Pioneer work with the lithium battery began in 1912 under G.N. Lewis but it was not until the
early 1970s that the first non-rechargeable lithium batteries became commercially available.
Attempts to develop rechargeable lithium batteries followed in the 1980s, but failed due to
Lithium is the lightest of all metals, has the greatest electrochemical potential and provides
the largest energy density per weight. Rechargeable batteries using lithium metal anodes
(negative electrodes) are capable of providing both high voltage and excellent capacity,
resulting in an extraordinary high energy density.
After much research on rechargeable lithium batteries during the 1980s, it was found that
cycling causes changes on the lithium electrode. These transformations, which are part of
normal wear and tear, reduce the thermal stability, causing potential thermal
runaway conditions. When this occurs, the cell temperature quickly approaches the melting
point of lithium, resulting in a violent reaction called ‘venting with flame’. A large quantity of
rechargeable lithium batteries sent to Japan had to be recalled in 1991 after a battery in a
mobile phone released flaming gases and inflicted burns to a person’s face.
Because of the inherent instability of lithium metal, especially during charging, research
shifted to a non-metallic lithium battery using lithium ions. Although slightly lower in energy
density than lithium metal, the Li-ion is safe, provided certain precautions are met when
charging and discharging. In 1991, the Sony Corporation commercialized the first Li-ion
battery. Other manufacturers followed suit. Today, the Li-ion is the fastest growing and most
promising battery chemistry.
The energy density of the Li-ion is typically twice that of the standard NiCd. Improvements in
electrode active materials have the potential of increasing the energy density close to three
times that of the NiCd. In addition to high capacity, the load characteristics are reasonably
good and behave similarly to the NiCd in terms of discharge characteristics (similar shape of
discharge profile, but different voltage). The flat discharge curve offers effective utilization of
the stored power in a desirable voltage spectrum.
The Li-ion is a low maintenance battery, an advantage that most other chemistries cannot
claim. There is no memory and no scheduled cycling is required to prolong the battery’s life.
In addition, the self-discharge is less than half compared to NiCd and NiMH, making the Li-ion
well suited for modern fuel gauge applications.
The high cell voltage of Li-ion allows the manufacture of battery packs consisting of only one
cell. Many of today’s mobile phones run on a single cell, an advantage that simplifies battery
design. Supply voltages of electronic applications have been heading lower, which in turn
requires fewer cells per battery pack. To maintain the same power, however, higher currents
are needed. This emphasizes the importance of very low cell resistance to allow unrestricted
flow of current.
Chemistry variations — During recent years, several types of Li-ion batteries have emerged
with only one thing in common — the catchword 'lithium'. Although strikingly similar on the
outside, lithium-based batteries can vary widely.
Sony’s original version of the Li-ion used coke, a product of coal, as the negative electrode.
Since 1997, most Li-ions (including Sony’s) have shifted to graphite. This electrode provides a
flatter discharge voltage curve than coke and offers a sharp knee bend at the end of
discharge. As a result, the graphite system delivers the stored energy by only
having to discharge to 3.0V/cell, whereas the coke version must be discharged to 2.5V to get
similar runtime. In addition, the graphite version is capable of delivering a higher discharge
current and remains cooler during charge and discharge than the coke version.
For the positive electrode, two distinct chemistries have emerged. They are cobalt and
spinel (also known as manganese). Whereas cobalt has been in use longer, spinel is
inherently safer and more forgiving if abused. Small prismatic spinel packs for mobile phones
may only include a thermal fuse and temperature sensor. In addition to cost savings on a
simplified protection circuit, the raw material cost for spinel is lower than that of cobalt.
As a trade-off, spinel offers a slightly lower energy density, suffers capacity loss at
temperatures above 40°C and ages quicker than cobalt.
Based on present generation 18650 cells. The energy density tends to be lower for prismatic
The choice of metals, chemicals and additives help balance the critical trade-off between high
energy density, long storage time, extended cycle life and safety. High energy densities can
be achieved with relative ease. For example, adding more nickel in lieu of cobalt increases
the ampere/hours rating and lowers the manufacturing cost but makes the cell less safe.
