The energy efficiency of lithium-ion batteries
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2020/12/19 10:53:35
Coulomb efficiency, also known as charging efficiency, refers to the ratio of the discharging capacity of the battery to the charging capacity during the same cycle.The percentage of specific discharge capacity and specific charge capacity.
For positive electrode materials, it is lithium embedded capacity/lithium deactivated capacity, that is, discharge capacity/charging capacity.For negative electrode materials, it is lithium removal capacity/lithium insertion capacity, that is, discharge capacity/charging capacity.
Electric energy is converted into chemical energy in charging process, and chemical energy is converted into electric energy in discharging process. There is a certain efficiency in the input and output of electric energy in two conversion processes, which directly reflects the performance of the battery.
In professional physics, Coulomb efficiency differs from energy efficiency in that one is the ratio of electricity and the other is the ratio of work done.
The energy efficiency of the battery and coulomb efficiency, but mathematically there is a voltage relationship between the two.Charge and discharge is not equal to the average voltage, average discharge voltage generally less than the average voltage by the energy of the battery charging efficiency can judge the performance of the battery, by the conservation of energy, the loss of electricity mainly converted into heat energy, and energy efficiency can be analyzed in the working process of the heat generated by the battery, which can analyze the resistance to the heat.And given the energy efficiency can predict the amount of residual energy of the battery and manage the reasonable use of the battery.The coulomb efficiency is often reduced by 100% because the energy input is not used to convert the active substance into a charged state, but is partially consumed (for example, irreversible side reactions occur).But with current lithium-ion batteries, the Coulomb is 99.9 percent or more efficient.
Influencing factors: electrolyte decomposition, interface passivation, changes in structure, shape and conductivity of electrode active materials all reduce Coulomb efficiency.
In addition, it is worth mentioning that battery attenuation has little effect on Coulomb efficiency and is not related to temperature.The current density reflects the current passing per unit area. With the increase of current density, the current passing through the electric reactor increases, and the voltage efficiency decreases due to internal resistance, and the coulomb efficiency decreases due to concentration polarization and other reasons, finally resulting in the decrease of energy efficiency.
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