Lithium Ion Battery Offers More Energy and Longer Life Cycle

According to a recent report published by the Journal of Materials Handling Equipment Distributors Association (MHEDA), electric trucks accounted for more than half of the sales of new trucks in 2010. With the rising price of fuel in the past decade, the demand for equipment that runs on an alternative energy source has been at a steady incline. The rising popularity of electric trucks has created a need for efficient battery and battery-charging solutions. Lithium-ion (Li-Ion) batteries offer a higher depth of discharge (DoD), cycle life, and energy capacity than lead acid batteries, yet the traditional lead acid battery is still dominating the market as the number one non-IC power source used by companies in the material handling industry.
The explanation for this trend is affordability, as the estimated cost for Li-Ion batteries 3.5 to 5 times that of the traditional lead acid counterpart. This cost comparison, however, is overly simplistic in its analysis. The cost of a single installation may be lower for the lead acid battery, but its shorter lifetime in many applications may result in higher cost per kWh stored than the lithium-ion battery. When calculating the cost per energy storage system, it is important to factor in the expense for shipping, disposal, installation, and maintenance, along with the initial cost of the battery. Since Li-Ion batteries do not require regular maintenance, are less impacted by mechanisms that greatly degrade lead acid batteries, and have a significantly higher cycle life, the cost for lead acid batteries may in fact be higher in the long run when considering the lifetime cost of each energy source.
While the typical lead acid battery lasts for 1500 to 2000 cycles at 100% DOD, this rate is heavily influenced by the operating conditions. In comparison, the Li-Ion battery has an average cycle life of 2,000 at 100% DoD and 3,000 at 80% DoD, a significant advantage of the Li-Ion battery over lead acid. The disparity is even greater when temperatures fall outside of a moderate range, particularly if the temperature is below 40⁰F or above 80⁰F. While immoderate temperatures cause degradation in both types of batteries (which in-turn contributes to power fade) the energy capacity for lead acid batteries drops significantly outside of moderate temps, while Li-Ion batteries typically won’t fall below 70%.
It is important that the discharge level for Li-Ion cells does not dip below 15-20% of the remaining capacity, or it may jeopardize the battery’s life cycle and risk premature cell failure. It is also important to protect Li-Ion batteries against overcharging, as this poses a similar threat to cell failure. The fastest charge rate is shown at 1000Hz, or by using a varying-frequency pulse charge from 100-1000Hz. By maintaining a balanced state of charge, individual cells are kept from overcharging and discharging ahead of the rest of the cell pack. While charging and discharging are both important functions to monitor, the Li-Ion battery is able to perform at near-full capacity with minimal discharge time. The capacity of a lead acid battery, on the other hand, is greatly reduced with shorter discharge periods. Therefore, Lithium Ion batteries are much more suitable for applications where the full discharge time allotted is less than eight hours.
There are numerous other mechanisms that cause battery degradation, which in turn can cause decreased discharge power capability, charge acceptance, and cell efficiency. A proper battery management system can safeguard the Li-Ion battery pack by providing safety features that monitor and protect against excessive current flow, report the cell voltage and temperature, and tell the current charge and health of the battery. Li-Ion batteries have approximately a 1.5 X greater life cycle than lead acid batteries. The Li-Ion battery has a higher cost per single installation, however the lifetime costs are comparable over the system life span under moderate temperatures, and much higher for lead acid batteries under cold or hot conditions. When taking the longer life cycle into account, the advantages of the Li-Ion battery greatly outweighs those of the lead acid battery as an industrial-level energy source.

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