Is Lithium-ion an Ideal Battery?

G.N. Lewis started working on the lithium battery in 1912, but the first non-rechargeable lithium batteries became commercially available in the early 1970s. lithium is a lightest metal from all metals and it has the greatest electro-chemical potential and it provides the largest energy density for weight.

Many attempts made to develop rechargeable lithium batteries failed due to safety problems. Due to inherent instability of lithium metal, most of the time during charging, research has been shifted to a non-metallic lithium battery using lithium ions. Though slightly lower in energy density than lithium metal, lithium-ion found safe, with certain precautions done when charging and discharging. In the year 1991, the Sony Corporation first commercialized the lithium-ion battery. Other manufacturers then followed suit.

The energy density of lithium-ion is almost twice of the standard nickel-cadmium. There is greater potential for higher energy densities. The load characteristics are reasonably good and behavior is similar to nickel-cadmium in terms of discharge. The high cell voltage of 3.6 volts helps to allow battery pack designs with only one cell. Almost all of today’s mobile phones run on a single cell. While a nickel-based pack would require three 1.2-volt cells connected in series.



Lithium-ion is considered as low maintenance battery, an advantage over other chemistries. There is no memory and no scheduled cycling is required to enhance the battery’s life. Lithium ion cell has its self-discharge less than half when compared to nickel-cadmium, making lithium-ion well suited for modern applications. lithium-ion cells cause little harm compared with other cells, when disposed.

Despite lithium-ion’s overall advantages, it has its drawbacks. It is fragile in nature and requires a protection circuit to maintain its operation safe. Built into battery pack, the protection circuit limits its peak voltage of each cell during charge and prevents the cell voltage from dropping too low on discharge. In addition to this, the cell temperature is also monitored to prevent temperature extremes. Maximum charge and discharge current on most battery packs are is limited to between 1C and 2C. These precautions reduces the possibility of metallic lithium plating occurring in case of overcharge is virtually eliminated.

Aging is one of the concern with most lithium-ion batteries. Most of the manufacturers remain silent about this issue. Small amount of capacity deterioration is noticeable after one year, irrespective of the battery is in use or not. The battery frequently getting fail after two to three years. Other chemistry also have age-related degenerative effects. This is proven true for nickel-metal-hydride if exposed to high ambient temperatures. But, at the same time, in some cases lithium-ion packs have served for five years in some applications.

Manufacturers are continuously improving lithium-ion cells. In every six month or so, new and enhanced chemical combinations are introduced. With this rapid progress, it is difficult to assess revised battery age.

Storage in a cool place is a solution to the aging process of lithium-ion (and other chemistries). If battery is partially charged during storage, manufacturers recommended storage temperatures is at 15°C, and the battery should be partially charged during storage. A 40% charged battery is recommended for this application.

The most commercially economical in terms of cost to energy ratio is lithium-ion battery (cylindrical 18650). This cell is used for variety of applications that do not demand ultra-thin geometry. prismatic lithium-ion cell is the best choice for a slim pack. These cells are costly in terms of stored energy.

Advantages of lithium-ion

•               It has high energy density – potential for yet higher capacities.

•               Prolonged priming does not needed,  when new. One regular charge is just enough.

•               Low self-discharge – self-discharge is less than half compared to nickel-based batteries.

•               Relatively low Maintenance – no periodic discharge is needed; there is no memory.

•               Special composite cells can provide very high current to applications such as power tools.

Limitations

•               It requires protection circuit to safe limits to maintain voltage and current.

•               Aging Problem, even if not in use – storage in a cool place at 40% charge reduces the aging effect.

•               Shipment of larger quantities may be restricted and subject to regulatory control.

•               Expensive to manufacture – It is about 40% higher in cost compared to nickel-cadmium.

•               Not fully mature – metals and chemicals are changing on a continuing basis.



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