Lithium-Ion 18650 Battery Capacity vs Temperature Curve and Oversizing Methods

I’m trying to over-size a lithium-ion battery pack for cold cell temperatures. How does temperature affect the capacity of lithium-ion cells? A temperature-available capacity curve from a reputable source would be helpful if one exists. For example, lead-acid batteries have correction factors per IEEE Standard 485 for specific minimum expected cell temperatures. I would like to do something similar to over-size my lithium-ion battery pack. I suspect capacity is linearly affected with a large drop-off at very low temperatures. My pack will be made of 18650 cells, if that matters.

The information that you are looking for information is surprisingly hard to find. At least in a casual search. The closest I could come up with is a chart on this datasheet

https://b2b-api.panasonic.eu/file_stream/pids/fileversion/3450I've been researching batteries for a work project and have found battery manufacturer web sites to be consumer oriented and rather short on specifications.

Li-ion can be a generic term for a battery with a number of different chemistries, some will run quite happily at temperatures below zero C, but most should NOT be charged below zero C. First question, what type of Li-ion battery chemistry are you using.Second question, are they both being used and charged below zero C, or just used at that temperatureGenerically, they will operate with reduced capacity below zero C, down to around -40C in special cases.There are manufacturers who supply low temperature cells and specify temperature performance for their products, so I suggest that you buy your batteries from a known manufacturer, and get the data directly from them. They do tend to be expensive, and are often configured for specific applications, however.The Battery University is a good place to start to get general information.Have a look at this paper re charging and discharging for a specific cell type.Incidentally, how is your battery pack configured, since maintaining parallel/series battery packs at extreme temperatures will be critical, the worst cell in the pack could easily deteriorate more rapidly than normal, bringing the whole pack down with it. Charging to maintain the cells is equally as critical, but that is another whole topic, and without knowing your cell configuration,  no further comment is possiblecheers,Richard