When choosing a battery, most people will ask: what is the efficiency of the battery?
Battery efficiency refers to the ratio of energy input to energy output. The output energy is always less than the input energy. Nevertheless, there are factors affecting battery performance.
Measurement of a Battery’s Energy Efficiency
The energy efficiency of a battery can be measured using two methods: voltage efficiency and Coulombic efficiency (CE).
The voltage efficiency of a battery is the voltage difference between when it is charging and when discharging; this difference is produced by what is called over-potential.
Coulombic efficiency measures the transmission of electrons during charging and discharging together with the number of electrons lost during a complete cycle. The higher the Coulombic efficiency, the less the electrons lost, and the longer the battery life. Then what affects the efficiency of industrial batteries?
The factors affecting the efficiency of industrial batteries include:
- Charge current
- Internal resistance
- State of charge
- Battery temperature
The older a battery gets, the less efficient it becomes. However, the age of a battery is not counted in years. Generally, lead-acid accumulators last for 1,000 to 1,500 cycles, while lithium-ion batteries have a life of 2,000 to 3,000 cycles.
What are the signs of battery aging? When this happens, the battery experiences an irreversible capacity loss. Liquid electrolytes slowly dry up, and a lithium-ion layer builds up on the electrodes.
During the process of charging a battery, changes take place within its internal chemistry. Charging at a high current aggravates these effects.
When dealing with a lithium-ion battery, the best charging practice is to keep the current controlled at a moderate level to enhance the efficiency and lifespan battery.
Lithium electrolytes and atoms accumulate on the surface of the graphite anode, forming a solid electrolyte interface layer that protects the anode. This solid layer, however, grows thicker with time and may hinder ion access to the anode.
Similarly, on the cathode, an accumulation of lithium ions occurs, causing electrolyte oxidation that results in thermal runaway.
A low-charge current enhances the longevity of a battery. However, it reduces the capacity of the battery’s time efficiency.
State of Charge
The battery’s state of charge is its level of charge relative to its capacity at any time.
Throughout the cycle of discharge, the output voltage gradually drops as the state of charge reduces as well. The loss of capacity that batteries experience when they are cycled at relatively high temperatures is proportional to their state of charge. The higher the state of charge, the higher the capacity loss.
It is therefore vital to be aware of a battery’s state of charge to enhance its efficiency.
The internal resistance of a battery is affected by several factors including current, age, chemistry and size. The less the internal resistance, the greater the efficiency of the battery. Lithium-ion batteries contain one of the least internal resistance. In these batteries, the solid electrolyte interface layer enhances internal resistance. This layer is good for the battery’s functionality since it stabilizes the system and enhances lifespan. Nevertheless, it can lead to increased internal resistance with time.
Lithium-ion batteries should be charged at a range of 32° F to 113° F, and discharged between 4° F and 131° F. The charging and discharging performance are not affected by higher temperatures compared to other batteries. However, the more they are exposed to higher temperatures, the shorter their lifespan.
Categorised in: Batteries
This post was written by admin