EverExceed have recently introduced a new technology of low temperature
Lithium iron phosphate battery, which can be charged even under 0°C and in negative temperature. In a series of 5 technical articles we are going to elaborately describe the details of this revolutionary technology. In this article we are going to talk about the “principle” of the low temperature technology lithium battery.
Principles:
Users always make complaints about the performance of lithium batteries in low temperature. The reason of poor low temperature performance of Li battery can be explained from two aspects: material and electrochemical. Let's talk about the interpretation from the perspective of materials.
For electrolytes, the main components of solvents are cyclic esters and chain esters. A common feature of these solvents is that the fluidity of electrolytes becomes poor at low temperature, and some electrolytes even partially solidify at -30°C to-40°C. In this way, the conduction velocity of lithium in the electrolyte at low temperature will slow down, thus reducing the low-temperature charge discharge performance of the battery. The melting points of solvents commonly used in electrolyte are listed in the figure below. The solvent with lower melting point is more suitable for use at low temperature
For the positive and negative electrode materials, the discharge process of lithium battery is the process of lithium ion from the negative electrode to insert into the positive electrode. When the battery is discharged at low temperature, the impedance of lithium ion from the negative electrode to insert into the positive electrode will increase, thus increasing the resistance of the whole reaction.
When charging at low temperature, the anode has a very obvious tendency to maintain its original state, which makes it more difficult for lithium ion to be embedded.
Taking discharge as an example, the performance chapter has introduced that the voltage of low-temperature discharge will be significantly lower than that of normal temperature discharge. What is the electrochemical principle of this phenomenon? The answer is the increase in "polarization" of the battery at low temperature. The polarization in the battery refers to the difference between the battery and its equilibrium state (when in use) in the process of charging and discharging. Daily charge and discharge will lead to the polarization of the battery. One of the results of polarization is to produce a voltage different from the equilibrium state. For example, for a battery with an equilibrium state voltage of 3.9v, the discharge voltage at 0.5c at room temperature will instantly drop to about 3.8V, and the discharge voltage at 0.5c at low temperature will instantly drop to about 3.7V. The corresponding two voltage differences (3.9v-3.8v at room temperature and 3.9v-3.7v at low temperature) are the results of polarization, and the name of pressure difference is over potential.
The polarization in the battery consists of electrochemical polarization and concentration polarization.
Well, that's all for this article. Finally, let's summarize: from the material point of view, the main reasons for the poor performance of lithium-ion battery at low temperature are the decrease of ionic conductivity of electrolyte at low temperature, and the increase of impedance of lithium ion in the positive and negative electrodes at low temperature; From the electrochemical point of view, it is the increase of cell polarization at low temperature, and polarization can be divided into two parts: electrochemical polarization and concentration polarization.
Conclusion:
To match the requirement of cold countries where you need reliable
energy storage solution in outdoor application, EverExceed research and development engineers were working for long time for a suitable solution and thus came the new technology. So for your cold temperature energy storage solution choose EverExceed as your brand with complete reliability.
