Charging at low Temperatures

Lithium-ion cells can be damaged when charged at cold temperatures primarily because of lithium plating. Datasheets of Lithium-ion cells and batteries list charging temperatures with low charge limits somewhere between 10 °C and 0 °C being verboten. The processes in the cell slow down at cold temperatures, including the process of diffusion of lithium from the surface to the interior of the electrode particles.

Just like Mrs Marsh’s ink into chalk demonstration, Ions move from the surface to the interior of the electrode, this process is called diffusion, and it is not instant. The colder the cell, the slower the process. Perhaps a better and more universal illustration would be using a dropper to add food colouring into a glass of water. At first you can see where the drops entered the water, then at some point in the near future, the drop of colouring will diffuse throughout the glass of water. Doing the experiment again with a glass of frozen water would give you a very different result.

Diffusion limits the rate of lithium transfer, at cold temperatures the surface “fills up” and if charging is forced at a rate higher than the maximum diffusion rate at that temperature there is nowhere for lithium to intercalate into the particles, and so lithium metal starts to plate on the particle surfaces. Capacity is permanently lost when this occurs. The lithium stacks up building dendrites which can create high resistance points in the cell, increasing self-discharge. The worst case is that these dendrites can pierce the separator between electrodes and create an internal short which may initiate rapid and uncontrolled disassembly of the cell.

So, if the charging rate is reduced, it may still be possible for the lithium to diffuse from the surface to the interior of the particles more quickly than lithium is being introduced due to charging. The likelihood of lithium plating is reduced by charging at lower rates. Whether it still happens (or not) depends on the design of the cell.

 The Saft MP 176065XTD for example allows charge from -30 °C to +85 °C, with the proviso that you first consult Saft if charging below 0 °C and above 60 °C. Charge rates at the extreme ends of the temperature ranges will be in the order of C/20 or less. This level of information has never been made available to us by Panasonic/Samsung/(add any supplier), so we need to stay with the datasheet recommendations.

 Battery designs with the possibility of being charged in low (or high) temperatures require protection circuits with temperature sensing. Most of our MIPCMs with ‘BMS’ somewhere in their description should be used in these cases and custom programmed for each application.

 Ask your friendly Battery Engineer if you need to know more, Mrs Marsh won’t be of any help.

“It really does get in”