Lithium-Ion-Battery-Systems in comparison to Lead-Acid-Battery-Systems
A key difference, if not the most crucial, is the fact that lithium-lon-battery-systems are flexible. Means they have a large variance. This variance is due to the fact that a wide variety of cell types are available in various sizes. So from the variety of cells one can, within the physical limits of energy and specific power, realize very different designs. Lead-acid batteries, however, are usually arrested rigidly in the designs. Minimal changes have immense – often disproportionate – associated costs. In addition, lead-acid batteries are generally manufactured in large numbers to present their economic efficiency. Thus come lithium-ion battery systems very accommodating of Industry 4.0 philosophy, within the meaning of short delivery times, combined with smaller batch size and high variance.
Durable, Space-saving, and lightweight
Lithium-Ion accumulator systems are more durable, space-saving, and lighter than conventional systems with VLRA battery systems. They offer great advantages with regard to operational security as well as to economic viability.
Comparing Lithium-ion (li-ion) ac-cumulators with VRLA systems may cause misunderstandings. While the capacity of li-ion battery system normally is stated one- or two-hourly (C1 or C2), that of VRLA accumulators usually is declared for the discharge in five, ten ore twenty hours (C5, C10, C20). A real comparison is only possible by means of a simple conversion:
|C1 oder C2 in Ah||0,65 x C20 in Ah|
|C1 oder C2 in Ah||0.60 x C10 in Ah|
|C1 oder C2 in Ah||0.72 x C5 in Ah|
Volume and Weight
Lithium-ion battery systems require only 50 % of the volume of VRLA systems with the same capacity. Depending on design and type of the casing, the li-ion accumulator weighs only 25 to 35 % of a com-parable VRLA system.
Lithium-ion systems usually reach considerable more loading cycles than lead battery systems, which come to maximum 300 recharges after being completely discharged. Circulating rates of some thousand or even ten thousand cycles though have to be viewed with utmost skepticism. These figures mostly are based on lab results with 60, 70 or 80 % discharge depth and with single cells – and not with assemblies of 4, 7, 13 (15 for LiFePO4) or even up to 100 or more cells. More realistic are 800 to 1,000 loading cycles at 100 % discharge.
VRLA systems are offered with ten or more Years of service life. Nevertheless, it has to be con-sidered that above a surrounding temperature of 20 °C the service life will be halved every 10 °C (Arrhenius effect). With lithium-ion accumulators, the Arrhenius effect only occurs above 30 °C or, as often published, above 35 °C.
VRLA systems customarily cannot be fully recharged in less than eight hours. Lithium-ion accumulators usually can be fully loaded within 2.5 hours, specific systems even faster. For intermediate recharging, this means that li-ion systems are considerably more effective than VRLA systems. Even compared to so-called VRLA quick charging systems with cylindrical cells (e.g. Optima), Lithium-Ion systems lead by far, because they are in the constant-current phase until more than 85 % charge level. For VRLA systems, this is only possible up to 60 % maximum without disadvantages.
Changing the geometry of a VRLA battery system on the one hand is very limited (regarding the battery system plates) and on the other hand very expensive. Finally: The time to market of a new designed battery system is very long – possibly a year or more. With lithium-ion systems, this is clearly different. Smaller cells can be used. Within certain limits, the cells may be attractively arranged. The control and monitoring system also can be placed very flexible, so that the time to market depends only on the case – if a solid case shall be used –, and lasts often only few weeks.