Batteries and electrochemical capacitors stand at the forefront of electrical energy storage devices, with batteries being the most widely used. Functioning as a crucial component in our daily lives, batteries store electrical energy during charging and convert chemical energy back into electrical energy during discharge. An electrochemical battery is a reversible power source, capable of storing electrical energy in a chemical form and releasing it through a reversible transformation when needed.
A battery pack, on the other hand, is a module composed of identical battery cells connected both in series and parallel. Measured in ampere-hours (A·h), battery capacity refers to the amount of power a battery can release during a discharge cycle. This capacity is influenced by the discharge rate, with the rated capacity typically calculated after a 10-hour discharge (C/10 rate). Deviating from this rate affects the amount of electricity that can be released; higher rates result in decreased release, while lower rates lead to increased release. Battery discharge current is measured in amperes, often expressed as a fraction of ampere-hour capacity, such as C/100.
The Faradaic efficiency of a battery, denoted as g=Qp/Qc, represents the ratio of discharge capacity (QD) to charge capacity (Qc). Meanwhile, energy efficiency, measured in W·h, hinges on the charging and discharging technology utilized and the application environment.
The self-discharge rate, a crucial technical parameter reflecting internal characteristics, gauges the monthly average relative capacity loss at a specific temperature. With the internal resistance of batteries being generally small, inversely proportional to capacity, power-type energy storage tends to have lower internal resistance compared to energy-type storage.
However, this low internal resistance poses challenges in application. Accidental short-circuits can occur if the battery poles connect through a conductive object, resulting in a quick failure. Additionally, the battery’s life is directly tied to its working environment, especially in energy buffer storage, where lifespan hinges on the frequency and depth of charge and discharge.
Irrespective of technology type, batteries are evaluated by two key performance indicators: specific energy (w·h/kg), representing energy stored per unit mass, and specific power (W/kg), indicating power provided per unit mass. The cycle life, measured in charge and discharge cycles, offers insight into the longevity of the battery. For instance, common evaluations often consider the number of discharges above 80% of the rated capacity, a benchmark frequently used in mobile battery applications.
In essence, the measurement of battery life adapts to various applications, underscoring the dynamic nature of battery technology in diverse scenarios.
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