Electrochemical storage systems
Electrochemical storage systems In this article various types of batteries are described. Most of them are technologically mature for practical use. First, six secondary battery types are listed: lead acid, NiCd/NiMH, Li-ion, metal air, sodium sulphur and sodium nickel chloride; then follow two sorts of flow battery.
Continued from technical article: Different types of battery used for auxiliary power supply in substations and power plants
Lead acid battery (LA)
Lead acid batteries are the world’s most widely used battery type and have been commercially deployed since about 1890. Lead acid battery systems are used in both mobile and stationary applications.
Their typical applications are emergency power supply systems, stand-alone systems with PV, battery systems for mitigation of output fluctuations from wind power and as starter batteries in vehicles. In the past, early in the “electrification age” (1910 to 1945), many lead acid batteries were used for storage in grids.
Stationary lead acid batteries have to meet far higher product quality standards than starter batteries. Typical service life is 6 to 15 years with a cycle life of 1 500 cycles at 80 % depth of discharge, and they achieve cycle efficiency levels of around 80 % to 90 %. Lead acid batteries offer a mature and well-researched technology at low cost.
There are many types of lead acid batteries available, e.g. vented and sealed housing versions (called valveregulated lead acid batteries, VRLA). Costs for
stationary batteries are currently far higher than for starter batteries. Mass production of lead acid batteries for stationary systems may lead to a price
One disadvantage of lead acid batteries is usable capacity decrease when high power is discharged.
For example, if a battery is discharged in one hour, only about 50 % to 70 % of the rated capacity is available. Other drawbacks are lower energy density and the use of lead, a hazardous material prohibited or restricted in various jurisdictions.
Advantages are a favourable cost/performance ratio, easy recyclability and a simple charging technology. Current R&D on lead acid batteries is trying to improve their behaviour for micro-hybrid electric vehicles.
Nickel cadmium and nickel metal hydride battery (NiCd, NiMH)
Before the commercial introduction of nickel metal hydride (NiMH) batteries around 1995, nickel cadmium (NiCd) batteries had been in commercial use since about 1915. Compared to lead acid batteries, nickel-based batteries have a higher power density, a slightly greater energy density and the number of cycles is higher; many sealed construction types are available.
From a technical point of view, NiCd batteries are a very successful battery product; in particular, these are the only batteries capable of performing well
even at low temperatures in the range from -20 °C to -40 °C. Large battery systems using vented NiCd batteries operate on a scale similar to lead acid batteries. However, because of the toxicity of cadmium, these batteries are presently used only for stationary applications in Europe.
Since 2006 they have been prohibited for consumer use. NiMH batteries were developed initially to replace NiCd batteries. Indeed, NiMH batteries have all the positive properties of NiCd batteries, with the exception of the maximal nominal capacity which is still ten times less when compared to NiCd and lead acid.
Furthermore, NiMH batteries have much higher energy densities (weight for weight).
In portable and mobile applications sealed NiMH batteries have been extensively replaced by lithium ion batteries. On the other hand, hybrid vehicles available on today’s market operate almost exclusively with sealed NiMH batteries, as these are robust and far safer than lithium ion batteries.
NiMH batteries currently cost about the same as lithium ion batteries.
Lithium ion battery (Li-ion)
Lithium ion batteries have become the most important storage technology in the areas of portable and mobile applications (e.g. laptop, cell phone, electric bicycle, electric car) since around 2000. High cell voltage levels of up to 3.7 nominal Volts mean that the number of cells in series with the associated connections and electronics can be reduced to obtain the target voltage.
For example, one lithium ion cell can replace three NiCd or NiMH cells which have a cell voltage of only 1.2 Volts.
Another advantage of Li-ion batteries is their high gravimetric energy density, and the prospect of large cost reductions through mass production.
Although Li-ion batteries have a share of over 50 % in the small portable devices market, there are still some challenges for developing larger-scale Li-ion
batteries. The main obstacle is the high cost of more than USD 600/kWh due to special packaging and internal overcharge protection circuits.
Lithium ion batteries generally have a very high efficiency, typically in the range of 95 % – 98 %. Nearly any discharge time from seconds to weeks can be realized, which makes them a very flexible and universal storage technology.
Standard cells with 5 000 full cycles can be obtained on the market at short notice, but even higher cycle rates are possible after further development, mainly depending on the materials used for the electrodes. Since lithium ion batteries are currently still expensive, they can only compete with lead acid
batteries in those applications which require short discharge times (e.g. as primary control backup).
Safety is a serious issue in lithium ion battery technology. Most of the metal oxide electrodes are thermally unstable and can decompose at elevated temperatures, releasing oxygen which can lead to a thermal runaway. To minimize this risk, lithium ion batteries are equipped with a monitoring unit to avoid over-charging and overdischarging.
Usually a voltage balance circuit is also installed to monitor the voltage level of each individual cell and prevent voltage deviations among them. Lithium ion battery technology is still developing, and there is considerable potential for further progress. Research is focused on the development of cathode materials.
Reference // Types and features of energy storage systems by IEC