LiFePO4 is an energy dense type of battery that offers a high discharge rate, superior safety and long cycle life. LiFePO4s have a charge voltage three times greater than a nickel-cadmium cell and nearly 10 times the energy density of comparable SLA batteries.
Using LiFePO4 batteries enables battery design engineers to provide the required 300 W in a compact 4S2P form factor. Moreover, this basic design can be scaled up to deliver many more watts of standby power if necessary.
Because LiFePO4 uses a very stable cathode nicd rechargeable battery technology, the cells perform well when maintained between 50 and 108F. It’s not unrealistic to expect a modular LiFePO4 battery pack will be able to deliver up to 500 discharge events over its projected lifetime under optimal temperatures. A comparable lead-acid BBU would probably sustain only 50 to 200 events before becoming unreliable and having to be replaced. This longer life cycle is one of the reasons that technology is now a cost-competitive alternative to lead-acid batteries.
The lead-acid batteries in traditional BBUs are sealed, but not maintenance free. They must be routinely monitored using voltage checks, load tests and physical inspection. All common battery technologies are subject to sulfation, in which small sulfate crystals form on the battery plates if stored for long periods without recharging. However, LiFePO4 batteries are better able to resist sulfation under partial-charge conditions.
The phosphates component of the LiFePO4 cathode also means the battery can handle high temperatures as well as overcharge and short-circuit conditions quite well. The cells are unlikely to experience thermal runaway and the memory effect that affects some other technologies. 18650 batteries also do not require scheduled cycling to prolong service life. As long as the electronic drain is low, they can maintain a minimum state of charge for up to one year with no external power.
While a distributed BBU design is attractive from an efficiency standpoint, today’s data centers and battery providers are turning to a hybrid approach that would be more appropriate for a heterogeneous computing environment with different types of servers and data processing requirements.