Lithium-ion batteries (LIBs) find their use in applications ranging from small-scale portable devices to large-scale centralised backup facilities. This is due to the excellent performance, long-term storage, and charge-discharge life. One of the most exciting applications of LIBs is electric vehicles.
A LIB consists of two porous electrodes and a porous membrane, wherein a liquid electrolyte is used to fill the pores in the electrodes and the membrane. This is depicted in Figure 1. The negative electrode in a LIB is typically made of carbon and the positive of a Lithium metal oxide. During discharge, the Li+ flows from the negative electrode, through the membrane, to the positive electrode. Electrons, on the other hand, can't enter the electrolyte and thus not cross the membrane. Instead, they travel through the external circuit that connects the negative electrode with the positive electrode, thereby generating electricity. When a Lithium-Ion battery is charging, LI+ ions flow from the positive electrode through the electrolyte and membrane, to the negative electrode. The electrons are forced towards the negative electrode by using power from an external source, thereby storing electricity.
In the context of LIB storage systems, batteries in the form of cells are assembled into modules, and thereafter into packs. The battery packs consist of a Battery Management System (BMS), which is an electronic system aimed at protecting the cells from operating outside the safe operating area. Additionally, the storage system consists of a Thermal Management System (TMS) to regulate the temperature for the battery and storage system as well as an Energy Management System (EMS) to control the charge/discharge of the grid-connected storage system.
Power conversion systems may also include one or several power-converter units (DC/AC link) depending on the application. In addition, a transformer may be needed for system coupling with the grid at higher voltage levels to render services such as increased reliability, load shifting, frequency regulation, etc. A schematic of the battery storage system with grid coupling is displayed in Figure 2.
These applications have resulted in a large decline in cost. The recent industry outlook from Bloomberg’s New Energy Outlook 2018, shown in Figure 3 , indicates that the price is expected to reach 40$/kWh by 2050. This decrease is expected based on the installed capacity and the increased demand.
Currently, the battery price is approximately 200$/kWh, which is expected to go down to 70$/kWh by 2030 and 40$/kWh by 2050 due to an expected increase in installed capacity / increased demand.
The technical and economic aspects to be considered on system-level, coupling, and grid integration. The overall details regarding the system can be seen below:
LIB Battery Energy Storage System (BESS) is accompanied by relatively low electricity storage cost which makes them highly suitable for applications ranging from peak load shaving where the BESS provides or consumes energy to reduce peaking in a power system, to renewable integration, e.g. time or load shifting of photovoltaic power from day to night and to transmission congestion relief where locally deployed BESS reduces the load in the transmission and distribution system, making BESS economic for transmission and distribution network.
Additionally, the fast response time associated with BESS enables primary control provisions including Frequency regulation where the BESS is used to alleviate deviations in the AC frequency. The BESS can also be used to improve network reliability by reacting immediately after a contingency by maintaining stability in the power system until the operator has re-dispatched generation. BESS can effectively be used for black-starting distribution grids and BESS systems are suitable for enhancing the power quality and reducing voltage deviations in distribution networks. The BESS can further be used to provide spinning reserves and regulate active and reactive power, thereby improving the network voltage profile. This can improve the integration of renewable energy by reducing the events triggering the protections of the inverters.
Most of the current LIB systems have been deployed to perform fast reactive renewables smoothing and firming with storage periods ranging from seconds to minutes, until recently. New systems are increasingly used for renewables time-shifting with typical storage periods of a few hours , . The ongoing research in the field of materials to increase the energy density of LIB cells includes high-voltage electrolytes allowing charging voltages of up to 5 volts  and silicon nanoparticle-based anodes to boost the charge capacity .
Lithium-Sulfur batteries, where sulfur is used as an active material, are one of the most promising technologies with energy densities as high as 400 Wh/kg. Another alternative technology is Lithium-air where oxygen is an active material and can be drawn from ambient air with the highest potential energy and power density of all battery storage systems.
To read more about LIB BESS, please visit Lithium batteries for grid storage at https://ens.dk/sites/ens.dk/files/Analyser/technology_data_catalogue_for_energy_storage.pdf
 Energistyrelsen, “Technology Data Energy Storage.” [Online]. Available: https://ens.dk/sites/ens.dk/files/Analyser/technology_data_catalogue_for_energy_storage.pdf. [Accessed: 16-Jul-2020].
 Bloomberg New Energy Finance, “New Energy Outlook 2018,” 2018.
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