LFP Cell Compression: The What & The Why || Part 1/3

What is Cell Compression?
Cell compression is quite literally squeezing/fixturing the outer aluminum case of LFP (LiFePO4) cells to prevent delamination of the internal components. Delamination leads to a reduced lifespan of the cells, as well as additional stress on electrical terminals. Internal forces are constantly acting on a thin aluminum case that is not strong enough to resist these forces. Lack of compression leads to damage of the cells, as indicated by swelling and premature battery failure.
Why Is Cell Compression Needed?
With the latest technology of LFP cells, many advances have been made to increase how much energy can be stored in a given volume. Engineers in general regularly face the challenge of fitting “more” into “less”. Sometimes to accomplish such a challenging task, compromises must be made. In this case, to create more space, a thinner, less structurally integral material has been chosen.
The thin aluminum case cannot withstand the internal forces exerted when the cells are charged, but the new design never expected the cells to be used on their own. The greater majority of these LiFePO4 cells on the market today are originally intended for use in Electric Vehicles (EV’s). Automakers and pack manufacturers are already designing the packs with the compression in mind, because the demands of a solidly held pack in an electric vehicle where vibration is guranteed are much more intense than a stationary solar power system. By using a single compression fixture on an entire pack as compared to many thick plastic cases, significant space and weight is saved, leading to higher capacities in the same space.

[@theanonymous6289]

Great video! When using a compression jig like this, do you recommend NOT using VHB tape between cells? Seems like tape would impede uniform compression between planes, but not sure if there's still some benefit to using it.

[@montaguemonro565]

I have heard that with very low c charging and discharging, as may be found on a solar only setup, the delamination is negligible. What is your opinion on this? Cheers!

[@CurrentConnected]

In our testing, swelling began any time the cell was over 3.4v and even after discharge they had not returned to their original thickness.

[@MP-ep9ur]

This 'swelling' is molecular. It cannot be 'mechanical' stopped. It is a waste of time.
Use within manufacturers parameters or choice a different battery manufacture or chemistry.