Pioneering work for the lithium battery began in 1912 by G. N. Lewis but it was not until the early 1970’s that the first non-rechargeable lithium batteries became commercially available. Attempts to develop rechargeable lithium batteries followed in the eighties, but failed due to safety concerns.

Lithium is the lightest of all metals, has the greatest electrochemical potential and provides the largest energy content. Rechargeable batteries using lithium metal as an electrode are capable of providing both high voltage and excellent capacity, resulting in an extraordinary energy density.

After much research during the eighties, it was found that occasional shorts from lithium dendrites could cause thermal run-away. The cell temperature quickly approaches the melting temperature of lithium which results in violent reactions. A large quantity of rechargeable lithium batteries sent to Japan had to be recalled in 1991 after a battery in a cellular phone exploded and inflicted burns to a man’s face.

Because of the inherent instability of lithium metal, especially during charging, research shifted to a non-metallic lithium battery using lithium ions from chemicals such as Lithium-Cobalt Dioxide (LiCoO2 ). Although slightly lower in energy density than with lithium metal, the Li-ion is safe, provided certain precautions are met when charging and discharging. In 1991, Sony commercialized the Li-ion and is presently the largest supplier of this type of battery.

The energy density of the Li-ion is at least twice that of the NiCd and its load current rating is reasonably high. In fact, the Li-ion behaves similarly to the NiCd in terms of discharge characteristics. In addition, the Li-ion has a relatively low self-discharge.

For safety and longevity reasons, each battery pack must be equipped with a control circuit to limit the peak voltage of each cell during charge and prevent the cell voltage from dropping too low on discharge. In addition, the maximum charge and discharge current must be limited and the cell temperature monitored. With these precautions in place, the possibility of metallic lithium plating occurring due to overcharge is virtually eliminated.

There are two basic Li-ion types that have emerged: the coke version by Sony and the graphite version that has now been adapted by most other manufacturers. The new graphite electrode provides a flatter discharge voltage curve than the coke electrode and offers a sharp knee bend, followed by a rapid voltage drop before the discharge cut off point (see Figure below). As a result, the graphite Li-ion needs to be discharged to only 3.0V per cell whereas Sony’s coke version must be discharged to 2.5V to obtain maximum capacity. In addition, the graphite version is capable of delivering a higher discharge current and remains cooler during charge and discharge than the coke version. Discharge characteristics of Li-ion with coke and graphite electrode.

Discharge characteristics of Li-ion with coke and graphite electrode.

The graphite’s higher end-of-discharge voltage of 3.0V has a major advantage because its useful energy is concentrated within a tight upper voltage range, simplifying equipment design. It is speculated that a single graphite Li-ion cell will be capable of powering most cellular phones by the year 2000, with notebook computers to follow.

Manufacturers are constantly changing and improving the chemistry of the Li-ion battery. New carbons are being tried for the negative electrode that are said to double the capacity of the Li-ion battery. Further work is required to assure that safety is not compromised because the energy content available with Li-ion approaches that of Lithium metal.

The Li-ion is one of the most expensive commercial batteries available today. Better manufacturing techniques and the replacement of cobalt with a less expensive material will likely reduce its price by 50% after the year 2000.

Other Li-ion systems are being developed that show promising results. According to Fujifilm, their amorphous, tin-based composite oxide material as the negative electrode offers 50% more capacity than Li-ion batteries using the conventional carbon electrode. Other said advantages of the tin-based composite oxide are: enhanced safety, quick charging, good load characteristics and good performance at low temperature. Disadvantages new discoveries bring along are commonly not mentioned in the early stages.

Caution: Li-ion batteries have a very high energy density. Exercise precaution when handling and testing. Do not short circuit, overcharge, crush, mutilate, nail penetrate, apply reverse polarity, expose to high temperature or disassemble. High case temperature resulting from abuse of the cell could cause physical injury.

Charging the Lithium Ion Battery

Frequently Asked Questions About Li-ion Batteries

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