Instantaneous discharge current of energy storage battery

A battery energy storage system (BESS) is an electrochemical device that charges (or collects energy) from the grid or a power plant and then discharges that energy at a later time to provide electricity or other grid services when needed.

As a key factor, discharge rate has a great influence on battery characteristics. Therefore, it is particularly important to study the characteristics of LIB at different discharge rates. Battery discharge is the process of converting chemical energy into electrical energy and releasing the energy to the load.

Rated power capacity is the total possible instantaneous discharge capability (in kilowatts or megawatts ) of the BESS, or the maximum rate of discharge that the BESS can achieve, starting from a fully charged state. Storage duration is the amount of time storage can discharge at its power capacity before depleting its energy capacity.

Under the condition of discharge rate of 0.5C, 0.8C, 1C, 2C, 3C and 4C, the discharge capacity of the cell is 3312mAh, 3274mAh, 3233mAh, 2983mAh, 2194mAh and 976mAh, which is 3.58%, 4.69%, 5.88%, 13.16%, 36.13% and 71.59% lower than the standard capacity 3435mAh provided by the battery manufacturer.

In addition, when the discharge current is high, the local current density and battery overpotential become larger, resulting in faster and faster conversion of chemical energy to thermal energy . At the end of discharge, as the discharge rate decreases, the cell temperature slope becomes smaller.

For example, a battery with 1 MW of power capacity and 4 MWh of usable energy capacity will have a storage duration of four hours. Cycle life/lifetime is the amount of time or cycles a battery storage system can provide regular charging and discharging before failure or significant degradation.