What are the problems with LiFePo4 float charging? How should I charge them?

I can't find any reliable info on float charging LiFePo4 cells. It's quite clear that it's not possible to float charge Li-ion and Lipo cells, but LiFePo4 looks like quite different technology.

I'm interested in building a simple charger using a constant voltage with a very limited current (0.1C). I don't care about a charging speed and a maximal capacity, but I want to maximize a battery lifetime.

I looked into few datasheets but they deal only with classic CC/CV charging. I can't find any info about float charging. Is it OK to charge LiFePo4 with constant voltage (3.5V? 0.1C)? Is it necessary to remove voltage when charging is finished?

Answer

The LiFePO4 technology is not that sensible against overcharging like normal Lithium Ion batteries, which tend to destroy themselves. The Problem about float charging is

1. your charger produces power dissipation,


2. a full cell tends to convert the applied power into heat, which accelerates aging,


3. the electrode is likely to produce pure Lithium out of the Lithium ions which lowers the capacity.

To sum this up, float charging LiFePO4s is not as dangerous as overcharging normal Lithium Ion batteries, but has an bad influence on the aging of the cells. The best practice is to charge the cells with CC, then CV. If the current drops below a certain limit (e.g. 5% of C) turn the charging off.