cycle life and can operate in harsh environments such as temperatures of -40°C to +60°C. For these reasons they can be found in application in energy grid storage, such as storing energy from intermittent energy sources such as wind- and solar-power.
Unlike many batteries, sodium based batteries consist of a solid or solid and molten electrolyte with liquid sodium acting as the negative electrode. These batteries are usually constructed in a cylindrical form, encased in a container which acts as the positive electrode. The chemistry is quite simple with no side reactions and roundtrip efficiency (charge/discharge) of up to 85%.
Sodium – Nickel Chloride Technology
The cathode is Nickel Chloride (Ni CL2) while the anode is made of Sodium (Na). The electrolyte is made up of tetrachloralluminate of sodium (such as NaAlCL4), and is liquid at the operating temperature of the cells (and battery) in between 270 °C and 350°C.
When the battery is being charged the Sodium atoms in the cathode become ions and migrate through the ceramic electrolyte (beta Al). Available free electrons could flow as current to an external load. This process is reversed during discharge.
The main advantages of Na- NiCl2 batteries, compared to other advanced batteries, are:
- No needs of air conditioning
- High energy density (cell level: 328 KWh/ m3 , 142 KWh/ton , complete battery level: 170 kWh/m3,120 kWh/ton)
- Long cycle life (2,000 cycles @ 80% depth of discharge) combined with a long calendar life of more than 15 years
- SOC (State of Charge) & SOH (State of Health) indication, remote monitoring of the systems
- Zero emission and high recyclability of the raw material
Commercialized since the middle of the 1990’s, Sodium Nickel Chloride batteries have found application in EV (electric vehicle) cars and HEV (hybrid electric vehicle) buses, trucks, vans. The implementation of Sodium Nickel Chloride batteries in the stationary field is in its starting phase. Demonstration systems combined with distributed renewable generators (large PV plants and micro wind turbine) as well as for grid support with voltages up to 600V have been designed and are now in field test phase.
No toxic or dangerous materials are used during manufacture of Sodium – Nickel Chloride batteries. The battery is fully recyclable within existing industries for the production of stainless steel and road paving.
Sodium – Sulfur technology
This battery has a solid electrolyte membrane between the anode and cathode, compared to liquid metal batteries where the anode, the cathode, and also the membrane are liquids. The cell is usually made in a tall cylindrical configuration. The entire cell is enclosed by a steel casing that is protected, usually by chromium and molybdenum, from corrosion on the inside. This outside container serves as the positive electrode, while the liquid sodium serves as the negative electrode. The container is sealed at the top with an airtight alumina lid. An essential part of the cell is the presence of a BASE (Beta-alumina solid electrolyte) membrane, which selectively conducts Na+. The cell becomes more economical with increasing size. In commercial applications the cells are arranged in blocks for better conservation of heat and are encased in a vacuum-insulated box.
During the discharge phase, molten elemental sodium at the core serves as the anode, meaning that the Na donates electrons to the external circuit. The sodium is separated by a beta-alumina solid electrolyte (BASE) cylinder from a container of molten sulfur, which is fabricated from an inert metal serving as the cathode. The sulfur is absorbed in a carbon sponge. BASE is a good conductor of sodium ions, but a poor conductor of electrons, and thus avoids self-discharge.
As the cell discharges, the sodium level drops. During the charging phase the reverse process takes place. Once running, the heat produced by charging and discharging cycles is sufficient to maintain operating temperatures and usually no external source is required.
The NaS battery is used in pilot projects to develop a durable utility power storage device due to its efficiency of 70% or better and a lifetime of over 1,500 cycles.