Nickel metal hydride (NiMh) and Lithium-Ion (Li-ion) are two of the most popular rechargeable battery technologies available for many popular electronics, such as laptop computers and digital cameras. They are also used in the newest hybrid vehicles. Both NiMh and Li-ion emerged in the 1990s, replacing nickel-cadmium as the rechargeable battery technology of choice. When it comes to energy density, lifespan, environmental benefits and weight, NiMh and Li-ion both offer advantages for common consumer products.
Nickel Metal Hydride
The NiMh battery system is popular in wireless communications and mobile computing because it offers two major advantages over older nickel-based technologies such as nickel-cadmium. First, today's NiMh batteries offer about 40 percent higher energy capacity than nickel-cadmium, according to Battery University. Second, NiMh is more environmentally friendly than nickel-cadmium, containing only minor toxins, so the batteries can be recycled more easily. However, NiMh is also known to require more maintenance. The batteries must be stored in a cool place, or they will lose performance.
Lithium-ion
Lithium-Ion is the fastest growing type of rechargeable battery technology as of 2011, according to Battery University. Lithium-Ion batteries offer about twice the energy density of a nickel-cadmium battery, and about 33 percent more energy density than a NiMh battery. In addition, Li-ion batteries generally require less maintenance, as they don't require a periodic discharge as nickel-based batteries do. However, Li-ion batteries cost twice as much as NiMh batteries, and they tend to not work well in extreme temperatures.
Recharging
One of the key differences between Li-ion and NiMh batteries is how they should be recharged to maintain their performance over time. Nickel-based batteries are susceptible to what's known as a "memory effect." This means that because of the way it's designed, a NiMh battery would "remember" how much energy was drawn from it in a previous discharge, and would not provide more energy than this after the next charge. Therefore, if a NiMh battery is not fully drained and then recharged to its full capacity periodically, crystals will form on the cell plates and the battery will lose its capacity. To prevent memory, NiMh need to be fully discharged every so often. Li-ion batteries are not prone to the memory effect, and don't need to be exercised this way.
Automotive
Both NiMh and Li-ion are popular battery technologies in hybrids and electric vehicles such as the Toyota Prius, Tesla Roadster and Honda Civic, according to a September 2010 article by AOL Autos. Both NiMh and Li-ion batteries have fewer toxic chemicals than traditional lead-acid batteries. Compared to Li-ion, NiMh batteries are less expensive for vehicles. But Li-ion batteries offer more energy storage in the smallest space, compared to nickel batteries, and the fact that Li-ion batteries aren't affected by memory means they require less maintenance when used in vehicles.
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