Menu

LiFePO4 vs NMC batteries in power stations

All 54 power stations in the Enough Watts data set use LiFePO4 batteries. NMC is the other lithium chemistry you will meet on spec sheets. The choice changes weight, cycle life and heat stability, and not how long a station runs your list.

Updated

What the names mean

Both names describe the cathode, the positive electrode of a lithium ion cell. LiFePO4 is lithium iron phosphate, often shortened to LFP; a spec sheet may use any of those three names for the same chemistry. NMC is lithium nickel manganese cobalt oxide. Sandia National Laboratories names these two as the most common cathodes in lithium ion batteries for grid storage. Both also turn up on power station spec sheets, and the comparison below uses what those government sources state about them.

The differences, side by side

LiFePO4 and NMC compared
PropertyLiFePO4 (LFP)NMC
Energy for its weightLowerHigher
Cycle lifeLongerShorter
Heat stabilityMore stableLess stable
CobaltNonePart of the cathode

The Department of Energy safety plan for energy storage (2024) gives lower cost, better cycle life and higher thermal stability as the reasons recent installations chose LFP, and its lower energy density as the drawback. Sandia adds that the low cost comes from leaving out metals such as cobalt.

Weight

Lower energy density means more weight for the same watt hours. Among the 52 single piece stations in the data set with a published weight, energy per pound runs from 21.7 Wh per lb (Goal Zero Yeti 300) to 52 Wh per lb (BLUETTI Elite 300), or 48 to 115 Wh/kg. Every one of them is LiFePO4, so chemistry does not explain that spread: the case, the inverter and the ports weigh something too.

Cycle life, and how to read a rating

A cycle rating has two parts: a number of full charge and discharge cycles, and the share of the original capacity left at the end. "3,000 cycles to 80%" means the maker rates the battery to keep 80% of its capacity after 3,000 full cycles. A rating without its end point cannot be compared with one that has it.

48 of the 54 stations in the data set publish a cycle rating, and 43 of those state the end point. The most common rating with an end point is 4,000 to 80% (13 stations). At one full cycle a day, 4,000 cycles is 11 years. For a 1,000 Wh station on that rating, the maker's figure leaves 800 Wh of capacity at the end, and 800 × 0.85 = 680 Wh at the outlets.

4,000 to 80%133,000 to 80%94,000 to 70%83,500 to 80%6Not published66,000 to 80%46,000 to 70%33,500, end point not published34,000, end point not published2
Cycle ratings published for the 54 stations in the data set, by number of stations.

Cycle life does not change the calculator's answer for a new station. It tells you how long that answer holds. A battery near the end of its rating holds less, and why you get less than the rated capacity shows how to plan for it.

Heat and safety

In LFP, the bond between phosphorus and oxygen is stronger than the metal to oxygen bond in most other cathodes, and Sandia and the Department of Energy both give this as the reason LFP is more thermally stable. The same DOE plan warns that LFP systems have had incidents too. Chemistry is no substitute for safe use: follow the manual on charging temperatures, ventilation and storage.

What else to read on the spec sheet

  • Charging temperature. 48 of the 54 stations publish a lowest temperature for charging. 43 of them set it at 32 °F (0 °C), so by their own limits they do not charge below freezing. The coldest limit in the data set is -4 °F (-20 °C).
  • Warranty. 53 stations publish a warranty length, from 2 to 5 years. A cycle rating describes the battery; a warranty is a promise you can claim on.
  • The cycle rating end point. Without it, a large cycle number tells you little. With it, you can work out the capacity to expect late in the life of the battery.

What chemistry does not change

The runtime math is the same for both: rated capacity × the share that reaches the outlets ÷ the load. The calculator ranks stations that are enough by capacity, then price, then weight, and never by chemistry. Output and surge come from the published ratings of each station, whatever its cells.

Buying an older or used unit

Check the spec sheet or the manual for the chemistry and for a cycle rating with its end point. A unit with an unknown history may hold less than its rating. Lower the share of capacity under Assumptions and solar in the runtime calculator to plan for that.

Sources