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The energy storage of the future

Lithium-ion batteries work by storing lithium ions in the battery’s electrodes.

 

The smallest unit of a battery, the cell, consists of a positive and negative electrode, an ion-permeable separator, which isolates the two electrodes from one another electrically, and the liquid electrolytes that enable migration of the ions between the electrodes. Such battery cells are combined into battery modules by means of parallel and/or serial interconnection. These modules are in turn interconnected to produce battery systems that can be connected to the inverters. Stationary battery systems have a very different structure to mobile battery systems. Achieving as high as possible a power density tends to be less important, while safety aspects, ease of maintenance and the use of standardised systems for high cost-efficiency are prioritised.

There are various lithium-ion battery technologies available that are differentiated according to the electrode and separator materials and associated characteristics. The key properties are battery capacity, internal resistance, from which the ratio of capacity to output can be derived indirectly, as well as service life and safety features. Due to way these characteristics vary in different lithium-ion batteries, the suitability of the different technologies depends on the requirements for the respective application. Lithium-ion batteries offer high efficiency and a long service life, so they are more suitable for high performance applications with greater dynamics, where these benefits can be exploited.

Two different lithium-ion battery technologies (LMO and LFP) have already been installed in M5BAT.LMO (lithium-manganese-oxide) from Samsung SDI batteries have been installed by the system integrator Qinous. The system comprises sixteen LMO battery cells per tray. The trays are combined in racks with one rack having approximately a usable capacity of around 40 kWh. The whole system contains 64 racks in four parallel strings with an usable capacity of approximately 2,400 kWh.

The LMO battery contains lithium-manganese-oxide as active material in the cathode. This cathode material is often mixed with other cathode material (e.g. nickel-cobalt-manganese) to improve the characteristics regarding capacity and performance. As Manganese, the main raw material, is broadly available. LMO provides savings compared to other lithium-ion battery technologies. Furthermore LMO batteries show a very good safety behavior.

The lithium-iron phosphate (LFP) batteries from CATL have been installed by the system integrator RES. The LFP-technology uses iron phosphate with lithium addition as cathode material leading to an increase in service life and very good safety behavior. Moreover the material is cost-efficient resulting in cost savings for this technology.

Thanks to the expansion of e-mobility and the associated increase in the number of lithium-ion batteries being produced, a gradual reduction in costs can be expected.