While a start-up company may focus on high energy density to gain quick market acceptance,
safety, cycle life and storage capabilities may be compromised. Reputable manufacturers,
such as Sony, Panasonic, Sanyo, Moli Energy and Polystor place high importance on safety.
Regulatory authorities assure that only safe batteries are sold to the public.
Li-ion cells cause less harm when disposed of than lead or cadmium-based batteries. Among
the Li-ion family, the spinel is the friendliest in terms of disposal.
Despite its overall advantages, Li-ion also has its drawbacks. It is fragile and requires a
protection circuit to maintain safe operation. Built into each pack, the protection circuit limits
the peak voltage of each cell during charge and prevents the cell voltage from dropping too
low on discharge. In addition, the maximum charge and discharge current is limited and the
cell temperature is monitored to prevent temperature extremes. With these precautions in
place, the possibility of metallic lithium plating occurring due to overcharge is virtually
Aging is a concern with most Li-ion batteries. For unknown reasons, battery manufacturers
are silent about this issue. Some capacity deterioration is noticeable after one year, whether
the battery is in use or not. Over two or perhaps three years, the battery frequently fails. It
should be mentioned that other chemistries also have age-related degenerative effects. This
is especially true for the NiMH if exposed to high ambient temperatures.
Storing the battery in a cool place slows down the aging process of the Li-ion (and other
chemistries). Manufacturers recommend storage temperatures of 15°C (59°F). In addition, the
battery should only be partially charged when in storage.
Extended storage is not recommended for Li-ion batteries. Instead, packs should be rotated.
The buyer should be aware of the manufacturing date when purchasing a replacement Li-ion
battery. Unfortunately, this information is often encoded in an encrypted serial number and is
only available to the manufacturer.
Manufacturers are constantly improving the chemistry of the Li-ion battery. Every six months,
a new and enhanced chemical combination is tried. With such rapid progress, it becomes
difficult to assess how well the revised battery ages and how it performs after long-term
Cost analysis — The most economical lithium-based battery in terms of cost-to-energy ratio
is a pack using the cylindrical 18650 cell. This battery is somewhat bulky but suitable for
portable applications such as mobile computing. If a slimmer pack is required (thinner than
18 mm), the prismatic Li-ion cell is the best choice. There is little or no gain in energy density
per weight and size over the 18650, however the cost is more than double.
If an ultra-slim geometry is needed (less than 4 mm), the best choice is Li-ion polymer. This is
the most expensive option in terms of energy cost. The Li-ion polymer does not offer
appreciable energy gains over conventional Li-ion systems, nor does it match the durability of
the 18560 cell.
Advantages and Limitations of Li-ion Batteries
High energy density — potential for yet higher capacities.
Relatively low self-discharge — self-discharge is less than half that of
NiCd and NiMH.
Low Maintenance — no periodic discharge is needed; no memory.
Limitations Requires protection circuit — protection circuit limits voltage and
current. Battery is safe if not provoked.
Subject to aging, even if not in use — storing the battery in a cool
place and at 40 percent state-of-charge reduces the aging effect.
Moderate discharge current.
Subject to transportation regulations — shipment of larger quantities
of Li-ion batteries may be subject to regulatory control. This
restriction does not apply to personal carry-on batteries.
Expensive to manufacture — about 40 percent higher in cost than
NiCd. Better manufacturing techniques and replacement of rare
metals with lower cost alternatives will likely reduce the price.
Not fully mature — changes in metal and chemical combinations
affect battery test results, especially with some quick test methods.
Caution: Li-ion batteries have a high energy density. Exercise precaution when handling and
testing. Do not short circuit, overcharge, crush, drop, mutilate, penetrate, apply reverse
polarity, expose to high temperature or disassemble. Only use the Li-ion battery with the
designated protection circuit. High case temperature resulting from abuse of the cell could
cause physical injury. The electrolyte is highly flammable. Rupture may cause venting with