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Glossary and clarifications about lithium battery LifePO4

Capacity Usually stated in Ah (Ampere-hours) but sometimes also in Wh (Watt-hours). We specify the capacity in Ah when discharging from 14.6 Volts down to 12.0 Volts. For the sake of simplicity, we can say that the average voltage during the discharge process is about 13 volts, then the capacity of a 40 Ah battery will be about 520Wh (13V x 40A = 520Wh).

Cycling endurance The number of charge-in and charge-out cycles that a battery can undergo under favorable conditions without the capacity decreasing by more than 20%. For example, the standard "SS-EN 60896-21, ed. 1:2004" shows details of how this can be tested.

Efficiency Simply put, it is a measure of the battery's energy efficiency calculated as a percentage. High efficiency means low internal losses and vice versa. Of course, losses in cables and connections are not included here, but are measured directly on the battery. The losses result in heat generation inside the battery. An internal temperature rise during rapid charging and discharging increases wear on the battery (temperature stresses and material ageing). The low internal losses therefore contribute to the long service life. Furthermore, it should be pointed out that a low efficiency in the battery means that it also takes longer to charge the battery, other factors being equal. Sometimes the efficiency of these batteries is stated as 99%. This applies to the ratio between charged and discharged current (Ah).

BMS = Battery Management System: Electronic circuit to extend the life of lithium batteries. It can, for example, interrupt the current if there is a risk of deep discharge of the battery. In our system, the BMS consists of the battery monitor and the generator regulator.

Matched cells = The lithium batteries we sell are built from what are called matched cells. Each cell has a pole voltage of about 3 volts. Because the cells, as due to manufacturing tolerances, have slightly different characteristics, they will normally be strained differently on charge and discharge. Matching the cells means that these are sorted before assembly. Next, the battery is built from cells that have very homogeneous properties among themselves. The result is a battery with improved service life thanks to the symmetrical loading of the individual cells. A battery built from matched cells needs a BMS, because over time the cells will become unbalanced. Matching the cells in a battery places higher demands on the manufacturing process but provides a more reliable end product.

Cell Balancing System to equalize the voltage across the individual cells to improve the life of a battery built from cells with different characteristics (not matched).

Batteries with iron in the cathode. Does not contain so-called conflict metals. Lower energy density (approx. 100Wh per kilo) than e.g. Lithium polymer batteries but significantly higher safety. Today known as the safest battery technology. High performance and with very good cycling endurance.

The amount of Lithium in a Lithium iron phosphate battery is in the order of some % of the battery's total weight. Most of the weight is aluminium, copper and the strong aluminum housing.

Lithium iron phosphate is a naturally occurring mineral used as an electrode in LiFePo4 batteries. The technology was first described by John Goodenough's research group in Texas in 1996. Thanks to the low cost, good availability of the iron, its high thermal stability, electrical performance and specific capacity (170Ah per kg), a marketability was quickly achieved.

Lithium iron phosphate batteries (LiFePO4) use a lithium ion-based chemistry and share many advantages and disadvantages with other lithium ion technologies. However, there are also big differences. Lithium iron phosphate offers better cycling endurance than other lithium ion chemistries. Like nickel-based rechargeable batteries, and unlike other lithium-ion technologies, lithium iron phosphate batteries have a very flat discharge curve. The voltage stays very close to 3.2 Volts during most of the discharge process. At 3.0 Volts, only a few percent of the energy content remains.

Thanks to the fact that 4 series-connected battery cells of the lithium iron phosphate type form 12.8 Volts, the battery technology is a very suitable replacement for 6-cell lead-acid batteries, not least in vehicles, leisure boats, UPSs and solar systems. Thanks to very high safety, lithium iron phosphate batteries are a likely future replacement for almost all lead-acid batteries. This provided that consideration is given to how lithium iron phosphate cells are to be charged. They should not, for the best lifespan, be charged over 3.65 Volts per cell for a long time. For the same reason, the cell voltage should never fall below approx. 2.5 Volts per cell. Exposing batteries of this type to voltages outside the range of 2.5 to 4.0 Volts per cell will in most cases lead to some form of damage to the battery. The most common is a capacity deterioration. The battery cells must at least be balanced when first connected, but can then manage around 3000 charging cycles with active balancing without losing more than about 20% of the original capacity.

The phosphate in the batteries replaces cobalt and the difficulties that cobalt brings regarding mining and the environment, but also cobalt chemistry's problems with thermal instability. Several cases of so-called thermal rush have been described with lithium-cobalt batteries (mobile phones, starter batteries, etc. More information is available for the interested party at the National Transportation Safety Board, the report points out some shortcomings both in manufacturing and validation of the Lithium-Cobalt-Oxide- battery that produced heavy smoke after an internal short circuit.Lithium iron phosphate batteries are recognized as safer.The reasons for this are mainly a lower specific energy content and a higher thermal stability.

Lithium iron phosphate batteries (LiFePO4)
-allows greater current draw than LiCoO batteries
-has approx. 14% lower energy density than LiCoO batteries
-ages more slowly (calendarly) than LiCoO and LiMn batteries
-is safer thanks to higher chemical and thermal stability
-LiFePo4 has a higher built-in safety in the cathode material because the oxygen bonds are stronger and do not release as easily if the battery is exposed to a short circuit, e.g.
-LiFePO also has a smaller structural change than LiCoO between charged and uncharged state.
-The oxygen is more strongly bound in LiFePo4 than LiCoO.

As a result, Lithium Iron Phosphate cells are significantly more difficult to ignite if mishandled (especially charging). Overcharging can only turn into heat, which is why the battery can be destroyed in case of overcharging. It is common knowledge that LiFePo4 batteries are not as easily damaged by high temperatures.

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