What is the low temperature technology of Li ion battery?-Cell improvement
09 Aug 2021
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 “Cell improvement” of the low temperature technology lithium battery.
Cell improvement:
The previous article introduced how to improve the low-temperature performance of the battery through the modification of positive and negative electrodes and electrolyte. However, due to the limitations of materials, it is obviously unrealistic to expect the material factory to solve the low-temperature problem one-stop. At this time, the battery factory needs to stand up.
When it comes to the improvement of battery factory, we should carry out cell design and pack design. This article introduces cell design to you.
Before design the low-temperature battery, need to check four requirements: low-temperature range, low-temperature target capacity, charge discharge ratio and discharge cut-off voltage. Taking low-temperature discharge as an example, the difference in the discharge capacity of the battery at different magnification will be greater than that at room temperature, and the capacity below 3V will be much more than that at room temperature.
When discharging at low temperature, the difference between 0.5c and 0.2C curves is obvious (they basically overlap at room temperature, the figure is omitted)
When discharging at low temperature, the capacity below 3V is much more than that at room temperature
Select the low-temperature electrolyte:
Only when the electrolyte is not solidified, the low-temperature charging rate control step is the insertion of lithium ions into the negative electrode. However, the reality is that the conventional electrolyte often contains more than 25% EC and lacks sufficient low melting point solvent, resulting in the solidification of the electrolyte at very low temperature, and the conduction of lithium ions in the electrolyte becomes a rate control step. The states of several solvent formulations electrolyte at different temperatures are listed below:
Determine the positive and negative design scheme:
Therefore, in order to improve the low-temperature performance, first prepare an electrolyte especially for low-temperature.
After the electrolyte is selected, it is the turn to design the positive and negative materials. The main improvement directions include reducing the coating thickness of positive and negative electrodes, increasing the amount of conductive agent or selecting conductive agent with better performance, selecting main materials with smaller particle size and reducing the compaction density of positive and negative electrodes. The purpose of these improvements is to reduce the migration path of lithium ions or reduce the resistance of migration, embedding and de embedding.
Don't be obsessed with multi-pole structure:
Compared with uni-polar structure batteries, multi-pole ear batteries (laminated batteries and wound multi-pole batteries) have better magnification. Does that mean that multi-pole ear batteries must have better low-temperature performance? Let's look at the following curve:
It can be seen from the above figure that during low-temperature high rate discharge, the voltage of multi-pole structure battery is higher than that of uni-polar structure at the beginning of discharge, but with the temperature rise caused by high rate discharge, the voltage and capacity retention rate of multi-pole ear structure are lower than that of uni-polar structure. The reason is that the monopole structure battery has greater internal resistance and produces more heat during low-temperature discharge, which has become its advantage during low-temperature discharge: faster temperature rise and easier discharge of capacity.
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.
